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Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

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At least 775 records · Page 43Linked to original sources

USGS2008

Effects of habitat disturbance on survival rates of softshell turtles (Apalone spinifera) in an urban stream

We monitored Spiny Softshell Turtles (Apalone spinifera) using mark-recapture during 1994-2005 in Gin Creek, Searcy, Arkansas. In 1997-2000 the creek bed and riparian zone were bulldozed in an effort to remove debris and improve water flow. This disturbance appeared to reduce the quantity and quality of turtle habitat. We tested for the potential effect of this habitat disturbance on the survival rates of marked turtles. We estimated annual survival rates for the population using models that allowed for variation in survival by state of maturation, year, and effects of the disturbance; we evaluated two different models of the disturbance impact. The first disturbance model incorporated a single change in survival rates, following the disturbance, whereas the second disturbance model incorporated three survival rates: pre- and postdisturbance, as well as a short-term decline during the disturbance. We used a state-transition model for our mark-recapture analysis, as softshells transition from juveniles to adults in a variable period of time. Our analysis indicated that survival varied by maturation state and was independent of a time trend or the disturbance. Annual survival rates were lower for juveniles (S?? = 0.717, SE = 0.039) than for adults (S?? = 0.836, SE = 0.025). Despite the dramatic habitat disturbance, we found no negative effects on survival rates. Our results demonstrate that, like a few other freshwater turtle species known to thrive in urban environments, populations of A. spinifera are resilient and can persist in urban environments despite periodic habitat disturbances. Copyright 2008 Society for the Study of Amphibians and Reptiles.

Journal of Herpetology↗

USGS2017

Groundwater-level trends in the U.S. glacial aquifer system, 1964-2013

The glacial aquifer system in the United States is a major source of water supply but previous work on historical groundwater trends across the system is lacking. Trends in annual minimum, mean, and maximum groundwater levels for 205 monitoring wells were analyzed across three regions of the system (East, Central, West Central) for four time periods: 1964-2013, 1974-2013, 1984-2013, and 1994-2013. Trends were computed separately for wells in the glacial aquifer system with low potential for human influence on groundwater levels and ones with high potential influence from activities such as groundwater pumping. Generally there were more wells with significantly increasing groundwater levels (levels closer to ground surface) than wells with significantly decreasing levels. The highest numbers of significant increases for all four time periods were with annual minimum and/or mean levels. There were many more wells with significant increases from 1964 to 2013 than from more recent periods, consistent with low precipitation in the 1960s. Overall there were low numbers of wells with significantly decreasing trends regardless of time period considered; the highest number of these were generally for annual minimum groundwater levels at wells with likely human influence. There were substantial differences in the number of wells with significant groundwater-level trends over time, depending on whether the historical time series are assumed to be independent, have short-term persistence, or have long-term persistence. Mean annual groundwater levels have significant lag-one-year autocorrelation at 26.0% of wells in the East region, 65.4% of wells in the Central region, and 100% of wells in the West Central region. Annual precipitation across the glacial aquifer system, on the other hand, has significant autocorrelation at only 5.5% of stations, about the percentage expected due to chance.

Journal of Hydrology↗

USGS2013

Rapid chemical evolution of tropospheric volcanic emissions from Redoubt Volcano, Alaska, based on observations of ozone and halogen-containing gases

We report results from an observational and modeling study of reactive chemistry in the tropospheric plume emitted by Redoubt Volcano, Alaska. Our measurements include the first observations of Br and I degassing from an Alaskan volcano, the first study of O 3 evolution in a volcanic plume, as well as the first detection of BrO in the plume of a passively degassing Alaskan volcano. This study also represents the first detailed spatially-resolved comparison of measured and modeled O 3 depletion in a volcanic plume. The composition of the plume was measured on June 20, 2010 using base-treated filter packs (for F, Cl, Br, I, and S) at the crater rim and by an instrumented fixed-wing aircraft on June 21 and August 19, 2010. The aircraft was used to track the chemical evolution of the plume up to ~ 30 km downwind (2 h plume travel time) from the volcano and was equipped to make in situ observations of O 3 , water vapor, CO 2 , SO 2 , and H 2 S during both flights plus remote spectroscopic observations of SO 2 and BrO on the August 19th flight. The airborne data from June 21 reveal rapid chemical O 3 destruction in the plume as well as the strong influence chemical heterogeneity in background air had on plume composition. Spectroscopic retrievals from airborne traverses made under the plume on August 19 show that BrO was present ~ 6 km downwind (20 min plume travel time) and in situ measurements revealed several ppbv of O 3 loss near the center of the plume at a similar location downwind. Simulations with the PlumeChem model reproduce the timing and magnitude of the observed O 3 deficits and suggest that autocatalytic release of reactive bromine and in-plume formation of BrO were primarily responsible for the observed O 3 destruction in the plume. The measurements are therefore in general agreement with recent model studies of reactive halogen formation in volcanic plumes, but also show that field studies must pay close attention to variations in the composition of ambient air entrained into volcanic plumes in order to unambiguously attribute observed O 3 anomalies to specific chemical or dynamic processes. Our results suggest that volcanic eruptions in Alaska are sources of reactive halogen species to the subarctic troposphere.

Alaska↗

USGS2003

Inverse modeling of BTEX dissolution and biodegradation at the Bemidji, MN crude-oil spill site

The U.S. Geological Survey (USGS) solute transport and biodegradation code BIOMOC was used in conjunction with the USGS universal inverse modeling code UCODE to quantify field-scale hydrocarbon dissolution and biodegradation at the USGS Toxic Substances Hydrology Program crude-oil spill research site located near Bemidji, MN. This inverse modeling effort used the extensive historical data compiled at the Bemidji site from 1986 to 1997 and incorporated a multicomponent transport and biodegradation model. Inverse modeling was successful when coupled transport and degradation processes were incorporated into the model and a single dissolution rate coefficient was used for all BTEX components. Assuming a stationary oil body, we simulated benzene, toluene, ethylbenzene, m , p -xylene, and o -xylene (BTEX) concentrations in the oil and ground water, respectively, as well as dissolved oxygen. Dissolution from the oil phase and aerobic and anaerobic degradation processes were represented. The parameters estimated were the recharge rate, hydraulic conductivity, dissolution rate coefficient, individual first-order BTEX anaerobic degradation rates, and transverse dispersivity. Results were similar for simulations obtained using several alternative conceptual models of the hydrologic system and biodegradation processes. The dissolved BTEX concentration data were not sufficient to discriminate between these conceptual models. The calibrated simulations reproduced the general large-scale evolution of the plume, but did not reproduce the observed small-scale spatial and temporal variability in concentrations. The estimated anaerobic biodegradation rates for toluene and o -xylene were greater than the dissolution rate coefficient. However, the estimated anaerobic biodegradation rates for benzene, ethylbenzene, and m , p -xylene were less than the dissolution rate coefficient. The calibrated model was used to determine the BTEX mass balance in the oil body and groundwater plume. Dissolution from the oil body was greatest for compounds with large effective solubilities (benzene) and with large degradation rates (toluene and o -xylene). Anaerobic degradation removed 77% of the BTEX that dissolved into the water phase and aerobic degradation removed 17%. Although goodness-of-fit measures for the alternative conceptual models were not significantly different, predictions made with the models were quite variable.

Minnesota↗

USGS1976

Fresh ground water found deep beneath Nantucket Island, Masachusetts

In a deep water-resources and stratigraphic test well near the center of Nantucket Island, about 30 miles (48 kilometres) off the New England coast, freshwater has been found at greater depths than predicted by the Ghyben-Herzberg principle. An uppermost lens of freshwater, which occupies relatively permeable glacial-outwash sand and gravel to a depth of 520 feet (158 metres), is believed to be in hydrodynamic equilibrium with the present level of the sea and the height of the water table. However, two zones of freshwater at 730 to 820 ft (222-249 m) and 900 to 930 ft (274-283 m) are anomalously deep. Although several explanations are possible, the most likely is that the entire surface of the Continental Shelf was exposed to recharge by precipitation during long periods of low sea level in Pleistocene time. After the last retreat of glacial ice, seawater rapidly drowned the shelf around Nantucket Island. Since then, about 8,000 years ago, the deep freshwater zones which underlie dense clay layers have not had time to adjust to a new equilibrium. Under similar circumstances, freshwater may remain trapped under extensive areas of the Continental Shelf wherever clay confining beds have not permitted saltwater to intrude rapidly to new hydrodynamic equilibria positions. The implications are far reaching because all continental shelves worldwide were exposed to similar hydrologic influences during Pleistocene time.

Massachusetts↗

USGS1998

Noble gases, stable isotopes, and radiocarbon as tracers of flow in the Dakota aquifer, Colorado and Kansas

A suite of chemical and isotope tracers (dissolved noble gases, stable isotopes of water, radiocarbon, and CI) have been analyzed along a flow path in the Dakota aquifer system to determine likely recharge sources, ground water residence times, and the extent of mixing between local and intermediate flow systems, presumably caused by large well screens. Three water types were distinguished with the tracers, each having a very different history. Two of the water types were found in south-eastern Colorado where the Dakota is poorly confined. The tracer data suggest that the first group recharged locally during the last few thousand years and the second group was composed of ground water that recharged earlier during a cooler climate, presumably during the last glacial period (LGP) and mixed aged water. The paleotemperature record archived in this groundwater system indicates that south-eastern Colorado was about 5??C cooler during the LGP than during the late Holocene. Similar temperature changes derived from dissolved noble gases in other aquifer systems have been reported earlier for the south-western United States. The third water type was located down gradient of the first two in the confined Dakota in western and central Kansas. Groundwater residence time of this water mass is on the order of 104-105 yrs and its recharge location is near the Colorado and Kansas border down gradient of the other water types. The study shows the importance of using multiple tracers when investigating ground water systems.A suite of chemical and isotope tracers (dissolved noble gases, stable isotopes of water, radiocarbon, and CL) were analyzed along a flow path in the Dakota aquifer system to determine likely recharge sources, ground water residence times, and the extent of mixing between local and intermediate flow systems. Three water types were distinguished with the tracers, each having a very different history. Two of the water types were located in south-eastern Colorado where the Dakota is poorly confined. The third water type was located down gradient of the first two in the confined Dakota in western and central Kansas.

Journal of Hydrology↗

USGS2020

A 450-year record of environmental change from Castle Lake, California (USA), inferred from diatoms and organic geochemistry

A 39-cm sediment core from Castle Lake, California (USA) spans the last ~ 450 years and was analyzed for diatoms and organic geochemistry (δ 15 N, δ 13 C, and C:N), with the goal of determining sensitivity to natural climate variation and twentieth century anthropogenic effects. Castle Lake is a subalpine, nitrogen-limited lake with ~ 5 months of annual ice cover. Human impacts include light recreational use, past fish stocking, and experimental use by the Castle Lake Research Station. The base of the core (below 32 cm; pre mid-1700s) represents the period of maximum ice cover. In contrast, the end of the Little Ice Age (mid 1700s–early 1800s) is dominated by cyclotelloids (mostly Discostella stelligera ), indicating significant open-water periods, a condition that persisted into the early 1900s. Cyclotelloids began to decline in the 1960s and were replaced by the Fragilaria tenera grp. (peak in 1970s), succeeded by Asterionella formosa (peak ~ 2010), and accompanied by a reduction in δ 15 N values and a decrease in C:N that may represent increased atmospheric nitrogen deposition. Another anthropogenic signal was discerned in the core and was interpreted to be the result of an ammonium nitrate fertilization experiment of the epilimnion that was conducted in 1980 and 1981. This signal was manifested in the core largely by a negative excursion in δ 15 N, possibly caused by fractionation during denitrification in surface sediment. A phytoplankton monitoring dataset collected by the Castle Lake Research Station from 1967 to 1984 corroborates the timing of increased araphid euplanktonic species in the 1970s, and increases in two benthic diatoms ( Staurosirella pinnata and Tabellaria fenestrata) , entrained in the phytoplankton tows during the experimentation years. Both ice cover and nitrogen addition appear to be strong drivers that affected the lake diatoms, although additional drivers, such as fish stocking and associated cascade effects need further exploration. These data will be helpful for interpreting longer core records from Castle Lake, should the opportunity arise, as well as cores from similar systems in the region.

California↗

USGS2004

Evaluation of multidimensional transport through a field-scale compacted soil liner

A field-scale compacted soil liner was constructed at the University of Illinois at Urbana-Champaign by the U.S. Environmental Protection Agency (USEPA) and Illinois State Geological Survey in 1988 to investigate chemical transport rates through low permeability compacted clay liners (CCLs). Four tracers (bromide and three benzoic acid tracers) were each added to one of four large ring infiltrometers (LRIs) while tritium was added to the pond water (excluding the infiltrometers). Results from the long-term transport of Br - "> Br - from the localized source zone of LRI are presented in this paper. Core samples were taken radially outward from the center of the Br - "> Br - LRI and concentration depth profiles were obtained. Transport properties were evaluated using an axially symmetric transport model. Results indicate that (1) transport was diffusion controlled; (2) transport due to advection was negligible and well within the regulatory limits of k sat ⩽ 1 × 10 - 7 cm / s ; "> k sat ⩽ 1 × 10 − 7 cm / s; (3) diffusion rates in the horizontal and vertical directions were the same; and (4) small positioning errors due to compression during soil sampling did not affect the best fit advection and diffusion values. The best-fit diffusion coefficient for bromide was equal to the molecular diffusion coefficient multiplied by a tortuosity factor of 0.27, which is within 8% of the tortuosity factor (0.25) found in a related study where tritium transport through the same liner was evaluated. This suggests that the governing mechanisms for the transport of tritium and bromide through the CCL were similar. These results are significant because they address transport through a composite liner from a localized source zone which occurs when defects or punctures in the geomembrane of a composite system are present.

Journal of Geotechnical and Geoenvironmental Engin↗

USGS1995

Mudflow generated by retrogressive slope failure, Santa Barbara Basin, California continental borderland

The morphology and internal geometry of a mudflow deposit on the mainland slope of the Santa Barbara Basin are defined using high-resolution seismic-reflection data in combination with core samples. Sediment failure occurred on a 4 degrees slope in the uppermost part of late Quaternary well-bedded slope deposits. The failure zone extends from water depths of 374-510 m near the base of slope, occupies an area of 4 km 2 , and involved the translation of 0.01-0.02 km 3 of sediment. Major geomorphic features of the mudflow deposit include a headscarp 6-8 m high, a scar 50-700 m wide, and a main body 1 km long and 12 m thick. The hummocky surface of the mudflow deposits, their chaotic internal structure, and the bulbous toe tapering upslope to a thin tail are consistent with mass flow involving extensive internal deformation. Sediment failed in stages, ending with upslope retrogressive retreat of the headwall along the east side of the failure zone. Known sedimentation rates of 0.8-1.4 m/k.y., as well as the presence of a thin (0.15-0.5 m thick) sediment cap resting atop the scar surface, indicate that the failure probably occurred within the past few centuries. A geotechnical analysis incorporating the results of both static and dynamic triaxial strength tests shows that the failure was probably caused by a strong (M nearly equal 7.5) nearby earthquake. The weakened sediment that remained after earthquake shaking continued to flow down the gentle basin slope under the stresses generated by gravity alone. The analysis also shows that much of the slope sediment is marginally stable and that additional mudflows will probably occur during future strong seismic shaking.

California↗

USGS2011

Long-term trends in the St. Marys River open water fish community

We examined trends in species composition and abundance of the St. Marys River fish community. Abundance data were available approximately once every six years from 1975 through 2006, and size and age data were available from 1995 through 2006. We also compared survey data in 2006 with results of a concurrent creel survey that year, as well as data from prior surveys spanning a 69 year time frame. The St. Marys River fish community was best characterized as a coolwater fish community with apparent little variation in species composition, and only slight variation in overall fish abundance since 1975. However, we did find recent trends in abundance among target species sought by anglers: centrarchids increased, percids appeared stable, and both northern pike Esox lucius and cisco Coregonus artedii declined. Survey results suggested that walleye ( Sander vitreus ) and yellow perch ( Perca flavescens ) experienced moderate exploitation but benefited from recent strong recruitment and faster growth. Mechanisms underlying declines of northern pike and cisco were not clear; reduced abundance could have resulted from high exploitation, variation in recruitment, or a combination of both factors. Despite these challenges, the St. Marys River fish community appears remarkably stable. We suggest that managers insure that creel surveys occur simultaneously with assessments, but periodic gill net surveys may no longer provide adequate data in support of recent, more complex management objectives. While additional surveys would add costs, more frequent data might ensure sustainability of a unique fish community that supports a large proportion of angler effort on Lake Huron.

Michigan;Ontario↗

USGS2020

High-resolution mapping of the freshwater-brine interface using deterministic and Bayesian inversion of airborne electromagnetic data at Paradox Valley, USA

Salt loads in the Colorado River Basin are a primary water quality concern. Natural groundwater brine discharge to the Dolores River where it passes through the collapsed salt anticline of the Paradox Valley in western Colorado is a significant source of salt to the Colorado River. An airborne electromagnetic survey of Paradox Valley has provided insights into the 3D distribution of brine in the surficial aquifer. A combination of stochastic and deterministic resistivity inversions were used to interpret the top of the freshwater-brine interface and to qualitatively describe the vertical salinity gradients across the interface. Low-resistivity regions indicative of brine occur near the land surface where brine discharges to the Dolores River and increase in depth several kilometers up-gradient along the axis of the valley. The most conductive parts of the brine plume are found in the areas below and adjacent to the river, suggesting that the brine becomes shallower and more concentrated as it reaches its natural discharge location. A significant freshwater lens overlying the brine west of the Dolores River is spatially correlated to the intermittent West Paradox Creek and agricultural irrigation. Below this lens, the transition from freshwater to brine appears to occur abruptly over a few meters and correlates to available well information. However, away from these regions and particularly with distance from the river, the freshwater-brine interface appears to be more diffuse.

Colorado↗

USGS2012

Seasonal zooplankton dynamics in Lake Michigan: disentangling impacts of resource limitation, ecosystem engineering, and predation during a critical ecosystem transition

We examined seasonal dynamics of zooplankton at an offshore station in Lake Michigan from 1994 to 2003 and 2007 to 2008. This period saw variable weather, declines in planktivorous fish abundance, the introduction and expansion of dreissenid mussels, and a slow decline in total phosphorus concentrations. After the major expansion of mussels into deep water (2007–2008), chlorophyll in spring declined sharply, Secchi depth increased markedly in all seasons, and planktivorous fish biomass declined to record-low levels. Overlaying these dramatic ecosystem-level changes, the zooplankton community exhibited complex seasonal dynamics between 1994–2003 and 2007–2008. Phenology of the zooplankton maximum was affected by onset of thermal stratification, but there was no other discernable effect due to temperature. Interannual variability in zooplankton biomass during 1994 and 2003 was strongly driven by planktivorous fish abundance, particularly age-0 and age-1 alewives. In 2007–2008, there were large decreases in Diacyclops thomasi and Daphnia mendotae possibly caused by food limitation as well as increased predation and indirect negative effects from increases in Bythotrephes longimanus abundance and in foraging efficiency associated with increased light penetration. The Bythotrephes increase was likely driven in part by decreased predation from yearling and older alewife. While there was a major decrease in epilimnetic–metalimnetic herbivorous cladocerans in 2007–2008, there was an increase in large omnivorous and predacious calanoid copepods, especially those in the hypolimnion. Thus, changes to the zooplankton community are the result of cascading, synergistic interactions, including a shift from vertebrate to invertebrate planktivory and mussel ecosystem impacts on light climate and chlorophyll.

Journal of Great Lakes Research↗

USGS2021

Incorporation of non-native species in the diets of cisco (Coregonus artedi) from eastern Lake Ontario

Cisco Coregonus artedi was once an important native fish in Lake Ontario; however, after multiple population crashes, the cisco stock has yet to recover to historic abundances. Rehabilitation of cisco in Lake Ontario is a fish community management objective, but the extent to which recent non-native species and pelagic food web changes have influenced cisco is not well understood. We described cisco diets in contemporary Lake Ontario following the addition and spread of non-native zooplankton species. We collected 618 cisco and processed 178 for full diet analysis in eastern Lake Ontario using mid-water trawls and bottom-set gill nets from 2016 to 2020. We found that Lake Ontario cisco were mostly zooplanktivorous, and non-native zooplankton dominated their diet during July and September. Cisco smaller than 300 mm had a more diverse diet including both native and non-native zooplankton, while cisco larger than 300 mm fed almost exclusively on non-native predatory cladocerans Bythotrephes longimanus and Cercopagis pengoi (98.9% consumed prey dry mass). We also found fish eggs, presumed to be of coregonine origin in 75% of non-empty December-collected cisco diets, suggesting eggs subsidize cisco diets when available. Juvenile round goby Neogobius melanostomus , alewife Alosa pseudoharengus and rainbow smelt Osmerus mordax were found in 2% of all analyzed non-empty stomachs. Lake Ontario cisco diet appears to be more similar to zooplanktivorous Lake Superior cisco than Lake Michigan where piscivory is prevalent. Lake Ontario cisco diets reflected zooplankton community changes indicating that non-native predatory cladocerans are now an important energy source supporting this native species.

Eastern Lake Ontario↗

USGS2022

Natural inactivation of MS2, poliovirus type 1 and Cryptosporidium parvum in an anaerobic and reduced aquifer

Aims The study of microbial inactivation rates in aquifer systems has most often been determined in aerobic and oxidized systems. This study examined the inactivation (i.e. loss of infectivity) of MS2, poliovirus type 1 (PV1) and Cryptosporidium parvum in an anaerobic and reduced groundwater system that has been identified as storage zones for aquifer storage and recovery (ASR) facilities. Methods and Results Anaerobic and reduced (ORP < − 250 mV) groundwater from an artesian well was diverted to an above-ground, flow-through mesocosm that contained diffusion chambers filled with MS2, PV1 or Cryptosporidium parvum . The respective infectivity assays were performed on microorganisms recovered from the diffusion chambers during 30- to 58-day experiments. The net reduction in infectivity was 5.73 log 10 over 30 days for MS2, 5.00 log 10 over 58 days for PV1 and 4.07 log 10 over 37 days for C . parvum . The best fit inactivation model for PV1 was the log-linear model and the Weibull model for MS2 and C . parvum , with respective inactivation rates (95% confidence interval) of 0.19 (0.17–0.21) log 10 day −1 , 0.31 (0.19–0.89) log 10 day −1 and 0.20 (0.14–0.37) log 10 day −1 . Conclusions The groundwater geochemical conditions in this aquifer enhanced the inactivation of MS2, PV1, and C . parvum at rates approximately 2.0–5.3-fold, 1.2–17.0-fold, and 4.5–5.6-fold greater, respectively, than those from published studies that used diffusion chambers in aerobic-to-anoxic groundwater systems, with positive redox potentials. Significance and Impact of the Study Geochemical conditions like those in the aquifer zone in this study can naturally and significantly reduce concentrations of microbial indicators and pathogens of human health concern in injected surface water. Appropriate storage times for injected surface water could complement above-ground engineered processes for microorganism removal and inactivation (e.g. filtration, disinfection) by naturally increasing overall microorganism log-inactivation rates of ASR facilities.

Journal of Applied Microbiology↗

USGS1999

Determining travel time and stream mixing using tracers and empirical equations

Water-supply managers need adequate warning to protect water supplies if a contaminant is spilled in an upgradient tributary. The city of Lincoln draws water from alluvium associated with the Platte River near Ashland, eastern Nebraska. Using constant-rate injection methods and a conservative tracer, travel time and degree of mixing of contaminants in the Elkhorn and Platte Rivers were evaluated in 1995 and 1996. The results indicate that, for flows of 584 to 162 m 3 /s in the Platte River at Ashland with 13 to 28% of its flow contributed by the Elkhorn River, 8.2 to 13.2 h are required for the leading edge of a chemical plume to travel from the Elkhorn River at Waterloo to the Platte River at Ashland. The peak concentration of a chemical spilled as a slug in the Elkhorn River near Waterloo would pass the well field after 11.3 to 16.1 h. Existing empirical equations for calculation of travel time were shown to apply to reaches of streams studied, but underestimated the leading edge up to 14% and overestimated the plateau concentration up to 11% at Site 5. However, time of travel may be influenced by the relative contribution of a tributary. The plateau concentration of the chemical in the Platte River at Ashland was 45 to 60% of its concentration in the Elkhorn River. The degree of mixing of the tracer in the Platte River at Ashland increased from 53 to 65% as the relative contribution of the Elkhorn River increased.

Journal of Environmental Quality↗

USGS2020

Conceptualizing alternate regimes in a large floodplain-river ecosystem

Regime shifts –persistent changes in the structure and function of an ecosystem - are well-documented in many ecosystems but remain poorly understood in floodplain-river ecosystems. We apply a resilience perspective to large floodplain-river ecosystems by presenting three examples of plausible sets of alternate regimes that are relevant to natural resource management interests within the Upper Mississippi River and Illinois River. These alternate regimes include: 1) a clear water and abundant vegetation regime vs. a turbid water and sparse vegetation regime in lentic, off-channel areas, 2) a diverse native fish community regime vs. an invasive-dominated fish community regime, and 3) a regime characterized by a diverse and dynamic mosaic of floodplain vegetation types vs. one characterized as a persistent invasive wet meadow monoculture. For each set of potential alternate regimes, we synthesize known or hypothesized feedback mechanisms that reinforce regimes, controlling variables that drive regime transitions, and restoration pathways. The conceptual models presented here provide a framework for synthesizing our understanding of the dynamics of this ecosystem and are relevant to other large floodplain-river ecosystems that face similar human pressures across the world. The models are currently being used to prioritize future research, test hypotheses, and inform restoration and management on the Upper Mississippi River and Illinois River. Through sharing our approach, we provide a case study in which we document an important step in operationalizing resilience concepts for the management of natural resources.

Minnesota, Wisconsin, Iowa, Illinois, Missouri↗

USGS2015

Age and growth of round gobies in Lake Michigan, with preliminary mortality estimation

The round goby ( Neogobius melanostomus ) is a prevalent invasive species throughout Lake Michigan, as well as other Laurentian Great Lakes, yet little information is available on spatial variation in round goby growth within one body of water. Age and growth of round goby at three areas of Lake Michigan were studied by otolith analysis from a sample of 659 specimens collected from 2008 to 2012. Total length ( TL ) ranged from 48 to 131 mm for Sturgeon Bay, from 50 to 125 mm for Waukegan, and from 54 to 129 mm for Sleeping Bear Dunes. Ages ranged from 2 to 7 years for Sturgeon Bay, from 2 to 5 years for Waukegan, and from 2 to 6 years for Sleeping Bear Dunes. Area-specific and sex-specific body–otolith relationships were used to back-calculate estimates of total length at age, which were fitted to von Bertalanffy models to estimate growth rates. For both sexes, round gobies at Sleeping Bear Dunes and Waukegan grew significantly faster than those at Sturgeon Bay. However, round goby growth did not significantly differ between Sleeping Bear Dunes and Waukegan for either sex. At all three areas of Lake Michigan, males grew significantly faster than females. Based on catch curve analysis, estimates of annual mortality rates ranged from 0.79 to 0.84. These relatively high mortality rates suggested that round gobies may be under predatory control in Lake Michigan.

Lake Michigan↗

USGS2018

The suitability of using dissolved gases to determine groundwater discharge to high gradient streams

Determining groundwater discharge to streams using dissolved gases is known to be useful over a wide range of streamflow rates but the suitability of dissolved gas methods to determine discharge rates in high gradient mountain streams has not been sufficiently tested, even though headwater streams are critical as ecological habitats and water resources. The aim of this study is to test the suitability of using dissolved gases to determine groundwater discharge rates to high gradient streams by field experiments in a well-characterized, high gradient mountain stream and a literature review. At a reach scale (550 m) we combined stream and groundwater radon activity measurements with an in-stream SF 6 tracer test. By means of numerical modeling we determined gas exchange velocities and derived very low groundwater discharge rates (∼15% of streamflow). These groundwater discharge rates are below the uncertainty range of physical streamflow measurements and consistent with temperature, specific conductance and streamflow measured at multiple locations along the reach. At a watershed-scale (4 km), we measured CFC-12 and δ 18 O concentrations and determined gas exchange velocities and groundwater discharge rates with the same numerical model. The groundwater discharge rates along the 4 km stream reach were highly variable, but were consistent with the values derived in the detailed study reach. Additionally, we synthesized literature values of gas exchange velocities for different stream gradients which show an empirical relationship that will be valuable in planning future dissolved gas studies on streams with various gradients. In sum, we show that multiple dissolved gas tracers can be used to determine groundwater discharge to high gradient mountain streams from reach to watershed scales.

California↗