Effect of fish farming on the water column nutrient concentration in a semi-enclosed gulf of the Eastern Mediterranean

Abstract

The spatial and seasonal impact of ¢sh farming on the water column of two ¢sh farms in the Eastern Mediterranean was investigated, between July 2004 and April 2005. In the area of each ¢sh farm, three stations were sampled. One was located at the centre of the ¢sh farm, the other at a distance of 50 m from the centre and the last one at a distance of 300 m from the ¢sh farm centre. At each sampling station, water samples were collected at the surface, at 5 m and at every further 10-m depth from the surface to the bottom, for nutrient analysis (ammonium, nitrite, nitrate, phosphate, silicate). Statistical analysis showed signi¢cant di¡erences between seasons for all nutrients, with the exception of nitrite in one of the farms. Furthermore, ammonium, nitrite, phosphate and silicate values showed signi¢cant di¡erences among sampling stations. The maximum concentrations of the above nutrients (1.64, 0.10, 2.57, 0.28 and 4.89 mM respectively) were recorded at the sampling stations located at the centre of each ¢sh farm and they were gradually reduced with increasing distance from the cages. The concentrations of nutrients did not appear to exceed permitted levels for the appearance of eutrophication. The maximum concentrations were considerably lower than those observed previously in the study area.

Water quality and plankton populations in an earthen polyculture pond

“…Nitrate is found in well-oxygenated waters and its variability is due to biological activity (Neofitou and Relative abundance (%) of zooplankton groups in the fish pond at the different samples sites (P 1 -P 6 ) during the studied period. Klaoudatos, 2008). The above was confirmed in current research since high nitrate concentrations, when compared with other nutrients (TP, orthophosphate and ammonia), may be associated with dissolved oxygen above 4 mg.L -1 and the continuous water flow which is heightened during the summer when heavy rains occur.…”

“…The greatest abundances of Cyanobacteria were observed in the site P 1 where orthophosphate concentration was at its lowest Cyanobacteria abundance might have been influenced by a favourable N:P ratio. Further shallow systems are characterised by phosphate limitation because the biologically available phosphorus amount is small when the quantity required for algal growth is take into consideration (Neofitou and Klaoudatos, 2008). Orthophosphate concentrations in the current study were lower than 50 mg.L -1 , except at the P 6 (September) site.…”

“…In this study, phosphorus and nitrogen concentrations were below characteristic eutrophication conditions, which are 0.3 mg.L -1 for nitrogen and 0.001 mg.L -1 for phosphorus in fish ponds, considering the maximum value recommended as an environmental quality standard to avoid eutrophication (Neofitou and Klaoudatos, 2008). The opposite behaviour was observed with chlorophyll-a, which has shown concentrations of over 10 mg.L -1 .…”

Biofilm responses to marine fish farm wastes

“…The impact of fin fish aquaculture has been widely reported in the benthos, where common degradation patterns have been observed (Kalantzi and Karakassis, 2006), since the seabed is able to record possible detrimental effects to the environment over long periods of time (Danovaro, 2003). In the water column however, the effects are less obvious (Neofitou and Klaoudatos, 2008), and any differences in the measured parameters are usually more influenced by seasonality than aquaculture wastes (Pitta et al, 1998;Yucel-Gier et al, 2008). Indeed, water column parameters are often not correlated with the extent of benthic impact.…”

Exchange of nutrients and oxygen across the sediment–water interface below a Sparus aurata marine fish farm in the north-western Mediterranean Sea

“…Some studies have analysed metals and pigments found in sediments as well as bacteria and multiple stable isotopes as indicators of environmental impact (Mazzola et al 2000;Kaymakci et al 2010). Others have focused on the environmental impact of aquaculture activities on nutrients and plankton (Neofitou and Klaoudatos 2008); on nutrients and benthic community structure (Mazzola et al 2000;Yucel-Gier et al 2007); and on the geochemistry of sediments and benthic organisms Mazzola et al 2000).…”