hide
Free keywords:
-
Abstract:
The conversion of reactive nitrogen species to N-2 during
denitrification in sediments may be one of the most valuable ecosystem
services provided by estuarine and intertidal environments near river
discharge areas. To quantify the rates and limiting factors of
denitrification in the estuary of the Elbe River and adjacent Wadden Sea
(SE North Sea), we measured sediment N2 fluxes across subtidal and
intertidal sediments, and along gradients in nitrate and organic matter
concentrations. We conducted 2 sampling campaigns, in March and
September 2009, during which N2 fluxes were quantified by N-2/Ar
measurements in sediment core incubations, and compared to isotope
pairing results in September 2009. At ambient nitrate concentrations,
sediments in the inner Elbe Estuary produced N2 fluxes of up to 156 mu
mol N m(-2) h(-1). In September, nitrate concentration in bottom water
and organic matter content in sediments limited N-2 production; such
limitations were not observed in March. We extrapolated the estuarine
sediment nitrogen removal of March and September to the present-day area
of intertidal and subtidal sediments in the Elbe Estuary between the
port of Hamburg and the transition to the North Sea. Our estimate
suggests that 3.3 +/- 1.2 kt nitrate-N are removed in sediments in this
region in spring and summer. This implies that reactive nitrogen removal
in the inner Elbe Estuary reduces the spring/summer load of the Elbe
River (47 kt N) by around 7%, a reduction that is much lower than
commonly assumed for estuaries, and significantly lower than nitrate
removal in the Elbe was in historical times.
