Long-term effects of successive Ca(OH)(2) and CaCO3 treatments on the water quality of two eutrophic hardwater lakes

1. Whole-lake experiments were conducted in two hardwater lakes (Half-moon and Figure Eight) in Alberta, Canada, to investigate the effectiveness of r epeated lime (slaked lime: Ca(OH)(2) and/or calcite: CaCO3) treatments (5-7 8 mg L-1) for up to 7 years. 2. Randomized intervention analysis of intersystem differences between the experimental and three reference lakes demonstrated a decline in euphotic t otal phosphorus and chlorophyll a concentrations in the experimental lakes after repeated lime treatments. 3. After the second lime application to Halfmoon Lake, mean winter total ph osphorus release rates (TPRR) decreased to < 1 Mg m(-2) day(-1) compared wi th 3.6 mg m(-2) day(-1) during the winter after initial treatment. In the f inal year of lime application, mean summer TPRR decreased to 4.5 mg m(-2) d ay(-1) compared with 7.6 mg m(-2) day(-1) in the pretreatment year. 4. Mean macrophyte biomass declined and species composition was altered at 1 and 2 m depths in Figure Eight Lake during lime application. Over the fir st 6 years of treatment, macrophyte biomass at 2 m declined by 95% compared with concentrations recorded during the initial treatment year. In the las t year of the study, macrophyte biomass at 2 m reached initial treatment co ncentrations, which coincided with the greatest water transparency. Over th e treatment period, macrophyte species shifted from floating to rooted plan ts. 5. Multiple lime applications can improve water quality in eutrophic hardwa ter lakes for periods of up to 7 years.