Terrestrial net primary productivity (NPP) plays an essential role in the global carbon cycle as well as for climate change. However, in the past three decades, terrestrial ecosystems across mainland China suffered from frequent drought and, to date, the adverse impacts on NPP remain uncertain. This study explored the spatiotemporal features of NPP and discussed the influences of drought on NPP across mainland China from 1982 to 2015 using the Carnegie Ames Stanford Application (CASA) model and the standardized precipitation evapotranspiration index (SPEI). The obtained results indicate that: (1) The total annual NPP across mainland China showed an non-significantly increasing trend from 1982 to 2015, with annual increase of 0.025 Pg C; the spring NPP exhibited a significant increasing trend (0.031 Pg C year⁻¹, p < 0.05) while the summer NPP showed a higher decreasing trend (0.019 Pg C year⁻¹). (2) Most areas of mainland China were spatially dominated by a positive correlation between annual NPP and SPEI and a significant positive correlation was mainly observed for Northern China; specific to the nine sub-regions, annual NPP and SPEI shared similar temporal patterns with a significant positive relation in Northeastern China, Huang-Huai-Hai, Inner Mongolia, and the Gan-Xin Region. (3) During the five typical drought events, more than 23% areas of mainland China experienced drought ravage; the drought events generally caused about 30% of the NPP reduction in most of the sub-regions while the NPP in the Qinghai-Tibet Plateau Region generally decreased by about 10%.

Landslide susceptibility assessment is presently considered an effective tool for landslide warning and forecasting. Under the assessment procedure, a credible index weight can greatly increase the rationality of the assessment result. Using the Beijiang River Basin, China, as a case study, this paper proposes a new weight-determining method based on random forest (RF) and used the weighted linear combination (WLC) to evaluate the landslide susceptibility. The RF weight and eight indices were used to construct the assessment model. As a comparison, the entropy weight (EW) and weight determined by analytic hierarchy process (AHP) were also used, respectively, to demonstrate the rationality of the proposed weight-determining method. The results show that: (1) the average error rates of training and testing based on RF are 18.12% and 15.83%, respectively, suggesting that the RF model can be considered rational and credible; (2) RF ranks the indices elevation (EL), slope (SL), maximum one-day precipitation (M1DP) and distance to fault (DF) as the Top 4 most important of the eight indices, occupying 73.24% of the total, while the indices runoff coefficient (RC), normalized difference vegetation index (NDVI), shear resistance capacity (SRC) and available water capacity (AWC) are less consequential, with an index importance degree of only 26.76% of the total; and (3) the verification of landslide susceptibility indicates that the accuracy rate based on the RF weight reaches 75.41% but are only 59.02% and 72.13% for the other two weights (EW and AHP), respectively. This paper shows the potential to provide a new weight-determining method for landslide susceptibility assessment. Evaluation results are expected to provide a reference for landslide management, prevention and reduction in the studied basin.

The need for valuable land has encouraged reclamation in coastal areas worldwide in the past decades. Land reclamation can alter the groundwater quality in coastal aquifers. The purpose of this study is to identify the effect of land reclamation on groundwater chemistry, especially the major ions, and heavy metals on Zhoushan Island, China. The subsurface media on the island is composed of two layers, i.e., an upper infill layer and an underlain clay layer. The upper layer is previously ocean and filled with various materials. The clay layer is the original marine sediment. The dominated Na and Cl ions in groundwater illustrate high salinity sources of groundwater in the subsurface of the reclaimed land. A mixing trend between seawater and river water of the groundwater in infill layer is also detected based on the ratios of Cl and Br. Though the heavy metal concentrations (Cd, Cr, Zn and Hg) are high in marine sediments, no significant releasing trends in the groundwater are detected in a short-term after reclamation (based on standard GB18668). Meanwhile, Fe-III concentrations in the aquifer have a strong correlation with precipitation events. Column desorption experiments and simulations indicate the Cd and Cr release from the sediment would pose a health risk when the groundwater in the infill layer being gradually flushed by fresh water. These results provide a foundation for the prediction of groundwater quality and are helpful for the future water management in a newly reclaimed land.