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Item The moisture origin of dew: Insights from three sites with contrasting climatic conditions(Wiley, 2023-06) Tian, Chao; Wang, Lixin; Li, Fadong; Zhang, Xiao; Jiao, Wenzhe; Medici, Marie-Gabrielle; Kaseke, Kudzai Farai; Beysens, Daniel; Earth and Environmental Sciences, School of ScienceDew is one of the important moisture sources in many arid and semiarid regions. The knowledge of moisture origin of dew under various climatic conditions is still lacking. Isotopic variations can preserve information about moisture origin and formation mechanisms. Therefore, the isotopic compositions of dew and precipitation (δ2H, δ18O, δ17O, d-excess, lc-excess and 17O-excess) were investigated at three sites with different climatic conditions (i.e., Gobabeb with extremely dry climate, Nice with Mediterranean climate and Indianapolis with humid continental climate). The results showed that there were three types of dew at Gobabeb: advective dew, groundwater-derived dew, and shallow soil water-derived dew, accounting for 27.3%, 45.4% and 27.3% of the dew events, respectively. The ultimate moisture sources of advective dew and the other two types of dew at Gobabeb were from the South Atlantic Ocean and a mixture of the Indian and South Atlantic Oceans, respectively. Dew in Nice included ocean-derived dew from the North Atlantic Ocean with local evapotranspiration replenishment, and local-derived dew, mainly from the continental Europe and Mediterranean Sea, accounting for 39.1% and 60.9% of the dew events, respectively. All the Indianapolis dew were likely local-derived dew. Based on the moisture origins, the future dew trends were speculated under global warming. Dew frequencies at Gobabeb and Indianapolis under future climates are uncertain due to the concurrent increases in atmospheric water vapour and temperature. The local-derived dew in Nice would likely decrease due to the decreasing precipitation and increasing drought, and the ocean-derived dew under future climates is uncertain. This study provides a practical method to distinguish dew moisture sources, and such information is useful for future prediction of dew trends under climate change.Item Water surface albedo and its driving factors on the turbid lakes of Northeast China(Elsevier, 2023-02) Du, Jia; Jacinthe, Pierre-Andre; Song, Kaishan; Zhou, Haohao; Earth and Environmental Sciences, School of ScienceLake water surface albedo (LWSA) is a critical parameter for describing energy flux balance at the air–water interface. It is used to measure the capacity of lake water surface reflectance in the shortwave radiation band, which controls the energy partitioning between atmosphere and lake. LWSA and its driving factors, including solar radiation angle, water quality and meteorology, in lakes of Northeast China was analyzed in this research. Solar altitude angle emerged as the most important controlling factor of LWSA. The results showed a strong reduction in LWSA values with increase in solar altitude angle. The study also documented a strong effect of suspended matter on the radiative properties of lakes surface, leading to increased LWSA with increased in suspended matter concentration, especially at high solar altitude angles (R2: 0.76). While no significant association (R2: 0.11) was found between LWSA and chlorophyll-a concentration, LWSA was positively correlated with wind speed (R2 of 0.62 and 0.50 at high and low solar altitude angles, respectively), likely a consequence of wind-driven sediment resuspension in lake waters. Although chromophoric dissolved organic matter (CDOM) and organic particulate matter can affect energy partitioning and spectral distribution of incident solar radiation in lake waters, there was insufficient evidence of measurable effects on LWSA. Variations in LWSA recorded in this study were primarily dependent on similar solar altitude angles and backscattering properties of inorganic particulate matter suspended in the water column. Higher surface albedo was found in the turbid lakes.Item Spatial Heterogeneity of Vegetation Resilience Changes to Different Drought Types(AGU, 2023-04) Zhang, Yu; Liu, Xiaohong; Jiao, Wenzhe; Wu, Xiuchen; Zeng, Xiaomin; Zhao, Liangju; Wang, Lixin; Guo, Jiaqi; Xing, Xiaoyu; Hong, Yixue; Earth and Environmental Sciences, School of ScienceResilience is a fundamental concept for vegetation health. The increasing drought frequency and severity may pose severe threat to vegetation resilience. However, it is still not clear how vegetation resilience is evolving in response to climate change in pivotal biographical zones. Here, we examined the resilience changes in terms of leaf area index (LAI, an indicator of canopy structure) and gross primary productivity (GPP, an indicator of carbon uptake) in responding to the Standardized Precipitation-Evapotranspiration Index (SPEI) and vapor pressure deficit (VPD) over China's Loess Plateau and Qinling Mountains. Linking remote sensing variables and tree ring width allows the upscaling of plot-based vegetation growth information. We further explored potential explanatory factors associated with the heterogeneous spatial distributions of resilience changes. Results revealed that the resilience of GPP weakened more than LAI in response to drought, suggesting that compared to LAI, productivity requires more time to recover to the pre-drought levels. Regionally, the change of vegetation resilience on the Loess Plateau and in high-altitude areas was highly susceptible to SPEI and VPD, respectively. The observed spatial heterogeneity in resilience changes was mainly attributed by climate zone, water deficit, and their interactions. Our findings provide direct and empirical evidence that the vegetation in the Loess Plateau and Qinling Mountains is gradually losing resilience. The results indicate that sustained ecosystem water deficit and atmospheric dryness will continue to threaten vegetation survival and terrestrial ecosystem service.Item Precipitation and discharge changes drive increases in Escherichia coli concentrations in an urban stream(Elsevier, 2023-08) Li, Rui; Filippelli, Gabriel; Wang, Lixin; Earth and Environmental Sciences, School of ScienceDetermining the driving factors of E. coli dynamics and predicting future E. coli changes in urban aquatic systems are important for regulating water quality. In this study, data from 6985 measurements of E. coli from 1999 to 2019 in an urban waterway Pleasant Run in Indianapolis, Indiana (USA) were statistically analyzed by Mann-Kendall and multiple linear regression to assess the long-term trends in E. coli concentrations and to project E. coli concentrations under future climate change scenarios. E. coli concentrations monotonically increased over the last two decades, with the value increasing from 111 Most Probable Number (MPN)/100 mL in 1999 to 911 MPN/100 mL in 2019. E. coli concentrations have exceeded the Indiana standard of 235 MPN/100 mL since 1998. E. coli showed peak concentration in summer and higher concentration in sites with combined sewer overflows (CSOs) relative to those without. Precipitation had both direct and indirect impacts on E. coli concentrations meditated by stream discharge. Multiple linear regression results showed that annual precipitation and discharge accounted for 60 % of E. coli concentration variability. Based on the observed precipitation-discharge-E. coli concentration relationship, the projected results showed that, in the highest emission representative concentration pathways (RCP) 8.5 climate scenario, E. coli concentrations in the 2020s, 2050s, and 2080s will be 1350 ± 563 MPN/100 mL, 1386 ± 528 MPN/100 mL, and 1443 ± 479 MPN/100 mL, respectively. This study illustrates that climate change can impact E. coli concentrations by altering temperature, precipitation patterns, and stream flow in an urban stream and predicts an undesired future situation under a high CO2 emission scenario.Item Streamflow decreases in response to acid deposition in a subtropical forest watershed in China(Nature, 2023) Wang, Linhua; Lanning, Matthew; Wang, Lixin; Yu, Mengxiao; Ye, Shu; Tian, Lei; Yen, Haw; Yan, Junhua; Earth and Environmental Sciences, School of ScienceStreamflow reductions have been attributed to the impacts of soil nutrient availability on plant transpiration, connecting soil biogeochemical and hydrological processes. Here we conducted a plot-scale acid addition experiment and monitored long-term hydrology in a subtropical watershed to provide direct evidence for the underlying mechanisms of these connections. These results showed that acid deposition enhanced plant growth and thus increased plant transpiration in the early treatment period. It indicates that plants can increase their transport of water and nutrients to satisfy physiological demands under continuous acid deposition. Acid deposition mainly contributed to increased evapotranspiration and decreased streamflow at the watershed scale. These results provide complementary evidence of plants adjusting to acid deposition-induced changes in soil nutrient availability and these acclimations result in streamflow reductions at the watershed scale. Our results call for integrating forest biogeochemical feedback into watershed hydrology.Item Quantitative contribution of cryogenic vacuum extraction and radial water transport to xylem-source water deuterium offsets(Elsevier, 2024-02) Li, Yue; Song, Xianfang; Wang, Lixin; Sprenger, Matthias; Ma, Ying; Earth and Environmental Sciences, School of ScienceThe positions and magnitudes of deuterium offsets between bulk xylem and corresponding source waters are under debate and quantifying them is essential for isotope-based ecohydrological investigations. In this study, stable isotopes (δ2H, δ18O, and δ13C), iteration method, and rehydration experiments were combined to quantitatively determine the magnitude of cryogenic vacuum extraction (CVE)- and radial water transport (RWT)-induced deuterium offsets using one riparian tree species Salix babylonica L. A modified potential water source line (MPWL) was proposed to identify the total δ2H offsets between bulk xylem and source waters. The relationships between δ2H offsets induced by CVE or RWT and plant water content, leaf δ13C values, soil water content (SWC), and the depth to the water table (WTD) were investigated. Results showed that the bulk xylem waters in different tissue positions of S. babylonica showed −7.0 ‰ to −4.0 ‰ deuterium depletion relative to MPWL at four different sites (p < 0.01). The isotopic compositions of sap water coincided well with MPWL on the dual-isotope plot at the four sites. The CVE- and RWT-induced δ2H offsets accounted for 75.1 % and 24.9 % of the total δ2H offsets, respectively. The CVE-induced δ2H offsets were significantly negatively correlated with plant water content. In comparison, the RWT-induced δ2H offsets were negatively related to plant leaf δ13C values, trunk water content, and SWC, but positively correlated with WTD. This study provides a quantitative contribution of two major sources of deuterium offsets. The results provide critical insights into isotope-based plant water source identification and evapotranspiration partitioning.Item Quantifying river water contributions to the transpiration of riparian trees along a losing river: lessons from stable isotopes and an iteration method(EGU, 2023) Li, Yue; Ma, Ying; Song, Xianfang; Zhang, Qian; Wang, Lixin; Earth and Environmental Sciences, School of ScienceRiver water plays a critical role in riparian plant water use and riparian ecosystem restoration along losing rivers (i.e., river water recharging underlying groundwater). How to quantify the contributions of river water to the transpiration of riparian plants under different groundwater levels and the related responses of plant water use efficiency is a great challenge. In this study, observations of stable isotopes of water (δ2H and δ18O), 222Rn, and leaf δ13C were conducted for the deep-rooted riparian weeping willow (Salix babylonica L.) in 2019 (dry year) and 2021 (wet year) along the Chaobai River in Beijing, China. We proposed an iteration method in combination with the MixSIAR model to quantify the river water contribution to the transpiration of riparian S. babylonica and its correlations with the water table depth and leaf δ13C. Our results demonstrated that riparian S. babylonica took up deep water (in the 80–170 cm soil layer and groundwater) by 56.5 % ± 10.8 %. River water recharging riparian deep water was an indirect water source and contributed 20.3 % of water to the transpiration of riparian trees near the losing river. Significantly increasing river water uptake (by 7.0 %) and decreasing leaf δ13C (by −2.0 ‰) of riparian trees were observed as the water table depth changed from 2.7 m in the dry year of 2019 to 1.7 m in the wet year of 2021 (p<0.05). The higher water availability probably promoted stomatal opening and thus increased transpiration water loss, leading to the decreasing leaf δ13C in the wet year compared to the dry year. The river water contribution to the transpiration of riparian S. babylonica was found to be negatively linearly correlated with the water table depth and leaf δ13C (p<0.01). The rising groundwater level may increase the water extraction from the groundwater and/or river and produce a consumptive river-water-use pattern of riparian trees, which can have an adverse impact on the conservation of both river flow and riparian vegetation. This study provides new insights into understanding the mechanisms of the water cycle in a groundwater–soil–plant–atmosphere continuum and managing water resources and riparian afforestation along losing rivers.Item Response of Ecosystem Productivity to High Vapor Pressure Deficit and Low Soil Moisture: Lessons Learned From the Global Eddy-Covariance Observations(AGU, 2023-08) Xu, Shiqin; Gentine, Pierre; Li, Lingcheng; Wang, Lixin; Yu, Zhongbo; Dong, Ningpeng; Ju, Qin; Zhang, Yuliang; Earth and Environmental Sciences, School of ScienceAlthough there is mounting concern about how high vapor pressure deficit (VPD) and low soil moisture (SM) affect ecosystem productivity, their relative importance is still under debate. Here, we comprehensively quantified the relative impacts of these two factors on ecosystem gross primary production (GPP) using observations from a global network of eddy-covariance towers and two approaches (sensitivity analysis and linear regression model). Both approaches agree that a higher percentage of sites experience GPP reduction from high VPD than from low SM over the growing season. However, the constraint of high VPD and low SM on GPP reduction is tightly linked with climates and plant functional types. Humid and mesic ecosystems including forests and grasslands are dominated by VPD, while the semi-arid and arid ecosystems including shrublands and savannas are dominated by SM. The varying dominant role of these two factors on GPP is closely related to plant stomatal behavior, as predicted by a stomatal conductance model. Additionally, we highlight the non-linear impact of SM on GPP during droughts and the possible underestimation of the SM effects for deep-rooted plants when only using surface-layer SM. Our results shed light on a better understanding of the impacts of VPD and SM on vegetation productivity, with important implications for modeling the response and feedback of ecosystem dynamics to current and future climates.Item Phosphorus Mobility in Gypsum-Amended Soils in Relation to Soil Type and Timing of P Fertilizer Application(Springer Nature, 2023) Haehnle Cox, Kristiana; Jacinthe, Pierre-Andre; Earth and Environmental Sciences, School of ScienceGypsum (CaSO4∙2H2O) amendment can reduce phosphorus (P) export from agricultural fields and protect water quality. Past studies have examined the impact of gypsum application rate, but limited research has been conducted to assess the effect of the time interval between gypsum application and P fertilization on treatment effectiveness and P mobility. To address this question, a mesocosm-scale experiment was conducted using 36 soil columns packed with either Brookston clay-loam (total phosphorus, TP: 0.46 g kg−1) or Fincastle silt-loam soil (TP: 4.63 g kg−1). For each soil type, 9 columns were treated with gypsum (5 Mg ha−1) and an equal number served as untreated controls. At different time intervals (2, 30, and 58 days after gypsum application), one-third of the columns received P fertilizer (34 kg P ha−1). Rainwater was added to generate leachate that was collected over a 3-week period and analyzed for pH, sulfate (SO4−2), dissolved reactive P (DRP), and TP. At the end of each leaching period, soil columns were sliced (2–5 cm layers), and the amount of water-extractable P (WEP) and Olsen-P was quantified. The gypsum treatment had generally no effect on Olsen-P, but it consistently resulted in lower WEP level (1.8-fold) compared to controls. Likewise, during the later stage of the experiment (> 30 days), the gypsum treatment resulted in DRP concentration reduction (28–52%) in leachate from the Fincastle soil columns (but the effect was marginal in the Brookston columns likely due to limited distribution of surface applied gypsum in this fine-textured soil). These results indicated that the effect of gypsum on DRP leaching varies with the timing of P application. Depending on soil type, an interval of 1–2 months (shorter interval for coarse-textured soils; longer interval if soils are fine-textured) should be adopted before applying P fertilizer in order to optimize the effectiveness of the gypsum treatment.Item A “Local First” Approach to Glacigenic Sediment Provenance Demonstrated Using U-Pb Detrital Zircon Geochronology of the Permo-Carboniferous Wynyard Formation, Tasmanian Basin(Society for Sedimentary Geology (SEPM), 2022) Ives, Libby R. W.; Isbell, John L.; Licht, Kathy J.; Earth and Environmental Sciences, School of ScienceWe propose that a “local first” approach should be applied to the interpretation of provenance indicators in glacigenic sediments of all depositional ages, especially where the glacier flow path is poorly constrained and the records of potential source lithologies are incomplete. Provenance proxies, specifically U-Pb detrital zircon geochronology, of glacigenic sediments are commonly used to infer the size and distribution of past ice centers, which are in turn used to inform ancient climate reconstructions. Interpretations of these proxies often assume that similar provenance signals between glacigenic units of the same depositional age are evidence that they were deposited by the same glacier, even when those units are, not infrequently, separated by thousands of kilometers. Though glaciers are capable of transporting sediment great distances, this assumption is problematic as it does not acknowledge observations from the geologic records of Pleistocene ice sheets that show provenance proxies in glacial sediments are most likely to reflect proximal (within 100 km) sediment sources located along a specific flow path. In a “local first” approach, provenance indicators are first compared to local source lithologies. If the indicator cannot be attributed to proximal sources, only then should progressively more distal sources be investigated. Applying a local first approach to sediment provenance in ancient glacial systems may result in significant revisions to paleo ice sheet reconstructions. The effectiveness of the local first approach is demonstrated here by comparing new U-Pb detrital zircon dates from the Permo-Carboniferous glacigenic Wynyard Fm with progressively distal source lithologies along the glacier’s inferred flow path. The Wynyard Fm and source lithologies were compared using an inverse Monte-Carlo unmixing model (DZMix). All measured Wynyard Fm detrital zircon dates can be attributed to zircon sources within 33 km of the sample location along the glacier’s flow path. This interpretation of a proximal detrital zircon provenance does not conflict with the popular interpretation made from sedimentological observations that the Wynyard Fm was deposited by a large, temperate outlet glacier or ice stream that flowed south-to-north across western Tasmania. Overall, a local first approach to glacial sediment provenance, though more challenging than direct comparisons between glacigenic sedimentary deposits, has the potential to elucidate the complex histories and flow paths of glacial sedimentary systems of all depositional ages.