Lime treatment and its effects on the chemistry and biota of hardwater eutrophic lakes

1. The main focus of this study was to investigate the effects of single and multiple moderate doses of lime (slaked lime, Ca(OH)(2), and/or calcite, CaCO3) on eutrophic hardwater lakes. This information would contribute to strategies to manage phytoplankton and macrophyte biomass in eutrophic lakes. 2. Water chemistry and biota were monitored for up to 7 years after initial lime treatment and results were compared with reference systems. 3. Complementary studies investigated the effect of lime on macrophytes in ponds, irrigation canals and microcosm experiments. 4. When water pH was kept within its natural range (less than or equal to 10), single and multiple lime applications to lakes and ponds controlled macrophyte biomass, without negatively affecting invertebrate communities. 5. Single lime treatments at moderate dosages of lakes and ponds resulted in variable and mostly temporary changes in chlorophyll a (chl a) and phosphorus (P) concentration. Although sediment P release was reduced in single-dose lakes during the first winter following treatment, reductions appeared temporary. 6. Multiple treatments of lakes and ponds were effective at reducing both chl a and P concentrations over longer periods. Mean winter P release rate was also reduced after initial treatment. 7. In laboratory studies, sediment cores were incubated with eight different treatments to assess P release. Redox-sensitive treatments were no more effective at lowering total P concentration in overlying water than some redox-insensitive treatments. Lime reduced total P concentrations, but was not as effective as treatments with alum. 8. The use of lime in managing macrophyte and phytoplankton biomass in shallow, hardwater lakes and ponds may be preferable over other treatments, because lime is economical and non-toxic as long as pH is kept within a natural range.