Using the criteria laid down by the European Environmental
Agency (EEA, 2001, 2003), water quality is assessed with reference
to the N/P ratio and the concentration of dissolved nitrogen and
orthophosphate. Autumn and winter (monthly averages) are
characterised by poor and bad water quality in terms of N
concentration; N/P ratios in this period are high, confirming that
the waters are affected by agricultural runoff. The summer months
have good water quality, partly due to the fall in DIN. December and
January also have poor water quality in terms of phosphate
concentration. The rest of the samples are mostly of good quality
(Fig. 8a and b)