Nutrient Dynamics in a Small Agricultural Lake Erie Tributary

Abstract

ABSTRACT This study examined how land use, water level fluctuations of Lake Erie, and discharge all affect seasonal nutrient concentrations and delivery on Crane Creek, a small agricultural tributary of Lake Erie in Northwest Ohio. Seventeen sites were sampled in the Crane Creek watershed from May to November 2004 and April to June 2005. These sites were chosen to capture the variability of land use in the watershed and included potential point sources, catchments with a variety of land uses, sites within the Ottawa National Wildlife Refuge, and a near-shore Lake Erie site. Hydrologic measurements along with water samples were taken at each site and evaluated for nitrite-nitrate nitrogen, SRP, ammonia nitrogen, and several other water quality parameters. There were three major findings. First, both water level fluctuations driven by Lake Erie seiches and higher discharge make the downstream sites less spatially and temporally variable than the upstream sites. The downstream sites also had higher water quality because of wetland transformation of nutrients and dilution from lake water inflow. Second, while agricultural and urban land use likely contribute nutrients from fertilizer use and urban runoff, point sources in the catchment seem to have a greater influence on water quality in Crane Creek, particularly in times of low stream discharge. The influence of varying patterns of land use was difficult to determine because homogeneity of the landscape and point sources confounded the analysis. Finally, within the lower estuary, water quality in the system was similar to water quality in surrounding diked pools. This similarity makes hydrologic reconnection of these wetlands a possibility, although physical constraints complicate the restoration process. These findings have implications for other small Lake Erie tributaries.