Transformation Process of Five Water in Epikarst Zone: A Case Study in Subtropical Karst Area

Five water stand for five forms existence models of water. In Karst area, Five water means precipitation, groundwater, evapotranspiration water, soil water, and overland flow. The complicated water-bearing hydrogeological media and the inhomogeneous water storage structure leads to low efficiency of water utilization. To reveal intricated water resources transformation in karst areas, a typical epikarst zone was selected. The Five water and their conversion processes were studied and the transformation models was built based on the long-term positioning observations. The results show that: (1) Overland flow can be generated when precipitation reaches 6 mm and lasts for 6 h. Under light and moderate rainfall (LMR) conditions, less than 6% of the precipitation is converted to overland flow. Under heavy rainfall and rainstorm (HRR) conditions, the conversion rate is 3.5%-6%. (2) Under the condition of LMR, there are 2%-3.5%, 40%-60% and 25%-35% that transformed to vegetation water, soil water and groundwater respectively, while it is 1.5%-2.2%, 25%-30% and 32%-50% under the condition of HRR. (3) The proportion of precipitation was transformed to soil water is 20%-70%. (4) The conversion rate of groundwater and karst fissure water for LMR conditions are 8%-15% and 10%-15%, and that for HRR is 15%- 20% and 20%-35%. (5) The proportions of different degrees of precipitation transformed into vegetation transpiration and evaporation water are 1.5%-3.5% and 6%-9%, respectively. (6) Generally, about 0%-4% of the precipitation is converted into overland flow, 20%-70% into soil water, 25%-50% into karst groundwater, and 1%-10% into evaporative water.

Hellenic Karst Aquifers Vulnerability Approach Using Factor Analysis: The Example of the Louros Karst Aquifers

The karst aquifers of the Hellenic territory display high vulnerability that is related to the existence of the epikarst zone. If present, the epikarst zone regulates the vertical movement of the groundwater, which results in the chemical pollutants staying longer within it, thus facilitating the inactivation of the microbial loads. The Hellenic karst is well developed; it displays high hydraulic conductivity, relatively large storage, and the characteristics of an important water reservoir. Although its porosity was calculated to be between 0.005–8%, the statistical processing of the springs’ discharge time series points to an increased storage. The increased storage was attributed to the presence of the epikarst zone, which regulates the water movement to the underlying formations, and finally to its discharge from the karst system through springs. In these areas, the influence of nitrogen compounds on the water quality is evident. The presence of cyanobacteria and toxic substances at concentrations that are too high for fresh, flowing waters whose temperature does not exceed 17 °C advocates the role of nutrients, even at concentrations that do not exceed the maximum permissible limits of drinking water. In mountainous areas, where agriculture is limited, the presence of these compounds is attributed to heavily polluting land uses. The impact of such uses became apparent from the application of factor analysis, which not only highlighted their contribution to the overall groundwater quality, but also determined their geographical distribution and origin. From the above, it becomes evident that there is a need for protection of the karst aquifers, and investigation of their vulnerability mechanisms. The Hellenic karst, which is expected to cover the drinking water needs in the near future, proves to be very vulnerable to any kind of pollution.