Title: Assessment of impact of sewage effluents on coastal water quality in Hafnarfjörður, Iceland

The impact of sewage disposal on water quality in Hafnafjordur was assessed in December 2003 using sewage pollution markers. Feacal coliforms were used as indicators of bacterial pollution while phosphate, nitrate, silicate and oxygen were used as indicators of possible nutrient enrichment in the bay. Also monitored were salinity, temperature and depth. Measurements were done on surface waters. Sea-surface temperatures ranged from 2.2 to 9.7ºC increasing towards the sewage outlets. Oxygen values ranged from 6.23 to 9.66 mg/l. Salinlity measurements were generally low and ranged from 15.59 to 32.79 PSU. The counts of feacal coliform were generally high with the counts ranging between 170 to > 16,000 MPN/100 ml. The bacterial counts were higher close to the sewage outlets and decreased with distance from the sewage outlets. Feacal coliform counts were above the limits recommended by European Community Bathing Water Directive (1976) for drinking and bathing and Icelandic regulation for several water uses and may present potential risk to human health. However, it should be mentioned that this monitoring was undertaken when most adverse effects would be expected regarding feacal coliforms since it was the darkest period of the year when bacteria die-off time is longest and during the low tide close to spring tide when influence of freshwater and sewage is high.

The distribution pattern of nutrients in this study indicates that the influence of sewage on nutrients concentrations within the bay was highest close to the sewage outlets. Silicates, TD-P and DP concentrations ranged from 10.1 to 79.8 µM, 0.9 to 5457 µM and 0.73 to 279 µM respectively. Nitrate concentrations were between 7.3 and 25.65µM closer look at the relationships between different nutrients using established relationships from previous work, revealed deviations that are herein attributed to sewage effluent effects. There was a tendency of increase in feacal coliform counts with increasing nutrient load and depth. There is need to prioritize action to minimize or combat the current impacts from sewage disposal reflected in the water quality. Management options are discussed.