The Development Of Macro-Scale Vegetation In A Fishpond Ecosystem With Considerably Reduced Fish Stocking - A Case Study

The case study was carried out in locality of Rod fishpond, South Bohemia, Czech Republic. The site merges with the Tfeborisko protected landscape area and UNESCO biosphere reserve. In agreement with local farming subject these management practices were altered significantly during 2014 and 2015. The fishpond was left free from carp stock and small number of breeding tench and pikeperch was stocked instead. Such a dramatic reduction of fish population induced fundamental change in plankton structure and consequently in the whole fishpond biocenosis.Over the past 20 years, Rod fishpond was exhibiting characteristics of shallow turbid lake with high abundance of phytoplankton biomass comprising of green algae, blue-green algae and flagellates. In 2014, when fish stock had already been reduced, large zooplankton development brought about a clear water stage. At the same time, considerable nutrient reserves in the ecosystem lead to enormous Aphanizomenon flosaquae blooms. These blue-green algae species have not been observed in Rod fishpond in past two decades. The second year was characterised with remarkable development of macro-scale vegetation of Ceratophyllum demersum and Potamogeton pectinatus. Plant coverage of the open water area reached 6.13 ha during the growing season maximum. Also, a significant volume of nutrients was bound in the macro-vegetation. Neither such vigorous growth of submerged vegetation has been observed over the past 20 years.Extreme phosphorus mobilization was recorded during the two years of extensive management practices. Concentration of total phosphorus in Aphanizomenonflos-aquae reached 1.4 mg/l. Analysis of Ceratophyllum demerswn biomass samples confirmed phosphorus concentration of 0.4%, meaning 1.408 g of phosphorus per meter squared of the pond area. Related to the total coverage area, phosphorus bound in aquatic vegetation amounted for 86,310 g. At the same time, concentration of phosphorus measured in water amounted to 0.82 mg/l.