NUTRIENT GEOCHEMISTRY OF LAKES AND RESERVOIRS IN NORTH-CENTRAL OHIO: PHYSICAL AND ANTHROPOGENIC CONTROLS

Aquatic ecosystems are particularly vulnerable to environmental change and many are currently under pressure from direct human impacts such as hydraulic modifications, channelization, water abstraction, eutrophication and climate change. A recent national assessment revealed that almost a quarter of lakes and reservoirs across the lower 48 states are in poor biological condition. This study also shows that poor habitat conditions along the lakeshore and high levels of plant nutrients (nitrogen and phosphorus) are the most significant stressors of lakes and reservoirs in the US. About 20% of all lakes/reservoirs evaluated in the study contain high levels of nutrients, mostly resulting from anthropogenic pressure. This human-induced eutrophication affects the water quality and the ecosystem structure and function of these freshwater habitats. It can also have a significant economic impact due to losses in recreational water usage, waterfront real estate, spending on recovery of threatened and endangered species, and drinking water. Recent estimates have suggested that the economic losses due to eutrophication of US freshwaters are over $2 billion annually. Therefore, assessing the physical and anthropogenic controls on the water quality of lakes/reservoir is a critical challenge for both environmental scientists and water resource managers. Here we present the preliminary results of an ongoing study to determine the trophic state of nine lakes and reservoirs in north-central Ohio, as well as the physical and anthropogenic factors controlling the spatial and seasonal changes on the nutrient dynamic in these systems. We evaluate the influence of land and water use, geology, vegetation, snowmelt, precipitation and atmospheric deposition on the water quality in these lakes, and what are the sources and sinks of nutrients and the magnitude of these material fluxes. The surface area of the studied lakes/reservoirs varies from 28 to 1350 acres. They are nested in mixed-use catchments, with some being surrounded by parks, state forests, and wilderness areas, and others by cropland and developed landscapes. Since this is the first time these ecosystems are being assessed, we also evaluated the geochemistry of major ions (Mg²⁺, Ca²⁺, Na⁺, K⁺, Cl^-, SO₄^2-) and trace elements concentration on all nine lakes/reservoirs.