Ecohydrology最新文献

North American Southwest semi-arid forests are experiencing unprecedented stress due to the combination of the 21st century megadrought and abnormally dense, young forest stands. Restoration thinning is being widely implemented across the region with the aim of restoring historical stand structures, improving forest health and decreasing the risk of unnaturally severe wildfire. While restoration thinning likely affects soil moisture as well, it is unknown how significant or long-lasting such effects are. Especially little is known about the influence of thinning on root-zone soil moisture used by mature trees. In this study, we used 5 years of data from 126 soil water potential sensors to examine patterns in root-zone (25–100 cm) soil moisture in thinned and non-thinned dense ponderosa pine (Pinus ponderosa) forests as well as the edge areas (boundary) between them during 1–6 years post-thinning. We focused on the spring dry season and calculated three metrics: mean soil water potential, days to onset of soil drying and days spent under a critical drying threshold beyond which ponderosa pine experiences physiological drought stress. We found that thinned areas were consistently significantly wetter and spent less time under critical drying conditions than either non-thinned edge or non-thinned dense forest. Importantly, the thinned forest also experienced more consistent water availability compared to non-thinned forest, regardless of year-to-year precipitation variability. South-facing non-thinned edge areas dried earlier than either of the other treatments and may be especially vulnerable to drought. Our results strongly suggest that restoration thinning significantly improves forest resilience to climate change.

A quantification of the mechanisms underlying plant water use strategies is central to understanding plant stress vulnerability, productivity and subsequent responses to hydroclimatic shifts. To explore such dynamics, we developed a dynamical model for the changes of internal plant water storage (PWS) and soil moisture given a set of coupled balance equations. This trade-off was explored through the analysis of long-term plant fluxes over a range of climate regimes, providing constraints on water availability and demand while incorporating plant physiological mechanisms into the model framework. In conjunction, plant productivity was considered, taken as the plant carbon dioxide assimilation with an additional maintenance cost subtracted to account for varying internal plant water capacities. To explore these trade-offs analytically and characterize the long-term response to changing rainfall frequencies, a conceptual model was developed by linearizing the coupled ordinary differential equations (ODEs) governing PWS and soil moisture dynamics. This conceptual model produced clear PWS optima that decreased nonlinearly with increasing rainfall frequency, as plants with a higher PWS capacity maintained a higher minimum internal water storage overall. The model was then extended to include nonlinear components, including stochastic rainfall forcing. Under constant meteorological conditions, due to the cost associated with plant size along with the timescale of intake and water release, we found that net carbon uptake does not necessarily increase with larger maximum PWS capacities but is sustained for longer periods during drought due to transpiration being facilitated by internal water stores. This PWS reduces stress for water storing plants in climate regimes with high-intensity, low-frequency precipitation. Increased rainfall frequency and a decrease in intensity greatly reduce the overall optimal PWS capacity. Thus, the extended model confirms that optimal PWS decreases nonlinearly as the rainfall becomes more frequent and less intense, as in the conceptual model. This suggests that water storage plays a less critical role in wet environments that may show an increase in wet days, but not necessarily an increase in water availability. We then analysed remote sensing data trends in seasonally dry ecosystems and compared them with the nonlinear model to identify physically based mechanisms governing plant water use, identifying plant functional traits potentially coordinated with PWS.

In many rural areas of arid and semiarid regions, balancing agricultural and environmental water needs is a key challenge facing resource managers. This is complicated by the tendency for the water needs of cultivated crops to be better understood than those of aquatic ecosystems. This work aims to quantify hydrologic conditions that support the persistence of key ecosystem species using functional flows, not in the context of a prescribed flow regime, but in terms of identifying features of the hydrograph that are empirically correlated with specific ecological outcomes. We use the coho (Oncorhynchus kisutch) and Chinook (Oncorhynchus tshawytscha) salmon runs in Scott Valley, a 2 109 km² undammed rural watershed in northern California, USA, as a case study. Taking advantage of a nearly two-decade ecological monitoring dataset and long-term stream gauge measurements, we first examined hydrological–ecological correlations; then compared six different statistical modelling structures, using two techniques: LASSO and MARSS. In LASSO regressions, to balance the explanatory power of the models with the risk of overfitting, we used k-fold cross-validation to find the lowest error value of the tuning parameter lambda. In MARSS, we calculated models for each individual hydrologic metric and compared them using AICc values. Correlation coefficients indicate that hydrologic factors and spawner abundance both exert influence on juvenile fish production. Statistical models generally agreed that the hydrologic metrics with the highest coefficients are earlier river reconnection and greater fall flow magnitude during parents' spawning for coho, and lower wet season median flow and slower spring recession rate for Chinook (though this could change with additional years of data, especially for the smaller coho dataset). The influence of some metrics, notably fall flow difference from dry season, was positive or negative depending on the fish life stage in which the flow occurred. This approach for empirically identifying hydrologic metrics with high ecological importance for a threatened species may be useful in other watersheds, where sufficient ecological data are available; it could be used to evaluate trade-offs and support water management decisions in human-altered novel ecosystems.

Fine sediment (particles < 2 mm) is a natural and important component of riverine systems. However, excessive loads are one of the leading causes of ecological degradation globally. The flow regime is intrinsically linked to fine sediment dynamics (erosion, transport and deposition) and is further considered a ‘master’ variable in structuring the invertebrate community of lotic systems. To date, limited research has examined how the interaction of these variables affects the response of the ecological community, and how this varies temporally. Paired invertebrate, fine sediment and daily flow discharge data were acquired for 28 sites across England. Mixed effects models were used to determine the influence of fine sediment and flow, both individually and in interaction, on invertebrate indices and by season (spring and autumn). Our results indicate that some flow metrics were more influential in structuring the invertebrate community than others (including low pulse count and maximum annual monthly discharge), and flow metrics were more likely to have a significant effect on invertebrate indices in autumn than in spring. Flow was found to mitigate the negative effect of deposited fine sediment on invertebrate communities in some instances. This was particularly the case for high antecedent flow metrics (e.g., high flows in the seven days prior to sampling). However, overall, there was little evidence of an interaction between flow and fine sediment detected. Our study highlights the nuanced relationships between flow dynamics and deposited fine sediment, in influencing the composition of macroinvertebrate communities in lotic environments. Effective catchment management could integrate this knowledge, emphasising seasonality and site-specific hydrological characteristics to maximise ecological benefits.

Fish population dynamics are influenced by intrinsic and environmental drivers across multiple spatial and temporal scales. A thorough understanding of these drivers is essential for maintaining fish recruitment in flow-regulated rivers. In the Murray–Darling Basin (MDB) in Australia, golden perch (Macquaria ambigua) are an iconic species with a life history characterised by irregular, strong recruitment of year classes. In-channel flow pulses and overbank flows are important for spawning and recruitment; however, the drivers of fluctuations in golden perch recruitment have not been sufficiently quantified to allow for full operationalisation into river and fishery management. We used long-term standardised electrofishing data to model relationships between the relative abundance of young-of-the-year (YOY) golden perch with large-scale climate indices, local river hydrology and temperature, and river/fishery management actions. While consistent recruitment was observed in only five rivers, there were strong, positive associations between the abundance of YOY golden perch and two broadscale climatic drivers (Australian Monsoonal Index and total rainfall across the northern MDB). The driver of these relationships is likely to be the effects of climate on local river discharge and temperature. YOY abundance increased with temperature and generally increased with river discharge to an optimum before declining at a very high discharge. We also found positive but variable effects of stocking, suggesting that stocking of fish can augment natural populations but that outcomes are spatially and temporally inconsistent. Our results have the potential to enable proactive management targeted towards supporting the hydrological conditions necessary for self-sustaining golden perch populations.