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  • MDPI AG  (2)
  • Bai, Li  (2)
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  • MDPI AG  (2)
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  • 1
    In: Water, MDPI AG, Vol. 13, No. 22 ( 2021-11-11), p. 3194-
    Abstract: Watershed-scale nitrogen pollution in aquatic systems has become a worldwide concern due to its continuous impact on water quality deterioration, while the knowledge of key influencing factors dominating nitrogen transportation and transformation at the sediment-water interface (SWI) remains limited, especially in impounded rivers with an artificial reservoir. Hence, for a better understanding of the effects of thermal stratification on nitrogen transformation, we investigated the nitrogen species and isotopes in the sediment of a deep reservoir in Southwest China. Our results confirmed a significant difference in nitrogen species and isotopic composition in sediment between those in the thermal stratification period and non-thermal stratification period and indicated that the sediment biogeochemical process and transportation were clearly linked to the variations in water temperature and dissolved oxygen dominated by the process of thermal stratification. Significant seasonal differences in NH4+-N and NO3−-N in pore water of the upper layer (0–19 cm) revealed that nitrification exhausted NH4+ in the non-stratified period (NSP), and a potential low mineralization rate appeared when compared with those in the stratified period (SP). Seasonal differences in nitrogen species and isotope fractionation of δ15N-PON (about 2.3‰ in SP) in the upper layer sediment indicated a higher anaerobic mineralization rate of organic matter in SP than that in NSP. The diffusion fluxes of NH4+-N at SWI were 9.48 and 15.66 mg·m−2·d−1 in NSP and SP, respectively, and annual NH4+-N diffusion accounted for 21.8% of total storage in the reservoir. This study demonstrated that the nitrogen cycling processes, especially nitrification, denitrification, and mineralization, have been largely altered along with the changes in dissolved oxygen and that the diffusion of nitrogen species varied with the presence of the oxygen. The results contribute to the future study of watershed nitrogen budget evaluation and suggest that the endogenous nitrogen released from the sediment-water interface should be emphasized when aiming to fulfil water management policies in deep reservoirs.
    Type of Medium: Online Resource
    ISSN: 2073-4441
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2521238-2
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  • 2
    In: Atmosphere, MDPI AG, Vol. 13, No. 8 ( 2022-07-29), p. 1200-
    Abstract: Incubation experiments using a typical cornfield soil in the Wujiang River watershed, SW China, were conducted to examine the impacts of soil moisture and fertilizer on N2O emissions and production mechanisms. According to the local fertilizer type, we added NH4NO3 (N) and glucose (C) during incubation to simulate fertilizer application in the cornfield soil. The results showed that an increase in soil moisture and fertilizer significantly stimulated N2O emissions in cornfield soil in the karst area, and it varied with soil moisture. The highest N2O emission fluxes were observed in the treatment with nitrogen and carbon addition at 70% water-filled pore space (WFPS), reaching 6.6 mg kg−1 h−1, which was 22,310, 124.9, and 1.4 times higher than those at 5%, 40%, and 110% WFPS, respectively. The variations of nitrogen species indicated that the production of extremely high N2O at 70% WFPS was dominated by nitrifier denitrification and denitrification, and N2O was the primary form of soil nitrogen loss when soil moisture was 〉 70% WFPS. This study provides a database for estimating N2O emissions in cropland soil in the karst area, and further helped to promote proper soil nitrogen assessment and management of agricultural land of the karst watersheds.
    Type of Medium: Online Resource
    ISSN: 2073-4433
    Language: English
    Publisher: MDPI AG
    Publication Date: 2022
    detail.hit.zdb_id: 2605928-9
    SSG: 23
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