Arbuckle, K. E. Iowa StateUniversity, karbuck@iastate.edu
Downing, J. E. Iowa State University, downing@iastate.edu

 
THE INFLUENCE OF LANDUSE ON LAKE N:P IN A PREDOMINANTLY AGRICULTURAL LANDSCAPE
 
Agricultural activities are well known to impact both nutrient export rates and the N and P composition of runoff. A recent stoichiometric model proposes that surface waters in agricultural drainage basins should have low N:P. However, different agricultural production systems employ practices that can yield widely divergent ratios of major nutrients. Livestock operations tend to yield manure leachates with sub-Redfield N:P, whereas row-crop production culture (e.g., maize, soja) employs nitrogen-biased amendments (e.g., anhydrous ammonia, ammonium nitrate) which can result in extremely high N:P (e.g., >200 by mass). Lakes in predominantly agricultural regions should therefore have N:P correlated with agricultural landuse. We studied 115 lakes in Iowa relating average seasonal N:P stoichiometry to drainage basin characteristics. Seasonal average N:P in these lakes varied from 4 to >100 (as mass). Lakes in basins dominated by row-crop agriculture had significantly higher N:P than those with large amounts of pasturelands. These impacts were greater in basins with relatively high hydraulic loads and less pronounced in basins with higher evapotranspiration.
 
Day: Tuesday, Feb. 2
Time: 11:15 - 11:30am
Location: Sweeney Center
 
Code: SS07TU1115S