Comparing the effects of temperature and C/N ratios on denitrification between point bar and straight channel sediments

Abstract

The riverbed and riparian zone are the hotspots of nitrogen removal in rivers. Denitrification plays an important role in the process of nitrogen removal. In this study, sediments from the straight channel riverbed and point bars were examined using indoor culture and acetylene inhibition techniques. The primary focus was to investigate the differences in denitrification rates between these sediments. The secondary focus was on the effects of temperature and carbon-nitrogen (C/N) ratios on the denitrification process. The results showed that denitrification rates were higher in point bar sediments compared to those in the straight channel bed. Denitrification rates were also higher in the near water area of the point bar than in the near bank area. Denitrification rates at 30 °C were significantly higher than at 10 °C for each sediment group as well as in samples having carbon and nitrogen amendments. Notably, when the C/N ratio was 2.5, the denitrification rate for samples with carbon and nitrogen additions was significantly higher than for samples without them. On average, denitrification rates increased by 2.56 times, 2.73 times and 2.87 times for sediments from the straight channel, inner part of the point bar, and near bank of the point bar, respectively. At the same time, the number of denitrifying bacteria was found to be higher in the point bar than in the straight channel. These findings highlight the beneficial role of point bars in accelerating sediment denitrification rates and emphasize the potential for increasing nitrogen removal capacity in rivers by optimizing temperature and C/N ratios. Changing the diversity of riverbed geomorphology, temperature and C/N can effectively enhance the nitrogen removal capacity of river ecosystems.

Keywords

• Denitrification
• point bar
• straight channel
• C/N ratio
• temperature