|
|
Surface waters chemistry in Třeboň and Nové Hrady regions - the effects of catchment on major ions concentrations
BAXOVÁ CHMELOVÁ, Iva
Water management in landscapes, the relationships between water and water regime and level of agricultural management soil cultivation are very important and noteworthy areas of global discussion. Nevertheless, issues related to landscape management are often ignored. Difficulty of assessing the state of the landscape and its functioning is one reason for this. Healthy ecosystems tend to retain substances in the system and reduce matter losses. This concept was used as background for this thesis, which evaluates long-term trends in changes in surface water chemistry in the model areas of Novohradsko (upper Stropnice catchment) and Třeboňsko (Lužnice catchment). Surface water chemistry of both running (small streams) and standing waters (ponds) was described in relation to natural and anthropogenic catchment patterns, especially in terms of the influence of land cover, agricultural management and the overall impact of human activities. The functioning of the landscape was more detailed assessed in the selected catchments in terms of land surface temperatures and vegetation cover and of its ability of matter retention. Attention was paid to the role of wetlands in the landscape. Changes in surface water chemistry in the Třeboň region and in the upper Stropnice catchment reflect changes in management, especially in agricultural catchments. In both the Stropnice and the Lužnice basins and in the Třeboň ponds, an increase in the concentrations of the major ions (SO42-, HCO3-, Cl-, Ca2+, Mg2+, K+ and Na+) is evident from the 1960s to the 1990s. The total dissolved content doubled during this period. The substantial reduction in agricultural intensity after 1990 showed very similar trends, with a decrease in the concentrations of the major ions, especially SO42-, HCO3- and the alkaline cations, Ca2+, Mg2+. Changes in concentrations of major ions are well documented by changes in conductivity. The overall long-term trend undoubtedly shows an increase in the last century and a subsequent decrease in concentrations. This decreasing trend has stopped in the last decade in Stropnice. In the Lužnice, the trend is even reversing and conductivity is beginning to increase again. The decline in concentrations of the major ions stopped around 2010. Currently, the concentrations of some ions are increasing again. This most likely reflects gradually increasing fertilization and liming of agricultural soils. Significant changes in agricultural practices have very similar consequences at the level of very small catchments of a few tens to hundreds of hectares, as well as medium-sized ones such as the upper Lužnice and upper Stropnice catchments. The downstream increase in total dissolved solids is evident in all sub-basins of the monitored streams (Bedřichovský, Váčkový, Pasecký, Veverský, Nakolický). The condition of the catchment, i.e. the extent of agricultural land, the proportion of forest or the presence of wetlands, modifies the effects of catchment management on the chemistry of runoff. The large areas of arable land have significantly increase of the major ions concentrations. In contrast cathment with the minimal agricultural activities has almost negligible impact on chemistry of runoff. Effect of catchment character is surprisingly stable over a decade or more and is evident on both running waters and ponds. The similarity in the patterns and long-term trends of changes in major ion concentrations even at the level of large catchment, such as the part of the Vltava basin adjacent to the South Bohemia Region, indicates the robustness of these processes. The hydrochemical conditions of surface waters reflect to a large extent the physical and biological processes occurring in the basin. The movement of water in the terrain and its interaction with soil, and vegetation are linked to the dissipation of energy that passes through the system. The surface temperature of the landscape is the result of these processes. The temperature distri
|
guest ::
