Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/20/2001
Publication Date: 10/20/2001
Citation: Lindsey, B.D., Gburek, W.J., Folmar, G.J. 2001. Watershed scaling effect on base flow nitrate, valley and ridge physiographic province. Journal of the American Water Resources Association. 37(5):1103-1117. Interpretive Summary: Nitrogen loss from agriculture to streamflow is of concern because of its role in promoting eutrophication. To study the role of land-use distribution and watershed scale in controlling nitrate in streamflow, flow and nitrate concentrations were measured simultaneously in 51 subwatersheds of the 116-sq-km Mahantango Creek Watershed near Klingerstown, PA. The purpose of the study was to see if observations previously made within a smaller watershed area were extendable to a larger scale. Detailed land use data was available for the small watershed scale from farmer surveys, but for the large watersheds, the only land use data available was from satellite observations. A stream nitrate prediction model developed for the small watershed based on the detailed land use data was shown to work equally well for the larger watershed scale using the satellite data, suggesting that the differences in the two land-use data sources were minimal when used for prediction of nitrate concentrations. The study showed that the variability in flow and nitrate concentrations in larger streams is dominated by the inputs from the smaller contributing watersheds rather than the contribution of ground water discharge directly to the larger streams. Further, we found that a relatively simple categorization of agricultural land use can be used to predict nitrate concentrations in the larger streams.
Technical Abstract: A study of stream base flow and NO3-N concentration was conducted simultaneously in 51 subwatersheds within the 116-sq-km watershed of East Mahantango Creek near Klingerstown, PA. The study was designed to test whether processes and observations within the smaller watersheds were similar to or transferable to a larger scale. Ancillary data on land use were available for both the small and large watersheds. Although the source of land-use data was different for the small and larger watersheds, comparisons showed that the differences in the two land-use data sources were minimal. A land use-based water-quality model developed for the small-scale 7.3-sq-km watershed for a previous study accurately predicted NO3-N concentrations from this sampling in the same watershed. The water- quality equation was modified, and using the imagery-based land use, was found to accurately predict NO3-N concentrations in the subwatersheds of the large-scale 116-square-kilometer watershed as well. Because the model accurately predicts NO3-N concentrations at both small and large scales, it is likely that in second-order streams and higher, discharge of water and NO3-N is dominated by flow from smaller first-order streams and the contribution of ground-water discharge to higher order streams is minimal at the large scale.