Effects of Urban and Non-Urban Land Cover on Nitrogen and Phosphorus Runoff to Chesapeake Bay
Allen
D
Roberts, University of Maryland at College Park, allenr@umd.edu
(Presenting)
Stephen
D
Prince, University of Maryland at College Park, sprince@umd.edu
The aim of this study was to determine the effects of catchment and riparian stream buffer-wide urban and non-urban land cover/land use (LC/LU) on total nitrogen (TN) and total phosphorus (TP) runoff to the Chesapeake Bay. In particular, the effects of the composition and configuration of LC/LU patches were explored. A hybrid statistical-process model, the SPAtially Referenced Regression On Watershed Attributes (SPARROW), was calibrated with year 2000 Chesapeake Bay watershed-wide land surface data. SPARROW estimates average annual discharges. Two variables were predicted: 1) yield per unit area and 2) mass delivered to the upper estuary. The 166,534 km2 watershed was divided into 2339 catchments averaging 71 km2. LC/LU was described using sixteen classes applied to each entire catchment and confined to riparian buffers. Seven sophisticated landscape metrics of each LC/LU class were tested. In all, 167 (TN) and 168 (TP) LC/LU class metric combinations were tested in each model calibration run. Runs were made with LC/LU in six riparian buffer widths (31, 62, 125, 250, 500, and 1000 m) and each entire catchment. A 31 m riparian stream buffer width model most adequately accounted for mean annual TN (r2 =.9366) and TP (r2 =.7503) yield. TN and TP loadings estimated to enter the Chesapeake Bay were 1.449 x 108 and 5.367 x 106 kg/yr, respectively. Five of the 167 TN and three of the 168 TP metrics were shown to be either significant (p value ≤ 0.05) descriptors of non-point sources or land-to-water delivery variables. This is the first demonstration of the significance of riparian LC/LU in a Chesapeake Bay-wide water quality simulation. Furthermore, these metrics were also significantly correlated to helping improve the precision of estimated TN and TP annual loadings to the Chesapeake Bay. Findings that also suggest changes in land management that may be beneficial in similar watersheds elsewhere.
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