Chara beds acting as nutrient sinks in shallow lakes—a review

Abstract

The capability of Chara beds to act as nutrient sinks in shallow lakes is reviewed. Under favorable conditions charophytes form dense meadows. Biomass and nutrient content in such beds are comparable or even higher than in beds of vascular aquatic macrophytes. As some Chara species are capable of overwintering, the nutrient storage in plant biomass may extend beyond the growing season. Some commonly observed phenomena in vascular plants (nutrient uptake and mobilization of nutrients from the sediment) appear to be unlikely or negligible in Characeae. Charophytes have been reported to decompose slower than their vascular counterparts prolonging nutrient storage in plant biomass. Charophytes may also indirectly affect nutrient cycling in lakes. Utilization of bicarbonate is accompanied by precipitation of calcite during periods of intensive photosynthesis, favoring immobilization of P by binding in the crystal structure or sorption on sedimenting mineral particles. Charophytes are able to deliver oxygen to the sediment, thus potentially enhancing nitrification/denitrification processes and preventing iron-bound sediment phosphorus from being released to the overlying water. Furthermore, dense Chara meadows restrict sediment resuspension, consequently blocking an important internal source of nutrients to planktonic algae. We conclude that Chara meadows probably are an efficient nutrient trap in shallow lakes.