A study was undertaken to evaluate the suitability of the SLURP hydrological model for simulating the hydrology of the Saint Esprit watershed (26 km 2) in Quebec. Climatic data and other input were made available through a monitoring program set up in the watershed from 1994 to 1998. GIS was used to store, analyze and export the watershed information into the model. The continuous semi-distributed model SLURP was calibrated using three years of data (1994--1996). Parameter calibration, except that of snowpack melt-rate, was done through an automatic optimization technique. The model was validated using graphical outputs, the Nash/Sutcliffe (R2) coefficient of performance for daily runoff, and the percent difference of predicted versus computed runoff on a monthly, seasonal and annual basis. Additionally, the evapotranspiration (ET) component of the model was compared with an ET estimated using the Baier & Robertson model (BR) calibrated for the region. (Abstract shortened by UMI.)

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The purpose of this study was to determine how much phosphorus could be lost from soils in Quebec. Samples of four soil series and 3 sediment samples from the St. Esprit watershed, Quebec, Canada were treated with KH2PO 4 solutions of 0, 50,100, and 500 mg kg--1 of soil. The relationship between water-extractable phosphorus (soluble phosphorus) and Mehlich III available phosphorus was determined at water: soil ratios 100:1, 200:1, 500:1. Measurements were made on a LACHAT QuickChem AE instrument (based on EPA method 365.3; USEPA, 1983) after 4 hours of shaking. More than 90% of the soluble phosphorus was released after 3 hours of shaking for all the soil samples and the sediment sample. Therefore, the shaking time for release of soluble P was set at 4 hours for all soil groups of the watershed. Mehlich III extractable phosphorus was also determined for each soil and sediment sample. Using a modified form of a well-known equation, it was possible to show that, with appropriate values for the constants, linear relationships exist between the logarithm of soluble phosphorus and the logarithm of Mehlich III extractable phosphorus at different water soil ratios. This was true for all soil groups and the sediment sample. Thus, given the soil type of a particular watershed, and using the linear relationship (isotherm) for that type, it becomes possible to predict the phosphorus yields from agricultural lands with reasonable confidence.

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The Saint-Esprit watershed project was initiated to address the issue of nonpoint source agricultural pollution and relies on the adoption of sustainable practices tested on-farm by willing farmers. To study the economic impact of an increasing erosion constraint at the farm and the watershed scales, four Mixed Integer Linear Programming (MILP) models, corresponding to three selected farms and the watershed, were built. The models maximize the sum of field net margins subject to singleness of field use, animal nutrient requirements, and erosion. / Scenario results show that increasing the erosion constraint: (1) reduces soil loss from agricultural production; (2) forces cropping patterns and farming practices to change; (3) reduces profits; and (4) induces marginal and average costs to increase at an increasing rate. Also, with comparable average soil losses per hectare, farms with lower net margins would be worse off if the erosion target was set at the watershed level.

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