Search

Although constructed wetlands (CWs) are used as one relatively low-cost technology for livestock wastewater treatment, the improvement of phosphorus removal in CWs is urgently needed. In this study, a three-stage pilot-scale CW system consisting of three surface flow CWs (SFCWs; CW1, CW2, and CW3) in series from inlet to outlet was constructed to treat swine wastewater (SW) from a lagoon. The CWs were planted with Myriophyllum aquaticum . Considering different inlet loading rates, three strengths of swine wastewater (low: 33% SW, medium: 66% SW, and high: 100% SW) were fed to the CW system to determine total phosphorus (TP) removal efficiency and clarify the important role of plant harvest. Results from the period 2014–2016 indicate that the three-stage CW system had mean TP cumulative removal efficiencies and removal rates of 78.2–89.8% and 0.412–0.779 g m − 2 d − 1 respectively, under different inlet loading rates. The TP removal efficiency and removal rate constant had temporal variations, which depended on temperature condition and the annual growth pattern of M . aquaticum . The harvested phosphorus mass was 15.1–40.9 g m − 2 yr − 1 in the CWs except for CW1 with high strength SW, and contributed 22.5–59.6% of TP mass removal rate by the SFCWs. The TP removal was mainly by adsorption and precipitation in the substrate in CW1 but by uptake and multiple harvests of M . aquaticum in CW2 and CW3. The results suggest the three-stage CW system planted with M . aquaticum is suited for removing high TP concentrations from swine wastewater with a high removal efficiency. However, TP removal in high strength SW amounted to 70.1 ± 23.3%, and the outflow concentration of 17.0 ± 14.9 mg L − 1 was still high. Optimal loading rates for high strength SW still need to be investigated for the CW system presented here. [ABSTRACT FROM AUTHOR]

Nowadays, there has been a rapid expansion of tea field converted from forestry for pursuing higher economic benefits. However, few researches focus on the effects of transient land-use conversion from Masson pine forest to artificial tea fields on soil N 2 O and NO emissions and the underlying mechanisms. A parallel field experiment was conducted from Masson pine forest and a newly converted tea plantation from Masson pine forest from 2013 to 2017 in subtropical central China. Masson pine forest conversion to tea field dramatically increased soil N 2 O and NO emissions (up to 4.00 ± 0.43 and 1.93 ± 0.45 kg N ha−1 yr−1, respectively) in the first year possibly due to enhanced soil organic N mineralization. With the extension of tea planting age, N 2 O and NO emissions showed an upward trend (ranged from 1.19 to 5.28, and 0.15 to 1.78 kg N ha−1 yr−1, respectively) influenced by fertilization and soil organic matter accumulation. The direct emission factors for N 2 O and NO in the newly converted tea fields were the largest in the first year (2.64 and 1.07%, respectively) after land-use conversion, and higher than the default value recommended by IPCC. The NO/N 2 O ratio was mainly lower than 1 in the fertilized tea field, and soil N 2 O and NO emission peaks mainly occurred in tea-growing season (wet season) with higher soil moisture and NH 4 +-N concentrations, and dominated by amoA -containing bacteria (AOB), suggesting nitrifier-denitrification could be the dominant process involved in soil nitrogenous gases emissions in tea field. These results can be summarized as dramatically increased soil N 2 O and NO emissions during the transient land-use conversion from Masson pine forest to tea field were possibly due to the substantial net soil organic N mineralization and the enhanced abundance of nitrification functional genes (AOB). Dynamics of annual cumulative N 2 O and NO emissions after land use conversion from Masson pine forest to tea field from 2013 to 2017. Unlabelled Image • Forest conversion to tea field dramatically increased soil N 2 O and NO emissions. • A substantial net mineralization of SON occurred in the newly converted tea field. • The abundance of N cycle genes varied between different land-use types and seasons. • Nitrifier-denitrification could be the main source of tea soil N 2 O + NO emissions. [ABSTRACT FROM AUTHOR]