Use of sedimentary pigments to infer past phosphorus concentration in lakes

Excessive nutrient loading is one of the major human pressures affecting lake water quality in the world. In Europe, most of the lakes are P-limited, and since the 80s, extensive effort has been accomplished to reduce Ploading in eutrophic lakes, to avoid massive algal blooms and to reduce excessive phytoplankton biomass. In spite of this effort, lake eutrophication remain a widespread problem in Europe. The enforcement of the Water Framework Directive requested to Member States to restore all significant water bodies close to their pristine conditions or to a "good reference" state. Defining reference conditions becomes then a major step in defining management goals and to calibrate restoration targets. A new palaeolimnological method for inferring past total phosphorus (TP) concentrations in lakewater from sedimentary pigments, particularly total carotenoids (TC), was proposed. It is based on a strong statistical correlation (p < 0.001) between total carotenoids (TC) in the surface sediment of a number of Italian lakes and TP concentrations measured in these lakes at overturn. This "training" set was used to obtain a transfer function to estimate past TP concentrations from sediment cores. Root mean square error of prediction (RMSEP) of the pigment model is lower than those derived from certain diatom inference models. Predicted and residual values are not related to the estimated values, and their average is not statistically different from zero. Errors were estimated via. a 'leave-oneout' re-sampling technique. The results generally agreed with TP values as measured by long-term water quality monitoring programs. Contrasting results were obtained respect to diatom-inferred TP. Diatom model tend to overestimate TP values above 100 mg l 1, pigment model correctly estimated TP in lakes when TP was <100 mg l 1, but not when lakes were rich in macrophytes. Pigment method permits rapid and relatively inexpensive determination of reference trophic conditions.