Seepage springs are common ephemeral freshwater habitats in the Washington DC area that are home to a variety of invertebrates including the endemic and rare Stygobromus hayi, the official amphipod of Washington DC, USA. However, little is known about the community structure of these habitats. In this study, we analyzed the general food web dynamics of two seepage springs (Pimmit Run and Goldmine Tract) in the Washington DC area that are known to include a congener of S. hayi, Stygobromus tenuis potomacus. Within these two seepage springs, we identified 29 taxa, with varying degrees of abundances, from 18 field excursions over three seasons: Winter, Spring, and Summer. Using dual abundance stable isotope analysis of delta C-13 and delta N-15, we estimated the trophic positions of Lumbriculidae, Conasellus kenki, S. tenuis potomacus, Crangonyx shoemakeri, Tipula sp., Pseudolimnophila sp., and a species of Platyhelminthes. S. tenuis potomacus was the dominant predator in both locations, with delta N-15 and delta C-13 values between 7 parts per thousand and 10 parts per thousand and -25 parts per thousand and -27 parts per thousand respectively. C. kenki and C. shoemakeri were consistently lower in the food web, with delta N-15 and delta C-13 values between 4 parts per thousand and 7 parts per thousand and -24 parts per thousand and -27 parts per thousand respectively and, in some cases, C. kenki may be prey for S. tenuis potomacus. In both seeps leaf material was 4 parts per thousand to 5 parts per thousand lower in delta C-13 than the shredding/grazing invertebrates suggesting that they derive nutrients from microbes colonizing leaves not from leaf carbon itself.

In response to climate change, species may shift their ranges toward the poles, alter their phenotypes, change their physiological resilience to rapidly rising temperatures, or some combination of the three. Physiological resilience is particularly important for species that are unable to migrate. For ectotherms, metabolic rates adjust to environmental temperatures; however, the degree to which their metabolism can adapt to temperature change is not well studied. Assessing invertebrate resilience to a rapidly warming environment is crucial for gauging their ability to adapt to climate change. Resilience to the metabolic stress associated with rapid temperature shifts may be assessed by determining how flexible the metabolic rate is at different temperatures. Here we examine the degree of metabolic plasticity (assessed via stable carbon isotope turnover proxy) for the adults of two species of invertebrates, the amphipod Gammarus minus and the isopod Caecidotea kenki, at temperatures ranging from 5 degrees C to 18 degrees C over the course of 24 days. Not surprisingly, isotope turnover increased with temperature for both species. The carbon isotopic endmembers were maple leaves (-30.4 +/- 0.2 parts per thousand, N = 20) and corn leaves (-12.2 +/- 0.4 parts per thousand, N = 20). Half-lives were between 60 and 90 days at 5 degrees C and between 20 and 35 days at 18 degrees C. G. minus showed a small but significantly greater variation in metabolic response to elevated temperatures than C. kenki, suggesting that it has a greater potential for successfully adapting to a warming climate.

The waterways adjacent to Washington DC, USA have a history of contamination from heavy metals, nutrients, pesticides, and industrial chemicals. Among the chemicals of concern are PAHs, which are a historical contaminant but also have modern pyrogenic and petrogenic sources in the area’s waterways. Another group of contaminants that are of emerging interest are siloxanes (silicones), which are widely used as lubricants, sealants, and cosmetics. Some lower-molecular-weight siloxanes are regulated by the EU in recognition of harm to aquatic life, but there are no restrictions in the United States. In fact, studies examining water pollutants do not typically test for siloxanes. Here, we present the concentrations of specific PAHs and siloxanes from surface sediments in the Potomac and Anacostia Rivers (including the Anacostia’s tributaries) collected between 2018 and 2023. Both D5 (decamethylcyclopentasiloxane) and D6 (dodecamethylcyclohexasiloxane) were found in most locations, with concentrations averaging 0.13 and 0.006 mg/g (dry mass), respectively. Pyrene, fluoranthene, bibenzyl, and phenanthrene were also found in the Anacostia and some of its tributaries, with concentrations increasing downstream. In the Potomac, concentrations were generally lower than those observed in the Anacostia. Based on ratios of pyrene to fluoranthene + pyrene, the likely source of PAHs was petrogenic.

Microplastics (small plastic particles < 5 mm, MPs) are an emerging pollutant of concern as they are found in the water and sediment of aquatic habitats. Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants which tend to accumulate in aquatic sediments and may be associated with MP degradation. Urban streams have a large impact on these pollutant budgets of large rivers and marine areas. Up to today, there are just a few studies performed on MPs and PAHs together in river systems. MPs and PAHs were investigated to study their abundance and spatial distribution in the Nash Run, a tributary of the Anacostia River in Washington, DC, USA. A chemical characterization of the MPs in the sediment samples was also performed. The total MP concentration ranged from 24 to 127 MP particles/L in water samples. In the sediments, the MP concentrations varied from 0.35 to 4.1 MP particles/g showing a correlation to distance from roadways. Chemical MP analysis revealed that high-density polyethylene (HDPE) was the main chemical MP composition and chemical additives were also identified. Three PAHs, phenanthrene, fluoranthene, and pyrene, were observed in the sediment samples. These PAHs (commonly associated with microplastics) showed a higher concentration than those often occurring in sediments of similar freshwater environments. This is the first study that shows the presence of MPs in both water and sediment and the presence of specific PAHs in sediment at the same sites in a Washington, DC freshwater system.

Tributaries are important for fish recruitment and diversity. Here, we examine the biological impact of inorganic and organic contaminants in Paint Branch stream (PBS), a tributary of the Anacostia river in Washington D.C. The Anacostia has suffered severe ecological damage because of decades of pollution and deposited wastewater runoff; however, PBS, which connects to the northern part of the river, is forested and less urbanized, suggesting higher water quality. However, the impact of PBS water on early fish development has not been studied. To address this question, we examined if chronic (28 day) exposure to water collected from PBS can support the proper early development of zebrafish (Danio rerio), a vertebrate model in toxicological studies. We assessed their overall growth and swimming behaviors and correlated these results with a water quality analysis. The water chemistry identified high levels of calcium, sodium, and nitrate in PBS water samples. A gas chromatography–mass spectroscopy analysis of extracted non-polar compounds in the water column revealed siloxanes (congeners D6–D10) were the only component identified with >90% certainty. In our fish experiments, we observed age-dependent increases in growth and eye development, consistent with normal development. In contrast, general swimming behaviors showed an early increase in angular velocity at 7 days postfertilization (dpf; p = 0.001) and a decreased total distance traveled at 14 dpf (p = 0.015) for PBS-treated larvae. Using the open field test, we observed that the PBS-treated fish made fewer visits to the edge at 7 (p = 0.01), 14 (p < 0.001), and 21 dpf (p = 0.038) and spent significantly more time at the edge at 21 dpf (p < 0.001). Fewer visits to the center were also noted at 14 and 21 dpf, suggesting reduced overall movement at these two ages in response to chronic PBS water exposure. Interestingly, by 28 dpf, no differences were noted in any parameter measured. Overall, these results indicate zebrafish larvae grew well in PBS water; however, their reduced movement and anxiogenic behavior suggested subtle behavioral abnormalities. The identified chemicals likely originated from runoff or sewage and have potentially deleterious consequences for fish living in PBS or migrating to/from upstream spawning/nursery locations.

The Anacostia River in Washington, D.C. has been experiencing the challenges typical of urban rivers over the last 70+ years. Here, we examine six years (2014 to 2020) of base-flow geochemistry of three tidal Anacostia sites and three suburban sites. Parameters examined include pH, hardness, SAR, alkalinity, TDS, Ca, Mg, Na, K, Fe, Mn, Zn, Al, As, B, Ba, Be, Cd, Cr, Cu, Co, Mo, Ni, Pb, total P, S, Sr, Ti, NO3−, and NH4+. Not surprisingly, winter and spring months showed very high Na (means of 786 mg/L and 1000 mg/L, respectively). Plotting Na/(Na + Ca) versus TDS shows contributions from groundwater, but also differences from major world rivers. Main stem locations usually had Ca/Sr ratios > 200, suggesting that concrete was the source of Ca; however, suburban sites showed high Ca as well and suburban Ca/Sr ratios were frequently <200, indicating a different source for Ca. Most sites showed low median Si:NO3 ratios (between 3 and 5), suggesting elevated NO3− from non-natural sources. The data are consistent with freshwater salinization syndrome (a specific type of urban stream syndrome), and also show that the developed landscape in suburban environments influences geochemistry differently than in urban environments.

Siloxanes are used in personal care, biomedical, and industrial products. Their worldwide use and persistence in the environment cause consistent exposure for both humans and aquatic animals. Two siloxane congeners, decamethylcyclopentasiloxane (D5; CAS 541-02-6) and octamethylcyclotetrasiloxane (D4; CAS 556-67-2), are among the most prevalent, with measurable levels in air, sediment, water, and biological samples. However, few studies have examined the impact of developmental (embryo/larva) exposure. To address this gap, we performed parallel experiments using wildtype zebrafish (Danio rerio). One set of experiments used laboratory-mixed individual solutions containing either D4, D5, or 2,4,6,8-tetramethylcyclotetrasiloxane (D-4(H); CAS 2370-88-9); the other used environmental water samples containing a mixture of siloxanes, including D4 and D5. These samples were collected from Bladensburg Waterfront Park (BWP) a site along the Anacostia River, Washington, DC. In both experiments, zebrafish (24-48 h postfertilization, hpf) were exposed until 7 or 14 days (d)pf. Chronic exposure to D4, D5, or BWP water until 7 dpf caused stress-like behaviors and reduced swim velocities; anatomical differences were noted only in BWP-exposed larvae. At 14 dpf, BWP-treated larvae still showed slower swimming velocities and increased immobility; anatomical differences were no longer evident and thigmotactic behavior was reduced. D4 and D5-exposed larvae did not survive after 10 dpf. Larvae exposed to D-4(H) showed no decreases in behavior or growth at either age. These results suggest early developmental sensitivity to siloxane exposure and point to the need to consider embryonic/larval endpoints when assessing aquatic contaminants.

Rapid urbanization, industrial activity, and runoff have all played a role in transforming the Anacostia River from a biologically rich ecosystem to an ecologically threatened environment facing extensive pollution. In recent decades, numerous groups have worked to document and begin to address pollution in the waterway, but few have examined the biological impact of these contaminants. To assess water quality, the current study examined the effects of Anacostia water on early fish development and behavior using zebrafish (Danio rerio). Zebrafish embryos and larvae were reared in water samples collected from the Washington Navy Yard from 0–30dpf (days post fertilization). At 7, 15, 20, and 30dpf, larvae were subsampled for morphological (length, girth, eye diameter, inter-eye distance) and behavioral (angular velocity, total distance traveled, swimming velocity, total activity duration, time immobile, frequency and duration of burst swimming, time at the edge of the dish) assessment. Water samples were processed using gas chromatography-mass spectroscopy (GC–MS) to identify major organic contaminants. Results indicated the presence of 13 bioactive organic contaminants, including siloxane species and hormone derivatives, and accelerated growth and altered swim behaviors in Anacostia-exposed fish after 30 days of exposure. These findings emphasize sublethal but significant impacts of exposure to organic contaminants experienced by fish residing in urban waterways.

The ability of foam-based unplanted and green surfaces (Aqualok™) to remove pollutants (total suspended solids (TSS), NO3, NH4, total organic carbon (TOC) and total phosphorus (TP)) from direct precipitation and roof runoff passing through the surfaces was assessed. The assessments were conducted using unplanted Aqualok™ and planted Aqualok™ roof panels and a bioswale Aqualok™ installed on two Fire and Emergency Medical Service Stations (FEMSs) in Washington, D.C., USA. During a three-year period, impacts on water chemistry were evaluated by examining overall averages as well as performance over time. Upon installation, all Aqualok™ surfaces released a “pulse” of TSS and NO3, which decreased over time. TP concentrations from the planted panels were elevated relative to conventional roof runoff throughout the study. TOC was generally higher for planted Aqualok™ compared to unplanted Aqualok™, and did not decrease over time. Excluding the three months post-installation, TSS in throughflow from planted and unplanted Aqualok™ surfaces was 88% and 90% lower, respectively, than in runoff from a conventional tar and gravel roof. No significant differences between green surface throughflow and conventional roof runoff for NO3 or NH4 were observed.

A consequence of land-use change and increasing human population in the United States and Central America has been an increase in nitrogen availability to coastal systems. Whereas many studies evaluate the influence of anthropogenically derived nutrients in modern oceans, fewer studies evaluate nutrient sources in coastal environments before the 1960s. This study used stable C and N isotope values of 35 big-claw snapping shrimps (Alpheus heterochaelis) and 48 ivory barnacles (Balanus eburneus) across the Gulf of Mexico, southeast coast of the United States, and the Caribbean over 121 y to examine whether human-derived nitrogen was used by coastal invertebrates. Gulf of Mexico and southeast U.S. collections were divided into pre-and post-1960 groups for analysis, roughly coinciding with the increase in fertilizer use associated with the "Green Revolution" and large coastal population increases. For B. eburneus, delta N-15 decreased in the coastal United States after 1960, but that was not the case for A. heterochaelis. N-15-depleted fertilizer would be quickly incorporated by filter-feeding B. eburneus (via plankton). By contrast, the scavenging, omnivorous, A. heterochaelis would obtain more N from heterotrophic organic matter more isolated from the N-15-depleted fertilizer signal. The Caribbean A. heterochaelis incorporated seagrass C and N. Local variation in N sources from the different collection areas was clearly observed. Although anthropogenic N has been making its way into the filter-feeding barnacles, it is not as apparent in the scavengers.

Marine Mammal ScienceVolume 33, Issue 4 p. 1224-1234 Notes Sources of stable isotope variation among stranded Western Atlantic dolphins (Tursiops truncatus) in North Carolina Stephen E. MacAvoy, Corresponding Author Stephen E. MacAvoy macavoy@american.edu Department of Environmental Science, American University, Washington, DC, 20016 U.S.ACorresponding author (e-mail: macavoy@american.edu).Search for more papers by this authorNicole Cortese, Nicole Cortese Department of Environmental Science, University of Virginia, Charlottesville, Virginia, 22904 U.S.ASearch for more papers by this authorJonathan Cybulski, Jonathan Cybulski Department of Environmental Science, American University, Washington, DC, 20016 U.S.ASearch for more papers by this authorAleta A. Hohn, Aleta A. Hohn orcid.org/0000-0002-9992-7062 National Marine Fisheries Service, National Oceanic and Atmospheric Administration Beaufort Laboratory, 101 Pivers Island Road, Beaufort, North Carolina, 28516 U.S.ASearch for more papers by this authorStephen A. Macko, Stephen A. Macko Department of Environmental Science, University of Virginia, Charlottesville, Virginia, 22904 U.S.ASearch for more papers by this author Stephen E. MacAvoy, Corresponding Author Stephen E. MacAvoy macavoy@american.edu Department of Environmental Science, American University, Washington, DC, 20016 U.S.ACorresponding author (e-mail: macavoy@american.edu).Search for more papers by this authorNicole Cortese, Nicole Cortese Department of Environmental Science, University of Virginia, Charlottesville, Virginia, 22904 U.S.ASearch for more papers by this authorJonathan Cybulski, Jonathan Cybulski Department of Environmental Science, American University, Washington, DC, 20016 U.S.ASearch for more papers by this authorAleta A. Hohn, Aleta A. Hohn orcid.org/0000-0002-9992-7062 National Marine Fisheries Service, National Oceanic and Atmospheric Administration Beaufort Laboratory, 101 Pivers Island Road, Beaufort, North Carolina, 28516 U.S.ASearch for more papers by this authorStephen A. Macko, Stephen A. Macko Department of Environmental Science, University of Virginia, Charlottesville, Virginia, 22904 U.S.ASearch for more papers by this author First published: 01 June 2017 https://doi.org/10.1111/mms.12425Citations: 4Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume33, Issue4October 2017Pages 1224-1234 RelatedInformation

In some environments, species may exhibit trophic plasticity, which allows them to extend beyond their assigned functional group. For Gammarus minus , a freshwater amphipod classified as a shredder or detritivore, cave populations have been observed consuming heterotrophs as well as shredding leaves, and therefore may be exhibiting trophic plasticity. To test this possibility, we examined the C and N stable isotope and C/N ratios for cave and spring populations of G. minus . A 15-day feeding experiment using leaves and G. minus from a spring population established that the diet-tissue discrimination factor was 3.2 ‰ for δ 15 N. Cave G. minus were 8 ‰ higher in δ 15 N relative to cave leaves, indicating they did not derive nitrogen from leaves, whereas field collected spring populations were 2–3 ‰ higher than spring leaves, indicating that they did. Cave G. minus were 2.6 ‰ higher in δ 15 N than the cave isopod, Caecidotea holsingeri . Relative to spring populations, Organ Cave G. minus were 15 N enriched by 6 ‰, suggesting they occupied a different trophic level, or incorporated an isotopically distinct N source. While stable isotopes cannot tell what the cave G. minus are eating, the isotopes certainly show that G. minus are not eating leaves and are trophically distinct form the surface populations. Differences in C/N ratios were observed, but reflect the size of the G. minus examined and not feeding group or habitat. The isotope data strongly support the hypothesis that cave populations of G. minus have become generalist or omnivorous by including animal protein in their diet.

Table S1. Sulfur stable isotope data for manatee with sex, bone type sampled, and location. δ34S values are relative CDT. ID number is that of the marine mammal stranding response team of southern Florida. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Ecologists interested in studying fluctuating relationships between consumers and nutrient sources are increasingly involved in modeling the rate at which consumers incorporate dietary components. In mammals a correlation between resting metabolic rate (RMR) and tissue turnover may exist across a range of species. Less is known about the variation of tissue turnover rate within a species, and how that correlates with RMR. Here we examine two strains of rats (Rattus norvegicus) with different RMR to test whether variation in RMR is positively correlated with tissue turnover rate within a species. If RMR, a relatively simple measurement, can be correlated with tissue turnover, then this relationship could be used to better interpret ecological functions, including impact of migratory or seasonally available nutrient sources. Here, the changing isotope signature in rat whole blood was modeled using a modified exponential decay equation and a reaction progress variable model. The modeled rate of turnover, metabolic rate (O2 consumed), and mass were then compared between strains of rats. The mass and RMRs (conditions during which RMRs were determined modified from the ideal, as outlined in the Methods) were significantly different between strains, but half-life and the metabolic tissue replacement component of turnover (as opposed to turnover from mass gain) were not. No significant correlation was found between RMR and metabolic tissue replacement between the strains. Results suggest that within a species showing a range of RMRs, blood tissue turnover should not vary significantly.