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Lakes are regarded as important nodes in water resources, playing pivotal roles in the regional hydrological cycle. However, the systematic study on lake water balance is scarce in Mt. Yulong region. Here, we study the stable isotope compositions of precipitation, inflowing rivers and lake water to exploit the characteristics of hydrological supply and lake water balance. The results showed that there was a typical spatial distribution of surface isotope in August and April. Relatively high d18O values with low d-excess were found on the east and west shores of the lake in August and in the middle part of the lake in April. The lowest d18O with highest d-excess were found in the north and south shores in August and April, respectively. Meanwhile, slight isotopic stratification indicated that the lake water was vertically mixed-well. Subsequently, the evaporation-to-inflow ratios (E/Is) during the two periods were further derived based on the isotope mass balance model. Approximately 51% in August and 12% in April of the water flowing into Lashi Lake underwent evaporation. This study provides a reference for the long-term monitoring and modeling the hydrology processes of the basin, and is important for the regional water resource. [ABSTRACT FROM AUTHOR]

Channel bends are one of the most important characteristic features of natural streams. These bends often create the conditions for a hyporheic zone, which has been recognized as a critical component of stream ecosystems. The streambed vertical hydraulic conductivity (Kv), vertical hydraulic gradient (VHG) and Darcian flux (DF) in the hyporheic zone were estimated at 61 locations along a channel bend of the Beiluo River during July 2015 and January 2016. All the streambed attributes showed great spatial variability along the channel bend. Both upward fluxes and downward fluxes occurred during the two test periods, most of studied stream sections were controlled by downwelling, indicating stream water discharge into the subsurface. The average downward flux was higher at the downstream side than at the upstream side of the channel bend, especially in July 2015. The distribution of streambed sediment grain size has a significant influence on the variability of Kv; high percentages of silt and clay sediments generally lead to low Kv values. Higher Kv at the depositional left bank at the upstream site shifted toward the erosional right bank at the downstream site, with Kv values positively correlated with the water depth. This study suggested that the variabilities of Kv and VHG were influenced by the stream geomorphology and that the distribution of Kv was inversely related, to a certain extent, to the distribution of VHG across the channel bend. Kv and VHG were found to have opposite effects on the DF, and the close relationship between Kv and DF indicated that the water fluxes were mainly controlled by Kv. [ABSTRACT FROM AUTHOR]

Nitrate contamination in rivers has raised widespread concern in the world, particularly in arid/semi-arid river basins lacking qualified water. Understanding the nitrate pollution levels and sources is critical to control the nitrogen input and promote a more sustainable water management in those basins. Water samples were collected from a typical semi-arid river basin, the Weihe River watershed, China, in October 2014. Hydrochemical assessment and nitrogen isotopic measurement were used to determine the level of nitrogen compounds and identify the sources of nitrate contamination. Approximately 32.4% of the water samples exceeded the World Health Organization (WHO) drinking water standard for NO3--N. Nitrate pollution in the main stream of the Weihe River was obviously much more serious than in the tributaries. The δ15N-NO3- of water samples ranged from +8.3h to +27.0h. No significant effect of denitrification on the shift in nitrogen isotopic values in surface water was observed by high dissolved oxygen (DO) values and linear relationship diagram between NO3--N and δ15N-NO3-, except in the Weihe River in Huayin County and Shitou River. Analyses of hydrochemistry and isotopic compositions indicate that domestic sewage and agricultural activities are the main sources of nitrate in the river. [ABSTRACT FROM AUTHOR]

This study demonstrates the spatial and temporal variations of streambed vertical hydraulic conductivity Kv from October 2011 to November 2014 along the Weihe River, the largest tributary of the Yellow River. The streambed Kv values of a total number of 385 locations from five test sites were estimated on the basis of in situ falling-head standpipe permeameter tests. The difference of Kv values for all test locations reaches five orders of magnitude with a range from 5.87E-04 to 61.3 m/d and a median value of 1.62E-01 m/d. The streambed Kv values are neither normally nor log-normally distributed, but display significant spatial variability among the five test sites. The highest Kv values occur at the site with mainly sandy sediment, while the Kv values at the other four sites with mainly silt-clay sediment are relatively close and have less variability than those at the sandy sediment site. The median Kv values from all of the sites exhibit no statistically significant temporal trends. However, the median Kv values indeed show temporal variations that might be influenced by changes in silt-clay content of the sediment, especially for the sandy sediment site and the combined data from all sites. Weak evidence demonstrates that streambed Kv values decrease with depth. [ABSTRACT FROM AUTHOR]