Estimating total ecosystem metabolism (TEM) from the oxygen rate of change: A comparison of two Connecticut estuaries

Total ecosystem metabolism (TEM) refers to the sum of the metabolic processes carried out by all organisms within a defined system. The ecosystems considered here include the water column and that portion of the sediment which communicates with the overlying waters in small, shallow coastal embayments. The tracer for measuring TEM is free-water oxygen concentration. To estimate TEM, observed changes in oxygen concentration in the water column due to the biological processes of primary production and respiration must be separated from those due to physical processes of exchange with the atmosphere and horizontal movement of the water. Rates of TEM can be used as an indicator of the trophic status of an ecosystem and to assess the effects of changes in the driving forces of primary productivity, both natural and human-induced. ^ The advent of unattended instruments capable of monitoring salinity, temperature, and dissolved oxygen at short time intervals for multi-week deployments make this method potentially attractive for tidal systems. However, critical assumptions need to be tested: (1) sampling time span and number of stations provide a meaningful average; (2) subsequent samples are made on either the same water mass or different water masses with similar ecological history; (3) biologically driven rates can be separated from physical ones. I evaluated the validity of using unattended instruments as a means of estimating TEM and determined that the method was valid in the shallow (\u3c2m) tidal embayments included in this study. Guidelines were for determining when the method can be applied to a particular body of water and for determining an adequate deployment length. ^ In addition to an evaluation of the method, the TEM data, coupled with ancillary data (wind, light, primary producer biomass and C:N, estuaree characteristics) were used to compare the two estuaries included in this study: Niantic River and Mumford Cove. Both estuaries appear to be experiencing the effect of anthropogenic nutrient loading, as evidenced by the C:N of the primary producers and the TEM data. Niantic River is experiencing higher nutrient loads, which corresponds to a greater impact on the ecosystem, relative to Mumford Cove.