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At least 1,351 records · Page 75Linked to original sources
USGS2020

Extreme arsenic and antimony uptake and tolerance in toad tadpoles during development in highly contaminated wetlands

The effects of extreme concentrations of toxic metalloids, such as arsenic (As) and antimony (Sb), on larval amphibians are not well-understood. We sampled Western Toad tadpoles ( Anaxyrus boreas ) living in As- and Sb-contaminated wetlands throughout their development. Although the tadpoles completed metamorphosis, they accumulated among the highest concentrations of As and Sb ever reported for a living vertebrate (3866.9 mg/kg; 315.0 mg/kg (dry weight), respectively). Ingestion of contaminated sediment had a more important role in metalloid accumulation than aqueous exposure alone. Metalloids were initially concentrated in the gut; however, by metamorphosis, the majority were found in other tissues. These concentrations subsequently decreased with the onset of metamorphosis, yet remained quite elevated. Sublethal effects, including delayed development and reduced size at metamorphosis, were associated with elevated metalloid exposure. The presence of organic arsenicals in tadpole tissues suggests they have the ability to biomethylate inorganic As compounds. The arsenical trimethyl arsine oxide accounted for the majority of extractable organic As, with lesser amounts of monomethylarsonic acid and dimethylarsinic acid. Our findings demonstrate remarkable tolerance of toad tadpoles to extreme metalloid exposure and implicate physiological processes mediating that tolerance.

Environmental Science and Technology↗
USGS2002

Using groundwater temperature data to constrain parameter estimation in a groundwater flow model of a wetland system

Parameter estimation is a powerful way to calibrate models. While head data alone are often insufficient to estimate unique parameters due to model nonuniqueness, flow‐and‐heat‐transport modeling can constrain estimation and allow simultaneous estimation of boundary fluxes and hydraulic conductivity. In this work, synthetic and field models that did not converge when head data were used did converge when head and temperature were used. Furthermore, frequency domain analyses of head and temperature data allowed selection of appropriate modeling timescales. Inflows in the Wilton, Wisconsin, wetlands could be estimated over periods such as a growing season and over periods of a few days when heads were nearly steady and groundwater temperature varied during the day. While this methodology is computationally more demanding than traditional head calibration, the results gained are unobtainable using the traditional approach. These results suggest that temperature can efficiently supplement head data in systems where accurate flux calibration targets are unavailable.

Water Resources Research↗
USGS2020

Modeling soil porewater salinity response to drought in tidal freshwater forested wetlands

There is a growing concern about the adverse effects of saltwater intrusion via tidal rivers, streams and creeks into tidal freshwater forested wetlands (TFFW) due to sea‐level rise (SLR) and intense and extended drought events. However, the magnitude and duration of porewater salinity in exceedance of plant salinity stress threshold (2 practical salinity units, psu) and the controlling factors remain unclear. In this study, we developed a TFFW soil porewater salinity model, in which the feedback mechanisms between soil salinity and evapotranspiration and hydraulic conductivity were incorporated. We selected sites (upper, middle, lower tidal freshwater forest sites and oligohaline marsh site) along the coastal floodplains of two rivers, the Waccamaw River (SC, USA) and the Savannah River (GA and SC, USA), that represent landscape salinity gradients from tidal influence of the Atlantic Ocean. The model results agreed well with field measurements and revealed that with drought‐induced saltwater intrusion, the mean annual soil porewater salinity and duration of elevated soil porewater salinity (> 2 psu) increased significantly compared to the normal (non‐drought) condition, posing a threat to the health and ecosystem services of TFFW even in the absence of SLR. Model results also showed more severe salinity stress under drought for the lower forest sites along the two rivers, where soil salinity values have already been at or in exceedance of the 2 psu threshold.

Georgia, South Carolina↗
USGS2014

Carbon flow from volcanic CO 2 into soil microbial communities of a wetland mofette

Effects of extremely high carbon dioxide (CO 2 ) concentrations on soil microbial communities and associated processes are largely unknown. We studied a wetland area affected by spots of subcrustal CO 2 degassing (mofettes) with focus on anaerobic autotrophic methanogenesis and acetogenesis because the pore gas phase was largely hypoxic. Compared with a reference soil, the mofette was more acidic (ΔpH ~0.8), strongly enriched in organic carbon (up to 10 times), and exhibited lower prokaryotic diversity. It was dominated by methanogens and subdivision 1Acidobacteria, which likely thrived under stable hypoxia and acidic pH. Anoxic incubations revealed enhanced formation of acetate and methane (CH 4 ) from hydrogen (H 2 ) and CO 2 consistent with elevated CH 4 and acetate levels in the mofette soil. 13 CO 2 mofette soil incubations showed high label incorporations with ~512   ng 13 C   g   (dry weight (dw)) soil −1   d −1 into the bulk soil and up to 10.7   ng 13 C   g   (dw) soil −1   d −1 into almost all analyzed bacterial lipids. Incorporation of CO 2 -derived carbon into archaeal lipids was much lower and restricted to the first 10   cm of the soil. DNA-SIP analysis revealed that acidophilic methanogens affiliated withMethanoregulaceae and hitherto unknown acetogens appeared to be involved in the chemolithoautotrophic utilization of 13 CO 2 . Subdivision 1 Acidobacteriaceae assimilated 13 CO 2 likely via anaplerotic reactions because Acidobacteriaceae are not known to harbor enzymatic pathways for autotrophic CO 2 assimilation. We conclude that CO 2 -induced geochemical changes promoted anaerobic and acidophilic organisms and altered carbon turnover in affected soils.

The ISME Journal↗
USGS2021

Substantial hysteresis in emergent temperature sensitivity of global wetland CH4 emissions

Wetland methane (CH 4 ) emissions ( FCH 4 ) are important in global carbon budgets and climate change assessments. Currently, FCH 4 projections rely on prescribed static temperature sensitivity that varies among biogeochemical models. Meta-analyses have proposed a consistent FCH 4 temperature dependence across spatial scales for use in models; however, site-level studies demonstrate that FCH 4 are often controlled by factors beyond temperature. Here, we evaluate the relationship between FCH 4 and temperature using observations from the FLUXNET-CH 4 database. Measurements collected across the globe show substantial seasonal hysteresis between FCH 4 and temperature, suggesting larger FCH 4 sensitivity to temperature later in the frost-free season (about 77% of site-years). Results derived from a machine-learning model and several regression models highlight the importance of representing the large spatial and temporal variability within site-years and ecosystem types. Mechanistic advancements in biogeochemical model parameterization and detailed measurements in factors modulating CH 4 production are thus needed to improve global CH 4 budget assessments.

Nature Communications↗
USGS2026

Permafrost thaw controls iron flux from wetlands and sulfide-bearing rocks to Arctic rivers and streams

Recent warming has caused widespread iron mobilization into Arctic waterbodies that degrades ecosystems and threatens natural resources. Yet, understanding where and when iron flux occurs remains limited. Here, we investigate iron loading across regional to local scales in Arctic Alaska using climate, water chemistry, and borehole data together with mapped geology and permafrost presence. We show that both anoxic microbial iron reduction and acid rock drainage from iron-sulfide oxidation mobilize iron. Iron influx is strongly associated with lowland wetlands, sulfide-rich upland bedrock, and near-surface permafrost. Acid rock drainage chemistry correlates very strongly with the depth of seasonal thaw above permafrost from the previous year, indicating a one-year lag. These findings clarify the spatial and temporal dynamics of Arctic river rusting, provide a mechanistic understanding of the phenomenon, and may allow anticipation of its occurrence and assessment of its implications for aquatic ecosystem health and subsistence resources under ongoing climate change.

Alaska↗
USGS2003

Phosphorus cycling and partitioning in an oligotrophic Everglades wetland ecosystem: A radioisotope tracing study

1. Our goal was to quantify short-term phosphorus (P) partitioning and identify the ecosystem components important to P cycling in wetland ecosystems. To do this, we added P radiotracer to oligotrophic, P-limited Everglades marshes. 32PO4 was added to the water column in six 1-m2 enclosed mesocosms located in long-hydroperiod marshes of Shark River Slough, Everglades National Park. Ecosystem components were then repeatedly sampled over 18 days. 2. Water column particulates (>0.45 ??m) incorporated radiotracer within the first minute after dosing and stored 95-99% of total water column 32P activity throughout the study. Soluble (<0.45 ??m) 32P in the water column, in contrast, was always <5% of the 32P in surface water. Periphyton, both floating and attached to emergent macrophytes, had the highest specific activity of 32P (Bq g-131P) among the different ecosystem components. Fish and aquatic macroinvertebrates also had high affinity for P, whereas emergent macrophytes, soil and flocculent detrital organic matter (floc) had the lowest specific activities of radiotracer. 3. Within the calcareous, floating periphyton mats, 81% of the initial 32P uptake was associated with Ca, but most of this 32P entered and remained within the organic pool (Ca-associated = 14% of total) after 1 day. In the floc layer, 32P rapidly entered the microbial pool and the labile fraction was negligible for most of the study. 4. Budgeting of the radiotracer indicated that 32P moved from particulates in the water column to periphyton and floc and then to the floc and soil over the course of the 18 days incubations. Floc (35% of total) and soil (27%) dominated 32P storage after 18 days, with floating periphyton (12%) and surface water (10%) holding smaller proportions of total ecosystem 32P. 5. To summarise, oligotrophic Everglades marshes exhibited rapid uptake and retention of labile 32P. Components dominated by microbes appear to control short-term P cycling in this oligotrophic ecosystem.

Freshwater Biology↗
USGS2002

A comparative assessment of genetic diversity among differently-aged populations of Spartina alterniflora on restored versus natural wetlands

We collected naturally recolonizing Spartina alterniflora (smooth cord grass) from each of three restored sites and one undisturbed reference site in southwestern Louisiana to assess the impact of wetland restoration on genetic diversity. We used amplified fragment length polymorphisms (AFLPs) to produce 94 polymorphic genetic markers, which were used to characterize genetic diversity as average heterozygosity and the proportion of polymorphic loci . Overall our findings indicate that restored populations of S. alterniflora maintain levels of genetic diversity comparable to natural populations, which should provide some measure of resistance against environmental disturbances. Diversity estimates were lowest for the natural reference site ( = 0.1059; = 0.2763), whereas estimates for the three restored sites ranged from = 0.1148 to 0.1256 and = 0.3114 to 0.3202. All sites maintained sufficiently high diversity levels to suggest significant rates of outcrossing. Overall, genetic differentiation among populations was small (Weir and Cockerham's ?? = 0.0645), with the values from each pairwise comparison among the populations increasing with the geographic distance between sites (range = 0.0490-0.1101). These values indicate an average migration rate of 3.6 migrants, either pollen or seeds, per generation.

Restoration Ecology↗
USGS2012

Field evaluation of distance-estimation error during wetland-dependent bird surveys

Context: The most common methods to estimate detection probability during avian point-count surveys involve recording a distance between the survey point and individual birds detected during the survey period. Accurately measuring or estimating distance is an important assumption of these methods; however, this assumption is rarely tested in the context of aural avian point-count surveys. Aims: We expand on recent bird-simulation studies to document the error associated with estimating distance to calling birds in a wetland ecosystem. Methods: We used two approaches to estimate the error associated with five surveyor's distance estimates between the survey point and calling birds, and to determine the factors that affect a surveyor's ability to estimate distance. Key results: We observed biased and imprecise distance estimates when estimating distance to simulated birds in a point-count scenario ( x̄ error = -9 m, s.d. error = 47 m) and when estimating distances to real birds during field trials ( x̄ error = 39 m, s.d. error = 79 m). The amount of bias and precision in distance estimates differed among surveyors; surveyors with more training and experience were less biased and more precise when estimating distance to both real and simulated birds. Three environmental factors were important in explaining the error associated with distance estimates, including the measured distance from the bird to the surveyor, the volume of the call and the species of bird. Surveyors tended to make large overestimations to birds close to the survey point, which is an especially serious error in distance sampling. Conclusions: Our results suggest that distance-estimation error is prevalent, but surveyor training may be the easiest way to reduce distance-estimation error. Implications: The present study has demonstrated how relatively simple field trials can be used to estimate the error associated with distance estimates used to estimate detection probability during avian point-count surveys. Evaluating distance-estimation errors will allow investigators to better evaluate the accuracy of avian density and trend estimates. Moreover, investigators who evaluate distance-estimation errors could employ recently developed models to incorporate distance-estimation error into analyses. We encourage further development of such models, including the inclusion of such models into distance-analysis software.

Wildlife Research↗
USGS2012

Accumulation of impact markers in desert wetlands and implications for the Younger Dryas impact hypothesis

The Younger Dryas impact hypothesis contends that an extraterrestrial object exploded over North America at 12.9 ka, initiating the Younger Dryas cold event, the extinction of many North American megafauna, and the demise of the Clovis archeological culture. Although the exact nature and location of the proposed impact or explosion remain unclear, alleged evidence for the fallout comes from multiple sites across North America and a site in Belgium. At 6 of the 10 original sites (excluding the Carolina Bays), elevated concentrations of various "impact markers" were found in association with black mats that date to the onset of the Younger Dryas. Black mats are common features in paleowetland deposits and typically represent shallow marsh environments. In this study, we investigated black mats ranging in age from approximately 6 to more than 40 ka in the southwestern United States and the Atacama Desert of northern Chile. At 10 of 13 sites, we found elevated concentrations of iridium in bulk and magnetic sediments, magnetic spherules, and/or titanomagnetite grains within or at the base of black mats, regardless of their age or location, suggesting that elevated concentrations of these markers arise from processes common to wetland systems, and not a catastrophic extraterrestrial impact event.

Proceedings of the National Academy of Sciences of↗
USGS2011

An approach to regional wetland digital elevation model development using a differential global positioning system and a custom-built helicopter-based surveying system

Accurate topographic data are critical to restoration science and planning for the Everglades region of South Florida, USA. They are needed to monitor and simulate water level, water depth and hydroperiod and are used in scientific research on hydrologic and biologic processes. Because large wetland environments and data acquisition challenge conventional ground-based and remotely sensed data collection methods, the United States Geological Survey (USGS) adapted a classical data collection instrument to global positioning system (GPS) and geographic information system (GIS) technologies. Data acquired with this instrument were processed using geostatistics to yield sub-water level elevation values with centimetre accuracy (±15 cm). The developed database framework, modelling philosophy and metadata protocol allow for continued, collaborative model revision and expansion, given additional elevation or other ancillary data.

Florida↗
USGS2018

Analysis of vegetation recovery surrounding a restored wetland using the normalized difference infrared index (NDII) and normalized difference vegetation index (NDVI)

Watershed restoration efforts seek to rejuvenate vegetation, biological diversity, and land productivity at Cienega San Bernardino, an important wetland in southeastern Arizona and northern Sonora, Mexico. Rock detention and earthen berm structures were built on the Cienega San Bernardino over the course of four decades, beginning in 1984 and continuing to the present. Previous research findings show that restoration supports and even increases vegetation health despite ongoing drought conditions in this arid watershed. However, the extent of restoration impacts is still unknown despite qualitative observations of improvement in surrounding vegetation amount and vigor. We analyzed spatial and temporal trends in vegetation greenness and soil moisture by applying the normalized difference vegetation index (NDVI) and normalized difference infrared index (NDII) to one dry summer season Landsat path/row from 1984 to 2016. The study area was divided into zones and spectral data for each zone was analyzed and compared with precipitation record using statistical measures including linear regression, Mann– Kendall test, and linear correlation. NDVI and NDII performed differently due to the presence of continued grazing and the effects of grazing on canopy cover; NDVI was better able to track changes in vegetation in areas without grazing while NDII was better at tracking changes in areas with continued grazing. Restoration impacts display higher greenness and vegetation water content levels, greater increases in greenness and water content through time, and a decoupling of vegetation greenness and water content from spring precipitation when compared to control sites in nearby tributary and upland areas. Our results confirm the potential of erosion control structures to affect areas up to 5 km downstream of restoration sites over time and to affect 1 km upstream of the sites.

Cuenca Los Ojos, San Bernardino National Wildlife ↗
USGS1988

Environmental impacts and regulatory policy. Implications of spray disposal of dredged material in Louisiana wetlands

The capabilities of a new wetland dredging technology were assessed along with associated newly developed state and federal regulatory policies to determine if policy expectations realistically match the technological achievement. Current regulatory practices require amelioration of spoil bank impacts upon abandonment of an oil/gas well, but this may not occur for many years or decades, if at all. Recently, a dreding method (high-pressure spray spoil disposal) was developed that does not create a spoil bank in the traditional sense. Its potential for reducing environmental impacts was recognized immediately by regulatory agencies for whom minimizing spoil bank impacts is a major concern. The use of high-pressure spray disposal as a suitable alternative to traditional dreding technology has been adopted as policy even though its value as a management tool has never been tested or verified. A qualitative evaluation at two spoil disposal sites in saline marsh indicates that high-pressure spray disposal may indeed have great potential to minimize impacts, but most of this potential remains unverified. Also, some aspects of current regulatory policy may be based on unrealistic expectations as to the ability of this new technology to minimize or eliminate spoil bank impacts.

Louisiana↗
USGS2011

The role of the Everglades Mangrove Ecotone Region (EMER) in regulating nutrient cycling and wetland productivity in South Florida

The authors summarize the main findings of the Florida Coastal Everglades Long-Term Ecological Research (FCE-LTER) program in the EMER, within the context of the Comprehensive Everglades Restoration Plan (CERP), to understand how regional processes, mediated by water flow, control population and ecosystem dynamics across the EMER landscape. Tree canopies with maximum height <3 m cover 49% of the EMER, particularly in the SE region. These scrub/dwarf mangroves are the result of a combination of low soil phosphorus (P < 59 μg P g dw −1 ) in the calcareous marl substrate and long hydroperiod. Phosphorus limits the EMER and its freshwater watersheds due to the lack of terrigenous sediment input and the phosphorus-limited nature of the freshwater Everglades. Reduced freshwater delivery over the past 50 years, combined with Everglades compartmentalization and a 10 cm rise in coastal sea level, has led to the landward transgression (∼1.5 km in 54 years) of the mangrove ecotone. Seasonal variation in freshwater input strongly controls the temporal variation of nitrogen and P exports (99%) from the Everglades to Florida Bay. Rapid changes in nutrient availability and vegetation distribution during the last 50 years show that future ecosystem restoration actions and land use decisions can exert a major influence, similar to sea level rise over the short term, on nutrient cycling and wetland productivity in the EMER.

Florida↗
USGS1998

Application of an index of biotic integrity for dunal, palustrine wetlands: Emphasis on assessment of nonpoint source landfill effects on the Grand Calumet Lagoons

Using a newly modified index of biotic integrity for assessing biological integrity of fish communities in dunal, palustrine wetlands, we assessed the non-point source influence of an industrial landfill on the Grand Calumet Lagoons. The landfill is primarily an iron and steel manufacturer's slag waste. No sensitive species, hybrids, headwater species, and either few or no simple lithophilic spawning species were collected from any of the sites in the Grand Calumet Lagoons. Species catch-per-unit of effort varied significantly between reaches in the Middle Lagoon and the West Lagoon. The most disturbed areas were adjacent to the industrial landfill and along the southern shore near the outflow from the West Lagoon. Near- and far-field stations possessed similar numbers of species and relative abundance. The near-field stations showed an increase in tolerant species, a higher proportion of omnivores and carnivores, and a lower environmental quality rating of ‘poor-very poor’. The far-field sites were classified as having ‘fair’ biological integrity and showed an increase in relative abundance, proportion of sensitive species, and an increase in simple lithophils. The loss of biological integrity in the West Pond was not accurately predicted using the modified index of biotic integrity, even though it was rated as extremely degraded by the biological diversity indices. Fish communities were negatively impacted by proximity to the landfill.

Indiana↗
USGS2002

Lead distribution throughout soil, flora, and an invertebrate at a wetland skeet range

Lead pellets from a skeet range impart Pb to the local soil, plants, and animals. Concentrations and distributions of Pb in the various media were studied at the now-abandoned skeet range bordering a cordgrass marsh at the Naval Weapons Station Seal Beach in Southern California. The concentrations of Pb in soil (maximum = 16,200 ppm, dry mass) are significantly correlated to the shot pellet densities. Lead concentrations in plants vary according to species' abilities to inhibit Pb uptake from soil. Horn snails had a mean Pb concentration (1987 ppm, dry mass) over 100 times greater than the leaves of the plant species with the highest mean concentration (18.1 ppm, dry mass) at the same site. Avian predators of gastropods may receive minimum exposure to Pb due to calcium in the shells, but incidental ingestion of soil in addition to direct ingestion of shot pellets may provide significant exposure to birds. Because shotgun pellets may persist in wetland soil for 300 yr, reduction of wildlife exposure to Pb in such cases requires deliberate action.

Journal of Toxicology and Environmental Health, Pa↗
USGS2008

Modeling wetland blackbird populations as a function of waterfowl abundance in the prairie pothole region of the United States and Canada

Blackbirds share wetland habitat with many waterfowl species in Bird Conservation Region 11 (BCR 11), the prairie potholes. Because of similar habitat preferences, there may be associations between blackbird populations and populations of one or more species of waterfowl in BCR11. This study models populations of red-winged blackbirds and yellow-headed blackbirds as a function of multiple waterfowl species using data from the North American Breeding Bird Survey within BCR11. For each blackbird species, we created a global model with blackbird abundance modeled as a function of 11 waterfowl species; nuisance effects (year, route, and observer) also were included in the model. Hierarchical Poisson regression models were fit using Markov chain Monte Carlo methods in WinBUGS 1.4.1. Waterfowl abundances were weakly associated with blackbird numbers, and no single waterfowl species showed a strong correlation with any blackbird species. These findings suggest waterfowl abundance from a single species is not likely a good bioindicator of blackbird abundance; however, a global model provided good fit for predicting red-winged blackbird abundance. Increased model complexity may be required for accurate predictions of blackbird abundance; the amount of data required to construct appropriate models may limit this approach for predicting blackbird abundance in the prairie potholes. Copyright ?? Taylor & Francis Group, LLC.

Environmental Bioindicators↗
USGS2019

Modeling connectivity of non‐floodplain wetlands: Insights, approaches, and recommendations

Representing hydrologic connectivity of non‐floodplain wetlands (NFWs) to downstream waters in process‐based models is an emerging challenge relevant to many research, regulatory, and management activities. We review four case studies that utilize process‐based models developed to simulate NFW hydrology. Models range from a simple, lumped parameter model to a highly complex, fully distributed model. Across case studies, we highlight appropriate application of each model, emphasizing spatial scale, computational demands, process representation, and model limitations. We end with a synthesis of recommended “best modeling practices” to guide model application. These recommendations include: (1) clearly articulate modeling objectives, and revisit and adjust those objectives regularly; (2) develop a conceptualization of NFW connectivity using qualitative observations, empirical data, and process‐based modeling; (3) select a model to represent NFW connectivity by balancing both modeling objectives and available resources; (4) use innovative techniques and data sources to validate and calibrate NFW connectivity simulations; and (5) clearly articulate the limits of the resulting NFW connectivity representation. Our review and synthesis of these case studies highlights modeling approaches that incorporate NFW connectivity, demonstrates tradeoffs in model selection, and ultimately provides actionable guidance for future model application and development.

Journal of the American Water Resources Associatio↗