Ecohydrology最新文献

Non-perennial streams are globally prevalent. These streams are vital components of ecosystems, yet their drying patterns and resulting impacts on hydrologic connectivity remain poorly understood at the watershed scale. Aridity is a dominant driver of stream drying, but its influences on hydrologic connectivity have not been fully explored. In this study, we investigated the role of aridity in shaping streamflow and connectivity patterns in non-perennial stream networks that span the continental United States aridity gradient. Using hydrologic models, we simulated daily streamflow and stream network connectivity under current and future climate scenarios. Our findings support previous research showing that aridity and streamflow are strongly linked. We also found that connectivity was related to aridity, although this relationship was weaker. Under the future climate scenario, mean runoff increased in most watersheds in the future, while mean connectivity decreased in the majority of watersheds. This difference is an indicator of the complex relationship between streamflow and connectivity. Aridity was a strong predictor of changes in very high and very low connectivity periods that resulted from climate change, but aridity did not predict changes in mean connectivity. Arid watersheds tended to experience more high connectivity days due to climate change while humid networks tended to have more low connectivity days. By modelling climate impacts at the network scale and across a broad hydroclimatic gradient, we highlight the importance of considering context-dependent changes in network connectivity in river flow management and watershed conservation plans.

Extreme climatic events can cause a high degree of impacts on forest carbon dynamics, particularly in more sensitive subtropical regions. We investigated the dynamics of carbon exchange, light use efficiency (LUE) and water use efficiency (WUE) in a subtropical forest ecosystem representing Central China's Yangtze River basin. The region is located at the East Asian monsoonal zone largely characterized by hot and humid summers and cold and dry winters. Using eddy-covariance measurements, we find that the climatically sensitive subtropical forest ecosystem acts as a robust carbon sink, sequestering carbon at an annual rate of 8.26 t C ha⁻¹, exceeding the average C sink of broadleaf forests. Despite favourable hydrothermal conditions in summer, excessive solar radiation and vapour pressure deficit (VPD) suppress carbon sink potential, highlighting the sensitivity of carbon exchange to extreme climatic events. The LUE of the subtropical forest exhibits a nonlinear relationship with leaf area index (LAI) as high as 2.6 m² m⁻², while water use efficiency (WUE) variability is strongly driven by VPD, reflecting the combined effects of environmental factors including temperature, precipitation and biological factors. In comparison, carbon exchange in the subtropical forest in YRB is highly sensitive to climate change, while LUE remains the most stable. The critical balance of water and thermal conditions for optimal carbon uptake of subtropical forests in YRB provides insights into the climatic extremities, as revealed by strong interactions among carbon exchange, LUE and WUE, highlighting the potentially important role in carbon offsets in the region.

Understanding the influence of vegetation on nitrogen transport is crucial for assessing the ‘nitrogen status’ of watersheds and advancing sustainable ecosystem management, particularly in vulnerable permafrost-affected regions. Daily riverine nitrogen data during the ice-free period (from 9 April to 26 October) in 2021 of a boreal forest watershed of the permafrost region in northeast China were investigated. Results showed that the nitrogen wet deposition during the growing season significantly exceeded the riverine nitrogen export. The vegetation (including trees, shrubs, herbs and mosses) significantly influenced the riverine nitrogen export during this period. The modified double mass curve and Pettitt's test were used to quantitatively assess the impact of vegetation on riverine nitrogen export. Runoff variations could explain 51.35% of the riverine nitrogen export in the non-growing season. However, vegetation attenuated the impact of runoff on riverine nitrogen export, thus ensuring a relatively stable relationship between runoff and riverine nitrogen export in the growing season. When daily runoff was below 1.40 mm (the daily runoff threshold at which riverine nitrogen export underwent a significant change), vegetation reduced nitrogen export by 31.89%. Above this threshold, the reduction increased to 60.51%. These results provide new mechanistic insights into the seasonal nitrogen dynamics of permafrost watersheds under climate change.

Disassociating the independent effects of flow and water quality on the ecology of flowing waters is an overarching goal in water resource science needed to improve the efficacy of watershed management. However, the interrelatedness of these gradients and their subsequent alteration due to land use change has constrained progress made on this front. The objective of this study was to use benthic macroinvertebrate and fish assemblage data to characterize flow-ecology relationships that were unchanged by water quality impacts across two southeastern landscapes in the USA to help detect ecological change driven by flow alteration. General linear latent models were used to identify taxa that were responsive to high or low flow metrics and water quality gradients. Bayesian hierarchical generalized additive models were then developed using these indicator taxa and three biological metrics to identify flow-specific relationships that were unaffected by water quality impacts. Three low flow-specific relationships were identified, illustrating how potential agricultural or urban impacts to hydrology reduced stream biological health. Importantly, flow-ecology relationships developed using indicator taxa in this study effectively captured hydrology-specific impacts while biological metrics typical of state monitoring and assessment programs did not. Therefore, developing flow-specific biological metrics is a critical step when developing management strategies targeting flow alteration. Implementing standardized frameworks such as the one characterized here can limit contradictory findings and improve streamflow enhancement and restoration project efficacy. These low flow-specific relationships will enhance managers' capacity to develop environmental flow standards, monitor their success, and better understand urban and agricultural impacts on stream assemblages.

Efforts to protect freshwater ecosystems, and the biodiversity that supports their essential services, are increasing globally, yet biological connectivity still receives less attention compared to physical or chemical connectivity. This study piloted a basin-scale assessment of biological connectivity in the Seomjin River basin, Korea, which recently experienced an extreme flood, using biodiversity indicators (species richness and similarity). Results show that the flood affected freshwater fish at smaller spatial scales and benthic macroinvertebrates at larger scales, while impoundments disrupted upstream–downstream biological connectivity. Expanded monitoring, standardized methods and integration with multispecies conservation will further strengthen this approach for holistic water management.

Using combined hydrogen–oxygen stable isotope (δD, δ¹⁸O) tracing, the MixSIAR model and the Levins niche index, this study investigated the dominant mangrove species Bruguiera sexangula and Aegiceras corniculatum in Dongzhaigang, Hainan, to assess the spatiotemporal dynamics of their water use and the symbiotic mechanisms of mangroves. The mangroves mainly rely on surface water or soil water (> 80%) during the dry (November–January) and transitional (February–April) seasons, while groundwater utilization increases in the rainy season (May–October), reaching 21.9% for B. sexangula. Significant variation in the contribution rates of different water sources is observed within the same season. For example, in the dry season, B. sexangula used shallow, middle and deep soil water at proportions of 16.8%, 20.6% and 21.3%, respectively, whereas A. corniculatum used them at 18.2%, 21.6% and 25.1%. Temporally, the hydrological niche breadth of B. sexangula (8.619) is wider than that of A. corniculatum (7.004) during the dry season, but this pattern reverses in the rainy season, with A. corniculatum showing a broader niche breadth (9.111). Spatially, B. sexangula maintains a wider hydrological niche breadth than A. corniculatum across the bay. Meanwhile, A. corniculatum reduces competition through vertical resource differentiation, as indicated by a niche overlap value of 0.774 between the two species. The two species achieve symbiosis through differentiated water utilization strategies and the spatiotemporal complementarity of their hydrological niches. These findings provide a theoretical basis for selecting and configuring tree species in mangrove ecological restoration.