LAKE ECOLOGICAL ASSESSMENT METRICS IN IRELAND: RELATIONSHIPS WITH PHOSPHORUS AND TYPOLOGY PARAMETERS AND THE IMPLICATIONS FOR SETTING NUTRIENT STANDARDS

摘要

The current national surface water monitoring programme in Ireland includes 224 lakes. Monitoring data from the period 2012-14 are used to evaluate the performance of ecological assessment metrics in responding to eutrophication pressure, as indicated by average total phosphorus concentration (TP). For 70 surveillance lakes, the r(2) for relationships with TP was 0.65 for phytoplankton, 0.65 for macrophytes, 0.59 for phytobenthos and 0.32 for fish. Following normalisation of the Ecological Quality Ratios (EQR) to a 0-1 scale; averaging together the results for phytobenthos, phytoplankton and macrophytes resulted in a higher r(2) of 0.84 with TP. Using the ecological boundaries intercalibrated across the EU, the corresponding TP concentrations for the high/good and good/moderate boundary ranged from 8 to 11 and 16 to 30 mu g l(-1) respectively. Non-parametric multiplicative regression was used to examine the strength of influence of typological parameters on the relationship between the assessment metrics and TP. Typological factors found to be significant for these models included lake area, mean depth and alkalinity. However, the most important model parameter, as indicated by higher sensitivity values, was TP. This was in part because metrics were designed to detect eutrophication pressure, but also because typological factors are already considered in both metric application and through type-specific EQR boundaries (for example, through incorporating depth or alkalinity in typology). Marl lakes may represent a more sensitive lake subtype requiring derivation of separate, more appropriate environmental quality standards. Further analysis in this regard is required.