ABSTRACT: Ecosystem metabolism was measured from diel changes in free-water dissolved oxygen in 3 shallow subestuaries of Waquoit Bay on Cape Cod, Massachusetts, USA. Our goal was to relate metabolism to the different levels of nitrogen loading to the subestuaries. Automatic meters recorded O₂, temperature, and conductivity continuously at 2 depths in each estuary for 5 to 25 d, 7 to 10 times throughout a year. Day-to-day rates of daytime ecosystem production and nighttime respiration were quite variable, up to ±10 g O₂ m^-2 d^-1 for consecutive days. Daytime ecosystem production was correlated with daily irradiance. At equivalent values of daily insolation, higher production rates were measured in the more heavily N-loaded estuary. Enrichment also resulted in higher rates of respiration. Daily rates of respiration and production were uncorrelated during most deployments, yet a strong correlation emerged over the year because both rates changed with season. Annual ecosystem net and gross production (ENP and EGP) increased with N loading in the 3 estuaries. Significant ENP (about 180 g O₂ m^-2 yr^-1) occurred in the highly enriched system; in the 2 other estuaries receiving lower enrichment rates system respiration (R) and production (P) both increased and thus ENP was small (P~R). On an annual basis, metabolism in these estuaries is in balance or slightly autotrophic.

KEY WORDS: Ecosystem metabolism· Eutrophication · Estuary

Published in MEPS Vol. 141 (1996) on October 3
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996