Summer Water Research Articles

Repair of severe winter xylem embolism supports summer water transport and carbon gain in flagged crowns of the subalpine conifer Abies veitchii.

Xylem embolism induced by winter drought is a serious dysfunction in evergreen conifers growing at wind-exposed sites in the mountains. Some coniferous species can recover from winter embolism. The aim of this study was to determine whether wind direction influences embolism formation and/or repair dynamics on short windward and long leeward branches of asymmetrical `flagged' crowns. We analyzed the effect of branch orientation on percentage loss of xylem conductive area (PLC), leaf functional traits and the xylem:leaf area ratio for subalpine, wind-exposed flagged-crown Abies veitchii trees in the northern Yatsugatake Mountains of central Japan. In late winter, the shoot water potential was below -2.5MPa, and the PLC exceeded 80% in 2-year-old branches, independent of branch orientation within a flagged crown. Both of these parameters almost fully recovered by summer. At branch internodes 4years of age and older, seasonal changes in PLC were not found in either windward or leeward branches, but the PLC was higher in less leafy windward branches. The leaf nitrogen content and water-use efficiency of mature leaves were comparable between windward branches and leafy leeward branches. The ratio of xylem conductive area to total leaf area was the same for windward and leeward branches. These results indicate that the repair of winter xylem embolism allows leaf physiological functions to be maintained under sufficient leaf water supply, even on winter-wind-exposed branches. This permits substantial photosynthetic carbon gain during the following growing season on both windward and leeward branches. Thus, xylem recovery from winter embolism is a key trait for the survival of harsh winters and to support productivity on the individual level in flagged-crown A. veitchii trees.

The Interdecadal Change of Summer Water Vapor over the Tibetan Plateau and Associated Mechanisms

Abstract In recent decades, long-term changes of the Tibetan Plateau (TP) water vapor and the associated mechanisms have not been investigated fully. This study aims to examine the interdecadal change of summer TP water vapor using the monthly mean European Centre for Medium-Range Weather Forecasts interim reanalysis during 1979–2014. The results show a drier phase in the TP during 1979–94, with a subsequent wetter phase, which suggests an interdecadal variation of summer TP water vapor around the middle of the 1990s. This interdecadal variation is mainly due to a significant change of the water vapor export on the eastern boundary of the TP, which is closely associated with a summer atmospheric circulation anomaly near Lake Baikal. When a cyclonic (an anticyclonic) anomaly occurs near Lake Baikal, there is less (more) water vapor over the TP. On the interdecadal scale, the atmospheric circulation anomaly near Lake Baikal is related to an extratropical large-scale anomalous wave train over the northwestern Atlantic–East Asian region, with an eastward propagation of the anomalous wave energy from the Atlantic to East Asia. Climate model simulations further demonstrate an impact of sea surface temperature (SST) anomalies in the northwestern Atlantic on the anomalous wave train. Both the extratropical tropospheric anomalous wave train and the anomalous atmospheric circulation near Lake Baikal are successfully simulated by changing the summer northwestern Atlantic SST. Therefore the warming northwestern Atlantic is an important factor contributing to the wetting TP in recent decades.

Stream channel restoration increases climate resiliency in a thermally vulnerable Appalachian river

We quantified stream temperature response to in‐stream habitat restoration designed to improve thermal suitability and resiliency of a high‐elevation Appalachian stream known to support a temperature‐limited brook trout population. Our specific objectives were to determine if: (1) construction of deep pools created channel unit‐scale thermal refugia and (2) reach scale stream channel reconfiguration reduced peak water temperatures along a longitudinal continuum known to be highly susceptible to summer‐time warming. Contrary to expectations, constructed pools did not significantly decrease channel unit‐scale summer water temperatures relative to paired control sites. This suggests that constructed pools did not successfully intercept a cool groundwater source. However, we did find a significant effect of stream channel restoration on reach‐scale thermal regimes. Both mean and maximum daily stream temperatures experienced significantly reduced warming trends in restored sections relative to control sections. Furthermore, we found that restoration efforts had the greatest effect on stream temperatures downstream of large tributaries. Restoration appears to have significantly altered thermal regimes within upper Shavers Fork, largely in response to changes in channel morphology that facilitated water movement below major cold‐water inputs. Decreased longitudinal warming will likely increase the thermal resiliency of the Shavers Fork main‐stem, sustaining the ability of these key large river habitats to continue supporting critical metapopulation processes (e.g. supplemental foraging and dispersal among tributary populations) in the face of climate change.

Phenotypic integration and life history strategies among populations of Pinus halepensis: an insight through structural equation modelling.

Understanding inter-population variation in the allocation of resources to specific anatomical compartments and physiological processes is crucial to disentangle adaptive patterns in forest species. This work aims to evaluate phenotypic integration and trade-offs among functional traits as determinants of life history strategies in populations of a circum-Mediterranean pine that dwells in environments where water and other resources are in limited supply. Adult individuals of 51 populations of Pinus halepensis grown in a common garden were characterized for 11 phenotypic traits, including direct and indirect measures of water uptake at different depths, leaf area, stomatal conductance, chlorophyll content, non-structural carbohydrates, stem diameter and tree height, age at first reproduction and cone production. The population differentiation in these traits was tested through analysis of variance (ANOVA). The resulting populations' means were carried forward to a structural equation model evaluating phenotypic integration between six latent variables (summer water uptake depth, summer transpiration, spring photosynthetic capacity, growth, reserve accumulation and reproduction). Water uptake depth and transpiration covaried negatively among populations, as the likely result of a common selective pressure for drought resistance, while spring photosynthetic capacity was lower in populations originating from dry areas. Transpiration positively influenced growth, while growth was negatively related to reproduction and reserves among populations. Water uptake depth negatively influenced reproduction. The observed patterns indicate a differentiation in life cycle features between fast-growing and slow-growing populations, with the latter investing significantly more in reproduction and reserves. We speculate that such contrasting strategies result from different arrays of life history traits underlying the very different ecological conditions that the Aleppo pine must face across its distribution range. These comprise, principally, drought as the main stressor and fire as the main ecological disturbance of the Mediterranean basin.

Influence of Regional Water Temperature Variability on the Flowering Phenology and Sexual Reproduction of the Seagrass Zostera marina in Korean Coastal Waters

Increasing sea surface temperature due to global climate change is a major threat to the growth and survival of many temperate seagrasses, while cold-water upwelling can potentially ameliorate high-temperature stress on temperate seagrass meadows during growing seasons. Seagrasses in the coasts of Korea are increasingly influenced by rising water temperatures and water temperature anomalies in recent decades due to climate change, but the impacts of such events on reproductive phenology of seagrasses remain poorly understood. We investigated the reproductive phenology and sexual reproduction of Zostera marina in four seagrass meadows along the coasts of Korea. Two study sites were located on the south coast where water temperature shows significant warming trends, while two other study sites were located on the east coast where coastal cold-water upwelling is prevalent. Water temperature exhibited stronger seasonality with cooler winter and warmer summer in the south coast sites than in the east coast sites. Cold-water upwelling events occurred frequently along the east coast of Korea, leading to anomalously cool water temperatures during the growing season. Z. marina flowering was prolonged and/or precocious at the east coast sites relative to the south coast sites. The mean flowering period was 5–7.5 months at the east coast sites and 3.5 months at the south coast sites. Moreover, reproductive shoot density and biomass, as well as the corresponding flowering frequency and reproductive efforts were much higher (2–3 times) at the east coast sites than at the south coast sites. Consequently, the potential seed production was higher in the east coast sites than in the south coast sites. Overall, high summer water temperature appeared to reduce sexual reproduction of Z. marina in the south coast sites, while regional cold-water upwelling on the east coast changed seasonal temperature patterns and decreased summer temperature highs, consequently provided a relatively long period of optimal water temperature for production of reproductive shoots. Regional water temperature variability has an important role in shifting the flowering responses of seagrass, which could affect the long-term stability and maintenance of seagrass meadows via the regulation of the sexual-asexual reproductive trade-off.

Patterns of flow in the canyons of the northern Gulf of Alaska

The continental shelf around Kodiak Island is incised with numerous submarine canyons, which play an important role in the cross-shelf transport of heat, salt, and nutrients, and the transport of ichthyoplankton of deep-spawning fish from the slope region into the shallow nursery grounds surrounding Kodiak Island. To explore the pathways and variability of flow, and the extent of tidal mixing within the canyons, moorings were placed in the Chiniak, Barnabas, and Amatuli troughs, and off the shelf from Resurrection Bay (Seward Line) and the Kenai Peninsula (Gore Point). In the troughs, intensified flow was evident near the trough walls, and flow was directed by bathymetry with inflow along the upstream (northern) side and outflow along the downstream (southern) side. The presence of mesoscale eddies in the gulf had no unique influence on currents or salinity in the troughs. Tidal mixing was strongest in Chiniak Trough, and this introduced cold, nutrient-rich bottom waters into the upper water column. Intensified bottom flow associated with the Alaskan Coastal Current was evident along the Seward Line and Gore Point, and directed toward the Kennedy-Stevenson Entrances, which are also regions of strong tidal mixing. Observations of tidal mixing were consistent with model results and satellite images showing cooler, phytoplankton-rich water in summer in the nursery grounds that surround Kodiak Island. Patterns of flow within the troughs and in Shelikof Strait were consistent with the springtime advance of ichthyoplankton across the shelf.

The life history with seasonal migration of the lacustrine shrimpPalaemon paucidensin an ancient lake in Japan

AbstractThe lacustrine shrimpPalaemon paucidensundertakes seasonal migration between shallow waters in spring and summer to deep waters in autumn and winter in Lake Biwa in Japan. Previous studies hypothesized that the migration to deep waters was for hibernation. The findings of this study oppose this hypothesis. We showed thatP. paucidensis physiologically active in deep waters during winter; that the carbon stable isotope ratio indicated that the species forages in winter and that there was a difference in food sources between summer and winter; that lipid content was highest in January; and that gene expression activity (as measured by theRNA/DNAratio) remained constant throughout the year. Thus,P. paucidensindividuals that migrate to the bottom are likely to forage in winter, but do not hibernate. Nutrients gained in winter were not reflected in individual growth but may have been allocated to gonadal growth and the production of gametes, suggesting that winter foraging by this species in deep sites contributes to obtain resources for reproductive investment. In addition, we found that both small individuals with no reproductive experience and relatively large females with reproductive experience overwintered, indicating thatP. paucidenshas a life‐cycle that is longer than 1 yr in Lake Biwa.

Modeling Extreme Warm‐Air Advection in the Arctic: The Role of Microphysical Treatment of Cloud Droplet Concentration

AbstractAs the Arctic climate is changing fast, with increasing areas of open water in summer, there is a growing interest in the processes related to the marginal ice zones. Recent studies have indicated that such a critical process may be the advection of warm and moist air from the south. In this study, the performance of the Weather Research and Forecasting (WRF) model is evaluated during an extreme warm advection episode over melting sea ice that occurred near the Arctic ice edge in summer 2014. The model gives a reasonably good representation of the atmospheric conditions and the Arctic boundary layer, characterized by very strong surface inversions and the frequent presence of low‐level jets. However, the representation of the highly variable cloud conditions, from optically thick to optically thin, dissipating clouds, is sensitive to the choice of cloud droplet treatment in WRF. Simulations with relatively high cloud droplet number concentrations (Ndrop ≥ 100 cm−3) are more successful in representing the optically thick cloud state, whereas to reproduce optically thin and tenuous clouds Ndrop should be <50 cm−3. The WRF‐Chem model, with a realistic treatment of the cloud‐aerosol interactions, allows for large variations in Ndrop and hence can reproduce the cloud water properties reasonably well for most of the simulation time. This contributes to an improved representation of the cloud longwave radiative effect, compared to the simulations where a less adaptive treatment of Ndrop is applied.

Modelling induced bank filtration effects on freshwater ecosystems to ensure sustainable drinking water production

Induced bank filtration (IBF) is a water abstraction technology using different natural infiltration systems for groundwater recharge, such as river banks and lake shores. It is a cost-effective pre-treatment method for drinking water production used in many regions worldwide, predominantly in urban areas. Until now, research concerning IBF has almost exclusively focussed on the purification efficiency and infiltration capacity. Consequently, knowledge about the effects on source water bodies is lacking. Yet, IBF interrupts groundwater seepage and affects processes in the sediment potentially resulting in adverse effects on lake or river water quality. Securing sufficient source water quality, however, is important for a sustainable drinking water production by IBF.In this study, we analysed the effects of five predicted mechanisms of IBF on shallow lake ecosystems using the dynamic model PCLake: declining CO2 and nutrient availability, as well as increasing summer water temperatures, sedimentation rates and oxygen penetration into sediments. Shallow lake ecosystems are abundant worldwide and characterised by the occurrence of alternative stable states with either clear water and macrophyte dominance or turbid, phytoplankton-dominated conditions. Our results show that IBF in most scenarios increased phytoplankton abundance and thus had adverse effects on shallow lake water quality. Threshold levels for critical nutrient loading inducing regime shifts from clear to turbid conditions were up to 80% lower with IBF indicating a decreased resilience to eutrophication. The effects were strongest when IBF interrupted the seepage of CO2 rich groundwater resulting in lower macrophyte growth. IBF could also enhance water quality, but only when interrupting the seepage of groundwater with high nutrient concentrations. Higher summer water temperatures increased the share of cyanobacteria in the phytoplankton community and thus the risk of toxin production. In relative terms, the effects of changing sedimentation rates and oxygen penetration were small. Lake depth and size influenced the effect of IBF on critical nutrient loads, which was strongest in shallower and smaller lakes. Our model results stress the need of a more comprehensive ecosystem perspective including an assessment of IBF effects on threshold levels for regime shifts to prevent high phytoplankton abundance in the source water body and secure a sustainable drinking water supply.

Increased snowfall weakens complementarity of summer water use by different plant functional groups.

Winter snowfall is an important water source for plants during summer in semiarid regions. Snow, rain, soil water, and plant water were sampled for hydrogen and oxygen stable isotopes analyses under control and increased snowfall conditions in the temperate steppe of Inner Mongolia, China. Our study showed that the snowfall contribution to plant water uptake continued throughout the growing season and was detectable even in the late growing season. Snowfall versus rainfall accounted for 30% and 70%, respectively, of the water source for plants, on the basis of hydrogen stable isotope signature (δD) analysis, and accounted for 12% and 88%, respectively, on the basis of oxygen stable isotope signature (δ18O) analysis. Water use partitioning between topsoil and subsoil was found among species with different rooting depths. Increased snowfall weakened complementarity of plant water use during summer. Our study provides insights into the relationships between precipitation regimes and species interactions in semiarid regions.

Accidental ecosystem restoration? Assessing the estuary-wide impacts of a new ocean inlet created by Hurricane Sandy

Barrier island lagoons are the most common type of estuary in the world and can be prone to eutrophication as well as the formation and closure of ocean inlets via severe storm activity. This study describes the biological, chemical, and physical changes that occurred along the south shore of Long Island, NY, USA, following the formation of a new ocean inlet in eastern Great South Bay (GSB) by Hurricane Sandy in October of 2012. Time series sampling and experiments were performed at multiple locations within GSB and neighboring Moriches Bay from 2013 through to 2018. Historical comparisons to prior water quality monitoring data, fecal coliform concentrations, and hard clam growth rates were also made. Measurements indicated that the New Inlet provided asymmetrical ocean flushing. Within locations north (Bellport Bay) and east (Narrow Bay, western Moriches Bay) of the New Inlet, water residence times, summer water temperatures, total and dissolved nitrogen, chlorophyll a, the harmful brown tide alga, Aureococcus anophagefferens, pigments associated with diatoms and dinoflagellates (fucoxanthin and peridinin), and fecal coliform bacteria levels all significantly decreased, while salinity, dissolved oxygen, and water clarity significantly increased. In contrast, waters west of the New Inlet within the center of GSB experienced little change in residence times, significant increases in chlorophyll a and harmful brown tides caused by A. anophagefferens, as well as a significant decrease in water clarity and summer dissolved oxygen levels. Growth rates of juvenile hard clams (Mercenaria mercenaria) near the New Inlet increased compared to before the inlet and were significantly higher than in central GSB, where growth rates significantly declined compared to before the inlet. Hence, while enhanced ocean flushing provided a series of key ecosystem benefits for regions near the New Inlet, regions further away (> 10 km) experienced more frequent HABs and poorer performance of bivalves, demonstrating that enhanced ocean flushing provided by the breach was not adequate to fully restore the whole GSB ecosystem.

Acclimatization of massive reef-building corals to consecutive heatwaves.

Reef-building corals typically live close to the upper limits of their thermal tolerance and even small increases in summer water temperatures can lead to bleaching and mortality. Projections of coral reef futures based on forecasts of ocean temperatures indicate that by the end of this century, corals will experience their current thermal thresholds annually, which would lead to the widespread devastation of coral reef ecosystems. Here, we use skeletal cores of long-lived Porites corals collected from 14 reefs across the northern Great Barrier Reef, the Coral Sea, and New Caledonia to evaluate changes in their sensitivity to heat stress since 1815. High-density ‘stress bands’—indicative of past bleaching—first appear during a strong pre-industrial El Niño event in 1877 but become significantly more frequent in the late twentieth and early twenty-first centuries in accordance with rising temperatures from anthropogenic global warming. However, the proportion of cores with stress bands declines following successive bleaching events in the twenty-first century despite increasing exposure to heat stress. Our findings demonstrate an increase in the thermal tolerance of reef-building corals and offer a glimmer of hope that at least some coral species can acclimatize fast enough to keep pace with global warming.

Distribution and emission of N2O in the largest river-reservoir system along the Yellow River

Rivers and reservoirs are affected by human activities and are sources of the greenhouse gas nitrous oxide (N2O). Concentrations of N2O in the middle and lower reaches of the Yellow River and Xiaolangdi Reservoir, China, were measured in June and December 2017. Fluxes were estimated by boundary layer method to explore their controlling factors, especially the impact of damming and reservoir operation. In the middle and lower reaches of the Yellow River, N2O concentrations in surface waters were 26.65 ± 14.67 nmol L−1 in summer and 21.16 ± 5.35 nmol L−1 in winter. In comparison, the concentrations of N2O in the reservoir were 32.94 ± 17.32 nmol L−1 in summer and 23.73 ± 5.60 nmol L−1 in winter. The longitudinal distribution of N2O along the river exhibited different patterns with surface N2O decreasing downstream towards the dam in summer but increasing in winter. Vertical profiles of N2O concentrations in the reservoir showed an increase with depth in summer but were almost vertically uniform in winter. In winter, N2O that had accumulated in the bottom water in summer was transported to the surface by vertical mixing and released into the atmosphere. Dissolved oxygen (DO), water temperature, and in situ biological production were the main factors affecting the distribution of N2O. The mean emissions rates of N2O from the surface waters were 13.7 ± 8.8 μmol m−2 d−1 in summer and 13.2 ± 7.6 μmol m−2 d−1 in winter. Approximately 1.31 × 106 mol N2O was released from the reservoir surface in 2017, which represents 0.12% of the annual N2O emissions from global reservoirs. The construction of dams increased N2O emission from the lower reaches of the river by 4.53 × 105 mol and 1.22 × 105 mol due to the discharge of the bottom water and the water and sediment regulation, respectively. This study demonstrates that the construction of dams and reservoir operation practices have made the Xiaolangdi Reservoir a key area for N2O emissions.

Dynamics of urban water supply management of two Himalayan towns in India

Abstract Many towns in the Indian Himalayan Region (IHR) are experiencing permanent water crises due to increasing population pressure, urbanization, and poor management of existing water sources. This paper focuses on two towns – Mussoorie and Devprayag in the western IHR – to understand various aspects of the growing water scarcity and urban water management. In the current scenario of a changing climate, natural springs, their main water resource, are drying up. Mussoorie experiences an acute shortage of water in summer, precisely when the town hosts numerous tourists. In Devprayag, religious tourism and in-migration from rural areas contribute to rising demand. The reduced discharge in nearby streams has widened the demand–supply gap. An integrated management of water sources is crucial to solving water problems in Mussoorie and Devprayag. In both towns, little effort has been made towards recharging existing water sources. Detailed planning of the water supply system while being mindful of the floating population, a proper sewage and storm water management system, and rainwater harvesting schemes, are absent. There is an urgent need to adopt a comprehensive approach to solving urban water issues, covering aspects of demand, supply and water resources management in these hill towns for adaptive water management.

Present and future water scarcity in Switzerland: Potential for alleviation through reservoirs and lakes

In Alpine regions, future changes in glacier and snow cover are expected to change runoff regimes towards higher winter but lower summer discharge. The low summer discharge will coincide with the highest water demand for irrigation, and local and regional water shortages are expected to become more likely. One possible measure to adapt to these changes can be the extension of current uses of artificial reservoirs and natural lakes to the provision of water for the alleviation of water shortage. This study assesses the potential of reservoirs and natural lakes for the alleviation of water shortages in a nationwide analysis in Switzerland. To do so, we estimated water supply and demand under current and future conditions both under normal and extreme runoff regimes for 307 catchments. Water demand was assessed for various categories including drinking water, industrial use, artificial snow production, agriculture, ecological flow requirements, and hydropower production. The aggregated supply and demand estimates were used to derive water surplus/shortage estimates. These were then compared to the storage capacity of reservoirs and natural lakes within a catchment to determine the potential for alleviating summer water scarcity. Our results show that water shortage is expected mainly in the lowland region north of the Alps, and less in the Alps. In this lowland region, the potential of natural lakes for alleviating water scarcity is high. This potential is lower in the Alps where it is expected to increase or decrease under future conditions depending on the region of interest. Catchments with a high storage capacity can potentially contribute to the alleviation of water shortage downstream. We conclude that a spatial mismatch between water scarcity and storage availability exists since water stored in reservoirs on the southern side of the Alps is often not available for the use on the northern side.

On the nature of wind-forced upwelling in Barrow Canyon

Using time series from a mooring deployed from 2002 to 2004 near the head of Barrow Canyon, together with atmospheric and sea-ice data, we investigate the seasonal signals in the canyon as well as aspects of upwelling and the wind-forcing that drives it. On average, the flow was down-canyon during each month of the year except February, when the up-canyon winds were strongest. Most of the deep flow through the head of the canyon consisted of cold and dense Pacific-origin winter water, although Pacific-origin summer waters were present in early autumn. Over the two-year study period there were 54 upwelling events: 33 advected denser water to the head of the canyon, while 21 upwelled lighter water due to the homogeneous temperature/salinity conditions during the cold season. The upwelling occurs when the Beaufort High is strong and the Aleutian Low is deep, consistent with findings from previous studies. Most events resulted in the reintroduction of Pacific Winter Water onto the Chukchi Shelf, rather than advection of Atlantic Water. Overall there were more than twice as many upwelling events during the cold season as the warm season due to the seasonal strengthening of the winds. An analysis of temporally integrated measures revealed a statistically significant relationship between the atmospheric forcing and upwelling response, such that stronger storms tend to result in stronger upwelling. Finally, it is demonstrated that upwelling typically corresponds to the occurrence of the Northeast Chukchi Polynya.

Climate-growth relationships in a Larix decidua Mill. network in the French Alps

A better understanding of the respective role of key climatic variables on tree growth is crucial for an accurate assessment of how ongoing global changes may affect both dynamics and distribution of forest tree species in the future. The aim of this study was (i) to explore growth patterns of European larch (Larix decidua Mill.) through a network of tree-ring chronologies developed for the French Alps and (ii) to identify the main climatic drivers explaining radial growth. Climate-growth relationships were coupled with a hierarchical analysis. This relationship revealed significant variability expressed spatially by the existence of five clusters, initially discriminated by an elevational contrast related to (i) a negative correlation between summer temperatures and larch growth at lower elevations and (ii) a stronger response of low-elevation larch stands to winter precipitation. In the high-elevation clusters, tree growth depends on previous autumn and current summer temperatures and water supply in July. The differentiation, that portrays a strong geographical coherence, is mainly related to the latitudinal gradient; (i) the northwestern stands are mostly sensitive to high temperatures in summer; (ii) the growth of the southernmost clusters is equally driven by temperatures during autumn, winter, and summers; (iii) the populations of a cluster located in a transitional zone of the inner French Alps, subject to both Mediterranean and Continental influences, exhibit negative correlations to late winter and early spring precipitation. This significant spatial heterogeneity of climate–tree ring relationships in L. decidua clearly underlines the high plasticity of the species to adapt its growth to local climate conditions.

Native shrubland and managed buffelgrass savanna in drylands: Implications for ecosystem carbon and water fluxes

Land cover and land-use change (LCLUC) between woody- and grass-dominated ecosystems in drylands comprise one of the largest uncertainties in the land CO2 sink. This is especially true for the widespread transition from shrublands to grasslands/savannas caused by the establishment of exotic C4 grass species for grazing or through biological invasion of these species, where information about its impacts on ecosystem CO2 fluxes is limited. For studying this, we used three years of eddy covariance measurements of net ecosystem production (NEP), gross primary production (GPP), ecosystem respiration (Reco) and evapotranspiration (ET) over a Sonoran Desert shrubland and an adjacent grazing savanna of buffelgrass (Cenchrus ciliaris L.), established 35 years ago. At monthly, seasonal and annual time scales, we assessed whether between-site differences in CO2 fluxes were related to differences in ecosystem water use, measured as the fraction ET to precipitation, water use efficiency (WUE, i.e. the ratio between GPP and ET) and/or to the relation between Reco and GPP. Although the savanna had higher WUE than the shrubland, its summer NEP was limited by water use, due to limitations in leaf area index and likely rooting patterns. Conversely, the savanna had higher NEP than the shrubland during fall to spring due to increased WUE; possibly due to activity of buffelgrass and remaining woody species using (summer) water from deeper soil layers. However, differences across these seasons compensated each other at the inter-annual scale, and both sites had comparable net carbon sinks over the three-year study period. Further studies are needed to understand and reduce the uncertainty associated with carbon and water fluxes associated with LCLUC in dryland ecosystems.

Projected changes in summer water vapor transport over East Asia under the 1.5°C and 2.0°C global warming targets

This study investigates changes in summer water vapor transport (WVT) over East Asia under 1.5°C and 2.0°C global warming (GW) for the +4.5 and +8.5 W m−2 Representative Concentration Pathway (RCP)...

Plasticity of response of tree-ring width of Scots pine provenances to weather extremes in Latvia

Climatic changes and weather extremes are causing shifts in distribution of tree species, affecting productivity of forests. With the northwards advance of deciduous species in Northern Europe, Scots pine (Pinus sylvestris L.) is predicted to decrease survival and productivity. Nevertheless, Scots pine have adapted to diverse environments, hence selection among its populations could be applied to sustain productivity of stands under changing climate. In this study, sensitivity of tree-ring width of Eastern European provenances of Scots pine differing by field performance (Dippoldiswalde, Eibenstock, Rytel, Gustrow, and Kalsnava) to weather extremes in three trials in Latvia (hemiboreal zone) was assessed via pointer year and tolerance analyses. The studied provenances were sensitive to winter temperature regime; the effects of water deficit and vegetation period’s length were also observed, likely due to warming. The sensitivity of tree-ring width to weather extremes, which differed among the provenances indicating plasticity of growth, correlated with field performance. Although transferred north, the top-performing provenances (Gustrow and Rytel) were able to promptly recover after cold spells as well as dry summers and were able to benefit from warm winters and precipitation-rich summers. The bottom-performing provenances (Dippoldiswalde and Eibenstock) were sensitive to cold spells and summer water deficit, yet were unable to benefit from warm winters, nor moist summers. Considering sensitivity and resilience of growth, the studied top-performing provenances, particularly Rytel, showed commercial potential in the hemiboreal region under warming climate.