An Assessment of the Frequency and Cause of Concentrated Flow on Agricultural Fields in the Virginia Coastal Plain Portion of the Chesapeake Bay Watershed PDF Download
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Author: Monica H. Stone Publisher: ISBN: Category : Chesapeake Bay Watershed Languages : en Pages : 106
Book Description
Agricultural lands are the largest non-point source of nitrogen, phosphorous, and sediment that is delivered to Chesapeake Bay. There has been an increase in the amount of these nutrients and sediment being delivered to the Bay over the last century, which has caused extensive eutrophication and subsequent anoxic zones in the Bay. The Chesapeake Bay Act attempted to mitigate this problem by mandating 100-foot riparian buffer zones between agricultural fields and perennial streams in the Coastal Plain region of Virginia. Previous studies have shown that riparian buffers increase infiltration of runoff into the groundwater system, where nutrients and sediment can be removed from the water before it discharges into perennial streams. However, riparian buffers require flow to be widely disseminated throughout the buffer area in order for them to be effective. No declining trends have been noted in the amounts of nutrients and sediment being delivered to Chesapeake Bay since 1990, when buffers were required to be maintained in the Coastal Plain region of Virginia. I hypothesized that flow concentration, which can promote channel incision and allow agricultural runoff to bypass riparian buffers, is widespread in the Coastal Plain region of Virginia and may be one reason why reductions of nutrients and sediment in Bay waters have not been as great as expected. Geographic Information Systems (GIS) was used to determine flow accumulation patterns across 74 agricultural fields in the Coastal Plain region of Virginia. The percentage of each field drained by the 5 field margin points of greatest flow accumulation area was used as a proxy for measuring flow concentration. The cell size for points along each field margin was 3 m by 3 m. Further, 4 field indexes that related topographic and soil parameters on a field (wetness index, topographic index, water retention index, sediment transport index) were calculated for each field. These indexes were analyzed to determine if any were correlated with and could be used to easily predict places of flow concentration over a large geographic area, such as the Coastal Plain region of Virginia. Flow concentration occurred on all 74 study fields. On average, 70% of a field was drained through just 5 points along its field margin. The strongest field index relationship existed between the Wetness Index and flow concentration (R2 = 0.323). The field indexes were not good predictors of areas of high flow concentration because for any given value of an index, there was a large range of possible flow concentrations. Of the 6 topographic/soil property characteristics analyzed by these 4 field indexes (specific catchment area, runoff source area, slope, saturated hydraulic conductivity, depth to impermeable subsurface layer, and rainfall erosivity), the field slope showed the strongest relationship with flow concentration (R2 = 0.270). Principle component analysis on these 6 topographic/soil property characteristics had a first component that described 47% of the variance among these 6 variables and displayed the strongest relationship with flow concentration (R2 = 0.403). Rather than being attributable to characteristics of the topography or soil that vary from place to place, flow concentration seems to be a phenomenon that is of widespread occurrence in all areas of the Coastal Plain region of Virginia. I recommend requiring farmers to maintain riparian buffers on their land yearly. Future research should focus on determining how to reduce flow concentration through and increase the effectiveness of riparian buffers in the Coastal Plain region of Virginia.
Author: Monica H. Stone Publisher: ISBN: Category : Chesapeake Bay Watershed Languages : en Pages : 106
Book Description
Agricultural lands are the largest non-point source of nitrogen, phosphorous, and sediment that is delivered to Chesapeake Bay. There has been an increase in the amount of these nutrients and sediment being delivered to the Bay over the last century, which has caused extensive eutrophication and subsequent anoxic zones in the Bay. The Chesapeake Bay Act attempted to mitigate this problem by mandating 100-foot riparian buffer zones between agricultural fields and perennial streams in the Coastal Plain region of Virginia. Previous studies have shown that riparian buffers increase infiltration of runoff into the groundwater system, where nutrients and sediment can be removed from the water before it discharges into perennial streams. However, riparian buffers require flow to be widely disseminated throughout the buffer area in order for them to be effective. No declining trends have been noted in the amounts of nutrients and sediment being delivered to Chesapeake Bay since 1990, when buffers were required to be maintained in the Coastal Plain region of Virginia. I hypothesized that flow concentration, which can promote channel incision and allow agricultural runoff to bypass riparian buffers, is widespread in the Coastal Plain region of Virginia and may be one reason why reductions of nutrients and sediment in Bay waters have not been as great as expected. Geographic Information Systems (GIS) was used to determine flow accumulation patterns across 74 agricultural fields in the Coastal Plain region of Virginia. The percentage of each field drained by the 5 field margin points of greatest flow accumulation area was used as a proxy for measuring flow concentration. The cell size for points along each field margin was 3 m by 3 m. Further, 4 field indexes that related topographic and soil parameters on a field (wetness index, topographic index, water retention index, sediment transport index) were calculated for each field. These indexes were analyzed to determine if any were correlated with and could be used to easily predict places of flow concentration over a large geographic area, such as the Coastal Plain region of Virginia. Flow concentration occurred on all 74 study fields. On average, 70% of a field was drained through just 5 points along its field margin. The strongest field index relationship existed between the Wetness Index and flow concentration (R2 = 0.323). The field indexes were not good predictors of areas of high flow concentration because for any given value of an index, there was a large range of possible flow concentrations. Of the 6 topographic/soil property characteristics analyzed by these 4 field indexes (specific catchment area, runoff source area, slope, saturated hydraulic conductivity, depth to impermeable subsurface layer, and rainfall erosivity), the field slope showed the strongest relationship with flow concentration (R2 = 0.270). Principle component analysis on these 6 topographic/soil property characteristics had a first component that described 47% of the variance among these 6 variables and displayed the strongest relationship with flow concentration (R2 = 0.403). Rather than being attributable to characteristics of the topography or soil that vary from place to place, flow concentration seems to be a phenomenon that is of widespread occurrence in all areas of the Coastal Plain region of Virginia. I recommend requiring farmers to maintain riparian buffers on their land yearly. Future research should focus on determining how to reduce flow concentration through and increase the effectiveness of riparian buffers in the Coastal Plain region of Virginia.
Author: National Research Council Publisher: National Academies Press ISBN: 0309210828 Category : Political Science Languages : en Pages : 258
Book Description
The Chesapeake Bay is North America's largest and most biologically diverse estuary, as well as an important commercial and recreational resource. However, excessive amounts of nitrogen, phosphorus, and sediment from human activities and land development have disrupted the ecosystem, causing harmful algae blooms, degraded habitats, and diminished populations of many species of fish and shellfish. In 1983, the Chesapeake Bay Program (CBP) was established, based on a cooperative partnership among the U.S. Environmental Protection Agency (EPA), the state of Maryland, and the commonwealths of Pennsylvania and Virginia, and the District of Columbia, to address the extent, complexity, and sources of pollutants entering the Bay. In 2008, the CBP launched a series of initiatives to increase the transparency of the program and heighten its accountability and in 2009 an executive order injected new energy into the restoration. In addition, as part of the effect to improve the pace of progress and increase accountability in the Bay restoration, a two-year milestone strategy was introduced aimed at reducing overall pollution in the Bay by focusing on incremental, short-term commitments from each of the Bay jurisdictions. The National Research Council (NRC) established the Committee on the Evaluation of Chesapeake Bay Program Implementation for Nutrient Reduction in Improve Water Quality in 2009 in response to a request from the EPA. The committee was charged to assess the framework used by the states and the CBP for tracking nutrient and sediment control practices that are implemented in the Chesapeake Bay watershed and to evaluate the two-year milestone strategy. The committee was also to assess existing adaptive management strategies and to recommend improvements that could help CBP to meet its nutrient and sediment reduction goals. The committee did not attempt to identify every possible strategy that could be implemented but instead focused on approaches that are not being implemented to their full potential or that may have substantial, unrealized potential in the Bay watershed. Because many of these strategies have policy or societal implications that could not be fully evaluated by the committee, the strategies are not prioritized but are offered to encourage further consideration and exploration among the CBP partners and stakeholders.
Author: National Research Council Publisher: National Academies Press ISBN: 0309172683 Category : Nature Languages : en Pages : 569
Book Description
In 1997, New York City adopted a mammoth watershed agreement to protect its drinking water and avoid filtration of its large upstate surface water supply. Shortly thereafter, the NRC began an analysis of the agreement's scientific validity. The resulting book finds New York City's watershed agreement to be a good template for proactive watershed management that, if properly implemented, will maintain high water quality. However, it cautions that the agreement is not a guarantee of permanent filtration avoidance because of changing regulations, uncertainties regarding pollution sources, advances in treatment technologies, and natural variations in watershed conditions. The book recommends that New York City place its highest priority on pathogenic microorganisms in the watershed and direct its resources toward improving methods for detecting pathogens, understanding pathogen transport and fate, and demonstrating that best management practices will remove pathogens. Other recommendations, which are broadly applicable to surface water supplies across the country, target buffer zones, stormwater management, water quality monitoring, and effluent trading.
Author: Prabisha Shrestha Publisher: ISBN: Category : Agriculture Languages : en Pages : 398
Book Description
Field scale research shows concentrated flow paths (CFPs) are prevalent in agricultural watersheds. They are an important source of soil erosion in cropland and significantly contribute to the transport and delivery of agricultural pollutants such as sediment and nutrients to nearby water resources. High resolution LiDAR data have enabled the investigation of the prevalence of concentrated flow at a large geographic extent. This study focused on identifying CFPs in 389 agricultural fields in Jackson County in southern Illinois and estimating the contribution of the CFPs to drainage of the fields. Addressing the lack of literature on factors influencing CFP characteristics, this study also investigates various topographical and soil factors that influence CFP development. LiDAR derived DEMs with a cell resolution of 3 meters were used to identify areas of flow concentration and delineate a drainage basin of each CFP using the Hydrology tools in the Spatial Analyst toolbox in ArcMap 10.3.1. Information on the topographical and soil characteristics were obtained from the DEMs and SSURGO database using the Soil Data Viewer 6.2 extension for ArcMap. Multiple regression analysis in SAS v. 9.4 was used to identify factors influencing CFP characteristics, while CART analysis in R v. 3.3.1 was conducted to detect linear dependencies among predictor variables. An average of 5 CFPs per agricultural field were observed in the study area with a minimum of 0 and maximum of 17 CFPs, but only two fields had no CFPs indicating a high prevalence of CFPs throughout the study area. The mean percent of field area drained by CFPs was estimated to be 81 percent with minimum of 36 percent and ii maximum of 100 percent. The majority of the fields, 85 percent, had more than 70 percent of their area drained by CFPs. Statistically significant regression equations were found for all CFP characteristics with slope, LS factor, K factor and organic matter as the factors influencing CFP characteristics. However, the factors only explained 2 to 22 percent of variation observed. Both multiple regression and CART analysis indicated slope as the most important influencing factor. Variation in CFP characteristics followed regional trends with higher values in the floodplain region and lower values in the rough hills region suggesting residual variation could be explained by other environmental factors along with topographical and climatological factors which were not included in the study. Results from this study highlight the prevalence of CFPs at a regional scale and their substantial contribution to field drainage identifying a need for research in quantifying the impacts of CFP on soil loss and water quality. This study also reports a need of future research to identify important factors controlling CFP formation and development that could help build empirical and physical models to accurately predict CFP locations and morphology. Such information could be useful in designing and targeting conservation practices that protect both soil health and water quality.
Author: Monica H. Stone
Author: Monica H. Stone
Author: 
Author: United States. Soil Conservation Service
Author: Vijay P. Singh
Author: 
Author: Sharon E. Kroening
Author: 
Author: National Research Council
Author: National Research Council
Author: Prabisha Shrestha