Evaluation of Nutrient Release from Sediments of Artificial Lake

This study examined nutrient fluxes between sediment and water with a laboratory-scale benthic chamber. This research targeted an artificial lake that had undergone water-quality problems. Two sites at Lake Asan, Site A in the vicinity of the dam and Site B at the inflow of the lake, were selected and characteristics of the sediments and their influence on the water quality of the lake were evaluated. Most of the inorganic phosphorus in the study area was in the form of apatite and nonapatite phosphorus (91.9% of Site A, 83.3% of Site B). Site B, with a fast-stream velocity, had larger particle size, smaller nutrient level, and smaller amounts of inorganic phosphorus than Site A. The benthic chamber experiment showed that overall fluxes of Site A were as follows: ammonia is $0.003\mu \mathrm{mol}{\mathrm{cm}}^{-2}{\mathrm{day}}^{-1}$, nitrate is $-0.067\mu \mathrm{mol}{\mathrm{cm}}^{-2}{\mathrm{day}}^{-1}$, and phosphate is $1.049\mathrm{nmol}{\mathrm{cm}}^{-2}{\mathrm{day}}^{-1}$. Site B showed an increase in phosphate concentration after a dissolved oxygen (DO) drop ($<3\mathrm{mg}/\mathrm{l}$), which resulted in smaller negative nitrate fluxes ($-0.043\mu \mathrm{mol}{\mathrm{cm}}^{-2}{\mathrm{day}}^{-1}$), larger positive ammonia ($0.137\mu \mathrm{mol}{\mathrm{cm}}^{-2}{\mathrm{day}}^{-1}$), and larger phosphate fluxes ($2.120\mathrm{nmol}{\mathrm{cm}}^{-2}{\mathrm{day}}^{-1}$) than at Site A. The movement of nutrients at the sediment-water interface was more sensitive to environmental conditions such as DO than other factors, such as sediment characteristics and chemical forms of nutrients. On the basis of the fluxes obtained from the benthic chamber, positive values are estimated for both phosphorus and nitrogen release rates. This indicates that during the sampling period sediment acted as a source of nitrogen as well as phosphorus to the overlying waterbody.