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PAVLÍK, F., DUMBROVSKÝ, M., PODHRÁZSKÁ, J., KONEČNÁ, J.: The infl uence of water erosion processes on sediment and nutriet transport from a small agricultural catchment area. Acta univ. agric. et silvic. Mendel. Brun., 2012, LX, No. 3, pp. 155–164 Erosion processes in catchment areas cause serious ecologic and economic problems because of their negative consequences in terms of soil and water deterioration as well as for the environment as a whole. The soil particles washed down by water erosion are the biggest pollution factor due to their amount and volume. Sediments are the product of a selective process in which smaller and lighter particles are separated from eroded soil and taken away by water fi rst. This means that the sediments contain a higher amount of organic, clay, and silt particles than the the original soils. Washed down sediments consist mainly of particles smaller than 0.05 mm (40–90% of the mixture). Other studies in the Czech Republic have focused on the assessment of soil erosion, based upon principles and parameters defi ned in the Universal Soil Loss Equation, but none of them has dealt with nutrient transport assessment as a consequence of water erosion. This paper presents a summary concerning the nutrient content in erosion sediment in a selected catchment area. Research work was conducted to identify and quantify the sediment load associated with nutrient transport especially from arable land on diff erent soil types. soil erosion, nutrient transport, catchment area, water quality Soil and water are two important and closely related components of the environment. Permanent soil characteristics infl uence the amount of water retained in the soil profi le, quantity and rate of runoff , infi ltration, and evaporation. The presence and movement of water in the soil profi le aff ects the stable characteristics of soil. The shi of these materials has an impact on environmental quality. In particular, water erosion removes topsoil and subsequently causes pollution of watercourses and water reservoirs with both suspended matter and dissolved and colloidal substances. It is therefore necessary to address the protection of soil and water simultaneously. Negative eff ects of water erosion on soil degradation and pollution of surface water have been studied at various scales by many authors (Bečvář, 2006; Kvítek & Doležal, 2003; Owens & Collins, 2006; Russell et al., 2001). The advantage of studying very small basins (up to approximately 10 km2) is the relative ease of making exact measurements of hydrological and meteorological characteristics in the real natural environment and the exact defi nability of the natural and anthropic conditions. The most intensive manifestations of water erosion in small agricultural catchments are caused by torrential rainfall or local melting of snow (Janeček et al., 2007; Fulajtár & Jánský, 2001). Soil particles washed away by water erosion are the biggest polluting factors with regard to their amount and volume. Sediments are the product of a selective process. In this process of soil erosion initially the smaller and lighter particles are separated and carried by water. This means that the sediments contain more organic, clay, and dust 156 F. Pavlík, M. Dumbrovský, J. Podhrázská, J. Konečná particles than the soil from which they originate. According to Dub (1957) and Janeček et al. (2007) the dri ing sediment particles consist mainly of particles smaller than 0.05 mm (40–90% mixture). Together with the downhill sediment runoff , mainly nutrients are transported, whose main sources are fertilizers and pesticides. Mostly phosphorus and nitrogen are taken away from agricultural land by water erosion. MATERIALS AND METHODS Monitoring and quantifi cation of sediment delivery from the catchment can be made by direct measurement of the quantity and concentrations in the output profi le or by mathematical modelling. The article deals with the possibilities of direct measurements as well as the possibilities of model calculations (especially the possible ways to estimate the amount of soil washout and its nutrient content) and with a mutual comparison of diff erent approaches. The experimental chapter contains basic information about chemicals and experimental and analytical equipment as well as experimental and mathematical techniques used to obtain the results presented. Detailed information about well-known facts or previously published techniques and illustrative fi gures, mainly the setup and equipment schemes, has been omitted. Determination of sediment transport of undissolved substances and of nutrients from a catchment area by a model calculation Quantifi cation of sediment transport of suspended solids in small agricultural catchment areas is based on the assumption that the loss of substances is caused by water erosion. The methods used to estimate soil erosion in the catchment areas are based on the RUSLE (Revised Universal Soil Loss Equation). The RUSLE is an empirical model that was developed using statistical techniques derived from analysis of runoff plot data by Wischemeier and Smith (1978). Hillslope erosion from sheet and rill erosion processes is estimated using RUSLE (Renard et al., 1997). The RUSLE calculates mean annual soil loss (Y, tonnes ha−1 y−1) as a product of six factors: rainfall erosivity (R), soil erodibility (K), hillslope length (L), hillslope gradient (S), ground cover (C), and land use practice factor (P): Y = R × K × L × S × C × P. (1) It is designed for calculating the long-term average soil loss. This equation was used in the modifi cation of the grid in an interface with a geographic information system (GIS) for the selected model agricultural catchment areas. The soil loss is determined according to the method on the basis of a digital elevation model (DEM) with the use of the USLE 2D program and the McCool LS algorithm (Govers, 2000). However calculation by this method does not indicate a signifi cant soil loss from ephemeral gullies (Fig. 1). They are generated in the paths of concentrated surface runoff . Ephemeral gullies occur on arable land more frequently due to more intense precipitations. Loss of soil from the paths of concentrated surface runoff is an important component in the total balance of the soil loss in the catchment area. Several models (EGEM, AnnAGNPS, CREAMS) of the components of the total soil loss calculation exist, but these are not calibrated for conditions of the Czech Republic (CR). Consequently direct measurement of these ephemeral gullies was realized in the selected catchments. The Landscape Water Management Institute has developed a special device for this measurement called an erosion bridge, which works on a mechanical principle (Fig. 2). The cross profi les are measured along the ephemeral gully and subsequently the volume of the soil lost in the ephemeral gully is determined (Fig. 3). When using this method, knowledge of the total balance of the soil loss in the catchment is necessary for the purpose of calculation of soil transported out of the river basin. The total soil loss in a catchment area had to be reduced by the soil delivery ratio 1: Example of an ephemeral gully 2: Erosion bridge The infl uence of water erosion processes on sediment and nutriet transport from a small agricultural catchment 157 (SDR) to determine the amount of transported soil load in a catchment area outfl ow profi le. Mostly in the water fl ow, the sediment delivery ratio (SDR) multiplied. The SDR depends on the size of the catchment area (Janeček et al., 2007). The nutrient load from hillslope erosion is calculated as the product of the hillslope sediment yield (hillslope erosion × SDR) multiplied by the nutrient concentration (NC) of this load. The nutrient concentration of the sediment load is determined from the proportion of clay and nutrient concentration of the bulk soil (BS). The model assumes that all nutrients are associated with the clay fraction. For internal catchment links when the percentage of clay is greater than the SDR, all sediment delivered to the channel is assumed to be clay. The nutrient concentration is then the bulk soil concentration enriched by the proportion of clay (Cp) in the hillslope soil: SC NC =  × 0.5, Cp (2) for Cp < SDR. In the few cases where the proportion of clay is less than the SDR, only a portion of the delivered sediment is clay and so the nutrient concentration is reduced by the ratio of the proportion of clay to the SDR. In previous projects (Brodie et al., 2003) it was found that the nutrient enrichment ratio simulated by the above equation gave nutrient concentrations signifi cantly higher than those observed in river sediments of the region. The enrichment ratios were also larger than those recorded in fi eld experiments. Thus the eff ect of nutrient enrichment was reduced by half (the 0.5 factor in Equation 1). Data on soil clay proportions and nutrient concentrations for phosphorus and nitrogen were extracted from the Australian Soil Resource Information System (Henderson et al., 2001). The nutrient loads from riverbank erosion were calculated as the product of their respective sediment yields multiplied by the soil nutrient concentration, which for phosphorous was taken to be 0.25 g kg − 1 and for nitrogen 1 g kg − 1. To determine the total nutrient loss per year from a catchment the long term average concentrations of individual chemical elements in soils set by the Central Institute for Supervising and Testing in Agriculture (ÚKZÚZ) were considered. The contents of phosphorus, potassium, magnesium, and calcium were measured in soils. Long term average concentrations for selected localities in the monitored periods 1999–2003 and 2004–2009 are listed in Table 1, where the fi nal concentration for the period 1999–2009 was determined as the weighted mean throughout the area tested. Samples from each locality were taken from representative rectangular areas wh

The influence of water erosion processes on sediment and nutriet transport from a small agricultural catchment area