Objectives:

The project will study the fate of anthropogenic nitrogen
discharged into estuaries and coastal waters. The removal
of nitrogen in these waters will be quantified in order
to evaluate to what extent nitrogen is being transported
from land to the open seas.

Contents:

The processes leading to removal of nitrogen is burial of
organic nitrogen in the sediment and bacterial
denitrification which is preceded by a number of
microbial processes in the sediment. To assess the
importance of nitrogen removal on a European scale it is
important to understand its regulation. A number of key
parameters for the regulation of nitrogen removal have
been identified: the presence of benthic primary
producers, tidal range and climate.

The benthic primary producers have been divided into
three functional groups: benthic microalgae, marine
angiosperms and floating macroalgae. One major part of
the project deals with investigation of the mechanisms by
which the benthic primary producers affect nitrogen
turnover and the processes ultimately leading to nitrogen
removal in coastal areas.

The effects of tidal range and climate will be analysed
by comparing four different study areas. We have selected
two study areas in southern and two in northern Europe
each representing micro and macro tidal conditions. The
macro tidal areas are the Great Ouse Estuary in England
and the Tagus Estuary in Portugal and the micro tidal
areas are the Kattegat area between Sweden and Denmark
and the Valli di Comacchio in Italy. In each of the micro
tidal areas study sites have been selected in order to
represent ecosystems dominated by each of the three
functional groups of benthic primary producers. In the
macro tidal areas benthic microalgae are the dominant
benthic primary producers and they hence dominate the
study sites selected.

Technical approach:

On each of these study sites a measuring program will be
conducted using standardised methods. Sampling will be
frequent and nitrogen removal and turnover will be
quantified on an annual basis.

The techniques used will be traditional methods for
estimating sediment-water fluxes and nitrogen -15
techniques combined with newly developed/adapted
techniques for estimating nitrogen turnover and primary
production. This will include the use of microsensors for
oxygen, nitrate and nitrous oxide. Experiments will be
carried out as a combination of laboratory and in situ
measurements.

Achievements:

The comparable study of areas with distinct climatic and
tidal characteristics combined with the study of the role
of benthic primary producers in nitrogen turnover and
removal will allow separation of the effects of these
variables. On this basis a classification system of
estuaries and coastal waters will be developed in order
to assess the nitrogen removal ability of these waters.