Sediment geochemistry in a eutrophic lake colonized by the submersed macrophyte Myriophyllum spicatum

Summary

The chemical composition of sediment pore water and solid phase was studied in a shallow, eutrophic, hardwater lake (Lake Buckhorn, Ontario, Canada) colonized by M. spicatum. Sediments sustaining a high macrophyte density were characterized by elevated total phosphorus and pore water nutrient concentrations relative to deeper pelagic sediments. This observation suggests that at high densities, macrophytes cause an increase in organic matter and nutrient loading to the sediments. Sediments sustaining low or declining biomasses were characterized by the authogenic formation of a carbonate apatite, very low (< 10⁻⁷M) pore water Fe and PO₄^3-, low redox potential, and relatively high levels of H₂S and NH₄⁺. In laboratory experiments, the growth of Myriophyllum was slightly (15–20%) stimulated by Fe additions to the sediments. The natural levels of H₂S observed in these sediments did not inhibit growth. In this lake, the presence of high densities of macrophytes appears to trigger a series of sedimentary geochemical reactions unfavourable to plant growth and explaining the site-specific decline of Myriophyllum.