Abstract
Hydrologic alternation of river systems is an essential factor of human activity. Cascade-dammed waters are characterized by the disturbed outflow of material from the catchment. Changes in sediment, dissolved load and nutrient balance are among the base indicators of water resource monitoring. This research was based on the use of hydrological and water quality data (1984–2017) and the Indicators of Hydrologic Alteration (IHA) method to determine the influence of river regime changes on downstream transfer continuity of sediments and nutrients in the example of the Lower Brda river cascade dams (Poland). Two types of regimes were used: hydropeaking (1984–2000) and run–of–river (2001–2017). Using the IHA method and water quality data, a qualitative and quantitative relationship were demonstrated between changes of regime operation and sediment and nutrient balance. The use of sites above and below the cascade made it possible to determine sediment, dissolved load, and nutrient trapping and removing processes. Studies have shown that changes in operation regime influenced the supply chain and continuity of sediment and nutrient transport in cascade-dammed rivers. The conducted research showed that sustainable management of sediment and nutrient in the alternated catchment helps achieve good ecological status of the water.
Highlights
The hydrological cycle is limited by natural and anthropogenic factors
Based on the results of conducted studies on the influence of hydropower plant regime change on suspended sediment transport dynamics on the example Lower Brda River Cascade (LBC), the following conclusions were drawn: 1. The commission of the reservoirs in the cascade system influenced the hydrological regime on the section of the reservoirs themselves and the river below
The hydropeaking operating regime resulted in high water flow dynamics, especially below the Lower Brda Cascade dams (LBC), reflecting high Hydrologic alternation (HA) values
Summary
The hydrological cycle is limited by natural and anthropogenic factors. The first group includes, e.g., atmospheric circulation, precipitation, geological structure and soil erosion among others; the second group includes modifying river systems for flood control, water supply, irrigation, land cover changes and electricity production, among others. The appearance of large dams and their reservoirs increased sediment retention on the terrestrial part of the hydrosphere, with estimated retention of suspended particles as 50% of the load that would have been transported to the oceans [4,14]. Dams influence changes in the timing and frequency of high and low flows [16] In many cases, this is due to hydropower plant regimes, which should preserve ecological base flow (environmental flow). Dams reduce the natural connectivity of the fluvial system [26], and the natural regime of rivers is changed [27] This reflects on the sediment budget, where accumulation processes are dominant. Changes in river regime caused by reservoir function is reflected by nutrient trapping [32] or altering the original nutrient biogeochemical cycle [33]
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