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Monthly precipitation δ18O averaged between Avignon and Thonon Les Bains () from the Global Network for Isotopes in Precipitation (GNIP—http://www-naweb.iaea.org/napc/ih/IHS_resources_gnip.html), demonstrating a seasonal cycle of increasing δ18O during the growing season. Note: δ18O precipitation value of −5.3‰ is computed as an average of growing season monthly averages (shown as dashed line).
Source publication
Key points:
Water shifts due to climatic fluctuations between floodplain storage reservoirsAnthropogenic changes to hydrology directly impact water available to treesEcohydrologic approaches to integration of hydrology afford new possibilities.
Contexts in source publication
Context 1
... seasonal cycle of d 18 O in P has been observed in the Rh^ one basin, wherein oxygen isotopic signatures peak during the growing season ( Figure 3). A regionally representative value of d 18 O in precipitation for our study site was obtained by averaging the mean monthly values from the Global Network for Isotopes in Pre- cipitation (GNIP) for the two nearest monitoring stations at Thonon Les Bains and Avignon (northeast and south of Pierre-B enite, respectively, Figure 2), which we assume will best reflect the potentially different sources of growing season (May-August) precipitation in the basin (Atlantic versus Mediterranean Figure 2). ...
Context 2
... If the infiltrating water does in fact get stored in small pores, disconnected from translatory flow yet avail- able for subsequent extraction by vadose zone roots, this should occur at various elevations in the soil col- umn. In other words, early autumn/winter rains that have a relatively depleted isotopic signature (Figure 3) would be responsible for filling up small soil pores throughout the draining soil column. However, water stored in such fine pores closer to the soil surface would likely undergo evaporative enrichment in various periods through the hydrologic year, and especially during the warm spring/summer months. ...
Context 3
... the year 1997, Q was reduced and spring rains dominated growing season floodplain hydrology. While Fraxinus did not exhibit any significant differences between the various cohorts, Populus at high floodplain elevations, high gravel elevations, and those rooted in deep soils apparently took advantage of enriched soil moisture from relatively warm and high growing season rains (Figures 3 and 9d). This source of water may have allowed these cohorts to maintain their growth in high spring rainfall years and more steady annual growth overall, compared to their low gravel elevation cohort (Figure 10d and Table 1). ...
Citations
... DOC transported back to the river can be an important energy source for aquatic organisms (Baldwin and Mitchell, 2000). Shifts in water sources under the influence of human management are usually accompanied by shifts of water distribution and water availability for the floodplain fauna (Singer et al., 2014). Habitats in the Oder floodplain are affected by this management; e.g., the late mowing activities in the Lower Oder Valley are detrimental to some bird (e.g., Aquatic warbler (Acrocephalus)) habitats (Tanneberger et al., 2008) and the limited water availability in the floodplain during summer limits aquatic habitats. ...
... As riparian plants serve as vital ecological barriers, their water uptake patterns vary spatially and temporally, influenced by climate, hydrology and plant species (Snyder and Williams 2000;Singer et al. 2012;Volkmann et al. 2016). While previous studies indicate that mature riparian trees predominantly utilize soil water over groundwater and river water (Dawson and Ehleringer 1991;Bowling et al. 2016), recent research has demonstrated a more complex pattern of water source utilization, involving a mix of river water, soil water, and groundwater (Dawson and Pate 1996;Singer et al. 2014). Plant water use is a nuanced ecological process significantly influenced by tree species, root system characteristics, and water source diversity. ...
Background and aims
In arid areas, the temporal and spatial distribution of water resources is a key factor determining plant growth, and plants’ self-regulated flexible water use patterns are beneficial for the survival of vegetation. This study investigates the impact of reservoirs on ecological forest water use patterns around a plain reservoir.
Methods
We established a systematic monitoring network to study the Populus euphratica forests along the Hongyashan Reservoir in northwest China. Through stable isotope analysis of samples of soil, tree xylem tissue, precipitation, groundwater, and reservoir water, we examined the water use patterns of poplar trees across a distance gradient from the reservoir.
Results
Our findings revealed that: (1) Poplar primarily utilized 0–60 cm soil water and groundwater in areas proximal to the reservoir, and 60–100 cm soil water and groundwater in areas distal from the reservoir. The reservoir’s influence was primarily reflected in the groundwater contribution rate, which decreases with increasing reservoir distance. (2) Water utilization patterns and consumption exhibited significant variations within 2 km of the reservoir, while remaining relatively consistent beyond this distance, indicating that the reservoir’s impact on vegetation growth is predominantly confined to a 2 km radius.
Conclusion
Based on these findings, we recommend that irrigation strategies should be tailored according to the distance from the reservoir. Furthermore, considering the substantial water demand of poplars, careful consideration should be given to the appropriate scale and tree species selection in ecological forest planning.
... This suggests that water availability is a critical factor for tree species to be able to profit from increased light availability due to canopy disturbances, supporting our second hypothesis that growth responses to ash dieback are dependent on hydrological conditions. Most floodplain forest tree species usually develop a shallow root system as an adaptation to the ample water availability in floodplains, relying more on surface water and top soil moisture 90,91 , with the disadvantage that especially in dry periods there is limited connectivity to the groundwater. Thus, when the groundwater level drops, roots may lose contact to the groundwater and the negative effect of hot summers as experienced during the 2018-2020 consecutive droughts may increase and cause drought stress, usually resulting in reduced growth rates 23,24,92,93 . ...
Floodplain forests are currently undergoing substantial reorganization processes due to the combined effects of management-induced altered hydrological conditions, climate change and novel invasive pathogens. Nowadays, the ash dieback is one of the most concerning diseases affecting European floodplain forests, causing substantial tree mortality and threatening the loss of the dominant key tree species of the hardwood floodplain forest, Fraxinus excelsior. Understanding how the increased light availability caused by pathogen-driven mortality in combination with altered hydrological conditions and climate change affects growth responses in a diverse forest community is of crucial importance for conservation efforts. Thus, we examined growth of the main tree species in response to ash dieback and how it depended on altered hydrological conditions under novel climatic conditions for the lower and upper canopy in the floodplain forest of Leipzig, Germany. Our study period encompassed the consecutive drought years from 2018 to 2020. We found that tree growth responded mostly positively to increased light availability, but only on moist sites, while tree growth largely declined on dry sites, suggesting that water availability is a critical factor for tree species to be able to benefit from increased light availability due to canopy disturbances caused by ash dieback. This hydrological effect was species-specific in the lower canopy but not in the upper canopy. While, in the lower canopy, some species such as the competitive shade-tolerant but flood-intolerant Acer pseudoplatanus and Acer platanoides benefited from ash dieback on moist sites, others were less affected or suffered disproportionally, indicating that floodplain forests might turn into a novel ecosystem dominated by competitive Acer species, which may have detrimental effects on ecosystem functioning. Our results give hints on floodplain forests of the future and have important implications for conservation measures, suggesting that a substantial revitalization of natural hydrological dynamics is important to maintain a tree composition that resembles the existing one and thus sustain their conservation status.
... Riparian trees are particularly vulnerable and sensitive to fluctuations in water availability because they rely primarily on soil moisture and groundwater availability for their long-term survival Pettit and Froend, 2018;Sabathier et al., 2021;Sargeant and Singer, 2021;Singer et al., 2014;Warter et al., 2023). A common response of trees to drought is to reduce their stomatal conductance, which prevents excessive canopy transpiration and reduces water loss and the risk of cavitation, but at the cost of slower growth and development. ...
... Riparian woodlands are productive and biodiverse ecosystems in dryland regions that owe their persistence in the landscape to groundwater (Bateman & Merritt, 2020;Sabathier et al., 2021;Singer et al., 2014;Stella et al., 2013). Most dryland riparian trees are assumed to be phreatophytes that rely on consistent root access to groundwater to tolerate seasonally intermittent precipitation and high vapor pressure deficits (Hultine et al., 2020); as such, they are highly susceptible to groundwater decline (Rood et al., 2003;Stromberg et al., 1996). ...
Drought‐induced groundwater decline and warming associated with climate change are primary threats to dryland riparian woodlands. We used the extreme 2012–2019 drought in southern California as a natural experiment to assess how differences in water‐use strategies and groundwater dependence may influence the drought susceptibility of dryland riparian tree species with overlapping distributions. We analyzed tree‐ring stable carbon and oxygen isotopes collected from two cottonwood species (Populus trichocarpa and P. fremontii) along the semi‐arid Santa Clara River. We also modeled tree source water δ¹⁸O composition to compare with observed source water δ¹⁸O within the floodplain to infer patterns of groundwater reliance. Our results suggest that both species functioned as facultative phreatophytes that used shallow soil moisture when available but ultimately relied on groundwater to maintain physiological function during drought. We also observed apparent species differences in water‐use strategies and groundwater dependence related to their regional distributions. P. fremontii was constrained to more arid river segments and ostensibly used a greater proportion of groundwater to satisfy higher evaporative demand. P. fremontii maintained ∆¹³C at pre‐drought levels up until the peak of the drought, when trees experienced a precipitous decline in ∆¹³C. This response pattern suggests that trees prioritized maintaining photosynthetic processes over hydraulic safety, until a critical point. In contrast, P. trichocarpa showed a more gradual and sustained reduction in ∆¹³C, indicating that drought conditions induced stomatal closure and higher water use efficiency. This strategy may confer drought avoidance for P. trichocarpa while increasing its susceptibility to anticipated climate warming.
... Riparian ecosystems are relatively protected from climatic drought impacts due to their favourable geomorphic setting, which enables them to access water from precipitation, surface flow and shallow groundwater (Singer et al., 2014;Mayes et al., 2020). Nevertheless, prolonged and severe droughts can significantly affect surface water resources . ...
Droughts significantly impact forest ecosystems, reducing forest health and productivity, compromising ecosystem functioning, and nature-based solutions for climate change. The response and resilience of riparian forests to drought are poorly understood despite their key role in the functioning of aquatic and terrestrial ecosystems. Here we investigate riparian forest drought responses and resilience to an extreme drought event at a regional scale. We also examine how drought event characteristics, average climate conditions, topography, soil, vegetation structure, and functional diversity shape the resilience of riparian forests to drought. We used a time series of the Normalized Difference Vegetation Index (NDVI) and Normalized Difference Water Index (NDWI) to calculate the resistance to and recovery after an extreme drought (2017-2018) in 49 sites across an Atlantic-Mediterranean climate gradient in North Portugal. We used generalized additive models and multi-model inference to understand which factors best explained drought responses. We found a trade-off between drought resistance and recovery (maximum r = -0.5) and contrasting strategies across the climatic gradient of the study area. Riparian forests in the Atlantic regions showed comparatively higher resistance, while Mediterranean forests recovered more. Canopy structure and climate context were the most relevant predictors of resistance and recovery. However, median NDVI and NDWI had not returned to pre-drought levels (RcNDWI mean = 1.21, RcNDVI mean = 1.01) three years after the event. Our study shows that riparian forests have contrasting drought response strategies and may be susceptible to extended legacy effects associated with extreme and/or recurring droughts, similarly to upland forests. This work highlights the drought vulnerability of riparian ecosystems and emphasises the need for further studies on long-term resilience to droughts.
... These two winter deciduous species share some traits such as relatively shallow roots, ring-porous wood, and water-spending strategies (Köcher et al., 2009). In floodplain forests, the radial growth of non-phreatophyte ash depends on shallow soil water sources (Singer et al., 2013(Singer et al., , 2014. Ash species constrain stomatal conductance more than most co-occurring riparian tree species below specific thresholds of soil water availability (Lemoine et al., 2001). ...
... Cumulative stress due to consecutive hotter droughts (heatwaves coinciding with low precipitation) could affect tree growth in temperate floodplain forests (Schnabel et al., 2022). Our findings agree with those of previous research demonstrating the high radial growth sensitivity of ash species to drought , which confirms that this species is vulnerable to the drying of upper unsaturated soil horizons (Sánchez-Pérez et al., 2008;Singer et al., 2013Singer et al., , 2014. The correlations between SPEI and ash growth found in Ticino also agree with the findings of a previous study conducted in a nearby stand . ...
Floodplain forests are sensitive to climate warming and increased drought, as showed by recent oak (Quercus robur) dieback and mortality episodes. However, a comprehensive comparison of coexisting tree species under different climate settings or biomes are lacking. Herein, we compared growth rates, growth responses to climate and drought severity, and modeled climate mediated growth of oak and three coexisting tree species (ash, Fraxinus angustifolia; alder, Alnus glutinosa; elm, Ulmus minor). Two floodplain forests subjected to cooler (temperate climate, Ticino) and warmer (Mediterranean climate, Bosco Pantano) conditions in northern and southern Italy, respectively, were analyzed. Ash seemed to be the most sensitive to drought, particularly at the Mediterranean site where oak and elm growth were also negatively affected by water shortages. Alder appeared to be the least sensitive species in terms of growth variability to drought under both temperate and Mediterranean climate conditions. Furthermore, the growth model revealed the influence of soil moisture in spring and summer on the constrained growth of ash and oak and illustrated how oak growth could be severely reduced during drastic hotter droughts. Alder seemed to be the most drought-resistant species under both environmental conditions. These results could represent the first attempts in documenting the ecological consequences of drought in terms of projected climate trends in less investigated Mediterranean floodplain forests. Furthermore, these results highlight how climate and tree-ring data combined with growth models could be useful tools to detect early warning signals of growth decline and impending dieback in floodplain forests in response to dry spells.
... The movement of groundwater through coastal landscapes contributes to the functional coupling of habitats, food webs and biogeochemical processes (Singer et al., 2014). Connectivity is facilitated by baseflow-fed rivers, subterranean estuaries and hydraulic connectivity between aquifers. ...
Coastal groundwater‐dependent ecosystems (GDEs), such as wetlands, estuaries and mangrove forests, are globally important habitats that promote biodiversity, provide climate regulation and serve as refugia for plant and animal communities. However, global warming, coastal development and over‐abstraction threaten the availability and quality of groundwater in coastal aquifers and, by extension, the ecohydrological function of dependent ecosystems. Because ecohydrological knowledge of coastal groundwater is disparate across disciplines and habitat types, we begin by summarising the physiochemical, biological and hydrological processes supported by groundwater across coastal watersheds. Groundwater makes a significant but poorly recognised contribution to the function and resilience of coastal ecosystems and will play an essential role in climate change mitigation and adaptation. This review then explores how critical ecosystem processes supported by groundwater will be affected in areas of the humid subtropics that are expected to be impacted by climatic drying. Where rainfall is predicted to decrease, reduced groundwater recharge will interrupt the hydrology of coastal GDEs, while anthropogenic pressures, such as land‐use intensification and pollution, will diminish the quality of remaining groundwater. The challenges of managing groundwater for multiple purposes under climate change predictions are highlighted. To improve the management of coastal GDEs, research should be aimed at developing robust conceptual models of coastal groundwater systems that quantify biophysical linkages with ecological communities across relevant spatiotemporal scales.
... This observation is consistent with other riparian studies that have found tree growth to be more directly influenced by local hydrology compared with climate (Antunes et al., 2018;Sabathier et al., 2021;Sargeant & Singer, 2021;Schook et al., 2020;Singer et al., 2014;Valor et al., 2020). However, it is possible that other influences, such as increased nutrient availability and release from competition following drought-induced mortality events, obscured climate-growth comparisons and could be partly responsible for the enhanced growth during the drought recovery period (Gessler F I G U R E 5 Scatterplot of correlation coefficients between annual values of Δ 13 C and ring-width indices as a function of groundwater (GW) trend for earlywood (panel a), and latewood (panel b) at sites along the lower Santa Clara River, California. ...
Dryland riparian woodlands are considered to be locally buffered from droughts by shallow and stable groundwater levels. However, climate change is causing more frequent and severe drought events, accompanied by warmer temperatures, collectively threatening the persistence of these groundwater dependent ecosystems through a combination of increasing evaporative demand and decreasing groundwater supply. We conducted a dendro‐isotopic analysis of radial growth and seasonal (semi‐annual) carbon isotope discrimination (Δ¹³C) to investigate the response of riparian cottonwood stands to the unprecedented California‐wide drought from 2012 to 2019, along the largest remaining free‐flowing river in Southern California. Our goals were to identify principal drivers and indicators of drought stress for dryland riparian woodlands, determine their thresholds of tolerance to hydroclimatic stressors, and ultimately assess their vulnerability to climate change. Riparian trees were highly responsive to drought conditions along the river, exhibiting suppressed growth and strong stomatal closure (inferred from reduced Δ¹³C) during peak drought years. However, patterns of radial growth and Δ¹³C were quite variable among sites that differed in climatic conditions and rate of groundwater decline. We show that the rate of groundwater decline, as opposed to climate factors, was the primary driver of site differences in drought stress, and trees showed greater sensitivity to temperature at sites subjected to faster groundwater decline. Across sites, higher correlation between radial growth and Δ¹³C for individual trees, and higher inter‐correlation of Δ¹³C among trees were indicative of greater drought stress. Trees showed a threshold of tolerance to groundwater decline at 0.5 m year⁻¹ beyond which drought stress became increasingly evident and severe. For sites that exceeded this threshold, peak physiological stress occurred when total groundwater recession exceeded ~3 m. These findings indicate that drought‐induced groundwater decline associated with more extreme droughts is a primary threat to dryland riparian woodlands and increases their susceptibility to projected warmer temperatures.
... Therefore, reliable quantification of the hydrological cycle, its key fluxes and stores and its spatiotemporal variability is crucial for many applications related to hydrometeorology, water resources, and landatmosphere interactions, including flood and drought monitoring and prediction (Forootan et al., 2019Houborg et al., 2012;Li et al., 2019;Long et al., 2013;Slater et al., 2015), assessing water resources sustainability (Castellazzi et al., 2016;Forootan et al., 2014b;Scanlon et al., 2012), and identifying ecohydrological links between climate and vegetation (Singer et al., 2014). ...
Gravity Recovery and Climate Experiment (GRACE) and its Follow-On mission (GRACE-FO) have become an indispensable tool in monitoring global mass variations. However, separating GRACE(-FO) signals into its individual Terrestrial Water Storage Changes (TWSC) and surface deformation contributors, i.e. Post-Glacial Rebound (PGR), is desirable for many hydro-climatic and geophysical applications. In this study, a hierarchical constrained Bayesian (ConBay) approach is formulated to apply GRACE(-FO) fields and the uplift rate measurements from the Global Navigation Satellite System (GNSS) stations to simultaneously estimate the contribution of TWSC and PGR. The proposed approach is formulated based on a hierarchical Markov Chain Monte Carlo optimisation algorithm within a dynamic multivariate state-space model, while accounting for the uncertainties of a priori information and observations. The numerical implementation is demonstrated over the Great Lakes area, covering 2003–2017, where the W3RA water balance and the ICE-5G(VM2) and ICE-6G-D(VM5a) GIA models are merged with GRACE and GNSS data. Validations are performed against independent measurements, which indicate that the average root-mean-squares-of-differences between the PGR estimates and independent measurements reduced by 72% after merging observations with models through ConBay. The ConBay updates, introduced to the long-term trends, as well as the seasonal and inter-annual components, are found to be realistic.
