Groundwater Quality on the Adriatic Karst Island of Mljet (Croatia) and Its Implications on Water Supply

Abstract

Water supply of the islands is a global challenge, especially in the countries which have highly indented coastlines with numerous islands. The island of Mljet in Croatia was investigated due to its unique source of water supply: desalination of water from brackish lakes—blatinas—fed by groundwater and connected to the sea by karst conduits. Water sampling and chemical analyses were performed during hydrological minimum and maximum with regard to groundwater levels in 2005/2006 and minimum in 2016. A total of 13 samples were analysed within the study: 10 samples were taken from blatinas, 1 from pit well, and 2 from borehole wells. All waters sampled from the lakes are of Na-Cl type. The seawater percentage in the lakes used to extract feed water for desalination plants, calculated by conservative mixing approach, is relatively low (0.7-9.8%) and varies in correlation with hydrological seasons. Low proportion of seawater is an essential factor of cost minimisation in desalination by the installed reverse osmosis (RO) plants. Daily monitoring of total dissolved solids in the feed water was introduced in May 2016, and its results were analysed in the context of precipitation—a sole source of island aquifer recharge. Maximum concentrations were observed during September and interpreted to be caused by a combination of natural and anthropogenic pressure during the summer tourist season. Minimum concentrations were expected after the rainy season in the cold part of the year but were observed in June instead. Due to a short observation period and untypical distribution of precipitation in the same time interval, the data can only be considered indicative. An unusual pattern of sulphate anion concentrations, which cannot be attributed solely to fresh- and seawater mixing, was observed in one of the blatinas, but its origin could not be determined based on available data. Taking into account all the presented data on groundwater quality, climate change predictions, the connection of water supply system to the mainland and problems with the effluent treatment, it is clear that the main future challenge will be the creation of an island-wide sustainable water management plan followed by continuous monitoring and research.

Analyses of Climate Variations at Four Meteorological Stations on Remote Islands in the Croatian Part of the Adriatic Sea

“…Lastovo has a distance from the mainland similar to Vis ( Table 1). Part of the drinking water on Lastovo is obtained by desalination of brackish water from wells [11] and part is delivered through a regional water supply network from the mainland. The study area is part of the Outer Dinaric range, an area characterized by very deep and irregular karstification [9].…”

“…Lastovo has a distance from the mainland similar to Vis ( Table 1). Part of the drinking water on Lastovo is obtained by desalination of brackish water from wells [11] and part is delivered through a regional water supply network from the mainland. Note: AMS-automatic meteorological station; MMS-main meteorological station; PS-precipitation station; A-area of the island; L-minimum distance of the island from the mainland; H max -maximum altitude of the island.…”

“…The Croatian coast comprises 79 islands, 525 islets, and 642 rocks and reefs [11,12]. Merely a few Croatian islands have favorable hydrological or hydrogeological conditions for a sufficient local water supply [11]. Numerous archaeological sites have been discovered in this area testifying to its important position and historical role [13,14].…”

Review of Modeling Approaches to Groundwater Flow in Deformed Carbonate Aquifers

“…Similar to other authors, we consider fractured carbonate aquifers strongly anisotropic and heterogeneous due to the coupling of pervasive fracturing and karstification (Worthington 1991;West and Odling 2007;Goldscheider and Drew 2014;Hartmann et al 2014a;Borović et al 2019). However, the majority of groundwater flow models only account for the vertical flow anisotropy (K h /K v ), which is in a wide range (∼10 2 -10 3 ) in karst environments (Neymeyer et al 2007;Odling et al 2013;Goldscheider and Drew 2014;Zuffianò et al 2016).…”

DOC and nitrate fluxes from farmland; impact on a dolostone aquifer KCZ

“…This category of fractured aquifers is particularly prone to dissolution that enlarges bedding planes, fractures and faults. Consequently, karst aquifers are characterized by a high degree of hydraulic connectivity with the land surface and transport of contaminants is therefore particularly rapid (Ford and Williams 1989;Worthington et al 2012;Goldscheider and Drew 2014;Medici et al 2016;Borović et al 2019;Torresan et al 2020). The Critical Zone in karst environment is considered as the most vulnerable to contamination due to the above mentioned dissolution processes in the vadose and shallow saturated zone of carbonate aquifers (Lian et al 2011;Kogovsek and Petric 2014;Zhang et al 2017;Jiang et al 2019;Jourde et al 2018;Green et al 2019;Sullivan et al 2019).…”