Abatement of water nutrient load in a fish culture system using the aquatic trophic levels.

Integrated aquatic systems are used to decrease the nutrient loads of effluents negating the negative environmental impacts of aquacultural systems. Some of these systems have a separate algae compartment requiring high maintenance. An integrated culture system was set up with different trophic levels: algae, zooplankton, and fish. The algal tank was in-line with the fish and zooplankton components to minimize the maintenance required for the algae. A control flow-through system was also set up without the algae and zooplankton compartments. The systems were run for 6 weeks, and water temperature, pH, dissolved oxygen, NO3 , NO2 , NH4 , and PO4 concentrations were measured. A removal rate was determined for each water parameter and the densities of the algae and zooplankton species were measured in each compartment of the integrated system. The concentrations of most nutrients in the integrated system were similar to those of the control system. The density of algae increased during the first 3 weeks and remained almost stable until the end of the experiment. There was an inverse relationship between the densities of two zooplankton suggesting compensatory effects on the control of the algal bloom. The integrated system improved water quality with minimal algal culture maintenance, water exchange, and no fish mortality. PRACTITIONER POINTS: An integrated system could effectively reduce the nutrient load of water. Water replacement in the integrated system was significantly lower than that of a flow through system. The inline plankton culture tanks decreased greatly the maintenance of the system.

Environmental indicators in effluent assessment of rainbow trout (Oncorhynchus mykiss) reared in raceway system through phosphorus and nitrogen / Indicadores ambientais na avaliação de efluentes de truta arco-íris (Oncorhynchus mykiss) criados em sistema de raceway através do fósforo e nitrogênio

Abstract The phosphorus and nitrogen discharge via effluent of intensive trout farming system was quantified through the use of environmental indicators. The nutrient loads, the mass balance, the estimated amount of nutrients in feed and the amount of nutrients converted in fish biomass were calculated based on the concentrations of phosphorus (P) and nitrogen (N) in the feed and in the water. Of the offered feed, 24.75 kg were available as P and 99.00 kg as N, of these, 9.32 kg P (38%) and 29.12 kg N (25%) were converted into fish biomass and 15.43 kg P (62%) and 69.88 kg N (75%) were exported via effluent. The loads and the mass balance show the excessive discharge of nutrients via effluent, corroborated by the feed conversion ratio (2.12:1) due to the low efficiency of feed utilization, therefore, it is proposed the use of this zootechnical parameter as environmental indicator. In addition, feed management practices are not adequate, highlighting the low frequency of feeding during the day, excessive amount and low quality of feed offered. These results demonstrate the need for adequate feed management and the need for careful monitoring of effluent.

Resumo A descarga de fósforo e nitrogênio via efluente do sistema intensivo de truticultura foi quantificada através da utilização de indicadores ambientais. As cargas de nutrientes, o balanço de massa, a quantidade estimada de nutrientes na ração e a quantidade de nutrientes convertidos em biomassa de peixes foram calculados com base nas concentrações de fósforo (P) e nitrogênio (N) na ração e na água. Da ração oferecida, 24,75 kg estavam disponíveis como P e 99,00 kg como N, destes, 9,32 kg de P (38%) e 29,12 kg de N (25%) foram convertidos em biomassa de peixe e 15,43 kg P (62%) e 69,88 kg N (75%) foram exportados via efluente. As cargas e o balanço de massa mostram a descarga excessiva de nutrientes via efluente, corroborado pela taxa de conversão alimentar (2,12:1), devido à baixa eficiência na utilização da ração, portanto, propõe-se a utilização deste parâmetro zootécnico como indicador ambiental. Além disso, as práticas de manejo alimentar não são adequadas, destacando a baixa frequência de alimentação durante o dia, quantidade excessiva e baixa qualidade da alimentação ofertada. Esses resultados demonstram a necessidade de manejo alimentar adequado e de monitoramento do efluente.

Linking river nutrient concentrations to land use and rainfall in a paddy agriculture-urban area gradient watershed in southeast China.

The effects of land use and land-use changes on river nutrient concentrations are not well understood, especially in the watersheds of developing countries that have a mixed land use of rice paddy fields and developing urban surfaces. Here, we present a three-year study of a paddy agricultural-urban area gradient watershed in southeast China. The annual anthropogenic nitrogen (N) input from the agricultural region to the urban region was high, yet the results showed that the monthly nutrient concentrations in the river were low in the rainy seasons. The nutrient concentrations decreased continuously as the river water passed through the traditional agriculture region (TAR; paddy rice and wheat rotation) and increased substantially in the city region (CR). The traditional agricultural reference region exported most of the nutrient loads at high flows (>1mmd(-1)), the intensified agricultural region (IAR, aquaculture and poultry farming) exported most of the nutrient loads at moderate flows (between 0.5 and 1mmd(-1)), and the CR reference area exported most of the nutrient loads under low to moderate flows. We developed a statistical model to link variations in the nutrient concentrations to the proportion of land-use types and rainfall. The statistical results showed that impervious surfaces, which we interpret as a proxy for urban activities including sewage disposal, were the most important drivers of nutrient concentrations, whereas water surfaces accounted for a substantial proportion of the nutrient sinks. Therefore, to efficiently reduce water pollution, sewage from urban areas must be addressed as a priority, although wetland restoration could also achieve substantial pollutant removal.