Effect of water temperature on internal nitrogen release from sediments in the Pearl River Delta region, China

Abstract

Nitrogen (N) has received attention as an indicator of water quality and pollution. However, the N content of rivers, lakes, and reservoirs varies significantly by season, and environmental factors such as temperature affect it. An experiment was conducted with a series of tanks containing sediments from the Pearl River Delta region of China and distilled water to assess the release of N from sediments under controlled conditions; temperatures from 10 to 30℃ were assessed. Results show that the effect of temperature on N in the water column and sediment is nonlinear. Only temperatures ranging from 20 ~ 25℃ affected NO3-N in shallow sediments. Temperatures lower than 20℃ had more effect on NH4-N concentration in the water column, while NO3-N concentration was affected heavily at higher temperatures. NH4-N typically is stable at a relatively high concentration in the water column at 20℃. While NO2-N is stable in the water column at higher temperatures, NO3-N is the dominant form of N in water bodies at temperatures from 25℃ to 30℃. At 20℃, dissolved inorganic nitrogen was released from the sediment to the water column, gradually reaching equilibrium. Temperature could affect the internal release of NH4-N; this process gradually accelerated as the temperature rose. However, the presence of NH4-N in a water body can inhibit its release, thus the relationship between the diffusive flux with temperature is not linear. The relationship between N diffusive flux at the sediment-water interface can be described by Polynomial2D and Lorentz2D models (R2 > 0.87).