Biogeochemical indicators as tools for assessing sediment quality/vulnerability in transitional aquatic ecosystems

1. We review the major variables that can be used to monitor sediment characteristics and benthic processes in transitional water bodies with respect to ecological significance, cost/time demands, method consensus, and uncertainty of the current techniques. 2. Most of the state variables, namely organic matter, total nitrogen and phosphorus contents, are easily determined at low monetary/time cost using standardized techniques. However, they are not sufficiently informative to be used as individual-specific indicators. 3. The speciation analysis of nitrogen, phosphorus, iron and reduced sulphur provides much more precise information on the sedimentary buffering capacity. However, analytical techniques are cost/time expensive and often present some critical step, which biases their generalized application. 4. A good understanding of sedimentary processes can also be achieved by measuring benthic fluxes and process rates, but analytical techniques are too expensive to be applied in conventional monitoring programmes. 5. A tentative integrated index, based on a few low-cost simple measures of sediment characteristics (granulometry, organic matter, carbonates, reactive iron and acid volatile sulphides) is proposed, which, in parallel with the water retention time, could provide a rapid assessment of sediment vulnerability status.