T299 Advances in Understanding Processes at or Near the Groundwater–Surface Water Interface

Wednesday, 25 September 2019
1:30 PM - 5:30 PM
Room 105BC, West Building

NITRATE REMOVAL WITHIN HETEROGENEOUS FLUVIAL SEDIMENTS UNDER TIDAL INFLUENCE

Paper number: T299-2
Program: Technical Sessions
Time: 1:50 PM – 2:05 PM

Authors

Abstract

Denitrification serves as an important sink for nitrate loads to the coast, which otherwise degrade coastal waters. Along tidal rivers, stage fluctuations enhance surface water-groundwater exchange (hyporheic exchange). Nitrification and denitrification are strongly coupled near the fluctuating water table and across heterogeneous high- and low-permeability floodplain deposits. Preferential flow along permeable pathways causes relatively high velocities and mobilizes oxygen and other nutrients, while low-permeability facies high in organic matter supply dissolved organic carbon but limit groundwater movement. Nitrogen processes reflect a balance of transport and reactant availability; nitrification dominates within oxic, high-permeability facies at the fluctuating water table, while denitrification dominates within anoxic, low-permeability layers where water movement is more limited. The net nitrate removal rate from surface water increases with permeability but accounts for a smaller fraction of the nitrate exchanged through sediments, amounting to a decline in removal efficiency. Knowledge of the effects of tidal flow conditions and sediment lithology is necessary for a more comprehensive understanding of the processing, retention, and export of nitrogen within these heterogeneous systems.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-338852

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