ECOSYSTEM PRODUCTION AND RESPIRATION IN RESPONSE TO EUTROPHICATION INSHALLOW TEMPERATE ESTUARIES

Ecosystem metabolism was measured from diel changes in free-water diss olved oxygen in 3 shallow subestuaries of Waquoit Bay on Cape God, Mas sachusetts, USA. Our goal was to relate metabolism to the different le vels of nitrogen loading to the subestuaries. Automatic meters recorde d O-2. 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 rat es of daytime ecosystem production and nighttime respiration were quit e variable, up to +/-10 g O-2 m(-2) d(-1) for consecutive days. Daytim e ecosystem production was correlated with daily irradiance. At equiva lent values of daily insolation, higher production rates were measured in the more heavily N-loaded estuary. Enrichment also resulted in hig her rates of respiration. Daily rates of respiration and production we re uncorrelated during most deployments, yet a strong correlation emer ged over the year because both rates changed with season. Annual ecosy stem net and gross production (ENP and EGP) increased with N loading i n the 3 estuaries. Significant ENP (about 180 g O-2 m(-2) yr(-1)) occu rred 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, metabolis m in these estuaries is in balance or slightly autotrophic.