A rapid protocol for assessing sediment condition in eutrophic estuaries

The enrichment of sediments with nutrients and organic matter (eutrophication) is a key anthropogenic stressor of estuaries worldwide, impacting their sediment condition, ecology and ecosystem service provision. A key challenge for estuary managers and scientists is how to effectively quantify and monitor these changes in ecological condition in a timely and cost-effective manner. We developed a Rapid Assessment Protocol (RAP) for characterizing sediment condition based on the qualitative characteristics of sediment colour, odour and texture. We evaluated its utility for assessing sediment condition, and particularly the degree and effects of sediment enrichment (as quantified by complementary measurements of total C, organic C and total N) across 97 sites throughout a eutrophic microtidal estuary. RAP results were strongly and significantly correlated with the degree of sediment enrichment, with RAP scores correctly identifying the assigned enrichment class (low, medium, high) of 83.5% of sites. More enriched sediments exhibited poorer condition, manifested as significantly lower RAP scores for sediment colour, texture and odour, particularly (but not only) where enrichment coincided with elevated mud content. The RAP was particularly successful (<12% misclassification) at identifying sites with low levels of enrichment, indicating its promise as a first-pass survey approach for identifying potential reference or control sites to support impact assessments. RAP approaches based on qualitative sediment characteristics can provide a useful proxy for the degree and impacts of inorganic and organic enrichment, with potentially broad applicability for supporting timely, cost-effective assessment and monitoring of sediment condition in estuaries worldwide.