In terms of carbon and nutrients cycling, ecosystems may be classified according to their trophic status. An ecosystems is net autotrophic when production of organic carbon is higher than consumption and storage. Conversely, it is net heterotrophic when consumption exceeds production. River input constitutes the main flux of material from the continents to the ocean and can considerably influence the trophic status of the coastal zone. Despite its fundamental aspect in terms of carbon and nutrients cycling, the net metabolic state of the coastal ocean is still a matter of debate. This is primarily due to lack of data covering adequately the very high spatial and temporal variability characteristic for coastal ecosystems and because of the complexity of the involved processes occurring in these environments. Both the riverine fluxes of nutrients and organic carbon have been significantly affected by human activities and have probably modified the autotrophic versus heterotrophic conditions in estuaries and, locally, in the coastal ocean. Any change or improvement in anthropogenic carbon and nutrients loads will affect the trophic status of coastal ecosystems in a way that still have to be understood.
One of the classical concepts of marine ecology is that dissolved inorganic nitrogen (DIN) availability limits primary production in the marine environment. This view of nitrogen-controlled carbon cycling has been developed for autotrophic systems and forms the basis for the management of the coastal environment with respect to eutrophication due to enhanced nitrogen loadings. In heterotrophic systems there may be net generation of DIN from organic nitrogen rather than a net consumption. Consequently, environmental policies and management strategies to reduce DIN loadings alone are not sufficient for heterotrophic systems.
Objective 1. To quantify the trophic status of coastal ecosystems using different approaches at various time scales.
A wide range of techniques are used to estimate the trophic status of coastal ecosystems. Each techniques involves one or several assumptions and refer to different time scales. As a result, available estimates are difficult to compare and, even at local scale, the link to environmental quality/disturbance is not well established so far. In this proposal, we propose to determine the trophic status of four European coastal ecosystems using simultaneously different available techniques and to compare the estimates at several time scales. These ecosystems have been selected according to major physical characteristics that initiate the trophic status (light, nutrients, organic matter), to the level of human pressure and to their global economic values : the Randers fjord (Kattegat), the inner estuary and the plume of the Scheldt (North Sea) and a Posidonia seagrass meadow (Mediterranean Sea).
Objective 2. To breakdown, unravel and understand the nutrients cycle in autotrophic and heterotrophic systems .
In order to improve our knowledge on nutrient cycling and to assess its relationship with the metabolic state of the ecosystem, we propose to quantify the uptake and turnover of dissolved inorganic and organic nitrogen and phosphorus, as well as to study the distribution, composition and turnover of particulate and dissolved organic matter (labile and refractory). Quantification of the assimilation rates of various N and P species, organic and inorganic, is a necessary step in the assessment of nutrient fluxes as well as phytoplankton and bacterial dynamics. It has also deep implications for food quality in relation to heterotrophic consumption.
Objective 3. To integrate and disseminate results to all appropriate user communities
An important current issue is the translation and implementation of scientific research information onto environmental management strategies. This transfer between intrinsically different fields is not straightforward but nevertheless essential. Scientific results are socially useful only if they are made available and understandable for use by legislators and managers. Scientists are then increasingly required to make explicit to the public and policy-makers the consequences of human activities, so they must be able to derive and make full use of the models and/or other decision supporting instruments, by means of which future developments under different policy options can be explored.
The present proposal is devoted to major environmental issues, notably coastal ecosystems changes. Biogeochemical and socio-economic models will be used to simulate possible future scenarios including better management options. Data that will be generated by the project are novel and will interest a wide audience, including policy makers, global scientific databases, local environmental agencies and the general public. The project as a whole is a major step towards the integration of scientific knowledge into management tools: improvement of monitoring procedures (what has to be monitored and when), better use of historical data, regulations adapted to the trophic status,.... The outputs of the project will notably be of particular interest to countries that will join the EU and where treatment plants are not yet available.