Impact of a trout farm on the water quality of an Apennine creek from daily budgets of nutrients.

A detailed 24-h investigation in August 2005 evaluated net dissolved and particulate nutrient budgets in a small trout farm located in the Parma Apennines. During the monitoring period, due to water shortage, the Cedra Creek was almost entirely diverted into the farm; the water flow was 190 l s-1, and the fish standing stock about 20 t. Inflow and outflow waters were characterized for dissolved gases (O2 and CO2) and dissolved and particulate inorganic nutrients ([image omitted] , [image omitted] , [image omitted] , [image omitted] , PN, and PP). Solute concentrations in outflowing waters were found to fluctuate considerably during the day, due to fish metabolic activity and farm-management practices. Despite the small amount of feed supplied to the fish (75 kg d-1) due to high water temperatures (∼20 °C) and the high feed conversion factor (∼1.2), the farm released net amounts of 2.20 and 0.76 kg d-1 of nitrogen and phosphorus, respectively, to the Cedra Creek. Of the nutrients produced, 68% of the nitrogen was as [image omitted] , while 67% of the phosphorus was particulate. Significantly different [image omitted] , [image omitted] , and PP concentrations were measured 500 m downstream of the fish farm compared with inflowing water. This study supports the hypothesis that the ecological quality of creeks or streams receiving fish farm effluents can be seriously affected due to fine particle sedimentation, interstice clogging, simplification of benthic macrofauna communities, and stimulation of microfitobenthos growth. [ABSTRACT FROM AUTHOR]