Effects of Agriculture on Discharges of Nutrients from Coastal Plain Watersheds of Chesapeake Bay (original) (raw)
Related papers
Nonpoint Source Discharges of Nutrients from Piedmont Watersheds of Chesapeake Bay
Journal of the American Water Resources Association, 1997
We measured annual discharges of water, sediments, and nutrients from 10 watersheds with differing proportions of agricultural lands in the Piedmont physiographic province of the Chesapeake Bay drainage. Flow-weighted mean concentrations of total N, nitrate, and dissolved silicate in watershed discharges were correlated with the proportion of cropland in the watershed. In contrast, concentrations of P species did not correlate with cropland. Organic P and C correlated with the concentration of suspended particles, which differed among watersheds. Thus, the ratio of N:P:Si in discharges differed greatly among watersheds, potentially affecting N, P or Si limitation of phytoplankton growth in the receiving waters. Simple regression models of N discharge versus the percentage of cropland suggest that croplands discharge 29-42 kg N ha-1 y r l and other lands discharge 1.2-5.8 kg N ha-1 yr-1. We estimated net anthropogenic input of N to croplands and other lands using county level data on agriculture and N deposition from the atmosphere. For most of the study watersheds, N discharge amounted to less than half of the net anthropogenic N.
The Chesapeake Bay watershed: effects of land use and geology on dissolved nitrogen concentrations
1994
We measured the concentrations of dissolved nitrogen fractions in the streams draining 153 subwatersheds of Chesapeake Bay. Six "clusters" of nested watersheds were sampled eight times during the period from the summer of 1992 to the summer of 1993. Clusters were located on the Coastal Plain (2) in Maryland, the Piedmont (1) in Maryland and Pennsylvania, and in the Appalachians (3) in Pennsylvania and New York. Clusters were selected to avoid urbanized areas, but included forest, cropland, pastureland, and residential areas. The sampling times included before, during, and after the record spring Susquehanna River freshet of 1993. Concentrations of nitrate and dissolved ammonium were measured in all samplings of all subwatersheds, while dissolved organic nitrogen was measured on a subset of sites. Differences in concentrations of dissolved nitrogen fractions were related to the proportion of forest versus agriculture on the subwatersheds and to geological differences among clusters. Although little nitrate was discharged from any of the forested watersheds, high concentrations were discharged from agricultural watersheds. The concentrations of nitrate discharged from agricultural watersheds were highest in the Great Valley, followed by the Ridge and Valley, Piedmont, Coastal Plain, and Appalachian Plateau. Concentrations of dissolved ammonium were 20-fold lower than nitrate and there was less variation among sites, but the Conestoga River usually had the highest and Owego Creek the lowest concentrations. Concentrations of dissolved organic nitrogen were higher than ammonium concentrations but 10-fold lower than nitrate concentrations. For primarily forested watersheds, nitrate concentrations were much lower. Coastal Plain forests had the lowest nitrate concentrations, but the highest ammonium concentrations. Dissolved organic nitrogen concentrations were much less variable among both forested and agricultural watersheds and thus constituted a larger proportion of total nitrogen in streams draining forested sites.
Water, Air, & Soil Pollution, 2011
Land use and its relation to nutrient concentrations and loading via streams is an important issue in coastal lagoons and embayments worldwide including the Maryland coastal bays system, USA. As in many coastal areas around the globe, declining water quality in the bays is the result of nutrient inputs from the surrounding watershed. In this study, the sources of the nutrient inputs were examined. Monthly concentrations of total nitrogen (TN), ammonium (NH 4 + ), nitrate (NO 3 -), phosphate (PO 4 -3
Digital data used to relate nutrient inputs to water quality in the Chesapeake Bay watershed
Open-File Report, 1999
Introduction Purpose and scope Acknowledgments Data sets Water-quality data Segmented-watershed network Nutrient-input sources Atmospheric deposition Septic systems Point sources Land use and land cover Agricultural sources Land-surface characteristics Precipitation Temperature Slope Soil permeability Hydrogeomorphic regions Nutrient yield estimates Summary Selected References Appendix Metadata for data sets FIGURES Maps showing: 1. The Chesapeake Bay watershed and surrounding area 2. Streamflow data-collection sites used to estimate stream-nutrient loads in the Chesapeake Bay watershed, 1992 3. A segmented-watershed network used in the Chesapeake Bay watershed, 1992 4. Atmospheric deposition in the Chesapeake Bay region, 1992 5. Loads of nitrogen from septic systems in the Chesapeake Bay watershed, 1990 8 6. Average-annual loads of nitrogen and phosphorus from point-source discharge in the Chesapeake Bay watershed, 1992 7. Land use and land cover in the Chesapeake Bay watershed modified from Multi Resolution Land Characterization (MRLC), 1992 8. Land use and land cover in the Chesapeake Bay watershed modified from the Chesapeake Bay Program 10 9. Loads of nitrogen from manure and commercial fertilizer applied to agricultural land in the Chesapeake Bay watershed, 1992 10. Loads of phosphorus from manure and commercial fertilizer applied to agricultural land in the Chesapeake Bay watershed, 1992 11. Average-annual precipitation in the Chesapeake Bay region v 12. Average-annual temperature in the Chesapeake Bay region 12 13. Slope shown as percentages in the Chesapeake Bay region 14. Soil permeability in the Chesapeake Bay watershed 13 15. Hydrogeomorphic regions in the Chesapeake Bay watershed 13 16. Incremental yields of total nitrogen and total phosphorus from all sources in the Chesapeake Bay Watershed, 1992 13 17. Delivered yields of total nitrogen and total phosphorus from all sources in the Chesapeake Bay Watershed, 1992 13 18. Total yields of total nitrogen and total phosphorus from all sources in the Chesapeake Bay Watershed, 1992 13
Estuaries and Coasts, 2017
Nutrient inputs have degraded estuaries worldwide. We investigated the sources and effects of nutrient inputs by comparing water quality at shallow (< 2m deep) nearshore (within 200 m) locations in a total of 49 Chesapeake subestuaries and Mid-Atlantic coastal bays with differing local watershed land use. During July-October, concentrations of total nitrogen (TN), dissolved ammonium, dissolved inorganic N (DIN), and chlorophyll a were positively correlated with the percentages of cropland and developed land in the local watersheds. TN, DIN, and nitrate were positively correlated with the ratio of watershed area to subestuary area. Total phosphorus (TP) and dissolved phosphate increased with cropland but were not affected by developed land. The relationships among N, P, chlorophyll a, and land use suggest N limitation of chlorophyll a production from July-October. We compared our measurements inside the subestuaries to measurements by the Chesapeake Bay Program in adjacent estuarine waters outside the subestuaries. TP and dissolved inorganic P concentrations inside the subestuaries correlated with concentrations outside the subestuaries. However, water quality inside the subestuaries generally differed from that in adjacent estuarine waters. The concentration of nitrate was lower inside the subestuaries, while the concentrations of other forms of N, TP, and chlorophyll a were higher. This suggests that shallow nearshore waters inside the subestuaries import nitrate while exporting other forms of N as well as TP and chlorophyll a. The importance of local land use and the distinct biogeochemistry of shallow waters should be considered in managing coastal systems.
Estuaries, 1992
Human activities on coastal watersheds provide the major sources of nutrients entering shallow coastal ecosystems. Nutrient loadings from watersheds are the most widespread factor that alters structure and function of receiving aquatic ecosystems. To investigate this coupling of land to marine systems, we are studying a series of subwatersheds of Waquoit Bay that differ in degree of urbanization and hence ;ire exposed to widely different nutrient loading rates. The subwatersheds differ in the number of septic tanks and the relative acreage of forests. In the area of our study, groundwater is the major mechanism that transports nutrients to coastal waters. Although there is some attenuation of nutrient concentrations within the aquifer or at the sediment-water interface, in urbanized areas there are significant increases in the nutrient content of groundwater arriving at the shore's edge. The groundwater seeps or flows through the sediment-water boundary, and sufficient groundwater-borne nutrients (nitrogen in particular) traverse the sediment-water boundary to cause significant changes in the aquatic ecosystem. These loading-dependent alterations include increased nutrients in water, greater primary production by phytoplankton, and increased macroalgal biomass and growth (mediated by a suite of physiological responses to abundance of nutrients). The increased macroalgai biomass dominates the bay ecosystem through second-or third-order effects such as alterations of nutrient status of water columns and increasing frequency of anoxic events. The increases in seaweeds have decreased the areas covered by eelgrass habitats. The change in habitat type, plus the increased frequency of anoxic events, change the composition of the benthic fauna. The data make evident the importance of bottom-up control in shallow coastal food webs. The coupling of land to sea by groundwater-borne nutrient transport is mediated by a complex series of steps; the cascade of processes make it unlikely to find a oneto-one relation between land use and conditions in the aquatic ecosystem. Study of the process and synthesis by appropriate models may provide a way to deal with the complexities of the coupling.
Base Flow Nutrient Discharges from Lower Delmarva Peninsula Watersheds of Virginia, USA
2070 Proper management of shallow coastal systems, which are vulnerable to nutrient enrichment, requires knowledge of land use impacts on nutrient discharges. Th is study quantifi ed base fl ow nutrient concentrations and yields for 1 yr (May 2001–April 2002) from 14 fi rst-order streams on the Virginia Eastern Shore (VaES) on the Delmarva Peninsula and assessed their relationships with land cover and soil drainage class in their watersheds. Base fl ow water discharge rates (1.4–31.5 cm yr −1) were likely lower than the long-term average due to a severe drought. Seasonal mean nitrate concentrations were higher in winter, while mean dissolved organic carbon and ammonium concentrations were higher in summer. Annual base fl ow-weighted mean total dissolved nitrogen (TDN) concentrations were positively related to percent (%) agricultural land cover (r 2 = 0.43; p = 0.02) and % very poorly drained soils (r 2 = 0.51; p = 0.009) and negatively related to % forested land cover (r 2 = 0.54; p = 0.005). Patterns of base fl ow TDN yields were similar to those of concentrations but were also positively related to % developed land cover (r 2 = 0.40; p = 0.03). Agricultural and developed land covers, together with very poorly drained soil, accounted for 91% of the variability of TDN yields (p = 0.0001). Using a multiple regression model, the base fl ow TDN loading rate to a coastal lagoon on the VaES, a system vulnerable to nutrient enrichment, was estimated to be 28,170 kg N yr −1 .