Sediment oxygen demand and its controls in the affected by weir impoundments: A case study at major Korea river system

Abstract

The Four Major River Restoration Project (FMRRP), one of the most expensive civil-engineering projects in Korean history was dredged 520 million cubic meters of mud and sand from river beds and massive 16 weirs built in April 2012. To elucidate the organic carbon (Corg) cycle and biogeochemical dynamics in the river systems associated with the construction and operation of weirs, we investigated the geochemical constituents, sediment oxygen demand (SOD) and burial rates of Corg in major rivers of Korea. The diffusive nutrients fluxes calculated from pore-water distribution ranged from 4.5 to 190.0 mg N m-2 d-1 and from -0.12 to 0.64 mg P m-2 d-1, which accounted for 0–488% and 0–32%, respectively, of the N and P demand for primary production. The SOD20 in May (1.79±0.63 g m-2 d-1) exhibited higher than in August (1.01±0.39 g m-2 d-1), October (1.18±0.31 g m-2 d-1) and June (1.43±0.36 g m-2 d-1), significantly (p<0.05). Principal component analysis revealed that discharge volume controlled by precipitation was negatively correlated with the SOD20. The organic carbon (Corg) burial efficiency (1–94%), calculated from a simplified mass balance model, were orders of magnitude higher than those reported natural lakes and coastal areas. The Corg burial efficiency were positively related to concentration of pore-water methane (y=82.8(1-e-0.21x), n=30, R2=0.524, p<0.0001). Overall results indicated that the discharge has profound impacts on the Corg oxidation rates and availability of electron acceptors is an overriding factor in controlling Corg cycles in the river systems.