[Differences in Nitrogen Sources and Contributions in Shallow Groundwater in Plateau Lake Area with Different Climate Types].

Clarifying the concentration, major sources, and contribution differences of nitrogen in shallow groundwater in plateau lake areas with different climate types can provide a novel direction for the control of nitrate （NO） pollution in regional groundwater. Taking the shallow groundwater around Erhai Lake in the subtropical monsoon climate zone and Chenghai Lake in the dry-hot valley area of the Jinsha River as the research objects, using hydrochemical indexes and multi-isotope techniques （N-NO, O-NO, O-HO, and H-HO） combined with the stable isotope （SIAR） model； the differences in nitrogen concentration in shallow groundwater around Erhai Lake and Chenghai Lake were analyzed, the sources of NO were identified, and the contribution rates of each pollution source were calculated. The results showed that water quality of more than 33% and 5% of shallow groundwater sampling points around Erhai Lake and Chenghai Lake was worse than the groundwater Class Ⅲ quality requirements （GB/T 14848） of 20 mg·L for nitrate nitrogen （NO-N）, respectively.

Shallow groundwater table fluctuations weaken nitrogen accumulation in the thin layer vadose zone of cropland around plateau lakes, Southwest China.

Excessive accumulation of nitrogen (N) in the soil profile in the intensive agricultural region will seriously threaten groundwater quality and safety. However, the impact of shallow groundwater table (SGWT) fluctuations driven by seasonal variations on the N accumulation characterizations in the soil profiles has not been well quantified, particularly in the regions with thin layer vadose zone. Through in-situ monitoring and simulation experiments, the changes in the SGWT and N accumulation of soil profile in intensive cropland around 7 plateau lakes in Yunnan were studied during the rainy season (RS) and dry season (DS), and the N loss in soil profile of cropland driven by SGWT fluctuations was estimated.

[Effect of Fallow on Nitrogen Accumulation in Soil Profile and Shallow Groundwater in Cropland Around Fuxian Lake].

Soil nitrogen accumulation in cropland and groundwater nitrogen pollution can be effectively alleviated by reducing exogenous nitrogen input, and fallow is an important measure for reducing exogenous nitrogen input. To explore the effects of fallow on nitrogen accumulation in the soil profile and shallow groundwater, the soil profile and shallow groundwater in cropland around Fuxian Lake were selected as research objects. The changes in nitrogen accumulation in the 0-100 cm soil profile and nitrogen concentration in shallow groundwater before (December 2017) and after (August 2020 and April 2021) fallow and their relationships were analyzed.

[Identification of Nitrate Source and Transformation Process in Shallow Groundwater Around Dianchi Lake].

Elucidating the main sources and transformation process of nitrate for the prevention and control of groundwater nitrogen pollution and the development and utilization of groundwater resources has great significance. To explore the current situation and source of nitrate pollution in shallow groundwater around the Dianchi Lake, 73 shallow groundwater samples were collected in the rainy season in 2020(October) and dry season in 2021(April). Using the hydrochemistry and nitrogen and oxygen isotopes(N-NO and O-NO), the spatial distribution, source, and transformation process of nitrate in shallow groundwater were identified.