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At least 433 records · Page 24Linked to original sources

USGS1991

Great lakes embryo mortality, edema, and deformities syndrome (glemeds) in colonial fish-eating birds: Similarity to chick-edema disease

Several species of colonial fish-eating birds nesting in the Great Lakes basin Includ-ing herring gulls, common terns and double-crested cormorants, have exhibited chronic impairment of reproduction. In addition to eggshell thinning caused by high levels of DDT and metabolites, the reproductive impairment is characterized by high embryonic and chick mortality , edema, growth retardation, and deformities, hence the name Great Lakes embryo mortality , edema, and deformities syndrome (GLEMEDS). The hypothesis has been advanced that GLEMEDS in colonial fish-eating birds resembles chick-edema disease of poultry and has been caused by exposure to chick- edema active compounds that have a common mode of action through the cytochrome P-448 system. Detailed evidence has been collected from the following three groups of studies on herring gulls in the lower Great Lakes during the early 1970s; Forster’s terns in Green Bay, Wisconsin in 1983; and double-crested cormorants and Caspian terns in various locations in the upper Great Lakes from 1986 onwards. It has proved difficult to establish not only the onset of the disease in the various species at various locations but also the period in which chick-edema active compounds were released. Anecdotal evidence suggested that serious egg mortality . © 1988 by Hemisphere Publishing Corporation.

Illinois, Indiana, Michigan, Wisconsin, Minnesota,↗

USGS2001

The search for reliable aqueous solubility (Sw) and octanol-water partition coefficient (Kow) data for hydrophobic organic compounds; DDT and DDE as a case study

The accurate determination of an organic contaminant’s physico-chemical properties is essential for predicting its environmental impact and fate. Approximately 700 publications (1944–2001) were reviewed and all known aqueous solubilities (S w ) and octanol-water partition coefficients (K ow ) for the organochlorine pesticide, DDT, and its persistent metabolite, DDE were compiled and examined. Two problems are evident with the available database: 1) egregious errors in reporting data and references, and 2) poor data quality and/or inadequate documentation of procedures. The published literature (particularly the collative literature such as compilation articles and handbooks) is characterized by a preponderance of unnecessary data duplication. Numerous data and citation errors are also present in the literature. The percentage of original S w and K ow data in compilations has decreased with time, and in the most recent publications (1994–97) it composes only 6–26 percent of the reported data. The variability of original DDT/DDE S w and K ow data spans 2–4 orders of magnitude, and there is little indication that the uncertainty in these properties has declined over the last 5 decades. A criteria-based evaluation of DDT/DDE S w and K ow data sources shows that 95–100 percent of the database literature is of poor or unevaluatable quality. The accuracy and reliability of the vast majority of the data are unknown due to inadequate documentation of the methods of determination used by the authors. [For example, estimates of precision have been reported for only 20 percent of experimental S w data and 10 percent of experimental K ow data.] Computational methods for estimating these parameters have been increasingly substituted for direct or indirect experimental determination despite the fact that the data used for model development and validation may be of unknown reliability. Because of the prevalence of errors, the lack of methodological documentation, and unsatisfactory data quality, the reliability of the DDT/ DDE S w and K ow database is questionable. The nature and extent of the errors documented in this study are probably indicative of a more general problem in the literature of hydrophobic organic compounds. Under these circumstances, estimation of critical environmental parameters on the basis of S w and K ow (for example, bioconcentration factors, equilibrium partition coefficients) is inadvisable because it will likely lead to incorrect environmental risk assessments. The current state of the database indicates that much greater efforts are needed to: 1) halt the proliferation of erroneous data and references, 2) initiate a coordinated program to develop improved methods of property determination, 3) establish and maintain consistent reporting requirements for physico-chemical property data, and 4) create a mechanism for archiving reliable data for widespread use in the scientific/regulatory community.

Water-Resources Investigations Report↗

USGS2025

Comparing SMART and ELECTRE methods for multi-criteria decision analysis: A case study evaluating conservation strategies

Tradeoffs are part of the inherent challenge of making decisions. Defaulting to a prevalent method can mask methodological variation and potential improvement in decision quality. We applied and compared methods for multi-criteria decision analysis (MCDA) in real-world environmental planning. Decision makers at a global conservation organization formed teams to review and prioritize the allocation of resources across a set of existing strategies across seven teams. Each team evaluated and rated strategies based on a common scale composed of weighted objectives and criteria. Sensitivity analysis included implementing two different MCDA methods, varying strategy ratings, and using two different criteria weighting techniques. The MCDA methods were SMART (Simple Multi-Attribute Rating Technique) and ELECTRE (ELimination and Choice Expressing The REality). We tested user satisfaction between methods, overall rankings between methods, and whether MCDA improved the decision-making process. The methods did not differ in most comparisons, although participants were more likely to use the SMART method in future tradeoff decisions. We found evidence of rank correlation between methods. Lastly, the teams’ final recommendations were consistent with MCDA results. This study highlights the advantages and disadvantages of MCDA in real-world applications.

Environmental and Sustainability Indicators↗

USGS2011

Divergence in forest-type response to climate and weather: Evidence for regional links between forest-type evenness and net primary productivity

Climate change is altering long-term climatic conditions and increasing the magnitude of weather fluctuations. Assessing the consequences of these changes for terrestrial ecosystems requires understanding how different vegetation types respond to climate and weather. This study examined 20 years of regional-scale remotely sensed net primary productivity (NPP) in forests of the northern Lake States to identify how the relationship between NPP and climate or weather differ among forest types, and if NPP patterns are influenced by landscape-scale evenness of forest-type abundance. These results underscore the positive relationship between temperature and NPP. Importantly, these results indicate significant differences among broadly defined forest types in response to both climate and weather. Essentially all weather variables that were strongly related to annual NPP displayed significant differences among forest types, suggesting complementarity in response to environmental fluctuations. In addition, this study found that forest-type evenness (within 8 × 8 km 2 areas) is positively related to long-term NPP mean and negatively related to NPP variability, suggesting that NPP in pixels with greater forest-type evenness is both higher and more stable through time. This is landscape- to subcontinental-scale evidence of a relationship between primary productivity and one measure of biological diversity. These results imply that anthropogenic or natural processes that influence the proportional abundance of forest types within landscapes may influence long-term productivity patterns.

Ecosystems↗

USGS2017

Temporal variability of foliar nutrients: responses to nitrogen deposition and prescribed fire in a temperate steppe

Plant nutrient concentrations and stoichiometry drive fundamental ecosystem processes, with important implications for primary production, diversity, and ecosystem sustainability. While a range of evidence exists regarding how plant nutrients vary across spatial scales, our understanding of their temporal variation remains less well understood. Nevertheless, we know nutrients regulate plant function across time, and that important temporal controls could strongly interact with environmental change. Here, we report results from a 3-year assessment of inter-annual changes of foliar nitrogen (N) and phosphorus (P) concentrations and stoichiometry in three dominant grasses in response to N deposition and prescribed fire in a temperate steppe of northern China. Foliar N and P concentrations and their ratios varied greatly among years, with this temporal variation strongly related to inter-annual variation in precipitation. Nitrogen deposition significantly increased foliar N concentrations and N:P ratios in all species, while fire significantly altered foliar N and P concentrations but had no significant impacts on N:P ratios. Generally, N addition enhanced the temporal stability of foliar N and decreased that of foliar P and of N:P ratios. Our results indicate that plant nutrient status and response to environmental change are temporally dynamic and that there are differential effects on the interactions between environmental change drivers and timing for different nutrients. These responses have important implications for consideration of global change effects on plant community structure and function, management strategies, and the modeling of biogeochemical cycles under global change scenarios.

Biogeochemistry↗

USGS2017

Geographic and temporal patterns of variation in total mercury concentrations in blood of harlequin ducks and blue mussels from Alaska

We compared total mercury (Hg) concentrations in whole blood of harlequin ducks ( Histrionicus histrionicus ) sampled within and among two geographically distinct locations and across three years in southwest Alaska. Blue mussels were collected to assess correlation between Hg concentrations in locally available forage and birds. Mercury concentrations in harlequin duck blood were significantly higher at Unalaska Island (0.31 ± 0.19 mean ± SD, μg/g blood) than Kodiak Island (0.04 ± 0.02 mean ± SD, μg/g blood). We found no evidence for annual variation in blood Hg concentration between years at Unalaska Island. However, blood Hg concentration did vary among specific sampling locations (i.e., bays) at Unalaska Island. Findings from this study demonstrate harlequin ducks are exposed to environmental sources of Hg, and whole blood Hg concentrations are associated with their local food source.

Alaska↗

USGS2007

Use of stage data to characterize hydrologic conditions in an urbanizing environment

This paper presents the results of a study on the use of continuous stage data to describe the relation between urban development and three aspects of hydrologic condition that are thought to influence stream ecosystems - overall stage variability, stream flashiness, and the duration of extreme- stage conditions . This relation is examined using data from more than 70 watersheds in three contrasting environmental settings - the humid Northeast (the metropolitan Boston, Massachusetts, area); the very humid Southeast (the metropolitan Birmingham, Alabama, area); and the semiarid West (the metropolitan Salt Lake City, Utah, area). Results from the Birmingham and Boston studies provide evidence linking increased urbanization with stream flashiness. Fragmentation of developed land cover patches appears to ameliorate the effects of urbanization on overall variability and flashiness. There was less success in relating urbanization and streamflow conditions in the Salt Lake City study. A related investigation of six North Carolina sites with long term discharge and stage data indicated that hydrologic condition metrics developed using continuous stage data are comparable to flow based metrics, particularly for stream flashiness measures.

Journal of the American Water Resources Associatio↗

USGS2016

Formation of the Isthmus of Panama

The formation of the Isthmus of Panama stands as one of the greatest natural events of the Cenozoic, driving profound biotic transformations on land and in the oceans. Some recent studies suggest that the Isthmus formed many millions of years earlier than the widely recognized age of approximately 3 million years ago (Ma), a result that if true would revolutionize our understanding of environmental, ecological, and evolutionary change across the Americas. To bring clarity to the question of when the Isthmus of Panama formed, we provide an exhaustive review and reanalysis of geological, paleontological, and molecular records. These independent lines of evidence converge upon a cohesive narrative of gradually emerging land and constricting seaways, with formation of the Isthmus of Panama sensu stricto around 2.8 Ma. The evidence used to support an older isthmus is inconclusive, and we caution against the uncritical acceptance of an isthmus before the Pliocene.

Science Advances↗

USGS2024

Groundwater quality near the Placerita Oil Field, California, 2018

Groundwater-quality data and potential fluid-migration pathways near the Placerita Oil Field in Los Angeles County, California, were examined by the U.S. Geological Survey to determine if oil-field fluids (water and gas from oil-producing and non-producing zones) have mixed with groundwater resources. Six of the 13 new groundwater samples collected for this study contained petroleum hydrocarbons, thermogenic gas, inorganic chemical signatures, and (or) isotopic values consistent with potential mixing with fluids from hydrocarbon-bearing formations. For historical groundwater samples, benzene was the most detected petroleum hydrocarbon. The historical groundwater samples with a benzene concentration greater than 0.5 micrograms per liter were from environmental monitoring wells at industrial or commercial facilities unrelated to oil and gas development that, in many cases, have identified soil or groundwater contamination and were not typically analyzed for other constituents that could provide additional lines of evidence for potential mixing with oil-field fluids. Methane was not detected in any of the 12 historical samples with a reported measurement. Reviewing historical data revealed factors that could potentially adversely affect groundwater quality in the study area. These factors include modified hydraulic gradients caused by large volumes of water extracted from the main production area and reinjected downgradient into nonproducing zones, well-barrier failures in wells constructed in the northern part of the oil field before the 1970s, well-barrier failures in produced-water disposal wells downgradient from the main production area, and naturally occurring hydrocarbons at shallow intervals. The groundwater samples most geochemically similar to samples from hydrocarbon-bearing formations were in areas where hydrocarbons are naturally occurring at shallow intervals and where oil development is at shallow depths. Additional data for hydraulic heads, water quality, and formation temperatures at multiple depths in areas with large injection volumes and well-integrity issues are needed to evaluate whether those factors have contributed to mixing between fluids from oil-producing or injection formations and groundwater resources.

California↗

USGS2008

Relation Between Solid-Phase and Dissolved Arsenic in the Ground-Water System Underlying Northern Preble County, Ohio

The U.S. Geological Survey (USGS), in cooperation with the Miami Conservancy District, collected and analyzed samples of the aquifer materials and ground water from multiple depths at two sites in northern Preble County, Ohio. The aquifer materials included glacial deposits and Silurian carbonate bedrock. In the study area, elevated arsenic concentrations have been detected in ground water from both types of aquifers. The aquifer materials were described in terms of the stratigraphy and the bulk elemental composition of 70 samples. In addition, six water-producing horizons were selected for more detailed study; ground-water quality was analyzed, microanalytical techniques were used to examine thin sections of the aquifer materials, and simplified geochemical modeling was done to identify plausible reactions between the ground water and aquifer materials. At both study sites, the highest solid-phase arsenic concentrations were from a roughly similar stratigraphic position - a transition zone that extends from just above the Wisconsinan/Illinoian contact to just below the Pleistocene/Silurian contact. For carbonate bedrock, the solid-phase arsenic concentrations were generally low (<1 to 4 mg/kg (milligrams per kilogram)). The one notable exception was a thin horizon about 10 feet below the top of bedrock, which had an arsenic concentration of 42 mg/kg. This horizon showed some textural and compositional evidence of alteration by geothermal fluids. Additional study might be warranted to investigate whether arsenic concentrations in ground water from carbonate bedrock could be decreased by excluding discrete horizons from the open intervals of wells. For glacial deposits, solid-phase arsenic concentrations were slightly higher in fine-grained deposits (2 to 20 mg/kg) than in coarse-grained deposits (2 to 9 mg/kg). In ground water, arsenic concentrations ranged from <1 to 51 ug/L (micrograms per liter); samples from two horizons had concentrations greater than the U.S. Environmental Protection Agency Maximum Contaminant Level (MCL) of 10 ug/L. Dissolved arsenic concentrations appear to be more closely related to redox conditions of the ground water than to the arsenic content of the aquifer materials. Geochemical modeling and thin-section analysis were generally consistent with the idea that arsenic was released to water from iron oxides under iron-reducing conditions. In addition, there was some evidence in support of the idea that arsenic can be removed from ground water by precipitation of sulfide minerals, which occurs under sulfate-reducing conditions. At one site, the dissolved arsenic concentrations in two water-bearing horizons increased from <1 to 51 ug/L over a depth of 15 feet. The large increase might be due to a shift from sulfate-reducing to methanogenic conditions; in the absence of sulfate reduction, arsenic is not sequestered in sulfide minerals and may accumulate in the ground water.

Scientific Investigations Report↗

USGS2016

Response of fish assemblages to declining acidic deposition in Adirondack Mountain lakes, 1984–2012

Adverse effects of acidic deposition on the chemistry and fish communities were evident in Adirondack Mountain lakes during the 1980s and 1990s. Fish assemblages and water chemistry in 43 Adirondack Long-Term Monitoring (ALTM) lakes were sampled by the Adirondack Lakes Survey Corporation and the New York State Department of Environmental Conservation during three periods (1984–87, 1994–2005, and 2008–12) to document regional impacts and potential biological recovery associated with the 1990 amendments to the 1963 Clean Air Act (CAA). We assessed standardized data from 43 lakes sampled during the three periods to quantify the response of fish-community richness, total fish abundance, and brook trout ( Salvelinus fontinalis) abundance to declining acidity that resulted from changes in U.S. air-quality management between 1984 and 2012. During the 28-year period, mean acid neutralizing capacity (ANC) increased significantly from 3 to 30 μeq/L and mean inorganic monomeric Al concentrations decreased significantly from 2.22 to 0.66 μmol/L, yet mean species richness, all species or total catch per net night (CPNN), and brook trout CPNN did not change significantly in the 43 lakes. Regression analyses indicate that fishery metrics were not directly related to the degree of chemical recovery and that brook trout CPNN may actually have declined with increasing ANC. While the richness of fish communities increased with increasing ANC as anticipated in several Adirondack lakes, observed improvements in water quality associated with the CAA have generally failed to produce detectable shifts in fish assemblages within a large number of ALTM lakes. Additional time may simply be needed for biological recovery to progress, or else more proactive efforts may be necessary to restore natural fish assemblages in Adirondack lakes in which water chemistry is steadily recovering from acidification.

New York↗

USGS2023

Periodical cicada emergences affect masting behavior of oaks

Oaks ( Quercus spp.) are masting species exhibiting highly variable and synchronized acorn production. We investigated the hypothesis that periodical cicadas ( Magicada spp.), well known to have strong effects on the ecosystems in which they occur, affect acorn production of oaks through their xylem feeding habits as nymphs, the oviposition damage they inflict as adults during emergences, or the nutrient pulse resulting from the decomposition of their bodies following breeding. We found negative effects on acorn production during emergence years and the year following emergences and enhanced acorn production 2 years after emergence. We also found evidence indicating a significant effect of cicada emergences on spatial synchrony of acorn production by trees growing within the range of the same cicada brood compared with different broods. These results demonstrate that periodical cicadas act as a trophic environmental “veto” depressing acorn production during and immediately following emergences, after which the nutrient pulse associated with the cicada’s demise enhances oak reproduction.

The American Naturalist↗

USGS2023

A global perspective on bacterial diversity in the terrestrial deep subsurface

While recent efforts to catalogue Earth’s microbial diversity have focused upon surface and marine habitats, 12–20 % of Earth’s biomass is suggested to exist in the terrestrial deep subsurface, compared to ~1.8 % in the deep subseafloor. Metagenomic studies of the terrestrial deep subsurface have yielded a trove of divergent and functionally important microbiomes from a range of localities. However, a wider perspective of microbial diversity and its relationship to environmental conditions within the terrestrial deep subsurface is still required. Our meta-analysis reveals that terrestrial deep subsurface microbiota are dominated by Betaproteobacteria, Gammaproteobacteria and Firmicutes , probably as a function of the diverse metabolic strategies of these taxa. Evidence was also found for a common small consortium of prevalent Betaproteobacteria and Gammaproteobacteria operational taxonomic units across the localities. This implies a core terrestrial deep subsurface community, irrespective of aquifer lithology, depth and other variables, that may play an important role in colonizing and sustaining microbial habitats in the deep terrestrial subsurface. An in silico contamination-aware approach to analysing this dataset underscores the importance of downstream methods for assuring that robust conclusions can be reached from deep subsurface-derived sequencing data. Understanding the global panorama of microbial diversity and ecological dynamics in the deep terrestrial subsurface provides a first step towards understanding the role of microbes in global subsurface element and nutrient cycling.

Microbiology↗

USGS2009

Organochlorine contaminants in fishes from coastal waters west of Amukta Pass, Aleutian Islands, Alaska, USA

Organochlorines were examined in liver and stable isotopes in muscle of fishes from the western Aleutian Islands, Alaska, in relation to islands or locations affected by military occupation. Pacific cod (Gadus macrocephalus) , Pacific halibut (Hippoglossus stenolepis) , and rock greenling (Hexagrammos lagocephalus) were collected from nearshore waters at contemporary (decommissioned) and historical (World War II) military locations, as well as at reference locations. Total (Σ) polychlorinated biphenyls (PCBs) dominated the suite of organochlorine groups (ΣDDTs, Σchlordane cyclodienes, Σother cyclodienes, and Σchlorinated benzenes and cyclohexanes) detected in fishes at all locations, followed by ΣDDTs and Σchlordanes; dichlorodiphenyldi-chloroethylene ( p , p ′DDE) composed 52 to 66% of ΣDDTs by species. Organochlorine concentrations were higher or similar in cod compared to halibut and lowest in greenling; they were among the highest for fishes in Arctic or near Arctic waters. Organochlorine group concentrations varied among species and locations, but ΣPCB concentrations in all species were consistently higher at military locations than at reference locations. Moreover, all organochlorine group concentrations were higher in halibut from military locations than those from reference locations. A wide range of molecular weight organochlorines was detected at all locations, which implied regional or long-range transport and deposition, as well as local point-source contamination. Furthermore, a preponderance of higher-chlorinated PCB congeners in fishes from contemporary military islands implied recent exposure. Concentrations in all organochlorine groups increased with δ 15 N enrichment in fishes, and analyses of residual variation provided further evidence of different sources of ΣPCBs and p , p ′DDE among species and locations.

Alaska↗

USGS2016

Wastewater disposal from unconventional oil and gas development degrades stream quality at a West Virginia injection facility

The development of unconventional oil and gas (UOG) resources has rapidly increased in recent years; however, the environmental impacts and risks are poorly understood. A single well can generate millions of liters of wastewater, representing a mixture of formation brine and injected hydraulic fracturing fluids. One of the most common methods for wastewater disposal is underground injection; we are assessing potential risks of this method through an intensive, interdisciplinary study at an injection disposal facility in West Virginia. In June 2014, waters collected downstream from the site had elevated specific conductance (416 μS/cm) and Na, Cl, Ba, Br, Sr, and Li concentrations, compared to upstream, background waters (conductivity, 74 μS/cm). Elevated TDS, a marker of UOG wastewater, provided an early indication of impacts in the stream. Wastewater inputs are also evident by changes in 87Sr/86Sr in streamwater adjacent to the disposal facility. Sediments downstream from the facility were enriched in Ra and had high bioavailable Fe(III) concentrations relative to upstream sediments. Microbial communities in downstream sediments had lower diversity and shifts in composition. Although the hydrologic pathways were not able to be assessed, these data provide evidence demonstrating that activities at the disposal facility are impacting a nearby stream and altering the biogeochemistry of nearby ecosystems.

Environmental Science & Technology↗

USGS2002

Toxicological assessment of aquatic ecosystems: application to watercraft contaminants in shallow water environments

Recreational boating and personal watercraft use have the potential to adversely impact shallow water systems through contaminant release and physical disturbance of bottom sediments. These nearshore areas are often already degraded by surface runoff, municipal and industrial effluents, and other anthropogenic activities. For proper management, information is needed on the level of contamination and environmental quality of these systems. A number of field and laboratory procedures can be used to provide this much needed information. Contaminants, such as metals, pesticides, polychlorinated biphenyls and polycyclic aromatic hydrocarbons, entering aquatic environments generally attach to particulate matter that eventually settles and becomes incorporated into the bottom sediments. Because bottom sediments serve as a sink and as a source for contaminants, environmental assessments generally focus on this matrix. While contaminant residues in sediments and sediment pore waters can reflect environmental quality, characteristics of sediment (redox potential, sediment/pore-water chemistry, acid volatile sulfides, percent organic matter, and sediment particle size) influence their bioavailability and make interpretation of environmental significance difficult. Comparisons of contaminant concentrations in pore water (interstitial water) and sediment with water quality criteria and sediment quality guidelines, respectively, can provide insight into potential biological effects. Laboratory bioaccumulation studies and residue concentrations in resident or caged biota also yield information on potential biological impacts. The usefulness of these measurements may increase as data are developed relating in-situ concentrations, tissue residue levels, and biological responses. Exposure of test organisms in situ or to field-collected sediment and pore water are additional procedures that can be used to assess the biological effects of contaminants. A battery of tests using multi-species and/or various life stages with different sensitivities to contaminants may offer a more conservative assessment of toxicity than single species testing. Using a ?weight of evidence? approach, the Sediment Quality Trial produces a robust evaluation of habitat quality and includes a measure of contaminant concentrations in the sediment, an assessment of sediment/pore-water toxicity to laboratory animals, and an evaluation of in situ biological assemblages. Field and laboratory procedures are available that can be used to ascertain habitat quality, identify contaminants causing environmental degradation and delineate aquatic systems requiring mitigation of protective efforts. These studies provide the scientific data that are integral to developing an environmental risk assessment of contaminants from watercraft use in shallow water systems.

Book chapter↗

USGS2023

White perch health relative to urbanization and habitat degradation in Chesapeake Bay tributaries. II. Hepatic and splenic macrophage aggregates

Macrophage aggregate (MA) abundance in fish is a useful general biomarker of contaminant exposures and environmental stress. Hepatic and splenic MAs were evaluated in semi-anadromous white perch Morone americana (Gmelin, 1789) from the urbanized Severn River (S) and the more rural Choptank River (C), Chesapeake Bay. Fish were collected from different sites in the annual migratory circuit in each river that corresponded to active spawning in late winter-early spring, summer regenerating, autumn developing, and winter spawning-capable phases. An age-associated progressive increase in the total volume of MAs (MAV) was evident in the liver and spleen. Mean hepatic MAV (range in seasonal means, C: 6.4-23.1 mm 3 ; S: 15.7-48.7 mm 3 ) and mean splenic MAV (C: 7.3-12.6 mm 3 ; S: 16.0-33.0 mm 3 ) differed significantly among seasons and were significantly greater in females and in Severn River fish. Age and river were the most influential factors, suggesting that increased MAV in Severn River fish resulted from chronic exposures to higher concentrations of environmental contaminants. Hepatic MAV was directly related to the relative volume of copper granules in the liver. Less influential factors on splenic MAV included fish condition, trematode infections, and granulomas, indicating possible functional differences in MAs by organ. While organ volumes were strongly linked to gonadosomatic index (GSI) and reproductive phase, the reason for seasonal differences in MAV was less clear. Water temperature, salinity, and dissolved oxygen were not significantly related to MAV, and indicators of reproductive phase (hepatosomatic index and GSI) were significant but less important in explaining variation in MAV.

Chesapeake Bay watershed↗

USGS2020

Patterns of denitrification potential in tidal freshwater forested wetlands

Limited evidence for spatial patterns of denitrification in tidal freshwater forested wetlands (TFFWs), seemingly due to high spatial variability in the process, is surprising considering the various spatial gradients of its biogeochemical and hydrogeomorphic controls in these ecosystems. Because certain physical environmental gradients may be useful for the prediction of denitrification in TFFWs, we measured denitrification and ecosystem attributes in hummock-hollow microtopography of TFFWs along longitudinal riverine positions (upper, middle, and lower tidal river sites, and nearby upstream nontidal forested floodplains) of the adjoining Pamunkey and Mattaponi Rivers, Virginia. We tested differences by river, site, and plot in denitrification enzyme activity (DEA) and substrate limitations of denitrification potential (DP). The Pamunkey River carries greater river nitrate concentrations, and we found less nitrate limitation of DP and greater soil nitrate in hollows of this river. DEA in tidal hummocks was positively correlated with soil organic matter, nitrogen, and carbon, with the highest rates in lower tidal sites. Hummocks also promoted greater oxygen-controlled substrate limitation of DP, whereby experimental aeration stimulated DP under subsequent inundation more in hummocks than hollows. Additionally, tidal sites had greater DEA than nontidal sites, inferred to be caused by a combination of higher moisture, organic, and nutrient content. Our results indicate that the increasing nitrogen concentrations in these rivers will increase denitrification more on the Mattaponi River by alleviating its greater nitrogen limitation compared to the Pamunkey River, and modification to sedimentation, inundation, or microtopography from sea level rise may alter denitrification gradients in TFFWs and upstream low-elevation nontidal floodplains.

Virginia↗