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REFRESH Catchment case studies - responding to future change: Vltava catchment, Czech Republic
The upper River Vltava catchment stretches from the border mountain range of the Bohemian Forest between the Czech Republic, Austria and Germany to the Orlík reservoir situated ca 70 km south of Prague.
This landscape is naturally lakeless, but there are numerous artificial ponds and reservoirs. Most of these water bodies are shallow and were created in the Middle Ages and early Modern Ages for fish production. Four large and deep hydropower, water supply and flood protection reservoirs were constructed by damming the Vltava River and its tributaries during the second half of the 20th century The main land use classes are farmland and forestry with 52% and 42% coverage, respectively. The population density in the catchment is moderate (ca 60 inhabitants per km2). The intensification of agricultural production during the post-war communist regime in the Czech Republic had Significant impacts on water quality.
More environmentally friendly management practices were adopted when the Czech Republic joined the EU with the implementation of the CAP. Fishpond production of carp is a key feature of the South Bohemian region and the area of production fishponds in the upper Vltava catchment covers ca 160 km2. During the past 50 years these have gradually become a significant source of diffuse nutrient pollution. In the upper Vltava catchment, N concentrations generally comply with the WFD standard, however, the P concentrations are high in many parts of the catchment resulting in failure to achieve good ecological status, particularly in reservoirs. This is a major challenge for mitigation measures.
A model chain system was developed to describe the effects of land use and climate change on hydrology and water quality in the Vltava River catchment and consists of two major model components, models for simulations of the precipitation-runoff process in the catchment and those that model the reservoir hydrodynamics and water quality. A set of scenarios were produced for the upper Vltava catchment to evaluate potential mitigation measures for improvement of water quality and ecology of rivers and reservoirs to meet the WFD standards and also to gauge effects of land use change according to storylines of the IPCC SRES framework. All scenarios were run under predicted future climate in 2031–2060 using three regional climate models.
Caption The Orlik dam on the River Vltava
In the middle of the 21st century (2031–2060), a temperature increase of 1–2.2 °C was forecast by the climate models resulting in a lengthening of the growing season. Future precipitation is also expected to increase moderately. According to model runs changing climate conditions will affect the hydrology and water quality of the river network and reservoirs. The mean runoff from the catchment showed little change in future, however the seasonal distribution of runoff was significantly modified with increased winter values, decreased spring and summer values and large changes in the autumn. These hydrological changes resulted in an increase in the average TP concentration, mainly in summer. The increases were associated with low flow reducing dilution of wastewater inputs into the river system.
Effects of management measures
Examining the effects of mitigation measures and their optimum cost-efficient combinations suggest that mitigation measures in agriculture have a limited capacity to decrease P concentrations but can markedly decrease nitrate concentrations. The mitigation measures at fishpond fisheries and wastewater treatment are much more important for the control of P concentrations. Compliance with the WFD standards for P can be attained only through a joint application of combined measures. The optimum cost-effective combination of measures can achieve WFD compliance under current climate conditions but not in the future.
The future alternatives for socio-economic development in the upper Vltava catchment indicate large differences in their impacts on surface water quality. Only under scenario B1 (Global Sustainability), which is characterized by extensive agriculture, extensive fisheries, as well as by the highest efficiency of phosphorus removal from wastewaters (90%), were the P concentrations in runoff from the catchment and in the Orlík reservoir reduced to levels compliant with WFD.
These scenario runs have shown that changes in land use and wastewater discharges might have much greater impact than climate change on nutrient concentrations in runoff from the catchment, even if the effects of climate change on the nutrient regime of the catchment are also clearly discernible.
In this study, we assessed mitigation measures in the upper Vltava catchment to reduce phosphorus concentration in the inflow into its largest reservoir (Orlík reservoir) to a non-eutrophying level, which would meet the WFD TP standard of 0.05 mg l-1. It is apparent that this target will not be achieved in 2015 when the first planning period of the River Basin Management Plans (RBMPs) ends, although some mitigation measures, mainly targeted at point sources, have been taken. Our goal was to select an optimum cost-effective set of measures that could reduce the export of phosphorus from the catchment for the second RBMP (2016–2023). The measures should cover all three types of major phosphorus sources, i.e. wastewater discharges, agricultural losses and fisheries, because only efforts tackling all sources of phosphorus pollution will result in sufficient reduction in phosphorus concentrations.
It is apparent that the cost-optimum set of measures creates a mismatch between polluters and cost bearers for the reduction of pollution. Although more than half the phosphorus pollution is the responsibility of the municipalities and only one fifth from fisheries, most of the costs for improving water quality is borne by fisheries (51%) and municipalities cover only 44% of the cost. This is mainly due to the fact that the construction of new WTTPs in small municipalities is very expensive but with little effect on the removed amount of phosphorus and, on the other hand, the extensive fishpond fisheries actually do not pollute but can absorb phosphorus from the other sources.
The results were presented and discussed with major stakeholder groups within the catchment (municipalities, farmers, fishpond owners, river basin authority, regional authorities, academic sector) at several workshops. These workshops revealed that representatives of municipalities admit partial responsibility for phosphorus pollution, however the implementation of measures at point sources would require large investments that may be beyond municipal budgets (especially the smaller ones). Any voluntary reduction of fish production cannot be expected without compensation or a stricter regulatory framework as this would reduce profits. The majority of the fishpond owners and managers disputed the results of research and argued that the real extent of their pollution and also their potential for mitigation measures should be further investigated.
For further information see REFRESH reports