Changes of water systems in submountain catchments: Case study of Blanice River, Šumava/ Bohemian Forest Mts., Czechia
Abstrakt
Šumava Mts. played an important role during initial formation of catastrophic floods in Czechia. It is a significant area for water retention and a potential source of drinking water.
In recent decades, there have been significant changes associated with changes in land use, climate change as well as changes in atmospheric deposition. Intensively cultivated fields were grassed for cattle grazing in the context of a change in the policy since the end of the 1990s.
Non-maintained meadows are overgrown with wooded vegetation. A significant part of the area is protected.
A number of measures related to socialist past economic activities, in particular artificial drainage system, straightened and concreted river channels, type of settlement affect both outflow and ecohydrological conditions at present. The aim of the contribution is to evaluate changes of water systems from the points of hydrological and biogeochemical aspects in the headwater area of Blanice River.
Both the data from the long-term time series from the beginning of the measurement, and especially the data from own automatic monitoring and field campaigns in period 2006-2017, were used for the analyzes. Rainfall-runoff processes were detailed investigated on the basis of comparative research in small-scale experimental subcatchments (wooded Tetrivcí Brook, grassed Zbytinsky Brook and restored Svinovický Brook).
Specific attention was paid to assessing the success of the present-day streamrestoration measures. The results of trend analyzes have shown seasonal changes of flow in relation to global warming: increase in winter (March) and decrease in summer (May-June).
The anthropogenic impact associated with land use changes, changes in soil water retention, and drainage effects modify average hydrological characteristics and are significantly manifested in the rainfall-runoff events. The forest subcatchment with drainage ditches system showed more dramatic runoff responses and overall higher outflow variability than the farmland subcatchments.
A different land use together with anthropogenic influence and global trends reflect the changes of biogeochemistry parameters. The water quality in upper Blanice watershed can be classified as good to moderately polluted.
Farmer grassland has higher values of electrical conductivity, higher concentration of nutrients and other substances (e. g. Fe2+, Cl-) than forest area.
The highest pollution is caused by settlements and waste dump. Overall, NO3- has decreased.
A general trend following the reduction of acidic industrial emissions is the decrease in sulphates and a slight increase in Ca2+ and pH. TOC and COD in wetlands have increased due to global warming.
The seasonality of biogeochemistry parameters and influence of runoff conditions (flow waves and dry period) were also studied. Construction of small WWTPs and restoration of water courses can be positively evaluated in headwater area.
An example is restoration of Svinovicky Brook channel which had been stripped of artificial concrete fortification and left to develop spontaneously. Different investigations including fluvial dynamic monitoring and hydrobiological approaches like an evaluation of change of species composition of macroinvertebrates confirmed an improved ecological status.