Effects of lime-induced inorganic carbon reduction on the growth of three aquatic macrophyte species

Lime application to aquatic systems may be an effective means of stressing macrophyte growth and promoting changes in species assemblage by inducing temporary dissolved inorganic carbon (DIC) limitation of productivity. Shoot and root growth response to lime (as Ca(OH)2) application was investigated for three macrophyte species (Elodea canadensis, Stuckenia pectinata, and Vallisneria americana) grown in experimental outdoor mesocosms. Lime was applied to mesocosms at three treatment levels to maintain pH for 1 week at 9.8–10.0 (1.64 mM), 10.3–10.5 (at the bicarbonate–carbonate equivalence point; 3.00 mM), and 10.8–11.0 (4.34 mM). pH recovered to control levels in all treated mesocosms 20 days after lime application. After treatment, HCO3− and DIC declined by 66, 93, and 93% and 60, 89, and 87%, respectively, versus increasing lime application. Concentrations remained lower in treated mesocosms versus the control throughout post-treatment. Differential growth response was observed in the 1.64 and 3.00 mM treatments, suggesting species-specific tolerances to both DIC concentration and form. V. americana was most sensitive to lime as the 1.64 mM treatment resulted in 54% shoot growth suppression versus the control and shoot plus root biomass loss in the 3.00 and 4.34 mM treatments. S. pectinata and E. canadensis exhibited net shoot and root growth (although significantly lower than controls) in both the 1.64 and 3.00 mM treatments and complete growth suppression in the 4.34 mM treatment. Selective control and shifts in species assemblage may be possible by adjusting lime concentration in relation to compensation point and needs to be investigated under field conditions.