Abstract
Seven agricultural watersheds in southwestern Quebec and southeastern Ontario, ranging in area from 2,000 to 20,000 hectares, were monitored systematically during 1973–75 for soluble inorganic nitrogen, total soluble phosphorus, calcium, magnesium, potassium, sulfate-sulfur, chemical oxidation demand, discharge, suspended sediment concentration, sediment Kjeldahl nitrogen, Bray extractable phosphorus, and ammonium acetate extractable calcium, magnesium and potassium.
For 1974–75, annual Kg/ha, loss rates were calculated for the soluble and sediment associated nutrients. Losses varied with nutrient and watershed, with volume of runoff being an important control of nutrient loss variation. Significant amounts of SO4−S in precipitation were suggested by an average watershed soluble N:P:S loss ratio of 10:1:92. Sediment nutrient losses were especially important for N and P, comprising over 40% of their total loss. The importance of spring snow-melt runoff was demonstrated by the high proportion of all nutrients lost at this time. Correlations of nutrient loss, land use and soils suggested that certain land uses resulted in increased stream nutrient losses while increased watershed area of soils with a high surface runoff potential was particularly conducive to increased soluble nutrient and sediment losses.
NITROGEN EXPORT FROM FORESTED AND AGRICULTURAL WATERSHEDS OF SOUTHERN CHILE