PURPOSE: The research reported herein investigated the effects of a range of lime (as calcium hydroxide; Ca(OH) 2) dosage levels on the growth of Sago pondweed in outdoor experimental mesocosms. BACKGROUND: Lime (CaCO 3 and Ca(OH) 2) application has been used primarily as a lake rehabilitation technique for limiting algal growth by controlling phosphorus availability in the water column and its release from the sediment (Prepas et al. 1990). At supersaturated concentrations, calcium co-precipitates with phosphorus and settles from the water column. As a deposited layer on the sediment, it can adsorb additional phosphorus (at pH > 8), preventing it from diffusing into the water column for algal uptake. More recently, researchers have found that lime additions can suppress submersed macrophyte growth as well (Babin et al. 1992, Chambers et al. 2001, Prepas et al. 2001). However, the mode of growth suppression, dosage levels, and exposure time requirements are not entirely known. Since lime application drives the pH upward, it may stress macrophyte metabolic activities by inducing inorganic carbon limitation for photosynthesis in hardwater systems. Lime additions to aquatic systems at varying concentrations have not resulted in clear macrophyte community responses. For instance, single dosages of lime at modest concentration levels (<110 mg Ca L-) to hardwater lakes were accompanied by control of macrophyte biomass (species) for over a year (Reedyk et al. 2001). However, Chambers et al. (2001) indicated that exposure time, in addition to concentration, might be important in the control of macrophytes in aquatic systems located in the Canadian Great Plains. These findings suggest that lime application may be a very promising technique for integrated control of both macrophyte and algal production in eutrophic hardwater systems. More information is needed regarding the mode of action, dosage requirements, and impacts on different aquatic macrophyte species in order to develop sound integrated management and control strategies using lime.

The addition of 0.5 and 5.0 ppmw of 7-oxabicyclo [2.2.1] = heptane-2,3-dicarboxylic acid (endothall) to solutions of copper sulfate pentahydrate (CSP) at 1.0 ppmw of copper applied to the roots of emersed parrotfeather (Myriophyllum brasiliense(Camb.) increased the copper content of the roots of these plants. Growth of parrotfeather was inhibited by root applications of 0.5 and 5.0 ppmw of endothall, but CSP did not increase its phytotoxicity. However, a synergistic effect, as determined by dry weight, was calculated after treatment of hydrilla (Hydrilla verticillataCasp.) with a combination of 5.0 ppmw of endothall plus CSP at 1.0 ppmw of copper. An increase in copper uptake and a reduction in phosphorus levels was associated with those plants treated with the combination.