24Soil erosion is a severe ecological problem. Most conventional methodologies for 25 soil-erosion assessment are appropriate for small or medium river basins. This paper 26 presents an approach to soil-erosion intensity assessment in large basins, utilizing 27 coded polygons identified by spatially overlapping gradation levels of primary 28 environmental factors. Efficient assessment of soil-erosion intensity is achieved by 29 matching the coded polygons to selected polygons pre-assigned to reference groups.
Hydrological connectivity has significant effects on the functions of estuarine wetland ecosystem. This study aimed to examine the dynamics of hydrological connectivity and its impact on soil carbon pool in the Yellow River Delta, China. We calculated the hydrological connectivity based on the hydraulic resistance and graph theory, and measured soil total carbon and organic carbon under four different hydrological connectivity gradients (Ⅰ 0-0.03, Ⅱ 0.03-0.06, Ⅲ 0.06-0.12, Ⅳ 0.12-0.39). The results showed that hydrological connectivity increased in the north shore of the Yellow River and the south tidal flat from 2007 to 2018, which concentrated in the mainstream of the Yellow River and the tidal creek. High hydrological connectivity was maintained in the wetland restoration area. The soil total carbon storage and organic carbon storage significantly increased with increasing hydrological connectivity from Ⅰ to Ⅲgradient and decreased in Ⅳ gradient. The highest soil total carbon storage of 0-30 cm depth was 5172.34 g/m 2 , and organic carbon storage 2764.31 g/m 2 in Ⅲ gradient. The hydrological connectivity changed with temporal and spatial change during 2007-2018 and had a noticeable impact on soil carbon storage in the Yellow River Delta. The results indicated that appropriate hydrological connectivity, i.e. 0.08, could effectively promote soil carbon storage.
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