Tidal effect on dynamics of pore water nitrate in intertidal sediment of a eutrophic Estuary |
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Authors: | Toshihiro Usui Isao Koike Norio Ogura |
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Institution: | (1) Department of Environmental Science and Natural Resources, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Fuchu-shi, 183 Tokyo, Japan;(2) Ocean Research Institute, University of Tokyo, Nakano-ku, 164 Tokyo, Japan |
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Abstract: | To evaluate the effect of the tidal cycle on the pore water nitrate dynamics in intertidal sediment, concentrations of inorganic
nitrogen in water and sediment were monitored during tidal cycles in the mud flat of Tama Estuary, Japan. During submergence,
nitrate concentration was highest in the overlying water and decreased monotonically with increasing depth in the sediment,
suggesting that the primary source of nitrate in the sediment was nitrate transported from the overlying water. Pore water
nitrate decreased remarkably during the initial 3–4 hours after the onset of exposure. Thereafter, it was constant or slightly
increased until tidal flooding.In situ accumulation of nitrate at the end of exposure, however, did not exceed the nitrate concentrations in the overlying water.
The inhibition of nitrate reduction and the stimulation of nitrification would explain the change of nitrate concentration,
both consistent with the input of oxygen into the sediment following a 10 mm drop of the water table. In Tama Estuary sediments,
the effect of the tidal cycle on the removal of combined nitrogen is rather negative, because high nitrate concentrations
in the overlying water canceled the positive effect of nitrate accumulation by nitrification during exposure, while tidal
oxygen intrusion have an inhibitory effection sedimentary denitrification. |
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Keywords: | Tidal variations tidal flats nitrates nitrogen cycle sediments sequeezers Tama Estuary Japan |
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