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Liu X.,Chinese Academy of Sciences | Li Z.,Chinese Academy of Sciences | Li Z.,State Key Laboratory Base of Eco Hydraulic Engineering in Arid Area at XAUT | Li P.,State Key Laboratory Base of Eco Hydraulic Engineering in Arid Area at XAUT | And 5 more authors.
Quaternary International | Year: 2015

Understanding the composition and changes in nutrients in sediments and soil will enable a better description of sedimentation and environmental processes. In this study, soil from the source (Ss) of the Dan River and sediments along the river were sampled. The particle size distribution (PSD) of sediment and soil was analyzed, together with the total nitrogen (TN), total organic carbon (TOC) and the C/N ratio. The dominant particle size of Ss was <0.05 mm, while the sediments showed no obvious dominant particles. Concentrations of TN and TOC in sediments were significantly lower than in Ss. The <0.05 mm fraction of sediments manifested good ability to maintain TN and TOC, as indicated by average levels of 0.59 g N/kg and 13.85 g/kg, respectively. In the downstream portion of the Dan River, the TN contents decreased, while the TOC contents remained stable throughout the river. Cluster analysis indicated that TN division became simpler as the particle size decreased, while it became more complicated for TOC. There was no significant difference in the C/N ratio of Ss among particle sizes, and the ratio was below 25:1 for all groups. Conversely, the C/N ratio of sediments increased obviously with decreasing distance to the Danjiangkou reservoir. The nitrogen levels in particles <0.05 mm were preserved relatively well so that the C/N ratio of this fraction was relatively stable. The enrichment ratio of nutrients in sediments of the upstream portion of the river also showed that a finer fraction was associated with a greater capacity for holding nutrients, especially particles <0.05 mm. Overall, comprehensive control of sediments in rivers should focus on large particle sediments. © 2015 Elsevier Ltd and INQUA.

Liu X.J.,Chinese Ministry of Water Resources | Li Z.B.,Chinese Ministry of Water Resources | Li Z.B.,State Key Laboratory Base of Eco Hydraulic Engineering in Arid Area at XAUT | Li P.,State Key Laboratory Base of Eco Hydraulic Engineering in Arid Area at XAUT | And 3 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2016

Serious soil erosion by the Yellow River has not only led to ecological deterioration, but also heightened the risk of floods downstream. Land use change is the main factor responsible for the ecological and environmental issues. Sedimentation and runoff variation caused by land use change has emerged as one of the popular topics of discussion. Researchers usually select landscape pattern as an important indicative factor of land use for analyzing the tense relationship between the socioeconomic system and natural ecosystem. The purpose of this study was to determine the characteristics of landscape patterns, runoff, and sedimentation changes, and discuss the relationship between landscape indices (LIs), runoff, and sedimentation. Two typical watersheds (Tuweihe and Gushanchuan watersheds) in the Yellow River basin were selected as the study sites. Long-term historical land use, runoff, and sediment data (1985-2010) were analyzed relying on geographic information system and Fragstats software. Landscape indices included NP (number of patches), PD (patch density), LPI (largest patch index), LSI (landscape shape index), PAFRAC (perimeter area fractal dimension), CONTAG (contagion index), COHESION (patch cohesion index), DIVISION (landscape division index), and SHDI (Shannon’s diversity index). The following results were obtained: (1) Grassland was the dominant landscape in the two watersheds. Unused land in Tuweihe watershed and farmland in Gushanchuan watershed experienced the greatest changes with areas of 453.94 km2 and 52.85 km2, respectively, from 1985 to 2010. Deforestation and reconversion of cultivated land to forest and grassland were the main reasons for the land cover change. (2) The calculation of coefficient of variation (CV) revealed that LPI of Tuweihe watershed had intermediate variability (CV = 27.29%), while all the others including LIs of Gushanchuan watershed had little variability (CV < 10%). The landscape in Tuweihe watershed tended to become regular, connected, and aggregate, indicating that with time, the influences of human activities on the area were growing. The diversity and aggregation index increased and the landscape pattern improved. For grassland and unused land, the landscape stability had been increasing gradually but decreased as farmland and urban and rural land became increasingly affected by human activities. The landscape stability of Tuweihe watershed was higher than that of Gushanchuan watershed. (3) The annual runoff and sediments decreased gradually. The runoff in Tuweihe watershed was greater than that in Gushanchuan watershed, and the sediment yields of the two watersheds were similar owing to the bigger area of farmland in Gushanchuan watershed and more check dams in Tuweihe watershed. A Pearson correlation analysis showed that there was a significant relationship between annual runoff and sedimentation (P < 0.01). The coefficient of determination in Tuweihe watershed (0.48) was obviously lower than that in Gushanchuan watershed. (4) The Pearson correlation analysis showed that the LIs were in significant linear relationship with runoff and sedimentation (P < 0.01). SHDI, SIDI, SHEI, and SIEI were positively correlated with annual runoff, whereas CONTAG and COHESION were negatively correlated with annual sedimentation. Compared to annual sedimentation, the correlation coefficients for LIs and runoff were higher, indicating that the land use/cover change affected runoff more than it affected sedimentation. Our results suggest that discussing the relationship between the LIs and runoff and sedimentation could provide scientific basis for the prevention and treatment of water loss and soil erosion. © 2016, Ecological Society of China. All rights reserved.

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