Phytoplankton - coastal waters

The current phytoplankton assessment criteria are based on chlorophyll a concentration and total phytoplankton biomass (from microscopic cell counts), resulting in a relatively straightforward link to the nutrient loading along the coast. The assessment period comprises the summer months, i.e., June to August. However, according to the WFD, phytoplankton quality element assessment should also take account of the phytoplankton species composition.

Phytoplankton in WATERS
This sub-project will explore potential indices based on phytoplankton species information, to complement the existing phytoplankton assessment system.

General improvements of the phytoplankton assessment system will include the evaluation of seasonal periods other than those currently used. Use of a more restricted period would likely reduce classification uncertainty.

The project will review studies evaluating indicator species and the use of phytoplankton species or group data in WFD environmental assessment. For the development and testing of indicators, the project depends on existing phytoplankton data, giving priority to high-quality data and previously unused data (e.g., from the 2010 national sampling campaign). We also need to collate corresponding physical–chemical data and data on other factors, such as the water retention times and depth morphology of sampling basins.

Indicator development will be approached by exploring, evaluating, and testing promising phytoplankton indicators based on species composition in relation to gradients of salinity, nutrients, as well as chlorophyll and total phytoplankton biovolume. The available data will also be explored using multivariate statistical tests to find possible links between taxa and nutrients present. Existing data from high-frequency monitoring will be used to test for improvement due to changed assessment period. This will influence all pelagic variables, i.e., chlorophyll, biomass, tot-N, tot-P, and Secchi depth.

In WATERS, new phytoplankton data will be collected in the joint field studies, to evaluate phytoplankton species composition indicators, biovolume, and chlorophyll along well-described environmental gradients. To save costs, the first priority is to complement existing monitoring programmes with additional phytoplankton sampling and analysis. This probably means that sampling will have to be distributed over several years for selected gradients. The selection of gradients represented by many existing data must also be prioritized.

In summary, the sub-project will refine the phytoplankton assessment criteria by adjusting the sampling period and evaluating how phytoplankton species composition can be used in the assessment.