Effects of Spartina alterniflora invasion on quality of the red-crowned crane (Grus japonensis) wintering habitat.

The core zone of the Yancheng National Natural Reserve (YNNR) in China is the largest wintering habitat of red-crowned cranes (cranes) in the world. However, the invasion of Spartina alterniflora (S. alterniflora) not only changed the original landscape structure of the wetlands but also impacted the cranes' habitats in the YNNR. In this paper, field investigation data and landscape pattern indices were used to analyze the effects of the S. alterniflora invasion on the habitat quality of wintering cranes. The results indicate that the seep weed (Suaeda salsa) in the natural wetland and the common reed (Phragmites australis) in the managed wetland both provide suitable habitats for cranes. However, the cranes prefer the natural wetland more. The explosive growth of S. alterniflora in the natural area has led to a significant reduction of the cranes' habitat. The area of crane habitat decreased from 52.07 km2 in 2000 to 22.36 km2 in 2015. As a result of the S. alterniflora invasion, the benthic biomass has declined, which has negatively impacted the quantity and structure of the food utilized by the cranes. This study has both theoretical and practical significance and provides a scientific basis for protecting the wintering habitat of the red-crowned cranes.

[Effect of Different Multi-pond Network Landscape Structures on Nitrogen Retention Over Agricultural Watersheds].

Nitrogen (N) loss from agricultural fields can cause eutrophication in downstream freshwater systems, but the use of multi-pond networks can mitigate N losses from agricultural runoff. This study presents an analysis of the relationships between N retention and land use before and after rainfall events with the goal of identifying differences in agricultural runoff in four sub-watersheds with 3, 3, 7, and 7 ponds, respectively. The total N concentrations before rainfall ranged from 1.32 mg·L-1 to 6.32 mg·L-1, and total N (TN) levels in the ponds after rainfall varied from 2.8 mg·L-1 to 16.99 mg·L-1 and typically contained 20%-74% nitrate (NO3--N). The mean concentration retention efficiencies in the four sub-watersheds for TN, NO3--N, and ammonium (NH4+-N) were 50.09%, 48.71%, and 52.75%, respectively. The N retention efficiency in sub-watershed 1 (3 ponds) was the lowest among the four sub-watersheds. The N retention mass in sub-watershed 2 (3 ponds) was only 56.10 kg, and this value was far lower than that of sub-watershed 4 (324.43 kg, 7 ponds). The number of ponds in the sub-watersheds was not the only factor that contributed to the effective retention of non-point source N in-situ, but pond area and ditch density also significantly affected N retention. Thus, pond area and ditch density should be increased for similar multi-pond areas. However, managing multi-ponds to maximize N retention requires dynamic monitoring and management over the long term.

Relationships of relative humidity with PM2.5 and PM10 in the Yangtze River Delta, China.

Severe particulate matter (PM, including PM2.5 and PM10) pollution frequently impacts many cities in the Yangtze River Delta (YRD) in China, which has aroused growing concern. In this study, we examined the associations between relative humidity (RH) and PM pollution using the equal step-size statistical method. Our results revealed that RH had an inverted U-shaped relationship with PM2.5 concentrations (peaking at RH = 45-70%), and an inverted V-shaped relationship (peaking at RH = 40 ± 5%) with PM10, SO2, and NO2. The trends of polluted-day number significantly changed at RH = 70%. The very-dry (RH < 45%), dry (RH = 45-60%) and low-humidity (RH = 60-70%) conditions positively affected PM2.5 and exerted an accumulation effect, while the mid-humidity (RH = 70-80%), high-humidity (RH = 80-90%), and extreme-humidity (RH = 90-100%) conditions played a significant role in reducing particle concentrations. For PM10, the accumulation and reduction effects of RH were split at RH = 45%. Moreover, an upward slope in the PM2.5/PM10 ratio indicated that the accumulation effects from increasing RH were more intense on PM2.5 than on PM10, while the opposite was noticed for the reduction effects. Secondary transformations from SO2 and NO2 to sulfate and nitrate were mainly responsible for PM2.5 pollution, and thus, controlling these precursors is effective in mitigating the PM pollution in the YRD, especially during winter. The conclusions in this study will be helpful for regional air-quality management.

Socioeconomic Drivers of PM2.5 in the Accumulation Phase of Air Pollution Episodes in the Yangtze River Delta of China.

Recent studies in PM2.5 sources show that anthropogenic emissions are the main contributors to haze pollution. Due to their essential roles in establishing policies for improving air quality, socioeconomic drivers of PM2.5 levels have attracted increasing attention. Unlike previous studies focusing on the annual PM2.5 concentration (Cyear), this paper focuses on the accumulation phase of PM2.5 during the pollution episode (PMAE) in the Yangtze River Delta in China. This paper mainly explores the spatial variations of PMAE and its links to the socioeconomic factors using a geographical detector and simple linear regression. The results indicated that PM2.5 was more likely to accumulate in more developed cities, such as Nanjing and Shanghai. Compared with Cyear, PMAE was more sensitive to socioeconomic impacts. Among the twelve indicators chosen for this study, population density was an especially critical factor that could affect the accumulation of PM2.5 dramatically and accounted for the regional difference. A 1% increase in population density could cause a 0.167% rise in the maximal increment and a 0.214% rise in the daily increase rate of PM2.5. Additionally, industry, energy consumption, and vehicles were also significantly associated with PM2.5 accumulation. These conclusions could serve to remediate the severe PM2.5 pollution in China.