Eutrophication of a Coastal Marine Ecosystem — An Experimental Study Using the Merl Microcosms

Abstract

Preliminary results are reported from the first 7 mos (June 1981-Feb. 1982) of a nutrient addn. expt. using large seawater tanks at the Marine Ecosystem Research Lab. (MERL) of the University of Rhode Island. N, P, and Si gradients were added in geom. series (1 X to 32 X) to the tanks, in which seawater was pumped at a replacement rate (once every 27 days) to approx. the flushing time of Narragansett Bay. After 3-mo enrichment, at the end of the first summer, denitrification was clearly enhanced at the higher treatment levels. However, at the lower treatment levels, denitrification was capable of removing >100% of the N added while in the 32X system only .apprx.20% of the N could be eliminated. O uptake by the benthos during the first 7 mos increased by .apprx.60% in the enriched tanks and accounted for a variable fraction of the total system O consumption. The mean standing crop of phytoplankton increased with nutrient input, though not in strict proportion to the loading, and showed periodic blooms of diatoms in summer and fall.