Geology topics

Research about Minnesota

Source-linked reports with geographic coverage including Minnesota.

At least 379 records · Page 21Linked to original sources

USGS2006

Degradation of phenolic contaminants in ground water by anaerobic bacteria: St. Louis Park, Minnesota

Coal-tar derivatives from a coal-tar distillation and wood-treating plant that operated from 1918 to 1972 at St. Louis Park, Minnesota contaminated the near-surface ground water. Solutions of phenolic compounds and a water-immiscible mixture of polynuclear aromatic compounds accumulated in wetlands near the plant site and entered the aquifer. The concentration of phenolic compounds in the aqueous phase under the wetlands is about 30 mg/1 but decreases to less than 0.2 mg/1 at a distance of 430 m immediately downgradient from the source. Concentrations of naphthalene (the predominant polynuclear compound in the ground water) and sodium (selected as a conservative tracer) range from about 20 mg/1 and 430 mg/1 in the aqueous phase at the source to about 2 mg/1 and 120 mg/1 at 430 m downgradient, respectively. Phenolic compounds and naphthalene are disappearing faster than expected if only dilution were occurring. Sorption of phenolic compounds on aquifer sediments is negligible but naphthalene is slightly sorbed. Anaerobic biodegradation of phenolic compounds is primarily responsible for the observed attenuation. Methane was found only in water samples from the contaminated zone (2-20 mg/1). Methane-producing bacteria were found only in water from the contaminated zone. Methane was produced in laboratory cultures of contaminated water inoculated with bacteria from the contaminated zone. Evidence for anaerobic biodegradation of naphthalene under either field or laboratory conditions was not obtained.

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USGS2006

Lake Sturgeon, Acipenser fulvescens, movements in Rainy Lake, Minnesota and Ontario

Rainy Lake, Minnesota-Ontario, contains a native population of Lake Sturgeon ( Acipenser fulvescens ) that has gone largely unstudied. The objective of this descriptive study was to summarize generalized Lake Sturgeon movement patterns through the use of biotelemetry. Telemetry data reinforced the high utilization of the Squirrel Falls geographic location by Lake Sturgeon, with 37% of the re-locations occurring in that area. Other spring aggregations occurred in areas associated with Kettle Falls, the Pipestone River, and the Rat River, which could indicate spawning activity. Movement of Lake Sturgeon between the Seine River and the South Arm of Rainy Lake indicates the likelihood of one integrated population on the east end of the South Arm. The lack of re-locations in the Seine River during the months of September and October may have been due to Lake Sturgeon moving into deeper water areas of the Seine River and out of the range of radio telemetry gear or simply moving back into the South Arm. Due to the movements between Minnesota and Ontario, coordination of management efforts among provincial, state, and federal agencies will be important.

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USGS2006

Characterization of surface and ground water δ18O seasonal variation and its use for estimating groundwater residence times

18 O is an ideal tracer for characterizing hydrological processes because it can be reliably measured in several watershed hydrological compartments. Here, we present multiyear isotopic data, i.e. 18 O variations (δ 18 O), for precipitation inputs, surface water and groundwater in the Shingobee River Headwaters Area (SRHA), a well-instrumented research catchment in north-central Minnesota. SRHA surface waters exhibit δ 18 O seasonal variations similar to those of groundwaters, and seasonal δ 18 O variations plotted versus time fit seasonal sine functions. These seasonal δ 18 O variations were interpreted to estimate surface water and groundwater mean residence times (MRTs) at sampling locations near topographically closed-basin lakes. MRT variations of about 1 to 16 years have been estimated over an area covering about 9 km 2 from the basin boundary to the most downgradient well. Estimated MRT error (±0·3 to ±0·7 years) is small for short MRTs and is much larger (±10 years) for a well with an MRT (16 years) near the limit of the method. Groundwater transit time estimates based on Darcy's law, tritium content, and the seasonal δ 18 O amplitude approach appear to be consistent within the limits of each method. The results from this study suggest that use of the δ 18 O seasonal variation method to determine MRTs can help assess groundwater recharge areas in small headwaters catchments.

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USGS2006

Trace element concentrations and bioindicator responses in tree swallows from northwestern Minnesota

Extremely high concentrations of cadmium (3.5 μ g/g dry wgt.) and elevated concentrations of chromium (>10 μ g/g dry wgt.) and mercury (1.6 μ g/g dry wgt.) were reported in waterbird tissues at Agassiz National Wildlife Refuge in northwestern Minnesota in 1994. Tree swallows ( Tachycineta bicolor) were studied during 1998–2001 at three drainages into the Refuge, two pools on the Refuge, and at a nearby reference location to document whether high levels of contaminants were still present, and if so to quantify the source and severity of the contamination. Trace elements were measured in tree swallow eggs, livers, and diet. Reproductive success and bioindicator responses were monitored. In 2000, water was drawn down on Agassiz Pool, one of the main pools on the Refuge. This presented an opportunity to evaluate the response of trace element concentrations in the diet and tissues of tree swallows after reflooding. High concentrations of trace elements were not detected in swallow tissues, nor were there differences among locations. Less than 20% of swallow samples had detectable concentrations of cadmium or chromium. Mercury concentrations were low and averaged <0.25 μ g/g dry wgt. in swallow tissues. Trace elements, including mercury, did not increase in tree swallows following the 2000 drawdown at Agassiz Pool. Hatching success and survival of nestlings to 12 days-of-age for tree swallows on the Refuge were similar to the national average and consistent with background trace element concentrations. Bioindicator measurements were within the normal ranges as well.

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USGS2006

A 3-decade dearth of deer (Odocoileus virginianus) in a wolf (Canis lupus)-dominated ecosystem

Some 30 y after wolves ( Canis lupus ) were implicated in decimating wintering white-tailed deer ( Odocoileus virginianus ) in a 3000-km 2 area of northeastern Minnesota, wintering deer still have not recolonized the area. From 1976 to 2004, we aerially radio-tracked wolves there during 250 h and recorded 2 deer (in 1985 and 2000) killed or eaten by wolves during February and March. We observed no other deer or deer sign, but regularly observed deer, deer sign and wolf-killed deer in adjacent wolf-pack territories. Although habitat in the study area generally remains poor, some regeneration has taken place, and deer have increased adjacent to the area. However, wolf numbers have persisted by preying on moose ( Alces alces ). We could detect no reason other than wolf predation and deer migration traditions for why wintering deer have not recolonized the area.

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USGS2006

Pathogens, nutritional deficiency, and climate influences on a declining moose population

Several potential proximate causes may be implicated in a recent (post-1984) decline in moose ( Alces alces andersoni ) numbers at their southern range periphery in northwest Minnesota, USA. These causes include deleterious effects of infectious pathogens, some of which are associated with white-tailed deer ( Odocoileus virginianus ), negative effects of climate change, increased food competition with deer or moose, legal or illegal hunting, and increased predation by gray wolves ( Canis lupus ) and black bears ( Ursus americanus ). Long-standing factors that may have contributed to the moose decline include those typically associated with marginal habitat such as nutritional deficiencies. We examined survival and productivity among radiocollared ( n = 152) adult female and juvenile moose in northwest Minnesota during 1995–2000, and assessed cause of death and pathology through carcass necropsy of radiocollared and non-radiocollared animals. Aerial moose surveys suggested that hunting was an unlikely source of the numerical decline because the level of harvest was relatively low (i.e., approx. 15% / 2 yr) and the population usually grew in years following a hunt. The majority of moose mortalities (up to 87% of radiocollared moose [ n = 76] and up to 65% of non-radiocollared moose [ n = 84]) were proximally related to pathology associated with parasites and infectious disease. Liver fluke ( Fascioloides magna ) infections apparently constituted the greatest single source of mortality and caused significant pathology in the liver, thoracic and peritoneal cavities, pericardial sac, and lungs. Mortality due to meningeal worm ( Parelaphostrongylus tenuis ) was less prevalent and was manifested through characteristic neurological disease. Several mortalities apparently were associated with unidentified infectious disease, probably acting in close association with malnutrition. Bone-marrow fat was lower for moose dying of natural causes than those dying of anthropogenic factors or accidents, implying that acute malnutrition contributed to moose mortality. Blood profiles from live-captured animals indicated that those dying in the subsequent 18 months were chronically malnourished. Relative to other populations, average annual survival rates for adult females (0.79 [0.74–0.84; 95% CI]) and yearlings (0.64 [0.48–0.86]) were low, whereas those for calves (0.66 [0.53–081]) were high. Pregnancy (48%) and twinning (19%) rates were among the lowest reported for moose, with reproductive senescence among females being apparent as early as 8 years. Pregnancy status was related to indices of acute (i.e., bone-marrow fat) and chronic (i.e., blood condition indices) malnutrition. Opportunistic carcass recovery indicated that there likely were few prime-aged males (>5 yr old) in the population. Analysis of protein content in moose browse and fecal samples indicated that food quality was probably adequate to support moose over winter, but the higher fecal protein among animals that died in the subsequent 18 months could be indicative of protein catabolism associated with malnutrition. Trace element analysis from moose livers revealed apparent deficiencies in copper and selenium, but there was limited evidence of direct association between trace element concentrations and moose disease, pathology, or mortality. Time-series analysis of regional moose counts (1961–2000) indicated that annual population growth rate was related negatively to mean summer temperature, with winter and summer temperatures increasing by an average of 6.8 and 2.1 C, respectively, during the 40-year period. This change may have increased moose thermoregulatory costs and disrupted their energy balance, and thereby reduced their fitness. Time-series analysis failed to show a relationship between annual population growth rate and moose or deer abundance, indicating that food limitation via resource competition was unlikely. Population viability analyses, using count data (1961–2000) and demographic data collected during this study, suggested that the northwest Minnesota moose population likely would not persist over the next 50 years. More broadly, we conclude that the southern distribution of moose may become restricted in areas where climate and habitat conditions are marginal, especially where deer are abundant and act as reservoir hosts for parasites.

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USGS2006

Geomorphic characteristics and classification of Duluth-area streams, Minnesota

In 2003 and 2004, a geomorphic assessment of streams in 20 watersheds in the Duluth, Minn., area was conducted to identify and summarize geomorphic characteristics, processes, disturbance mechanisms, and potential responses to disturbance. Methods used to assess the streams included watershed characterization, descriptions of segment slopes and valley types, historical aerial photograph interpretation, and rapid field assessments and intensive field surveys of stream reaches. Geomorphic conditions were summarized into a segment-scale classification with 15 categories mainly based on drainage-network position and slope, and, secondarily, based on geologic setting, valley type, and dominant geomorphic processes. Main causes of geomorphic disturbance included historical logging and agriculture, and ongoing urban development, human-caused channel alterations, road and storm sewer drainage, ditching, hiking trails, and gravel pits or quarries. Geomorphic responses to these disturbances are dependent on a combination of drainage-network position, slope, and geologic setting. Geologic setting is related to drainage-network position because the geologic deposits parallel the Lake Superior shoreline. Headwater streams in large watersheds flow over glacial deposits above altitudes of about 1,200 feet (ft). Headwater tributaries and upper main stems have ditch-like channels with gentle slopes and no valleys. Urban development and road drainage cause increased runoff and flood peaks in these segments resulting in channel widening. Below about 1,200 ft, main-stem segments generally are affected by bedrock type and structure and have steep slopes and confined or entrenched valleys. Increases in flood peaks do not cause incision or widening in the bedrock-controlled valleys; instead, the flow and scour areas are expanded. Feeder tributaries to these main stems have steep, confined valleys and may be sources for sediment from urban areas, road runoff, or storm sewer outfalls. Main-stem segments near the glacial deposits/surficial bedrock contact (1,000–1,200 ft) have the most potential for response to disturbance because they tend to have narrow valleys with sandy glacial lakeshore deposits and moderate slopes. Increases in flood peaks (from upstream increases in runoff) increase the potential for landslides and mass wasting from valley sides as well as channel widening.

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USGS2006

Ground-water/surface-water interaction in nearshore areas of Three Lakes on the Grand Portage Reservation, northeastern Minnesota, 2003-04

The U.S. Geological Survey (USGS), in cooperation with the Grand Portage Band of Chippewa Indians, applied three techniques to assess ground-water/surface-water interaction in nearshore areas of three lakes (North, Teal, and Taylor) on the Grand Portage Reservation in northeastern Minnesota. At each lake, analyses of existing aerial photographs, in-situ temperature measurements of shoreline lake sediment, and chemical analyses of surface water and pore water were conducted. Surface-water and pore-water samples were analyzed for major constituents, nutrients, and stable isotopes of oxygen and hydrogen. Bulk precipitation samples were collected and analyzed (1) for nutrient concentrations to determine nutrient input to the lakes through atmospheric deposition and (2) for stable isotope ratios of oxygen and hydrogen to determine a meteoric waterline that was needed for the stable isotope analyses of surface-water and pore-water samples. Total nitrogen concentrations in the precipitation samples ranged from 0.51 to 8.4 mg/L (milligrams per liter) as nitrogen at the North Lake precipitation station and from 0.42 to 2.3 mg/L as nitrogen at the Grand Portage precipitation station. Oxygen-18/oxygen-16 and deuterium/protium isotope ratios for the bulk precipitation samples lie relatively close to a meteoric waterline for northern Wisconsin, except for the ratios for samples collected on May 20, 2004. Analyses of existing aerial photographs, nearshore lake-sediment temperatures, and seasonal isotope ratios of surface-water and pore-water samples were the most valuable data for identifying locations of ground-water inflow and surface-water outseepage. Analyses of existing aerial photographs of the three lakes indicated the location of potential inflow channels and lineaments identifying potential ground-water inflow locations for pore-water sampling. Lake-sediment temperatures at potential ground-water inflow locations ranged from 4 to 16 ºC, varying between lakes, seasons, and climatic conditions. Major constituent chemistry was valuable at Taylor Lake, and to a limited extent at North and Teal Lakes, in confirming results from the isotope and lake-sediment temperature data. Ground-water inflow to North Lake likely occurs along the southwest and south shores, and along portions of the west, southeast, north, and northeast shores. Relatively cool lake-sediment temperatures along the southwest, south, west, and southeast shores, and in isolated beaver channels along the north and northeast shores of North Lake indicate potential ground-water inflow at these locations. Both localized ground-water inflow and surface-water outseepage occurs along portions of the north, northeast, southeast, and south shores, varying seasonally. Conflicting evidence for ground-water flow conditions exist for the northwest and north-northwest pore-water samples. Only minor differences in the major constituent concentrations were seen between the surface-water and pore-water samples from the North Lake area with the exception of iron and manganese concentrations. Ground-water inflow likely takes place along the south-southwest and north shores of Teal Lake, with a mixture of ground-water inflow and surface-water outseepage occurring in other areas of the lake. Cooler lake-sediment temperatures occurred along the south-southwest, west, and northwest shores, portions of the north shore, and in channels identified in aerial photographs throughout the lake, indicating potential ground-water inflow at those locations. Warmer lake-sediment temperatures along the northeast and portions of the southwest and northwest shores of Teal Lake indicate potential locations where surface-water outseepage or little ground- and surface-water interaction occurs. The major constituent concentrations were higher in the pore-water samples collected from the south-southwest and northeast shores of Teal Lake, indicating ground-water inflow. Cation adsorption, cation exchanges with hydrogen ions, and chelation with organic materials occurring in the fen surrounding the lake likely resulted in the low dissolved calcium, magnesium, and sodium concentrations in north, northwest, and west pore-water samples from the Teal Lake area. Pore-water samples from the south-southwest, north, and southwest shores of Teal Lake had isotopic compositions that plotted closest to the meteoric waterline, indicating that little evaporation or transpiration occurred in these samples and that ground-water inflow may be occurring at these locations. Surface-water outseepage from Teal Lake likely occurs along the northeast shore even though major constituent concentrations were high. Major constituent concentrations may be high because of a nearby beaver dam. Ground-water inflow to Taylor Lake likely occurs at the north and south pore-water sampling sites. Higher major constituent concentrations and the least evaporative isotope ratios were found in pore-water samples along the south, north, and west shores of Taylor Lake, indicating potential locations of ground-water inflow. However, a combination of warmer and cooler lake-sediment temperatures along the west lowland indicated that ground-water inflow and surface-water outseepage may occur at that location. Surface-water outseepage likely occurs from Taylor Lake along the south shore through a surface-water drainage channel to a downgradient bog. Warmer lake-sediment temperatures along portions of the south and southeast shores indicate that surface-water outseepage may occur at those locations. Both ground-water inflow and surface-water outseepage may occur along the west, southeast, and east shores of Taylor Lake, varying seasonally and with local precipitation. Knowledge of general water-flow directions in lake watersheds and how they may change seasonally can help water-quality specialists and lake managers address a variety of water-quality and aquatic habitat protection issues for lakes. Results from this study indicate that ground-water and surface-water interactions at the study lakes are complex, and the ability of the applied techniques to identify ground-water inflow and surface-water outseepage locations varied among the lakes. Measurement of lake-sediment temperatures proved to be a reliable and relatively inexpensive reconnaissance technique that lake managers may apply in complex settings to identify general areas of ground-water inflow and surface-water outseepage.

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USGS2006

Water resources data, Minnesota, water year 2005

Water resources data for the 2005 water year for Minnesota consist of records of stage, discharge, and water quality of streams; stage of lakes and reservoirs; ground-water quality; and water quality in wells. This report contains discharge records for 116 stream-gaging stations; stage for 11 lakes and reservoirs; water quality for 12 stream-gaging stations; peak flow data for 87 highflow partial-record stations, and water levels for 2 ground water observation wells. Additional water data were collected at various sites that are not part of the systematic data collection program, and are published as miscellaneous measurements. These data represent that part of the National Water Data System operated by the U.S. Geological Survey for cooperating State and Federal agencies in Minnesota.

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USGS2005

Geophysical monitoring of a field-scale biostimulation pilot project

The USGS conducted a geophysical investigation in support of a U.S. Naval Facilities Engineering Command, Southern Division field‐scale biostimulation pilot project at Anoka County Riverfront Park (ACP), downgradient of the Naval Industrial Reserve Ordnance Plant, Fridley, Minnesota. The goal of the pilot project is to evaluate subsurface injection of vegetable oil emulsion (VOE) to stimulate microbial degradation of chlorinated hydrocarbons. To monitor the emplacement and movement of the VOE and changes in water chemistry resulting from VOE dissolution and/or enhanced biological activity, the USGS acquired cross‐hole radar zero‐offset profiles, traveltime tomograms, and borehole geophysical logs during five site visits over 1.5 years. Analysis of pre‐ and postinjection data sets using petrophysical models developed to estimate VOE saturation and changes in total dissolved solids provides insights into the spatial and temporal distribution of VOE and ground water with altered chemistry. Radar slowness‐difference tomograms and zero‐offset slowness profiles indicate that the VOE remained close to the injection wells, whereas radar attenuation profiles and electromagnetic induction logs indicate that bulk electrical conductivity increased downgradient of the injection zone, diagnostic of changing water chemistry. Geophysical logs indicate that some screened intervals were located above or below zones of elevated dissolved solids; hence, the geophysical data provide a broader context for interpretation of water samples and evaluation of the biostimulation effort. Our results include (1) demonstration of field and data analysis methods for geophysical monitoring of VOE biostimulation and (2) site‐specific insights into the spatial and temporal distributions of VOE at the ACP.

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USGS2005

Nitrogen isotopes as indicators of nitrate sources in Minnesota sand-plain aquifers

Nitrate concentrations in excess of national drinking-water standards (10 mg/1 as N) are present in certain sand-plain aquifers in central Minnesota. To investigate nitrate sources in the aquifers, nitrogen-isotope values of nitrate (δ 15 N NO3 No3) were measured in shallow ground water from 51 wells in five land-use settings. The land-use settings and corresponding average nitrate concentrations (as N) and δ 15 N NO3 values are: livestock feedlots, 12.7 mg/1, 21.3% 0 ; cultivated-irrigated fields, 13 mg/1, 7.4% 0 ; residential areas with septic systems, 8.3 mg/1, 6.0% 0 ; cultivated-nonirrigated fields, 15.5 mg/1, 3.4% 0 ; and natural, undeveloped areas, 3.8 mg/1, 3.1% 0 . Values of δ 15 N NO3 less than 2% 0 suggest that nitrogen from commercial inorganic fertilizers exists in ground water beneath all settings except the feedlots. Values of δ 15 N NO3 greater than 10% 0 suggest that nitrogen from animal waste is present in ground water beneath certain feedlots, cultivated-irrigated fields that are fertilized with manure, and residential areas with septic systems. Values of δ 15 N NO3 between 22 and 43% 0 in ground water beneath the feedlots probably result from denitrification. Values of δ 15 N NO3 increase with depth in many locations in the sand-plain aquifers. These increases may be caused by progressive denitrification with depth or by changes with depth in the proportions of nitrate from different sources. Similarly, variations of δ 15 N NO3 values from 1986 to 1987 in certain locations may be due to temporal variations in the amounts of denitrification or to changes in the proportions of nitrate from different sources. Ambiguities in the interpretation of changes in δ 15 N NO3 values could be eliminated by increasing the spatial and temporal frequency of sampling.

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USGS2005

Multiport well design for sampling of ground water at closely spaced vertical intervals

Detailed vertical sampling is useful in aquifers where vertical mixing is limited and steep vertical gradients in chemical concentrations are expected. Samples can be collected at closely spaced vertical intervals from nested wells with short screened intervals. However, this approach may not be appropriate in all situations. An easy-to-construct and easy-to-install multiport sampling well to collect ground-water samples from closely spaced vertical intervals was developed and tested. The multiport sampling well was designed to sample ground water from surficial sand-and-gravel aquifers. The device consists of multiple stainless-steel tubes within a polyvinyl chloride (PVC) protective casing. The tubes protrude through the wall of the PVC casing at the desired sampling depths. A peristaltic pump is used to collect ground-water samples from the sampling ports. The difference in hydraulic head between any two sampling ports can be measured with a vacuum pump and a modified manometer. The usefulness and versatility of this multiport well design was demonstrated at an agricultural research site near Princeton, Minnesota where sampling ports were installed to a maximum depth of about 12 m below land surface. Tracer experiments were conducted using potassium bromide to document the degree to which short-circuiting occurred between sampling ports. Samples were successfully collected for analysis of major cations and anions, nutrients, selected herbicides, isotopes, dissolved gases, and chlorofluorcarbon concentrations.

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USGS2005

Plants as indicators of focused ground water discharge to a northern Minnesota lake

Determining the discharge of ground water to Shingobee Lake (66 ha), north-central Minnesota, is complicated by the presence of numerous springs situated adjacent to the lake and in the shallow portion of the lakebed. Springs first had to be located before these areas of more rapid discharge could be quantified. Two methods that rely on the distribution of aquatic plants are useful for locating springs. One method identifies areas of the near-shore lakebed where floating-leaf and emergent aquatic vegetation are absent. The second method uses the distribution of marsh marigold (Caltha palustris L.) to locate springs that discharge on land near the shoreline of the lake. Marsh marigold produces large (2 to 4 cm diameter) yellow flowers that provide a ready marker for locating ground water springs. Twice as many springs (38) were identified using this method as were identified using the lack of near-shore vegetation. A portable weir was used to measure discharge from onshore springs, and seepage meters were used to measure discharge from near-shore springs. Of the total 56.7 L s −1 that enters the lake from ground water, approximately 30% comes from onshore and near-shore springs.

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USGS2005

Causes of wolf depredation increase in Minnesota from 1979-1998

Wolf ( Canis lupus ) depredations on livestock in Minnesota have been increasing over the last 20 years. A major explanation cited for this increase is wolf range expansion, but no studies have tested this explanation. Additional reasons could include 1) wolf colonization of new areas within long-existing wolf range, 2) learning by wolves in established range, and 3) increased wolf density. We did not assess increasing wolf density as a factor because estimated wolf density in Minnesota has not increased. To assess how each of the other factors might have affected depredations, we created and analyzed a database of Minnesota's 923 verified depredations at 435 farms. We graphed the numbers of verified depredations and the number of farms with verified depredations to assess temporal trends and used ArcView GIS software to assess spatial relationships of the depredations. All 3 factors tested (colonization, range expansion, and learning) seemed to have contributed to wolf depredation increase. However, the proportion of depredations occurring due to wolf range expansion increased from 20% in 1989 to 48% in 1998.

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USGS2005

Water-quality assessment of part of the Upper Mississippi River Basin, Minnesota and Wisconsin — Ground-water quality along a flow system in the Twin Cities metropolitan area, Minnesota, 1997-98

As part of a national analysis of the effects of land use on ground-water quality for the National Water-Quality Assessment Program, the U.S. Geological Survey sampled wells along a flow system in surficial glacial aquifers in the northwestern part of the Twin Cities metropolitan area during 1997 and 1998. In addition, a reconnaissance steady-state ground-water model was developed to estimate flowpaths and dates of ground-water recharge using a particle-tracking routine. Sediment samples collected during drilling had high horizontal hydraulic conductivities (ranging from about 3.1 to about 190 feet per day, based on sediment-size analysis of well cuttings), small organic carbon concentrations (ranging from less than 0.2 to 160 grams per kilogram), and pH values that were mostly alkaline (ranging from 4.9 to 8.2). Water samples were analyzed for physical properties, major ions, iron, manganese, nutrients, organic carbon, radon, pesticides, volatile organic compounds (VOCs), chlorofluorocarbons, tritium, and isotopes of nitrogen, hydrogen, and oxygen. Most of the water samples had small dissolved-oxygen concentrations (less than 1 milligram per liter). Calcium, magnesium, sodium, bicarbonate, sulfate, and chloride were the primary dissolved constituents in water samples. Nitrite plus nitrate as nitrogen (nitrate) concentrations were less than the U.S. Environmental Protection Agency (USEPA) Maximum Contaminant Level of 10 mg/L. Nitrogen isotope ratios indicated that the sources of nitrate primarily were soils, animal waste, or denitrification that increased nitrogen isotope ratios in nitrate. Small concentrations of pesticides were detected in the shallow parts of the aquifer. The herbicide prometon was the most frequently detected pesticide. Herbicides applied to control grasses and weeds in corn (atrazine, simazine, and metolachlor) also were frequently detected in water samples. All pesticide and VOCs detected were below USEPA Maximum Contaminant Levels or Health Advisory Limits. Chlorofluorocarbon compounds and tritium concentrations were used to estimate dates of recharge of ground-water samples. In general, shallower ground-water samples were more recently recharged although most water sampled from the aquifer was recharged after 1955. Although land use had substantial effects on ground-water quality, the distribution of contaminants in the aquifer also is affected by complex combinations of factors and processes that include sources of natural and anthropogenic contaminants, three-dimensional advective flow, physical and hydrologic settings, age and evolution of ground water, and transformation of chemical compounds along the flow system. Compounds such as nitrate and dissolved oxygen were greatest in water samples from the upgradient end of the flow system and near the water table. Specific conductance and dissolved solids increased along the flow system and with depth due to increase in residence time in the flow system and dissolution of aquifer materials.

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USGS2005

Simulated effects of water-level changes in the Mississippi River and Pokegama Reservoir on ground-water levels, Grand Rapids area, Minnesota

The U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, used an existing, three-dimensional, numerical ground-water flow model (referred to as the calibrated model) to assess the effects of water-level changes in the Mississippi River and Pokegama Reservoir on ground-water levels in adjacent glaciofluvial aquifers in the Grand Rapids area of north-central Minnesota. Pokegama Reservoir consists of Pokegama Lake, Little Jay Gould Lake, Jay Gould Lake, Cut-off Lake, and Blackwater Lake. Water levels in the Pokegama Reservoir are regulated at Pokegama Dam on the Mississippi River west of Grand Rapids. A steady-state model was used, and simulations represent “worse-case” scenarios for the effects of lowering or raising the river and lake water levels. The simulated ground-water levels represent levels that would result if the river and lake stages permanently declined or rose by the specified amounts. Eight hypothetical scenarios were simulated by varying water levels in the Mississippi River and Pokegama Reservoir from values used in the calibrated model. In the simulations, water levels for the Mississippi River, riverine wetlands of the Mississippi River, and lakes of the Pokegama Reservoir were raised and lowered uniformly by 0.50, 1.00, 2.00, and 3.00 feet from calibrated water levels. The extent of aquifer water-level changes resulting from these river, wetland, and lake water-level changes varied because of the complex hydrogeology of the study area. A 1.00-foot decline in reservoir/river water levels caused a maximum simulated ground-water-level decline in the middle aquifer near Jay Gould and Little Jay Gould Lakes of 1.09 feet and a maximum simulated ground-water-level decline of 1.00 foot in the lower aquifer near Cut-off and Blackwater Lakes. The amount and extent of ground-water-level changes in the middle and lower aquifers can be explained by the thickness, extent, and connectivity of the aquifers. Surface-water/ground-water interactions near wetlands and lakes with water levels unchanged from the calibrated model resulted in small water-table altitude differences among the simulations. Results of the ground-water modeling indicate that lowering of the reservoir and river water levels by 1.00 foot likely will not substantially affect water levels in the middle and lower aquifers.

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USGS2005

Hydrologic conditions and lake-level fluctuations at Long Lost Lake, 1939-2004, White Earth Indian Reservation, Clearwater County, Minnesota

Long Lost Lake, a closed-basin lake in Clearwater County, Minnesota, has had a substantial rise in lake level since 1990. The increased level and surface area of the lake has led to the inundation of nearby homes and roads. The U.S. Geological Survey, in cooperation with the White Earth Band of Chippewa Indians, conducted a study to document the historical lake-level fluctuations, to investigate reasons for hydrologic change, and to develop a general understanding of the hydrology of lakes that have had rapid changes in lake level. Lake levels were recorded continuously from August 2003 through December 2004. The purpose was to establish a temporal, detailed record of lake levels and to connect this record to precipitation and ground-water-level data. A long-term record is critical to understanding the relation between surface water and ground water. This is especially true for closed-basin lakes. Between August 2003 and December 2004, the lake level generally declined. The highest lake altitude was 492.58 meters above NAVD 88 on August 5, 2003, and the low of 492.11 meters above NAVD 88 occurred on August 29, 2004. Results of water-level measurements in 5 observation wells and 14 wetlands and ponds show that the water-table level is substantially higher on the north side of the lake than the lake level, providing the head pressure necessary for ground-water discharge into Long Lost Lake. In contrast, on the south and east sides of the lake, water-table levels are similar to the lake level. This indicates a general north-northwest to south-southeast ground-water flow direction. Results of a synoptic survey of lake temperature and other measurements supported the direction of water inflow and outflow. Aerial photography and a geographic information system were used to construct a historical lake record from 1939 to 2001. Lake-level increases match similar increases in precipitation, indicating a strong link between the two. Results show that lake-level increases in Long Lost Lake appear to primarily be due to natural rather than anthropogenic effects.

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USGS2005

Physical, chemical, and biological characteristics of Sturgeon Lake, Goodhue County, Minnesota, 2003-04

The U.S. Geological Survey, in cooperation with the Prairie Island Indian Community and the Minnesota Department of Natural Resources, conducted a study of Sturgeon Lake (a backwater lake in Navigation Pool 3 of the Mississippi River) during 2003-04 to describe the physical, chemical, and biological characteristics of the lake. Riparian and shoreline areas surrounding Sturgeon Lake consist primarily of deciduous tree and shrub cover with minimal amounts of commercial or residential land use. Woody debris and aquatic vegetation are the major types of physical habitat suitable for fish and invertebrates. Among 10 bottom-sediment sampling sites, 24 organic wastewater compounds, 1 organochlorine pesticide metabolite (p,p’DDE), and total polychlorinated biphenyls (PCBs) were detected in the bottom sediments of Sturgeon Lake. The most prevalent class of compounds detected were polyaromatic hydrocarbons. Other classes of compounds detected include sterols, disinfectants, plastic components, alkylphenols, and fragrances. Three compounds detected (bisphenol A, benzo[a]pyrene, and triclosan) are considered endocrine disrupting compounds. Twenty-one and 49 invertebrate taxa were identified from 10 bottom-sediment and 6 woody-debris/vegetation samples, respectively. Most of the taxa were Diptera in the family Chironomidae. The most common invertebrate in terms of density in bottom-sediment samples was the burrowing mayfly ( Hexagenia sp.). Trichoptera in the families Hydropsychidae or Polycentropodidae were common in most of the woody-debris samples. The presence of the Hexagenia larvae in samples indicates that the bottom sediments are stable and that dissolved oxygen concentrations in the lake do not drop to acute or sub-lethal anoxic conditions. Backwater lakes such as Sturgeon Lake are important areas of habitat for aquatic organisms along the Mississippi River, and this report provides baseline physical, chemical, and biological information that resource managers can compare with future investigations.

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