Factors to change two alternative systems, macrophyte-rich macrophyte-free in shallow lakes

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We investigated aquatic macrophytes, water quality, and phytoplankton biomass and species composition in three shallow lakes with different levels of vegetation coverage and nutrient concentrations in Kushiro Moor during August 2000. Trapa japonica can live at a wide range of nutrient levels. It forms an environment with a steeper extinction of light, higher concentrations of dissolved organic carbon (DOC), lower concentrations of dissolved oxygen (DO) near the bottom, and lower concentrations of nitrate + nitrite, and soluble reactive phosphorus (SRP). The pH was much higher In a Polygonum amphibium community, and the DO near the bottom did not drop. The relationship between chlorophyll a and the limiting nutrient (TP when TN : TP 【greater than or equal】 10, and TN/10 when TN : TP < 10) significantly differed between lakes with and without submerged vegetation. The chlorophyll a concentrations at a given nutrient level were significantly lower in water with submerged macrophytes than in water without them. Correspondence analysis showed that the difference in phytoplankton community structure among sites is due largely to the presence or absence of submerged macrophytes, and the ordination of phytoplankton species in the lakes with submerged macrophytes is best explained by environmental gradients of TN, chlorophyll, pH, and SRP