The Effect of Charophyte Communities on Phosphorus Flow in Lake Shinji, Japan

Abstract

Charophytes are a group of aquatic algae similar to vascular plants; they play an important role in the nutrient cycling of lakes. Specifically, under eutrophication, charophytes have a greater capacity for phosphorus accumulation than vascular plants. During their development, charophytes accumulate calcium within their structures, along with dissolved phosphorus from the water column. The calcified structures are deposited onto the lakebed after the death of the plant, with phosphorus co-precipitating with calcium, limiting its return to the water. Lake Shinji is one of many lakes in Japan where the charophyte population is in decline or extinct. Using aerial photographs acquired 70 years ago, we estimate the extent of the historical charophyte community in Lake Shinji, and quantitatively evaluate and examine the extent to which charophytes accumulated phosphorus in the lake sediment. The amount of phosphorus accumulated by the charophyte community in Lake Shinji is estimated to be 0.56-25.5 t P y^-1. Charophytes are not found in Lake Shinji today, and although various species of vascular plants have recolonised the lake, no significant improvement in water transparency has been observed. This study concludes that charophytes are likely to be a more effective measure in combating eutrophication than vascular plants.