Temporal and Vertical Variability in the Relationship Among Organic Matter Indices in a Deep Reservoir Ecosystem

Variation in carbon and nitrogen stable isotopes in POM and zooplankton in a deep reservoir and relationship to hydrological characteristics

“…The difference in 13 C-POM (À23.5 AE 1.0%, average AE SD) in the post-monsoon metalimnion among the study years was small. 13 C-POM was similar to 13 C values for terrestrial leaf litter (À24.9 AE 1.5%) and soil (À23.4 AE 0.8%) in the watershed, probably resulting from the inflow of the turbid density current and the descending thermocline in Lake Soyang (Choi et al 2004; Table 3). Kim (2007) also measured 13 C-organic matter in streams from forest and paddy fields located in the Han River watershed and found averages values of À25.1 AE 1.2% and À24.7 AE 0.8%, respectively.…”

“…The lowering of the thermocline into the dam's discharge layer results in increased concentrations of nutrients available for phytoplankton in the epilimnion (Heo et al 1998). Although most of the allochthonous organic matter is discharged during the post-monsoon period (July to September), nutrients from the input of the sediment-laden density current can diffuse into the epilimnion (Heo et al 1998, Choi et al 2004). Therefore, chlorophyll-a concentrations may increase from this resupply of nutrients, as postmonsoon epilimnetic 13 C-POM was found to increase compared to pre-monsoon 13 C-POM.…”

“…Namkung et al (2001) reported that allochthonous organic matter from the watershed accounted for about 43% of the total organic load to Lake Soyang. Nevertheless, the allochthonous contribution to the POM in the epilimnion would be expected to be small in Lake Soyang because most terrestrial organic matter is discharged from the dam outlet without affecting the epilimnion (Namkung et al 2001;Choi et al 2004). Nutrients in the turbid layer (metalimnion) are supplied to the epilimnion with deepening of the thermocline in late summer, which may stimulate cyanobacterial blooms (Heo et al 1998).…”

“…The turbid storm runoff flowing into reservoirs inserts itself at metalimnetic depths because its density is greater than that of the surface water (Heo et al 1998;Park et al 2005). Turbid runoff to the metalimnion is the source of massive quantities of allochthonous organic matter (especially particulate organic matter (POM)) and nutrients to reservoirs during summer storms and the post-monsoon season (Heo et al 1998;Choi et al 2004;Park et al 2011). Studies are needed to identify the sources and fates of POM, quantify organic matter and nutrient budgets and understand linkages to biological processes as well as the implications of the highly turbid water to trophic relationships in reservoirs.…”