Abstract
AbstractNutrient enrichment is a significant cause of ecosystem change in coastal habitats worldwide. This study focuses on the change in a benthic macroinvertebrate community and environmental quality as assessed through different biotic indices following the construction of a sewage outfall pipe in the west of Scotland, from first implementation to seven years after operation of the pipe. Benthic macroinvertebrates are an important part of marine ecosystems because they mediate ecosystem processes and functions, are a key part of food webs and they provide many ecosystem services. Results indicated a clear change in benthic communities over time with an increase in species richness and changes to benthic community composition (specifically feeding type, bioturbation mode and ecological group) towards those indicative of organic enrichment. No clear spatial zonation was observed because organic carbon content increased over the entire area. According to a suite of benthic indices calculated, some negative changes were detectable following the start of sewage disposal, but largely negative community changes, and a change from ‘good’ to ‘moderate’ quality, only occurred seven years after implementation. The increase in species richness in response to increasing disturbance reduced the utility of a multi-metric index, the Infaunal Quality Index, which, instead of amplifying the signal of negative impact, dampened it. We suggest that any change in communities, regardless of direction, should be heeded, and species richness is a particularly sensitive and early warning indicator for this, but a suite of approaches is required to understand benthic community changes.
Highlights
Nutrient enrichment is recognized worldwide as one of the most important causes of change in aquatic ecosystems and one of the leading sources of nutrients comes from sewage discharge, with other significant inputs coming from diffuse, agriculturally derived run-off (Diaz & Rosenberg, 2008; Smith & Schindler, 2009; WWAP, 2017)
For the five indices (IQI, BQI, Azti Marine Biotic Index (AMBI), Benthic Opportunistic Polychaete to Amphipod Ratio (BOPA) and Infaunal Trophic Index (ITI)) that have associated quality classifications, we investigated consistency between classifications to assess whether they performed differently in their ability to detect changes
Organic carbon increased over time from an overall average of 1.2% in 1989 and 1.8% in 1992 to 8% in 1995, where the minimum found at any point in 1995 was greater than the maximum found at any point in 1989 or 1992 (Figure 2)
Summary
Nutrient enrichment is recognized worldwide as one of the most important causes of change in aquatic ecosystems and one of the leading sources of nutrients comes from sewage discharge, with other significant inputs coming from diffuse, agriculturally derived run-off (Diaz & Rosenberg, 2008; Smith & Schindler, 2009; WWAP, 2017). In Europe, even where there are strict regulations on the discharge of sewage, it is still an issue in many areas due to outdated sewage systems or a lag in infrastructure developments achieving the required capacity to match increasing urban populations (Kiedrzyńska et al, 2014) In this sense, coastal habitats are intentionally or unintentionally used to treat waste (Watson et al, 2016). Eutrophication with deoxygenation due to organic enrichment, can lead to lower benthic species richness; degraded ecosystem functioning, such as bioturbation and nutrient cycling; and decreased capacity to provide ecosystem services, including waste treatment, and climate regulation through reduced carbon sequestration (Worm et al, 2006; Smith & Schindler, 2009; Caswell et al, 2018). Changes to benthic invertebrate communities, such as loss of larger species, can have impacts on the wider ecosystem, since they are a key part of the food chain, in particular on predators with specialized feeding strategies, such as some wading birds (Bowgen et al, 2015)
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