Browsing by Author "Wang, Lixin"
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Item A global synthesis of transpiration rate and evapotranspiration partitioning in the shrub ecosystems(Elsevier, 2022-03) Gao, Guangyao; Wang, Di; Zha, Tianshan; Wang, Lixin; Fu, Bojie; Earth and Environmental Sciences, School of ScienceTranspiration (T) is a fundamental process in understanding the ecophysiology of plants, and it is the dominant component of evapotranspiration (ET) in the terrestrial water cycle. Although previous studies have examined T characteristics of shrub ecosystems in some regions, global-scale synthesis that integrates the spatial variations of T, ET and ratio of T to ET (T/ET) and the associated influences of bio-/abiotic factors in the shrub ecosystems is currently lacking. In this study, we synthesized and analyzed T rate, ET rate and T/ET of the shrub ecosystems from the peer-reviewed articles using field observations around the world. These studies were mainly distributed in drylands with aridity index (ratio of precipitation to potential ET) < 0.65, which accounted for 86.4% of the study locations. Globally, the mean daily T and ET rates of shrubs were 1.5 ± 1.0 mm d−1 and 2.4 ± 0.8 mm d−1, with coefficient of variation of 63.2% and 36.2% among the study locations, respectively. Mean T/ET of the shrubs over the growing season was 0.54 ± 0.14, which was generally lower compared with forest, grassland and cropland ecosystems. The T rate of shrubs was positively related to shrub age, shrub height, leaf area index, and vegetation coverage (p < 0.05), and the effects of biotic factors on T rate were stronger compared with abiotic factors. The ET rate of shrubs was positively related to aridity index, long-term annual mean precipitation, mean soil water content, as well as shrub height and vegetation coverage (p < 0.05). By contrast, the effects of biotic factors on variations of shrub T/ET were weaker than those of abiotic factors, and the T/ET of shrubs was negatively related to aridity index, long-term annual mean precipitation and mean soil water content, but positively related to latitude (p < 0.05). This study is an important supplement of our knowledge gap in terrestrial water cycle, and the findings suggest that T accounted for about half of the water into atmosphere from shrub ecosystems, and the variations of T rate of shrubs were mainly controlled by biotic factors, whereas ET rate and T/ET was mainly affected by abiotic factors.Item African dryland ecosystem changes controlled by soil water(Wiley, 2019-08) Wei, Fangli; Wang, Shuai; Fu, Bojie; Wang, Lixin; Liu, Yi Y.; Li, Yan; Earth Sciences, School of ScienceMonitoring long‐term vegetation dynamics in African drylands is of great importance for both ecosystem degradation studies and carbon‐cycle modelling. Here, we exploited the complementary use of optical and passive microwave satellite data— normalized difference vegetation index (NDVI) and vegetation optical depth (VOD)—to provide new insights of ecosystem changes in African drylands. During 1993–2012, 54% of African drylands experienced a significant increase of VOD, mainly located in southern Africa and west and central Africa, with an average rate of increase of (1.2 ± 2.7) × 10−3 yr−1. However, a significant decreasing NDVI was observed over 43% of the African drylands, in particular in western Niger and eastern Africa, with an average browning rate of (−0.13 ± 1.5) × 10−3 yr−1. The contrasting vegetation trends (increasing VOD and decreasing NDVI) were largely caused by an increase in the relative proportion of the woody component of the vegetation, as a result of the prevailing woody encroachment in African drylands during the study period. Soil water emerges as the dominant driver of ecosystem changes in African drylands, in particular in arid and semiarid areas. This is evidenced by a strong spatio‐temporal correlation between soil water and vegetation, where soil water changes explain about 48% of vegetation variations. This study emphasizes the potential of utilizing multiple satellite products with different strengths in monitoring different characteristics of ecosystems to evaluate ecosystem changes and reveal the underlying mechanisms of the observed changes.Item Age-related water use characteristics of Robinia pseudoacacia on the Loess Plateau(Elsevier, 2021-05) Wang, Jian; Fu, Bojie; Jiao, Lei; Lu, Nan; Li, Jianye; Chen, Weiliang; Wang, Lixin; Earth Sciences, School of ScienceUnderstanding water use characteristics of revegetation species is crucial for evaluating plant adaptability and guiding the sustainability of vegetation restoration in semiarid regions. Ecological restoration projects have been implemented for decades in degraded ecosystems, achieving significant changes in vegetation cover. However, water use characteristics of the main tree species at different ages remain poorly understood in such systems. We investigated water use characteristics of Robinia pseudoacacia in plantations of different stand-age (18 and 30 years). The species is the most widely planted tree in revegetation efforts on the Loess Plateau. The δ2H and δ18O of xylem and soil water within 500 cm of the soil surface and the δ13C values of plant leaves were measured during two consecutive hydrological years. The results showed that that water uptake proportions from across the soil columns changed in 18-yr R. pseudoacacia between a drier (2016) and wetter year (2017). In contrast, shallow soil water was largely comparable in a stand of 30-yr R. pseudoacacia in 2016 and 2017, and similarly the pattern of water uptake by roots from the middle and deep soil column was comparable. However, leaf-level water use efficiency (WUEi) of trees in the older plantation was higher during the wetter year, thereby partly alleviating a low infiltration to precipitation ratio. These findings suggest that different stand-age plantation trees have distinct water use characteristics and display different responses to variations in precipitation. Older plantation trees respond to increased water availability by increasing WUEi instead of switching water sources. This means that stand-age is an essential factor to be considered in ecological restoration management, which can enhance the effectiveness of vegetation restoration strategies. The study indicates useful input from research to management throughout the continuity of restoration effort.Item Analysing Urban Air Pollution Using Low-Cost Methods and Community Science(2022-12) Heintzelman, Asrah; Filippelli, Gabriel; Moreno-Madriñan, Max J.; Wilson, Jeffrey S.; Wang, Lixin; Druschel, Gregory K.Rise in air pollution resulting in negative health externalities for humans has created an urgent need for cities and communities to monitor it regularly. At present we have insufficient ground passive and active monitoring networks in place which presents a huge challenge. Satellite imagery has been used extensively for such analysis, but its resolution and methodology present other challenges in estimating pollution burden. The objective of this study was to propose three low-cost methods to fill in the gaps that exist currently. First, EPA grade sensors were used in 11 cities across the U.S. to examine NO2. This is a simplistic way to assess the burden of air pollution in a region. However, this technique cannot be applied to fine scale analysis, which resulted in the next two components of this research study. Second, a citizen science network was established on the east side of Indianapolis, IN who hosted 32 Ogawa passive sensors to examine NO2 and O3 at a finer scale. These low-cost passive sensors, not requiring power, and very little maintenance, have historically tracked very closely with Federal Reference Monitors. Third, a low-cost PurpleAir PA-II-SD active sensors measuring PM2.5 were housed with the citizen scientists identified above. This data was uploaded via Wi-Fi and available via a crowd sourced site established by PurpleAir. These data sets were analyzed to examine the burden of air pollution. The second and third research studies enabled granular analyses utilizing citizen science, tree canopy data, and traffic data, thus accommodating some of the present limitations. Advancement in low-cost sensor technology, along with ease of use and maintenance, presents an opportunity for not just communities, but cities to take charge of some of these analyses to help them examine health equity impacts on their citizens because of air pollution.Item An Analysis of Precipitation Isotope Distributions across Namibia Using Historical Data(Plos, 2016-05-04) Kaseke, Kudzai Farai; Wang, Lixin; Wanke, Heike; Turewicz, Veronika; Koeniger, Paul; Department of Earth Sciences, School of ScienceGlobal precipitation isoscapes based on the Global Network for Isotopes in Precipitation (GNIP) network are an important toolset that aid our understanding of global hydrologic cycles. Although the GNIP database is instrumental in developing global isoscapes, data coverage in some regions of hydrological interest (e.g., drylands) is low or non-existent thus the accuracy and relevance of global isoscapes to these regions is debatable. Capitalizing on existing literature isotope data, we generated rainfall isoscapes for Namibia (dryland) using the cokriging method and compared it to a globally fitted isoscape (GFI) downscaled to country level. Results showed weak correlation between observed and predicted isotope values in the GFI model (r2 < 0.20) while the cokriging isoscape showed stronger correlation (r2 = 0.67). The general trend of the local cokriging isoscape is consistent with synoptic weather systems (i.e., influences from Atlantic Ocean maritime vapour, Indian Ocean maritime vapour, Zaire Air Boundary, the Intertropical Convergence Zone and Tropical Temperate Troughs) and topography affecting the region. However, because we used the unweighted approach in this method, due to data scarcity, the absolute values could be improved in future studies. A comparison of local meteoric water lines (LMWL) constructed from the cokriging and GFI suggested that the GFI model still reflects the global average even when downscaled. The cokriging LMWL was however more consistent with expectations for an arid environment. The results indicate that although not ideal, for data deficient regions such as many drylands, the unweighted cokriging approach using historical local data can be an alternative approach to modelling rainfall isoscapes that are more relevant to the local conditions compared to using downscaled global isoscapes.Item Antarctica’s Dry Valleys: A potential source of soluble iron to the Southern Ocean?(AGU, 2015-03) Bhattachan, Abinash; Wang, Lixin; Miller, Molly F.; Licht, Kathy J.; D'Odorico, Paolo; Department of Earth Sciences, IU School of ScienceThe soluble iron content and dust emission potential of sediment samples collected from the Taylor Valley in the McMurdo Dry Valleys (MDVs) and sea ice in the McMurdo Sound were evaluated to determine whether inputs to the Southern Ocean may be sufficient to affect ocean productivity. Our results show that the dust-generating potential from the MDVs soils are comparable to those of sediments from other major dust sources in the Southern Hemisphere. Sediments from the MDVs and sea ice are one order of magnitude richer in soluble iron than those in other dust sources in the Southern Hemisphere. Forward trajectory analyses show that the dust from the MDVs is likely to be deposited in the Southern Ocean. These results provide evidence of the possible supply of soluble iron to the Southern Ocean associated with dust transport from the MDVs, should climate change expand the exposed areas of the continent.Item Applications of geospatial analysis techniques for public health(2016-05-02) Stanforth, Austin Curran; Filippelli, Gabriel; Johnson, Daniel P.; Wang, Lixin; Wilson, Jeffrey; Moreno-Madriñán, Max J.; Jacinthe, Pierre-AndréGeospatial analysis is a generic term describing several technologies or methods of computational analysis using the Earth as a living laboratory. These methods can be implemented to assess risk and study preventative mitigation practices for Public Health. Through the incorporation Geographic Information Science and Remote Sensing tools, data collection can be conducted at a larger scale, more frequent, and less expensive that traditional in situ methods. These techniques can be extrapolated to be used to study a variety of topics. Application of these tools and techniques were demonstrated through Public Health research. Although it is understand resolution, or scale, of a research project can impact a study’s results; further research is needed to understand the extent of the result’s bias. Extreme heat vulnerability analysis was studied to validate previously identified socioeconomic and environmental variables influential for mitigation studies, and how the variability of resolution impacts the results of the methodology. Heat was also investigated for the implication of spatial and temporal resolution, or aggregation, influence on results. Methods studying the physical and socioeconomic environments of Dengue Fever outbreaks were also studied to identify patters of vector emergence.Item Are the shoreline and eutrophication of desert lakes related to desert development?(Springer, 2021-01) Luo, Lihui; Zhao, Wenzhi; Wang, Lixin; Ogashawara, Igor; Yang, Qiyue; Zhou, Hai; Yang, Rong; Duan, Quntao; Zhou, Chenglin; Zhuang, Yanli; Earth Sciences, School of ScienceDesert lakes are unique ecosystems found in oases within desert landscapes. Despite the numerous studies on oases, there are no reports regarding the spatiotemporal distribution and causes of eutrophication in the desert lakes that are located at the edge of the Linze Oasis in northwestern China. In this study, the seasonal shoreline and eutrophication of a desert lake were monitored using an unmanned aerial vehicle (UAV) and water sampling during three crop growth stages. The spatial extents of the shoreline and algal blooms and the chromophoric dissolved organic matter (CDOM) absorption coefficient were derived through UAV images. The desert lake shoreline declined during the crop growing stage, which exhibited the largest water demand and began to expand after this stage. The estimated CDOM absorption coefficient measurements and classified algal bloom area showed seasonal variations that increased from spring to late summer and then decreased in autumn. The first two crop growth stages accounted for most of the water and fertilizer requirements of the entire growth period, which may have contributed to large amounts of groundwater consumption and pollution and resulted in peak eutrophication of the lake in the second growth stage. However, the CDOM absorption coefficient of the third stage was not well correlated with that of the first two stages, suggesting that the lake may be affected by the dual effects of groundwater and precipitation recharge in the third stage. These results indicate that the water quality of desert lakes may be affected by agricultural cultivation. The agricultural demands for water and fertilizer may change the spatiotemporal changes in water quality in the lake, especially in the middle and early stages of crop growth.Item Assessing Temperate Forest Growth and Climate Sensitivity in Response to a Long-Term Whole-Watershed Acidification Experiment(Wiley, 2020-06) Malcomb, Jacob D.; Scanlon, Todd M.; Epstein, Howard E.; Druckenbrod, Daniel L.; Vadeboncoeur, Matthew A.; Lanning, Matthew; Adams, Mary Beth; Wang, Lixin; Earth Sciences, School of ScienceAcid deposition is a major biogeochemical driver in forest ecosystems, but the impacts of long-term changes in deposition on forest productivity remain unclear. Using a combination of tree ring and forest inventory data, we examined tree growth and climate sensitivity in response to 26 years of whole-watershed ammonium sulfate ((NH4)2SO4) additions at the Fernow Experimental Forest (West Virginia, USA). Linear mixed effects models revealed species-specific responses to both treatment and hydroclimate variables. When controlling for environmental covariates, growth of northern red oak (Quercus rubra), red maple (Acer rubrum), and tulip poplar (Liriodendron tulipifera) was greater (40%, 52%, and 42%, respectively) in the control watershed compared to the treated watershed, but there was no difference in black cherry (Prunus serotina). Stem growth was generally positively associated with growing season water availability and spring temperature and negatively associated with vapor pressure deficit. Sensitivity of northern red oak, red maple, and tulip poplar growth to water availability was greater in the control watershed, suggesting that acidification treatment has altered tree response to climate. Results indicate that chronic acid deposition may reduce both forest growth and climate sensitivity, with potentially significant implications for forest carbon and water cycling in deposition-affected regions.Item Attributes of Organic Phosphorus Exported from a Central Indiana Agricultural Watershed: Effects of Season and Hydrologic Flowpath(2023-05) Pitcock, Rebecca Jo; Jacinthe, Pierre-Andre; Filippelli, Gabriel; Wang, LixinThe export of phosphorus (P) from agricultural watersheds has been extensively investigated but monitoring efforts have generally focused on inorganic P (Pi or soluble reactive phosphorus [SRP]), the P fraction thought to be immediately available to algae. However, in settings where no-till management is implemented and organic matter accumulates on soil surface, the amount of organic P (Po) in agricultural drainage waters can be significant and may represent another important P source to fuel algal growth in receiving water bodies. From a 2018 monitoring study at a Central Indiana agricultural watershed, measured total P and SRP loss amounted to 1.22 and 0.17 kg P/ha/year, respectively, indicating that the bulk (84%) of P exported from that watershed was in organic form. Results also showed that tile drainage was the main pathway for P transport (96% of Po loss). In light of these observations, the bioavailability of Po in agricultural drainage waters was investigated in 2019, and the effect of hydrologic flow path (surface versus subsurface flow) on the biochemical attributes of Po was examined. In these assessments, the iron strip method and a suite of enzymatic assays were used to gain a better understanding of the chemical composition of the exported Po. Higher concentration of labile Po was consistently measured in tile discharge than in surface runoff (59% versus 38% of the total bioavailable P). Further, the concentration of EHP (enzymatically hydrolysable P), in the form of monoester, diester, and phytate compounds, was highest during the summer season, for both tile and surface pathways. This elevated bioavailability of Po during the summer is a concern because, in combination with favorable water temperature and solar radiation during that period, this could lead to enhanced Po mineralization and release of Pi, resulting in further algal proliferation and continued degradation of water quality. Considering the high prevalence of tile drainage in agricultural landscapes of the US Midwest, this finding underscores the need for further investigation of the impact of land management and climate on the speciation and bioavailability of Po in the region’s agricultural waters. Data available from: https://doi.org/10.7912/D2/40.