Abstract
We evaluated the “salinity - water quality” and “salinity - macroalgal assemblage” relationships in summer on the polyhaline brackish Lake Nakaumi in western Japan. Temporal data on water variables at the lake center in 21 years (1984-2004 yr) and spatial data of 15 coastal sites within the lake in 2 years (2003, 2004 yr) were analyzed with attention to the salinity - water variables relationship (Secchi-depth, chl.a, TN, TP, DTN, DTP, DO). To evaluate the salinity - algal assemblage relationship, 2 years data at 15 coastal sites was analyzed to quantify the relationship between salinity and 3 assemblage characteristics (maximum vegetated depth, species richness, abundance of algae species). The results showed that the salinity increase resulted in both transparency improvement with decreasing chl.a and nutrient contents (TN and DTN), and the assemblage development with higher values of the three characteristics, both temporally and spatially. Previous studies on oligohaline lakes reported the opposite salinity - water quality/vegetation characteristics relationship, that is, the eutrophication and vegetation decline in higher saline years. This study and previous ones suggest that salinity increase affects many aspects of the ecosystem, and its consequences may differ depending on the location of lake (i.e. distance from sea).
