Three years long investigation of fishpond Dehtář - first fishpond in the NETLAKE COST action project

In 2014–2016 we monitored basic environmental parameters in the fishpond Dehtář near České Budějovice (Czech Republic) using system of sensors. Among other parametres we studied for instance water chemistry and phyto- and zooplankton community biomass, and species composition. Thank to the method used we recorded strong fluctuations in some of the environmental parameters, parrticularly in oxygen concentrations. Thank to the integration of the auomatic high frequency monitoring using the sensor system along with traditional research methods we were able to interpret the marked ecosystem changes. Several factors participated in the several days long oxygen depletion: warm and calm weather, later interchanged by cold front accompanied with mixing of water column and cloudy sky, fish farming management (high amount of nutrients related to manuring) and changes in biomass of phytoplancton (fast decomposition of high biomass amount of cyanobacteria). Our results enable to prevent similar situations in future, by e.g. lowering of nutrient input

Fishpond sediment – new approach to the nutrient recycling in the agricultural landscape

Possibilities of the use of the fishpond sediment in the improvement of arable land is discussed. Among others, this approach has a high potential to contribute to the recycling of phosphorus in the agriculture landscapes. For this purpose, we propose set of particular techniques which were tested in the field study

Látková bilance fosforu v produkčních a rekreačních rybnících

21021

Vliv rybníků na kvalitu vody VN Jordán v Táboře

Míra eutrofizace vodní nádrže Jordán v Táboře dosáhla na přelomu milénia velmi vysoké úrovně. To významně omezilo její vodárenské i rekreační využití. V letech 2011-2014 proběhlo na nádrži poměrně rozsáhlé odbahnění, v jehož průběhu bylo odstraněno téměř 270 tis. m3 sedimentů. Od roku 2015 provádí státní podnik Povodí Vltavy komplexní monitoring kvality vody VN Jordán a blízkého povodí. V roce 2017 bylo součástí tohoto monitoringu také sledování 11 rybníků, které byly vyhodnoceny jako potenciálně rizikové z pohledu eutrofizace VN Jordán. Cílem tohoto monitoringu je zjistit, zdali se realizovaná a plánovaná opatření projeví ve zlepšení kvality vody v této vodní nádrži. Doposud pořízené výsledky potvrzují, že pro zachování dobré kvality vody v nádrži i v budoucích letech je nezbytné výrazně snížit vstup fosforu přítoky. Aktuálně by tento požadavek mělo vyřešit vybudování centrální srážecí stanice pro fosfor umístěné na hlavním přítoku VN Jordán. Získané výsledky dále potvrdily, že většina vzorkovaných rybníků je rizikových nejen jako potencionální zdroje fosforu, ale obsahují také významné inokulum fytoplanktonu. Rybníky jsou také zdrojem drobných planktonofágních druhů ryb, které zhoršují celkový efekt biomanipulačních opatření, která jsou realizována v nádrži Jordán.222

Carbon metabolism and nutrient balance in a hypereutrophic semi-intensive fishpond

Eutrophication and nutrient pollution is a serious problem in many fish aquaculture ponds, whose causes are often not well documented. The efficiency of using inputs for fish production in a hypereutrophic fishpond (Dehtář), was evaluated using organic carbon (OC), nitrogen (N) and phosphorus (P) balances and measurement of ecosystem metabolism rates in 2015. Primary production and feeds were the main inputs of OC and contributed 82% and 13% to the total OC input, respectively. Feeds and manure were the major inputs of nutrients and contributed 73% and 86% of the total inputs of N and P, respectively. Ecosystem respiration, accumulation in water and accumulation in sediment were the main fates of OC, N and P, respectively. They accounted for 79%, 52% and 61% of OC, N and P inputs. The efficiency of using OC, N and P inputs to produce fish biomass was very low and represented 0.9%, 25% and 23% of total OC, N, and P inputs, indicating an excessive phytoplankton production and overdosing of fish feeds and manure. Dehtář pond was slightly autotrophic and phosphorus availability did not limit the phytoplankton growth. The low efficiency of using inputs was attributed to the low digestibility of raw cereals grain used as feed and the inability of planktonic food webs to transfer the primary production to fish due to high predatory pressure of fish stock on zooplankton. The primary production is an important input of OC in semi-intensive fishponds and should be considered in evaluations of fish production efficiency

Drivers of Macrophyte and Diatom Diversity in a Shallow Hypertrophic Lake

We studied macrophyte and diatom assemblages and a range of environmental factors in the large hypertrophic Dehtář fishpond (Southern Bohemia, Czech Republic) over the course of several growing seasons. The spatial diversity of the environment was considered when collecting diatoms and water samples in three distinct parts of the fishpond, where automatic sensor stations continually measuring basic factors were established. Macrophytes were mapped in 30 segments of the fishpond littoral altogether. High species richness and spatiotemporal variability were found in assemblages of these groups of autotrophs. Water level fluctuations, caused by the interaction of fish farming management and climatic extremes, were identified as one of the most important factors shaping the structure and species composition of diatom and macrophyte assemblages. The distance of the sampling sites from large inflows reflected well the spatial variability within the fishpond, with important differences in duration of bottom drainage and exposure to disturbances in different parts of the fishpond. Disturbances caused by intensive wave action are most probably a crucial factor allowing the coexistence of species with different nutrient requirements under the hypertrophic conditions of the Dehtář fishpond. Due to a range of variables tested and climatic extremes encountered, our study may be considered as a basis for predictive model constructions in similar hypertrophic water bodies under a progressing climate change

Automatic High Frequency Monitoring for Improved Lake and Reservoir Management

Recent technological developments have increased the number of variables being monitored in lakes and reservoirs using automatic high frequency monitoring (AHFM). However, design of AHFM systems and posterior data handling and interpretation are currently being developed on a site-by-site and issue-by-issue basis with minimal standardization of protocols or knowledge sharing. As a result, many deployments become short-lived or underutilized, and many new scientific developments that are potentially useful for water management and environmental legislation remain underexplored. This Critical Review bridges scientific uses of AHFM with their applications by providing an overview of the current AHFM capabilities, together with examples of successful applications. We review the use of AHFM for maximizing the provision of ecosystem services supplied by lakes and reservoirs (consumptive and non consumptive uses, food production, and recreation), and for reporting lake status in the EU Water Framework Directive. We also highlight critical issues to enhance the application of AHFM, and suggest the establishment of appropriate networks to facilitate knowledge sharing and technological transfer between potential users. Finally, we give advice on how modern sensor technology can successfully be applied on a larger scale to the management of lakes and reservoirs and maximize the ecosystem services they provide