Alkalinity and PO4 co-varies in Danish running waters, and this affects the applicability of the diatom-based indicator of eutrophication SID_TID. Through the analysis of physicochemical and diatom databases, we evaluated the influence of alkalinity on the ability to meet ecological targets and sought to disentangle the effect of alkalinity by the abundance of target diatom species as indicator of high alkalinity and low PO4. Alkalinity was correlated to trophic status indicators (PO4 and BI5), confirming that it is an important interfering factor influencing the SID_TID, and we thus discuss potential causes of the association between these factors. We found no relationship of alkalinity with the abundance of target diatom species. We then developed a probability model, which indicated that at alkalinity values greater than 2,6 mEq/L the probability of meeting ecological targets based on the SID_TID declines drastically and, therefore, the convenience of this index at higher alkalinities should be evaluated.
|Scientific Report from DCE – Danish Centre for Environment and Energy