No description available.

No description available.

There is mounting evidence that microplastics are a persistent and increasing hazard for aquatic organisms. The effects of microplastics on organisms and ecosystems are complex, however, and may be linked to a wide variety of particle characteristics including size, shape, polymer, additive chemistry, and degree of weathering. Assessing risk is complicated by the fact that many known effects of microplastics are sublethal, and that plastics have been postulated to interact with other stressors, such as pathogens. The work presented here expands our understanding of these complex effects. First, the impacts of microplastics on sedimentary microbial ecosystems and biogeochemical carbon and nitrogen cycles were investigated. A microcosm experiment using salt marsh sediment amended with polyethylene (PE), polyvinyl chloride (PVC), polyurethane foam (PUF) or polylactic acid (PLA) microplastics was conducted. We found that the presence of microplastics altered sediment microbial community composition and nitrogen cycling processes. Compared to control sediments without microplastics, PUF- and PLA-treated sediments promoted nitrification and denitrification, while PVC inhibited both processes. These results indicate that nitrogen cycling processes in sediments can be significantly affected by different microplastics, which may serve as organic carbon substrates for microbial communities. Second, we probed the virus-related mortality of a commercially important salmonid species under chronic exposure to nylon microfibers, polystyrene microplastics, and natural marsh grass microparticles. Mortality increased when fish were co-exposed to pathogen and microparticle, particularly nylon microfibers. This correlated with host viral load and mild gill inflammation. As such, we speculated that chronic exposure microplastics may create opportunities for pathogens to bypass defenses and colonize hosts via sensitive tissues. To investigate if this was enhanced by the physical properties of plastic microfibers, we assessed differences in mortality following chronic exposure to nylon microfibers and powder, finding that fibers had a greater effect than powdered counterparts. The importance of the timing of microplastic exposure was also confirmed by completing viral/microplastics co-exposures where microplastics were dosed before, after, or before and after viral introduction. Indeed, virulence was most enhanced when fish were exposed to microplastics pre-virus or chronically, significantly more so than post-virus only. Finally, we tested whether UV-weathering changed the effect of natural and plastic microparticles on disease-related mortality. We observed changes in the virulence effects of microparticles following UV-weathering, but the pattern of that change was inconsistent and merits further research. Considering their ubiquity and increasing concentrations globally, further research on the effects of microplastics is warranted. Particularly, the work here demonstrates that microplastics may influence entire communities and inorganic nutrient cycling systems, classifying microplastics as a potential planetary boundary threat. Further, we illustrate that even when microplastics alone may not have substantial effects on a fish population, when combined with disease they may amplify pathogen-related mortality significantly. More research on the interplay between microplastics and infectious disease is recommended, particularly as it may inform researchers on the risks of microplastics to human health.

Chesapeake Bay is one of the most productive ecosystems on the US east coast which supports various living resources and habitat, and therefore has significant impacts on human beings and ecosystem health. Developing the capability of accurately simulating the water quality condition in the Chesapeake Bay, such as seasonal hypoxia, phytoplankton production, and nutrient dynamics, helps to better understand the interactions of hydrodynamical and biochemical processes, and more importantly, to predict conditions under changing climate and human intervention. Currently, most Chesapeake Bay models use structured grids that lack the flexibility for local refinements to fit complex geometry over both large and small scales, which hampers the allocation of local TMDLs for shallow water and small tributaries. In addition, few of them extend their simulations beyond the water column state variables, such as dissolved oxygen and nutrients, to include other living resources such as vegetation. These limitations motivate the model developments in this dissertation of: (1) a new comprehensive water quality model using high-resolution unstructured grids, which possesses the cross-scale capability to study interactions among water bodies and processes of different scales; and (2) a tightly coupled tidal marsh model, which is linked to the water quality model for water column to study the interactions between the marshes and surrounding aquatic system. The new modeling tool can be effectively utilized as a powerful tool for adaptive management in the Chesapeake Bay and can also be exported to other estuaries in the world.In this dissertation, Chapter 2 focuses on the development of a high-resolution water quality model in the water column and sediment flux part of the water quality model. This part of this study also demonstrates the importance of the correct representation of geometry, and the detrimental effects of artificial bathymetry smoothing on model simulations. Chapter 3 of this dissertation studies the impacts of sea-level rise (SLR) on seasonal hypoxia and phytoplankton production in the Chesapeake Bay with the newly developed water quality model. SLR is predicted to increase the hypoxic volume in the Chesapeake Bay by altering the physical processes and enhancing the estuarine respirations. Phytoplankton production in the shallow shoals is also predicted to increase under SLR, as a result of increased light utilization. Chapter 4 of this dissertation focuses on developing a new marsh model in the hydrodynamic-water quality model framework. This new model extends the model coverage to the tidal wetlands which are periodically inundated. The tidal marshes are suggested to affect the estuarine oxygen, carbon, and nutrient dynamics through tidal exchange, e.g., contributing the diel DO cycle. Chapter 5 studies the impacts of SLR on the biochemical processes in the York River Estuary, a tributary of the Bay that has extensive tidal marshes, with the fully-coupled hydrodynamic-water quality-marsh model. The SLR is predicted to enhance the exchanges between the marshes and the adjacent channel, which in turn further impacts the estuarine biochemical processes.

No description available.

No description available.

<p> MONITOR is an active, automatic extraction sampler that collects daily, integrated extracts of hydrophobic compounds in water. Compounds partition from water, through a polydimethylsiloxane membrane and into hexane. The sampling rate, membrane-water partition coefficients (K_MW) and hexane-water partition coefficients (K_HW) were determined for atrazine and four nonpolar reference compounds. The reference compounds had high effective sampling rates (>10 L/day) while atrazine had a low effective sampling rate (&lt;1 L/day). Atrazine had intermediate hydrophobicity as determined by K_MW and octanol-water partition coefficient (KOW). However, atrazine had a low K_HW, which caused its low sampling rate. In spite of MONITOR's low sampling rate for atrazine, the concentration of atrazine in the drinking water of Syracuse, New York was observed from March - November 2012 using MONITOR. The average concentration was 0.016 &mu;g/L. MONITOR was able to capture fluctuations in the concentration of atrazine at very low levels over several months.</p>

Increasing dependence on groundwater in the Wakal River basin, India, jeopardizes water supply sustainability. A numerical groundwater model was developed to better understand the aquifer system and to evaluate its potential in terms of quantity and replenishment. Potential artificial recharge areas were delineated using landscape and hydrogeologic parameters, Geographic Information System (GIS), and remote sensing. Groundwater models are powerful tools for recharge estimation when transmissivity is known. Proper recharge must be applied to reproduce field-measured heads. The model showed that groundwater levels could decline significantly if there are two drought years in every four years that result in reduced recharge, and groundwater withdrawal is increased by 15%. The effect of such drought is currently uncertain however, because runoff from the basin is unknown. Remote sensing and GIS revealed areas with slopes less than 5%, forest cover, and Normalized Difference Vegetative Index greater than 0.5 that are suitable recharge sites.

No description available.

Living shoreline stabilization has become a popular practice in shoreline restoration and bank protection; however, there are still many uncertainties regarding effective site design using living materials. For example, natural wave-breaks may be formed of created reefs, but the optimum water depth for hydrodynamic influence may differ from the preferred depth to ensure organism recruitment. The objective of this research is to understand how water depth relative to the crest of submerged artificial oyster reef structures influences nearshore hydrodynamic processes and sediment transport or retention in nearshore areas. A field study, sited in a microtidal estuary on the Atlantic coast of Florida, applied a controlled, two-way block experimental design testing varied configurations of oyster reef structures constructed by bagged oyster shell: continuous vs. gapped structures located close (3 m) and far (12 m) from the edge of existing black mangrove vegetation. Bed elevations, sediment texture and organic matter content, and hydrodynamic data were measured in each treatment and control plot and compared before and after structure implementation over three years. Distance from shore influenced reef submergence such that far from shore structures were sited in deeper water and subtidal while closer to shore structures were in shallower water and were intertidal. The difference in water level over reefs influenced wave attenuation rates from the channel to shoreline, both at the individual plot level and across the treatments. More variable and lower attenuation rates were observed over structures far from shore in deeper water (range of mean attenuation, η = -6 – 36%). Shallower nearshore structures were associated with greater mean attenuation rates (η = 30 – 70 %), which also outpaced attenuation observed before structure placement (η = 0 – 10%). Repeat Real Time Kinematic (RTK) surveys before and after reef creation indicated that sizable sediment deposits formed in the areas between the created reefs and the shoreline, totaling a net gain of 418.5 m3 of sediment, an approximate mean deposition depth of 7.9 cm, within three years of reef creation. Accretion at gapped and continuous reef plots were similar whereas accretion behind far from shore reefs was about 20 % greater than behind near to shore reefs. Texture of nearshore sediments coarsened across all plots after structure placement, changing from majority fine sand (150-250 μm) to medium sand (250-500 μm). For example, fine sand composed of 69 % of nearshore sediments prior to structure placement, but only 11 % after three years. Additionally, mean organic matter content of shoreline sediments increased three folds, from 10.6 g/kg to 32.0 g/kg, while no change was documented seaward of reef structures. Study results can be applied to improve designs of created oyster reef as self-sustaining natural infrastructure. The results suggest that design water levels and thus placement of created reefs relative to shoreline vegetation can be flexible, as the far from shore reefs enhanced sediment retention and deposition nearshore despite the lower wave attenuation. Greater flexibility in living shoreline designs allowed under common permits would allow artificial reefs to be sited to better optimize conditions for oyster recruitment, which will ensure the longevity and ecological function of the infrastructure.