Effect of complex carbon sources on the vertical distribution and exchange flux of nitrogen nutrient at the sediment–water interface in aquaculture ponds

To further study the purification mechanism of complex carbon source in aquaculture ponds, two complex carbon sources (rice straw complex carbon source, and corn husk complex carbon source) were added into largemouth bass ( Micropterus salmoides ) ponds, and in situ water samples were collected across the entire vertical profile of the sediment–water interface using the Peeper (pore water equilibrium) technique. Ammonia nitrogen (NH 4 + –N), nitrate nitrogen (NO 3 – –N), nitrite nitrogen (NO 2 – –N), soluble phosphate (PO 4 3– –P), total nitrogen (TN), and total phosphate (TP), were determined to investigate the vertical distribution and exchange fluxes. Results showed: (1) nutrient generally decreased with depth except for NH 4 + –N and TN. Complex carbon source affected the vertical distribution of NH 4 + –N, NO 3 – –N, TN, PO 4 3– –P, and TP, and reduced the nutrient in overlying water and interstitial water in sediments. (2) Sediment act as “source” of nutrient, with NO 3 – –N being the largest internally released nutrient. Both the two carbon sources promoted sediment absorption of NH 4 + –N and inhibited the release of PO 4 3– –P, with corn husk being more effective. Additionally, the corn husk group mitigated the release of NO 3 – –N from sediment, but the rice straw group showed no effect. (3) Carbon sources enhanced nutrient removal in water, with corn husk group showing higher removal rate of TN, TP, and PO 4 3– –P. In conclusion, sediment is the potential source of eutrophic pollutants. The complex carbon sources can influence nutrient vertical distribution and diffusion fluxes at the sediment–water interface, with corn husk carbon source effectively reducing nutrient release from sediment and showing better water purification effect. These findings contribute to a deeper understanding of the purification mechanisms of complex carbon sources and provide data support for the application of complex carbon sources in environmental restoration of aquaculture. • Complex carbon sources can affect the vertical distribution and diffusion flux of nutrients. • Corn husk carbon source can effectively reduce the release of nutrients from sediments and show better water purification effect.