Daniele Longhi

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 ( , , , , 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 , while 67% of the phosphorus was particulate. Significantly different , , 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.

Persistence of meromixis and its effects on redox conditions and trophic status in Lake Idro (Southern Alps, Italy)

This paper reports a study of oxygen and redox conditions, trophic status, and phytoplankton community in the meromictic Lake Idro (Italy) from 2010 to 2014. The sequence of causes and effects of meromixis are also evaluated by comparing recent research with studies conducted from the late 1960s to the mid-1990s. In the last half century, Lake Idro was steadily meromictic due to solutes which accumulated in its deep waters, along with both dissolved nutrients and chemically reduced substances produced by the anaerobic microbial metabolism. These substances were retained in bottom waters and made unavailable to upper layers until stratification broke. Mixing episodes occurred in 2005–2006 altering stratification, and oxygen and nutrient distribution within the lake. The potential full overturn effects were also evaluated as potential oxygen consumption due to the oxidation of reduced substances to forecast possible oxygen exhaustion and collapse of biological communities. Finally, meromixis is discussed as a potential threat for deep perialpine lakes using Lake Idro as a reference to comparatively evaluate the present status and possible future trends.