Search

Accurately predicting species' distributions is critical for the management and conservation of fish and wildlife populations. Joint species distribution models (JSDMs) account for dependencies between species often ignored by traditional species distribution models. We evaluated how a JSDM approach could improve predictive strength for stream fish communities within large watersheds (the Chesapeake Bay Watershed, USA), using a cross-validation study of JSDMs fit to data from over 50 species. Our results suggest that conditional predictions from JSDMs have the potential to make large improvements in predictive accuracy for many species, particularly for more generalist species where single species models may not perform well. For some species there was no added explanatory effect from conditional information, most of which already exhibited strong marginal predictive ability. For several rare species there were significant improvements in occurrence predictions, while the results for two invasive species considered did not show the same improvements. Overall, the optimal number of species to condition upon, as well as the effects of conditioning upon an increasing number of species, varied widely among species. [ABSTRACT FROM AUTHOR]

The concern with preserving natural resources for the future has been capturing global attention due to the state of decline of productive ecosystems. Chesapeake Bay, a large estuary located on the mid-Atlantic coast of the United States of America is such a productive ecosystem supporting thousands of animal and plants species, and the surrounding human population. Despite the concept of sustainable development, there has been continued pressure on the natural resources and the ecosystem services of the Bay. Institutional restoration and management efforts have been extensive, generating organizations, agreements, regulations and projects, among others. This research assesses Chesapeake Bay’s sustainability in four domains: environment, social, economy, and governance, using the Circles of Coastal Sustainability methodology. Each of the four domains has five categories, and each category is evaluated by the authors’ expert judgment using indicators related to the socio-ecological system and the definition of sustainable development. The article proposes a global sustainability score developed by a literature review of sustainability evaluated through the expert judgment of the authors. The results from the framework gave a “Satisfactory” score to the overall system; the environment and economic domains obtained the “Satisfactory” score, whilst the government and social domains obtained “Good” and “Poor” scores, respectively. The categories ranged between “Excellent” and “Poor” scores. The “Excellent” score was obtained by organization. The “Poor” score was obtained by five categories across the domains including social benefits, demographic, identity, security, and economic wellbeing. The assessment showed that the system has degradation problems, but the results have provided a general foundation for management bridges and barriers for sustainable development, with the barriers used to discuss new bridges towards holistic management proposals. The framework is a tool in progress to communicate to various actors the current sustainability development with the available information, provide a holistic system view, and find knowledge gaps in the research of a system. Similarly, the framework and assessment can be complemented, adapted, refined, and improved with each application as part of an adaptive management iterative cycle.

This study assesses the economic and water quality impacts of implementing a dairy pricing policy under Federal Milk Marketing Order system designed to alleviate milk prices plummet occurred at the beginning of pandemic. Using a 12-region, positive mathematical programing model of livestock production in the Chesapeake Bay watershed, we find that pricing policy induces significant expansions in dairy sectors, generates higher level of total net revenue in regions having large baseperiod dairy sectors. For water quality, we find that policy leads to an increase in nitrogen emissions but a decrease in phosphorus emissions for the livestock industry as a whole in most studied regions. [ABSTRACT FROM AUTHOR]

Excessive nitrogen (N) pollution in the Chesapeake Bay is threatening ecological health. This study presents a multilayer N flow network model where each network layer represents a stage in the production step from raw agricultural commodities such as corn to final products such as packaged meat. We use this model to assess the impacts of alternative future agricultural production and land use changes on multiple pathways of N pollution within the Chesapeake Bay Watershed (CBW). We analyzed N loss via all pathways under multiple future scenarios, considering crop-specific projections based on empirical data and US Department of Agriculture projections. We found two model parameters, fertilizer nitrogen application rate (FNAR) and feed conversion ratio (FCR), to be particularly important for seeing measurable N loss reductions in the Bay. Our results indicate a large increase in N loss under the business-as-usual trajectory in geographic locations with intensive agricultural production. We found that numerous management scenarios including improvements in FNAR and FCR, N losses fall short of the 25% total maximum daily load targets. Our work suggests that achieving the CBW N loss reduction goals will necessitate large deviations from business as usual. Our model also highlights substantial regional variations in nitrogen loss across the U.S., with central regions like the Corn Belt and Central Valley of California experiencing the highest losses from crop-related stages, while eastern areas such as the Chesapeake Bay exhibit major losses from live animal production, underscoring the need for region-specific management strategies. Thus, implementation of effective N management strategies, combined with improved crop residue management, remains pivotal in mitigating N pollution in the Chesapeake Bay.

Throughout the watershed modeling process, modelers, collaborators, and stakeholders make decisions about how to study various challenges that impact watersheds. To understand these decisions, we investigated values held by modelers who have worked or collaborated on projects within the Chesapeake Bay Watershed and their influence on decisions made during the modeling process. Using a mixed‐methodological approach, we designed an online survey and semistructured interviews to evaluate these complexities. In total, we received 27 survey responses from Chesapeake Bay Watershed modelers and conducted four semistructured interviews. The results indicate that ethical and epistemic values impact every stage of the watershed modeling process. These values occur alongside decisions, motivations, outcomes, and objectives that often involve collaborators and stakeholders in addition to the modelers. Therefore, including these values in scientific discourse can increase transparency around watershed modeling that guides policy decision making processes. Our results articulate that a discussion of the ethical and epistemic values present throughout the watershed modeling process should be incorporated into model documentation to clearly explain assumptions and decisions. Plain Language Summary: Scientists use watershed models to determine how activities like farming and land development impact our waterways. Watershed models are computer‐based tools that allow the user to input information, such as land use, fertilizer use, and types of agricultural operations, to predict how these factors might contribute to pollution in waterways. Modelers often work alongside other people to determine what information should and should not be included in a model. During this process, modelers must make various decisions that can impact how the model predicts pollution levels, which has implications for policies established by decision makers. Like all people, modelers have their own values that can influence their decision making. Our work seeks to understand if and how values influence modelers' decisions in their modeling process. To understand this, we surveyed and interviewed researchers in the Chesapeake Bay Watershed. Our results demonstrated that values indeed impact every stage of the watershed modeling process. Because values have an impact, we suggest that modelers should describe how these values influence decisions in watershed modeling reports. Key Points: Modelers' ethical and epistemic values can impact decisions made at all stages of the watershed modeling processValues‐informed mental models (ViMMs) are a tool used to describe how modelers make decisions and highlight the values that influence these decisionsViMMs can help modelers become more aware of their values and encourage the documentation of implicit decisions driven by values [ABSTRACT FROM AUTHOR]

This article examines the evolution of the laws and practices governing the oyster fishery in Maryland's portion of the Chesapeake Bay. Specifically, this note focuses on poaching and the mismanagement of the resource. Currently, the Bay's oyster beds in Maryland are treated as a common resource, open to all license holders to exploit at their will. This has led to overfishing and an unsustainable depletion of the oyster fishery to the detriment of Maryland's oystermen and the shellfish market overall. To alleviate the problem, this note recommends that Maryland concentrate its courts that adjudicate natural resource violations and create a semi-private leasehold system to better ensure the health of the bay and the continued productivity of the fishery. These solutions will increase the expertise of the bench dealing with oyster related violations and simultaneously introduce incentives for oystermen to sustainably manage Maryland's oyster resources. [ABSTRACT FROM AUTHOR]

Landscape-scale maps of tree species densities are important tools for managing ecosystems threatened by forest pests. Eastern hemlock dominates riparian forests throughout its range. As a conifer in a deciduous landscape, hemlock plays an ecohydrological role, especially when other species are dormant. The nonnative, hemlock woolly adelgid has caused widespread hemlock decline and mortality. We used two existing basal area raster layers first to identify Chesapeake Bay subwatersheds with ≥6 percent hemlock basal area and second to quantify hemlock basal area densities within fixed-width riparian buffers of 50 m, 100 m, 250 m, and 500 m. Hemlock densities were higher in riparian zones compared with entire subwatersheds. In five subwatersheds, 50 m and 100 m zones had higher percentages of pixels with ≥25 percent hemlock basal area. We produced maps identifying hemlock riparian densities in the Pine Creek Watershed, which managers can use to prioritize sites for supplemental conifer planting under anticipated hemlock decline. [ABSTRACT FROM AUTHOR]

The lateral transport and degassing of carbon in riverine ecosystems is difficult to quantify on large spatial and long temporal scales due to the relatively poor representation of carbon processes in many models. Here, we coupled a scale‐adaptive hydrological model with the Dynamic Land Ecosystem Model to simulate key riverine carbon processes across the Chesapeake and Delaware Bay Watersheds from 1900 to 2015. Our results suggest that throughout this time period riverine CO2 degassing and lateral dissolved inorganic carbon fluxes to the coastal ocean contribute nearly equally to the total riverine carbon outputs (mean ± standard deviation: 886 ± 177 Gg C∙yr−1 and 883 ± 268 Gg C∙yr−1, respectively). Following in order of decreasing importance are the lateral dissolved organic carbon flux to the coastal ocean (293 ± 81 Gg C∙yr−1), carbon burial (118 ± 32 Gg C∙yr−1), and lateral particulate organic carbon flux (105 ± 35 Gg C∙yr−1). In the early 2000s, carbon export to the coastal ocean from both the Chesapeake and Delaware Bay watersheds was only 15%–20% higher than it was in the early 1900s (decade), but it showed a twofold increase in standard deviation. Climate variability (changes in temperature and precipitation) explains most (225 Gg C∙yr−1) of the increase since 1900, followed by changes in atmospheric CO2 (82 Gg C∙yr−1), atmospheric nitrogen deposition (44 Gg C∙yr−1), and applications of nitrogen fertilizer and manure (27 Gg C∙yr−1); in contrast, land conversion has resulted in a 188 Gg C∙yr−1 decrease in carbon export. Plain Language Summary: Rivers are an important component of the terrestrial‐aquatic ocean continuum as they serve as a conduit for transporting carbon from the land to the coastal ocean. It is essential to track the fate of this carbon, including how much carbon is buried in the riverbed, outgassed to the atmosphere, and exported to the ocean. However, it is often difficult to quantify these carbon transport processes on the watershed scale because observational data obtained by field surveys can only be used to estimate the magnitude of these processes at distinct points. In this study, we used a coupled terrestrial‐aquatic ecosystem model to assess the century‐long full carbon budget of the riverine ecosystem across the watersheds of Chesapeake Bay and Delaware Bay. In addition, we examined the individual and combined impacts of climate change and anthropogenic activities on these terrestrial ecosystems and the resultant CO2emissions of their associated rivers. We found that climate variability and land conversion (from cropland to impervious surfaces and forest) are the most important factors governing the long‐term change in riverine carbon dynamics. We also highlighted the importance of riverine CO2 emissions in the overall regional carbon budget. Key Points: Riverine carbon fluxes show twofold increase in standard deviation resulting from increased climate variabilityClimate variability explains most of the interdecadal change in riverine carbon export to the coastal ocean in the US Mid‐Atlantic watershedsAt the same time, land conversion from cropland to impervious surfaces and forest has decreased carbon export to the coastal ocean [ABSTRACT FROM AUTHOR]

We compared body morphology of two freshwater sculpin taxa that inhabit distinct environmental conditions in the Chesapeake Bay watershed of eastern North America: Potomac sculpin (C. girardi, Robins; PS) and checkered sculpin (C. sp. cf. girardi; CS). Both taxa are endemic to the study area, but PS are more broadly distributed than CS which are limited to karst groundwater-dominated streams in the central Potomac River basin. We examined preserved specimens from sites encompassing their geographic range (six sites per taxon) to evaluate taxonomic differences and environmental effects. Pelvic fin ray counts and body shape distinguished the study taxa. Morphological variation exhibited stronger relationships to environmental covariates (site elevation and basin size) in PS than CS as expected. In addition, the frequency of specimens with a united median chin pore increased with site elevation in PS (but not CS), suggesting thermal effects on preoperculomanibular canal development. However, contrary to expectation, PS did not exhibit greater among-population variation in body shape than CS, and this indicates the potential importance of unmeasured environmental differences among karst groundwater-dominated streams in the study area. Our study also indicated the utility of stream-level management units for CS, an undescribed species recognized as "critically imperiled" by state agencies. [ABSTRACT FROM AUTHOR]

Spatial and temporal patterns in low streamflows were investigated for 183 streamgages located in the Chesapeake Bay Watershed for the period 1939–2013. Metrics that represent different aspects of the frequency and magnitude of low streamflows were examined for trends: (1) the annual time series of seven‐day average minimum streamflow, (2) the scaled average deficit at or below the 2% mean daily streamflow value relative to a base period between 1939 and 1970, and (3) the annual number of days below the 2% threshold. Trends in these statistics showed spatial cohesion, with increasing low streamflow volume at streamgages located in the northern uplands of the Chesapeake Bay Watershed and decreasing low streamflow volume at streamgages in the southern part of the watershed. For a small subset of streamgages (12%), conflicting trend patterns were observed between the seven‐day average minimum streamflow and the below‐threshold time series and these appear to be related to upstream diversions or the influence of reservoir‐influenced streamflows in their contributing watersheds. Using multivariate classification techniques, mean annual precipitation and fraction of precipitation falling as snow appear to be broad controls of increasing and decreasing low‐flow trends. Further investigation of seasonal precipitation patterns shows summer rainfall patterns, driven by the Atlantic Multidecadal Oscillation, as the main driver of low streamflows in the Chesapeake Bay Watershed. [ABSTRACT FROM AUTHOR]

Endocrine-disrupting compounds (EDCs), specifically estrogenic endocrine-disrupting compounds, vary in concentration and composition in surface waters under the influence of different landscape sources and landcover gradients. Estrogenic activity in surface waters may lead to adverse effects in aquatic species at both individual and population levels, often observed through the presence of intersex and vitellogenin induction in male fish. In the Chesapeake Bay Watershed, located on the mid-Atlantic coast of the USA, intersex has been observed in several sub-watersheds where previous studies have identified specific landscape sources of EDCs in tandem with observed fish health effects. Previous work in the Potomac River Watershed (PRW), the largest basin within the Chesapeake Bay Watershed, was leveraged to build random forest regression models to predict estrogenic activity at unsampled reaches in both the Potomac River and larger Chesapeake Bay Watersheds (CBW). Model outputs including important variables, partial dependence plots, and predicted values of estrogenic activity at unsampled reaches provide insight into drivers of estrogenic activity at different seasons and scales. Using the US Environmental Protection Agency effects-based threshold of 1.0 ng/L 17 β-estradiol equivalents, catchments predicted to exceed this value were categorized as at risk for adverse effects from exposure to estrogenic compounds and evaluated relative to healthy watersheds and recreation access locations throughout the PRW. Results show immediate catchment scale models are more reliable than upstream models, and the best predictive variables differ by season and scale. A small percentage of healthy watersheds (< 13%) and public access sites were classified as at risk using the "Total" (annual) model in the CBW. This study is the first Potomac River Watershed assessment of estrogenic activity, providing a new foundation for future risk assessment and management design efforts, with additional context provided for the entire Chesapeake Bay Watershed. [ABSTRACT FROM AUTHOR]

Land‐use and climate change are significantly affecting stream ecosystems, yet understanding of their long‐term impacts is hindered by the few studies that have simultaneously investigated their interaction and high variability among future projections. We modeled possible effects of a suite of 2030, 2060, and 2090 land‐use and climate scenarios on the condition of 70,772 small streams in the Chesapeake Bay watershed, United States. The Chesapeake Basin‐wide Index of Biotic Integrity, a benthic macroinvertebrate multimetric index, was used to represent stream condition. Land‐use scenarios included four Special Report on Emissions Scenarios (A1B, A2, B1, and B2) representing a range of potential landscape futures. Future climate scenarios included quartiles of future climate changes from downscaled Coupled Model Intercomparison Project ‐ Phase 5 (CMIP5) and a watershed‐wide uniform scenario (Lynch2016). We employed random forests analysis to model individual and combined effects of land‐use and climate change on stream conditions. Individual scenarios suggest that by 2090, watershed‐wide conditions may exhibit anywhere from large degradations (e.g., scenarios A1B, A2, and the CMIP5 25th percentile) to small degradations (e.g., scenarios B1, B2, and Lynch2016). Combined land‐use and climate change scenarios highlighted their interaction and predicted, by 2090, watershed‐wide degradation in 16.2% (A2 CMIP5 25th percentile) to 1.0% (B2 Lynch2016) of stream kilometers. A goal for the Chesapeake Bay watershed is to restore 10% of stream kilometers over a 2008 baseline; our results suggest meeting and sustaining this goal until 2090 may require improvement in 11.0%–26.2% of stream kilometers, dependent on land‐use and climate scenario. These results highlight inherent variability among scenarios and the resultant uncertainty of predicted conditions, which reinforces the need to incorporate multiple scenarios of both land‐use (e.g., development, agriculture, etc.) and climate change in future studies to encapsulate the range of potential future conditions. [ABSTRACT FROM AUTHOR]

Atmospheric deposition is among the largest pathways of nitrogen loading to the Chesapeake Bay Watershed (CBW). The interplay between future climate and emission changes in and around the CBW will likely shift the future nutrient deposition abundance and chemical regime (e.g., oxidized vs. reduced nitrogen). In this work, a Representative Concentration Pathway from the Community Earth System Model is dynamically downscaled using a recently updated Weather Research and Forecasting model that subsequently drives the Community Multiscale Air Quality model coupled to the agroeconomic Environmental Policy Integrated Climate model. The relative impacts of emission and climate changes on atmospheric nutrient deposition are explored for a recent historical period and a period centered on 2050. The projected regional emissions in Community Multiscale Air Quality reflect current federal and state regulations, which use baseline and projected emission years 2011 and 2040, respectively. The historical simulations of 2‐m temperature (T2) and precipitation (PRECIP) have cool and dry biases, and temperature and PRECIP are projected to both increase. Ammonium wet deposition agrees well with observations, but nitrate wet deposition is underpredicted. Climate and deposition changes increase simulated future ammonium fertilizer application. In the CBW by 2050, these changes (along with widespread decreases in anthropogenic nitrogen oxide and sulfur oxide emissions, and relatively constant ammonia emissions) decrease total nitrogen deposition by 21%, decrease annual average oxidized nitrogen deposition by 44%, and increase reduced nitrogen deposition by 10%. These results emphasize the importance of decreased anthropogenic emissions on the control of future nitrogen loading to the Chesapeake Bay in a changing climate. Plain Language Summary: In this study a global climate scenario is used to drive a regional‐scale weather and air quality model to investigate the potential impacts of future climate and emission changes on atmospheric nitrogen loading to the Chesapeake Bay Watershed (CBW). While different scenarios are possible, here we delve into a specific climate projection that represents a future pathway for stabilization of radiative forcing by the year 2050 and use projected emissions (from human activity) that are based on historical and proposed regulations and controls from the U.S. Environmental Protection Agency. The combined climate and emission changes lead to decreases in the atmospheric nitrogen loading to the Chesapeake Bay Watershed by the year 2050, while the effects of climate alone lead to a small increase in atmospheric nitrogen loading. The results demonstrate the importance of emission reductions on nitrogen loading to the Chesapeake Bay, in the face of climate change. Key Points: Combined climate and emission changes lead to reduced nitrogen deposition (~21%) to the Chesapeake Bay Watershed by 2050There is an offset in nitrogen deposition (approximately +4%) due to the change in climate by 2050The composition of the nitrogen deposition is becoming increasingly dominated by reduced nitrogen by 2050 [ABSTRACT FROM AUTHOR]

Abstract Identifying floodplains with high rates of denitrification will help prioritize restoration projects for the removal of nitrogen. Currently, relationships of denitrification with hydrogeomorphic, physiographic, and climate (i.e. , largescale) characteristics of floodplains are relatively unknown, even though these characteristics have datasets (e.g. , geographic mapping tools) that are publicly available (or soon-to-become) that could be used to understand denitrification variability. Thus, we investigated control of denitrification by these largescale characteristics in eighteen nontidal floodplains of the Chesapeake Bay watershed (i.e. , at regional scale, >100 km, scale), using measurements or compiled data at the scales of the stream reach and respective catchment; floodplain soil and herbaceous vegetation (i.e. , local) characteristics were additionally investigated. Soil denitrification potentials were measured in May, July, and August using complementary acetylene-based techniques under an anoxic environment. Linear largescale predictors of denitrification potential measurements included stream nitrogen and phosphorus concentrations (+), channel width-to-depth ratio (+), floodplain sedimentation (+), forested (−) and urban (+) catchment land cover, and seasonal air temperature (−). Three predictors, catchment forested land cover (strongly related to agricultural land cover), catchment urban land cover, and floodplain sedimentation were related to the most number of denitrification potential measurements. Soil structure, soil nutrient concentrations, and herbaceous vegetation characteristics that were seasonally measured (with a few exceptions) were linear predictors of denitrification potentials in May and August, with nitrogen and carbon characteristics the most consistent (positive) predictors across measurements. Nutrient amendment assays further supported the importance of nitrogen and carbon controls. Using the local characteristics as statistical mediators in path analysis, greater non-forested catchment land cover indirectly increased denitrification through greater floodplain soil nitrate, total phosphorus, and herbaceous aboveground biomass. Additionally, greater floodplain sedimentation indirectly increased denitrification through greater soil pH, total phosphorus, and potential carbon mineralization. Due to the consistency of relationships across denitrification potential measurements along with path modeling results, hotspots of floodplain denitrification should be found in urban and agricultural catchments where river-floodplain hydrologic connectivity promotes sedimentation. Largescale predictors explained 43–57% of the variation in denitrification potentials and should be useful for prediction in floodplains. Siting restoration projects in watersheds for maximum nitrate removal using publicly available largescale datasets is both feasible and effective. Highlights • Land cover and floodplain sedimentation strong predictors of denitrification • Non-forested catchments with hydrologic connectivity should promote denitrification. • Largescale predictors linked to denitrification through local predictors • Largescale predictors explained 43–57% of the variation in denitrification. [ABSTRACT FROM AUTHOR]

Ecosystem services provided by depressional wetlands on the coastal plain of the Chesapeake Bay watershed (CBW) have been widely recognized and studied. However, wetland–groundwater interactions remain largely unknown in the CBW. The objective of this study was to examine the vertical interactions of depressional wetlands and groundwater with respect to different subsurface soil characteristics. This study examined two depressional wetlands with a low‐permeability and high‐permeability soil layer on the coastal plain of the CBW. The surface water level (SWL) and groundwater level (GWL) were monitored over 1 year from a well and piezometer at each site, respectively, and those data were used to examine the impacts of subsurface soil characteristics on wetland–groundwater interactions. A large difference between the SWL and GWL was observed at the wetland with a low‐permeability soil layer, although there was strong similarity between the SWL and GWL at the wetland with a high‐permeability soil layer. Our observations also identified a strong vertical hydraulic gradient between the SWL and GWL at the wetland with a high‐permeability soil layer relative to one with a low‐permeability soil layer. The hydroperiod (i.e., the total time of surface water inundation or saturation) of the wetland with a low‐permeability soil layer appeared to rely on groundwater less than the wetland with a high‐permeability soil layer. The findings showed that vertical wetland–groundwater interactions varied with subsurface soil characteristics on the coastal plain of the CBW. Therefore, subsurface soil characteristics should be carefully considered to anticipate the hydrologic behavior of wetlands in this region. [ABSTRACT FROM AUTHOR]

Despite recognizing the importance of wetlands in the Coastal Plain of the Chesapeake Bay Watershed (CBW) in terms of ecosystem services, our understanding of wetland functions has mostly been limited to individual wetlands and overall catchment-scale wetland functions have rarely been investigated. This study is aimed at assessing the cumulative impacts of wetlands on watershed hydrology for an agricultural watershed within the Coastal Plain of the CBW using the Soil and Water Assessment Tool (SWAT). We employed two improved wetland modules for enhanced representation of physical processes and spatial distribution of riparian wetlands (RWs) and geographically isolated wetlands (GIWs). This study focused on GIWs as their hydrological impacts on watershed hydrology are poorly understood and GIWs are poorly protected. Multiple wetland scenarios were prepared by removing all or portions of the baseline GIW condition indicated by the U.S. Fish and Wildlife Service National Wetlands Inventory geospatial dataset. We further compared the impacts of GIWs and RWs on downstream flow (i.e., streamflow at the watershed outlet). Our simulation results showed that GIWs strongly influenced downstream flow by altering water transport mechanisms in upstream areas. Loss of all GIWs reduced both water routed to GIWs and water infiltrated into the soil through the bottom of GIWs, leading to an increase in surface runoff of 9% and a decrease in groundwater flow of 7% in upstream areas. These changes resulted in increased variability of downstream flow in response to extreme flow conditions. GIW loss also induced an increase in month to month variability of downstream flow and a decrease in the baseflow contribution to streamflow. Loss of all GIWs was shown to cause a greater fluctuation of downstream flow than loss of all RWs for this study site, due to a greater total water storage capacity of GIWs. Our findings indicate that GIWs play a significant role in controlling hydrological processes in upstream areas and downstream flow and, therefore, protecting GIWs is important for enhanced hydrological resilience to extreme flow conditions in this region. [ABSTRACT FROM AUTHOR]

• A tool is proposed to evaluate incentive policies at a basin scale using coupled agent-based modeling. • Pay-for-performance policies outperform the pay-for-practice policy in the simulation, achieving faster sediment reduction. • Due to policy-induced collaboration, the group-based pay-for-performance policy shows reduced sensitivity to bonus payments. Cost-shared programs have been applied to incentivize the adoption of agricultural best management practices (BMPs) to address the long-standing water quality issue in the Chesapeake Bay watershed, US. However, the business-as-usual (BAU) incentive program (i.e., pay-for-practice, paying cost share for implementing BMPs) is likely to miss the Total Maximum Daily Load target to reduce 20% of the total suspended sediment (TSS) in 2010 by 2025. Some field experiments indicate that pay-by-performance (PFP; paying lower cost share but with additional bonus payment per unit sediment reduction) can better motivate community involvement leading to greater water quality control outcomes. However, the effectiveness of different incentive policies is still unclear at a basin scale. We propose a coupled agent-based modeling tool to quantify the performance of different incentive policies. The tool considers farmers' (i.e., agents') BMP adoption dynamics affected by the social norm and the potential bonus payment. Specifically, we compare individual-based PFP (PFP i) and group-based PFP (PFP g) with BAU. Results of our proposed model applied to the selected study area, the Susquehanna River Basin, Chesapeake Bay's largest tributary watershed, suggest that PFP can achieve higher TSS reduction with less cost. PFP g shows the best basin-wide TSS reduction associated with the least uncertainty among all tested policies. Also, the performance of PFP g is less impacted by the change in the bonus payment compared to PFP i attributed to farmers' collaboration efforts. Potentially, the proposed policy evaluation tool can better inform an achievable target with policy suggestions in assistance with social studies (e.g., surveys and behavioral experiments). [ABSTRACT FROM AUTHOR]

Water quality problems in the Chesapeake Bay Watershed (CBW) are expected to be exacerbated by climate variability and change. However, climate impacts on agricultural lands and resultant nutrient loads into surface water resources are largely unknown. This study evaluated the impacts of climate variability and change on two adjacent watersheds in the Coastal Plain of the CBW, using the Soil andWater Assessment Tool (SWAT) model.We prepared six climate sensitivity scenarios to assess the individual impacts of variations in CO2 concentration (590 and 850 ppm), precipitation increase (11 and 21 %), and temperature increase (2.9 and 5.0 °C), based on regional general circulation model (GCM) projections. Further, we considered the ensemble of five GCM projections (2085-2098) under the Representative Concentration Pathway (RCP) 8.5 scenario to evaluate simultaneous changes in CO2, precipitation, and temperature. Using SWAT model simulations from 2001 to 2014 as a baseline scenario, predicted hydrologic outputs (water and nitrate budgets) and crop growth were analyzed. Compared to the baseline scenario, a precipitation increase of 21% and elevated CO2 concentration of 850 ppm significantly increased streamflow and nitrate loads by 50 and 52 %, respectively, while a temperature increase of 5.0 °C reduced streamflow and nitrate loads by 12 and 13 %, respectively. Crop biomass increased with elevated CO2 concentrations due to enhanced radiation- and water-use efficiency, while it decreased with precipitation and temperature increases. Over the GCM ensemble mean, annual streamflow and nitrate loads showed an increase of ~70%relative to the baseline scenario, due to elevated CO2 concentrations and precipitation increase. Different hydrological responses to climate change were observed from the two watersheds, due to contrasting land use and soil characteristics. The watershed with a larger percent of croplands demonstrated a greater increased rate of 5.2 kgNha-1 in nitrate yield relative to the watershed with a lower percent of croplands as a result of increased export of nitrate derived from fertilizer. The watershed dominated by poorly drained soils showed increased nitrate removal due do enhanced denitrification compared to the watershed dominated by well-drained soils. Our findings suggest that increased implementation of conservation practices would be necessary for this region to mitigate increased nitrate loads associated with predicted changes in future climate. [ABSTRACT FROM AUTHOR]

The Chesapeake Bay (CB) basin is under a total maximum daily load (TMDL) mandate to reduce nitrogen, phosphorus, and sediment loads to the bay. Identifying shifts in the hydro-climatic regime may help explain observed trends in water quality. To identify potential shifts, hydrologic data (1927–2014) for 27 watersheds in the CB basin were analyzed to determine the relationships among long-term precipitation and stream discharge trends. The amount, frequency, and intensity of precipitation increased from 1910 to 1996 in the eastern U.S., with the observed increases greater in the northeastern U.S. than the southeastern U.S. The CB watershed spans the north-to-south gradient in precipitation increases, and hydrologic differences have been observed in watersheds north relative to watersheds south of the Pennsylvania—Maryland (PA-MD) border. Time series of monthly mean precipitation data specific to each of 27 watersheds were derived from the Precipitation-elevation Regression on Independent Slopes Model (PRISM) dataset, and monthly mean stream-discharge data were obtained from U.S. Geological Survey streamgage records. All annual precipitation trend slopes in the 18 watersheds north of the PA-MD border were greater than or equal to those of the nine south of that border. The magnitude of the trend slopes for 1927–2014 in both precipitation and discharge decreased in a north-to-south pattern. Distributions of the monthly precipitation and discharge datasets were assembled into percentiles for each year for each watershed. Multivariate correlation of precipitation and discharge within percentiles among the groups of northern and southern watersheds indicated only weak associations. Regional-scale average behaviors of trends in the distribution of precipitation and discharge annual percentiles differed between the northern and southern watersheds. In general, the linkage between precipitation and discharge was weak, with the linkage weaker in the northern watersheds compared to those in the south. On the basis of simple linear regression, 26 of the 27 watersheds are projected to have higher annual mean discharge in 2025, the target date for implementation of the TMDL for the CB basin. [ABSTRACT FROM AUTHOR]

Stormwater runoff and associated pollutants from urban areas in the greater Chesapeake Bay Watershed ( CBW) impair local streams and downstream ecosystems, despite urbanized land comprising only 7% of the CBW area. More recently, stormwater best management practices ( BMPs) have been implemented in a low impact development ( LID) manner to treat stormwater runoff closer to its source. This approach included the development of a novel BMP model to compare traditional and LID design, pioneering the use of comprehensively digitized storm sewer infrastructure and BMP design connectivity with spatial patterns in a geographic information system at the watershed scale. The goal was to compare total watershed pollutant removal efficiency in two study watersheds with differing spatial patterns of BMP design (traditional and LID), by quantifying the improved water quality benefit of LID BMP design. An estimate of uncertainty was included in the modeling framework by using ranges for BMP pollutant removal efficiencies that were based on the literature. Our model, using Monte Carlo analysis, predicted that the LID watershed removed approximately 78 kg more nitrogen, 3 kg more phosphorus, and 1,592 kg more sediment per square kilometer as compared with the traditional watershed on an annual basis. Our research provides planners a valuable model to prioritize watersheds for BMP design based on model results or in optimizing BMP selection. [ABSTRACT FROM AUTHOR]

Cellulosic biomass from winter crops can complement maize stover harvested from maize ( Zea mays L.) – soybean ( Glycine max L.) rotations. In this study, we assessed on-field environmental impacts related to carbon (C) and nitrogen (N) by modeling representative agro-ecological conditions prevalent in the mid-Atlantic region of the United States. We used the biophysical model Cycles to simulate management scenarios for maize-soybean cropping systems that included winter rye ( Secale cereale L.). The model was used to quantify changes in N losses via nitrate leaching (NO 3 ), emissions of nitrous oxide (N 2 O) and ammonia (NH 3 ), changes in soil organic carbon, and carbon dioxide equivalent emissions per megajoule (CO 2eq MJ − 1 ). Including winter rye in the rotation reduced NO 3 leaching over a winter fallow control (77% on average), even when the winter rye was fertilized and regardless of whether stover, winter rye, or both cellulosic feedstocks were harvested. Applying fertilizer to winter rye did however increase NO 3 leaching as well as NH 3 and N 2 O emissions. Model results consistently showed fertilizing the winter rye improved both biomass yield and soil C levels compared to unfertilized winter rye, regardless of location, soil, fertilizer type or stover harvest. While it is difficult to simultaneously reduce agricultural nitrogen losses, produce renewable energy and increase soil carbon, results can guide management of these trade-offs while tapping into an abundant energy resource and reducing greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Nitrous oxide (N2O) is a potent greenhouse gas. Wastewater treatment is considered to be a minor source of N2O; however, observed in-plant emission factors are more variable than previously considered. Further, emissions associated with treated wastewater effluent are highly uncertain. A model incorporating these uncertainties was compared with current N2O estimates. The modified model features distribution-based emission factors and Monte Carlo simulation. Results of these simulations indicate N2O emissions 7.3, 8.6, and 9.4 times estimates generated with the current method for in-plant, effluent-derived, and total emissions, respectively. Future changes in biological nitrogen removal (BNR) associated with clean water objectives may alter N2O releases. The model, which distinguishes between BNR and non-BNR treatment, predicts decreasing N2O emissions with increasing BNR treatment. Examining the Chesapeake Bay system, the model suggests 2012 BNR levels reduced N2O emissions by 0.86 MMT CO2 eq per year, and planned BNR expansions will result in emissions being reduced by 1.77 MMT CO2 eq relative to 0% BNR scenarios. The new estimation method would be improved through additional collection of data on effluent emissions. [ABSTRACT FROM AUTHOR]

The health of the Chesapeake Bay ecosystem has been declining for several decades due to high levels of nutrients and sediments largely tied to agricultural production systems. Therefore, monitoring of agricultural water use and hydrologic connections between crop lands and Bay tributaries has received increasing attention. Remote sensing retrievals of actual evapotranspiration (ET) can provide valuable information in support of these hydrologic modeling efforts, spatially and temporally describing consumptive water use by crops and natural vegetation and quantifying response to expansion of irrigated area occurring with Bay watershed. In this study, a multisensor satellite data fusion methodology, combined with a multiscale ET retrieval algorithm, was applied over the Choptank River watershed located within the Lower Chesapeake Bay region on the Eastern Shore of Maryland, USA to produce daily 30 m resolution ET maps. ET estimates directly retrieved on Landsat satellite overpass dates have high accuracy with relative error (RE) of 9%, as evaluated using flux tower measurements. The fused daily ET time series have reasonable errors of 18% at the daily time step - an improvement from 27% errors using standard Landsat-only interpolation techniques. Annual water consumption by different land cover types was assessed, showing reasonable distributions of water use with cover class. Seasonal patterns in modeled crop transpiration and soil evaporation for dominant crop types were analyzed, and agree well with crop phenology at field scale. Additionally, effects of irrigation occurring during a period of rainfall shortage were captured by the fusion program. These results suggest that the ET fusion system will have utility for water management at field and regional scales over the Eastern Shore. Further efforts are underway to integrate these detailed water use data sets into watershed-scale hydrologic models to improve assessments of water quality and inform best management practices to reduce nutrient and sediment loads to the Chesapeake Bay. [ABSTRACT FROM AUTHOR]

Floodgates or storm surge barriers are increasingly being considered as feasible climate change adaptation strategies to mitigate flooding risk. We developed a numerical modeling approach for a partially mixed estuary to simulate long-term alterations to hydrodynamics and transport processes induced from human modifications; two types of partially embanked storm surge barriers across the mouth of Chesapeake Bay were examined. Under modeled scenarios, surge barriers exerted a significant influence on the tide, salinity, residual current, and transport processes. The surge barrier caused (1) a reduction of tidal range inside the estuary, (2) stronger stratification and further salt intrusion, weaker vertical mixing and larger vertical exchange time, and (3) a decrease of bottom inflow in the mainstem and weakened horizontal water exchange. The change of horizontal water exchange and residence time was not a linear response with the barrier size and it varied at different regions of the estuary. The modeling approach is suitable to assess large-scale long-term ecosystem changes induced by human modifications or adaptations under a changing system. [ABSTRACT FROM AUTHOR]

A correction is presented to article "Identifying Key Stressors Driving Biological Impairment in Freshwater Streams in the Chesapeake Bay Watershed, USA" published in October 31, 2022 issue.

Best management practices (BMPs) have been predominantly used throughout the Chesapeake Bay watershed (CBW) to reduce nutrients and sediments entering streams, rivers, and the bay. These practices have been successful in reducing loads entering the estuary and have shown the potential to reduce other contaminants (pesticides, hormonally active compounds, pathogens) in localized studies and modeled load estimates. However, further understanding of relationships between BMPs and non-nutrient contaminant reductions at regional scales using sampled data would be beneficial. Total estrogenic activity was measured in surface water samples collected over a decade (2008–2018) in 211 undeveloped NHDPlus V2.1 watersheds within the CBW. Bayesian hierarchical modeling between total estrogenic activity and landscape predictors including landcover, runoff, BMP intensity, and a BMP*agriculture intensity interaction term indicates a 96% posterior probability that BMP intensity on agricultural land is reducing total estrogenic activity. Additionally, watersheds with high agriculture and low BMPs had a 49% posterior probability of exceeding an effects-based threshold in aquatic organisms of 1 ng/L but only a 1% posterior probability of exceeding this threshold in high-agriculture, high-BMP watersheds. [Display omitted] • Sampling of estrogenic activity in surface waters across Chesapeake Bay Watershed. • Intensity metric of agricultural Best Management Practices (BMP) developed. • Bayesian hierarchical modeling of BMP intensity, landuse, and climate variables. • 96% posterior probability of estrogenic activity reduction given BMP intensity. [ABSTRACT FROM AUTHOR]

Shoreline armoring is an ancient and globally used engineering strategy to prevent shoreline erosion along marine, estuarine, and freshwater coastlines. Armoring alters the land water interface and has the potential to affect nearshore submerged aquatic vegetation (SAV) by changing nearshore hydrology, morphology, water clarity, and sediment composition. We quantified the relationships between the condition (bulkhead, riprap, or natural) of individual shoreline segments and three measures of directly adjacent SAV (the area of potential SAV habitat, the area occupied by SAV, and the proportion of potential habitat area that was occupied) in the Chesapeake Bay and nearby Atlantic coastal bays. Bulkhead had negative relationships with SAV in the polyhaline and mesohaline zones. Salinity and watershed land cover significantly modified the effect of shoreline armoring on nearshore SAV beds, and the effects of armoring were strongest in polyhaline subestuaries with forested watersheds. In high salinity systems, distance from shore modified the relationship between shoreline and SAV. The negative relationship between bulkhead and SAV was greater further off shore. By using individual shoreline segments as the study units, our analysis separated the effects of armoring and land cover, which were confounded in previous analyses that quantified average armoring and SAV abundance for much larger study units (subestuaries). Our findings suggest that redesigning or removing shoreline armoring structures may benefit nearshore SAV in some settings. Because armoring is ubiquitous, such information can inform efforts to reverse the global decline in SAV and the loss of the ecosystem services that SAV provides. [ABSTRACT FROM AUTHOR]

Concern for the health of the Chesapeake Bay and the establishment of the Bay Total Maximum Daily Load have led to growing interest in restoring and creating wetlands to mitigate agricultural nitrogen inputs. All Bay states have included wetland restoration in their watershed implementation plans (WIPs) to help meet their required reduction in nitrogen loading. In agricultural areas of the coastal plain, efforts to develop a watershed-scale approach to siting and designing wetlands have been met with considerable challenges. Nitrate loss is primarily attributed to base-flow conditions, and groundwater flow is multidimensional and highly variable, so accounting for nitrate transport connectivity between agricultural N source areas and potential wetland restoration areas is difficult. Socioeconomic and political challenges also constrain implementation. Our ability to account for subsurface connectivity may be improved with better assessment of hydrologic connectivity in areas with artificial drainage, catchment-scale studies of hydrogeomorphic predictions of hydrologic connectivity, and improved use of geospatial data. A coordinated monitoring program would improve our ability to estimate wetland nitrogen removal efficiencies across environmental and management conditions. The addition of a requirement that water quality should be an explicit objective of restorations included within WIP accounting would avoid the inclusion of projects with minimal water quality benefits. Research is also needed on farmer attitudes in the Chesapeake Bay watershed toward wetlands for water quality protection. These proposed actions would improve our ability to understand and implement wetland restoration as a component of our response to meet water quality objectives. [ABSTRACT FROM AUTHOR]

Models which use species-specific trade-offs of life-history traits have been widely used to simulate stable, diverse communities of sessile organisms. However, the precise estimation of trade-off parameters required by many models cannot be easily realized for multiple species living within rapidly changing environments. We developed a spatially-explicit model, MCAP, that uses empirically estimated parameters to define species-specific life-history functions. This approach did not require trade-offs to be explicitly stated, but rather intrinsically represented trade-offs within the data structure defining each species life-history functions (e.g., age or size dependent changes in reproduction, dispersal, establishment, mortality and growth). The use of species-specific functions with empirically estimated parameters allowed each species to be uniquely characterized with subsequent estimation of model sensitivities due to changing functional forms or parameter errors. Empirical data was obtained from field observations and experiments for 16 species within tidal freshwater marsh communities of the Chesapeake Bay. Model results compared with these data showed that MCAP realistically represented processes structuring these tidal marsh communities. Model experiments varying weather and the range of habitat conditions accessible to each species showed that patterns of abundance and diversity were most affected by local habitat conditions and neighborhood interactions among competing species. The simulation approach used in MCAP was effective and efficient, providing a comprehensive tool for assessing the simultaneous effects of changing environmental drivers and species composition on the persistence and biodiversity of marsh communities. [ABSTRACT FROM AUTHOR]

Abstract: Coastlines worldwide are being altered due to shoreline hardening and stabilization and while highly altered systems are subject to change, variability exists in how shoreline hardening affects benthic communities depending on the landscape features of the system and regional production. Oyster reefs have been used to stabilize shorelines and offer a potentially positive effect on shoreline communities. In a field survey, we used 29 sites throughout the Lynnhaven River System, a highly developed yet productive subestuary of Chesapeake Bay, to determine effects of shoreline type (natural marsh, oyster shell reef, rip-rap, and bulkhead), sediment characteristics (grain size and total organic carbon and total nitrogen), and predators on benthic infaunal density, biomass, and diversity. An information-theoretic approach was used to determine which of several hypothesized Generalized Linear Models were supported by the data. Shoreline type was the best predictor of benthic infaunal density, with oyster reefs having the highest benthic density and bulkhead the lowest. In contrast, sediment characteristics and predators were the best predictors of benthic infaunal biomass and diversity. The Lynnhaven system is shallow (~2.5m), and nearly 78% of the shoreline is natural marsh, which promotes high regional benthic productivity that may mask small-scale effects of shoreline stabilization on infauna. Our findings contrast with previous studies in moderately productive systems where altered shorelines had substantial direct effects on the benthos, suggesting that further studies need to take place across various systems among a range of upland usages to help clarify the impact of local shoreline stabilization versus regional watershed usage on benthic communities. Our results highlight that high ecosystem productivity is important for resilience to local shoreline modification. [Copyright &y& Elsevier]

While much has been written about collaborative federalism, the focus of this research has been on collaboration between governmental agencies at the national, state, and local levels. However, a growing body of evidence suggests there is a greater role available for nongovernmental actors in collaborative federalism. This article presents a case in which a local grassroots environmental nonprofit organization plays a critical role in the implementation of Total Maximum Daily Load (TMDL) requirements in the Chesapeake Bay watershed. We conclude that such collaboration provides local governments with a “force multiplier” that can enhance both collaborative federalism and policy outcomes. [ABSTRACT FROM PUBLISHER]

We used statistical models to provide the first empirical estimates of riparian buffer effects on the cropland nitrate load to streams throughout the Chesapeake Bay watershed. For each of 1,964 subbasins, we quantified the 1990 prevalence of cropland and riparian buffers. Cropland was considered buffered if the topographic flow path connecting it to a stream traversed a streamside forest or wetland. We applied a model that predicts stream nitrate concentration based on physiographic province and the watershed proportions of unbuffered and buffered cropland. We used another model to predict annual streamflow based on precipitation and temperature, and then multiplied the predicted flows and concentrations to estimate 1990 annual nitrate loads. Across the entire Chesapeake watershed, croplands released 92.3 Gg of nitrate nitrogen, but 19.8 Gg of that was removed by riparian buffers. At most, 29.4 Gg more might have been removed if buffer gaps were restored so that all cropland was buffered. The other 43.1 Gg of cropland load cannot be addressed with riparian buffers. The Coastal Plain physiographic province provided 52% of the existing buffer reduction of Bay-wide nitrate loads and 36% of potential additional removal from buffer restoration in cropland buffer gaps. Existing and restorable nitrate removal in buffers were lower in the other three major provinces because of less cropland, lower buffer prevalence, and lower average buffer nitrate removal efficiency. [ABSTRACT FROM AUTHOR]

In the interest of assessing an alternative source of precipitation input for the Chesapeake Bay Watershed model, the goal of this study is to compare the next generation weather radar (NEXRAD)-based multisensor precipitation estimator (MPE) with currently available gauge-based precipitation inputs for the model at both point-pixel and spatially aggregated scales. The comparison of gauge-based data with MPE at a point-pixel scale offers insight into how commonly known characteristics of gauge-point data are reflected in the mean areal gauge-based precipitation product. The time and effort for recalibration using MPE can be significantly reduced by strategizing the procedure according to the results of this study. Techniques and findings described here should be of general value for model users to anticipate changes in model parameters and output when moving from gauge-based to MPE precipitation in continuous simulation models. [ABSTRACT FROM AUTHOR]

With increasing attention on the contribution of ecosystems to human well-being, there is a need for tools that integrate ecological and economic models for valuing ecosystem services. To address this, we develop a protocol for linking ecological processes and outcomes to human preferences, which combines environmental modeling, expert elicitation, and nonmarket valuation methods. Our application values reductions in nutrient loads to lakes in the southeastern US. The innovation centers on how biochemical measures of water quality (e.g., chlorophyll a) are translated into terms that are meaningful to individuals who derive ecosystem services from them. Using expert elicitation data, we estimate a model linking changes in biochemical measures to an index of eutrophication in lakes. We then develop a stated preference survey including (a) detailed descriptions of the perceptible outcomes – e.g., water color, clarity – associated each eutrophication index level; and (b) policy scenarios involving state-level changes in lake eutrophication conditions. We estimate a function that predicts households' willingness to pay for changes in lake water quality. We demonstrate the protocol through a case study examining the benefits of lake quality improvement in Virginia as a result of recent policies to reduce nutrient loads in the Chesapeake Bay watershed. [Copyright &y& Elsevier]

Purpose: Fine-grained sediment is an important pollutant in streams and estuaries, including the Chesapeake Bay in the USA. The objective of this study was to determine the sources of fine-grained sediment using the sediment fingerprinting approach in the Linganore Creek watershed, a tributary to the Chesapeake Bay. Materials and methods: The sediment fingerprinting approach was used in the agricultural and forested, 147-km Linganore Creek watershed, Maryland from 1 August 2008 to 31 December 2010 to determine the relative percentage contribution from different potential sources of fine-grained sediment. Fine-grained suspended sediment samples (<63 μm) were collected during storm events in Linganore Creek using an automatic sampler and manual isokinetic samplers. Source samples were collected from 40 stream bank sites, 24 agricultural (cropland and pasture) sites, and 19 forested sites. Suspended sediment and source samples were analyzed for elements and stable isotopes. Results and discussion: Results of sediment fingerprinting for 194 samples collected in 36 separate storm events indicate that stream banks contributed 53% of the annual fine-grained suspended sediment load, agriculture contributed 44%, and forests contributed 3%. Peak flows and sediment loads of the storms correlate to stream bank erosion. The highest peak flows occurred in the winter and, along with freeze-thaw activity, contributed to winter months showing the highest rate of stream bank erosion. Peak flow was negatively correlated to sediment sources from agricultural lands which had the greatest contribution in non-winter months. Caution should be observed when trying to interpret the relation between sediment sources and individual storms using the sediment fingerprinting approach. Because the sediment fingerprinting results from individual storms may not include the temporal aspects of the sourced sediment, sediment that is in storage from previous events, remobilized and sampled during the current event, will reflect previous storm characteristics. Stream bank sediment is delivered directly to the channel during an event, whereas the delivery of upland sediment to the stream is lower due to storage on hillslopes and/or in channels, sediment from stream banks are more likely to be related to the characteristics of the sampled storm event. Conclusions: Stream banks and agricultural lands are both important sources of fine-grained sediment in the Linganore Creek watershed. Peak flows and sediment loads for the 36 storms show a significant relation to sediment sources from stream bank erosion. Attempting to link upland sediment sources to flow and seasonal characteristics is difficult since much of the upland sediment eroded in an event goes into storage. By averaging sediment sources over several storms, it may be possible to determine not only the sediment sources that are directly contributed during the current event but also sediment from previous events that was in storage and remobilized. [ABSTRACT FROM AUTHOR]

Abstract: Chesapeake Bay is the largest and one of the most productive estuaries in the U.S., where long-term monitoring and assessment of its water quality are necessary to understand trends and events in order to support management decisions. Significant progress has been made during the past decade in developing remote sensing algorithms for estimating two key water quality parameters, chlorophyll-a concentration (Chla, mg m−3) and diffuse light attenuation coefficient at 490 nm (K d (490), m−1), from satellite ocean color measurements in oceanic, coastal, and estuarine waters. Yet deriving a robust Chla data product for Chesapeake Bay still remains a challenge because of its complex optical properties. Here, a recently developed algorithm approach (Red–Green Chlorophyll Index or RGCI, based on red–green remote-sensing reflectance (Rrs (λ)) ratios) was tested, validated, and applied to Sea-viewing Wide Field-of-view Sensor (SeaWiFS) and Moderate Resolution Imaging Spectroradiometer (MODIS) data to establish a 14-year (September 1997 to December 2011) Chla Environmental Data Record (EDR). The new approach showed significant improvement over the traditional blue–green Rrs (λ) band-ratio algorithms (e.g., OC4, OC3M), with consistent performance for MODIS (mean relative error = 40.9%, mean ratio = 1.09) and SeaWiFS (MRE = 45.8%, mean ratio = 1.09) for Chla ranging between 1 and 50 mg m−3. Anomaly and EOF analyses revealed strong spatial gradients, seasonality, and climate-driven inter-annual changes in the satellite-based Chla EDR. These changes were highly correlated with satellite-based K d (490) EDR, leading to the development of a Water Quality Decision Matrix (WQDM) and providing support to on-going nutrient reduction management programs for this estuary. [Copyright &y& Elsevier]

The article focuses on the problems related to the water quality trading. Topics discussed include health and quality of water resources, point source pollution and nutrient trading. It also discusses the environmental interventions, total maximum daily load (TMDL) cap for the assessment of the problems related to the nutrient trading and recommendations for protecting the Chesapeake Bay watershed.

The Chesapeake Bay is the largest estuary in the United States with a very large and diverse watershed. The health of the Bay related to pollution from nutrients and sediment has been in decline for many years. Agriculture in the watershed is one of the major contributors of nutrient and sediment pollution to the Chesapeake. The cause of the nutrient pollution from agriculture has usually been thought to have been the result of mismanagement of nutrients on farms. Consequently, the approaches to solving the problem have focused almost exclusively on changing farm management. As a result, significant progress has been made in improving on-farm nutrient management but the health of the Bay remains a concern. An analysis of the structure of animal agriculture in the Bay watershed reveals that the problem is much deeper than simply mismanagement on farms. A major underlying cause is a regional nutrient imbalance resulting from an economically driven system of animal production based on importing from outside the watershed a large amount of the animal feed. Therefore, a long-term, sustainable solution will require much more than just changing on-farm management. To really solve this problem will require a restructuring of the animal production systems to internalize the environmental costs of this structural imbalance of nutrients in the watershed. The challenge that must be met is how to accomplish this in a way that is sustainable. [ABSTRACT FROM AUTHOR]