Timmermann, K, Christensen, J.P.A. & Erichsen, A. 2021. Establishing Chlorophyll-a reference conditions and boundary values applicable for the River Basin Management Plans 2021-2027. Aarhus University, DCE – Danish Centre for Environment and Energy, 32 pp. Scientific Report No. 461 http://dce2.au.dk/pub/SR461.pdf
Summer Chlorophyll-a concentrations are used as environmental indicator to assess ecological status of Danish coastal waters regulated by the Water Framework Directive (WFD). According to WFD, ecological status has to be classified relative to a reference level corresponding to an undisturbed condition. In this report, we use established Bayesian and mechanistic models to establish water body specific Chlorophyll-a reference conditions for Danish WFD water bodies. Since no Danish coastal areas or similar coastal ecosystems in proximity can be regarded as undisturbed by human activities and no historical chlorophyll-a data from pristine conditions exists, we use water quality models to estimate the reference level of chlorophyll-a. Here we demonstrate how to combine reference scenarios from two independent water quality models, in a combined model using water body specific physical and hydromorphological data as forcing data for the model. This model allows us to obtain site-specific reference values for all Danish water bodies within the calibration range.
