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At least 109 records · Page 6Linked to original sources

USGS2017

Litterfall production of mangroves in the Huizache-Caimanero lagoon system, México

The ecological legacy of the Huizache-Caimanero lagoon system has long been known as a trophically rich and productive ecosystem that supported artisanal fisheries of local and regional importance; however, a decline in fisheries' yields has been observed in recent decades. Mangroves are a fundamental component of this ecosystem, though data records and field studies are lacking in describing their structure and seasonal characteristics. Mangrove litterfall production was monitored during 2012–13 and described for the dominant species, Avicennia germinans (L.) Stearn and Laguncularia racemosa (L.) C.F. Gaertn. Forest surveys and monthly litter collections were obtained along a latitudinal gradient within the larger lagoon system to characterize the forest structure, leaf biomass, and related biological indicators (chlorophyll a concentration and Normalized Difference Vegetation Index [NDVI] estimated on leaf tissues). Results showed that structural characteristics (diameter at breast height, basal area, height, and crown diameter) were greater in Huizache, corresponding to patches with a dominance of A. germinans , while higher stem density was recorded for L. racemosa in Caimanero, comparatively similar to other mangrove habitat in NW Mexico. Litterfall was highest from May to October for both species. Litterfall production was also higher overall in 2012 in comparison to 2013, possibly corresponding with meteorological differences, most notably wind conditions. Annual litterfall production was similar by species across northern and southern Sinaloa. A contrast of the NDVI by site and species showed a wide interval, including low values for A. germinans , suggesting stress conditions for this species.

Huizache-Caimanero lagoon system↗

USGS2011

Habitat selection by a focal predator (Canis lupus) in a multiprey ecosystem of the northern Rockies

Large predators respond to land cover and physiography that maximize the likelihood of encountering prey. Using locations from global positioning system-collared wolves (Canis lupus), we examined whether land cover, vegetation productivity or change, or habitat-selection value for ungulate prey species themselves most influenced patterns of selection by wolves in a large, intact multiprey system of northern British Columbia. Selection models based on land cover, in combination with topographical features, consistently outperformed models based on indexes of vegetation quantity and quality (using normalized difference vegetation index) or on selection value to prey species (moose [Alces americanus], elk [Cervus elaphus], woodland caribou [Rangifer tarandus], and Stone's sheep [Ovis dalli stonei]). Wolves generally selected for shrub communities and high diversity of cover across seasons and avoided conifer stands and non-vegetated areas and west aspects year-round. Seasonal selection strategies were not always reflected in use patterns, which showed highest frequency of use in riparian, shrub, and conifer classes. Patterns of use and selection for individual wolf packs did not always conform to global models, and appeared related to the distribution of land cover and terrain within respective home ranges. Our findings corroborate the biological linkages between wolves and their habitat related to ease of movement and potential prey associations. ?? American 2011 Society of Mammalogists.

Journal of Mammalogy↗

USGS2011

Continuous salinity and temperature data from San Francisco Estuary, 1982-2002: Trends and the salinity-freshwater inflow relationship

The U.S. Geological Survey and other federal and state agencies have been collecting continuous temperature and salinity data, two critical estuarine habitat variables, throughout San Francisco estuary for over two decades. Although this dynamic, highly variable system has been well studied, many questions remain relating to the effects of freshwater inflow and other physical and biological linkages. This study examines up to 20 years of publically available, continuous temperature and salinity data from 10 different San Francisco Bay stations to identify trends in temperature and salinity and quantify the salinity–freshwater inflow relationship. Several trends in the salinity and temperature records were identified, although the high degree of daily and interannual variability confounds the analysis. In addition, freshwater inflow to the estuary has a range of effects on salinity from −0.0020 to −0.0096 (m 3 s −1 ) −1 discharge, depending on location in the estuary and the timescale of analyzed data. Finally, we documented that changes in freshwater inflow to the estuary that are within the range of typical management actions can affect bay-wide salinities by 0.6–1.4. This study reinforces the idea that multidecadal records are needed to identify trends from decadal changes in water management and climate and, therefore, are extremely valuable.

California↗

USGS2013

Computationally efficient statistical differential equation modeling using homogenization

Statistical models using partial differential equations (PDEs) to describe dynamically evolving natural systems are appearing in the scientific literature with some regularity in recent years. Often such studies seek to characterize the dynamics of temporal or spatio-temporal phenomena such as invasive species, consumer-resource interactions, community evolution, and resource selection. Specifically, in the spatial setting, data are often available at varying spatial and temporal scales. Additionally, the necessary numerical integration of a PDE may be computationally infeasible over the spatial support of interest. We present an approach to impose computationally advantageous changes of support in statistical implementations of PDE models and demonstrate its utility through simulation using a form of PDE known as “ecological diffusion.” We also apply a statistical ecological diffusion model to a data set involving the spread of mountain pine beetle (Dendroctonus ponderosae) in Idaho, USA.

Journal of Agricultural, Biological, and Environme↗

USGS2011

Testing the effect of habitat structure and complexity on nekton assemblages using experimental oyster reefs

Structurally complex habitats are often associated with more diverse and abundant species assemblages in both aquatic and terrestrial ecosystems. Biogenic reefs formed by the eastern oyster ( Crassostrea virginica ) are complex in nature and are recognized for their potential habitat value in estuarine systems along the US Atlantic and Gulf of Mexico coasts. Few studies, however, have examined the response of nekton to structural complexity within oyster reefs. We used a quantitative sampling technique to examine how the presence and complexity of experimental oyster reefs influence the abundance, biomass, and distribution of nekton by sampling reefs 4 months and 16 months post-construction. Experimental oyster reefs were colonized immediately by resident fishes and decapod crustaceans, and reefs supported a distinct nekton assemblage compared to mud-bottom habitat. Neither increased reef complexity, nor age of the experimental reef resulted in further changes in nekton assemblages or increases in nekton abundance or diversity. The presence of oyster reefs per se was the most important factor determining nekton usage.

Journal of Experimental Marine Biology and Ecology↗

USGS2003

Arctic transitions in the Land - Atmosphere System (ATLAS): Background, objectives, results, and future directions

This paper briefly reviews the background, objectives, and results of the Arctic Transitions in the Land-Atmosphere System (ATLAS) Project to date and provides thoughts on future directions. The key goal of the ATLAS Project is to improve understanding of controls over spatial and temporal variability of terrestrial processes in the Arctic that have potential consequences for the climate system, i.e., processes that affect the exchange of water and energy with the atmosphere, the exchange of radiatively active gases with the atmosphere, and the delivery of freshwater to the Arctic Ocean. Three important conclusions have emerged from research associated with the ATLAS Project. First, associated with the observation that the Alaskan Arctic has warmed significantly in the last 30 years, permafrost is warming, shrubs are expanding, and there has been a temporary release of carbon dioxide from tundra soils. Second, the winter is a more important period of biological activity than previously appreciated. Biotic processes, including shrub expansion and decomposition, affect snow structure and accumulation and affect the annual carbon budget of tundra ecosystems. Third, observed vegetation changes can have a significant positive feedback to regional warming. These vegetation effects are, however, less strong than those exerted by land-ocean heating contrasts and the topographic constraints on air mass movements. The papers of this special section provide additional insights related to these conclusions and to the overall goal of ATLAS.

Journal of Geophysical Research D: Atmospheres↗

USGS2008

Groundwater's significance to changing hydrology, water chemistry, and biological communities of a floodplain ecosystem, Everglades, South Florida, USA

The Everglades (Florida, USA) is one of the world's larger subtropical peatlands with biological communities adapted to waters low in total dissolved solids and nutrients. Detecting how the pre-drainage hydrological system has been altered is crucial to preserving its functional attributes. However, reliable tools for hindcasting historic conditions in the Everglades are limited. A recent synthesis demonstrates that the proportion of surface-water inflows has increased relative to precipitation, accounting for 33% of total inputs compared with 18% historically. The largest new source of water is canal drainage from areas of former wetlands converted to agriculture. Interactions between groundwater and surface water have also increased, due to increasing vertical hydraulic gradients resulting from topographic and water-level alterations on the otherwise extremely flat landscape. Environmental solute tracer data were used to determine groundwater's changing role, from a freshwater storage reservoir that sustained the Everglades ecosystem during dry periods to a reservoir of increasingly degraded water quality. Although some of this degradation is attributable to increased discharge of deep saline groundwater, other mineral sources such as fertilizer additives and peat oxidation have made a greater contribution to water-quality changes that are altering mineral-sensitive biological communities. ?? Springer-Verlag 2008.

Hydrogeology Journal↗

USGS2006

Phosphate oxygen isotope ratios as a tracer for sources and cycling of phosphate in North San Francisco Bay, California

[1] A seasonal analysis assesing variations in the oxygen isotopic composition of dissolved inorganic phosphate (DIP) was conducted in the San Francisco Bay estuarine system, California. Isotopic fractionation of oxygen in DIP (exchange of oxygen between phosphate and environmental water) at surface water temperatures occurs only as a result of enzyme‐mediated, biological reactions. Accordingly, if phospate demand is low relative to input and phosphate is not heavily cycled in the ecosystem, the oxygen isotopic composition of DIP (δ 18 O p ) will reflect the isotopic composition of the source of phosphate to the system. Such is the case for the North San Francisco Bay, an anthropogenically impacted estuary with high surface water phosphate concentrations. Variability in the δ 18 O p in the bay is primarily controlled by mixing of water masses with different δ 18 O p signatures. The δ 18 O p values range from 11.4‰ at the Sacramento River to 20.1‰ at the Golden Gate. Deviations from the two‐component mixing model for the North Bay reflect additional, local sources of phosphate to the estuary that vary seasonally. Most notably, deviations from the mixing model occur at the confluence of a major river into the bay during periods of high river discharge and near wastewater treatment outlets. These data suggest that δ 18 O p can be an effective tool for identifying P point sources and understanding phosphate dynamics in estuarine systems.

Journal of Geophysical Research G: Biogeosciences↗

USGS2016

Analysis of environmental factors influencing salinity patterns, oyster growth, and mortality in lower Breton Sound Estuary, Louisiana using 20 years of data

Freshwater inflow characteristics define estuarine functioning by delivering nutrients, sediments, and freshwater, which affect biological resources and ultimately system production. Using 20 years of water quality, weather, and oyster growth and mortality data from Breton Sound Estuary (BSE), Louisiana, we examined the relationship of riverine, weather, and tidal influence on estuarine salinity, and the relationship of salinity to oyster growth and mortality. Mississippi River discharge was found to be the most important factor determining salinity patterns over oyster grounds within lower portions of BSE, with increased river flow associated with lowered salinities, while easterly winds associated with increased salinity were less influential. These patterns were consistent throughout the year. Salinity and temperature (season) were found to critically control oyster growth and mortality, suggesting that seasonal changes to river discharge affecting water quality over the oyster grounds have profound impacts on oyster populations. The management of oyster reefs in estuaries (such as BSE) requires an understanding of how estuarine hydrodynamics and salinity are influenced by forcing factors such as winds, river flow, and by the volume, timing, and location of controlled releases of riverine water.

Louisiana↗

USGS2023

Assessment of potential recovery viability for Colorado Pikeminnow Ptychocheilus lucius in the Colorado River in Grand Canyon

Colorado Pikeminnow Ptychocheilus lucius, the Colorado River’s top native predatory fish, was historically distributed from the Gulf of California delta to the upper reaches of the Green, Colorado, and San Juan rivers in the Colorado River basin in the Southwestern US. In recent decades Colorado Pikeminnow population abundance has declined, primarily due to predation by warmwater nonnative fish and habitat modification following dam construction. Small, reproducing populations remain in the Green and upper Colorado rivers, but their current population trajectory is declining and the San Juan River population is maintained primarily through stocking. As such, establishment of an additional population could aid recovery efforts and increase the species’ resilience and population redundancy. The Colorado River in Grand Canyon once supported Colorado Pikeminnow, but until recently habitat suitability in this altered reach was considered low due to a depressed thermal regime and abundant nonnative predators. Climate change and ongoing drought has presented an opportunity to evaluate the feasibility of native fish restoration in a system where declining reservoir storage has led to warmer releases and re-emergence of riverine habitat. These changes in the physical attributes of the river have occurred in concert with a system-wide decline in nonnative predators. Conditions ten years ago were not compatible with reintroduction feasibility in Grand Canyon; however, due to rapidly changing conditions an expert Science Panel was convened to evaluate whether the physical and biological attributes of this reach could now support various life stages of Colorado Pikeminnow. Here, we report on the evaluation process and outcome from the Science Panel, which developed a science-based recommendation to the U.S. Fish and Wildlife Service on reintroduction feasibility. The Science Panel concluded that current habitat attributes in Grand Canyon could satisfy some, but perhaps not all, Colorado Pikeminnow life history requirements. This reach has the potential to support adult and sub-adult growth, foraging, migrations, and spawning, but low juvenile survival may limit recruitment. However, populations of other native species are successfully reproducing and increasing in western Grand Canyon, even in areas once considered suboptimal habitat. Should managers decide to move to the next phase of this process, actions such as experimental stocking and monitoring, telemetry studies, bioenergetics modeling, and laboratory-based research may provide additional information to further evaluate a potential reintroduction effort in this rapidly changing but highly altered system.

Arizona↗

USGS2021

Flow dynamics influence fish recruitment in hydrologically connected river-reservoir landscapes

Hydrologic processes are often important determinants of successful recruitment of native fishes. However, water management practices can result in abnormal changes in daily and seasonal hydrology patterns. Rarely has fish recruitment across river–reservoir landscapes been considered in relation to flow management, despite the direct relationship between reservoir water management and the resulting upstream and downstream hydrology. We evaluated the relationships between lotic and lentic hydrology and recruitment of two native broadcast-spawning fishes, Freshwater Drum Aplodinotus grunniens and Gizzard Shad Dorosoma cepedianum . Four seasonal periods for each species were identified that related to the species’ spawning biology, from which we derived our remaining hydrology variables. Annual hydrology variables were also considered in our analysis. We developed regression models in conjunction with a model-selection procedure for each species and habitat type based on the catch-curve residuals from fish populations in hydrologically connected river–reservoir systems in the Ozark Highland and Ouachita Mountain ecoregions, USA. Our results indicated that recruitment of reservoir Freshwater Drum was negatively correlated to annual reservoir retention time. In lotic habitats, Freshwater Drum recruitment was positively correlated with prespawn discharge conditions and negatively correlated with annual flow variability. Similarly, riverine Gizzard Shad recruitment was positively correlated to the frequency of high-flow pulses during the spawning period. Our results indicate that releasing reservoir water to best mimic relatively natural flow patterns may benefit some broadcast-spawning species that occupy both lentic and downstream lotic environments, especially during the spring. This information, combined with future efforts on additional spawning guilds, will provide a foundation for developing holistic river–reservoir water-allocation plans.

Missouri, Oklahoma↗

USGS2024

Using the electron transport system as an indicator of organismal thermal tolerance and respiratory exploitation

Freshwater ecosystems are undergoing rapid thermal shifts, making it increasingly important to understand species-specific responses to these changes. Traditional techniques for determining a species’ thermal tolerance are often lethal and time consuming. Using the enzyme activity associated with the electron transport system (ETS; hereafter referred to as enzyme assay) may provide a non-lethal, rapid, and efficient alternative to traditional techniques for some species. We used largemouth bass Micropterus salmoides (Lacepede, 1802) to test the efficacy of using an enzyme assay to determine thermal tolerance and respiratory exploitation in response to variable acclimation temperatures. Three tissue types were dissected from fish acclimated to 20, 25, or 30 °C and used in ETS assays at temperatures ranging from 7.5 to 40 °C. While there were significant differences among tissue types and acclimation temperatures, maximal enzyme activity occurred from 25.23 to 31.91 °C. Fish lost equilibrium at 39–42 °C in traditional CT max trials, significantly higher than the upper optimum range determined via enzyme assays. The ratio of enzyme activity to measured whole organism respiration rate decreased with increasing water temperature, with the largest changes occurring at the upper optimum thermal range determined by enzyme assays. Our results indicate that ETS analysis may prove useful for obtaining biologically relevant thermal tolerances.

Canadian Journal of Zoology↗

USGS2011

New aerial survey and hierarchical model to estimate manatee abundance

Monitoring the response of endangered and protected species to hydrological restoration is a major component of the adaptive management framework of the Comprehensive Everglades Restoration Plan. The endangered Florida manatee (Trichechus manatus latirostris) lives at the marine-freshwater interface in southwest Florida and is likely to be affected by hydrologic restoration. To provide managers with prerestoration information on distribution and abundance for postrestoration comparison, we developed and implemented a new aerial survey design and hierarchical statistical model to estimate and map abundance of manatees as a function of patch-specific habitat characteristics, indicative of manatee requirements for offshore forage (seagrass), inland fresh drinking water, and warm-water winter refuge. We estimated the number of groups of manatees from dual-observer counts and estimated the number of individuals within groups by removal sampling. Our model is unique in that we jointly analyzed group and individual counts using assumptions that allow probabilities of group detection to depend on group size. Ours is the first analysis of manatee aerial surveys to model spatial and temporal abundance of manatees in association with habitat type while accounting for imperfect detection. We conducted the study in the Ten Thousand Islands area of southwestern Florida, USA, which was expected to be affected by the Picayune Strand Restoration Project to restore hydrology altered for a failed real-estate development. We conducted 11 surveys in 2006, spanning the cold, dry season and warm, wet season. To examine short-term and seasonal changes in distribution we flew paired surveys 1–2 days apart within a given month during the year. Manatees were sparsely distributed across the landscape in small groups. Probability of detection of a group increased with group size; the magnitude of the relationship between group size and detection probability varied among surveys. Probability of detection of individual manatees within a group also differed among surveys, ranging from a low of 0.27 on 11 January to a high of 0.73 on 8 August. During winter surveys, abundance was always higher inland at Port of the Islands (POI), a manatee warm-water aggregation site, than in the other habitat types. During warm-season surveys, highest abundances were estimated in offshore habitat where manatees forage on seagrass. Manatees continued to use POI in summer, but in lower numbers than in winter, possibly to drink freshwater. Abundance in other inland systems and inshore bays was low compared to POI in winter and summer, possibly because of low availability of freshwater. During cold weather, maps of patch abundance of paired surveys showed daily changes in manatee distribution associated with rapid changes in air and water temperature as manatees sought warm water with falling temperatures and seagrass areas with increasing temperatures. Within a habitat type, some patches had higher manatee abundance suggesting differences in quality, possibly due to freshwater flow. If hydrological restoration alters the location of quality habitat, postrestoration comparisons using our methods will document how manatees adjust to new resources, providing managers with information on spatial needs for further monitoring or management. Total abundance for the entire area was similar among survey dates. Credible intervals however were large on a few surveys, and may limit our ability to statistically detect trends in total abundance. Additional modeling of abundance with time- and patch-specific covariates of salinity, water temperature, and seagrass abundance will directly link manatee abundance with physical and biological changes due to restoration and should decrease uncertainty of estimates

Florida↗

USGS2005

A direct immunoassay for detecting diatoms in groundwater as an indicator of the direct influence of surface water

Groundwater under the direct influence of surface water (GWUDISW) is of concern in communities where growing public demand on groundwater resources has resulted in increased withdrawals and hydraulic stress near surface water bodies. Under these conditions, contaminants such as methyl-tert butyl ether (MTBE) and biological materials have been detected in domestic wells. Other contaminants and pathogens associated with surface water are not routinely tested for in groundwater-supplied systems. To address the need for methods to easily identify potentially vulnerable supplies, a direct immunoassay for the quantitative detection of diatoms in raw water samples was developed as a measure of surface water influence on groundwater. Cell wall preparations from Nitzschia palea Kützing, a freshwater diatom found throughout North America, were used to produce a polyclonal antibody that was applied in a direct enzyme-linked immunosorbent assay (ELISA) developed to detect the presence of N. palea cell wall components. The direct immunoassay allows detection at 500 cells L −1 , a level similar to diatom concentrations observed in samples of groundwater collected near the test site. This investigation was the first attempt to utilize an ELISA as an indicator of surface water influence on groundwater. Further research is needed to develop more specific diatom-based monoclonal antibodies, determine cross-reactivity, and optimize sample processing and ELISA procedures for development of a standardized method.

Journal of Applied Phycology↗

USGS2007

DIN retention-transport through four hydrologically connected zones in a headwater catchment of the Upper Mississippi River

Dissolved inorganic nitrogen (DIN) retention-transport through a headwater catchment was synthesized from studies encompassing four distinct hydrologic zones of the Shingobee River Headwaters near the origin of the Mississippi River. The hydrologic zones included: (1) hillslope ground water (ridge to bankside riparian); (2) alluvial riparian ground water; (3) ground water discharged through subchannel sediments (hyporheic zone); and (4) channel surface water. During subsurface hillslope transport through Zone 1, DIN, primarily nitrate, decreased from ∼3 mg-N/l to <0.1 mg-N/l. Ambient seasonal nitrate:chloride ratios in hillslope flow paths indicated both dilution and biotic processing caused nitrate loss. Biologically available organic carbon controlled biotic nitrate retention during hillslope transport. In the alluvial riparian zone (Zone 2) biologically available organic carbon controlled nitrate depletion although processing of both ambient and amended nitrate was faster during the summer than winter. In the hyporheic zone (Zone 3) and stream surface water (Zone 4) DIN retention was primarily controlled by temperature. Perfusion core studies using hyporheic sediment indicated sufficient organic carbon in bed sediments to retain ground water DIN via coupled nitrification-denitrification. Numerical simulations of seasonal hyporheic sediment nitrification-denitrification rates from perfusion cores adequately predicted surface water ammonium but not nitrate when compared to 5 years of monthly field data (1989-93). Mass balance studies in stream surface water indicated proportionally higher summer than winter N retention. Watershed DIN retention was effective during summer under the current land use of intermittently grazed pasture. However, more intensive land use such as row crop agriculture would decrease nitrate retention efficiency and increase loads to surface water. Understanding DIN retention capacity throughout the system, including special channel features such as sloughs, wetlands and floodplains that provide surface water-ground water connectivity, will be required to develop effective nitrate management strategies.

Minnesota↗

USGS2013

Ecological feedbacks can reduce population-level efficacy of wildlife fertility control

1. Anthropogenic stress on natural systems, particularly the fragmentation of landscapes and the extirpation of predators from food webs, has intensified the need to regulate abundance of wildlife populations with management. Controlling population growth using fertility control has been considered for almost four decades, but nearly all research has focused on understanding effects of fertility control agents on individual animals. Questions about the efficacy of fertility control as a way to control populations remain largely unanswered. 2. Collateral consequences of contraception can produce unexpected changes in birth rates, survival, immigration and emigration that may reduce the effectiveness of regulating animal abundance. The magnitude and frequency of such effects vary with species-specific social and reproductive systems, as well as connectivity of populations. Developing models that incorporate static demographic parameters from populations not controlled by contraception may bias predictions of fertility control efficacy. 3. Many population-level studies demonstrate that changes in survival and immigration induced by fertility control can compensate for the reduction in births caused by contraception. The most successful cases of regulating populations using fertility control come from applications of contraceptives to small, closed populations of gregarious and easily accessed species. 4. Fertility control can result in artificial selection pressures on the population and may lead to long-term unintentional genetic consequences. The magnitude of such selection is dependent on individual heritability and behavioural traits, as well as environmental variation. 5. Synthesis and applications . Understanding species' life-history strategies, biology, behavioural ecology and ecological context is critical to developing realistic expectations of regulating populations using fertility control. Before time, effort and funding are invested in wildlife contraception, managers may need to consider the possibility that many species and populations can compensate for reduction in fecundity, and this could minimize any reduction in population growth rate.

Journal of Applied Ecology↗

USGS2012

Effects of river regulation on aeolian landscapes, Colorado River, southwestern USA

Connectivity between fluvial and aeolian sedimentary systems plays an important role in the physical and biological environment of dryland regions. This study examines the coupling between fluvial sand deposits and aeolian dune fields in bedrock canyons of the arid to semiarid Colorado River corridor, southwestern USA. By quantifying significant differences between aeolian landscapes with and without modern fluvial sediment sources, this work demonstrates for the first time that the flow- and sediment-limiting effects of dam operations affect sedimentary processes and ecosystems in aeolian landscapes above the fluvial high water line. Dune fields decoupled from fluvial sand supply have more ground cover (biologic crust and vegetation) and less aeolian sand transport than do dune fields that remain coupled to modern fluvial sand supply. The proportion of active aeolian sand area also is substantially lower in a heavily regulated river reach (Marble–Grand Canyon, Arizona) than in a much less regulated reach with otherwise similar environmental conditions (Cataract Canyon, Utah). The interconnections shown here among river flow and sediment, aeolian sand transport, and biologic communities in aeolian dunes demonstrate a newly recognized means by which anthropogenic influence alters dryland environments. Because fluvial–aeolian coupling is common globally, it is likely that similar sediment-transport connectivity and interaction with upland ecosystems are important in other dryland regions to a greater degree than has been recognized previously.

Colorado↗

USGS2019

Seasonal patterns in hydrochemical mixing in three Great Lakes rivermouth ecosystems

Rivermouth ecosystems in the Laurentian Great Lakes represent complex hydrologic mixing zones where lake and river water combine to form biologically productive areas that are functionally similar to marine estuaries. As urban, industrial, shipping, and recreational centers, rivermouths are the focus of human interactions with the Great Lakes and, likewise, may represent critical habitat for larval fish and other biota. The hydrology and related geomorphology in these deltaic systems form the basis for ecosystem processes and wetland habitat structure but are poorly understood. To this end, a multidisciplinary team of scientists examined hydrogeomorphic structure and lake-tributary mixing in rivermouths using water chemistry, stable isotopes, and current profiling over a five-month period. Results showed that the maximum depth of the rivermouth ecosystem influenced mixing, with temperature-related, density-dependent wedging and layering that isolated lake water below river water occurring in deeper systems. The inherent size of the rivermouth ecosystem, local geomorphology, and human modifications such as shoreline armoring and dredging influenced mixing by altering the propensity for density differences to occur. The improved scientific understanding and framework for characterizing hydrogeomorphic processes in Great Lakes rivermouths across a disturbance gradient is useful for conservation, management, restoration, and protection of critical habitats needed by native species.

Michigan, Wisconsin↗