Mercury vertical and horizontal concentrations in agricultural soils of a historically contaminated site: Role of soil properties, chemical loading, and cultivated plant species in driving its mobility

The long term vertical and horizontal mobility of mercury (Hg) in soils of agricultural areas of a historically contaminated Italian National Relevance Site (SIN Brescia-Caffaro) was investigated. The contamination resulted from the continuous discharge of Hg in irrigation waters by an industrial plant (Caffaro S.p.A), equipped with a mercury-cell chlor-alkali process. The contamination levels with depth ranged from about 20 mg/kg dry weight (d.w.) of soil in the top (plow) layer to less than 0.1 mg/kg d.w. at 1 m depth. The concentrations varied also spatially, up to one order of magnitude within the same field and showing a decreasing trend from the Hg source (i.e., irrigation ditches). The concentration profiles and gradients measured were explained considering Hg loading, soil properties, such as the texture, organic carbon content, pH and cation exchange capacity. A Selective Sequential Extraction (SSE) was also applied on soil samples from an ad hoc greenhouse experiment to investigate the role of different plant species in influencing Hg speciation in soils. Although most of the extracted Hg was included in scarcely mobile or immobile forms, some plant species (i.e., alfalfa) showed to importantly increase the soluble and exchangeable fractions with respect to the unplanted control soils, thus affecting mobility and potential bioavailability of Hg.

Does global warming decrease the correlation between cherry blossom flowering date and latitude in Japan?

In Japan, the geographical distribution of the first date of flowering (FFD) of Yoshino cherry trees (Cerasus ×yedoensis) in 2020, a year when temperatures were mild during the previous December and March, was different from the average FFD, which progresses northward along a latitudinal gradient. We hypothesized that global warming may have changed the average geographical pattern of the FFD. To test this hypothesis, we examined the relationship between the observed FFD and latitude at 42 sites during the period 1953-2020. We found that the correlation between FFD and latitude had decreased since 1980. This decrease may have been caused by a rise of temperatures in winter that delayed dormancy release and the subsequent FFD in areas where the annual mean temperature is high. Our results suggest that the correlation between FFD and latitude will decrease further as the climate warms in the future.

Spatiotemporal variability of the near-surface CO2 concentration across an industrial-urban-rural transect, Nanjing, China

Urban lands are CO₂ emission hotspots. In this paper, we report the CO₂ concentration observations along an industrial-urban-rural transect and in a network of sites in the urban center, in Nanjing, China. The mean CO₂ concentration was highest at the industrial site, not at the densely populated urban center (urban: 429.2±8.7ppm, rural: 421.2±10.0ppm, industrial: 443.88±18.3ppm), based on four sampling periods in four different seasons in 2014 and 2015. At the urban sites, a reversed weekend effect was observed, whereby the weekend CO₂ concentration was higher than the weekday concentration by a mean of 0.9ppm over the four measurement periods and by 8.1ppm in the spring, suggesting higher traffic volume on weekends than on weekdays. The vertical CO₂ gradient was weak above the urban canopy layer, with a mean difference of only 1.1ppm between the 60-m and 110-m measurement heights, reflecting efficient mixing in both daytime and nighttime periods. The average along-wind concentration gradient was 0.25±0.87ppmkm^-1 at the height of 110m according to the observations made at five urban sites. Based on a simple box model, we estimated an anthropogenic surface flux of about 0.4mgCO₂m^-2s^-1 for the urban center.