Effects of Land Use Upon the Water Quality of Two Buena Vista Drainage Ditches

Abstract

A 16-month study was conducted on two ditches which drain a portion of the Buena Vista Marsh (Portage County, Wisconsin) to characterize water quality and determine nutrient loading from various land uses in the watershed. Surface samples and test wells revealed significant quantities of nitrate-N (averaging 7.60 mg/1) in the runoff from cropped land, and much lower concentrations in runoff from actively grazed pasture and idle land. Estimated annual losses of N and P from the heavily cropped headwater areas were 14.2 kg/haN and 0.09 kg/ha P. Losses from the grassland area were 5.1 kg/ha N and 0.04 kg/ha P, which accounted for decreasing concentrations at downstream sites. Because virtually all flow in the ditches originates as ground water discharge, N:P ratios were considerably higher (averaging 195:1) than has been reported in the . recent literature. Seasonal changes in chemical parameters were attributed primarily to nutrient loading differences and respiration and photosynthetic activity of aquatic organisms.