Summary
This report contains two parts which are self standing reports and a contribution to the HELCOM project EUTRO-OPER. The work has been funded and commissioned by SwAM (Swedish agency for marine and water management) 2014-2015.
- Coastal eutrophication status assessment using HEAT 1.0 (WFD methodology) versus HEAT 3.0 (MSFD methodology)
Eutrophication status is assessed nationally in coastal waters within the Water Framework Directive (WFD) and in open sea areas within the Marine Strategy Framework Directive (MSFD). Both WFD and MSFD consider eutrophication but with different approaches and it is therefore a need for harmonisation in the assessment process.
The Excel based tool HEAT (HELCOM Eutrophication Assessment Tool) has been used in previous assessments in the HELCOM region. There are two versions of the tool; HEAT 1.0 and HEAT 3.0, the first is based on the WFD methodology and the second is based on the MSFD methodology. The main difference between HEAT 1.0 and HEAT 3.0 is how the indicators are grouped. Here we assess the eutrophication status in coastal waters by applying HEAT and compare the results with the national WFD assessments. The present test includes data on 33 selected coastal water bodies in five countries: Estonia, Finland, Latvia, Poland and Sweden. Data on reference condition, acceptable deviation, status and class boundaries of all indicators used in WFD for reporting ecological status (biological and physical-chemical) have been provided for each tested water body. The data has been inserted in the HEAT 1.0 and HEAT 3.0 tools and been compared with the national WFD assessments.
Both HEAT versions gave lower status in more than 50 % of the cases. For some tests the status changed to sub-GES from GES when HEAT is applied. The good/moderate boundary is the same in both HEAT and the WFD while the lower class boundaries in general are stricter in HEAT, which explains the lower status. In national WFD assessments expert judgment is used when there is little, no or very uncertain in situ data. The status in HEAT is given by the one-out-all-out principle but it is still possible to include expert judgment through the weighting factors.
- Development of an oxygen consumption indicator
It was investigated if the oxygen consumption can be used as an oxygen indicator for the Baltic Sea. The method is based on the idea of calculating the oxygen consumption in a stabile layer below the productive zone during summer and relating this to nutrient concentrations. With more nutrients available there is an increased biological production. By estimating how much oxygen is needed to mineralise the biological material it may be possible to link the oxygen consumption to eutrophication.
The oxygen consumption was calculated for the BY15-Gotland Deep in the Eastern Gotland Basin. We identified a stabile layer between 30 and 50 m and a large change in both oxygen and nutrients from June to August. However, the oxygen consumption had a very high inter-annual variation and there were no significant correlation with the winter mean of nutrient concentrations. It was not possible to calculate the diffusion between the layers because of too sparse measurements at the stratification which limits the method. The calculation of the diffusion is however possible to improve with a model. Further on, the depth of the stabile layer is varying between areas and also between years.
We realised that the method has too many restrictions to be a functional indicator. A functional indicator shall not be dependent on heavy modelling or demand too much on expert judgement.
We also investigated if a possible candidate to use as a more simple oxygen consumption indicator could be the use of oxygen saturation at a specific depth. If we assume that the temperature has not changed much since the establishment of stratification we may expect that changes in oxygen saturation observed in August at this depth would be caused by the biological oxygen consumption occurring during late spring and summer. The correlation with winter mean nutrients slightly improved in this case.