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Assessment of marine benthic quality change in gradients of disturbance

Comparison of different Scandinavian multi-metric indices

image of Assessment of marine benthic quality change in gradients of disturbance

In this study we compared three Scandinavian multi-metric indices to assess marine coastal benthic ecological status in seven different gradients of disturbance related to pollution. The indices measure in different ways species diversity and species composition in terms of sensitivity. The impact factors in the gradients included organic load, hypoxia, sediment metal contamination, urban effluents and physical disturbance. The indices responded in a similar way, mostly as a threshold response, to the pressure factors irrespective if the factor was organic pollution, metal contamination or other pressures. Usually, the border between Good and Moderate Ecological Quality Status (EcoQS) according to the Water Framework Directive (WFD), the G/M border, is determined as some deviation from a reference, near-natural, situation. Reference data, however, are difficult to find. An alternative procedure is described here to estimate the G/M border, which does not require near-natural reference data. Threshold values, beyond which faunal structure deterioration commences, were identified from non-linear regressions between indices and impact factors. Index values from the less impacted side of the thresholds were suggested to come from environments of Good and High EcoQS, and the lower border of these data, estimated by the 5th percentile of data after bootstrapping, should form the G/M border. G/M borders for each coastal area (gradient) were calculated and compared with previous studies.

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Material and methods

Falconbridge Nikkelverk is a smelter and refinery plant in Kristiansand, South Norway (Fig. 1a). The plant is located close to Hannevika, a bay in the western part of the Kristiansandsfjord. The primary metals refined are nickel, copper and cobalt. Samples of benthic fauna and sediments were taken at 24 stations in the fjord, where 5 stations were sampled twice and the rest one time, during the last three decades. The fjord sediments in the vicinity of the plant are strongly contaminated with heavy metals (Oug et al., 2004; Berge et al., 2007). Here, we analyzed fauna status vs. nickel and lead. Other metals in the sediments (e.g. copper), were significantly correlated with nickel levels, but had fewer data.

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