**2. Materials and methods**

108 Studies on Water Management Issues

with surface runoff, depending on the geology and soil type. N leaching occur during wet periods of the year, after crops are harvested, fertilizers and mineralized crop biomass residues are exposed to leaching (Glavan & Pintar, 2010), and when N is not actively

Phosphorus (P) is known as the limiting factor in eutrophication of freshwater ecosystems (Khan & Ansari, 2005). P is a macronutrient required for the life of all living cells that plants

of P fertilizers may lead to P soil saturation, causing P transport with runoff bound to soil particles or through drainage (Bowatte et al., 2006). Most P in inland waters is contributed by point sources (wastewater treatment plants). Due to advances in wastewater, P stripping

Computer models in modern integrated catchment management are indispensable for studying the levels of pollutants from diffused sources, as they are capable of merging different spatial and environmental data (Dymond et al., 2003; Kummu et al., 2006). Catchment models can be divided into empirical-statistical (GLEAMS, MONERIS, N-LES), physical (WEPP, SA) and conceptual (distributed or partially distributed - SWAT, NL-CAT, TRK, EveNFlow, NOPOLU, REALTA) (Hejzlar et al., 2009; Kronvang et al., 2009a). Models connected with the Geographic Information System (GIS) has gained new values, as they are

Agricultural Research Service (ARS) of the U.S. Department of Agriculture is very active in developing models for agricultural hydrology, erosion and water quality. The Soil and Water Assessment Tool (SWAT) model was developed to assist the water managers in examining the impacts of agricultural activities in catchments (Arnold et al., 1998). The SWAT model is widely used for modelling the hydrology in terms of quantity of water (discharge, soil water, snow and water management), quality of water (land use, production technologies, good agricultural practices, agri-environmental measures) and the effects of climate changes (Gassman et al., 2007; Krysanova & Arnold, 2008). This model enables the modelling of long-term (more than 25 years) effects of agri-environmental measures (Bracmort et al., 2006). SWAT model has undergone several refinement and upgrades resulting in different model versions (SWAT2000, SWAT2005 and SWAT2009). The overall desire to adapt the model for the local conditions has resulted in many

The European Commission has, for the purposes of ensuring adequate tools, for the end user, that could meet the current European needs for harmonization and transparency in the quantitative assessment of diffused sources of nutrient losses, financially supported EUROHARP project (Kronvang et al., 2009b). This project compared nine different catchment models for simulation of the non-point sources of pollution from agriculture on numerous catchments in Europe. The results of the project ranked SWAT, along with NL-CAT and TRK models, in the top three of the best (Schoumans et al., 2009). EUROHARP study showed that the modellers are not yet able to propose only on the best and the most appropriate model for all river basins in Europe, because the quality of the models is based on the input data quality along with quality of the modellers (Kronvang et al., 2009a).

The aim of this chapter is to examine modelling of surface water quality by the catchment model Soil And Water Assessment Tool (SWAT). The capabilities of the model were tested

3-) (Khan & Ansari, 2005). Excessive use

absorbed by plants and precipitation exceeds evapotranspiration (Rusjan, 2008).

absorb directly in the form of ortho-phosphorus (PO4

has put more emphasis on P from agriculture (Buda et al., 2009).

more accessible and understandable to different target groups.

adaptations like G-SWAT, SWIM, E-SWAT, K-SWAT (Gassman et al., 2007).
