Second opinion on the JPI Oceans intercalibration of chlorophyll for NEA3/4

The results of JPI Oceans and the review in this report emphasize the very heterogeneous character of the coastal waters in NEA 3/4. The water bodies in NEA 3/4 are subject to many pressures, including eutrophication among others, and to a wide range in abiotic conditions. The concentrations of chlorophyll-a are thus influenced by multiple factors. The analysis of JPI Oceans has focused on the statistical relation between chlorophyll-a and total nitrogen, but has ignored the fact that there are multiple pressures and abiotic and biotic factors influencing chlorophyll. The statistical relations between chlorophyll-a and total nitrogen that were used by JPI Oceans as basis for the intercalibration were only for two out of nineteen monitoring stations statistically significant and show that using total nitrogen as only pressure does not provide a sufficient basis for the benchmarking procedure that was applied. We cannot recommend comparing the national status boundaries on this basis.