Ecosystem Water Balance Research Articles

Estimating cropland carbon fluxes: A process-based model evaluation at a Swiss crop-rotation site

In support of climate change mitigation strategies and food security, there is an ever-increasing requirement to understand the key drivers of cropland yields and carbon (C) budgets. Process-based crop models, driven by meteorological observations, can provide realistic simulations and diagnosis of the variability in crop C budgets. However, the field-scale observations required to validate the models, particularly across multiple growing seasons and crop types, are seldom available.This research evaluates the Soil-Plant-Atmosphere Crop (SPA-Crop) model for estimating the C fluxes of multiple crop types and seasons at the Swiss long-term flux site Oensingen (CH-OE2). SPA-Crop is a detailed parametric model, simulating ecosystem photosynthesis and water balance at fine temporal (half-hourly time-steps) and vertical scales (multiple canopy and soil layers). We initialised the model at the point-scale using management information and meteorological observations recorded during ten crop seasons from 2004 to 2015. SPA-Crop has been developed for simulating winter cereals (wheat and barley), we further evaluated the model performance for these crops at CH-OE2 and extended the simulation to include a crop-specific calibration for winter rapeseed and pea crops. Model estimates of net ecosystem exchange (NEE) of carbon dioxide (CO2), ecosystem respiration (Reco), and gross primary production (GPP) were evaluated based on gap-filled and partitioned eddy covariance (EC) fluxes. Further comparisons were made between modelled and observed yields.The daily SPA-Crop estimates had a high agreement with the EC measurements across the different crop types with a mean R2 of the NEE of 0.74 (wheat), 0.73 (barley), 0.71 (rapeseed) and 0.69 (pea). The modelled yield estimates had biases ranging from −22% (barley, measured-model difference −70 gC m–2; 0.31 t ha−1) to +56% (rapeseed, measured-model difference −85 gC m–2; −0.38 t ha−1), with the largest bias of wheat being only −13% (measured-model difference 34 gC m–2; 0.15 t ha−1) across four wheat seasons. We recommend future SPA-Crop developments – particularly with regards to improving the precision of Reco estimates. Our research demonstrates that SPA-Crop is a reliable tool for simulating the C budget and yield across the four crop types: winter wheat, winter barley, winter rapeseed, and peas.

Assimilating phenology datasets automatically across ICOS ecosystem stations

Abstract The presence or absence of leaves within plant canopies exert a strong influence on the carbon, water and energy balance of ecosystems. Identifying key changes in the timing of leaf elongation and senescence during the year can help to understand the sensitivity of different plant functional types to changes in temperature. When recorded over many years these data can provide information on the response of ecosystems to long-term changes in climate. The installation of digital cameras that take images at regular intervals of plant canopies across the Integrated Carbon Observation System ecosystem stations will provide a reliable and important record of variations in canopy state, colour and the timing of key phenological events. Here, we detail the procedure for the implementation of cameras on Integrated Carbon Observation System flux towers and how these images will help us understand the impact of leaf phenology and ecosystem function, distinguish changes in canopy structure from leaf physiology and at larger scales will assist in the validation of (future) remote sensing products. These data will help us improve the representation of phenological responses to climatic variability across Integrated Carbon Observation System stations and the terrestrial biosphere through the improvement of model algorithms and the provision of validation datasets.

Seasonal drought in North America's sagebrush biome structures dynamic mesic resources for sage-grouse.

The North American semi‐arid sagebrush, Artemisia spp., biome exhibits considerable climatic complexity driving dynamic spatiotemporal shifts in primary productivity. Greater and Gunnison sage‐grouse, Centrocercus urophasianus and C. minimus, are adapted to patterns of resource intermittence and rely on stable adult survival supplemented by occasional recruitment pulses when climatic conditions are favorable. Predictions of intensifying water scarcity raise concerns over new demographic bottlenecks impacting sage‐grouse populations in drought‐sensitive landscapes. We estimate biome‐wide mesic resource productivity from 1984 to 2016 using remote sensing to identify patterns of food availability influencing selective pressures on sage‐grouse. We linked productivity to abiotic factors to examine effects of seasonal drought across time, space, and land tenure, with findings partitioned along gradients of ecosystem water balance within Great Basin, Rocky Mountains and Great Plains regions. Precipitation was the driver of mesic resource abundance explaining ≥70% of variance in drought‐limited vegetative productivity. Spatiotemporal shifts in mesic abundance were apparent given biome‐wide climatic trends that reduced precipitation below three‐quarters of normal in 20% of years. Drought sensitivity structured grouse populations wherein landscapes with the greatest uncertainty in mesic abundance and distribution supported the fewest grouse. Privately owned lands encompassed 40% of sage‐grouse range, but contained a disproportional 68% of mesic resources. Regional drought sensitivity identified herein acted as ecological minimums to influence differences in landscape carrying capacity across sage‐grouse range. Our model depictions likely reflect a new normal in water scarcity that could compound impacts of demographic bottlenecks in Great Basin and Great Plains. We conclude that long‐term population maintenance depends on a diversity of drought resistant mesic resources that offset climate driven variability in vegetative productivity. We recommend a holistic public–private lands approach to mesic restoration to offset a deepening risk of water scarcity.

Varying responses of two Haloxylon species to extreme drought and groundwater depth

In the context of global change, frequent extreme droughts and artificial groundwater overexploitation have significantly changed water availability, which will have profound effects on ecosystem water balance and plant survival. However, few studies have explored the changes in physiology and water-use of desert plants caused by these emerging variations in water availability. Therefore, we investigated the photosynthesis, water potential, and water absorption of two dominant woody species (Haloxylon ammodendron and H. persicum) at three sites with different groundwater depths in the Gurbantunggut Desert of Central Asia during an extreme drought period. Our results showed that: (1) H. ammodendron exhibited more negative pre-dawn leaf water potential and lower photosynthetic capacity (–2.85 MPa, 24.19 μmol CO2 m−2 s−1) than H. persicum (–2.31 MPa, 33.92 μmol CO2 m−2 s−1) during the extreme drought period; (2) pre-dawn leaf water potential and carbon assimilation of H. ammodendron significantly decreased with declining groundwater depths, whereas those of H. persicum were barely affected; (3) both species converted to deeper but different water sources during the extreme drought period: H. ammodendron obtained 56–100% soil water from the near-groundwater layer, while H. persicum obtained 64–100% soil water from the deep soil layer; (4) the depths of water absorption constantly deepened with declining groundwater depths. Variations in water availability have led to the adjustment in plant water uptake, but this adjustment was not sufficient for the optimal physiological performance of H. ammodendron. Thus, under more intense and frequent drought events, further declines in groundwater depth could significantly inhibit growth of this species and may ultimately threaten its survival. Our findings on water use and physiological responses of dominant plant species to decreasing water availability provide a basis for predicting the future of desert plants under deteriorating water conditions.

Complex bog landscape model (COMBOLA) as an integrated tool for modeling of biotic turnover and peat deposit processes

Biotic cycling in ecosystems consists of live organic matter production and dead organic matter destruction. The latter is accompanied by the emission of greenhouse gases into the atmosphere. In peatland landscapes, additional conditions are imposed due to the presence of a water table depth (WTD), under which the destruction is anaerobic with methane generation, while above the WTD it is aerobic, and part of the diffusing methane is consumed by the methanotrophic bacteria. Hence, due to the complexity of heat and water transfer processes in the peat deposit and the nonlinearity of biological turnover, it is necessary to make a combination of their models. The COmplex Model of BOg LAndscapes (COMBOLA) is a set of dynamic models of carbon and nitrogen turnover, net ecosystem exchange, water balance, heat and water transport, generation and transfer of CO2 and CH4 in a peat deposit on annual, seasonal, and daily time scales. The main component includes a series of biotic turnover models – from a mass-balance equation on an annual time scale to a NEE dynamics model on a daily one. Biotic turnover can be represented by a single carbon cycle, a single nitrogen cycle or both. Another important component of the COMBOLA system is a one-dimensional vertical model of heat-water-gas exchange in a peat deposit. Thus, a number of interconnected modules constitute an integrated mathematical model of peatland landscapes adapted to any given initial information.

Scarce population genetic differentiation but substantial spatiotemporal phenotypic variation of water-use efficiency in Pinus sylvestris at its western distribution range

Water and carbon fluxes in forests are largely related to leaf gas exchange physiology varying across spatiotemporal scales and modulated by plant responses to environmental cues. We quantified the relevance of genetic and phenotypic variation of intrinsic water-use efficiency (WUEi, ratio of net photosynthesis to stomatal conductance of water) in Pinus sylvestris L. growing in the Iberian Peninsula as inferred from tree-ring carbon isotopes. Inter-population genetic variation, evaluated in a provenance trial comprising Spanish and German populations, was low and relevant only at continental scale. In contrast, phenotypic variation, evaluated in natural stands (at spatial level) and by tree-ring chronologies (at temporal inter-annual level), was important and ten- and threefold larger than the population genetic variance, respectively. These results points to preponderance of plastic responses dominating variability in WUEi for this species. Spatial phenotypic variation in WUEi correlated negatively with soil depth (r = − 0.66; p < 0.01), while temporal phenotypic variation was mainly driven by summer precipitation. At the spatial level, WUEi could be scaled-up to ecosystem-level WUE derived from remote sensing data by accounting for soil water-holding capacity (r = 0.63; p < 0.01). This outcome demonstrates a direct influence of the variation of leaf-level WUEi on ecosystem water and carbon balance differentiation. Our findings highlight the contrasting importance of genetic variation (negligible) and plastic responses in WUEi (large, with changes of up to 33% among sites) on determining carbon and water budgets at stand and ecosystem scales in a widespread conifer such as Pinus sylvestris.

Predictable Oxygen Isotope Exchange Between Plant Lipids and Environmental Water: Implications for Ecosystem Water Balance Reconstruction

AbstractIn this study, we present the first evidence for predictable exchange of oxygen isotopes between water and lipid compounds. Using laboratory incubations with aliphatic alcohols, hexadecanol and eicosanol, and bulk soil lipid extracts in isotopically enriched water for 160 days, we determined the magnitude and direction of exchange rates for bulk and compound‐specific lipid extracts. Our data show that δ18O ratios of long‐chain aliphatic lipids that persist in hydrophobic portions of soil organic matter integrate the signature of plant water δ18O values, which can be used to reconstruct hydrologic shifts in terrestrial systems. For bulk lipid extracts, equilibrium was reached, indicating that 22% of its oxygen content is exchangeable with a half‐life of 0.13 years. Incubations with the same bulk lipid extracts in contact with iron oxyhydroxide minerals showed no difference in exchange rates, although the exchangeable fraction decreases to 19% of the total. This result suggests that mineral surfaces can inhibit oxygen exchange for some oxygen‐containing functional groups. In contrast, pure compounds showed stable oxygen isotope signatures with no exchange under the same conditions. Taken together, these findings represent a significant development in the mechanistic understanding and application of oxygen isotopes in plant‐ and soil‐derived lipids, toward a path for the use of lipid extracts in reconstructions of ecosystem water balance.

Drivers of nocturnal water flux in a tallgrass prairie

Abstract Nocturnal transpiration can impact water balance from the local community to earth‐atmosphere fluxes. However, the dynamics and drivers of nocturnal transpiration among coexisting plant functional groups in herbaceous ecosystems are unknown. Here, we addressed the following questions: (1) How do nocturnal (Enight) and diurnal (Eday) transpiration vary among coexisting grasses, forbs, and shrubs in a tallgrass prairie? (2) What environmental variables drive Enight and do these differ from the drivers of Eday? (3) Is Enight associated with daytime physiological processes? We measured diurnal and nocturnal leaf gas exchange on perennial grass, forb and woody species in a North American tallgrass prairie. Measurements were made periodically across two growing seasons (May–August 2014–2015) on three C4 grasses (Andropogon gerardii, Sorghastrum nutans and Panicum virgatum), two C3 forbs (Vernonia baldwinii and Solidago canadensis), one C3 sub‐shrub (Amorpha canescens) and two C3 shrubs (Cornus drummondii and Rhus glabra). By extending our study to multiple functional groups, we were able to make several key observations: (1) Enight was variable among co‐occurring plant functional groups, with the highest rates occurring in C4 grasses, (2) Enight and Eday exhibited different responses to vapour pressure deficit and other environmental drivers, and (3) rates of Enight were strongly related to predawn leaf water potential for grasses and woody species, and were likely modulated by small‐scale changes in soil moisture availability. Our results provide novel insight into an often‐overlooked portion of ecosystem water balance. Considering the high rates of Enight observed in C4 grasses, as well as the widespread global occurrence of C4 grasses, nocturnal water loss might constitute a greater proportion of global evapotranspiration than previously estimated. Additionally, future predictions of nocturnal water loss may be complicated by stomatal behaviour that differs between the day and at night. Finally, these data suggest a water‐use strategy by C4 grasses wherein the high rates of Enight occurring during wet periods may confer a competitive advantage to maximize resource consumption during periods of greater availability. A plain language summary is available for this article.

Scenarios reveal pathways to sustain future ecosystem services in an agricultural landscape.

Sustaining food production, water quality, soil retention, flood, and climate regulation in agricultural landscapes is a pressing global challenge given accelerating environmental changes. Scenarios are stories about plausible futures, and scenarios can be integrated with biophysical simulation models to explore quantitatively how the future might unfold. However, few studies have incorporated a wide range of drivers (e.g., climate, land-use, management, population, human diet) in spatially explicit, process-based models to investigate spatial-temporal dynamics and relationships of a portfolio of ecosystem services. Here, we simulated nine ecosystem services (three provisioning and six regulating services) at 220×220 m from 2010 to 2070 under four contrasting scenarios in the 1,345-km2 Yahara Watershed (Wisconsin, USA) using Agro-IBIS, a dynamic model of terrestrial ecosystem processes, biogeochemistry, water, and energy balance. We asked (1) How does ecosystem service supply vary among alternative future scenarios? (2) Where on the landscape is the provision of ecosystem services most susceptible to future social-ecological changes? (3) Among alternative future scenarios, are relationships (i.e., trade-offs, synergies) among food production, water, and biogeochemical services consistent over time? Our results showed that food production varied substantially with future land-use choices and management, and its trade-offs with water quality and soil retention persisted under most scenarios. However, pathways to mitigate or even reverse such trade-offs through technological advances and sustainable agricultural practices were apparent. Consistent relationships among regulating services were identified across scenarios (e.g., trade-offs of freshwater supply vs. flood and climate regulation, and synergies among water quality, soil retention, and climate regulation), suggesting opportunities and challenges to sustaining these services. In particular, proactive land-use changes and management may buffer water quality against undesirable future climate changes, but changing climate may overwhelm management efforts to sustain freshwater supply and flood regulation. Spatially, changes in ecosystem services were heterogeneous across the landscape, underscoring the power of local actions and fine-scale management. Our research highlights the value of embracing spatial and temporal perspectives in managing ecosystem services and their complex interactions, and provides a system-level understanding for achieving sustainability of the food-water-climate nexus in agricultural landscapes.

Climate change may restrict dryland forest regeneration in the 21st century

The persistence and geographic expansion of dryland forests in the 21st century will be influenced by how climate change supports the demographic processes associated with tree regeneration. Yet, the way that climate change may alter regeneration is unclear. We developed a quantitative framework that estimates forest regeneration potential (RP) as a function of key environmental conditions for ponderosa pine, a key dryland forest species. We integrated meteorological data and climate projections for 47 ponderosa pine forest sites across the western United States, and evaluated RP using an ecosystem water balance model. Our primary goal was to contrast conditions supporting regeneration among historical, mid-21st century and late-21st century time frames. Future climatic conditions supported 50% higher RP in 2020-2059 relative to 1910-2014. As temperatures increased more substantially in 2060-2099, seedling survival decreased, RP declined by 50%, and the frequency of years with very low RP increased from 25% to 58%. Thus, climate change may initially support higher RP and increase the likelihood of successful regeneration events, yet will ultimately reduce average RP and the frequency of years with moderate climate support of regeneration. Our results suggest that climate change alone may begin to restrict the persistence and expansion of dryland forests by limiting seedling survival in the late 21st century.

Hydraulic redistribution under moderate drought among English oak, European beech and Norway spruce determined by deuterium isotope labeling in a split-root experiment.

Hydraulic redistribution (HR) of soil water through plant roots is a crucial phenomenon improving the water balance of plants and ecosystems. It is mostly described under severe drought, and not yet studied under moderate drought. We tested the potential of HR under moderate drought, hypothesizing that (H1) tree species redistribute soil water in their roots even under moderate drought and that (H2) neighboring plants are supported with water provided by redistributing plants. Trees were planted in split-root systems with one individual (i.e., split-root plant, SRP) having its roots divided between two pots with one additional tree each. Species were 2- to 4-year-old English oak (Quercus robur L.), European beech (Fagus sylvatica L.) and Norway spruce (Picea abies (L.) Karst). A gradient in soil water potential (ψsoil) was established between the two pots (-0.55 ± 0.02 MPa and -0.29 ± 0.03 MPa), and HR was observed by labeling with deuterium-enriched water. Irrespective of species identity, 93% of the SRPs redistributed deuterium enriched water from the moist to the drier side, supporting H1. Eighty-eight percent of the plants in the drier pots were deuterium enriched in their roots, with 61 ± 6% of the root water originating from SRP roots. Differences in HR among species were related to their root anatomy with diffuse-porous xylem structure in both beech and-opposing the stem structure-oak roots. In spruce, we found exclusively tracheids. We conclude that water can be redistributed within roots of different tree species along a moderate ψsoil gradient, accentuating HR as an important water source for drought-stressed plants, with potential implications for ecohydrological and plant physiological sciences. It remains to be shown to what extent HR occurs under field conditions in Central Europe.

Gap regeneration within mature deciduous forests of Interior Alaska: Implications for future forest change

Increased fire severity in boreal forests of Interior Alaska is shifting forest canopy composition from black spruce (Picea mariana) to deciduous species, including trembling aspen (Populus tremuloides) and Alaska paper birch (Betula neoalaskana). Because deciduous trees are less flammable than black spruce, the dominant disturbance regime in deciduous forests could move away from fire to one of gap disturbances. In this study, we quantified forest gap characteristics and vegetation within eight mature (62–119-yr-old) deciduous stands in Interior Alaska. Canopy gaps were generally small (true gap area <50m2), formed by the mortality of 4–16 gap makers (which were always deciduous trees), and occupied ∼17–29% of the forest except in the oldest stand, where gap fraction exceeded 45%, and in one anomalous 84-yr old stand, where gaps were absent. Canopy openness increased linearly with gap area, but density of both deciduous and evergreen tree recruits was generally low and insufficient to create future stands with densities similar to those currently found in mature stands across the landscape. Canopy openness was instead correlated with decreased leaf litter cover and increased cover of moss, lichen, and evergreen shrubs. Given the low recruitment of trees with canopy gaps and the decreased probability of fire, deciduous stands will likely transition to non-forested areas or low density stands once overstory trees reach maturity and die. This could have numerous implications for ecosystem function, including carbon (C), water, and energy balance, and potential feedbacks to future fire occurrence and regional climate.

On the variability of the ecosystem response to elevated atmospheric CO2 across spatial and temporal scales at the Duke Forest FACE experiment

While the significance of elevated atmospheric CO2 concentration on instantaneous leaf-level processes such as photosynthesis and transpiration is rarely disputed, its integrated effect at ecosystem level and at long-time scales remains a subject of debate. In part, the uncertainty stems from the inherent leaf-to-leaf variability in gas exchange rates. By combining 10 years of leaf gas exchange measurements collected during the Duke Forest Free Air CO2 Enrichment (FACE) experiment and three different leaf-scale stomatal conductance models, the leaf-to-leaf variability in photosynthetic and stomatal conductance properties is examined. How this variability is then reflected in ecosystem water vapor and carbon dioxide fluxes is explored by scaling up the leaf-level process to the canopy using model calculations. The main results are: (a) the space-time variability of the photosynthesis and stomatal conductance response is considerable as expected. (b) Variability of the calculated leaf level fluxes is dependent on both the meteorological drivers and differences in leaf age, position within the canopy, nitrogen and CO2 fertilization, which can be accommodated in model parameters. (c) Meteorological variability is playing the dominant role at short temporal scales while parameter variability is significant at longer temporal scales. (d) Leaf level results do not necessarily translate to similar ecosystem level responses due to indirect effects and other compensatory mechanisms related to long-term vegetation dynamics and ecosystem water balance.

Remote sensing and ground-based measurements of evapotranspiration in an extreme cold Patagonian desert

Accurate estimates of seasonal evapotranspiration (ET) at different temporal and spatial scales are essential for understanding the biological and environmental determinants of ecosystem water balance in arid regions and the patterns of water utilization by the vegetation. For this purpose, remote sensing ET estimates of a Patagonian desert in Southern Argentina were verified with field measurements of soil evaporation and plant transpiration using an open top chamber. Root distribution and seasonal variation in soil volumetric water content were also analysed. There was a high correlation between remote sensing and field measurements of ecosystem water fluxes. A substantial amount of the annual ET occurred in spring and early summer (73.4 mm) using winter rain stored in the soil profile and resulting in water content depletion of the upper soil layers. A smaller amount of annual ET was derived from few rainfall events occurring during the mid or late summer (41.4 mm). According to remote sensing, the 92.9% of the mean annual precipitation returns to the atmosphere by transpiration or evaporation from the bare soil and by canopy interception. Only 7.1% infiltrates to soil layers deeper than 200 cm contributing to the water table recharge. Fourier time series analysis, cross-correlation methods and multiple linear regression models were used to analyse 11 years of remote sensing data to assess determinants of water fluxes. A linear model predicts well the variables that drive complex ecosystem processes such as ET. Leaf area index and air temperature were not linearly correlated to ET because of the multiple interaction among variables resulting in time lags with ET variations and thus these two variables were not included in the linear model. Soil water content, the fraction of photosynthetic active radiation and precipitation explained 86% of the ET monthly variations. The high volumetric water content and the small seasonal variations at 200-cm depth were probably the result of little water uptake from deeper soil horizons by roots with low hydraulic conductivity. Copyright © 2016 John Wiley & Sons, Ltd.

Evapotranspiration partitioning, stomatal conductance, and components of the water balance: A special case of a desert ecosystem in China

Summary Partitioning evapotranspiration (ET) into its components reveals details of the processes that underlie ecosystem hydrologic budgets and their feedback to the water cycle. We measured rates of actual evapotranspiration (ETa), canopy transpiration (Tc), soil evaporation (Eg), canopy-intercepted precipitation (EI), and patterns of stomatal conductance of the desert shrub Calligonum mongolicum in northern China to determine the water balance of this ecosystem. The ETa was 251 ± 8 mm during the growing period, while EI, Tc, and Eg accounted for 3.2%, 63.9%, and 31.3%, respectively, of total water use (256 ± 4 mm) during the growing period. In this unique ecosystem, groundwater was the main water source for plant transpiration and soil evaporation, Tc and exceeded 60% of the total annual water used by desert plants. ET was not sensitive to air temperature in this unique desert ecosystem. Partitioning ET into its components improves our understanding of the mechanisms that underlie adaptation of desert shrubs, especially the role of stomatal regulation of Tc as a determinant of ecosystem water balance.

Effects of large-scale afforestation project on the ecosystem water balance in humid areas: An example for southern China

Massive afforestation and reforestation programs have been implemented around the world to restore degraded land and respond to climate change. Many studies suggest that such large-scale campaigns may be counterproductive if there is insufficient water to sustain the trees, especially in dryland. However, we suggest the large-scale afforestation may become a new problem even in humid regions with abundant water, and that the problem will be exacerbated by climate change. To test this hypothesis, we compared the water surplus (evapotranspiration) of natural vegetation and planted trees in 15 provinces of southern China using eight evapotranspiration models. The planted forests consumed considerably more water than natural vegetation, thereby utilizing water that would otherwise be available to support other uses. It may raise water conflicts among sectors in climatic change. We found that if artificial restoration by afforestation or reforestation were replaced by restoration of the natural vegetation, water-use efficiency would improve by 9.97–16.34% in different regions. Uncritical acceptance of large-scale planting of woody vegetation may therefore reduce the ecosystem's resilience against climate change in the short term and increase the long-term risks of water conflict in society in long run if major climatic shifts over. It is therefore necessary to carefully assess whether the benefits of the planted forests outweigh the potential negative environmental and socioeconomic consequences.

All Sonic Anemometers Need to Correct for Transducer and Structural Shadowing in Their Velocity Measurements

AbstractSonic anemometry is fundamental to all eddy-covariance studies of surface energy and ecosystem carbon and water balance. Recent studies have shown that some nonorthogonal anemometers underestimate vertical wind. Here it is hypothesized that this is due to a lack of transducer and structural shadowing correction. This is tested with a replicated intercomparison experiment between orthogonal (K-probe, Applied Technologies, Inc.) and nonorthogonal (A-probe, Applied Technologies, Inc.; and CSAT3 and CSAT3V, Campbell Scientific, Inc.) anemometer designs. For each of the 12 weeks, five randomly selected and located anemometers were mounted both vertically and horizontally. Bayesian analysis was used to test differences between half-hourly anemometer measurements of the standard deviation of wind (σu, συ, and σw) and temperature, turbulent kinetic energy (TKE), the ratio between vertical/horizontal TKE (VHTKE), and sensible heat flux (H). Datasets were analyzed with various applications of transducer shadow correction. Using the manufacturer’s current recommendations, orthogonal anemometers partitioned higher VHTKE and measured about 8%–9% higher σw and ~10% higher H. This difference can be mitigated by adding shadow correction to nonorthogonal anemometers. The horizontal manipulation challenged each anemometer to measure the three dimensions consistently, which allowed for testing two hypotheses explaining the underestimate in vertical wind. While measurements were essentially unchanged when the orthogonal anemometers were mounted sideways, the nonorthogonal anemometers changed substantially and confirmed the lack of shadow correction. Considering the ubiquity of nonorthogonal anemometers, these results are consequential across flux networks and could potentially explain half of the ~20% missing energy that is typical at most flux sites.

Evapotranspiration and its source components change under experimental warming in alpine meadow ecosystem on the Qinghai-Tibet plateau

Partitioning evapotranspiration (ET) into soil evaporation (Ea) and plant transpiration (Tr) is important to understand response of ecosystem water balance to climate warming. A field experiment was conducted to investigate the effect of additional infrared radiation as a simulation of climate warming (W1: 130Wm−2 and W2: 150Wm−2) on ET, Ea, Tr, and soil moisture in an alpine meadow in the Qinghai-Tibet plateau (QTP). ET was calculated by using an energy balance model and a soil moisture correction function. Ea in warm-rainy season was estimated by a multiple linear regression with latent heat, soil moisture in 0–10cm layer and soil temperature in 20cm depth as independent variables. Tr was quantified as the difference between ET and Ea. Results showed that annual ET increased by 92mm and 89mm, annual Ea increased by 29.12mm and 33.37mm, and annual Tr increased by 63.53mm and 55.81mm in W1 and W2 treatments, respectively. The results suggest that Tr stimulation accounts for most of the ET change and is the major reason for the soil surface layer drying in alpine meadow ecosystem on the QTP.

Stable isotope composition for atmospheric water vapor in the forest ecosystem of Mount Tianmu

Stable isotope techniques, one of the most effective techniques for understanding carbon and water relationships in terrestrial ecosystems, are commonly used domestically in agricultural but not in forest ecosystems. To establish long-term continuous observations with flux towers in forest ecosystems and to reveal stable isotopic composition of atmospheric water vapor for regional characteristics in ecosystem water balance research, a subtropical evergreen and deciduous broadleaf mixed forest observation tower was established for Mount Tianmu in Zhejiang Province. The tower detected hydrogen and oxygen isotopes and had an in situ measurement system based on Tunable Diode Laser Absorption Spectroscopy （TDLAS）. Also multi-layer gradients for temperature and humidity, wind speed, and radiation using conventional meteorological instruments were operational from December 2012 onward. Based on data observed from August to September 2013, the stable isotope composition of atmospheric water vapor influencing factors and their relationships were analyzed. Results showed that atmospheric rainfall, air temperature, soil temperature at 5 cm soil depth were important environmental factors in the forest ecosystem in Mount Tianmu; the air temperature and water vapor stable isotope composition were fitted in a linear relationship, while the soil temperature at 5 cm soil depth were fitted in a polynomial relationship with water vapor stable isotope composition, and also the statistics showed that the correlation was admirable. Thus, compared to agricultural ecosystems, water vapor stable isotope composition factors in this forest ecosystem had little influence.［Ch, 13 fig. 17 ref.]

Environmental hydrochemical characteristics of groundwater in Dnieper Prysamarya as state indicator of reference and destructive biogeocenoses

In the paper, there is a characteristic of hydrochemical properties of the groundwater lying within the river valley of Samara Dniprovska, on the steppe plakor areas, under the automorphic soils and the water of the Samara River. In characterizing of the hydrochemical properties of the groundwater the author came from the fact that the groundwater, according to the previous studies (Kotovich, 2010, 2014), with varying degrees of share participation, is an integral part of the water balance of forest ecosystems and used by the wood vegetation. Based on the landscape principle of groundwater formation there are those that lie within the valley of the river Samara, as well as the groundwater of steppe plain regions with automorphic soils and areas with developed gullies and ravines. The groundwater of the river valley for its hydrochemical properties is not homogeneous, and there is a clear binding of hydrochemical indicators to the main geomorphological elements with typical for them soil cover. It was established that the groundwater of flood plain lying directly in the area of undermining near the town of Ternivka is the most mineralized – 1928 mg/dm3, due to slow water exchange with surface water because of sedimentation of the surface. Out of the influence of undermining zone the floodplain groundwater do not differ from the zonal groundwater; its mineralization is 1560–1050 mg/dm3. The groundwater of sandy terraces of the Samara river valley has azonal signs, namely – reduced salinity (110–150 mg/dm3), hydrocarbonate and calcium ion composition and acidic reaction of pH (4,5–5,7). It is noted that due to favorable filtration properties of sandy soil, salt concentration varies synchronously with the fluctuations of groundwater level. At the same time in the area of coal mining with transformed soil and hydrological conditions the groundwater has a higher salinity than the groundwater, lying outside the influence of mine water drainage, while the dynamics of change in mineralization lags behind fluctuations in the groundwater level for more than three and a half months. Within the third terrace of the Samara river valley the mirror of the groundwater begins at a depth of 1,5 m. The total mineralization – 2640 mg/dm3 – is significantly higher than in the groundwater of the first and the second terraces. The ion composition is dominated by sodium and chloride ions, and the pH reaction is close to neutral. The groundwater of the watershed areas between the Samara and Oril rivers lies at a considerable depth – 20 m, has mineralization of 2100 mg/dm3, and the ionic composition is dominated by chloride ions and calcium. At the same time, the groundwater in the area of developed network of gullies and ravines has a lower mineralization – 650 mg/dm3. It can be assumed that the differences are related to the terms of draining of aquifers. Analysis of long-term data of salinity in the Samara river demonstrated an increase in this index from 1738 mg/dm3 in 1929 to 3540 mg/dm3 in 2006.