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Quality and quantity status and risk assessment of groundwater bodies in karst areas of Croatia

Karst areas in Croatia are a part of the regional geologic structure of Dinarides which cover an area from Slovenia across Croatia and Bosnia and Herzegovina up to Montenegro. Almost half of the Croatian territory belongs to the karst area of specific surface and underground morphological characteristics. In Croatia the karst groundwater quantities make a little less than a half of total disposable state potable water quantities. Geologically speaking, those are mostly carbonate rocks with fully developed karst forms. It is exceptionally difficult to separate the groundwater from surface waters in karst areas. Therefore the groundwater and surface water interaction is extremely large. Particular rivers start their flow at karst springs, flow partly on the surface, then swallow when facing the well permeable carbonate rocks, only to resurface again as ground waters at springs in the lower catchment area parts. The similar situation occurs in karst fields which, in the rainy parts seasons, are partly flooded due to the ground water level rise, while in the dry periods the springs in the fields run dry or are significantly reduced in the water amount. The water flows and disappears underground several times within the same catchment area, accepting all catchment area loadings created by human activities. From that reasons karst areas require an integrated water quality and quantity assessment as well as water resources risk assessment for each groundwater bodies (GWB). A part of Croatian karst waters is accumulated and used for electric power production, which causes changes in both outflow regime and dynamics and even changes of groundwater outflow directions. The largest part of karst area belongs to the Adriatic catchment and is subterraneously drained towards coastal springs and hydrologically uncontrolled submarine springs in the Adriatic littoral area. Consequently, the karst catchment areas are neither unambiguous (they depend on hydrological conditions), nor easily determinable. In heterogeneous karst conditions there are considerable difficulties in delineation of GWB's as well as in assessment the groundwater quality and quantity status which must be performed according to the EU Water Framework Directives (WFD). The fact that the groundwater monitoring is in Croatia in a developmental stage is an additional problem, so that the initial characterization and groundwater risk assessment have been performed according to data from the 2000–2007 period. This paper presents the methodological approach which was applied on Croatian karst area as well as the abbreviated summary of conducted analyses. Seventeen GWB's have been delineated in the Croatian karst area, nine of which are of transboundary character due to the characteristic shape of Croatia. In the quantity status assessment has been used the measured climatological and hydrological data as well as data of different forms of water usage, the regional hydrological analyses and estimations have been conducted as well as the time trends assessment. The regression relations between different hydrological elements have been established from which has been separated the catchment surface, mean annual flows and lowest mean monthly flows. The hydrological catchment area data have been extrapolated to the GWB level. It has been established that the global water resource utilization for water supply needs, industry and irrigation is extremely low compared to the total water potential — it amounts to an average of 2.3% only. Despite this fact there are two GWB's with an estimated poor quantity state and two GWB's with a probable poor state. The quantity status has been assessed as good for thirteen ground water areas. By estimating the risk of not meeting the WFD requirements additional two GWB's have been listed as “at risk”. In order to asses the quality status spatial analyses of natural vulnerability, hazard and pollution risk have been conducted. The GWB quality status assessment was performed by analyzing the water quality within the 2000–2007 period, taking water samples from 55 karst springs in monthly intervals (the total of 3887 analyses). The monitoring network mostly uniformly covers the singled out karst GWB's. For quality status assessment the following parameters have been used: the dissolved oxygen, pH, electric conductivity, nitrates and ammonia according to the WFD requirements, as well as the entire pesticides, arsenic, cadmium, lead, mercury, chloride, sulphate, trichloroethylene and tetrachloroethylene according to the Groundwater Directive requirements. Regarding the specificity of karst water system, the quality status analysis has also included the free CO2, the temperature, the orthophosphates, the turbidity, iron, manganese and mineral oils. It has been established that thirteen GWB's have a good quality status, two poor. In case of the remaining two the status has been assessed to be probably good based on an expert estimation since there were no or not enough data. An important element in assessment of the quality risk in accordance with the Article 4 of the WFD was the natural background level (BL) and threshold value (TV) for the selected parameters. Based on extrapolation of observed trends during the referential period of 2000–2007, the changes in several quality parameter characteristics have been established. At that time the value of 75% of the boundary value determined when estimating the groundwater quality status was taken as a risk indicator. It has been established that eleven GWB's are at no risk while four are at a potential risk. The paper points out the need to discuss the applied methodological procedures used for ground water state and risk estimation within the framework of their application on specific conditions of karst aquifers and under conditions of a limited fundus of available data.

karst aquifers; groundwater body (GWB); groundwater quality and quantity; Water Framework Directive (WFD); Croatia

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