SEASONALITY IN NUTRIENT CONCENTRATIONS IN GALVESTON-BAY

In order to investigate factors controlling nutrient cycling in the sh allow and turbid coastal ecosystem of Galveston Bay, data from: (I) th e Texas Water Commission (TWC) database 1980-1989, and (2) salinity tr ansects in 1989 and 1993 are presented and analyzed. Statistical regre ssion and time-series analysis were carried out on data acquired by TW C between 1980 and 1989, in an attempt to establish seasonality of nut rient and chlorophyll-a (chl.-a) concentrations in the bay and to dete rmine factors which regulate these concentrations. A strong seasonalit y was found for phosphorus and chl.-a in the upper and mid-bay station s. A recurring maximum for phosphate occurred in September and a chl.- a maximum occurred regularly in March-April. It is hypothesized that b enthic regeneration of phosphorus at the end of summer is responsible for the phosphate maximum. The inverse correlation of the partition co efficient (K-d) for phosphate with the concentration of suspended part iculate matter (SPM), coupled to a strong enrichment of phosphate in s uspended particles at low SPM concentrations, indicates additional con trol by geochemical and physical processes such as particle sorting an d/or particle-colloid interactions. Nitrate is inversely correlated wi th salinity at the upper and mid-bay stations, indicating the Trinity River is a major source. Nutrient concentrations in the lower bay (Eas t and West Bay stations) are considerably lower and less predictable, as they are nob correlated with salinity or temperature. Data from the 1989 and 1993 transects confirm the yearly maximum in phosphate conce ntration in late summer months, with peak concentrations in the upper Trinity Bay. It is concluded that despite possible phosphate buffering by physical and geochemical mechanisms, relatively large concentratio n maxima recur regularly every year during the summer, possibly caused by a benthic source of phosphate.