Deliverable 5.11

Abstract: River Vltava modelling, final report

Link http://www.refresh.ucl.ac.uk/webfm_send/2387

This report presents the outcomes of modelling undertaken at the Czech REFRESH demonstration site, the upper Vltava catchment in the southern Czech Republic. The specific aims for this catchment were to: (i) predict the effects of changes in climate and land use on water quality and eutrophication in the catchment-lake ecosystem; and (ii) integrate modelling outcomes with cost-effectiveness analysis, to determine the most cost effective options for reducing eutrophication, both at current conditions and under future scenarios of environmental change.

The upper Vltava catchment upstream from the dam of Orlík reservoir consists of a heterogeneous landscape with natural forested mountainous parts, agricultural river valleys and upland plains, urban areas, and numerous artificial reservoirs used for fish production and water storage. The Orlík reservoir is the largest reservoir in the Czech Republic and is primarily used for hydropower but it has also for recreation use. The eutrophication problems in the Orlík reservoir are mostly due to excessive phosphorus loading from municipal wastewater discharges, fishpond fisheries and agriculture losses have been a major concern since the 1990s when heavy cyanobacteria blooms started to seriously hamper recreation at this large water body and development of the surrounding region.

The model chain system for simulations of climate and land use change effects on hydrology, water quality and reservoir ecology in the Vltava catchment was used to simulate, river flow and nutrient concentrations in the catchment runoff and temperature stratification, water level fluctuation, hypolimnion oxygen deficit, phosphorus and chlorophyll-a concentrations in four major storage reservoirs, i.e. Lipno, Římov, Hněvkovice, and Orlík  for the baseline period of 1981-2010 and for the scenario period of 2031-2060, using predictions of three climate models and four different land use and socio-economic development scenarios.

All three future climate change scenarios in the Vltava catchment resulted in only small modifications of simulated mean river flow but in a significant increase in phosphorus and decrease in nitrate concentrations. In the Orlík reservoir, the climate change scenarios resulted in an increased water level fluctuation, prolonged anoxic conditions in the hypolimnion and decreased mean phosphorus, and chlorophyll-a concentrations that apparently resulted from increased phosphorus retention in the reservoir under the conditions of changed seasonal flow pattern. The simulations of future alternatives of socio-economic development according to A1 (World Markets), A2/B2 (National Enterprise / Local Stewardship), and B1 (Global Sustainability) scenarios indicated that impacts of land use change and wastewater management are far more important than the influence of climate change. 

Finally, a set of mitigation measures against eutrophication of the Orlík reservoir was selected to determine if compliance with the WDF quality standards could be achieved. The mitigation measures included: (i) the 90% efficiency of P removal from all municipal and other wastewater discharges, (ii) fishpond fishery production with zero phosphorus surplus, and (iii) the grassing of steep (>7°) arable land areas and 20-m wide buffer zones along streams. The resulting scenario runs for present and future climate indicated that it might be difficult to decrease the phosphorus concentrations in the runoff from catchment to the required level using the set of mitigation measures suggested. Despite this, the standards for phosphorus and chlorophyll a concentrations could be met in the Orlík reservoir. Under future climate conditions, the inflow concentrations tended to increase. The phosphorus and chlorophyll a concentrations remained near the required standard level, apparently due to increased phosphorus retention in the reservoir in conditions of prolonged water residence time and higher temperature. The nitrate concentration met the WFD standard in the current state as well as under the future climate conditions.

Annex to Deliverable 5.11 - Link http://www.refresh.ucl.ac.uk/webfm_send/2386

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