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USGS2016

Key ecological responses to nitrogen are altered by climate change

Climate change and anthropogenic nitrogen deposition are both important ecological threats. Evaluating their cumulative effects provides a more holistic view of ecosystem vulnerability to human activities, which would better inform policy decisions aimed to protect the sustainability of ecosystems. Our knowledge of the cumulative effects of these stressors is growing, but we lack an integrated understanding. In this Review, we describe how climate change alters key processes in terrestrial and freshwater ecosystems related to nitrogen cycling and availability, and the response of ecosystems to nitrogen addition in terms of carbon cycling, acidification and biodiversity.

Nature Climate Change↗

USGS2025

Prioritizing chemicals of emerging concern in the Great Lakes Basin using covariance of chemical concentrations and diverse biological responses from a variety of species

The Great Lakes Restoration Initiative aims to protect and restore the nation’s largest freshwater resource, in part, by furthering our understanding of the effects of contaminants of emerging concern (CECs) and chemical mixtures on aquatic and terrestrial organisms. To address this goal, an interagency team conducted field studies at sites along the Maumee River in Ohio, USA, in 2016–2017, monitoring CEC levels along with diverse in vitro and in vivo biological effects in ecologically relevant species (fathead minnows, tree swallows, and golden clams). The objective of the present work was to prioritize the CECs in these studies for further monitoring and assessment by determining if there are patterns in chemical–bioeffect relations across data sets, species, and response types that indicate relatively high or low hazard to aquatic life from CEC exposure. Of the 748 monitored chemicals, 425 were detected and were analyzed for covariance with bioeffects. All 748 chemicals were placed into 10 bins based on their frequencies of monitoring, detection, and covariance with bioeffects across studies and species. We describe how chemicals can be prioritized across bins to aid monitoring and assessment efforts. Our approach using effects-based monitoring data is especially useful for prioritizing chemicals with little or no traditional toxicity testing data. Similar evidence-based prioritizations will allow agencies to more efficiently allocate limited resources to improve the ability to protect aquatic and terrestrial organisms from adverse impacts due to contaminant exposure.

Ohio↗

USGS2018

Remaining populations of an upland stream fish persist in refugia defined by habitat features at multiple scales

Aim Conserving stream biota could require strategies that preserve habitats conveying resistance to ecological impacts of changing land use and climate. Retrospective analyses of species’ responses to anthropogenic disturbances can inform such strategies. We developed a hierarchical framework to contrast environmental conditions underlying persistence versus extirpation of an imperilled stream fish, Candy Darter ( Etheostoma osburni ), over decades of changing land use. The decline of E. osburni may broadly represent the challenge of conserving sensitive freshwater species in intensively used upland environments. Location New River drainage, Appalachian Mountains, USA. Methods We surveyed fish and habitat in historically occupied sites to identify population refugia, and used multivariate and spatial analyses to address three questions: (a) what are the environmental correlates of refugia? (b) are the pathways by which land use impacts instream habitat constrained by catchment- and/or segment-scale features? and (c) are E. osburni distributional dynamics spatially structured and explained by fine sediment and warm stream temperatures? Results We confirmed a recently localized distribution similar to other upland species, marked by at least seven extirpations from streams throughout E. osburni 's southern range. Catchment-scale features primarily constrained land use and finer-scale habitat, leading to either extirpations or population-supporting refugia defined by features at multiple scales. Refugium habitats contained cooler temperatures and less fine sediment. Rare mismatches between persistence and habitat suitability were explained by network location , suggesting unmeasured environmental gradients and/or dispersal contributed to distributional dynamics. Main conclusions We provided insight at multiple spatial scales into how aquatic species’ distributions become fragmented and localized. Our results demonstrate that natural landscape heterogeneity imparts spatially variable resistance of sensitive species to intensive land uses. By recognizing the scale-specific features that buffer populations from extirpation, conservation strategies could be tailored to protect naturally occurring refugium habitats and focus restoration in systems where such habitats are broadly lacking.

Virginia, West Virginia↗

USGS2021

Synthesis of data and studies relating to Delta Smelt biology in the San Francisco Estuary, emphasizing water year 2017

In the San Francisco Estuary (SFE), the effects of freshwater flow on the aquatic ecosystem have been studied extensively over the years and remains a contentious management issue. It is especially contentious with regards to the Delta Smelt (Hypomesus transpacificus), a species endemic to the SFE that has been listed as threatened under the Federal Endangered Species Act and endangered by the State of California. Early studies of Delta Smelt distribution within the SFE suggested that Delta Smelt habitat is determined largely by freshwater flow; however, the exact mechanisms and processes producing such benefits remained unclear. In the summer of 2017, the Flow Alteration Management, Analysis, and Synthesis Team (FLOAT-MAST) was established to analyze, synthesize, and summarize the data collected from the various flow-related monitoring and special studies occurring in 2017(see Table Intro 4). This report will focus on the 2017 summer-fall status of Delta Smelt and its habitat following a record wet year. There has been a long-term decline in the abundance of Delta Smelt associated with a decline in other pelagic fishes. Investigators concluded that the decline has likely been caused by the interactive effects of several causes, including changes in both physical and biotic habitats, many of which are tied to amount and timing of freshwater flow. For this report, we formulated a number of basic predictions about the likely effects of high flows in 2017 on Delta Smelt and their habitat (Table 3). We use a qualitative weight of evidence approach to evaluate whether these predictions were supported by available data. Data sources included a variety of long-term monitoring surveys conducted by Interagency Ecological Program (IEP) agencies, as well as model outputs. Delta Smelt population, health, and life history metrics rarely responded as predicted. Water temperature appears to have a stronger effect on Delta Smelt growth rate and some metrics of life history diversity than outflow or X2 position. Other life history diversity attributes varied but did not appear to be driven by outflow or temperature. Health status was difficult to interpret. Low prevalence of lesions and improved nutritional condition during the drought was contradicted by declining overall population levels. Because of the sparse catches of Delta Smelt in the post-POD years, we consider the data insufficient to reach firm conclusions about the predictions concerning range and distribution of Delta Smelt, especially in the fall. The prediction of high survival was not supported. The 2017 Delta Smelt year class began with poor recruitment in spring of 2017 and below average survival for spring to summer and summer to fall. Thus, low production and low survival led to low abundance of all life stages. During the fall to winter period survival improved, yet the resulting adults were low in number. Foraging success of the fish captured, as measured by stomach fullness, was high for juveniles and adults in 2017 relative to recent years associated with the higher densities of common zooplankton prey that occurred in 2017.

California↗

USGS2006

The importance of fluvial hydraulics to fish-habitat restoration in low-gradient alluvial streams

1. A major cause of degradation and loss of stream fish is alteration of physical habitat within and adjacent to the channel. We describe a potentially efficient approach to fish restoration based upon the relationship between fluvial hydraulics, geomorphology, and those habitats important to fish. 2. The aquatic habitat in a low-gradient, alluvial stream in the Ozark Plateaus physiographical province was classified according to location in the channel, patterns of water flow, and structures that control flow. The resulting habitat types were ranked in terms of their temporal stability and ability to be manipulated. 3. Delineation and quantification of discrete physical spaces in a stream, termed hydraulic habitat units, are shown to be useful in stream restoration programmes if the ecological importance of each habitat unit is known, and if habitats are defined by fluvial dynamics so that restoration is aided by natural forces. 4. Examples, using different taxa, are given to illustrate management options.

Missouri↗

USGS2016

Transboundary fisheries science: Meeting the challenges of inland fisheries management in the 21st century

Managing inland fisheries in the 21st century presents several obstacles, including the need to view fisheries from multiple spatial and temporal scales, which usually involves populations and resources spanning sociopolitical boundaries. Though collaboration is not new to fisheries science, inland aquatic systems have historically been managed at local scales and present different challenges than in marine or large freshwater systems like the Laurentian Great Lakes. Therefore, we outline a flexible strategy that highlights organization, cooperation, analytics, and implementation as building blocks toward effectively addressing transboundary fisheries issues. Additionally, we discuss the use of Bayesian hierarchical models (within the analytical stage), due to their flexibility in dealing with the variability present in data from multiple scales. With growing recognition of both ecological drivers that span spatial and temporal scales and the subsequent need for collaboration to effectively manage heterogeneous resources, we expect implementation of transboundary approaches to become increasingly critical for effective inland fisheries management.

Fisheries↗

USGS2018

Chasing a changing climate: Reproductive and dispersal traits predict how sessile species respond to global warming

Aim Studies of species' range shifts have become increasingly relevant for understanding ecology and biogeography in the face of accelerated global change. The combination of limited mobility and imperilled status places some species at a potentially greater risk of range loss, extirpation or extinction due to climate change. To assess the ability of organisms with limited movement and dispersal capabilities to track shifts associated with climate change, we evaluated reproductive and dispersal traits of freshwater mussels (Unionida), sessile invertebrates that require species‐specific fish for larval dispersal. Location North American Atlantic Slope rivers. Methods To understand how unionid mussels may cope with and adapt to current and future warming trends, we identified mechanisms that facilitated their colonization of the northern Atlantic Slope river basins in North America after the Last Glacial Maximum. We compiled species occurrence and life history trait information for each of 55 species, and then selected life history traits for which ample data were available (larval brooding duration, host fish specificity, host infection strategy, and body size) and analysed whether the trait state for each was related to mussel distribution in Atlantic Slope rivers. Results Brooding duration ( p < .01) and host fish specificity ( p = .02) were significantly related to mussel species distribution. Long‐term brooders were more likely than short‐term brooders to colonize formerly glaciated rivers, as were host generalists compared to specialists. Body size and host infection strategy were not predictive of movement into formerly glaciated rivers ( p > .10). Main conclusions Our results are potentially applicable to many species for which life history traits have not been well‐documented, because reproductive and dispersal traits in unionid mussels typically follow phylogenetic relationships. These findings may help resource managers prioritize species according to climate change vulnerability and predict which species might become further imperilled with climate warming. Finally, we suggest that similar trait‐based decision support frameworks may be applicable for other movement limited taxa.

Diversity and Distributions↗

USGS2023

Potential effects of climate change on Appalachian stoneflies ( Remenus kirchneri , Acroneuria kosztarabi , and Tallaperla lobata )

Plecoptera (stoneflies) are an order of insects where most species rely on clean, fast-moving freshwater for an aquatic larval stage followed by a short terrestrial adult stage. Most species of Plecoptera seem to be restricted to specific stream types and thermal regimes. Climate-driven changes are likely to alter stream temperatures and flow, resulting in physiological stress, reduced reproductive success, and possibly latitudinal or elevational distribution shifts. This report focuses on climate projections and the resulting ecological effect for three species of Appalachian stoneflies: Remenus kirchneri , Acroneuria kosztarabi , and Tallaperla lobata . Although species-specific information is sparse for these three species, climate studies for other Plecoptera spp. are applicable. In the focal region, temperature is increasing and likely leading to increased stream temperatures. In response, Plecoptera spp. will likely experience physiological stress from increasing metabolic rates and energy demands concurrent with changing food quality and access. Warming temperatures and decreased larval energy stores are likely to contribute to lower adult body size and longevity, thus decreasing reproductive success. Whereas projected changes to precipitation and runoff are less certain, under drier future climate projections, decreased streamflow may further stress larval Plecoptera. Remenus kirchneri , A. kosztarabi , and T. lobata will likely retain stable permanent stream habitats for the analyzed future (2006–99). Changing climate is of particular concern for mountaintop species R. kirchneri and T. lobata because they may be unable to track shifts in suitable climate and habitat.

North Carolina, Tennessee, Virginia↗

USGS2015

Reviews and syntheses: Effects of permafrost thaw on Arctic aquatic ecosystems

The Arctic is a water-rich region, with freshwater systems covering about 16 % of the northern permafrost landscape. Permafrost thaw creates new freshwater ecosystems, while at the same time modifying the existing lakes, streams, and rivers that are impacted by thaw. Here, we describe the current state of knowledge regarding how permafrost thaw affects lentic (still) and lotic (moving) systems, exploring the effects of both thermokarst (thawing and collapse of ice-rich permafrost) and deepening of the active layer (the surface soil layer that thaws and refreezes each year). Within thermokarst, we further differentiate between the effects of thermokarst in lowland areas vs. that on hillslopes. For almost all of the processes that we explore, the effects of thaw vary regionally, and between lake and stream systems. Much of this regional variation is caused by differences in ground ice content, topography, soil type, and permafrost coverage. Together, these modifying factors determine (i) the degree to which permafrost thaw manifests as thermokarst, (ii) whether thermokarst leads to slumping or the formation of thermokarst lakes, and (iii) the manner in which constituent delivery to freshwater systems is altered by thaw. Differences in thaw-enabled constituent delivery can be considerable, with these modifying factors determining, for example, the balance between delivery of particulate vs. dissolved constituents, and inorganic vs. organic materials. Changes in the composition of thaw-impacted waters, coupled with changes in lake morphology, can strongly affect the physical and optical properties of thermokarst lakes. The ecology of thaw-impacted lakes and streams is also likely to change; these systems have unique microbiological communities, and show differences in respiration, primary production, and food web structure that are largely driven by differences in sediment, dissolved organic matter, and nutrient delivery. The degree to which thaw enables the delivery of dissolved vs. particulate organic matter, coupled with the composition of that organic matter and the morphology and stratification characteristics of recipient systems will play an important role in determining the balance between the release of organic matter as greenhouse gases (CO 2 and CH 4 ), its burial in sediments, and its loss downstream. The magnitude of thaw impacts on northern aquatic ecosystems is increasing, as is the prevalence of thaw-impacted lakes and streams. There is therefore an urgent need to quantify how permafrost thaw is affecting aquatic ecosystems across diverse Arctic landscapes, and the implications of this change for further climate warming.

Biogeosciences↗

USGS2006

A review of major storm impacts on coastal wetland elevations

Storms have long been recognized as agents of geomorphic change to coastal wetlands. A review of recent data on soil elevation dynamics before and after storms revealed that storms affected wetland elevations by storm surge, high winds, and freshwater flushing of the estuary (inferred). The data also indicate that measures of sediment deposition and erosion can often misrepresent the amount and even direction of elevation change because of storm influences on subsurface processes. Simultaneous influence on both surface and subsurface processes by storms means that soil elevation cannot always be accurately estimated from surface process data alone. Eight processes are identified as potentiatly influencing soil elevation: sediment deposition, sediment erosion, sediment compaction, soil shrinkage, root decomposition (following tree mortality from high winds), root growth (following flushing with freshwater, inferred), soil swelling, and lateral folding of the marsh root mat. Local wetland conditions (e.g., marsh health, tide height, groundwater level) and the physical characteristics of the storm (e.g., angle of approach, proximity, amount of rain, wind speed, and storm surge height) were apparently important factors determining the storm's effect on soil elevation. Storm effects on elevation were both permanent (on an ecological time scale) and short-lived, but even short-term changes have potentially important ecological consequences. Shallow soil subsidence or expansion caused by a storm must be considered when calculating local rates of relative sea level rise and evaluating storm effects on wetland stability.

Estuaries and Coasts↗

USGS2010

Modeling seasonal dynamics of small fish cohorts in fluctuating freshwater marsh landscapes

Small-bodied fishes constitute an important assemblage in many wetlands. In wetlands that dry periodically except for small permanent waterbodies, these fishes are quick to respond to change and can undergo large fluctuations in numbers and biomasses. An important aspect of landscapes that are mixtures of marsh and permanent waterbodies is that high rates of biomass production occur in the marshes during flooding phases, while the permanent waterbodies serve as refuges for many biotic components during the dry phases. The temporal and spatial dynamics of the small fishes are ecologically important, as these fishes provide a crucial food base for higher trophic levels, such as wading birds. We develop a simple model that is analytically tractable, describing the main processes of the spatio-temporal dynamics of a population of small-bodied fish in a seasonal wetland environment, consisting of marsh and permanent waterbodies. The population expands into newly flooded areas during the wet season and contracts during declining water levels in the dry season. If the marsh dries completely during these times (a drydown), the fish need refuge in permanent waterbodies. At least three new and general conclusions arise from the model: (1) there is an optimal rate at which fish should expand into a newly flooding area to maximize population production; (2) there is also a fluctuation amplitude of water level that maximizes fish production, and (3) there is an upper limit on the number of fish that can reach a permanent waterbody during a drydown, no matter how large the marsh surface area is that drains into the waterbody. Because water levels can be manipulated in many wetlands, it is useful to have an understanding of the role of these fluctuations.

Landscape Ecology↗

USGS2015

Bistability of mangrove forests and competition with freshwater plants

Halophytic communities such as mangrove forests and buttonwood hammocks tend to border freshwater plant communities as sharp ecotones. Most studies attribute this purely to underlying physical templates, such as groundwater salinity gradients caused by tidal flux and topography. However, a few recent studies hypothesize that self-reinforcing feedback between vegetation and vadose zone salinity are also involved and create a bistable situation in which either halophytic dominated habitat or freshwater plant communities may dominate as alternative stable states. Here, we revisit the bistability hypothesis and demonstrate the mechanisms that result in bistability. We demonstrate with remote sensing imagery the sharp boundaries between freshwater hardwood hammock communities in southern Florida and halophytic communities such as buttonwood hammocks and mangroves. We further document from the literature how transpiration of mangroves and freshwater plants respond differently to vadose zone salinity, thus altering the salinity through feedback. Using mathematical models, we show how the self-reinforcing feedback, together with physical template, controls the ecotones between halophytic and freshwater communities. Regions of bistability along environmental gradients of salinity have the potential for large-scale vegetation shifts following pulse disturbances such as hurricane tidal surges in Florida, or tsunamis in other regions. The size of the region of bistability can be large for low-lying coastal habitat due to the saline water table, which extends inland due to salinity intrusion. We suggest coupling ecological and hydrologic processes as a framework for future studies.

Florida↗

USGS2026

Predicting reach-scale macroinvertebrate community changes due to declining flows in an aridland river

Understanding the connection between streamflow and macroinvertebrate community structure is critical for managing river ecosystems under scenarios of change caused by human activities and drought. Streamflow influences physical habitat characteristics, including depth, water velocity, and substrate composition, which structure macroinvertebrate communities. Although strong empirical evidence has linked macroinvertebrates to these variables, most studies are correlative, and predictive approaches that link altered streamflow to changes in habitat availability and community structure remain limited. To address this gap, we coupled benthic macroinvertebrate surveys with reach-scale, 2-dimensional hydraulic models to quantify changes in community structure in response to altered streamflows. We characterized macroinvertebrate communities and physical habitat conditions in riffle, run, and pool mesohabitats across 3 reaches of a free-flowing section of the Verde River (Arizona, USA) over 3 y and developed hydraulic models using overflight data, ground surveys, and streamflow monitoring. Macroinvertebrate communities differed among mesohabitats, with riffles supporting higher macroinvertebrate densities and pools exhibiting higher taxonomic richness. The 2-dimensional hydraulic models indicated that declining streamflows could reduce the area of suitable habitat in riffles and runs relative to pools, potentially shifting the distribution of mesohabitats and altering community composition. These changes may lead to declines in overall macroinvertebrate diversity and abundance under reduced flow conditions. By explicitly linking streamflow to habitat availability and community structure, this study demonstrates how integrating hydraulic modeling with biological surveys can improve predictions of ecological response to flow alteration. This framework provides a basis for flow management strategies aimed at maintaining habitat heterogeneity and supporting biodiversity in river networks.

Arizona↗

USGS2014

Latitudinal and photic effects on diel foraging and predation risk in freshwater pelagic ecosystems

1. Clark & Levy ( American Naturalist , 131 , 1988, 271–290) described an antipredation window for smaller planktivorous fish during crepuscular periods when light permits feeding on zooplankton, but limits visual detection by piscivores. Yet, how the window is influenced by the interaction between light regime, turbidity and cloud cover over a broad latitudinal gradi- ent remains unexplored. 2. We evaluated how latitudinal and seasonal shifts in diel light regimes alter the foraging- risk environment for visually feeding planktivores and piscivores across a natural range of turbidities and cloud covers. Pairing a model of aquatic visual feeding with a model of sun and moon illuminance, we estimated foraging rates of an idealized planktivore and piscivore over depth and time across factorial combinations of latitude (0 – 70 ° ), turbidity (0 1 – 5 NTU) and cloud cover (clear to overcast skies) during the summer solstice and autumnal equinox. We evaluated the foraging-risk environment based on changes in the magnitude, duration and peak timing of the antipredation window. 3. The model scenarios generated up to 10-fold shifts in magnitude, 24-fold shifts in duration and 5 5-h shifts in timing of the peak antipredation window. The size of the window increased with latitude. This pattern was strongest during the solstice. In clear water at low turbidity (0 1 – 0 5 NTU), peaks in the magnitude and duration of the window formed at 57 – 60 ° latitude, before falling to near zero as surface waters became saturated with light under a midnight sun and clear skies at latitudes near 70 ° . Overcast dampened the midnight sun enough to allow larger windows to form in clear water at high latitudes. Conversely, at turbidities ≥ 2 NTU, greater reductions in the visual range of piscivores than planktivores created a window for long periods at high latitudes. Latitudinal dependencies were essentially lost during the equinox, indicating a progressive compression of the window from early summer into autumn. 4. Model results show that diel-seasonal foraging and predation risk in freshwater pelagic ecosystems changes considerably with latitude, turbidity and cloud cover. These changes alter the structure of pelagic predator – prey interactions, and in turn, the broader role of pelagic consumers in habitat coupling in lakes.

Journal of Animal Ecology↗

USGS2023

Accounting for spatiotemporal sampling variation in joint species distribution models

Estimating relative abundance is critical for informing conservation and management efforts and for making inferences about the effects of environmental change on populations. Freshwater fisheries span large geographic regions, occupy diverse habitats and consist of varying species assemblages. Monitoring schemes used to sample these diverse populations often result in populations being sampled at different times and under different environmental conditions. Varying sampling conditions can bias estimates of abundance when compared across time, location and species, and properly accounting for these biases is critical for making inferences. We develop a joint species distribution model (JSDM) that accounts for varying sampling conditions due to the environment and time of sampling when estimating relative abundance. The novelty of our JSDM is that we explicitly model sampling effort as the product of known quantities based on time and gear type and an unknown functional relationship to capture seasonal variation in species life history. We use the model to study relative abundance of six freshwater fish species across the state of Minnesota, USA. Our model enables estimates of relative abundance to be compared both within and across species and lakes, and captures the inconsistent sampling present in the data. We discuss how gear type, water temperature and day of the year impact catchability for each species at the lake level and throughout a year. We compare our estimates of relative abundance to those obtained from a model that assumes constant catchability to highlight important differences within and across lakes and species. Synthesis and applications : Our method illustrates that assumptions relating indices of abundance to observed catch data can greatly impact model inferences derived from JSDMs. Specifically, not accounting for varying sampling conditions can bias inference of relative abundance, restricting our ability to detect responses to management interventions and environmental change. While our focus is on freshwater fisheries, this model architecture can be adopted to other systems where catchability may vary as a function of space, time and species.

Journal of Applied Ecology↗

USGS1985

Persistence of an introduced mud flat community in south San Francisco Bay, California

The benthic invertebrate community inhabiting the extensive and sedimentologically homogeneous mudflats of South San Francisco Bay has demonstrated a high degree of constancy in both species composition and relative abundance among species throughout 10 yr of observation. The community, composed predominantly of introduced species with opportunistic lifestyles, is dominated numerically by Gemma gernma , Ampelisca abdita , and Streblospio benedicti . The key to the persistent co-occurrence of these species on the mudflats seems to lie in the combination of (1) the recurrence of minor disturbances of the mudflat habitat (e.g. sediment deposition/erosion, inundation by low-salinity water) on time scales comparable to that of life cycles; (2) opportunistic life history strategies (rapid maturity, brooding of young, multiple generations each year, ease of local dispersal of both juveniles and adults) that permit continued colonization of the mudflat surface or rapid recolonization after disturbances. Only 1 of the 3 numerically-dominant species. A. abdita , displays an annual periodicity in abundance. S. benedicti and G. gemma , through broadly flexible reproductive strategies permitted in the mild San Francisco climate, can exhibit strong recruitment at any time between spring and autumn. The most extreme community changes, involving temporary reduction or elimination of normally dominant populations, occurred as a result of anomalous disturbances such as unusual buildup and decay of an algal mat during 1 summer and prolonged periods of unusually high freshwater inflow during 2 successive winters. The introduced opportunists routinely co-occur at high densities. However, one of these, the tube-dwelling amphipod A. abdita , may control the abundance of the native mollusk Macoma balthica .

Marine Ecology Progress Series↗

USGS1980

Laboratory procedure for estimating residue dynamics of xenobiotic contaminants in a freshwater food chain

A laboratory method of measuring the accumulation, transfer, elimination, and degradation of xenobiotic contaminants is described for organisms in a freshwater food chain (microorganisms, filter-feeder, and fish). A flow-through diluter-system, 14 C-labeled contaminants, gas and thin-layer chromatography, autoradiography, and liquid scintillation spectrometry are used in making residue determinations. Accumulation factors and various index values are developed for measuring and estimating potential accumulation of xenobiotic contaminants by aquatic organisms. The laboratory procedure is economical, simple, reproducible, and ecologically relevant.

Technical Paper↗

USGS2006

Coastal wetlands of the northern Gulf of California: Inventory and conservation status

1. Above 28°N, the coastline of the northern Gulf of California is indented at frequent intervals by negative or inverse estuaries that are saltier at their backs than at their mouths due to the lack of freshwater inflow. These ‘esteros’ total over 215 000 ha in area and encompass mangrove marshes below 29°N and saltgrass ( Distichlis palmeri ) marshes north of 29°N. An additional 6000 ha of freshwater and brackish wetlands are found in the Colorado River delta where fresh water enters the intertidal zone. 2. The mangrove marshes in the Gulf of California have been afforded some degree of protected status in Mexico, but the northern saltgrass esteros do not have priority conservation status and are increasingly becoming development targets for resorts, vacation homes and aquaculture sites. 3. We conducted an inventory of the marshes using aerial photography and satellite images, and evaluated the extent and type of development on each marsh. We reviewed the available literature on the marshes to document their vegetation types and ecological functions in the adjacent marine and terrestrial ecosystems. 4. Over 95% of the mangrove marshes have been developed for shrimp farming. However, the farms are built adjacent to, rather than in, the marshes, and the mangrove stands are still mostly intact. 5. The majority of saltgrass marshes above the mangrove line are still relatively unspoiled. However, resort and vacation home development is taking place on land surrounding them. 6. We recommend a system of protected reserves incorporating the pristine wetlands, along with water quality management and buffer zones for the more developed esteros. The saltgrass marshes should be considered for conservation protection, similar to the protection given to the southern mangrove marshes whose value has already been recognized.

Gulf of California↗