On the contribution of subtidal volume fluxes to algal blooms in long Island estuaries

Abstract A bloom of a new picoplankter species Aureococcus anophagefferens occurred in several estuaries in the northeast coast of the U.S.A. in 1985. The phenomenon is believed to be the result of a complex chain of physical-chemical-biological factors. Based on 9 years (1980-88) of tidal data taken at three oceanic locations (Nantucket, Montauk, Atlantic City) and four impacted estuaries on Long Island (Peconic, Shinnecock, Moriches and Great South Bays) it was found that the variance of the sea level fluctuations at subtidal frequencies was much higher than that of the tidal frequencies and highly dependent upon the season. These subtidal variances reached an absolute minimum in the spring of 1985, corresponding to the lowest subtidal volume exchange between shelf waters and the estuaries. Subtidal flushing times were computed taking into account an estimated recirculation parameter. These times were at an absolute high in the spring of 1985; increases of 16, 24 and 12% were determined for Great South Bay, Moriches and Shinnecock respectively. Along with reduced freshwater inflows due to the existing drought, the increased flushing times may have supported a longer permanence of available inorganic nutrient compounds contributing to a favourable environment for the ecological dominance of Aureococcus . The low subtidal sea level fluctuations of 1985 are related to a minimum energy content of the regional wind stress, particularly the alongshore (East-West) component which is responsible for the Ekman pumping into and out of the estuaries.