Heterotrophic slimes in Irish rivers: Evaluation of the problem

Abstract

A questionnaire survey was used to determine the frequency of occurrence, extent and duration of slime growth in Irish rivers. Other factors such as the source of slime-promoting effluents, the degree of treatment given to effluents prior to discharge and the effects slime growth was having on watercourses were also examined. 156 outbreaks were recorded throughout Ireland which affected approx. 350 km of channel. Discharges from the agricultural processing industry and domestic sewage were most frequently associated with slime outbreaks. Few of the outbreaks were insignificant in length with 33.7% in excess of 1 km and 13.5% in excess of 5 km. Although 12.6% of outbreaks resulted in no adverse effects on watercourses, major problems reported included the appearance and amenity value being adversely affected (86.4%), smell and deoxygenation (46.6%), damage to fish stocks (37.9%) and problems of sloughed flocs of slime (24.3%). The severity of these adverse effects was directly related to the length of outbreaks. The situation in Ireland is compared to England and Wales.