Relationship between water flow volume and in-lake total phosphorus concentrations via dissolved oxygen concentrations and temperature in a warm temperate reservoir: Implications by path analysis

The effects of water inflow-outflow volumes on the in-lake total phosphorus (TP) concentrations was investigated for the deep, stratified Çubuk II Dam Lake. The fluctuations in the TP concentrations followed a seasonal pattern, with lower values found during the summer, and peak values during wet seasons. Both the seasonal pattern and the horizontal/vertical heterogeneities in the TP concentrations were usually found to be in accordance with those of the water flow parameters. The vertical differences in the TP concentrations provided evidence that an interflow formed at the 5 m and 10 m depths by the water inflow resulted in higher mean TP concentrations at these depths. In contrast, the water outflows had a reducing effect on the TP concentrations, particularly at the 15 m depth, by promoting net TP export. Although the horizontal distribution of the TP concentrations differed slightly between the riverine, transition and lacustrine zones, the differences did not indicate any statistical significance (P>0.05, multivariate analysis of variance). The path analysis performed on the vertical data proved to be a promising tool in estimating the direct correlations between water flow dynamics and TP concentrations when the decomposition of indirect correlations via dissolved oxygen concentrations and temperature was accounted for in these mutual associations. © 2006 Blackwell Publishing Asia Pty Ltd