Factors Affecting Iowa Lake and Reservoir Water Quality

Abstract

ABSTRACT Iowa lake and reservoir water quality data collected during the summers of 1990 and 1992 were analyzed according to origin (lake vs. reservoir) and location, updating previous synoptic surveys. Morphometric comparisons between Iowa regions indicate unique characteristics for reservoirs, glacial lakes, oxbow lakes, and waterbodies on the Des Moines glacial lobe. All Iowa lakes and reservoirs are eutrophic although there is a significant range of water quality and within-region variability. Parameters such as chlorophyll a, total phosphorus (TP), and total nitrogen (TN) summer mean concentrations were highest on the Des Moines glacial lobe (means of 64 μg L−1, 164 μg L−1, and 4.4 mg L−1, respectively). A comparison of northern Iowa versus southern Minnesota lakes and southern Iowa versus northern Missouri reservoirs indicated that Iowa water quality is more eutrophic in both instances. Northern Iowa lakes had higher TN (3.0 mg L−1), total suspended solids (TSS, 39 mg L−1), and non-volatile suspended solids (NVSS, 18 mg L−1) summer mean concentrations than southern Minnesota lakes (2.1 mg L−1, 14 mg L−1, and 3 mg L−1, respectively). Southern Iowa reservoirs had higher TP (149 μg L−1), TN (1.8 mg L−1), TSS (34 mg L−1), and NVSS (25 mg L−1) summer mean concentrations than northern Missouri reservoirs (47 μg L−1, 0.7 mg L−1, 10 mg L−1, and 7 mg L−1, respectively).