Is the bioproduction number a good index of the trophic state in Mediterranean wetlands?

Eutrophication is one of the major problems affecting water quality of inland waters. Therefore trophic state evaluation is essential for the conservation, the management and the application of possible future restoration measures. The main aim of this work was to assess the effect of different land uses in the drainage basins of the Mediterranean wetlands on the bioproduction number (BPN), an indicator of the wetland trophic state. For this, we selected seven wetlands with different areal extension of agricultural land in their catchment area. The data obtained from BPN were compared with those obtained from the trophic state index (TSI). The results showed that there is a discrepancy between TSITP, TSIChl (a) and BPN values in our wetlands, and that the application of the BPN for estimating trophic state in Mediterranean wetlands has clear limitations when the organic matter content in surface sediments is low. This occurs in wetlands with a great proportion of drainage area covered by intensive agricultural uses, which causes high soil losses by accelerated erosion. As a conclusion, not only high organic matter contents, as it has been stated in previous literature, but also low organic matter contents limit the validity of BPN.