Abstract
In Chile, salt (NaCl) use per salmon fish farm ranges between 20-30 t yr-1and is used to prevent and control fungal infections. An increase in salinity in freshwater can have adverse effects on freshwater biodiversity and ecosystem functions and services. We studied the effects of fish-farm effluents on benthic macroinvertebrate communities in a northern Patagonian stream (Chile). Benthic samples were collected at 3 sites near a land-based salmon aquaculture facility (one located 100 m upstream from the fish-farm outlet for effluent, 2 sites located 200 and 400 m downstream from the effluent source). We found changes in benthic macroinvertebrate communities downstream from the effluent, with higher abundances of tolerant taxa and lower abundances of sensitive taxa, which was related to nutrient and salt concentration in the water. We also studied the effects of salinity on macroinvertebrate drift in a mesocosm experiment conducted in recirculating channels, measuring the drift of 2 salt-sensitive macroinvertebrates (Andesiops peruvianusandSmicridea annulicornis), collected from an unpolluted northern Patagonian stream, after exposure to a range of salinity concentration pulses similar to those from fish farms. Our results demonstrate that (1) fish-farm effluent can alter stream macroinvertebrate community composition and dynamics, and (2) such effects are at least partly driven by high salt concentrations in effluent waters.
Highlights
Increased salinity in freshwater is an emerging issue of global concern, with potentially adverse effects on human health, freshwater biodiversity and Publisher: Inter-Research · www.int-res.comAquacult Environ Interact 12: 205–213, 2020 salt, and is known to affect macroinvertebrate drift rates and macrozoobenthos structure in freshwater (Kefford et al 2002, Webb 2012, Cañedo-Argüelles et al 2014, Szöcs et al 2014, Dunlop et al 2015)
Water samples were analyzed for concentrations of total nitrogen (TN), total phosphorous (TP), ammonium (NH4+) and nitrite (NO2−), biological oxygen demand (BOD) and total suspended solids (TSS), all according the Standard Methods for the Examination of Water and Wastewater (APHA 2005)
A gradient in water quality was observed between E1 and E2, with intermediate values found at the downstream site furthest from the effluent outlet (E3), as obtained through principal component analysis (PCA) (Fig. 1)
Summary
Increased salinity in freshwater is an emerging issue of global concern, with potentially adverse effects on human health, freshwater biodiversity and Publisher: Inter-Research · www.int-res.comAquacult Environ Interact 12: 205–213, 2020 salt, and is known to affect macroinvertebrate drift rates and macrozoobenthos structure in freshwater (Kefford et al 2002, Webb 2012, Cañedo-Argüelles et al 2014, Szöcs et al 2014, Dunlop et al 2015). Discharges from land-based fish-farms contain dissolved nutrients, disinfectants and other substances that can have potentially harmful effects on freshwater communities. In southern Chile there are around 300 land-based salmon farms which produce up to 2000 t yr−1 of fish. Each farm utilizes 20–30 t yr–1 of salt (NaCl) in order to prevent and control infections (Marking et al 1994, Zaror et al 2004, Tello et al 2010), which have caused an increase in freshwater conductivity from 50 μS cm–1 to up to 1000 μS cm–1 downstream from where the effluents are discharged (Nimptsch et al 2014). In Chile, land-based fish-farm effluents must meet environmental emission standards (MINSEGPRES 2001), which set chloride to 2000 mg l−1 (5359 μS cm−1), but there are no specific standards for protecting river biota
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