Jakob Walve, Dept. Of Ecology, Environment and Plant Sciences and Carl Rolff, Baltic Sea Centre, both at Stockholm University
Jakob Walve, Dept. of Ecology, Environment and Plant Sciences and Carl Rolff, Baltic Sea Centre, both at Stockholm University

How would you describe your project in a few sentences?

The purpose of the project is to evaluate how the internal physical properties of archipelago basins can affect the levels and variability of nutrients, chlorophyll and water transparency, which are parameters that determine water quality in the European water framework directive. The water quality data used is from a unique program that samples twice annually in approximately 140 of the 170 identified archipelago basins along the Swedish Svealand coast. Properties such as water turnover time, wind induced mixing, ratio of volume to sediment area above the summer stratification depth etc. may cause levels of nutrients, chlorophyll and water transparency etc. to differ between basins for natural reasons. When using standardized methods to estimate water quality, such differences will be interpreted as different needs for amendment even though the differences may have entirely natural causes.

What are your most important results, and for whom are they particularly useful?

The work is still in the analytical phase but expected results are to identify conditions or properties that lead to potentially high variability in results or estimates which are not representative. In the water framework directive the periods between samplings can be very long (for waters of good quality six years). It is therefore paramount that the estimates are representative. If non-representative or highly variable results are obtained, time trends may be obscured or misinterpreted. Given the high costs of addressing water quality issues such misinterpretations can lead to misdirected and costly actions. A potential strategy can therefore be to avoid sampling in basins or during conditions which are likely to give uncertain estimates.

How can it assist an ecosystem-based management of the marine environment?

The actions taken to amend waters with deteriorated water quality are often dimensioned based on comparison with a desired state of the water quality. If the basin where samples are taken is not representative or if conditions at sampling lead to high variability, erroneous decisions can be made or uncertainty can arise of the need for action. If natural causes are the reason for elevated nutrient concentrations, action to reduce nutrient load may be misdirected, whereas if high variability causes uncertainty needed amendment measures may be considered a too uncertain investment. Hopefully the results will give guidance when sampling in complex archipelagos, such as the Svealand region.