Retraction Note: Global analysis of streamflow response to forest management.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Editorial Expression of Concern: Global analysis of streamflow response to forest management.

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Author Correction: Global analysis of streamflow response to forest management.

An Amendment to this paper has been published and can be accessed via a link at the top of the paper.

Spatiotemporal variations in the hydrochemical characteristics and controlling factors of streamflow and groundwater in the Wei River of China.

Analysis of hydrochemical characteristics and controlling factors of streamflow and groundwater in arid regions is important for water security. In this study, we collected samples of streamflow and groundwater from the Wei River in China, analyzed their hydrochemical characteristics, and identified the major solute sources using ion concentrations, δ15N-NO3- and δ18O-NO3-. The major downstream ion contents were greater than the corresponding upstream values and the ion content in streamflow during the wet season is much higher than that during the dry season. The water quality during the wet season was unsatisfactory as approximately one third of the water samples were categorized as the worst water quality based on excessive nitrates and carbonate weathering. Rock weathering contributed the greatest proportion of solutes to both streamflow and groundwater. Evaporite dissolution and carbonate weathering dominated solutes in the wet and dry seasons, respectively. Human activities cannot be ignored in certain areas. Fertilizer application accounts for 43% of the total anthropogenic solute inputs. These results point to the increasing impact of agriculture on water quality.

Global analysis of streamflow response to forest management.

Predicting the responses of streamflow to changes in forest management is fundamental to the sustainable regulation of water resources. However, studies of changes in forest cover have yielded unclear and largely unpredictable results. Here we compile a comprehensive and spatially distributed database of forest-management studies worldwide, to assess the factors that control streamflow response to forest planting and removal. We introduce a vegetation-to-bedrock model that includes seven key landscape factors in order to explain the impacts of forest removal and planting on water yield. We show that the amount of water stored in a landscape is the most important factor in predicting streamflow response to forest removal, whereas the loss of water through evaporation and transpiration is the most important factor in predicting streamflow response to forest planting. Our findings affect model parameterizations in climate change mitigation schemes (involving, for example, afforestation or deforestation) in different geologic and climate regions around the world, and inform practices for the sustainable management of water resources.

Prevalence and magnitude of groundwater use by vegetation: a global stable isotope meta-analysis.

The role of groundwater as a resource in sustaining terrestrial vegetation is widely recognized. But the global prevalence and magnitude of groundwater use by vegetation is unknown. Here we perform a meta-analysis of plant xylem water stable isotope (δ2H and δ18O, n = 7367) information from 138 published papers - representing 251 genera, and 414 species of angiosperms (n = 376) and gymnosperms (n = 38). We show that the prevalence of groundwater use by vegetation (defined as the number of samples out of a universe of plant samples reported to have groundwater contribution to xylem water) is 37% (95% confidence interval, 28-46%). This is across 162 sites and 12 terrestrial biomes (89% of heterogeneity explained; Q-value = 1235; P < 0.0001). However, the magnitude of groundwater source contribution to the xylem water mixture (defined as the proportion of groundwater contribution in xylem water) is limited to 23% (95% CI, 20-26%; 95% prediction interval, 3-77%). Spatial analysis shows that the magnitude of groundwater source contribution increases with aridity. Our results suggest that while groundwater influence is globally prevalent, its proportional contribution to the total terrestrial transpiration is limited.

Global separation of plant transpiration from groundwater and streamflow.

Current land surface models assume that groundwater, streamflow and plant transpiration are all sourced and mediated by the same well mixed water reservoir--the soil. However, recent work in Oregon and Mexico has shown evidence of ecohydrological separation, whereby different subsurface compartmentalized pools of water supply either plant transpiration fluxes or the combined fluxes of groundwater and streamflow. These findings have not yet been widely tested. Here we use hydrogen and oxygen isotopic data ((2)H/(1)H (δ(2)H) and (18)O/(16)O (δ(18)O)) from 47 globally distributed sites to show that ecohydrological separation is widespread across different biomes. Precipitation, stream water and groundwater from each site plot approximately along the δ(2)H/δ(18)O slope of local precipitation inputs. But soil and plant xylem waters extracted from the 47 sites all plot below the local stream water and groundwater on the meteoric water line, suggesting that plants use soil water that does not itself contribute to groundwater recharge or streamflow. Our results further show that, at 80% of the sites, the precipitation that supplies groundwater recharge and streamflow is different from the water that supplies parts of soil water recharge and plant transpiration. The ubiquity of subsurface water compartmentalization found here, and the segregation of storm types relative to hydrological and ecological fluxes, may be used to improve numerical simulations of runoff generation, stream water transit time and evaporation-transpiration partitioning. Future land surface model parameterizations should be closely examined for how vegetation, groundwater recharge and streamflow are assumed to be coupled.