NATURAL ESTUARINE PARTICLES AND THEIR UPTAKE OF
NITROGEN IN ESTUARIES (NEPTUNE)
A.D. Tappin, M.Fitzsimons and G.E. Millward
School of Earth, Ocean and Environmental Sciences, University of Plymouth, Drake
Circus, PL4 8AA, UK
Globally, total nitrogen (N) loadings to estuaries will continue to increase due to
changes in climate, urbanisation etc. Currently, organic N (ON) constitutes >50% of
the total N input to estuaries. However, the speciation and reactivity of ON in
estuaries are poorly quantified, thereby invoking major uncertainties regarding the
factors controlling the flux of N within and from estuaries. A key uncertainty
concerns the particle-water interactions of ON and the role of estuarine master
variables in modifying ON partitioning and reactivity.
Suspended particles (SPM) within turbid estuaries such as the Tamar, South West
England, can be broadly separated into permanently suspended particles (P-SPM) and
temporarily suspended particles (T-SPM), with the latter undergoing periodic
resuspension and deposition. P-SPM generally exhibits larger surface areas and
enhanced sorption properties compared to T-SPM. In addition, low settling velocities
(<0.01 cm s-1) mean that the residence time of P-SPM approximates to that of the
water and thus may potentially dominate the flux of particulate N exported from the
estuary.
NEPTUNE hypothesis: The reactivity and flux of ON in turbid estuarine systems is
significantly controlled by specific fractions within the SPM population.
NEPTUNE aims: (1) to fractionate estuarine SPM on the basis of particle settling
velocities (2) to characterise the particle fractions (physico-chemical and biological
properties) in relation to their ON loading (3) to determine the reactivity of the
particle fractions to ON in relation to particle characteristics and the potential master
variables of salinity, dissolved organic carbon and bacterial activity.
The NEPTUNE project began in September 2003 and this presentation will provide a
synopsis and discussion of the data acquired thus far.
Corresponding author: atappin@plymouth.ac.uk