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The turnover of matter and through-flow of energy in the intermittent Lake Cerknica is facilitated by the exchanging wet and dry periods, which either promote or suppress growth and development of organisms, depending on the season of the year. Any deviation from normal floods significantly affects the productivity of reed stands. Drainage of the lake prevents a constant presence of aquatic organisms, particularly planktonic species. Drying and wetting accelerates the decomposition of organic matter. The nutrient input into the lake by one surface tributary proved to be relatively high. The quantity of nutrients in the lake water is lower, however, because of the high buffering capacity of the densely vegetated ecosystem.

The quality of the aquatic environment and macrophytes were surveyed in the case of the remarkable karstic river Ljubljanica s. lat. (Slovenia). It consists of seven intermittent and permanent surface watercourses, connected by groundwater flows. We assessed 11 parameters describing the land use beyond the riparian zone, the structure of the riparian zone and stream channel morphology, as well as the distribution and abundance of macrophytes. The intermittent watercourses exhibited a relatively high level of naturalness, because the variable water regime prevents intensive human activity. Greater influence of the human activity on the permanent watercourses resulted in a modified riverine environment. The share of different ecological groups of macrophytes, i.e. submerged, emerged and amphibious species, reflected the water regimes of the different watercourses. A total of 62 taxa of macrophytes were identified in about 100 km of length examined. Of these, amphibious macrophytes dominated as a consequence of intermittent water regime. The relationship between environmental parameters and macrophytes, and the effects of the intermittent hydrology were investigated. All environmental parameters explained 28% of the variance in the distribution of macrophytes in watercourses, as determined by canonical correspondence analysis. Completeness of the riparian zone, bank undercutting and sediment accumulation were found to be the most influential.

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Constructed wetlands proved to be an effective and low-cost technology to control environmental pollution. The introduction of such low-tech systems is supported by the Slovenian Government. The aim of our research project was to intensify the reduction of nutrients (nitrogen compounds mainly) prior to discharging the effluents into the rivers, a contribution to the common target of the global environmental policy. The construction of the integrated system was completed in Autumn 1993 to treat domestic sewage for 10 PE. The system consists of three interconnected beds with vertical and horizontal flows. The vertical flow at the first stage is intermittent, while the horizontal one is continuous. The system is flexible due to mode of operation and the quality of the influent. Ten analyses were made during the initial months of operation. In bed B nitrification was taking place and the reduction of all other parameters but NO3-N was documented. In bed A denitrification was on in spite of intermittent vertical flow. Since the reed stand was scarce, recultivation was needed. The system showed its characteristics more clearly when more concentrated domestic wastewater was led in. Further investigation should reveal further details on proper media, surface area, and flow sequence selection. Reduction of some parameters was as follows: NH3-N 97.5%, NO3-N 74.5%, org-N 84.8%, P-tot 97.1% and COD 94.4%.

The Relationship of the Processes in the Rhizosphere of CommonReed Phragmites australis, (CAV.) TRIN. ex STEUDEL to Water Fluctuation key words: water level fluctuation, reed stand, ETS-activity, inorganic nutrients, soil water. AbstractIntermittent Lake Cerknica is characterised by extreme water level fluctuations. It is neither a lake, nor a terrestrial ecosystem. The decomposition processes in the rhizosphere of extended reed stands are essential for the entire ecosystem. The influence of intermittent water regime on the microbial activity and availability of nutrients in the rhizosphere in a terrestrial reed stand was investigated. The measurements revealed a relatively high soil water content, that was not related to underground water table. Mineralization processes in a soil profile were estimated by measuring microbial activity as electron transport system (ETS) activity and by nutrients in soil water. The microbial activity was determined in the whole depth profile. The highest ETS activity of a soil was 0. . The values were not related to underground water table. All forms of nutrients were constantly present, showing no correlation with the soil water content. ANOVA revealed significant decrease of nitrate with depth, but not for nitrite, ammonium and ortho-phosphate. IntroductionThe intermittent Lake Cerknica is characterised by extreme water level fluctuations. A part of the year the area is flooded, but from time to time, usually in summer, it becomes dry. The lake is the locus typicus for intermittent lakes and poljes (karst fields). Wetting and drying occurs seasonally, depending on precipitation. The exchanging of dry and wet periods influences the dynamics of biota and the process of mineralisation (URBANC-BERČIČ and GABERŠČIK, 2001). Common reed (Phragmites australis) is a dominant wetland species in the area. With respect to the water regime three types of reed stands were distinguished: terrestrial, land-water interface, and littoral stands. Stands exhibited significant differences in primary productivity parameters (GABERŠČIK et al., 2000), in the composition and depth of the soil layer, and in the variations of water regime (URBANC-BERČIČ and GABERŠČIK, 2001; URBANC-BERČIČ and GABERŠČIK, in press). Variations of water regime are fundamental for the nutrient cycling in the sediment (BROCK, 1986;BOULTON and BROCK, 1999). Most chemical features depending on aerobic and anaerobic conditions are highly variable. A presence of oxygen in a soil increases the microbial activity and the mineralization rate at the beginning of drying. Later on drying can cause considerable impact on sediment properties by affecting mineral phases and by killing up to 76% of the microbial biomass (QUI and MCCOMB, 1995). These changes reduce the capacity of the sediment to adsorb nutrients, such Internat. Rev. Hydrobiol.

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