Ecological evaluation of the Cumberland Basin ecosystem model

Abstract

A holistic ecosystem simulation model has been developed for the Cumberland Basin and upper Chignecto Bay, a turbid macrotidal estuary at the head of the Bay of Fundy. This one-dimensional deterministic model has three compartments, three boundaries and three interacting submodels (physical, pelagic and benthic). Twenty-eight biological state variables represent broad functional groups of organisms and non-living organic carbon pools. All major components of the estuarine ecosystem are included. At the present stage of development, individual pelagic state variables give reasonable annual simulations which are in general agreement with available calibration data. Major problems remain with some benthic state variables, especially the subtidal ones about which little is known. In aggregate, the model performs well and output at the ecosystem level agrees with field observations. In the Cumberland Basin water column, annual community respiration exceeds phytoplankton net production (1–3 g C m −3) by a factor of 2–5 suggesting the importance of carbon imported from surrounding saltmarshes and the seaward boundary. Annual community respiration and microalgal net production (28 g C m −2) on the other hand are closely balanced in intertidal sediments. Respiration in subtidal sediments is entirely dependent upon sedimented carbon. The model supports the hypothesis that the Cumberland Basin is a heterotrophic ecosystem with low primary production which requires imported organic carbon to support the production and respiration of higher trophic levels.