PREDICTING THE SPRING ALGAL BIOMASS IN LOUGH-NEAGH USING TIME-SERIES ANALYSIS

1. Lough Neagh is a large eutrophic lake covering 387 km(2) with a mea n depth of 8.9 m. It is an important natural resource, being the large st single source of potable water for Belfast, Northern Ireland. 2. Th is report examines the causes of the year-to-year variation in the Apr il-June (spring) algal biomass, measured as chlorophyll a, for the per iod 1974-92. 3. The spring chlorophyll a declined following the introd uction of a phosphorus (P) reduction programme at major sewage treatme nt works in 1981. However, since 1990 the chlorophyll a concentrations in the spring have increased. 4. Time series methodology was employed to develop a model which explained 76% of the annual variation in spr ing chlorophyll a concentrations. 5. The independent variables used in the multiple regression model were the previous year's spring chlorop hyll a concentration, soluble reactive P inputs for April-June and the particulate P concentration in the Lough during the previous summer.