Global rainfall erosivity database (GloREDa) and monthly R-factor data at 1 km spatial resolution.

Here, we present and release the Global Rainfall Erosivity Database (GloREDa), a multi-source platform containing rainfall erosivity values for almost 4000 stations globally. The database was compiled through a global collaboration between a network of researchers, meteorological services and environmental organisations from 65 countries. GloREDa is the first open access database of rainfall erosivity (R-factor) based on hourly and sub-hourly rainfall records at a global scale. This database is now stored and accessible for download in the long-term European Soil Data Centre (ESDAC) repository of the European Commission's Joint Research Centre. This will ensure the further development of the database with insertions of new records, maintenance of the data and provision of a helpdesk. In addition to the annual erosivity data, this release also includes the mean monthly erosivity data for 94% of the GloREDa stations. Based on these mean monthly R-factor values, we predict the global monthly erosivity datasets at 1 km resolution using the ensemble machine learning approach (ML) as implemented in the mlr package for R. The produced monthly raster data (GeoTIFF format) may be useful for soil erosion prediction modelling, sediment distribution analysis, climate change predictions, flood, and natural disaster assessments and can be valuable inputs for Land and Earth Systems modelling.

Hydrochemistry, chemical weathering and their significance on carbon cycle in the Heilong (Amur) River Basin, Northeast China.

Chemical weathering is regarded as a "geological thermostat", affecting the global carbon cycle and long-term climate stability, and hydrochemistry of river is the important way to study weathering. The Heilong River (Amur River), as one of the largest rivers in the temperate/cool temperate zone, has received few studies on the chemical weathering rate and its contribution to the global carbon cycle in the entire Chinese section. This paper presents the hydrochemistry of river water, lake water, and groundwater from the arid upper reaches, the Greater Hinggan Mountains in the middle reaches, and the fluvial plain in the lower reaches of the Heilong River. TDS values range from 26.8 mg/l to 1141 mg/l with an average of 189 mg/l. The arid upper reaches are affected by strong evaporation and/or evaporite minerals dissolution, and the ion contents of some surface water and underground water exceed the quality standard for drinking water. Although the downstream flood plain area is highly industrial and agricultural, water chemistry shows that anthropogenic activities have not significantly deteriorated water quality. The chemical weathering rate of the small granitic and basaltic watersheds in the Heilong River Basin is within the lowest range in the world, which further demonstrates the control of climate factors on chemical weathering. The calculated CO2 consumption flux from silicate weathering in the Heilong River Basin is from 82.3 × 109 to 196 × 109 mol/y, accounting for 0.95%-2.25% of the global consumption values with a proportion of area of ∼1.2%. Compared with other temperate/cool temperate rivers worldwide, it is comparable to the Yenisei River in Siberia, but much higher than the Ob River and Lena River in Siberia, Mackenzie River and Yukon River in North America.

Tracing and quantifying the sources of heavy metals in the upper and middle reaches of the Pearl River Basin: New insights from Sr-Nd-Pb multi-isotopic systems.

A method based on Sr, Nd and Pb multi-isotopic systems indicates that the different rock types (carbonate rock, basalt and black rock series) and sulfide deposits exposed in the Pearl River Basin show markedly different Sr, Nd and Pb isotopic characteristics. By establishing the mass balance equations of heavy metal content and isotope ratios, we use the inverse method to obtain the contribution that natural weathering of carbonate rocks, basalts and black rock series as well as the mining of sulfide deposits have on heavy metal content in riverbed sediments in the Pearl River Basin. Even though carbonate rocks constitute more than 60% of the exposed area in the upper reaches of the Pearl River Basin, this lithology only contributes 9% of the heavy metal content in sediments due to the relatively low content of heavy metals found in this rock type. Basalt weathering on average contributes 64% of the Cr content and 42% of the Ni content found in the sediments, while 53% of the Cd content is derived from the weathering of the black rock series. The negative impact mining has on this environment cannot be ignored as it is the most important source of As (71%) and Pb (60%) in all samples. This is especially the case in the Diaojiang River Basin, where sulfide mining activities still contribute more than 90% of the content of Zn, Pb, Cd and As within the sediments even though many mining sites have been closed since 2000.

The influence of natural weathering on the behavior of heavy metals in small basaltic watersheds: A comparative study from different regions in China.

This paper investigates the dynamics between basalt weathering and heavy metal accumulation through a comparative study of 37 small basaltic watersheds within different climate zones in the Yungui (the Pearl River Basin in southwest China), Xuyi (the Huaihe River Basin in east China) and Leiqiong regions (Hainan Island in south China). From a comprehensive sampling regime of stream water, riverbed sediments and bedrock, this study shows that the concentrations of heavy metals in river water are far below the national surface water quality standard and WHO quality standard for drinking water, indicating no significant ecological risk for water body in these basaltic areas. In contrast, the riverbed sediments exhibit varying degrees of heavy metal enrichment in the process of weathering from bedrock to sediments: without enrichment for Cr, Ni, Cu and Zn, but significant enrichment for Cd, As and Pb. Cd exhibits the largest ecological risk of all the heavy metals in the basaltic watersheds especially in the Yungui region, which can be mainly attributed to the high geological background values in this area. Comparative studies of some major basalt watersheds in the world show that temperature, runoff and elevation differences significantly affect the chemical weathering rates and thus the accumulation of heavy metals.

The impact of natural weathering and mining on heavy metal accumulation in the karst areas of the Pearl River Basin, China.

This paper presents the heavy metal content in river water, sediment and bedrock in the karst area of the Pearl River Basin in China to evaluate the long-term impact of natural weathering and mining on the ecological environment. The results show that Cd and As is 2-3 times more enriched within the carbonate bedrock of the Pearl River Basin compared to the upper continental crust (UCC), which is indicative of high geological background values. Within the river water of the upper reaches of the Diaojiang River (a tributary of the Pearl River), which flows through the Dachang super-large orefield, Zn, As, Cd and Sb exceeds the environmental quality standards for surface water (WQS) by more than an order of magnitude. Among these, Zn and Cd sharply decreases to within the WQS in the lower reaches of the river, but the content of As and Sb in the estuary is still several times higher than the WQS. Cd in the sediments of the small carbonate watersheds and in the mainstream of the Pearl River only present a low-moderate ecological risk. In contrast, severe heavy metal pollution of the sediments of the Diaojiang River Basin is observed. Even in the lower reaches, remote from the mining area, the content of Pb, Zn, As and Cd in the sediments is still two orders of magnitude higher than the soil background values. The content of both Cd and As presents a very high ecological risk, indicating that under the cumulative effect of high geological background values and mining, full restoration of the ecological environment in the Diaojiang River Basin is a complex and long-term process.

Geochemical behavior and potential health risk of heavy metals in basalt-derived agricultural soil and crops: A case study from Xuyi County, eastern China.

Basalt-derived agricultural soil is widely distributed around the world and is extensively used as a medium to plant many kinds of crops. Weathering of basalt can release heavy metals into the soils and may cause health risks via the food chain. However, the geochemical behavior and the potential human health risks of heavy metals remain poorly understood in these agro-systems. In this study, basalt bedrock, paired topsoil and crops (wheat and rice) samples were collected from a basaltic area located in Xuyi County, eastern China. Concentrations and bioavailability of heavy metals in the basalt-topsoil-crop system were measured to determine their geochemical behavior during the weathering and transfer processes as well as their potential risk to human health. Our results showed that basalt and topsoil were characterized by high levels of Ni, Cr and Zn. Topsoil and crop grains were highly polluted by Ni, and Ni accumulated more readily in rice grains than in wheat grains. Nickel, a high-risk metal in topsoil was mainly derived from the basalt bedrock, and its enrichment in topsoil was significantly related to the Fe oxide content of the soils. The accumulation of Ni in crop grains was mainly controlled by soil pH, and the 0.01 M CaCl2 extractable Ni was a good indicator in predicting Ni accumulation in crop grains. Risk analysis revealed that there are significant health risks to local inhabitants if rice grains contaminated with heavy metals are ingested. To our best knowledge, this is the first study to investigate the flow of heavy metals in a basalt-topsoil-crop-human system that focuses on geochemical behavior and human health risk. This study will aid the strategic design of evaluation and remediation protocols for basaltic soil.

The behavior of metals/metalloids during natural weathering: A systematic study of the mono-lithological watersheds in the upper Pearl River Basin, China.

The Pearl River Basin is a region with elevated geochemical baseline levels due to high metals/metalloids content in the sediments and soils. In this paper we systematically analyzed the behavior of these metals/metalloid (Cr, Ni, Cu, Zn, Cd, As, and Pb) in bedrock, riverbed sediments, soils, and river water in three different mono-lithological areas (carbonate, basalt, and mud-shale). The results show that the content of transition elements (Cr, Ni, Cu, and Zn) in carbonate rocks are much lower than for shales and basalts, but these metals produce higher enrichment levels in sediments and soils through rapid weathering. Furthermore, Cd, As and Pb are significantly enriched in the upper soils of the carbonate profile and the watersheds dispersed with black shales have distinctly higher Cd enrichment levels. This secondary enrichment of metals through the weathering and pedogenesis of carbonate rocks, and the discharge of metal elements by the weathering of the black rock series, leads to metal pollution in the Pearl River. Most of the small watersheds in the upper reaches of the Pearl River exhibit low or moderate ecological risk but considerable ecological risk exist in the watersheds dispersed with these black shales. Among all the trace elements, Cd generate the highest ecological risk in the individual small watersheds in the upper reaches of the Pearl River.

Global rainfall erosivity assessment based on high-temporal resolution rainfall records.

The exposure of the Earth's surface to the energetic input of rainfall is one of the key factors controlling water erosion. While water erosion is identified as the most serious cause of soil degradation globally, global patterns of rainfall erosivity remain poorly quantified and estimates have large uncertainties. This hampers the implementation of effective soil degradation mitigation and restoration strategies. Quantifying rainfall erosivity is challenging as it requires high temporal resolution(<30 min) and high fidelity rainfall recordings. We present the results of an extensive global data collection effort whereby we estimated rainfall erosivity for 3,625 stations covering 63 countries. This first ever Global Rainfall Erosivity Database was used to develop a global erosivity map at 30 arc-seconds(~1 km) based on a Gaussian Process Regression(GPR). Globally, the mean rainfall erosivity was estimated to be 2,190 MJ mm ha-1 h-1 yr-1, with the highest values in South America and the Caribbean countries, Central east Africa and South east Asia. The lowest values are mainly found in Canada, the Russian Federation, Northern Europe, Northern Africa and the Middle East. The tropical climate zone has the highest mean rainfall erosivity followed by the temperate whereas the lowest mean was estimated in the cold climate zone.