Ecohydrology最新文献

Spectral interference induced by the water and the spatial resolution of many satellite images (≥ 10 m) limit the efficiency of remote sensing for monitoring riverine aquatic plant stands. In this study, the potential of using PlanetScope satellite images (3 m in spatial resolution, ~daily acquisition) for monitoring seasonal and interannual aquatic vegetation surface area was evaluated. Airborne images (≤ 0.2 m) acquired on four dates on three aquatic plant stands were used to create, through visual interpretation, reference maps indicating whether the pixels of each PlanetScope image acquired at ±8 days correspond to aquatic vegetation or nonvegetated aquatic areas. For each PlanetScope image, the green normalized difference vegetation index (GNDVI) was calculated and centred on the mean (GNDVI_centred) to distinguish aquatic vegetation from nonvegetated aquatic areas while minimizing variations in their spectral signature over time. Reference maps from the date when aquatic vegetation was the least developed were used to calculate the GNDVI_centred classification threshold. To reduce classification errors from radiometric inconsistencies, the frequency at which pixels of PlanetScope images acquired at ±8 days from airborne images were classified as aquatic vegetation was also calculated. Aquatic vegetation was then empirically defined as pixels with a frequency ≥ 85%. Although the classification of PlanetScope images indicates that low abundances of aquatic vegetation cannot be detected, our results show that large changes in stand surface area can be monitored using a multidate classification threshold, thus providing new opportunities for the monitoring of riverine aquatic vegetation on large scales.

Benthic macroinvertebrates are indicators of water quality and riparian ecosystem health. Their abundance and distribution in streams are associated with river basin environmental factors, including stream biotic and abiotic fluvial processes. We examined benthic macroinvertebrate diversity and abundance in relation to large wood (LW) and pool-riffle morphology along the Geul River (NL), a small meandering river typical of European landscapes. Restoration since 1998 that includes remeandering and beaver (Castor fiber) reintroduction (2002 to 2004) has enhanced the riparian ecosystem. Field sampling was designed to determine abundance and taxa composition of benthic macroinvertebrates, differentiating between sites with LW and without (control) and between pools and riffles. Additional variables included velocity, depth, bed material and canopy cover. Macroinvertebrate diversity to measured environmental factors was evaluated with alpha and beta diversity indices and diversity t-tests. Relationships between LW and environmental variables on community composition were assessed using nonmetric multidimensional scaling (NMDS) and analysis of similarities (ANOSIM). Thirty-one macroinvertebrate taxa were identified, most at the Genus and Family level. Gammaridae (freshwater shrimp) was dominant across all sites. Macroinvertebrate diversity was significantly higher in riffles than pools, while taxa richness was higher for LW in comparison to control sites. Invertebrate community composition was not significantly affected by LW or measured environmental variables. Despite stream restoration, the index of Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa amounted to 33%, indicating degraded water quality. At a basin scale management authorities should strive to reduce agricultural runoff, especially silt inputs. At the channel-reach scale the pool-riffle morphology and design of effective LW structures should be a guiding management goal for attaining riparian health consistent with targets of the EU Water Framework Directive.

The interaction between macroinvertebrates and environmental factors has long been a question of great interest across a wide range of fields. However, our understanding of the impacts of environmental factors on macroinvertebrates remains vague. Moreover, the study of the distribution drivers of macroinvertebrates in mountainous rivers has been rarely undertaken, primarily due to the sampling difficulties and the inherent complexity of the terrestrial ecosystems in these regions. This study applied a partial least squares structural equation modelling (PLS-SEM) to investigate the interactions between specific environmental factors, namely, hydrometeorology, water temperature, nutrient levels and substrate composition, and their effects on macroinvertebrates. Five stations along the Lai Chi Wo River in the Northwest New Territories of Hong Kong, China, were selected for data monitoring. The model results reveal site-specific environmental influences on macroinvertebrates. The furthest downstream station, close to the sea, is vulnerable to seawater intrusion during the dry season, indicating a hydrometeorological-driven model as freshwater macroinvertebrates are intolerant to seawater. Two stations, one downstream and the other upstream, are occupied by rocks that stir river water and increase dissolved oxygen, forming a nutrient-driven model. The remaining two stations, located at small ponds next to man-made weirs, experienced accumulated sedimentation and debris, which are conducive to macroinvertebrates, resulting in a substrate-driven model. Furthermore, this study demonstrated that PLS-SEM provides a more precise understanding of the direct and indirect effects of environmental factors on macroinvertebrates compared to linear fitting and principal component analysis methods.

It is well established that changes in climatic conditions across Alpine environments have influenced tree-growth at altitudes close to the tree line. Less well known is the impact that increasing proportions of glacial melt water, which may accompany increasing temperatures and otherwise drier conditions during warmer summers, have on the tree growth along the glacial outwash rivers within the basin. In many Alpine basins in Switzerland, hydropower development further alters natural hydrological regimes by modifying runoff timing and flow composition. This study investigates the combined effects of climate variability and hydropower regulation on tree growth and isotopic compositions in the Turtmann River Basin in south-west Switzerland, where an upstream hydropower dam (2200 m a.m.s.l.) stores almost all glacial meltwater, and therefore, the riverine flow below the dam becomes increasingly dependent on snowmelt and rainfall from the unglaciated and unexploited basins. We analysed 75 years (1946–2020) of δ¹⁸O and the δ²H values in earlywood (EW) and latewood (LW) Larix decidua growing proximal and distal to the river at two sites within the Turtmann basin. The results show that tree ring growth was primarily temperature-limited at both sites, with a tendency for precipitation becoming a growth-limiting factor particularly at the downstream Site 2 in recent decades. The LW showed stronger climatic sensitivity than EW, reflecting increasingly dry summer conditions. Both δ¹⁸O and δ²H values of proximal trees are lower compared with those of the distal trees, reflecting snowmelt and summer precipitation but are not influenced by the glacial meltwaters draining from the upper catchment and/or released by the dam. These results demonstrate that tree-ring stable isotopic compositions can effectively trace changes in Alpine hydrologic regimes and provide valuable insights into how climate change and hydropower operations combine to influence water availability and tree growth dynamics in glaciated basins.

Coastal Upland Swamps of the Sydney Basin Bioregion, Australia, are highly biodiverse upland mires. Swamp vegetation organises into five communities, thought to occupy distinct positions along a hydrological gradient. Longwall mining reduces the duration of root zone saturation, but lack of quantitative understanding of hydrological niche dimensions limits our ability to predict the impacts of drawdown in terms of observed vegetation communities. Here, we use indicator species to quantify the hydrological niche of their corresponding plant communities and predict the impacts of mining-related drawdown. We first modelled the relative occurrence frequency of 20 vascular plant indicator species (four per community) from 11 unmined sites across four swamps and then used this model to predict their frequencies at a mine-impacted swamp. We quantified the hydrological niche for each community using the average number of days per year of root zone saturation (≤ 30 cm below surface) from time series soil moisture data. Inferred community hydrological niches were broadly consistent with qualitative ecological understanding, with estimated optimal mean days per year saturated ranging from Restioid heath at 17 [≤ 16, 49] (mean ± [95% uncertainty]) days to Ti-tree thicket at 348 [315, ≥ 353] days, with Banksia thicket 45 [16, 111], Sedgeland 187 [139, 264] and Cyperoid heath 243 [198, 290] communities intermediate. At the impacted Swamp, the model underpredicted wetter- and overpredicted drier-adapted community indicator species, suggesting vegetation has not yet reached hydrological equilibrium. Results suggest potential for using the modelled hydrological niche of wetland plant communities to predict community-level impacts of hydrological change in upland swamps.