Nutrient cycling in Galveston Bay, II - factors regulating their concentrations in the water column.
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In order to investigate factors controlling concentrations of nutrients in Galveston Bay, we carried out linear correlation analysis of chemical data sets from one of the stations occupied monthly by the Texas Water Commission (TWC): mid-Galveston Bay (half-way between Smith and Eagle Pt.). We made the following observations: The annual pattern of phosphate, total inorganic nitrogen and chl.a in the last 10 years exhibits strong seasonal cycles, which appear to be related to temperature. Optimum (P<0.001) cross correlations with temperature, T, were observed for phosphate data, with phase shifts of one month (i.e. PO4 maximum 1 month after T maximum, i.e. in September). This could indicate higher rates of phosphate regeneration from the sediments in the fall. The chl.a data from the last 3 years cross correlated well with temperature when the inorganic nitrogen significantly (p<0.001) and inversely correlates with salinity, with correlation optima at a phase shift of one month after the salinity optimum. Such a pattern could indicate nitrogen inputs from storm sewer overflows during high rainfall events. Frequent observations of close to zero concentration of nitrate in the summer months could indicate nitrogen losses by denitrification in the Bay.