In situ relationships between spatial-temporal variations in potential ecological risk indexes for metals and the short-term effects on periphyton in a macrophyte-dominated lake: a comparison of structural and functional metrics

Heavy metals may adversely affect the structure and function of the periphyton community in lake ecosystems. We carried out samplings of three habitats at eight sites located in the Lake Baiyangdian that is strongly influenced by wastewater discharge (Sites 1 and 2), aquaculture and densely populated villages (Sites 3, 6, and 8), and the least disturbed (Sites 4, 5, and 7). Cu, Ni, Pb, Zn, Hg, Cd, and Cr were determined in these samples, and the periphyton community was simultaneously studied. The contamination factor (C (f) (i) ) was estimated for every metal as the ratio between pre-industrial records from sediments (C (n) (i) ) and present concentration values (C (i) ), and the individual potential risk (E (r) (i) ) was calculated by multiply the toxic response factor (Tr (i) ) and C (f) (i) for a given substance were based on Hakanson's methodology. The RI was obtained for each sampling site by summing the values of E (r) (i) first and the average was calculated across the sampling sites. The results showed that the RI for all three habitats was lower than 94, and they are in decreasing order: wastewater discharge, aquaculture and densely populated villages, and the least anthropogenic impacted. When the three sampling seasons were compared, August appeared to show the highest risk, followed by April and November. The RI values showed negative correlations (r = -0.444 to -0.851, p < 0.05) with the structural and functional metrics. The best correlation was detected between chlorophyll c/chlorophyll a (Chl c/a) ratio and E (r) (i) Hg (r = -0.851, p < 0.01). Our results suggest the periphyton community can be used in bio-monitoring.