A Field Study on the Hydrochemistry of Land/Inland Water Ecotones with Reed Domination

The hydrochemistry of land/water ecotones dominated by a reed (Phragmites australis) community was studied in a eutrophic shallow lake in China. The ecotones are composed of reed beds divided by many artificial ditches and serve as a connecting link between the upstream Fuhe River mouth and the downstream central lake. This lake-side ecotone exhibited a strong chemical buffering function and high nutrient removal processes. In the subsurface water of reed beds, the partial CO2 pressure was 23…704 times of that in the atmosphere and the partial O2 pressure was 5…34% of atmospheric O2 pressure. The change of hydrochemical type and greatest nutrient reduction occurred at 0.5 m landward from the reed-bed/ditch boundary. The dominant cations in ditch water and subsurface water were Na+ and Ca2+, respectively. The nutrient level in the reed-bed subsurface water maintained low and stable despite the variable high concentrations of nutrients in the ditch water. The crisscrossed reed-bed/ditch landscape greatly increases the active area between eutrophic river mouth water and subsurface water. Since the area of reed fields in the lake occupies 22% of the lake area, the exchange between the subsurface water of reed beds and ditches can act as a huge buffer to reduce allochthonous nutrient input and the nutrient concentrations in the lake. Thus, the self-purification capacity of the lake ecosystem increased with the presence of an active ecotone.