Nagybivalyos Lake System, Lake Nagybivalyos

Nagybivalyos-tórendszer, Nagybivalyos-tó

Lake Nagybivalyos is the largest member of the Nagybivalyos Lake System with its 40-hectare area. It is the mostly loaded, and the mostly hypertrophic since it is located the closest to the tertiary treatment pond of the wastewater treatment plant of city Várpalota. Nutrient and organic load of the lake is amongst the highest among fresh water lakes in Hungary. Most of the reigning microorganisms and algae species like Euglena sp, Oscillatoria sp, Anabeana sp, Microcystis sp. are showing the origin of the load of the lake is wastewater. Highly resistant bluegreen species are reigning the algal biomass of the lake, which are still alive and blooming even in the colder late autumn months as well. The DO levels are not stable, the Secchi depth is around 20 cm or lower, the yearly sludge production due to the huge algal biomass is extremely high. Due to the high concentration of Ammonium, and the high pH, formation of free Ammonia is a constant threat, as well as the fish kill caused by that. The lake manager had been trying to control the diatoms, green algae and bluegreen algae blooms with chemical additions in the past with limited success.

Bioremediation of the lake has started in June 2007. Considering the extremely bad water quality we have used a very high dosage from Bioclean Pond Clarifier. In the first season we have reached mentionable results in the improvement of the water quality. The most important was decreasing the Ammonium levels, and by this decreasing the threat of fish kills occurring because of the formation of free Ammonia. DO levels have been stabilized quickly, the decrease of the sludge layer was measurable in several testing points. The sludge zone has become in oxidative state, as a result the formation of odorous compounds has decreased. The lake has not struggled with algae blooms during the summer, moreover a significant decrease could have been observed in the total algae count for the second half of the summer. Phosphate concentration has slightly increased at the beginning, the cause was the large amount of soluble Phosphorus becoming available from dead algae cells, and the continuous penetration of treated wastewater of the tertiary pond. From September Phosphorus concentration started to decrease continuously. Despite the good results the concentrations of all nutrients were way much above limiting levels, the blooming of various bluegreen species started in late August was unable to be stopped. Starting with Microcystis, continuing with Anabaena, and even in late autumn at a water temperature of 4 Celsius the Oscillatoria has kept the total algae count around 10 000 / ml in the lake.

The goals of 2008. are further decreasing the nutrient forms, improving the Secchi depth, and preventing the lake from bluegreen algae blooms.

NAGYBIVALYOS 14th June 2007. 24th September 2007. 26th November 2007.
Ammonium mg/l 0,73 0,37 0,49
Free Ammonia mg/l 0,2 0,04 0,04
Nitrite mg/l 0,91 0,24 0,34
Nitrate mg/l 40,31 39 18,5
Ortophosphate mg/l 0,53 0,92 0,29
Total Algae Count / ml 37 102 9 480 10 820