Watershed land use controls on chemical inputs to lake ontario embayments.

There is considerable interest in understanding the role of land use in controlling surface water quality. This study was conducted to assess the role of land cover in regulating temporal and spatial patterns in nutrients and major solutes in rivers that drain into Lake Ontario. Water samples were collected monthly from 22 river sites in subwatersheds of eight embayments along the New York coast of Lake Ontario over the period 2001-2003. Samples were analyzed for nutrients and major solutes. The land cover of the subwatersheds was varied, but largely a mixture of forest and agricultural lands. Rivers draining largely agricultural lands exhibited distinct seasonal patterns, particularly for nutrients. Nitrate and total nitrogen (TN) concentrations were generally low during the summer growing season, increased markedly during fall and decreased during winter and spring. Total phosphorus (TP), dissolved organic carbon (DOC), and most ion (Na(+), K(+), Ca(2+), Mg(2+), Cl(-), SO(4)(2-)) concentrations varied with seasonal discharge patterns. Distinct spatial patterns were observed in river solute concentrations that closely corresponded with land use. Solute concentrations increased markedly with increases in the percentage of the watershed occurring as agricultural lands. Such a pattern has been commonly observed for nutrients (e.g., TP, TN, NO(3)(-)), but this relationship was also evident for most non-nutrient solutes (e.g., DOC, Ca(2+), F(-), SO(4)(2-)), a pattern which has not previously been reported. These observations suggest that agricultural activities mobilize most major elements, enhancing transport across the temperate landscape and impacting downstream water resources, including embayments and the Lake Ontario ecosystem.