Influences of Spatial Scale and Soil Permeability on Relationships Between Land Cover and Baseflow Stream Nutrient Concentrations |
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Authors: | F Bernard Daniel Michael B Griffith Michael E Troyer |
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Institution: | (1) National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, 26 W. Martin Luther King Drive, Cincinnati, OH 45268, USA;(2) National Center for Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency, 26 W. Martin Luther King Drive, Cincinnati, OH 45268, USA |
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Abstract: | The Little Miami River (LMR) basin, dominated by agriculture, contains two geologically-distinct regions; a glaciated northern
till plain with soils three times more permeable than a southern, pre-Wisconsinan drift plain. The influences of two landscape
measures, percent row crop cover (%RCC, computed at three spatial scales), and soil permeability (PERM), on baseflow nutrient
concentrations were modeled using linear regressions. Quarterly water samples collected for four years were analyzed for nitrate-N
(NN), Kjeldahl-N (KN), total-N (TN), and total-P (TP). In till plain streams (n = 17), NN concentrations were 8.5-times greater than drift plain streams (n = 18), but KN and TP were 20–40% lower at comparable %RCC. These differences resulted in TN/TP molar ratios >80 in till plain
streams, but <6 in drift plain streams. For till plain steams regression models based on %RCC accounted for 79% of the variance
in NN concentrations but only 27% in drift plain streams. However, regressions on %RCC accounted for 68–75% of the KN and
TP concentration variance in the drift plain streams but essentially none in the till plain. Catchment PERM influenced the
regional NN/KN ratios which were 10-fold higher in the drift plain streams. For both till and drift streams the catchment
scale %RCC gave the best predictions of NN, a water soluble anion, but the smaller spatial scales produced better models for
insoluble nutrient species (e.g., KN and TP). Published literature on Ohio streams indicates that these inter-regional differences
in nutrient ratios have potential implications for aquatic biota in the receiving streams. |
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