WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 47 (CONTINUED ON PAGE 48) — Semi-intensive Vrkoč pond (VRK, 48°55‘30“N, 16°33‘46“E; Fig. 3). All ponds were located in depressions surrounded by arable land. Basic data on pond characteristics and stocking rates are presented in Table 1. Water Quality Measurements Water quality parameters were monitored monthly at inlet and outlet canals of each pond during the growing season. Water temperature, pH, and dissolved oxygen (DO) concentration and saturation were measured in situ. Hydrochemical determinant assessment included concentrations of suspended solids (SS), biochemical oxygen demand (BOD5), chemical oxygen demand (CODMn), total organic carbon (TOC), NH4-N, NO3-N total nitrogen (TN), PO4-P, total phosphorus (TP), chlorophyll a and trophic potential (the potential capacity for primary production). Microbiological evaluation included counts of enterococci, Escherichia coli, faecal coliform bacteria and mesophilic (22 °C) organisms (MO). A complex evaluation, utilizing saprobiological methods (saprobity index, SI) and diversity assessment, was applied to determine the response of macrozoobenthos community in outlet canals to discharge water quality. Water Quality Trends Water retention in carp ponds results in modification of many physicochemical parameters and biological traits that may influence environmental quality when water is discharged. Despite being extracted from near-bottom layers, pond outlet water temperature was greater than inlet water temperature (Fig. 4). The oxygen concentration of discharged pond water is affected by photosynthesis, fish feeding, manuring and inflow water quality. Generally the oxygen concentration of outlet water was nearly saturated, depending on solar radiation that drives photosynthesis and water temperature. Photosynthetic activity of phytoplankton was also a main driving force in the fluctuation of pH. The most important change in pond water pH occurred in June when pH increased from around 7.6 to 9.0. Concurrently, the DO concentration increased from 3.5 to 13 mg/L and chlorophyll-a concentration increased from 10 to 150 µg/L between inlet and outlet. Semi-intensive carp pond farming is associated with the introduction of allochtonous organic matter in the form of manure or supplementary feed, resulting in increased values of indicators of suspended organic matter (chlorophyll a, BOD, COD and TOC) in pond outlet water (Fig. 4). A considerable proportion of nutrients entering carp pond ecosystems with inflowing water is integrated into the pond trophic chain (Fig. 5). Thus, concentrations of nitrogen and phosphorus and trophic potential decline in the outlet water because a substantial proportion of nutrients were taken up by phytoplankton as the base of the pond food web. The decrease in nutrient concentrations was observable in all monitored forms of N and P, namely NH4-N, NO3-N, TN, PO4-P and TP, which indicate nutrient retention by the pond, confirming that ponds have significant self-cleaning abilities (Davies et al. 2001). The decrease in trophic potential of discharged water was most pronounced in October, when it was reduced by 95 to 99 percent. Contrary to nitrogen and phosphorus concentrations, the content of TOC and SS increased at pond outlets because of increased primary production. In addition, bioturbation activities of benthivorous carp, which are capable of deep penetration into bottom sediments during feeding, contributed to increased concentrations of organic and mineral solids (Roberts et al. 1995, Adámek and Maršálek 2012). Bioturbation was also responsible for an increase in BOD5 and CODMn values at pond outlets. The only exception was in extensive ponds with low fish stocking density and thus lower bioturbation by carp which led to considerably reduced resuspension of sediments into discharged water. These ponds show the decline in SS concentration, and BOD5 and CODMn values. TOP, FIGURE 1. The Velký Tisý carp pond, also an important nature reserve for birds (Photo: Josef Hlásek). MIDDLE, FIGURE 2. The KUR pond is an example of an on-growing pond (Photo: Zdeněk Adámek). BOTTOM, FIGURE 3. The VRK pond is an example of a marketing pond (Photo: Jiří Heteša).
RkJQdWJsaXNoZXIy MjExNDY=