Ecohydrology最新文献

The surface of peatlands is constantly in motion. While pristine mires are characterized by peat growth and reversible surface fluctuation, induced by water level fluctuations, drained peatlands show subsidence due to peat mineralization and physical compaction. Still, drained peatlands show smaller but marked short-term surface fluctuation as the water level continues fluctuating after drainage. This concurrence of physical and biochemical processes complicates the determination of greenhouse gas emissions from subsidence measurements. Restored peatlands may regain surface motion dynamics of pristine sites. Besides informing on carbon exchange, surface motion data might serve as an indicator for ecohydrological conditions. This review study compiles the key processes causing surface motion, methods to determine surface motion and subsidence models. A global meta-analysis of 670 data points on subsidence (121 studies) and 70 data points on surface oscillation (29 studies) revealed large variability, with subsidence rates from −3.2 to 37.5 cm yr⁻¹ and annual peak-to-peak amplitudes from 0.1 to 20 cm. Subsidence was influenced by time since drainage, climate, drainage depth, peat thickness and land use intensity. The subsidence rate decreased with time, while the share of physical compaction decreased, and the share of mineralization increased. With increasing temperature, mineralization and hence subsidence rate increased. Increasing drainage depth and thus land use intensity positively influence both mineralization and physical compaction. Subsidence rate and the share of physical compaction increased with increasing peat thickness. By combining existing model approaches, using the most available variables, we introduce four models to estimate subsidence rates on a global scale.

Beaver dams substantially reshape peatland hydrology, yet their influence on plant phenology, a key driver of ecosystem carbon dynamics, remains poorly understood. We used UAV-based RGB imagery to quantify seasonal changes in greenness (GCC) of sedge (Carex spp.) across three hydrological treatments in a Canadian Rocky Mountain peatland: flooded beaver pond, drained beaver pond and unimpacted fen. Repeat imagery captured from May to September 2023 revealed that beaver damming, whether current or legacy, significantly altered sedge phenology. Phenology in the flooded beaver pond followed a similar trajectory as the unimpacted fen but delayed green-up by 2.5 weeks. Interestingly, the drained beaver pond exhibited the earliest green-up, beginning 12 days earlier and reached a 12% higher peak greenness while having a similar length of season as the unimpacted fen, likely due to warmer peat and later-season water stress. The flooded beaver pond maintained a high, stable water table which delayed senescence and extended the growing season by 6 weeks. These hydrological legacies created a patchwork of phenological responses across the peatland. Our findings highlight how beaver engineering via manipulation of water table elevation controls plant phenology, with potential indirect downstream effects on carbon cycling and forage availability in montane peatlands.

Droughts can have significant impacts on forest ecosystems. To better understand how droughts affect tree transpiration across catchments, we studied the combined effects of landscape position (topography and related variability in soil moisture) and atmospheric demand (vapour pressure deficit, VPD) on sap flow velocities across a forested hillslope in central Italy. Our results show that sap flow velocities for trees on the upper part of the hillslope decreased during the hottest period in summer but remained relatively stable for the trees in the riparian zone. The variation in the mean daily sap flow velocity for trees on the hillslope was best explained by the variation in soil moisture, while for trees in the riparian zone, it was best explained by variations in VPD and temperature. The analysis of the time lag between daily peak VPD and peak sap flow velocity confirmed that the hillslope trees experienced moderate stress during the period with low water availability. On the contrary, the wet riparian zone limited tree water stress and early stomatal closure in summer. These results highlight the need to account for topography and related hillslope scale differences in soil moisture when analysing the response of forests to droughts and when simulating the effects of soil moisture on transpiration in catchment- or landscape-scale ecohydrological models. However, these results need to be validated for different hillslopes and different tree species.

Direct investigations of the connection between groundwater flow systems across multiple scales and groundwater-dependent ecosystems (GDEs) remain rare. Such studies offer valuable insights into the complex and scale-dependent relationships between groundwater dynamics and vegetation patterns. Our research in the Danube-Tisza Interfluve (DTI)—an area where the preservation of natural vegetation is of critical importance—demonstrates the effectiveness of this approach in revealing the hydraulic drivers behind the distribution of GDEs. In the area, the spatial distribution of groundwater-dependent vegetation is primarily governed by the characteristics of subsurface groundwater flow systems. Our results reveal that the chemical differences between the two dominant basin-scale flow domains—overpressure-related saline ascending system and topography-driven freshwater system—are responsible for the regional distribution of habitats with alkaline and fen characteristics. Local alkaline vegetation anomalies in the fen vegetation zone are predominantly associated with the discharge zones of intermediate and local flow systems of the topography-driven freshwater domain. Their anomalous chemical character is developed by local rock–water interactions along the local flow paths and/or by the sporadic ascent of deep saline groundwater via faults. At a small scale, the alignment between the differing chemical compositions of groundwater (saline and freshwater) and the spatial distribution of alkaline and fen vegetation could also be identified. Small-scale investigations demonstrated that deep ascending saline groundwater associated with alkaline habitats continues to maintain them; meanwhile, habitats formed by topography-driven flow systems are transforming, possibly because of the decreasing water supply. With this study, we highlight the critical importance of multiscale groundwater flow systems in understanding and protecting transforming GDEs—an issue that is particularly relevant in the era of climate change.

The alteration of the hydrological regime caused by damming remains a critical challenge for river systems. Rio Chama, a highly regulated river, has undergone severe alterations in its hydrological regime due to a series of dams that impact sediment transport mechanisms and riparian vegetation dynamics. This study employs remote sensing to assess reach-scale changes in riparian vegetation and geomorphology and field-informed 2D hydrodynamic modelling to determine sediment transport processes. We used a random forest classifier within Google Earth engine and high-resolution National Agriculture Imagery Program imagery (2011–2022) to assess changes in riparian vegetation and channel planform. We evaluated the impact of different flows on sediment transport mechanisms, along with field-data–informed sediment distribution at the sub-reach scale. Following a 2009 high-flow release, channel width remained relatively stable, although planform changes were observed, including shifts in the channel centre line and localised bank erosion, especially in the sinuous sections. Vegetation expanded over time and encroached along bars, linked to reduced overbank flooding and sustained base flow year-round. Furthermore, results indicated that even smaller flows can lead to fine sediment displacement, while higher flows are necessary to mobilise coarse sediments. This study offers valuable insights for ecological flow recommendations, particularly for Rio Chama, and supports improved restoration strategies and long-term river management in other dam-regulated systems across arid and semi-arid regions.