Factors controlling changes in the aquatic macrophyte communities from 1984 to 2009 in a pond in the cool-temperate zone of Japan

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We investigated changes in aquatic macrophyte communities over 25 years in Utonai-ko (42°42′N, 141°42′E) in northern Japan and determined the major change-producing factors using canonical correspondence analysis (CCA) of 21 measured hydrochemical variables with potential to influence the occurrence of communities. We then examined the corresponding changes in the 25-year fluctuation trends in the communities and measured variables. The most prominent changes were a decline in the Hippuris community and an increase in the Vallisneria and Myriophyllum communities. CCA revealed that the leading variable was significant wave height (SWH), followed by water depth (WD), total nitrogen (T-N), dissolved oxygen (DO), pH, chlorine ion (Cl−), transparency, mud thickness, and suspended solids (SS). The Hippuris community was positively correlated with T-N and Cl− and negatively with SWH, WD, DO, and pH. All of these variables were likewise correlated with the Vallisneria and Myriophyllum communities but in the reverse direction. SS and transparency exhibited no correlations. During the 25 years, WD and T-N increased, but annual maximum wind velocity and Cl− decreased. Fluctuation of DO was <2 mg ml−1 and pH was consistent. Considering the direction of correlations and 25-year trends, vital factors for the change in aquatic macrophyte communities were WD and Cl−. Because the concentration of C1− was low, the change in aquatic macrophyte communities likely resulted from the increase in WD.