In the Water Framework Directive (WFD), biological quality elements (BQEs) play a major role in allowing the evaluation of the ecological quality of waterbodies. Within the WFD, the request for a classification of waterbodies based on their ecological quality is accompanied by the need of an estimation of precision and reliability of the results of the classification itself. The latter is performed using the Ecological Qualitio Ratios (EQRs), i.e. the ratio between the present value of a biological indicator (or metric) and the value the same indicator would have had in reference conditions. For this reason, an estimation of precision and reliability of the EQRs needs an evaluation of present-time repeatability of the measurement, accompanied by an estimation of the reliability of the estimated reference conditions. In this report we consider both aspects: we compare the results of long-term ecological studies on the present-day temporal variability of phytoplankton indices and paleolimnological analyses of lake cores to estimate the variability of the BQEs in reference conditions, before the onset of strong human pressures. Furthermore, we examine spatial variability within waterbodies, using a san example the fish fauna, the composition of which is very sensitive to the presence of specific habitats (for example for feeding or reproduction), that can differ from one species to another Indices based on phytoplankton resulted to be sensitive to interannual meteorological and variability. This effect can be neutralized using a network of reference sites that can track the present day variability and be used to correct the estimation of the EQRs. The indices based on macrophytes are less sensitive to the meteorological variability, but they seem to be too strict, and we suggest they should be integrated with a phytobenthos metric in order to consider the whole non-phytoplanktonic flora, as requested by the annex 5 of the WFD. Finally, to evacuate the spatial variability of indices based of fish fauna, we compared the results obtained in the littoral areas (using electrofishing) and in the central area of the lake (using nets). In two out of five lakes, sampling a single area gave the same reults taht sampling both areas: this is the case for electrofishing in the shallow Lake Candia and nets in the deep Lake Mergozzo. However, in the other three lakes, sampling a single areas severely biased the estimated biological quality of the waterbody, with a worsening that caused in one case the misclassification of the lake in a poorer quality class. These results show that the sampling of the whole lake is in general needed for an unbiased estimation of the ecological quality of the waterbody based in fish fauna, but also suggest that the sampling protocol can be simplified in lakes where one of the areas in strongly dominant.
Variabilità temporale e spaziale delle condizioni di riferimento degli EQB e RQE
Aldo Marchetto;Andrea Lami;Piero Guilizzoni;Giuseppe Morabito;Alessandro Oggioni;Pietro Volta;Martina Austoni;Igorio Cerutti;Marzia Ciampittiello
2013
Abstract
In the Water Framework Directive (WFD), biological quality elements (BQEs) play a major role in allowing the evaluation of the ecological quality of waterbodies. Within the WFD, the request for a classification of waterbodies based on their ecological quality is accompanied by the need of an estimation of precision and reliability of the results of the classification itself. The latter is performed using the Ecological Qualitio Ratios (EQRs), i.e. the ratio between the present value of a biological indicator (or metric) and the value the same indicator would have had in reference conditions. For this reason, an estimation of precision and reliability of the EQRs needs an evaluation of present-time repeatability of the measurement, accompanied by an estimation of the reliability of the estimated reference conditions. In this report we consider both aspects: we compare the results of long-term ecological studies on the present-day temporal variability of phytoplankton indices and paleolimnological analyses of lake cores to estimate the variability of the BQEs in reference conditions, before the onset of strong human pressures. Furthermore, we examine spatial variability within waterbodies, using a san example the fish fauna, the composition of which is very sensitive to the presence of specific habitats (for example for feeding or reproduction), that can differ from one species to another Indices based on phytoplankton resulted to be sensitive to interannual meteorological and variability. This effect can be neutralized using a network of reference sites that can track the present day variability and be used to correct the estimation of the EQRs. The indices based on macrophytes are less sensitive to the meteorological variability, but they seem to be too strict, and we suggest they should be integrated with a phytobenthos metric in order to consider the whole non-phytoplanktonic flora, as requested by the annex 5 of the WFD. Finally, to evacuate the spatial variability of indices based of fish fauna, we compared the results obtained in the littoral areas (using electrofishing) and in the central area of the lake (using nets). In two out of five lakes, sampling a single area gave the same reults taht sampling both areas: this is the case for electrofishing in the shallow Lake Candia and nets in the deep Lake Mergozzo. However, in the other three lakes, sampling a single areas severely biased the estimated biological quality of the waterbody, with a worsening that caused in one case the misclassification of the lake in a poorer quality class. These results show that the sampling of the whole lake is in general needed for an unbiased estimation of the ecological quality of the waterbody based in fish fauna, but also suggest that the sampling protocol can be simplified in lakes where one of the areas in strongly dominant.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
