Kálmán Mátyás

The role of the Kis-Balaton Water Protection System in the control of water quality of Lake Balaton

Abstract Since the 1960s the nutrient load of Lake Balaton has increased significantly, causing a clear decline in water quality. To retain the nutrients from the lake, the Kis (small)-Balaton Water Protection System (KBWPS) was designed on the lower part of the main inflow, the River Zala. The first part of the KBWPS started to function in July 1985. After a few years the system became hypertrophic. According to our results, approximately 80 000 t of suspended solids, 300 t of total phosphorus (TP), 250 t of phosphate-P, 850 t of total nitrogen (TN), and 2450 t of nitrate-N were retained between 1986 and 1997 by the first part of the system. At present, the KBWPS retains about half of the suspended solids, more than one-third of TP, more than two-thirds of phosphate-P, only one-tenth of TN, but more than half of nitrate. A 16 km 2 area of the second part has been operating experimentally since 1992. This part retains approximately 75% of suspended solids (mostly of phytoplankton origin) coming from the first phase, but the phosphorus retention is low due to release of phosphorus from sediments. Until 1991 there were no significant differences in monthly means of the chlorophyll-a content from the western part of Lake Balaton. Since that time the chlorophyll-a content has been decreasing in the lake. This decrease could have been the result of the combined effects of weather conditions (temperature, rainfall) and nutrient availability.

Indirect effect of different fish communities on nutrient chlorophyll relationship in shallow hypertrophic water quality reservoirs

Effects of different fish communities on the proportion of different nitrogen and phosphorous forms and the amount of phytoplankton (chlorophyll a) were examined in two consecutive years (1992–1993) in three Hungarian shallow water reservoirs (Cassette and outer reservoir of the Kis–Balaton Water Protection System, and Marcali reservoir). Possible interactions between nutrient concentrations and the amount of phytoplankton in these reservoirs were also examined. Considerable differences in the proportions of different nutrient forms were observed between the three test sites, which could be explained by the presence of different fish stocks in these reservoirs. In the Cassette, the fish biomass necessary for a water quality improvement was around 50 kg ha−1. Phytoplankton biomass was controlled by the zooplankton, consequently chlorophyll a concentrations decreased considerably, while those of dissolved nutrients significantly increased. In the outer reservoir, phytoplankton was controlled bottom-up, since the 250 kg ha−1 fish biomass was larger than the critical value due to the high proportion of planktivorous species. Chlorophyll a concentrations were high, and nutrients were mainly in particulate form (in algal cells). In the Marcali reservoir, the recently introduced silver carp population could not control fully the phytoplankton. The biomass of phytoplankton decreased only slightly, while its composition changed considerably. Although biomanipulation with silver carp is suitable for ceasing cyanobacterial blooms, reduction of the amount of planktivorous fish seems to be a more adequate method for increasing water transparency, rather than introduction of phytoplankton feeding fish.

The effect of different fish communities on the cladoceran plankton assemblages of the Kis-Balaton Reservoir, Hungary

In 1995 the authors studied the effect of different fish communities on the structure of the cladoceran plankton in a shallow hypertrophic lake. After a fish kill of 1991, different fish communities developed in the Kazetta and the outer area of the Kis-Balaton reservoir. In the outer area of the reservoir, the densities of plankton feeding fish species were considerably higher than in the Kazetta. These differences induced changes in the structure and dynamics of the cladoceran plankton. The biomass of small-bodied cladocerans (mainly Bosmina longispina) was higher and the biomass of the large-bodied cladocerans (D. hyalina, D. magna) was lower in the western and eastern part of Kis-Balaton reservoir than in the Kazetta. A peak in cladoceran biomass in the Kis-Balaton reservoir was observed during the summer, close or during a bloom of filamentous cyanobacteria, whereas in the Kazetta a peak was observed during the spring, before the bloom of cyanobacteria. The adult females of D. hyalina were larger and produced more eggs in the Kazetta than in the outer area of the reservoir.

Management of fish communities and its impacts on the lower trophic levels in shallow ecosystems in Hungary

This study shows that multiyear control of phytoplankton by grazing is possible in otherwise cladoceran dominated ecosystems at low cyprinid fish stocks (around 100 kg ha−1) and where piscivore populations, following manipulation measure, can be sustained at the biomass ratio >15%. This reinforces the idea that fish community structure may be a key to the stability of trophic structures that suppress phytoplankton in ecosystems where otherwise cladoceran plankton dominates. Experimental ponds with lower fish biomass (<150-kg ha−1) had less chlorophyll-a concentration per unit TP than those with higher fish biomass. Regressions of chlorophyll-a vs. total phosphorus in the ponds and Major Lake were not significant at lower fish biomass. However, at higher fish biomass the bottom-up processes dominated across all types of ecosystems studied and the regressions were significant. The biomass of herbivorous Cladocera was significantly higher in ponds with a higher percentage of piscivores.

Regulation of plankton by omnivore cyprinids in a shallow lake in the Kis-Balaton Reservoir System

A long-term food web manipulation experiment was started in 1999 with monitoring in the eutrophic shallow Major Lake (area 11 ha, mean depth 1.1 m). In 2000, studies were continued with removal of 204 kg ha−1 of fish and restocking with 134 kg ha−1 of cyprinids. The removal of about 50% of cyprinid had a quite considerable impact on almost all of the observed parameters. Summer mean chlorophyll a values in 2000 decreased by 43%, phytoplankton community changed from being dominated by filamentous blue-greens causing blooms in 1999 to a much more diverse community with, e.g., green algae, dinoflagellates and cryptomonads in the year following fish removal. The zooplankton community showed the typical composition of lakes with very high predation pressure of omnivorous cyprinid fish leading to a decrease in both mean body length and fecundity of daphnids.

Intrinsic processes causing periodic changes in stability in a shallow biomanipulated lake

Shallow lakes experience alternative states in their biotic organisation over time. In this study, we analysed a long-term dataset on the recovery from eutrophication of a shallow hypertrophic lake (Lake Major, Hungary) following fish manipulation. Disturbances in the food web triggered a shift, markedly affecting both abiotic and biotic variables. Clear and turbid states of Lake Major over the period 1999–2009 were defined by concentrations of chlorophyll-a. Lake Major in a clear-water state had higher transparency and submerged macrophyte cover, lower turbidity and fish biomass, and total phosphorus was relatively low compared to that shown during the turbid-water state. It follows from our study that a regime shift from a turbid state to a clear state can be expected in response to fish manipulation. Reduction in fish biomass increases light conditions, decreases internal nutrient loading and promotes macrophyte dispersion. Food-web effects appear to be considerable in these shallow lakes containing benthic fishes. The roles of phosphorus and submerged macrophytes are essential in maintenance of alternative states of vegetation in shallow lakes of various climatic zones.

Changes in water clarity during fish manipulation and post-manipulation periods in a shallow eutrophic lake.

A food web manipulation experiment was conducted in the small, shallow, eutrophic Lake Major, part of the Kis-Balaton Water Protection System (KBWPS) wetland area. Several factors affected the development of turbid water during the fish manipulation period (FMP) in 2000-2001 versus clear water during the post manipulation period (PMP) in 2002 and 2005-2006. A > 40 % percentage macrophyte cover was the most important factor to differentiate between the years with diverse water quality. However, the concentrations of soluble reactive phosphorus (SRP) did not change significantly between the periods. Lake Major exhibited maximum fish species richness (12 species) during PMP, when richness was twice as high as during FMP. There was a clear succession of macrophyte taxa, mostly related to the natural variability in fish. Initially, the macrophyte community was dominated by Najadosum marini, but after fish removal and restocking of piscivores, Ceratophyllum demersi became dominant. This study showed that there is a high potential for restoration of species-rich submerged macrophyte stands even in a hypertrophic lake having been for more than two decades in a turbid state. Water of Lake Major, as the whole KBWPS wetland area, had not previously been in such a good ecological condition since its establishment in 1986. However, it cannot be concluded from this study whether the new trophic state created by fish manipulation is sustainable for longer period.

Effect of different fish stocks on phytoplankton dynamics in shallow ecosystems

Several studies have shown that grazers play an important role in determining the impacts of nutrient loading on algal biomass (LAMMENS et al. 1990). But in many cases the potenrial of controlling water quality of a eutrophic lake solely with zooplankton grazing is questionable (DEMELO et al. 1992). According to BENNDORF (1995), the maximum efficiency of food web manipulation as a management too! is achieved at an optimum biomass of planktivorous fish. The Kis-Balaton Water Protection System (KBWPS) is a hypertrophic reservoir (area, 18 km; a mean depth, 1.1 m). The separate part o f the reservoir is rhe Cassette (area, 3.5 km ; mean depth, l m) which operates independently of the ourer part of rhe system. In May 1991 and 1992, a mass fishkill occurred in rhe Cassette. During rhese 2 years, approximarely 500 kg/ha fish (rnainly Carassius au re atus gibelio) was removed an d rhe estimated fish biomass was less than 50 kg/ha. At the same time, rhe ou te r part o f the reservoir was no t affected by the fish kili. The estimated fish biomass was more than 150 kg/ha and Carassius aureatus gibelio was the dominanr species. In our study, we tested the effect of fish kili on phytoplankton dynamics in the Cassette, comparing i t to the outer part of the system. The investigations were completed with pond experimenrs from 1993. The ai m o f o ur experiments was to see how the differenr fish stock levels influence the phytoplankton biomass in eutrophic conditions.

Management of Lake Balaton: relations between trophic state and fish populations

M a result of different management measures, the fish fauna o f Lake Balaton has changed greatly during the past few years. These changes include a decline in both cyprinid and predatory fish stocks (TATRAI 1998) and a decrease in algal biomass. A large number of studies have shown that reduction o f the fish stock can cause a significant decrease in chlorophyll a content and the turbidity of water (SoNDERGAARD et al. 1990, T ÁTRAI et al. 1997). This is of special interese for the restoration o f turbid shallow lakes where biomanipulation can cause the system to switch to an alternative equilibrium given scable clear water (Moss 1990). To help arrest the degradation of the fishery in Lake Balaton by decelerating che rate of eurrophication, an extensive research programme was undertaken involving simulation experiments (KrRJASNIEMI et al. 1997, T ATRAI et al. 1997), an d direct scudies o f predator-prey relationships. The aim was to decermine if the water quality of the lake could be improved by fish stock management.