Effects of land use on water quality of cold-water streams in the driftless area of the midwestern U.S.

Abstract

Streams are important ecosystems that affect the dynamics of downstream ecosystems. Increased nutrient input and changes to land cover have altered the natural functioning of streams. The purpose of our study was to examine the seasonal and spatial relationships between land cover and nutrients in streams across the Driftless Area. We hypothesized that streams dominated by agricultural land use would have higher N, dominated by nitrate. We investigated if a threshold occurred as N changed in response to land cover and as percent NO3 --N changed in response to TDN. We sampled 77 streams in fall 2012, and winter, spring, and summer 2013. TDN ranged from 0.145 to 25.0 mg/L with higher concentrations in agricultural streams. Nitrate dominated the TDN pool in most streams. Land use was not a strong predictor of TDP or DOC, and concentrations were variable across seasons. A threshold occurred at 49.15% forested and 80.55% agricultural land use in response to TDN. We estimated water quality criteria to be between 1.7 to 2.1 mg/L TDN based on these results. Our results suggest that N saturation is likely occurring in streams in the DA, which could lead to an increase in export of N to downstream ecosystems.