Dynamic monitoring of the spatial pattern of winter continuously flooded paddies (WFP) at regional scales is a challenging but highly necessary process in analyzing trace greenhouse gas emissions, water resource management, and food security. The present study was carried out to demonstrate the feasibility of extracting the spatial distribution of WFP through time series imagery of volumetric surface soil moisture content (θ_v) at the field scale (30 m). A trade-off approach based on the synergistic use of tasseled cap transformation wetness and temperature vegetation dryness index was utilized to obtain paddy θ_v. The results showed that the modeled θ_v was in good agreement with in situ measurements. The overall correlation coefficient (R) was 0.78, with root-mean-square ranging from 1.96% to 9.96% in terms of different vegetation cover and surface water status. The lowest error of θ_v estimates was found to be restricted at the flooded paddy surface with moderate or high fractional vegetation cover. The flooded paddy was then successfully identified using the θ_v image with saturated moisture content thresholding, with an overall accuracy of 83.33%. This indicated that the derived geospatial dataset of WFP could be reliably applied to fill gaps in census statistics.

Denitrification is an important N removal process in aquatic systems but is also implicated as a potential source of global N₂O emissions. However, the key factors controlling this process as well as N₂O emissions remain unclear. In this study, we identified the main factors that regulate the production of net N₂ and N₂O in sediments collected from rivers with a large amount of sewage input in the Taihu Lake region. Net N₂ and N₂O production were strongly associated with the addition of NO₃ ⁻-N and NH₄ ⁺-N. Specifically, NO₃ ⁻-N controlled net N₂ production following Michaelis–Menten kinetics. The maximum rate of net N₂ production (V _max) was 116.3 μmol N₂-N m⁻² h⁻¹, and the apparent half-saturation concentration (k _m) was 0.65 mg N L⁻¹. N₂O to N₂ ratios increased from 0.18 ± 0.03 to 0.68 ± 0.16 with the addition of NO₃ ⁻-N, suggesting that increasing NO₃ ⁻-N concentrations favored the production of N₂O more than N₂. The addition of acetate enhanced net N₂ production and N₂O to N₂ ratios, but the ratios decreased by about 59.5 % when acetate concentrations increased from 50 to 100 mg C L⁻¹, suggesting that the increase of N₂O to N₂ ratios had more to do with the net N₂ production rate rather than acetate addition in this experiment. The addition of Cl⁻ did not affect the net N₂ production rates, but significantly enhanced N₂O to N₂ ratios (the ratios increased from 0.02 ± 0.00 to 0.10 ± 0.00), demonstrating that the high salinity effect might have a significant regional effect on N₂O production. Our results suggest that the presence of N-enriching sewage discharges appear to stimulate N removal but also increase N₂O to N₂ ratios.

The surge in solid waste (SW) has become major issues in the fields of public health and ecological environment fuelled by the rapid development of social economy. The fate of nitrogen contained in SW (SWN) varies with different treatment methods, which will affect the environment to varying degrees. It is of great practical and guiding significance to comprehensively evaluate the sources, fate and its cascading effects of SWN. Here, a systematic SWN flow evaluation of the generation, treatment and emissions in China from 2008 to 2017 was established. During this period, the SWN flow and the N pollution emissions from SW treatment increased by 19.7% and 27.6% respectively, with the domestic garbage being the largest contributor. This shows that it is particularly important to reinforce the classified of domestic garbage and resource recycling in China. Landfill was the main treatment, accounting for 51.8% of the total SWN. Landfill and incineration were the main sources of pollution N emissions, while compost treatment has the lowest contribution rate. It highlights the urgency of changing the waste treatment methods in China. About 92.3% of the N pollution emissions was lost to the atmosphere and 7.7% to the groundwater. NH₃ and NO_x were the main pollutants to the atmosphere. Special attention is paid to the reduction and control of NH₃ in landfill, dumping and compost processes, while NO_x in incineration. This study provides scientific basis for management and disposal of SW, so as to reduce its impact on the ecological environment and develop more sustainable policies for China and other developing countries.