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At least 1,045 records · Page 58Linked to original sources
USGS2014

Evaluation of the behavior and movement of adult summer steelhead in the lower Cowlitz River, Washington, following collection and release, 2013-2014

Summer steelhead ( Oncorhynchus mykiss ) produced by a hatchery on the lower Cowlitz River, Washington, support a popular sport fishery during June–September each year. Many of these fish return to the Cowlitz Salmon Hatchery and are held until they are spawned in December. In the past, fishery managers have released some of the steelhead that return to the hatchery at downstream release sites (hereafter referred to as “recycled steelhead”) to increase angling opportunity. The recycling of summer steelhead is a potential use of hatchery fish that can benefit anglers in the lower Cowlitz River, provided these fish are harvested or return to the hatchery. However, recycled steelhead that are not removed from the river could compete against or spawn with wild winter steelhead, which would be a negative consequence of recycling. The Washington Department of Fish and Wildlife (WDFW) conducted an evaluation during 1998 and recycled 632 summer steelhead. They determined that 55 percent of the recycled steelhead returned to the hatchery and 15 percent of the fish were harvested by anglers. The remaining 30 percent of recycled fish were not known to have been removed from the river. Recycling has not occurred in recent years because definitive studies have not been conducted to determine the fate of the fish that remain in the lower Cowlitz River after being recycled. The U.S. Geological Survey and WDFW conducted a 2-year study during 2012–2014 to quantify recycled steelhead that (1) returned to the hatchery, (2) were captured by anglers, or (3) remained in the river. All recycled steelhead were marked with a Floy ® tag and opercle punch, and 20 percent of the recycled fish were radio-tagged to determine post-release behavior and movement patterns, and to describe locations of tagged fish that remained in the river during the spawning period. During 2012–2013, we recycled 549 steelhead and determined that 50 percent of the fish returned to the hatchery, 18 percent of the fish were harvested by anglers, and 32 percent of the fish were not known to have been removed from the river. During October–December 2012, only 9 percent of the radio-tagged steelhead remained in the lower Cowlitz River and none of these fish entered tributaries monitored by fixed-telemetry sites. The second year of the evaluation was conducted during 2013–2014. A total of 502 steelhead were recycled during June–August and releases were conducted weekly with group sizes that ranged from 30 to 76 fish. Results from 2013–2014 were similar to results from 2012–2013. Fifty percent (251 fish) of the recycled steelhead returned to the hatchery, 20 percent (100 fish) were harvested by anglers, and 30 percent (151 fish) were unaccounted for. The median elapsed time from release to hatchery return was 13 days, and the median elapsed time from release to capture by an angler was 11 days. The percentage of unaccounted-for steelhead in the general population was moderately high (30 percent), but detection records of radio-tagged fish suggest that few recycled steelhead were present in the lower Cowlitz River during the spawning period. A total of 109 steelhead were radio-tagged during 2013–2014, and most of these fish (88 percent) moved upstream following release and entered the Trout Hatchery–Salmon Hatchery reach (river miles 44–51). The median elapsed time from release to reach entry was 4.6 days (range of 0.5–65.5 days). After fish entered this reach, they spent a considerable amount of time near the Cowlitz Trout Hatchery (median residence time of 16.7 hours) or Cowlitz Salmon Hatchery (median residence time of 146.3 hours), or they moved back and forth between these two sites. Thirty radio-tagged steelhead made at least two trips between the sites and some fish made as many as seven trips. Detection records showed that 61 percent (66 fish) of the radio-tagged fish returned to the hatchery reach and 21 percent (23 fish) of the fish were captured by anglers. The remaining 18 percent (20 fish) of the radio-tagged fish had various fates. One fish (less than 1 percent) left the Cowlitz River and nine fish (8 percent) died, were harvested, or spit their transmitter near boat launches in the river. The remaining 10 fish (9 percent) had the potential to interact with winter steelhead. Four tagged steelhead (4 percent) entered lower Cowlitz River tributaries (two fish in the Toutle River; two fish in Salmon Creek) during October and November, and five tagged fish (5 percent) were last detected in the lower Cowlitz River in October. One fish (less than 1 percent) was never detected after being released. We measured the diameter of opercle punches in recycled steelhead to determine the temporal effectiveness of these marks. A total of 116 opercle punches were measured—36 were measured at the time of tagging and 80 were measured when fish returned to the hatchery. Opercle punches remained open for less than 1 month. None of the fish that returned to the hatchery more than 30 days after release had opercle punches that were open. All recycled steelhead were marked with a Floy ® tag and opercle punch. However, if a steelhead lost its Floy ® tag and was captured by an angler, or returned to the hatchery more than 30 days after being recycled, it likely would not have been accurately identified as having been recycled because of regrowth of the opercle punch. During 2013–2014, at least 70 percent of the recycled steelhead were removed from the lower Cowlitz River by anglers, returned to the hatchery, or left the river. Radiotelemetry data indicated that a maximum of 9 percent of the radio-tagged fish remained in the lower Cowlitz River during the spawning period and only 4 percent of the radio-tagged fish entered tributaries where wild steelhead are known to spawn. These results are consistent with findings from previous studies. Overall, results from these studies suggest that about one-third of the recycled steelhead were not known to have been removed from the river. However, the radiotelemetry data indicated that only about 10 percent of the recycled steelhead were present in the lower Cowlitz River during late autumn and early winter, and few of those fish (0 in 2012–2013 and 4 in 2013–2014) entered tributaries where winter steelhead spawn. These results have management implications in the lower Cowlitz River where the risks and rewards of steelhead recycling will be weighed to determine the future of the recycling program.

Washinton↗
USGS2022

Relative contributions of suspended sediment between the upper Suiattle River Basin and a non-glacial tributary, Washington, May 2016–September 2017

Concentrations of suspended sediment were measured in discrete samples and turbidity was continuously monitored at four U.S. Geological Survey streamgages in western Washington State, including one gage on the Sauk River; two gages on the Suiattle River, a tributary to the Sauk River; and one gage on Downey Creek, a tributary to the Suiattle River. The Suiattle River is a sediment-rich stream with headwaters on Glacier Peak, a glaciated volcano in the northern Cascade Range. Contributions of suspended sediment to the Suiattle River from unglaciated tributaries, represented by Downey Creek, were compared to the contributions from Glacier Peak in the upper Suiattle River watershed. During summer 2017, a period for which complete records of discharge and sediment data were available for all three streamgages in the Suiattle River Basin, the suspended-sediment load from Downey Creek (drainage area [DA] 93 square kilometers [km 2 ]) was 1,400 metric tons, which is equivalent to a sediment yield of about 15 metric tons per km 2 . During the same period, the suspended-sediment load from the upper Suiattle River (DA 176 km 2 ) was 142,000 metric tons, or a sediment yield of about 800 metric tons per km 2 ; and the suspended-sediment load from the lower Suiattle River (DA 733 km 2 ) was 230,000 metric tons, or a sediment yield of about 300 metric tons per km 2 . The Downey Creek Basin accounts for 13 percent of the drainage area of the Suiattle River watershed but contributed only 0.6 percent of the suspended-sediment load over the summer of 2017 and water year 2017 (October 1, 2016–September 30, 2017). In contrast, the upper Suiattle River Basin, which accounts for 24 percent of the entire Suiattle River watershed, contributed 62 percent of the suspended-sediment load during the summer of 2017. Given the short period for which data were collected, it cannot be known with certainty whether the above values are representative of long-term means. The relatively minor contribution of suspended sediment from Downey Creek, however, is consistent with the expectation that the upper Suiattle River, which drains Glacier Peak, is the dominant contemporary source of suspended sediment to the Sauk River. During summer 2016, the suspended-sediment load in the upper Siuattle River (180,000 metric tons) was more than double the estimated load in the lower Sauk River (80,000 metric tons), even though the upper Suiattle River represents only 10 percent of the total contributing area to the lower Sauk River Basin. This ratio of relative contribution is interpreted as an indication of transient storage of sediment along the Suiattle and Sauk Rivers between the two streamgaging stations. In the glaciated upper Suiattle River Basin, sediment is transported by annual glacial-melt processes in spring and summer months, deposited during the summer base-flow period, and then remobilized by fall and winter floods for delivery to the lower Sauk River.

Washington↗
USGS2014

Sources, transport, and trends for selected trace metals and nutrients in the Coeur d'Alene and Spokane River Basins, Idaho, 1990-2013

Data collected at 18 streamflow-gaging and water-quality sampling sites in the Coeur d’Alene and Spokane River Basins of northern Idaho were used to estimate mean streamflow‑weighted concentrations and annual loads of total and dissolved cadmium, lead, and zinc, and total phosphorus (TP) and nitrogen (TN) for water years (WYs) 2009–13. Chronic Ambient Water Quality Criteria (AWQC) and AWQC ratios also were calculated to evaluate Idaho aquatic life criteria for chronic exposure to cadmium and zinc in streams. At four sites with a longer period of record, a Seasonal Kendall trend test was used to assess historical trends in the concentrations of total cadmium, lead, and zinc, and chronic AWQC ratios for cadmium and zinc during WYs 1990–2013. Concentrations of dissolved and total cadmium, lead, and zinc varied widely both at and among sites. At most sites, dissolved cadmium and zinc constituted most of the total concentrations; dissolved lead generally constituted less than 10 percent of the total lead concentration. Trace metal concentrations increased by 2 to 4 orders of magnitude along the South Fork Coeur d’Alene River (SFCDR) from near Mullan (site 2) downstream to near Pinehurst (site 13). The mean streamflow-weighted concentrations of total cadmium, lead, and zinc in the SFCDR near Pinehurst for WYs 2009–13 were 3.71, 61.4, and 514 micrograms per liter (μg/L), respectively. In the Coeur d’Alene River (CDR) near Harrison (site 15), downstream of the confluence of the metal-enriched SFCDR and the relatively dilute North Fork Coeur d’Alene River (NFCDR), the mean streamflow-weighted concentrations of total cadmium, lead, and zinc were 1.58, 125, and 236 μg/L, respectively. Trace‑metal concentrations were smaller in the Spokane River than in the CDR because of dilution and retention of trace metals in Coeur d’Alene Lake. The mean streamflow-weighted concentrations of total cadmium, lead, and zinc in the Spokane River near Post Falls (site 18) were 0.231, 2.91, and 48.9 μg/L, respectively. AWQC ratios indicate that cadmium and zinc concentrations met the chronic criteria (ratio of less than 1.0) for the protection of aquatic life at only three sites: the NFCDR at Enaville (site 1), the upper SFCDR near Mullan (site 2), and the St. Joe River near St. Maries (site 16). Cadmium and zinc concentrations at sites on the Spokane River (sites 17 and 18) generally were close to the chronic AWQC values. The sites with the largest chronic AWQC ratios in the Coeur d’Alene and Spokane River Basins for both cadmium and zinc were in the Canyon and Ninemile Creek basins (sites 3–6). Concentrations of TP and TN generally were low along the SFCDR downstream to Kellogg. From the SFCDR near Kellogg (site 9) downstream to the SFCDR above Pine Creek (site 11), the mean streamflow-weighted concentration of the nutrients TP and TN increased by 0.036 milligram per liter (mg/L) (200 percent) and 0.124 mg/L (78 percent), respectively. The increases in nutrient concentrations along the SFCDR likely are in response to discharge from wastewater‑treatment facilities. Mean streamflow-weighted concentrations for TP and TN (0.054 and 0.284 mg/L, respectively) were the highest in the sampling network in the SFCDR above Pine Creek (site 11). LOADEST modeling was used to relate mass transport, or load, of trace metals and nutrients to variations in streamflow and time. Results indicate that most of the cadmium and zinc load in the Coeur d’Alene and Spokane Rivers is derived from the SFCDR, and that most of the lead load is derived from the Coeur d’Alene River downstream of the confluence of the NFCDR and SFCDR. Major tributary sources of trace metals to the SFCDR are Canyon Creek and Ninemile Creek. Combined, these two tributaries contributed estimated mean loads of about 0.575 ton per year (ton/yr) of total cadmium, 5.29 ton/yr of total lead, and 90.9 ton/yr of total zinc to the SFCDR during WYs 2009–13. Groundwater discharge and tributaries near the Central Impoundment Area between SFCDR near Kellogg (site 9) and SFCDR near Smelterville (site 10) were other primary sources of cadmium and zinc. Combined, these sources contributed an estimated 1.39 ton/yr of total cadmium and 143 ton/yr of total zinc to the SFCDR during WYs 2009–13. Erosion and transport of sediment-bound lead contained in the CDR flood plain and on the river bottom between Cataldo (site 14) and Harrison (site 15) were the primary source of lead. During WYs 2009–13, the mean load of trace metals delivered to Coeur d’Alene Lake included about 4.66 ton/yr of total cadmium, 398 ton/yr of total lead, and 698 ton/yr of total zinc. About 99 percent of the trace-metal load to the lake was from the CDR as measured near site 15 at Harrison. During WYs 2009–13, about 1.48 ton/yr of cadmium, 18 ton/yr of lead, and 350 ton/yr of zinc were transported from Coeur d’Alene Lake into the Spokane River as measured at the lake outlet (site 17). During WYs 2009–13, the loads of TP and TN delivered from the Coeur d’Alene and St. Joe Rivers to Coeur d’Alene Lake were about equivalent. On average, the CDR transported about 93.6 tons of TP and 369 tons of TN, and the St. Joe River transported about 92.9 tons of TP and 360 tons of TN to the lake during 2009–13. About 52.9 ton/yr of TP and 628 ton/yr of TN were transported from Coeur d’Alene Lake to the Spokane River during WYs 2009–13. Results from Seasonal Kendall trend tests indicate statistically significant downward temporal trends during WYs 1990–2013 for total cadmium, lead, zinc, and chronic AWQC ratios of cadmium and zinc in the SFCDR at Elizabeth Park (site 8) and near Pinehurst (site 13), and in the CDR near Harrison (site 15). Statistically significant downward temporal trends for total lead, zinc, and the chronic AWQC ratio of zinc also occurred in the Spokane River near Post Falls (site 18) during WYs 1991–2013. Seasonal Kendall trend tests for WYs 2003–13 indicated statistically significant downward trends for total cadmium, zinc, and chronic AWQC ratios of cadmium and zinc in the SFCDR at Elizabeth Park (site 8). The Spokane River near Post Falls (site 18) had a statistically significant downward trend for total zinc during WYs 2003–13, and a significant upward trend for the chronic AWQC ratio of cadmium. No significant trends were found in trace-metal concentrations or chronic AWQC ratios in the SFCDR near Pinehurst (site 13) and the CDR near Harrison (site 15) during WYs 2003–13. Results from this study indicate that remedial activities conducted since the 1990s have been successful in reducing the concentrations and loads of trace metals in streams and rivers in the Coeur d’Alene and Spokane River Basins. Soils, sediment, surface water, and groundwater in areas of the Coeur d’Alene and Spokane River Basins are contaminated, and the hydrological relations between these media are complex and difficult to characterize. Trace metals have variable source areas, are transported differently depending on hydrologic conditions, and behave differently in response to remedial activities in upstream basins. Based on these findings, no single remedial action would be completely effective in reducing all trace metals to nontoxic concentrations throughout the Coeur d’Alene and Spokane River Basins. Instead, unique cleanup activities targeted at specific media and specific source areas may be necessary to achieve long-term water-quality goals.

Idaho↗
USGS2017

Hydrogeology and simulated groundwater flow and availability in the North Fork Red River aquifer, southwest Oklahoma, 1980–2013

On September 8, 1981, the Oklahoma Water Resources Board established regulatory limits on the maximum annual yield of groundwater (343,042 acre-feet per year) and equal-proportionate-share (EPS) pumping rate (1.0 acre-foot per acre per year) for the North Fork Red River aquifer. The maximum annual yield and EPS were based on a hydrologic investigation that used a numerical groundwater-flow model to evaluate the effects of potential groundwater withdrawals on groundwater availability in the North Fork Red River aquifer. The Oklahoma Water Resources Board is statutorily required (every 20 years) to update the hydrologic investigation on which the maximum annual yield and EPS were based. Because 20 years have elapsed since the final order was issued, the U.S. Geological Survey, in cooperation with the Oklahoma Water Resources Board, conducted an updated hydrologic investigation and evaluated the effects of potential groundwater withdrawals on groundwater flow and availability in the North Fork Red River aquifer in Oklahoma. This report describes a hydrologic investigation of the North Fork Red River aquifer that includes an updated summary of the aquifer hydrogeology. As part of this investigation, groundwater flow and availability were simulated by using a numerical groundwater-flow model. The North Fork Red River aquifer in Beckham, Greer, Jackson, Kiowa, and Roger Mills Counties in Oklahoma is composed of about 777 square miles (497,582 acres) of alluvium and terrace deposits along the North Fork Red River and tributaries, including Sweetwater Creek, Elk Creek, Otter Creek, and Elm Fork Red River. The North Fork Red River is the primary source of surface-water inflow to Lake Altus, which overlies the North Fork Red River aquifer. Lake Altus is a U.S. Bureau of Reclamation reservoir with the primary purpose of supplying irrigation water to the Lugert-Altus Irrigation District. A hydrogeologic framework was developed for the North Fork Red River aquifer and included a definition of the aquifer extent and potentiometric surface, as well as a description of the textural and hydraulic properties of aquifer materials. The hydrogeologic framework was used in the construction of a numerical groundwater-flow model of the North Fork Red River aquifer described in this report. A conceptual model of aquifer inflows and outflows was developed for the North Fork Red River aquifer to constrain the construction and calibration of a numerical groundwater-flow model that reasonably represented the groundwater-flow system. The conceptual-model water budget estimated mean annual inflows to and outflows from the North Fork Red River aquifer for the period 1980–2013 and included a sub-accounting of mean annual inflows and outflows for the portions of the aquifer that were upgradient and downgradient from Lake Altus. The numerical groundwater-flow model simulated the period 1980–2013 and was calibrated to water-table-altitude observations at selected wells, monthly base flow at selected streamgages, net streambed seepage as estimated for the conceptual model, and Lake Altus stage. Groundwater-availability scenarios were performed by using the calibrated numerical groundwater-flow model to (1) estimate the EPS pumping rate that guarantees a minimum 20-, 40-, and 50-year life of the aquifer, (2) quantify the potential effects of projected well withdrawals on groundwater storage over a 50-year period, and (3) simulate the potential effects of a hypothetical (10-year) drought on base flow and groundwater storage. The results of the groundwater-availability scenarios could be used by the Oklahoma Water Resources Board to reevaluate the maximum annual yield of groundwater from the North Fork Red River aquifer. EPS scenarios for the North Fork Red River aquifer were run for periods of 20, 40, and 50 years. The 20-, 40-, and 50-year EPS pumping rates under normal recharge conditions were 0.59, 0.52, and 0.52 acre-foot per acre per year, respectively. Given the 497,582-acre aquifer area, these rates correspond to annual yields of about 294,000, 259,000, and 259,000 acre-feet per year, respectively. Groundwater storage at the end of the 20-year EPS scenario was about 951,000 acre-feet, or about 1,317,000 acre-feet (58 percent) less than the starting EPS scenario storage. This decrease in storage was equivalent to a mean water-level decline of about 22 feet. Most areas of the active alluvium near the North Fork Red River, Elk Creek, and Elm Fork Red River remained partially saturated through the end of the EPS scenario because of streambed seepage. Lake Altus storage was reduced to zero after 6–7 years of EPS pumping in each scenario. Projected 50-year pumping scenarios were used to simulate the effects of selected well withdrawal rates on groundwater storage of the North Fork Red River aquifer and base flows in the North Fork Red River upstream from Lake Altus. The effects of well withdrawals were evaluated by comparing changes in groundwater storage and base flow between four 50-year scenarios using (1) no groundwater pumping, (2) mean pumping rates for the study period (1980–2013), (3) 2013 pumping rates, and (4) increasing demand pumping rates. The increasing demand pumping rates assumed a 20.4-percent increase in pumping over 50 years based on 2010–60 demand projections for southwest Oklahoma. Groundwater storage after 50 years with no pumping was about 2,606,000 acre-feet, or 137,000 acre-feet (5.5 percent) greater than the initial groundwater storage; this groundwater storage increase is equivalent to a mean water-level increase of 2.3 feet. Groundwater storage after 50 years with the mean pumping rate for the study period (1980–2013) was about 2,476,000 acre-feet, or about 7,000 acre-feet (0.3 percent) greater than the initial groundwater storage; this groundwater storage increase is equivalent to a mean water-level increase of 0.1 foot. Groundwater storage at the end of the 50-year period with 2013 pumping rates was about 2,398,000 acre-feet, or about 70,000 acre-feet (2.8 percent) less than the initial storage; this groundwater storage decrease is equivalent to a mean water-level decline of 1.2 feet. Groundwater storage at the end of the 50-year period with increasing demand pumping rates was about 2,361,000 acre-feet, or about 107,000 acre-feet (4.3 percent) less than the initial storage; this groundwater storage decrease is equivalent to a mean water-level decline of 1.8 feet. Mean annual base flow simulated at the Carter streamgage (07301500) on North Fork Red River increased by about 4,000 acre-feet (10 percent) after 50 years with no pumping and decreased by about 5,400 acre-feet (13 percent) after 50 years with increasing demand pumping rates. Mean annual base flow simulated at the North Fork Red River inflow to Lake Altus increased by about 7,400 acre-feet (15 percent) after 50 years with no pumping and decreased by about 5,800 acre-feet (12 percent) after 50 years with increasing demand pumping rates. A hypothetical 10-year drought scenario was used to simulate the effects of a prolonged period of reduced recharge on groundwater storage and Lake Altus stage and storage. Drought effects were quantified by comparing the results of the drought scenario to those of the calibrated numerical model (no drought). To simulate the hypothetical drought, recharge in the calibrated numerical model was reduced by 50 percent during the simulated drought period (1984–1993). Groundwater storage at the end of the drought period was about 2,271,000 acre-feet, or about 426,000 acre-feet (15.8 percent) less than the groundwater storage of the calibrated numerical model. This decrease in groundwater storage is equivalent to a mean water-table-altitude decline of 7.1 feet. At the end of the 10-year hypothetical drought period, base flows at the Sweetwater (07301420), Carter (07301500), Headrick (07305000), and Snyder (07307010) streamgages had decreased by about 37, 61, 44, and 45 percent, respectively. The minimum Lake Altus storage simulated during the drought period was 403 acre-feet, which was a decline of 92 percent from the nondrought storage. Reduced base flows in the North Fork Red River were the primary cause of Lake Altus storage declines.

Oklahoma↗
USGS2023

Comprehensive water-quality trend analysis for selected sites and constituents in the International Souris River Basin, Saskatchewan and Manitoba, Canada, and North Dakota, United States, 1970–2020

The Souris River Basin is an international basin in southeast Saskatchewan, north-central North Dakota, and southwest Manitoba. Sustained exceedances of water-quality objectives for total phosphorus, sodium, sulfate, total dissolved solids, and total iron have been reported since the late 1990s at the two binational sites on the Souris River (Souris River near Sherwood, North Dakota [U.S. Geological Survey station 05114000] and Souris River near Westhope, N. Dak. [U.S. Geological Survey station 05124000]). To understand conditions at the binational sites, it is important to understand water-quality changes on a basin-wide scale. Because streamflow is highly variable in the basin and changes in streamflow affect water-quality conditions, it is particularly important to use a trend-analysis method that accounts for changes in streamflow. Trends in water-quality concentrations can be affected by human-induced changes on the landscape or natural changes in land-runoff interactions that are driven by climate patterns and reflected by changes in streamflow (commonly referred to as “hydroclimatic variability”). In the primarily agricultural Souris River Basin, human-induced changes that are likely to affect trends are widespread changes in agricultural management such as fertilizer application, tilling practices, and crop types, as well as dam emplacement and artificial drainage. Around 1970, there was a long-term natural (hydroclimatic) change in the basin in which a significant transition from a dry climate state to a wet climate state resulted in higher streamflow in the basin. To assist the International Souris River Board in assessing current water-quality conditions in the Souris River Basin and exceedances of water-quality objectives at the binational sites, the U.S. Geological Survey, in cooperation with the International Joint Commission, completed a comprehensive analysis for selected ions, nutrients, and trace metals for many sites in the basin that included descriptive water-quality statistics, trend analysis using a trend method that considers interannual hydroclimatic variability, and an assessment of exceedances of the water-quality objectives for the binational sites. Water-quality and streamflow or reservoir inflow or outflow data were compiled for 34 sites (30 stream sites and four reservoir sites) and 23 constituents with established water-quality objectives from 1970 to 2020 in the Souris River Basin and were used for descriptive statistics and water-quality trend analysis. Median total dissolved solids, sulfate, and sodium concentrations were low in the headwaters of the Souris River and some of the highest median concentrations were measured in the upper basin. At main-stem Souris River sites, all median sodium concentrations were greater than the binational water-quality objective. Median total phosphorus concentrations in the Souris River Basin were highest in the headwaters of the Souris River and all sites had median concentrations greater than the water-quality objective. Median total iron concentrations were highly variable across the basin, and for most main-stem sites, median concentrations were greater than or equal to the water-quality objective. During the recent period (2009–19), the annual flow-averaged concentrations of total dissolved solids and sulfate increased for nearly all stream sites with most sites having mildly significant or significant increases. One-half of the sites had an annual flow-averaged geometric mean concentration greater than the total dissolved solids water-quality objective, and four sites had sulfate increases greater than 100 milligrams per liter. Trends in annual flow-averaged concentrations of sodium and chloride generally were small and nonsignificant. Most sites had concentrations greater than the sodium water-quality objective, whereas all sites had concentrations much less than the chloride water-quality objective. Annual flow-averaged geometric mean concentration of total phosphorus decreased for nearly all sites across the Souris River Basin, but all sites had concentrations greater than the total phosphorus water-quality objective for the entire period. Small and nonsignificant changes in annual flow-averaged geometric mean concentration of total iron were detected at all sites but the binational site at Sherwood, N. Dak., and by 2019 all sites had concentrations greater than the total iron water-quality objective. For the reservoir sites, during 2000–15, mostly significant increases for total dissolved solids, sulfate, and sodium were detected, whereas changes in total phosphorus and total iron were mixed. During the historical period (1976–2019), large and consistent increases in total dissolved solids and sulfate have occurred since the late 1980s, with the largest increases and the most sites with mildly significant or significant increases generally occurring during the middle period (1988–2005). Large and significant or mildly significant increases in sodium concentrations occurred at eight of 10 sites in the middle period (1988–2005), and by the late period (2005–19) changes were small and nonsignificant. Similar to other basins in the region, such as the Red River of the North and Heart River, large and overall consistent increases since the late 1980s in total dissolved solids and sulfate in the Souris River Basin suggest that long-term natural (hydroclimatic) processes are large contributors to increases in the concentration of salts in streams and reservoirs associated with the onset of wetter conditions. The concurrent increases in sulfate and sodium concentrations at all sites during the middle period (1988–2005) suggest that sodium-sulfate evaporite dissolution may be a factor contributing to increases. Total phosphorus concentrations oscillated between increasing and decreasing during the historical period, with concentrations increasing during the first trend period (1976–88) and decreasing in the fourth trend period (2009–19) to the lowest flow-averaged geometric mean concentration by 2019 for most sites. During the historical period, changes in total iron concentrations were mostly nonsignificant and generally small, and variability in total iron concentrations likely affected the ability to detect statistically significant changes in concentration. The probability of exceeding the water-quality objective for total dissolved solids, sulfate, and sodium increased between 1976 and 2019 for the binational sites, especially for sulfate, which more than doubled for Souris River near Sherwood, N. Dak. and increased more than seven times for Souris River near Westhope, N. Dak. Total phosphorus and total iron concentrations for the binational sites were likely to exceed the water-quality objective for most of the year, but seasonal patterns of total phosphorus and total iron concentrations were different between the sites, suggesting that different factors may affect concentrations at different times of the year. For sodium, total phosphorus, and total iron, exceedance of the water-quality objective most of the time is not unexpected given that the flow-averaged geometric mean concentration for these three constituents for most sites across the basin are greater than the water-quality objective for most of the period. If natural processes are affecting total dissolved solids and sulfate concentrations, concentrations would be expected to vary with time, and as a result, extended periods of concentrations greater or less than the water-quality objective are likely to occur depending upon climatic conditions. A better understanding of the state of water quality across the Souris River Basin is beneficial to understanding and interpreting water-quality conditions at the two Souris River binational sites. The most consistent spatial and temporal change observed for this study was large and consistent increases in sulfate and total dissolved solids among tributary and main-stem sites since the late 1980s. For sulfate and total dissolved solids, wetter climatic conditions combined with naturally occurring and abundant sources of sulfate likely contributed to sustained exceedances of water-quality objectives in recent decades, and extended periods of concentrations greater than or less than the water-quality objective are likely to occur depending on climatic conditions. For sodium, total iron, and total phosphorus, sustained exceedances of the current water-quality objective likely will continue because most sites across the basin had flow-averaged geometric mean concentrations greater than the water-quality objective; and during the 43-year period of analysis, regardless of climatic conditions, exceedances were consistently greater than the water-quality objective. Further investigation into the factors causing increasing sulfate concentrations and a better understanding of reservoir dynamics would enhance the understanding of changes in water-quality conditions in the Souris River Basin. The basin-wide approach of this report provided an improved understanding of water-quality conditions in the Souris River Basin, and results can be used to inform the current water-quality objectives, inform potential changes to water management in the basin, and serve as a starting point for tracking future progress. Gaps in understanding of water-quality conditions can be closed through continued monitoring and further investigation into causes behind changes in water-quality conditions identified in this report.

Manitoba, North Dakota, Saskatchewan↗
USGS2000

Method to identify wells that yield water that will be replaced by water from the Colorado River downstream from Laguna Dam in Arizona and California

Accounting for the use of Colorado River water is required by the U.S. Supreme Court decree, 1964, Arizona v. California. Water pumped from wells on the flood plain and from certain wells on alluvial slopes outside the flood plain is presumed to be river water and is accounted for as Colorado River water. The accounting-surface method developed for the area upstream from Laguna Dam was modified for use downstream from Laguna Dam to identify wells outside the flood plain of the lower Colorado River that yield water that will be replaced by water from the river. Use of the same method provides a uniform criterion of identification for all users pumping water from wells by determining if the static water-level elevation in the well is above or below the elevation of the accounting surface. Wells that have a static water-level elevation equal to or below the accounting surface are presumed to yield water that will be replaced by water from the Colorado River. Wells that have a static water-level elevation above the accounting surface are presumed to yield river water stored above river level. The method is based on the concept of a river aquifer and an accounting surface within the river aquifer. The river aquifer consists of permeable sediments and sedimentary rocks that are hydraulically connected to the Colorado River so that water can move between the river and the aquifer in response to withdrawal of water from the aquifer or differences in water-level elevations between the river and the aquifer. The subsurface limit of the river aquifer is the nearly impermeable bedrock of the bottom and sides of the basins that underlie the Yuma area and adjacent valleys. The accounting surface represents the elevation and slope of the unconfined static water table in the river aquifer outside the flood plain of the Colorado River that would exist if the river were the only source of water to the river aquifer. The accounting surface was generated by using water-surface profiles of the Colorado River from Laguna Dam to about the downstream limit of perennial flow at Morelos Dam. The accounting surface extends outward from the edges of the flood plain to the subsurface boundary of the river aquifer. Maps at a scale of 1:100,000 show the extent of the river aquifer and elevation of the accounting surface downstream from Laguna Dam in Arizona and California.

Arizona;California↗
USGS2001

Source identification and fish exposure for polychlorinated biphenyls using congener analysis from passive water samplers in the Millers River basin, Massachusetts

Measurements of elevated concentrations of polychlorinated biphenyls (PCBs) in fish and in streambed sediments of the Millers River Basin, Massachusetts and New Hampshire, have been reported without evidence of the PCB source. In 1999, an investigation was initiated to determine the source(s) of the elevated PCB concentrations observed in fish and to establish the extent of fish exposure to PCBs along the entire main stems of the Millers River and one of its tributaries, the Otter River. Passive samplers deployed for 2-week intervals in the water-column at 3 1 stations, during summer and fall 1999, were used to assess PCB concentrations in the Millers River Basin. The samplers concentrate PCBs, which diffuse from the water column through a polyethylene membrane to hexane (0.200 liters) contained inside the samplers. Only dissolved PCBs (likely equivalent to the bioavailable fraction) are subject to diffusion through the membrane. The summed concentrations of all targeted PCB congeners (summed PCB) retrieved from the samplers ranged from 1 to 8,000 nanograms per hexane sample. Concentration and congener-pattern comparisons indicated that the historical release of PCBs in the Millers River Basin likely occurred on the Otter River at the upstream margin of Baldwinville, Mass. Elevated water-column concentrations measured in a wetland reach on the Otter River downstream from Baldwinville were compatible with a conceptual model for a present-day (1999) source in streambed sediments, to which the PCBs partitioned after their original introduction into the Otter River and from which PCBs are released to the water now that the original discharge has ceased or greatly decreased. Two four-fold decreases in summed PCB concentrations in the Millers River, by comparison with the highest concentration on the Otter River, likely were caused by (1) dilution with water from the relatively uncontaminated upstream Millers River and (2) volatilization of PCBs from the Millers River in steep-gradient reaches. A relatively constant concentration of summed PCBs in the reach of the Millers River from river mile 20 to river mile 10 was likely a consequence of a balance between decreased volatilization rates in that relatively low-gradient reach and resupply of PCBs to the water column from contaminated streambed sediments. A second high-gradient reach from river mile 10 to the confluence of the Millers River with the Connecticut River also was associated with a decrease in concentration of water-column summed PCBs. Volatilization as a loss mechanism was supported by evidence in the form of slight changes of the congener pattern in the reaches where decreases occurred. Exposure of fish food webs to concentrations of dissolved PCBs exceeded the U.S. Environmental Protection Agency's water-quality criterion for PCBs throughout most of the Millers River and Otter River main stems. Because the apparent source of PCBs discharged was upstream on the Otter River, a large number of river miles downstream (more than 30 mi) had summer water-column PCB concentrations that would likely lead to high concentrations of PCBs in fish.

Water-Resources Investigations Report↗
USGS1992

Sediment transport, particle sizes, and loads in lower reaches of the Chippewa, Black, and Wisconsin Rivers in Western Wisconsin

Hydraulic and sediment data were collected at three sites on the Chippewa River (near Caryville, at Durand, and near Pepin); at one site near Galesville on the Black River; and at one site at Muscoda on the Wisconsin River during water years 1976-83. This report summarizes an interpretation of those data by providing (1) a description of the relation of suspended sediment, bedload, and total-sediment discharge to water discharge; (2) a description of particle-size characteristics of bed material, bedload, and suspended sediment; and (3) estimates of annual and average annual suspended load, bedload, and total-sediment load for water years 1974-83. Direct measurement with a Helley-Smith bedload sampler and calculations by the modified-Einstein procedure were used to estimate bedload. Single equations describe the suspended- and totalsediment transport-rate relations for Chippewa River at Durand and main channel at Pepin, and the Black River near Galesville. Two equations were needed to define the transport- rate relations for the Chippewa River near Caryville and Wisconsin River at Muscoda. Bed material at all sites except Chippewa River near Caryville were of similar particle size and exhibited little variation with time or location in the river cross sections. Median diameter at these sites ranged from 0.35 to 0.84 mm (millimeter). At Chippewa River near Caryville, median diameter ranged from 0.42 to 15 mm. Helley-Smith bedload at Chippewa River at Durand and near Pepin, Black River near Galesville, and Wisconsin River at Muscoda were of similar particle size. About 57 to 65 percent of bedload at all sites except Chippewa River near Caryville was in the 0.4- to 0.6- mm size range. About 50 percent of bedload at Chippewa River near Caryville was in the 0.5- to 1.0-mm size range. Suspended sediment at all sites except Chippewa River near Caryville was in the sand-size range; the average median diameters were between 0.17 and 0.22 mm. At Chippewa River near Caryville, 60 percent (on the average) of suspended sediment was finer than 0.062 mm. Average annual total-sediment load and the percentage transported as bedload were determined for a 10-year period (water years 1974-83)(October 1,1973-September 30, 1982). These loads and percentages were, respectively, 123,000 tons and 35 percent at Chippewa River near Caryville; 1,073,000 tons and 61 percent at Chippewa River at Durand; 940,000 tons and 44 percent at Chippewa River near Pepin; 277,000 tons and 43 percent at Black River near Galesville; and 558,000 tons and 49 percent at Wisconsin River at Muscoda.

Wisconsin↗
USGS1992

Distribution and variability of fecal-indicator bacteria in Scioto and Olentangy rivers in the Columbus, Ohio, area

This report presents the results of a study by the U.S. Geological Survey, in cooperation with the City of Columbus, Ohio, to determine the distribution and variability of fecal-indicator bacteria in Scioto and Olentangy Rivers. Fecal-indicator bacteria are among the contaminants of concern to recreational users of these rivers in the Columbus area. Samples were collected to be analyzed for fecal-coliform and Escherichia coli (E. coli) bacteria and selected water-quality constituents and physical properties at 10 sites-- 4 on the Olentangy River and 6 on the Scioto River during the recreational seasons in 1987, 1988, and 1989. Measurements of streamflow also were made at these sites at various frequencies during base flow and runoff. The concentrations of fecal-coliform and E. coli bacteria in the Scioto and Olentangy Rivers spanned a range of five orders of magnitude, from less than 20 to greater than 2,000,000 col/100 mL (colonies per 100 milliliters). In addition, the concentrations of fecal coliform and E. coli bacteria are well correlated (r=0.97) in the study area. At times, relatively high concentrations, for fecal-indicator bacteria (concentrations greater than 51,000 col/100 mL for fecal-coliform and E. coli ) were found in Olentangy River at Woody Hayes Drive and at Goodale Street, and in Scioto River at Greenlawn Avenue and at Columbus. Intermediate concentrations of fecal-indicator bacteria (from 5,100 to 50,000 col/100 mL for fecal coliform and (from 510 to 50,000 col/100 mL for E. coli ) were found in Scioto River at Town Street and below O'Shaughnessy Dam near Dublin, Ohio, and in Olentangy River at Henderson Road. The lowest (median) concentrations of fecal-indicator bacteria (from 20 to 5,000 col/100 mL for fecal coliform and from 20 to 500 col/100 mL for E. coli ) were found at Olentangy River near Worthington, Ohio, Scioto River at Dublin Road Water Treatment Plant and below Griggs Reservoir. Fecal-coliform concentrations exceeded the geometric mean and single-sample Ohio Water Quality Standards for recreation less frequently than E. coli concentrations. The E. coli numerical water-quality standards are more difficult to meet than the fecal coliform standards because they are as much as an order of magnitude lower in some instances. The geometric mean bathing-water and primary-contact standards for fecal-coliform and E. coli bacteria were exceeded in more samples for Olentangy River at Goodale Street than for any other site. The single-sample bathing-water standard for fecal-coliform bacteria was exceeded in 83 percent of all samples and for E. coli in 91 percent of samples for Olentangy River at Goodale Street. Compared to Olentangy River at Goodale Street, geometric means and single-samples exceeded the bathing-water standards somewhat less frequently for Scioto River at Town Street and far less frequently for Scioto River at Dublin Road Water Treatment Plant. In contrast to results for fecal-indicator bacteria, the differences between sites for pH and for concentrations for total alkalinity, total chloride, total nonfilterable residue, total nitrate plus nitrite as nitrogen, total phosphorus, and total organic carbon were small. The large contribution of streamflow and discharge of fecal-indicator bacteria from Olentangy River to Scioto River has a major effect on the Scioto River downstream from the confluence of Olentangy River during periods of rainfall and runoff. Fecal-indicator discharges were calculated for times before, during, and at 24-hour intervals for 48 to 72 hours after two runoff-producing storms. Fecal-coliform and E. coli concentrations were lower in samples collected before runoff and during receding streamflows at 24- to 48-hours after the storms than in samples collected during runoff. The fecal-indicator discharges entering Scioto River from Olentangy River ranged from 22.6 to nearly 100 percent of the total for two storms studied. Controlling nonpoint, unregulated,

Water-Resources Investigations Report↗
USGS1995

Quantity and quality of ground-water discharge to the South Platte River, Denver to Fort Lupton, Colorado, August 1992 through July 1993

Water-quality studies conducted by the Metro Wastewater Reclamation District have indicated that during low flow in segments of the South Platte River between Denver and Fort Lupton, concentrations of dissolved oxygen are less than minimum concen- trations set by the State of Colorado. Low dissolved-oxygen concentrations are observed in two reaches of the river-they are about 3.3 to 6.4 miles and 17 to 25 miles downstream from the Metro Waste- water Reclamation District effluent outfalls. Concentrations of dissolved oxygen recover between these two reaches. Studies conducted by the U.S. Geological Survey have indicated that ground-water discharge to the river may contribute to these low dissolved-oxygen concentrations. As a result, an assessment was made of the quantity and quality of ground-water discharge to the South Platte River from Denver to Fort Lupton. Measurements of surface- water and ground-water discharge and collections of surface water and ground water for water-quality analyses were made from August 1992 through January 1993 and in May and July 1993. The quantity of ground-water discharge to the South Platte River was determined indirectly by mass balance of surface-water inflows and outflows and directly by instantaneous measurements of ground-water discharge across the sediment/water interface in the river channel. The quality of surface water and ground water was determined by sampling and analysis of water from the river and monitoring wells screened in the alluvial aquifer adjacent to the river and by sampling and analysis of water from piezometers screened in sediments underlying the river channel. The ground-water flow system was subdivided into a large-area and a small-area flow system. The precise boundaries of the two flow systems are not known. However, the large-area flow system is considered to incorporate all alluvial sediments in hydrologic connection with the South Platte River. The small- area flow system is considered to incorporate the alluvial aquifer in the vicinity of the river. Flow-path lengths in the large-area flow system were considered to be on the order of hundreds of feet to more than a mile, whereas in the small-area flow system, they were considered to be on the order of feet to hundreds of feet. Mass-balance estimates of incremental ground-water discharge from the large- area flow system ranged from -27 to 17 cubic feet per second per mile in three reaches of the river; the median rate was 4.6 cubic feet per second per mile. The median percentage of surface-water discharge derived from ground-water discharge in the river reaches studied was 13 percent. Instantaneous measurements of ground-water discharge from the small-area flow system ranged from -1,360 to 1,000 cubic feet per second per mile, with a median value of -5.8 cubic feet per second per mile. Hourly measurements of discharge from the small-area flow system indicated that the high rates of discharge were transient and may have been caused by daily fluctuations in river stage due to changing effluent-discharge rates from the Metro Wastewater Reclamation District treatment plant. Higher river stages caused surface water to infiltrate bed sediments underlying the river channel, and lower river stages allowed ground water to discharge into the river. Although stage changes apparently cycled large quantities of water in and out of the small- area flow system, the process probably provided no net gain or loss of water to the river. In general, mass balance and instantaneous measurements of ground-water discharge indicated that the ground- water flow system in the vicinity of the river consisted of a large-area flow system that provided a net addition of water to the river and a small- area flow system that cycled water in and out of the riverbed sediments, but provided no net addition of water to the river. The small-area flow system was superimposed on the large-area flow system. The median values of pH and dissolved oxygen

Water-Resources Investigations Report↗
USGS2000

Role of lake regulation on glacier fed rivers in enhancing salmon productivity: The Cook Inlet watershed south central Alaska, USA

Rivers fed by glaciers constitute a major part of the freshwater runoff into the Cook Inlet basin of south-central Alaska. This basin is very important to the economy of the State of Alaska because it is home to more than half of the population and it supports multi-million dollar commercial, subsistence and sport fisheries. Hence an understanding of how glacial runoff influences biological productivity is important for managing rivers that drain into Cook Inlet. This paper examines the ways in which the regulation of glacier-fed rivers by proglacial lakes affects salmon productivity, with particular reference to the Kenai River. Salmon escapement per unit channel length on the Kenai River is between two and ten times that found for rain-and-snowmelt dominated rivers and glacier-fed rivers lacking lake regulation. Lakes are shown to influence biological processes in glacier-fed rivers by attenuating peak flows, sustaining high flows throughout the summer, supplementing winter low flows, settling suspended sediment, and increasing river temperatures. Downstream from large lakes, glacier-fed rivers are less disturbed, channels are relatively stable and have well-developed salmonid habitats. The positive influences are indicated by the high diversity and abundances of benthic macroinvertebrates, which are important food resources for juvenile salmonids. High summer flows allow access for up-river salmon runs and lakes also provide both overwintering and rearing habitat. Copyright ?? 2000 John Wiley & Sons, Ltd.Rivers fed by glaciers constitute a major part of the freshwater runoff into the Cook Inlet basin of south-central Alaska. This basin is very important to the economy of the State of Alaska because it is home to more than half of the population and it supports multi-million dollar commercial, subsistence and sport fisheries. Hence an understanding of how glacial runoff influences biological productivity is important for managing rivers that drain into Cook Inlet. This paper examines the ways in which the regulation of glacier-fed rivers by proglacial lakes affects salmon productivity, with particular reference to the Kenai River. Salmon escapement per unit channel length on the Kenai River is between two and ten times that found for rain-and-snowmelt dominated rivers and glacier-fed rivers lacking lake regulation. Lakes are shown to influence biological processes in glacier-fed rivers by attenuating peak flows, sustaining high flows throughout the summer, supplementing winter low flows, settling suspended sediment, and increasing river temperatures. Downstream from large lakes, glacier-fed rivers are less disturbed, channels are relatively stable and have well-developed salmonid habitats. The positive influences are indicated by the high diversity and abundances of benthic macroinvertebrates, which are important food resources for juvenile salmonids. High summer flows allow access for up-river salmon runs and lakes also provide both overwintering and rearing habitat.

Hydrological Processes↗
USGS2008

Survival and migration behavior of juvenile coho salmon in the Klamath River relative to discharge at Iron Gate Dam, Northern California, 2007

This report describes a study of survival and migration behavior of juvenile coho salmon in the Klamath River relative to discharge at Iron Gate Dam in 2006. This was the second year of a multi-year study with the goal of determining the effects of discharge at Iron Gate Dam on survival of juvenile coho salmon downstream. The study was a collaborative effort among U.S. Geological Survey (USGS), U.S. Fish and Wildlife Service (USFWS), and the Yurok and Karuk Tribal Fisheries Departments. The goals of the study included: 1) estimating the survival of wild and hatchery juvenile coho salmon in the Klamath River downstream from Iron Gate Dam, 2) determining the effects of discharge and other covariates on their survival and migration, and 3) determining if fish from Iron Gate Hatchery could be used as surrogates for the limited source of wild fish. The major findings of the study in 2006 include: River discharges during the 2006 study period (4 April through 21 July 2006) were among the greatest on record. Average daily discharge at Iron Gate Dam was 3,956 cubic feet per second (cfs) and ranged from 997 to 10,300 cfs. Discharge at Iron Gate Dam was positively correlated with discharges of tributaries downstream due to the above average water year and frequent occurrence of spill at Iron Gate Dam. Average daily discharge near the estuary was 25,789 cfs and ranged from 4,740 to 50,600 cfs. This study was based on hatchery fish taken directly from a tank at Iron Gate Hatchery and wild fish captured in a rotary trap on the Shasta River. Releases of both groups began on 4 April when the catch of wild fish in California Department of Fish and Game‟s Shasta River rotary trap increased, but trap catches varied throughout the study period, resulting in differences in release dates of hatchery and wild fish. A total of 211 hatchery fish were released from 4 April through 26 May. Wild and hatchery fish released on a regular schedule between 25 April and 16 May 2006 were used in comparisons of the survival and migration of hatchery (N = 120) and wild (N = 162) fish. Additional analyses were performed using hatchery fish from all dates. The data and models did not support clear differences between survivals of hatchery and wild fish released on common dates, so estimates of reach survivals were made after pooling these data. Estimates of survival were lowest in the Iron Gate Dam to Scott River reach (0.813) and greatest in the Salmon River to Trinity River reach (1.000). The overall survival from river kilometer 309 (Iron Gate Hatchery) to river kilometer 33 was 0.653 (95% CI 0.578 to 0.729). Estimates of survival based on all hatchery fish releases were similar to those from release dates common to hatchery and wild fish and are similar to those in other river systems over similar distances. The migrations of hatchery and wild fish were different in the uppermost sections of the study area and were similar thereafter. A lag between release and migration, primarily upstream from the Scott River (river kilometer 234), was present in hatchery fish to a greater extent than in wild fish, resulting in differences in migration rates. Fish from both origins spent more time between release and the Scott River than in individual reaches downstream, and this was the only reach in which travel times of fish increased as discharge decreased. The travel times of hatchery and wild fish between sites were statistically similar downstream from Indian Creek (river kilometer 178). There were differences and similarities in the analyses of the effects of covariates on survivals of hatchery and wild fish. The models of covariate effects based on hatchery and wild fish released on common dates indicated effects on wild fish survival that were not supported in data from hatchery fish. However, when the entire suite of hatchery fish releases were used the results of the analyses were similar to those based on wild fish. In both instances the effects of temperature and release date were primarily in the first reach, the reach fish of both origins spent most of their time within. The signs of the effects of these covariates differed among the fish origins (negative for wild and positive for hatchery fish), presumably due to differences in their migrations in the first reach. The effects of dam discharge on survivals of hatchery and wild fish were generally similar (positive relation), and the effects on hatchery, and to a lesser extent wild, fish were largely downstream from the Scott River. This is likely due to the prolonged residence of the naïve hatchery fish, and to a lesser extent, migrant wild fish between release and the Scott River. Inasmuch as the differences between hatchery and wild fish we observed were likely those of migrants vs. non-migrants, the use of hatchery fish captured as they are migrating downstream, rather than those directly from hatchery tanks (i.e., naïve), may improve similarities between hatchery and wild fish in future studies. The data and models used in 2006 do not support the use of naïve hatchery fish as surrogates for migrant wild fish in determining the effects of discharge on survival upstream from the Scott River. This conclusion is based on the different effects of covariates in this reach that were likely attributable to the differences in hatchery and wild migration behaviors in this reach. The results of this second year of research provide insight to the migration and survival of hatchery and wild juvenile coho salmon in the Klamath River, but the results are from a single unusual water year. The results may be different during other water year types. The current information supports a positive relation between discharge at Iron Gate Dam and survival of juvenile coho salmon downstream, but additional data should be used to refine this relation. Discharge at the dam was correlated with discharges of Klamath River tributaries during this above average water year. The data and models from the 2006 study provide the first estimates of survival of these fish in the Klamath River and can be used with data from years with other water year types to examine the effects of discharge on survival. This will only be possible over a period of years in which the correlations between discharge and other factors, such as water temperature and date, are diminished. An experimental approach in which discharges are varied at Iron Gate Dam is the most direct method to determine if survivals are affected by discharge, but this may not be feasible given the limited storage capacity of the project.

California↗
USGS2012

Dissolved oxygen analysis, TMDL model comparison, and particulate matter shunting—Preliminary results from three model scenarios for the Klamath River upstream of Keno Dam, Oregon

Efforts are underway to identify actions that would improve water quality in the Link River to Keno Dam reach of the Upper Klamath River in south-central Oregon. To provide further insight into water-quality improvement options, three scenarios were developed, run, and analyzed using previously calibrated CE-QUAL-W2 hydrodynamic and water-quality models. Additional scenarios are under development as part of this ongoing study. Most of these scenarios evaluate changes relative to a "current conditions" model, but in some cases a "natural conditions" model was used that simulated the reach without the effect of point and nonpoint sources and set Upper Klamath Lake at its Total Maximum Daily Load (TMDL) targets. These scenarios were simulated using a model developed by the U.S. Geological Survey (USGS) and Watercourse Engineering, Inc. for the years 2006–09, referred to here as the "USGS model." Another model of the reach was developed by Tetra Tech, Inc. for years 2000 and 2002 to support the Klamath River TMDL process; that model is referred to here as the "TMDL model." The three scenarios described in this report included (1) an analysis of whether this reach of the Upper Klamath River would be in compliance with dissolved oxygen standards if sources met TMDL allocations, (2) an application of more recent datasets to the TMDL model with comparison to results from the USGS model, and (3) an examination of the effect on dissolved oxygen in the Klamath River if particulate material were stopped from entering Klamath Project diversion canals. Updates and modifications to the USGS model are in progress, so in the future these scenarios will be reanalyzed with the updated model and the interim results presented here will be superseded. Significant findings from this phase of the investigation include: * The TMDL analysis used depth-averaged dissolved oxygen concentrations from model output for comparison with dissolved oxygen standards. The Oregon dissolved oxygen standards do not specify whether the numeric criteria are based on depth-averaged dissolved oxygen concentration; this was an interpretation of the standards rule by the Oregon Department of Environmental Quality (ODEQ). In this study, both depth-averaged and volume-averaged dissolved oxygen concentrations were calculated from model output. Results showed that modeled depth-averaged concentrations typically were lower than volume-averaged dissolved oxygen concentrations because depth-averaging gives a higher weight to small volume areas near the channel bottom that often have lower dissolved oxygen concentrations. Results from model scenarios in this study are reported using volume-averaged dissolved oxygen concentrations. * Under all scenarios analyzed, violations of the dissolved oxygen standard occurred most often in summer. Of the three dissolved oxygen criteria that must be met, the 30-day standard was violated most frequently. Under the base case (current conditions), fewer violations occurred in the upstream part of the reach. More violations occurred in the down-stream direction, due in part to oxygen demand from the decay of algae and organic matter from Link River and other inflows. * A condition in which Upper Klamath Lake and its Link River outflow achieved Upper Klamath Lake TMDL water-quality targets was most effective in reducing the number of violations of the dissolved oxygen standard in the Link River to Keno Dam reach of the Klamath River. The condition in which point and nonpoint sources within the Link River to Keno Dam reach met Klamath River TMDL allocations had no effect on dissolved oxygen compliance in some locations and a small effect in others under current conditions. On the other hand, meeting TMDL allocations for nonpoint and point sources was predicted to be important in meeting dissolved oxygen criteria when Upper Klamath Lake and Link River also met Upper Klamath TMDL water-quality targets. * The location of greatest dissolved oxygen improvement from nutrient and organic matter reductions was downstream from point and nonpoint source inflows because time and distance are required for decay to occur and for oxygen demand to be exerted. * After assessing compliance with dissolved oxygen standards at all 102 model segments in the Link River to Keno Dam reach, it was determined that the seven locations used by ODEQ appear to be a representative subset of the reach for dissolved oxygen analysis. * The USGS and TMDL models were qualitatively compared by running both models for the 2006–09 period but preserving the essential characteristics of each, such as organic matter partitioning, bathymetric representation, and parameter rates. The analysis revealed that some constituents were not greatly affected by the differing algorithms, rates, and assumptions in the two models. Conversely, other constituents, especially organic matter, were simulated differently by the two models. Organic matter in this river system is best represented by a mixture of relatively labile particulate material and a substantial concentration of refractory dissolved material. In addition, the use of a first-order sediment oxygen demand, as in the USGS model, helps to capture the seasonal and dynamic effect of settled organic and algal material. * Simulation of shunting (diverting) particulate material away from the intake of four Klamath Project diversion canals, so that the material stayed in the river and out of the Project area, caused higher concentrations of particulate material to occur in the river. In all cases modeled, the increase in in-river particulate material also produced decreased dissolved oxygen concentrations and an increase in the number of days when dissolved oxygen standards were violated. * If particulate material were shunted back into the river at the Klamath Project diversion canals, less organic matter and nutrients would be taken into the Klamath Project area and the Lost River basin, resulting in return flows to the Klamath River via Lost River Diversion Channel that may have reduced nutrient concentrations. Model scenarios bracketing potential end-member nutrient concentrations showed that the composition of the return flows had little to no effect on dissolved oxygen compliance under simulated conditions.

Oregon↗
USGS2002

Hydrology, vegetation, and soils of riverine and tidal floodplain forests of the lower Suwannee River, Florida, and potential impacts of flow reductions

A study relating hydrologic conditions, soils, and vegetation of floodplain forests to river flow was conducted in the lower Suwannee River, Florida, from 1996 to 2000. The study was done by the U.S. Geological Survey in cooperation with the Suwannee River Water Management District to help determine the minimum flows and levels required for wetlands protection. The study area included forests within the 10-year floodplain of the Suwannee River from its confluence with the Santa Fe River to the tree line (lower limit of forests) near the Gulf of Mexico, and covered 18,600 hectares (ha) of forests, 75 percent of which were wetlands and 25 percent uplands. The floodplain was divided into three reaches, riverine, upper tidal, and lower tidal, based on changes in hydrology, vegetation, and soils with proximity to the coast. The Suwannee River is the second largest river in Florida in terms of average discharge. Median flow at the confluence of the Suwannee and Santa Fe Rivers is approximately 181 cubic meters per second (m3/s) or 6,480 cubic feet per second (ft3/s) (1933-99). At the upper end of the riverine reach, river stages are unaffected by tides and have a typical annual range of 4.1 meters (m). Tides affect river stages at low and medium flows in the upper tidal reach, and at all flows in the lower tidal reach. Median tidal range at the mouth of the Suwannee River is about 1 m. Salinity of river water in the lower tidal reach increases with decreasing flow and proximity to the Gulf of Mexico. Vertically averaged salinity in the river near the tree line is typically about 5 parts per thousand at medium flow. Land-surface elevation and topographic relief in the floodplain decrease with proximity to the coast. Elevations range from 4.1 to 7.3 m above sea level at the most upstream riverine transect and from 0.3 to 1.3 m above sea level on lower tidal transects. Surface soils in the riverine reach are predominantly mineral and dry soon after floods recede except in swamps. Surface soils in upper and lower tidal reaches are predominantly organic, saturated mucks. In the downstream part of the lower tidal reach, conductivities of surface soils are high enough (greater than 4 milli-mhos per centimeter) to exclude many tree species that are intolerant of salinity. Species richness of canopy and subcanopy plants in wetland forests in the lower Suwannee River is high compared to other river floodplains in North America. A total of 77 tree, shrub, and woody vine species were identified in the canopy and subcanopy of floodplain wetland forests (n = 8,376). Fourteen specific forest types were mapped using digitized aerial photographs, defined from vegetative sampling, and described in terms of plant species composition. For discussion purposes, some specific wetland types were combined, resulting in three general wetland forest types for each reach. Riverine high bottomland hardwoods have higher canopy species richness than all other forest types (40-42 species), with Quercus virginiana the most important canopy tree by basal area. The canopy composition of riverine low bottomland hardwoods is dominated by five species with Quercus laurifolia the most important by basal area. Riverine swamps occur in the lowest and wettest areas with Taxodium distichum the most important canopy species by basal area. Upper tidal bottomland hardwoods are differentiated from riverine forests by the presence of Sabal palmetto in the canopy. Upper tidal mixed forests and swamps are differentiated from riverine forests, in part, by the presence of Fraxinus profunda in the canopy. Nyssa aquatica, the most important canopy species by basal area in upper tidal swamps, is absent from most forests in the lower tidal reach where its distribution is probably restricted by salinity. Hydric hammocks, a wetland type that is rare outside of Florida, are found in the lower tidal reach and are flooded every 1-2 years by either storm surge or river floods. Lower tidal mixed forests and swamps have continuously saturated muck soils and are differentiated from upper tidal forests, in part, by the presence of Magnolia virginiana in the canopy. Lower tidal swamps have the highest density of canopy trees (about 1,200 trees per hectare) of all floodplain forest types, with Nyssa biflora the most important canopy species by basal area. Water use in the Suwannee River basin in Florida and Georgia is expected to increase over time because of anticipated growth and development in the region and adjacent areas. If increased water consumption reduced river flow, river stage would decrease and salinity would increase, resulting in a variety of impacts on forest composition, wetland biogeochemical processes, and fish and wildlife habitat. Forest composition in the floodplain is primarily determined by duration of inundation and saturation, depth and frequency of floods, and salinity. Long-term flow reductions would result in shallower flood depths, allowing drier and more tidal species to invade wetland forests of the riverine and upper tidal reaches. If flows were reduced 2.8-56 m3/s (100-2,000 ft3/s), an estimated 52-1,140 ha, respectively, would change to a drier forest type, and 36-788 ha, respectively, would change to a more tidal forest type. The greatest impacts would occur in swamps, where important swamp species such as Taxodium distichum and Nyssa aquatica could have increased competition not only from drier or more tidal species, but also from opportunistic bottomland hardwoods or invasive exotic species. Reduced flows could also result in a conversion of some wetland forests to uplands, increasing vulnerability to human disturbance, and decreasing tree basal area, species richness, and diversity of wildlife habitat. Salt-intolerant species would move upstream if flow reductions increased salinity in the lower tidal reach. If flows were reduced 2.8-56 m3/s (100-2,000 ft3/s), the area of forests along the tree line that would convert to marshes is estimated to be 72-618 ha, respectively. Loss of forests at the tree line would result in a loss of complex vertical structural diversity and woody micro-habitats that are used by many animals. These changes are already occurring due to sea level rise, but changes would occur more quickly if salinities increased as a result of flow reductions. The amount of inundated and saturated area in the floodplain forest of the riverine reach would decrease if flows were reduced. The greatest impacts would result from flow reductions that occurred at low flows, when inundated and saturated areas in the floodplain are limited. Drier conditions would result in oxidation of organic matter in swamp soils, which would reduce the soil's water-holding capacity and ability to retain water during droughts. Drier soils would increase vulnerability of the floodplain to fire and could also reduce the ability of riverine forests to remove nitrates and other pollutants from river water. Loss of inundated areas resulting from flow reductions at low flow would eliminate aquatic habitats that are critical to the survival of floodplain fishes and aquatic invertebrates, and are important to many other animals that use the floodplain. If flow reductions occurred during high flows, main channel fishes could decrease in diversity and abundance because they are seasonally dependent on flooded forests for food, shelter, and reproduction. In addition, aquatic organisms in the river and estuary could be adversely affected because they depend on particulate organic detritus and other floodplain exports as food sources.

Florida↗
USGS2005

Water use and availability in the Woonasquatucket and Moshassuck River basins, north-central Rhode Island

The Woonasquatucket River Basin includes 51.0 square miles, and the Moshassuck River Basin includes 23.8 square miles in north-central Rhode Island. The study area comprises these two basins. The two basins border each other with the Moshassuck River Basin to the northeast of the Woonasquatucket River Basin. Seven towns are in the Woonasquatucket River Basin, and six towns are in the Moshassuck River Basin. To determine the water use and availability in the study area, water supply and discharge data were collected for these river basins for the 1995–99 period, and compared to estimated long-term water available. The study area is unique in the State of Rhode Island, because no withdrawals from major public suppliers were made during the study period. Withdrawals were, therefore, limited to self-supplied domestic use, two minor suppliers, and one self-supplied industrial user. Because no metered data were available, the summer water withdrawals were assumed to be the same as the estimates for the rest of the year. Seven major water suppliers distribute an average of 17.564 million gallons per day for use in the study area from sources outside of the study area. The withdrawals from minor water suppliers were 0.017 million gallons per day in the study area, all in the town of Smithfield in the Woonasquatucket River Basin. The remaining withdrawals in the study area were estimated to be 0.731 million gallons per day by self-supplied domestic, commercial, industrial, and agricultural users. Return flows in the study area included self-disposed water and disposal from permitted dischargers, including the Smithfield Sewage Treatment Plant. Return flows accounted for 4.116 million gallons per day in the study area. Most public-disposed water (15.195 million gallons per day) is collected by the Narragansett Bay Commission and is disposed outside of the basin in Narragansett Bay. The PART program, a computerized hydrograph-separation application, was used at one index stream-gaging station to determine water availability based on the 75th, 50th, and 25th percentiles of the total base flow, the base flow minus the 7-day, 10-year flow criteria, and the base flow minus the Aquatic Base Flow criteria. The index station selected was the Branch River at Forestdale, which is close to the study area and has a similar percentage of sand and gravel area. Water availability was estimated on the basis of baseflow contributions from sand and gravel deposits and till deposits at the index station. Flows were computed for June, July, August, and September 1957–2000, and a percentage of the total flow was determined to come from either sand and gravel deposits, or till, by using a regression equation. The base-flow contributions were converted to a flow per unit area at the station for the till and for the sand and gravel deposits and then applied to the deposits in the study area basins. These values were used to estimate the gross yield of base flow, as well as to subtract the two low flows (7-day, 10-year flow, and Aquatic Base Flow criteria). The results from the Branch River stream-gaging station were lowest in August at the 75th, 50th, and 25th percentile for total flow with either flow criteria subtracted. The estimated August gross yield at the 50th percentile from the Woonasquatucket River Basin was 12.94 million gallons per day, and 5.91 million gallons per day from the Moshassuck River Basin. A ratio was calculated that is equal to total withdrawals divided by water availability. Water-availability flow scenarios at the 75th, 50th, and 25th percentiles for the basins, which are based on total water available from base-flow contributions from till and sand and gravel deposits in the basins, were assessed. The ratios were the highest in July for the 50th percentile estimated gross yield minus Aquatic Base Flow (ABF) flow criteria, where withdrawals are close to the available water. Ratios are not presented if the available water is less than the flow criteria. The ratio of withdrawals to the July gross yield at the 50th percentile minus Aquatic Base Flow was 0.796 for the Woonasquatucket and 0.275 for the Moshassuck River Basin. A long-term hydrologic budget was calculated for the period of 1956–2000 for the Woonasquatucket River Basin and the period of 1964–2000 for the Moshassuck River Basin. The water withdrawals and return flows used in the budget were from 1995 through 1999. For the hydrologic budget, inflow was assumed to equal outflow and was about 120 million gallons per day in the Woonasquatucket River Basin and 56 million gallons per day in the Moshassuck River Basin. The estimated inflows from precipitation and water return flow were 97.3 and 2.7 percent, respectively, in the Woonasquatucket River Basin, and 98.3 and 1.7 percent, respectively, in the Moshassuck River Basin. The estimated outflows from evapotranspiration, streamflow, and water withdrawals were 43.4, 56.1, and 0.5 percent, respectively, in the Woonasquatucket River Basin, and 49.8, 50, and 0.2 percent, respectively, in the Moshassuck River Basin.

Rhode Island↗
USGS2005

Simulation of conservative-constituent transport in the Red River of the North Basin, North Dakota and Minnesota, 2003-04

Population growth along with possible future droughts in the Red River of the North (Red River) Basin will create an increasing need for reliable water supplies. Therefore, as a result of the Dakota Water Resources Act of 2000, the Bureau of Reclamation identified eight water-supply alternatives (including a no-action alternative) to meet future water needs in the basin. Because of concerns about the possible effects of the alternatives on water quality in the Red River and the Sheyenne River and in Lake Winnipeg, Manitoba, the Bureau of Reclamation needs to prepare an environmental impact statement that describes the specific environmental effects of each alternative. To provide information for the environmental impact statement, the U.S. Geological Survey, in cooperation with the Bureau of Reclamation, conducted a study to develop and apply a water-quality model, hereinafter referred to as the Red River water-quality model, to part of the Red River and the Sheyenne River to simulate conservative-constituent transport in the Red River Basin. The Red River water-quality model is a one-dimensional, steady-state flow and transport model for selected constituents in the Red River and the Sheyenne River. The model simulates the flow and transport of total dissolved solids, sulfate, and chloride during steady-state conditions. The physical model domain includes the Red River from the confluence of the Bois de Sioux and Otter Tail Rivers to the Red River at Emerson, Manitoba, and the Sheyenne River from above Harvey, N. Dak., to the confluence with the Red River. The Red River water-quality model was calibrated and tested using data collected at 34 sites from September 15 through 16, 2003, and from May 10 through 13, 2004. Water-quality samples were collected during low, steady-flow conditions from September 15 through 16, 2003, and during medium, unsteady-flow conditions from May 10 through 13, 2004. The simulated total dissolved-solids, sulfate, and chloride concentrations generally were within 5 percent of the measured concentrations. The Red River water-quality model was used to simulate conservative-constituent transport in the Red River and the Sheyenne River for the eight water-supply alternatives identified by the Bureau of Reclamation. For the first set of eight simulations, September 2003 streamflows were used with projected 2050 return flows and withdrawals. For the second set of eight simulations, the September 2003 streamflows were reduced by 25 percent. The simulated concentrations for three of the alternatives generally were lower than for the no-action alternative. Of those alternatives, one would result in a decrease in concentrations for two constituents, one would result in a decrease in concentrations for all three constituents, and one would result in a decrease in concentrations for one constituent and an increase in concentrations for another constituent. For four of the alternatives, the differences between the mean simulated concentrations were less than calibration errors, indicating the effects of those alternatives on water quality in the rivers is uncertain. The effects of reduced streamflow on simulated total dissolved-solids, sulfate, and chloride concentrations were greatest for alternative 2. Reduced streamflow probably has an effect on simulated total dissolved-solids concentrations for alternatives 2, 3, 5, and 7 and on simulated sulfate concentrations for alternatives 2 and 5. Except for alternative 2, reduced streamflow had little effect on simulated chloride concentrations.

Scientific Investigations Report↗
USGS2007

Water quality of the St. Clair River, Lake St. Clair, and their U.S. tributaries, 1946-2005

The St. Clair River/Lake St. Clair waterway forms an international boundary between the United States and Canada. The waters of the area are an important part of the cultural heritage of the area and serves as an important water-supply and power-generating resource; the waterway also supports an economy based largely on recreation, agriculture, and manufacturing. This report was undertaken as part of the Lake St. Clair Regional Monitoring Project for the purpose of providing a comprehensive assessment of the hydrological, chemical, and physical state of the surface water of Lake St. Clair and its tributaries. The data varied in focus and density over the period of compilation which in many cases this variation prevented the completion of statistical analyses because data did not meet minimum comparability or quality requirements for those tests. Comparison of water quality of the Belle, Black, Clinton, and Pine River Basins, as well as basins of minor rivers in the study area, showed that water quality in many of the tributaries, particularly the Clinton River and some of the minor rivers, was degraded compared to the water quality of the St. Clair River/Lake St. Clair waterway. Data analyses included comparison of nutrients, chloride, specific conductance, turbidity, biochemical oxygen demand (BOD), and pesticides among the basins and the St. Clair River. Median concentrations of total nitrate were well below the recommended USEPA total nitrogen ambient water-quality criterion of 0.54 mg/L as N for nutrient ecoregion VII for all study-area streams except the Clinton River. More than 93 percent of the phosphorus concentrations for the Belle, Black, Pine and minor river basins and 84 percent of the phosphorus concentrations for the Clinton River Basin are greater than the USEPA recommended ambient total phosphorus criterion of 0.033 mg/L for rivers and streams. Nine chloride concentrations exceeded the USEPA criterion maximum concentration (CMC) for chloride set at 860 mg/L for all study-area streams, with the six largest being in the Belle River Basin. Higher chloride concentrations were increasingly common from 2002 to 2005. The urban minor river basins had the highest median specific conductance, whereas the agricultural Pine River Basin had the lowest median specific conductance. The median values of BOD for the five basins in the study area ranged from 2.4 mg/L for the Pine River Basin to 3.2 mg/L for the Black and Clinton River Basins, whereas the median for the St. Clair River was 0.5 mg/L. In 1985, the highest concentrations of pesticides were found in samples from the mouth of the Clinton River; however, in 1996–98, the majority of high pesticide concentrations were found in samples from the Black River. Changing land-use patterns, specifically conversion of agricultural lands to urban/residential lands in the Clinton River Basin, may explain this difference. Trend analysis was done for four stream sites where adequate data were available. These analyses identified no significant water-quality changes at a stream site on the Black River, where land-use patterns have changed little in the past few decades. This stands in marked contrast to trend analysis for three stream sites in the Clinton River Basin, which has undergone significant land-use change. The changes at the Clinton River stream sites, ranging from 5 to 13 significant trends, were generally decreases in nutrients and increases in total dissolved solids (TDS) and chloride. The greater flow volume of the St. Clair River/Lake St. Clair waterway is able to assimilate incoming dissolved and suspended constituents from tributaries with little effect upon its overall water quality, although incomplete mixing may result in localized water-quality impairment downstream from tributary confluences. Mixing effects on Lake St. Clair water quality was also demonstrated in analysis of Escherichia coli ( E. coli ) data collected at paired nearshore/offshore sites, which reflected similarity in water quality among many paired sites.

Michigan↗
USGS2007

Ground water redox zonation near La Pine, Oregon: Relation to river position within the aquifer–riparian zone continuum

Increasing residential development since in the 1960s has lead to increases in nitrate concentrations in shallow ground water in parts of the 247 square mile study area near La Pine, Oregon. Denitrification is the dominant nitrate-removal process that occurs in suboxic ground water, and suboxic ground water serves as a barrier to transport of most nitrate in the aquifer. Oxic ground water, on the other hand, represents a potential pathway for nitrate transport from terrestrial recharge areas to the Deschutes and Little Deschutes Rivers. The effects of present and potential future discharge of ground-water nitrate into the nitrogen-limited Deschutes and Little Deschutes Rivers are not known. However, additions of nitrogen to nitrogen-limited rivers can lead to increases in primary productivity which, in turn, can increase the magnitudes of dissolved oxygen and pH swings in river water. An understanding of the distribution of oxic ground water in the near-river environment could facilitate understanding the vulnerability of these rivers and could be a useful tool for management of these rivers. In this study, transects of temporary wells were installed in sub-river sediments beneath the Deschutes and Little Deschutes Rivers near La Pine to characterize near-river reduction/oxidation (redox) conditions near the ends of ground-water flow paths. Samples from transects installed near the center of the riparian zone or flood plain were consistently suboxic. Where transects were near edges of riparian zones, most ground-water samples also were suboxic. Oxic ground water (other than hyporheic water) was uncommon, and was only detected near the outside edge of some meander bends. This pattern of occurrence likely reflects geochemical controls throughout the aquifer as well as geochemical processes in the microbiologically active riparian zone near the end of ground-water flow paths. Younger, typically less reduced ground water generally enters near-river environments through peripheral zones, whereas older, typically more reduced ground water tends to discharge closer to the center of the river corridor. Such distributions of redox state reflect ground-water movement and geochemical evolution at the aquifer-scale. Redox state of ground water undergoes additional modification as ground water nears discharge points in or adjacent to rivers, where riparian zone processes can be important. Lateral erosion of river systems away from the center of the flood plain can decrease or even eliminate interactions between ground water and reducing riparian zone sediments. Thus, ground water redox patterns in near-river sediments appear to reflect the position of a river within the riparian zone/aquifer continuum. Spatial heterogeneity of redox conditions near the river/aquifer boundary (that is, near the riverbed) makes it difficult to extrapolate transect-scale findings to a precise delineation of the oxic-suboxic boundary in the near-river environment of the entire study area. However, the understanding of relations between near-river redox state and proximity to riparian zone edges provides a basis for applying these results to the study-area scale, and could help guide management efforts such as nitrogen-reduction actions or establishment of Total Maximum Daily Load criteria. Coupling the ground-water redox-based understanding of river vulnerability with ground-water particle-tracking-based characterization of connections between upgradient recharge areas and receiving rivers demonstrates one means of linking effects of potential nitrate loads at the beginning of ground-water flow paths with river vulnerability.

Oregon↗