Objectives
- Examine land use and hydrology effects on pesticide and nutrient loads to streams.
- Improve estimates of nutrient reduction efficiency values for the widely accepted agricultural Best Management Practices (BMPs) within the Choptank.
- Utilize watershed water quality models to examine conservation practice implementation scenarios to achieve water quality improvements.
- Foster positive relationships with farmers, stakeholders, and customers to preserve the natural resources of the Chesapeake Bay Watershed.
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| Figure 1: Map of sampling sites. |
Photo 1: NOAA personnel taking water quality measurements in Choptank River. |
Project Summary
Excess nutrients and agrochemicals from non-point sources contribute to water quality impairment in the Chesapeake Bay watershed, with loading rates related to land use, agricultural practices, hydrology, and pollutant fate and transport processes. Under the auspices of USDA’s Conservation Effects Assessment Project (CEAP), a study was conducted to examine water quality in the Choptank River estuary, a tributary of the Chesapeake Bay that, since 1998, has been classified as “impaired” under the Federal Clean Water Act.
Subwatershed Near Tidal Sampling
Monthly baseflow stream samples from 15 agricultural subwatersheds of the Choptank River, Maryland (2005 to 2007) were characterized for nutrients, herbicides, and transformation products. Streams were gauged to determine loading rates. High resolution digital maps of land use and hydrologic features were derived from remote sensing imagery. Mean nitrate concentrations (overall mean 4.9 mg/L) were correlated positively with percent agriculture (R2 = 0.60) and negatively with percent forest (R2 = 0.75); however, concentrations were higher in the well-drained upland (WDU) subwatersheds than in poorly-drained upland (PDU) subwatersheds (p = 0.02) suggesting increased denitrification in the PDU landscape due to prevalence of hydric soils. Springtime atrazine concentrations (overall mean 0.29 µg/L) were higher in WDU subwatersheds where riparian stream buffers were prevalent than in PDU subwatersheds where forested patches are typically not near streams (p = 0.02). Strong correlation with percent forest in the WDU subwatersheds provided evidence for capture of herbicide drift by the riparian forest canopy and subsequent wash-off during rainfall. Loading rates for atrazine, metolachlor, metolachlor ethane sulfonic acid, and nitrate ranged from 0.1-7 g/y/ha, 0.2-2.7 g/y/ha, 6-89 g/y/ha, and 8-100 kg/y/ha, respectively.
Project Component 2: Tidal Estuary Sampling
Multiple water quality parameters (salinity, temperature, dissolved oxygen, chlorophyll a) and analyte concentrations (nutrients, herbicide and herbicide degradation products, arsenic, and copper) were measured at seven sampling stations in the Choptank River estuary. Samples were collected under base flow conditions in the basin on thirteen dates between March 2005 and April 2008. As commonly observed, results indicate that agriculture is a primary source of nitrate in the estuary and that both agriculture and wastewater treatment plants are important sources of phosphorus. Concentrations of copper in the lower estuary consistently exceeded both chronic and acute water quality criteria, possibly due to use of copper in antifouling boat paint. Concentrations of copper in the upstream watersheds were low, indicating that agriculture is not a significant source of copper loading to the estuary. Concentrations of herbicides (atrazine, simazine, and metolachlor) peaked during early-summer, indicating a rapid surface-transport delivery pathway from agricultural areas, while their degradation products (CIAT, CEAT, MESA, and MOA) appeared to be delivered via groundwater transport. Some in-river processing of CEAT occurred, whereas MESA was conservative. Observed concentrations of herbicide residues did not approach established levels of concern for aquatic organisms. Results of this study highlight the importance of continued implementation of best management practices to improve water quality in the estuary. This work provides a baseline against which to compare future changes in water quality and may be used to design future monitoring programs needed to assess restoration strategy efficacy.
Products & Services
David Whitall, W. Dean Hively, Andrew K. Leight, Cathleen J. Hapeman, Laura L. McConnell, Thomas Fisher, Clifford P. Rice, Eton Codling, Gregory W. McCarty, Ali M. Sadeghi, Anne Gustafson and Krystyna Bialek. 2010. Pollutant fate and spatio-temporal variability in the Choptank River estuary: Factors influencing water quality Science of the Total Environment. Available online at: http://dx.doi.org/10.1016/j.scitotenv.2010.01.006
G.W. McCarty, L.L. McConnell, C.J. Hapeman, A. Sadeghi, C. Graff, W.D. Hively, M.W. Lang, T.R. Fisher, T. Jordan, C.P. Rice, E.E. Codling, D. Whitall, A. Lynn, J. Keppler, and M.L. Fogel. 2008. Overview of the Choptank River watershed conservation effectiveness assessment project. Journal of Soil and Water Conservation. 63:461-474. Abstract available online at: http://www.jswconline.org/content/63/6/461.abstract
Hively D, Hapeman CJ, McConnell LL, Fisher TR, Rice CP, McCarty GW, Sadeghi AM, Whitall DR, Downey PM, Niño de Guzmán GT, Bialek-Kalinski K, Lang MW, Gustafson AB, Sutton AJ, Sefton KA, Harman Fetcho JA. 2011. Relating nutrient and herbicide fate with landscape features and characteristics of 15 subwatersheds in the Choptank River watershed. Science of the Total Environment 409: 3866-78. Available online at: http://www.sciencedirect.com/science/article/pii/S0048969711005274
Partners
Relevant Links
Time Frame
Completed January 2010
For More Information
Project Manager:
Dave Whitall@noaa.gov
1305 East West Highway
SSMC-IV, N/SCI-1
Silver Spring, MD 20910
301-713-3028 x138