Adrienne Clement

Updating water quality targets for shallow Lake Balaton (Hungary), recovering from eutrophication

The paper presents an overview about recovery of shallow Lake Balaton from eutrophication by assessing quantitative and qualitative changes in phytoplankton, zooplankton, and chironomids as a function of load reduction. The aim was to update the present water quality targets. The proposed targeting scheme supplements the existing one with a range of lake-specific ecological criteria. We conclude that simple targets (desired phytoplankton biomass and permissible load) are the best choice during the initial stage of eutrophication management, but more complex schemes including ecological criteria are needed to trace recovery when re-organization of the ecosystem takes place.

Identification of phosphorus emission hotspots in agricultural catchments

An enhanced transport-based management approach is presented, which is able to support cost-effective water quality management with respect to diffuse phosphorus pollution. Suspended solids and particulate phosphorus emissions and their transport were modeled in two hilly agricultural watersheds (Wulka River in Austria and Zala River in Hungary) with an improved version of the catchment-scale PhosFate model. Source and transmission areas were ranked by an optimization method in order to provide a priority list of the areas of economically efficient (optimal) management alternatives. The model was calibrated and validated at different gauges and for various years. The spatial distribution of the emissions shows that approximately one third of the catchment area is responsible for the majority of the emissions. However, only a few percent of the source areas can transport fluxes to the catchment outlet. These effective source areas, together with the main transmission areas are potential candidates for improved management practices. In accordance with the critical area concept, it was shown that intervention with better management practices on a properly selected small proportion of the total area (1–3%) is sufficient to reach a remarkable improvement in water quality. If soil nutrient management is also considered in addition to water quality, intervention on 4–12% of the catchment areas can fulfill both aspects.

Cyanobacteria-mediated internal eutrophication in shallow Lake Balaton after load reduction

Nutrient loads to large, shallow Lake Balaton have been reduced by 45-50% since mid-1980s. While a delayed, but still surprisingly fast recovery was observed in the hypertrophic western areas of the lake, eutrophication followed sewage diversion from the mesotrophic northern basins. We assessed factors that could lead to this unusual response. The prime reason of the observed biomass increase might be a trend of increasing mean water temperature during late summers and the concurrent invasion of the subtropical cyanobacterium, Cylindrospermopsis raciborskii with superior light and nutrient utilisation capabilities. In the mesotrophic areas, the prerequisite of the unforeseen success of C. raciborskii was the exceptionally high potential of this species to generate internal P load. Specific morphometric features of the lake rather than nutrient loads might substantiate the increasing dominance of the cyanobacterium in these areas. Our results stress the need to consider individual characteristics of aquatic ecosystems during eutrophication management.

Design of best management practice applications for diffuse phosphorus pollution using interactive GIS

The paper presents a complex environmental engineering tool, which is appropriate to support decision making in watershed management. The PhosFate tool allows planning best management practices (BMPs) in catchments and simulating their possible impacts on immissions. The method has two parts: (a) a simple phosphorus (P) fate model to calculate diffuse P emissions and their surface transport, and (b) an interactive tool to design BMPs in small catchments. The fate model calculates diffuse P emissions via surface pathways. It is a conceptual, distributed parameter and long-term (annual) average model. The model also follows the fate of emitted P from each cell to the catchment outlets and calculates the field and in-stream retention. The fate model performed well in the Zala River catchment as a case study. Finally, an interactive design tool was developed to plan BMPs in the catchments and simulate their possible impacts on diffuse P fluxes. Different management scenarios were worked out and their effects evaluated and compared to each other. The results show that the approach is suitable to test BMP scenarios at small catchment scale.

Impacts of the climate change on runoff and diffuse phosphorus load to Lake Balaton (Hungary).

The paper outlines a multi-component assessment of the impacts of the climate change on runoff and total phosphorus loads to the large shallow Lake Balaton in Hungary. Present hydrological cycle of the lake catchment has been examined using the rainfall-runoff model WetSpa. Particular phosphorus concentration in runoff was estimated on the basis of the simulated streamflow using an empirical power equation. Dissolved phosphorus concentrations were determined as a function of landuse and soil type of the corresponding sub-catchment. The model was calibrated and validated against daily observations manually at monitoring sites of sixteen inflowing streams around the lake. Runoff stemming from shoreline urban developments was calculated by the urban runoff simulation model SWMM. Phosphorus concentrations in urban runoff were calculated by an empirical relationship derived from field measurements. The model was henceforward run for climate change scenario analysis. Present weather data were modified by the climate change scenarios imported from the results of the CLIME project. The results indicate that the impact of the climate change on runoff and phosphorus load appears in the change of the distribution within a time period rather than in the total volume. However, due to the high uncertainties in climate models, the presented calculations are possible assumptions rather than established statements.

Modeling the phosphorus retention of the Kis-Balaton upper reservoir

The Kis-Balaton reservoir system, consisting of the upper and lower reservoirs, is located near to the mouth of the Zala River. It was established for the protection of Lake Balaton against high nutrient loads. In accordance with the original plan prepared at the end of 70s the aim was that before entering the lake, nutrients - primarily phosphorus - will be removed by macrophytes. The Upper Reservoir started to operate in 1985. In contrast to the predictions, it became an open lake dominated by algae. Until 1991 about 50% of the external phosphorus load has been removed yearly. However, the retention efficiency has decreased considerably after reduction of the external load upon phosphorus removal at the wastewater treatment plant of the largest town of the Zala catchment. This observation can be explained by the increased contribution of the internal loading. To analyze the phosphorus removal mechanisms and to understand the behavior of the sediment, different water quality models were applied. The results show that the P retention is characterized by different processes acting spatially differently. Essentially, abiotic processes like settling of inorganic particulate P and the adsorption of dissolved inorganic P are responsible for the P retention in the reservoir, mostly in the neck of the Upper Reservoir. Simple models indicated that the internal loading increased after the external load reduction. In fact, it was not that the internal loading increased, but the adsorption decreased.

Strategies for Approximating EU Legislation in Hungary: The Sajó River Case

The Hungarian watershed of the Sajo River (a shared river basin with Slovakia), representing about 5% of the countrys population and territory was used as a case study to analyze issues of EU accession with special regard to drinking water supply and urban wastewater management. In the past the Sajo was one of the most contaminated Hungarian rivers due to industrial, transboundary and municipal emissions. For today its quality became acceptable due to industrial transformation and municipal wastewater management. The uniqueness of the problem stems from the fact that 30% of the population lives in small settlements of low level of water service. In the frame of the present study large number of water supply, sewerage and wastewater treatment strategies were developed to study the solution of existing problems and to meet EU requirements. For transboundary loads several scenarios were prepared. The investment costs of alternatives were evaluated on the basis of a detailed comparison of international and national estimation techniques. Water quality impacts in terms of traditional components were assessed by using models. Affordability was analyzed and a phased development policy was recommended.