Abstract:
The European Water Framework Directive requires that surface water bodies (both fresh and
saline) reach a good ecological status by 2015. Dissolved oxygen is one of the indicators for
the evaluation of the quality of water bodies, because it is essential for the aquatic community.
Therefore, integrated tools that allow the study of the oxygen dynamics are useful to support
the sustainable management of these water bodies. This study aims at extending an existing
model (ECO-SELFE – Rodrigues et al., 2009) to include the oxygen cycle, and to validate it
for riverine and estuarine conditions, taking advantage of the recent detailed field campaigns in
the Aljezur coastal stream (southwest coast of Portugal) that included measurements of
physical, chemical and biological quantities. ECO-SELFE is a coupled 3D hydrodynamic and
ecological model which targets river to ocean scales. Although previous versions of ECOSELFE
include the simulation of the carbon, nitrogen, phosphorous, silica and iron cycles for
several variables (zooplankton, phytoplankton, dissolved organic and inorganic matter,
inorganic nutrients and dissolved inorganic carbon), the oxygen cycle was not explicitly solved
by the model. To allow the simulation of this cycle, two new state variables - dissolved oxygen
and chemical oxygen demand - were added in the model. The processes considered in the
oxygen cycle are: the gross primary production, the respiration of the community
(zooplankton, phytoplankton and bacterioplankton), the pelagic chemical reactions and the
reaeration. The extended ECO-SELFE was validated in the Aljezur coastal stream using two
different measurement periods (September and May). Data were measured at several stations
located along the stream, from freshwater to marine conditions, which allowed the evaluation
of both spatial and seasonal dynamics. Results showed the ability of ECO-SELFE to
adequately represent the oxygen dynamics in both rivers and estuaries.
