The impact of fish farming on the water column and marine sediments in three coastal regions from eastern Aegean coast

A spatial interpolation approach for environmental assessment of aquaculture effects on water quality of Pagasitikos Gulf (Eastern Mediterranean)

The impact of fish farming on the physicochemical and biological parameters of the water column was investigated between July and October 2021, in Pagasitikos Gulf. For this purpose, a sampling strategy based on Geographical Information System (GIS) was developed and a grid of 28 sampling stations was created for in situ measurements. The method of spatial interpolation and especially the Radial Basis Function (RBF) was used to estimate the spatial distribution of DO, chl α and nutrients by means of GIS. General Linear Model (GLM) analysis showed significant differences for all measured parameters except for NO₃. Nutrients remained at low concentrations without exceeding the permitted limits for eutrophication and welfare of cultivated organisms. GIS exhibited high usefulness for data analysis, with further studies warranted for its optimization on applications related to the environmental impact of fish farming.

Ecological risks assessment of sulfur and heavy metals in sediments in a historic mariculture environment, North Yellow Sea

The environment behaviors of sulfur and heavy metals in sediments are closely related to sediment aging in mariculture area. In this study, the distributions and ecological risks of reduced inorganic sulfur (RIS) and heavy metals were investigated, along with the relationships between different occurrences of RIS and heavy metals. The results indicated that the adequate organic matter in mariculture sediments significantly enhanced the accumulation of acid volatile sulfur (AVS) compared to the control area. In shellfish farming area, biological sedimentation contributed to accumulation of AVS. The chromium (II)-reducible sulfur (CRS) was the main component of RIS in mariculture area. The environmental risks of heavy metals in mariculture area presented low levels. Principal component analysis (PCA) showed that distribution of Cu closely related to mariculture activities compared to other heavy metals. For ecological risks of heavy metals, the ratio of ∑(acid-soluble fraction (F1) + reducible fraction (F2) + oxidizable fraction (F3))/AVS was the appropriate index rather than conventional simultaneous extraction of heavy metals (SEM)/AVS, because SEM/AVS would overestimate the toxicity of heavy metals. AVS/RIS ratios significantly positively correlated with Pb (F2/(F1 + F2 + F3 + residual fraction (F4)), F2/∑F), Pb (F3/∑F), and Zn (F3/∑F), while significantly negatively correlated with Pb (F4/∑F) and Cu (F1/∑F). These results indicated that the accumulation of AVS during the mariculture process was conducive to the formation of F2 and F3 of Pb, and F3 of Zn, conversely to the formation for F4 of Pb and F1 of Cu, because it was opposite to the accumulation of CRS.

Environmental impact of fish farming: assessment of metal contamination and sediment geochemistry at three aquaculture areas from the eastern Aegean coast

Metal contamination and geochemistry of surface sediments were assessed at three aquaculture sites from the eastern Aegean coast. The chlorophyll degradation products and organic carbon levels were used as indicators of eutrophication status. In Akköy, higher Hg, Pb, and Cd levels were observed around the cages, while maximum concentrations of other elements were determined at stations situated near the Büyük Menderes River estuary. Metal concentrations were less than the central Aegean coast background levels other than Zn, Ni, and Cr in Akköy. Several approximations have been utilized to evaluate potential toxicity of sediments and sediment quality guidelines (SQG) were used to estimate the risks for aquatic life. Ni was the only metal with concentrations exceeding all SQG values, which indicates the highest adverse biological effect in Ildır, Akköy, and occasionally toxic in Güllük. Based on Q_PEL and Q_TEL, Ni and Cr were the predominant metal contaminants in all areas. Similarly, Cr and Ni account for the most of the all sediment toxicity in the aquaculture areas according to toxic risk index. It is concluded that sediments around the fish farms are affected by growing input of elements because of aquaculture activity. The levels of chlorophyll degradation products showed oligotrophic and mesotrophic conditions in the three studied aquaculture areas.