Dissolved and particulate organic carbon fluxes from an agricultural watershed during consecutive tropical storms

Low‐frequency high‐magnitude hydrologic events mobilize a disproportionate amount of dissolved organic carbon (DOC) from watersheds, but few studies measure the role of extreme storms in exporting organic carbon from croplands. We use high‐resolution measurements of storm runoff to quantify DOC and particulate organic carbon (POC) fluxes from an agricultural field during consecutive tropical storms that delivered 41 cm of rainfall to the Virginia Coastal Plain. Over a 2 week period, we measured exports of 22 kg DOC ha−1 and 11.3 kg POC ha−1. Ultraviolet absorbance measurements indicate that the aromatic DOC fraction systematically increased as plant‐derived aliphatic carbon was depleted during the initial event. Croplands can have event‐scale carbon losses that equal or exceed published estimates of annual export for perennial streams draining forested and mixed land use watersheds. We quantify aromatic DOC fractions approaching 50%, indicating that agricultural stormflow can produce a significant load of relatively photoreactive carbon

Integrated carbon budget models for the Everglades terrestrial-coastal-oceanic gradient: Current status and needs for inter-site comparisons.

Recent studies suggest that coastal ecosystems can bury significantly more C than tropical forests, indicating that continued coastal development and exposure to sea level rise and storms will have global biogeochemical consequences. e Florida Coastal Everglades Long Term Ecological Research (FCE LTER) site provides an excellent subtropical system for examining carbon (C) balance because of its exposure to historical changes in freshwater distribution and sea level rise and its history of significant long-term carbon-cycling studies. FCE LTER scientists used net ecosystem C balance and net ecosystem exchange data to estimate C budgets for riverine mangrove, freshwater marsh, and seagrass meadows, providing insights into the magnitude of C accumulation and lateral aquatic C transport. Rates of net C production in the riverine mangrove forest exceeded those reported for many tropical systems, including terrestrial forests, but there are considerable uncertainties around those estimates due to the high potential for gain and loss of C through aquatic fluxes. C production was approximately balanced between gain and loss in Everglades marshes; however, the contribution of periphyton increases uncertainty in these estimates. Moreover, while the approaches used for these initial estimates were informative, a resolved approach for addressing areas of uncertainty is critically needed for coastal wetland ecosystems. Once resolved, these C balance estimates, in conjunction with an understanding of drivers and key ecosystem feedbacks, can inform cross-system studies of ecosystem response to long-term changes in climate, hydrologic management, and other land use along coastlines

Stormwater runoff drives viral community composition changes in inland freshwaters

Storm events impact freshwater microbial communities by transporting terrestrial viruses and other microbes to freshwater systems, and by potentially resuspending microbes from bottom sediments. The magnitude of these impacts on freshwater ecosystems is unknown and largely unexplored. Field studies carried out at two discrete sites in coastal Virginia (USA) were used to characterize the viral load carried by runoff and to test the hypothesis that terrestrial viruses introduced through stormwater runoff change the composition of freshwater microbial communities. Field data gathered from an agricultural watershed indicated that primary runoff can contain viral densities approximating those of receiving waters. Furthermore, viruses attached to suspended colloids made up a large fraction of the total load, particularly in early stages of the storm. At a second field site (stormwater retention pond), RAPD-PCR profiling showed that the viral community of the pond changed dramatically over the course of two intense storms while relatively little change was observed over similar time scales in the absence of disturbance. Comparisons of planktonic and particle-associated viral communities revealed two completely distinct communities, suggesting that particle-associated viruses represent a potentially large and overlooked portion of aquatic viral abundance and diversity. Our findings show that stormwater runoff can quickly change the composition of freshwater microbial communities. Based on these findings, increased storms in the coastal mid-Atlantic region predicted by most climate change models will likely have important impacts on the structure and function of local freshwater microbial communities

Photochemical and microbial alteration of dissolved organic matter in temperate headwater streams associated with different land use

Photochemical and microbial transformations of DOM were evaluated in headwater streams draining forested and human‐modified lands (pasture, cropland, and urban development) by laboratory incubations. Changes in DOC concentrations, DOC isotopic signatures, and DOM fluorescence properties were measured to assess the amounts, sources, ages, and properties of reactive and refractory DOM under the influence of photochemistry and/or bacteria. DOC in streams draining forest‐dominated watersheds was more photoreactive than in streams draining mostly human‐modified watersheds, possibly due to greater contributions of terrestrial plant‐derived DOC and lower amounts of prior light exposure in forested streams. Overall, the percentage of photoreactive DOC in stream waters was best predicted by the relative content of terrestrial fluorophores. The bioreactivity of DOC was similar in forested and human‐modified streams, but variations were correlated with temperature and may be further controlled by the diagenetic status of organic matter. Alterations to DOC isotopes and DOM fluorescence properties during photochemical and microbial incubations were similar between forested and human‐modified streams and included (1) negligible effects of microbial alteration on DOC isotopes and DOM fluorescence properties, (2) selective removal of 13C‐depleted and 14C‐enriched DOC under the combined influence of photochemical and microbial processes, and (3) photochemical alteration of DOM resulting in a preferential loss of terrestrial humic fluorescence components relative to microbial fluorescence components. This study provides a unique comparison of DOC reactivity in a regional group of streams draining forested and human‐modified watersheds and indicates the importance of land use on the photoreactivity of DOC exported from upstream watersheds

Use of ESI-FTICR-MS to Characterize Dissolved Organic Matter in Headwater Streams Draining Forest-Dominated and Pasture-Dominated Watersheds

Electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR-MS) has proven to be a powerful technique revealing complexity and diversity of natural DOM molecules, but its application to DOM analysis in grazing-impacted agricultural systems remains scarce. In the present study, we presented a case study of using ESI-FTICR-MS in analyzing DOM from four headwater streams draining forest- or pasture-dominated watersheds in Virginia, USA. In all samples, most formulas were CHO compounds (71.8–87.9%), with other molecular series (CHOS, CHON, CHONS, and CHOP (N, S)) accounting for only minor fractions. All samples were dominated by molecules falling in the lignin-like region (H/C = 0.7–1.5, O/C = 0.1–0.67), suggesting the predominance of allochthonous, terrestrial plant-derived DOM. Relative to the two pasture streams, DOM formulas in the two forest streams were more similar, based on Jaccard similarity coefficients and nonmetric multidimensional scaling calculated from Bray-Curtis distance. Formulas from the pasture streams were characterized by lower proportions of aromatic formulas and lower unsaturation, suggesting that the allochthonous versus autochthonous contributions of organic matter to streams were modified by pasture land use. The number of condensed aromatic structures (CAS) was higher for the forest streams, which is possibly due to the controlled burning in the forest-dominated watersheds and suggests that black carbon was mobilized from soils to streams. During 15-day biodegradation experiments, DOM from the two pasture streams was altered to a greater extent than DOM from the forest streams, with formulas with H/C and O/C ranges similar to protein (H/C = 1.5–2.2, O/C = 0.3–0.67), lipid (H/C = 1.5–2.0, O/C = 0–0.3), and unsaturated hydrocarbon (H/C = 0.7–1.5, O/C = 0–0.1) being the most bioreactive groups. Aromatic compound formulas including CAS were preferentially removed during combined light+bacterial incubations, supporting the contention that black carbon is labile to light alterations. Collectively, our data demonstrate that headwater DOM composition contains integrative information on watershed sources and processes, and the application of ESI-FTICR-MS technique offers additional insights into compound composition and reactivity unrevealed by fluorescence and stable carbon isotopic measurements

Occurrence and Distribution of the Freshwater AmphipodsGammarus pseudolimnaeus and Gammarus fasciatus inSoutheastern Virginia

The freshwater amphipod, Gammarus fasciatus, and a population that keys to Gammarus pseudolimnaeusare broadly sympatric in southeastern Virginia. By documenting the successful formation of pre-copulatory mate-guarding pairs between individuals collected from Virginia and New York, we confirmed the occurrence of a G. pseudolimnaeus population strongly disjunct from the previously described range in the Mississippi and St. Lawrence River drainage basins. Gammarus pseudolimnaeus appears restricted to high-quality, spring-fed streams that occur at low density across an increasingly fragmented natural landscape in Virginia. Gammarus fasciatus, however, occurs in lakes and streams of developed landscapes that typically are more degraded, and this species does not co-occur with G. pseudolimnaeus in high-quality habitat. Gammarus pseudolimnaeus reproduces year-round, with adults and juveniles of all size classes continuously present. Gammarus fasciatus reproduces primarily from February through June, at which point the adults die, and by late summer the population consists solely of immature individuals. If the two species overlapped in distribution, the smaller Gammarus fasciatus amphipods would have to compete with adult G. pseudolimnaeus for resources. We hypothesize that this competitively disadvantageous life cycle could account, in part, for the absence of G. fasciatus in high-quality streams occupied by G. pseudolimnaeus

The Influence of Recreational Crabbing Regulations on Diamondback Terrapin By-Catch

Malaclemys terrapin terrapin (Northern Diamondback Terrapin) is susceptible to drowning in commercial-style pots used for the Callinectes sapidus (Blue Crab) fishery. Regulations to reduce by-catch mortality vary by state. We compared three different regulatory strategies with respect to crab catch and their relative effectiveness at reducing terrapin by-catch. To mimic their possible use by recreational crabbers, we grouped and fished together ten unbaited crab pots with no by-catch reduction devices (BRDs), ten with large BRDs, and ten with small BRDs in a tidal creek in southeastern Virginia. Over 24 sampling days, the total legal crab catch (crabs ≥ 12.7 cm) in pots with no BRDs (29.9 ± 10.0 SD crabs pot-1) and large BRDs (27.9 ± 6.2 crabs pot-1) was significantly greater than catch in pots with small BRDs (14.0 ± 5.8 crabs pot-1). Legal crabs varied in average size from 14.1 ± 1.2 cm, 14.0 ± 1.2 cm, and 13.7 ± 1.0 cm from pots with no BRDs, large BRDs, and small BRDs, respectively, but these differences were not significant. Of a by-catch of 71 terrapins, 69 were from pots with no BRDs, 2 from pots with large BRDs, and none from pots with small BRDs. The potential mortality of terrapins in pots without BRDs would have reduced the population in this tidal creek by 42% in just 24 days. Based on these results, regulations requiring the use of large BRDs come closest to the objective of reducing by-catch mortality of terrapins without a large effect on crab capture in Virginia. Both recreational crabbing and commercial crabbing with no BRDs on pots in terrapin habitat can contribute to declines in local terrapin populations

Homing Behavior of Musk Turtles in a Virginia Lake

For nine weeks during the summer of 2002, a mark and recapture technique was used to study homing behavior of Musk Turtles (Sternotherus odoratus) living in Lake Matoaka, VA. During the first three weeks of the study, 119 turtles (83 male, 36 female) were captured using unbaited crabpots, then marked and displaced from the site of capture. Turtles were displaced 100 m across open water 4 m deep, 520 m along the same shore, or 550 m across open water. For the last six weeks of the study, 110 turtles (65 males, 45 females) were captured and released with no displacement. Overall, 39% (49/126) of males and 21% (15/71) of females in this study were captured more than once. Seventy-five of 118 recaptures (64%) were at the site of most recent release (sedentary behavior) and 11 recaptures (9%) were at neither the original nor most recent site of capture (non-homing behavior). Thirty- four of 118 recaptures of displaced turtles (29%) occurred at the site of original capture, and 31 (91%) of these movements were made by males, a significant difference in homing behavior between males and females during the time of the study. Neither distance nor open water significantly impeded turtle homing

Ecology of Phragmites australis and responses to tidal restoration

Tidal Marsh Restoration provides the scientific foundation and practical guidance necessary for coastal zone stewards to initiate salt marsh tidal restoration programs. The book compiles, synthesizes, and interprets the current state of knowledge on the science and practice of salt marsh restoration, bringing together leaders across a range of disciplines in the sciences (hydrology, soils, vegetation, zoology), engineering (hydraulics, modeling), and public policy, with coastal managers who offer an abundance of practical insight and guidance on the development of programs. The book is an essential work for managers, planners, regulators, environmental and engineering consultants, and others engaged in planning, designing, and implementing projects or programs aimed at restoring tidal flow to tide-restricted or diked salt marshes.https://scholarworks.wm.edu/asbookchapters/1065/thumbnail.jp