SWAT ver. 2000 was used to predict hydrographs, and sediment, nitrate and total phosphorus loadings from a 1349 km 2 mountainous/ agricultural watershed in Northern Greece. The model was calibrated and verified using continuous meteorological data from eight stations within the drainage area, and runoff, sediment and nutrient concentrations measured at nine stations located within the main tributaries of the watershed, for the time period from May 1st, 1998 to January 31st, 2000. Model validation methodology and resulting input parameters appropriate for Mediterranean drainage basins are presented. Predicted by the model hydrographs, sedimentographs and pollutographs are plotted against observed values and show good agreement. Model performance is evaluated using the root mean square error computation and scattergrams of predicted versus observed data. The validated model is also used to test the effectiveness of three alternative cropping scenarios in reducing nutrient loadings from the agricultural part of the watershed. The study showed that this model, if properly validated, can be used effectively in testing management scenarios in Mediterranean drainage basins.

Water quality data from two different monitoring periods are used to evaluate the trophic state and effectiveness of various protective measures on the restoration of a eutrophic, coastal Mediterranean lagoon. Main protective measures included elimination of municipal/industrial raw wastewater discharges in the rivers outflowing to the lagoon, sediment/erosion control practices in the lagoon's drainage basin (i.e., construction of sediment/debris dams and grade control structures, reforestation and ban on livestock grazing), and reduction of fertilizer application quantities as a result of changes in crops. Water quality data include, among others, chlorophyll a, dissolved oxygen and nutrient concentrations, various physicochemical parameters, and transparency, measured during two monitoring periods, i.e., before and after (1998-99) implementation of protective measures. Rainfall depth for the two time periods was also available. Empirical equations were developed, from statistical analyses of the data, relating the water quality parameters during the two monitoring periods. These models help identify water quality trends. Based on the analyses, it seems that measures were effective in reducing sediments transported into the lagoon. However, the lagoon remains eutrophic to hypereutrophic, mostly due to phosphorus released in the water column from bottom sediments. Therefore, future restoration efforts should be directed towards the management of bottom sediments.

The USEPA WASP5 modeling system was applied to simulate and evaluate the relationships between external and internal nutrient loadings and water quality of Vistonis lagoon, North Greece for a 2-year time period. The hydrodynamic model DYNHYD5 was calibrated to estimate daily lagoon water level. The water quality models TOXI5 and EUTRO5 were calibrated and verified using meteorological data from a station near the lagoon, and field data (salinity, dissolved oxygen, nutrients and chlorophyll-a concentrations) from seven stations located in the lagoon, for the time period April 1998 to May 1999. Predicted by the model salinity, dissolved oxygen, total phosphorus, total inorganic nitrogen and chlorophyll-a were plotted against observed values and showed good agreement. Model performance was evaluated using scattergrams of predicted versus observed values and the Kolmogorov-Smirnov two-sample goodness-of-fit test at p < 0.05. Sediment sources of nitrogen and phosphorus were important to achieve a successful model calibration. The validated model was also used to test the effectiveness of alternative management scenarios in relation to improvement of the trophic state of the lagoon.

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