Time filter

Source Type

Gao L.,Chinese Ministry of Water Resources | Gao L.,University of Chinese Academy of Sciences | Shao M.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research
Agricultural Water Management | Year: 2012

Identifying representative locations that estimate mean soil water content (SWC) for an area of interest is one of the most important applications of the concept of temporal stability but typically requires extensive sampling on multiple occasions. This study aimed to examine the feasibility of identifying temporally stable locations by using other properties (mainly soil) that were themselves relatively temporally stable, thus reducing the cost of sampling. From July 2008 to October 2010, SWCs at four soil depths (0.1, 0.2, 0.4 and 0.6. m) were measured using a neutron probe on 20 occasions, along three transects (∼30 locations for each transect) on a hillslope of the Loess Plateau, China. Summary variables were determined at corresponding locations. The results showed good temporal patterns, with mean Spearman correlation coefficients ranging from 0.63 to 0.83 for the three transects at four soil depths. Identified representative locations for the three transects well-represented the mean SWC, with a root mean square error of less than 2% and a mean error of less than 1%. Elevation and clay content of soil were the main factors affecting the spatial and temporal distribution of soil water at the hillslope scale. However, the characteristics of temporal stability differed in part among the three transects, both in temporal persistence and in the number of representative locations. Multiple linear regression equations, determined between the mean relative difference and the measured variables based on the datasets of transects 1 and 2, did not accurately predict temporally stable locations for transect 3. The a priori selection of representative locations based solely on properties of soil and elevation was determined to be infeasible at the present time. © 2012 Elsevier B.V.. Source

Hu J.,Chinese Ministry of Water Resources
Environmental science and pollution research international | Year: 2011

From December 2008 to November 2009, an investigation of water quality was performed in the 70-km long downstream from Gezhouba Dam in Yangtze River. Twelve sites in all were chosen. Nine parameters of water quality including the total phosphorus, the total nitrogen, chlorophyll a (Chl.a), nitrite, nitrate, ammonia, water temperature, DO, and pH were monitored almost monthly. The multivariate statistical technique (cluster analysis) and the nonparametric method (Kruskal-Wallis Test and Spearman's rank correlation) were applied to evaluate the spatiotemporal variations of water quality data sets. According to the Chinese environmental quality standards for surface water (GB3838-2002), the water quality in the river section investigated can attain to the III water standards except total nitrogen. Further analysis indicated that there were no significant spatial differences in these parameters of water quality, but the sampling date had a significant effect. The temporal variation of water quality can be related to the discharge of Gezhouba Dam and moreover be affected by the reservoir regulation. During the discharge, the discharge increased the concentration of total phosphorus and then decreased the N:P ratio, which helps to the occurrence of algae blooms. The high consternation of phosphorus and the low N:P ratio show that the water body can be in the process of eutrophication during the discharge of Gezhouba Dam. In fact, Chl.a had begun to rise in the same period. Source

Jia Y.-H.,Chinese Ministry of Water Resources | Jia Y.-H.,ShenYang Agricultural University | Jia Y.-H.,University of Chinese Academy of Sciences | Shao M.-A.,Chinese Academy of Sciences
Agricultural Water Management | Year: 2013

Conservation of soil water and restoration of vegetation have long been major subjects of concern on the northern Loess Plateau. Revegetation with species such as Korshinsk peashrub (KOP) and purple alfalfa (ALF), as well as with natural revegetation of fallow areas (NAF) have been used extensively. This paper examines the temporal stability of soil water storage (SWS) under these different revegetation types, including under millet (MIL) crops for comparison, grown in adjacent plots on a hillslope intending to provide information relevant to the strategic guidance of revegetation and soil water management practices. SWS was measured at 10-cm intervals in the soil profile to a depth of one meter using a neutron probe on 11 occasions between 2010 and 2011. The results indicated that: (1) time-averaged SWS relative to MIL decreased in the order of KOP (49.4. mm), ALF (32.4. mm) and NAF (14.9. mm) implying that shortages of soil water were induced largely by revegetation and were affected by the plant species. (2) Frequency distributions showed that points with probabilities of 0.5 were not stable between extreme soil water conditions; however, this result might be mitigated or avoided by increasing the sampling density and/or conducting measurement over a longer period. (3) Based on relative difference analysis, the most stable data points underestimated the mean SWS of the plots but were still valuable for precisely estimating the mean SWS of the experimental plot; in addition, among methods for estimating the plot average using representative points, directly using the value of relative difference or their standard deviation, or an index of temporal stability or the mean absolute bias error, no one method consistently performed better than another. (4) ALF presented the most temporally stable patterns among all types of revegetation tested, and vegetation cover and aboveground biomass were the main factors affecting SWS temporal stability. (5) Temporally stable points were located at the mid-slope of the plots. In conclusion, when temporal stability theory was applied to sloping lands mid-slope sampling is likely to give the best results but vegetation characteristics, and in particular vegetation cover should be highlighted. © 2012. Source

Yang K.,Chinese Ministry of Water Resources
Ying yong sheng tai xue bao = The journal of applied ecology / Zhongguo sheng tai xue xue hui, Zhongguo ke xue yuan Shenyang ying yong sheng tai yan jiu suo zhu ban | Year: 2011

Hydroelectric cascade exploitation, one of the major ways for exploiting water resources and developing hydropower, not only satisfies the needs of various national economic sectors, but also promotes the socio-economic sustainable development of river basin. unavoidable anthropogenic impacts on the entire basin ecosystem. Based on the process of hydroelectric cascade exploitation and the ecological characteristics of river basins, this paper reviewed the major impacts of hydroelectric cascade exploitation on dam-area ecosystems, river reservoirs micro-climate, riparian ecosystems, river aquatic ecosystems, wetlands, and river landscapes. Some prospects for future research were offered, e.g., strengthening the research of chain reactions and cumulative effects of ecological factors affected by hydroelectric cascade exploitation, intensifying the study of positive and negative ecological effects under the dam networks and their joint operations, and improving the research of successional development and stability of basin ecosystems at different temporal and spatial scales. Source

Gao L.,Chinese Ministry of Water Resources | Gao L.,University of Chinese Academy of Sciences | Shao M.,CAS Beijing Institute of Geographic Sciences and Nature Resources Research
Catena | Year: 2012

Knowledge of soil water storage (SWS) within soil profiles is crucial when selecting appropriate practices for the restoration of vegetation. To study the temporal stability of SWS and identify representative locations in diverse soil layers, an analysis of temporal stability was performed using Spearman rank correlation coefficients and relative differences. From July 2008 to October 2010, the SWS of three soil layers (0-1, 1-2, and 2-3. m) were measured using a neutron probe at 91 locations on a hillslope on the Loess Plateau, China. A total of 20 SWS datasets were collected over the period of measurement. The results showed that the variability of SWS decreased over time and increased over space with the increase in soil depth. High Spearman rank correlation coefficients (p< 0.01) indicated a strong temporal stability of spatial patterns for all soil layers. Temporal stability increased with increasing soil depth. Furthermore, the closer two soil layers were within a given profile and the deeper any two adjacent soil layers were, the more similar were the temporal patterns. A significant negative correlation (p< 0.01) existed between the status of soil moisture and temporal stability, and the dependency increased with soil depth. With increasing soil depth, more locations were able to estimate the mean SWS of the area. None, however, represented the mean values for all three soil layers separately. © 2012 Elsevier B.V. Source

Discover hidden collaborations