Influences of spatial scale and soil permeability on relationships between land cover and baseflow stream nutrient concentrations.
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.
Daniel
F Bernard
FB
National Exposure Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, Cincinnati, OH 45268, USA. daniel.bernie@epa.gov
Griffith
Michael B
MB
Troyer
Michael E
ME
D000383:Agriculture; D000818:Animals; D005843:Geography; D016014:Linear Models; D009820:Ohio; D010539:Permeability; D011891:Rain; D045483:Rivers / Q000737:chemistry*; D012987:Soil
D012987:Soil