Groundwater dependence of riparian woodlands and the disrupting effect of anthropogenically altered streamflow

Riparian ecosystems fundamentally depend on groundwater, especially in dryland regions, yet their water requirements and sources are rarely considered in water resource management decisions. Until recently, technological limitations and data gaps have hindered assessment of groundwater influences on riparian ecosystem health at the spatial and temporal scales relevant to policy and management. Here, we analyze Sentinel-2–derived normalized difference vegetation index (NDVI; n = 5,335,472 observations), field-based groundwater elevation (n = 32,051 observations), and streamflow alteration data for riparian woodland communities (n = 22,153 polygons) over a 5-y period (2015 to 2020) across California. We find that riparian woodlands exhibit a stress response to deeper groundwater, as evidenced by concurrent declines in greenness represented by NDVI. Furthermore, we find greater seasonal coupling of canopy greenness to groundwater for vegetation along streams with natural flow regimes in comparison with anthropogenically altered streams, particularly in the most water-limited regions. These patterns suggest that many riparian woodlands in California are subsidized by water management practices. Riparian woodland communities rely on naturally variable groundwater and streamflow components to sustain key ecological processes, such as recruitment and succession. Altered flow regimes, which stabilize streamflow throughout the year and artificially enhance water supplies to riparian vegetation in the dry season, disrupt the seasonal cycles of abiotic drivers to which these Mediterranean forests are adapted. Consequently, our analysis suggests that many riparian ecosystems have become reliant on anthropogenically altered flow regimes, making them more vulnerable and less resilient to rapid hydrologic change, potentially leading to future riparian forest loss across increasingly stressed dryland regions.

The Impact of Land Use Change on Water-Related Ecosystem Services in the Bashang Area of Hebei Province, China

Land use change is an important scientific issue recognized for its potential to alter ecosystem services (ESs), especially water-related ecosystem services (WRESs). Using the integrated valuation of ecosystem services and trade-offs (InVEST) model, this study quantified and mapped spatiotemporal variations in land use and corresponding WRESs in the Bashang area of Hebei Province, China (BAHP) to investigate how land use change impacted WRESs by means of scenario analysis, especially, in which a new evaluation indicator, average ecology effect (AEE) was proposed and well applied. The results indicated that woodland expansion (+602.61 km2) and grassland shrinkage (−500.57 km2) dominated the land use change in the BAHP in 2000–2018, which altered local WRESs, including the moderate declines in water purification and water yield, as well as a significant enhancement in soil conservation. In scenario analysis, compared to baseline levels, riparian woodland buffer and planting trees scenarios slightly decreased water yield but strengthened water purification and soil conservation; reclaiming wasteland and integrated development scenarios significantly enhanced soil conservation but lowered water yield and water purification; fertilizer reduction scenario effectively mitigated water deterioration. According to AEE, the riparian woodland buffer (RWB) scenario performed greater than the planting trees (PT) scenario on variations of WRESs per unit area, which differed completely from the results based on total variations. Overall, a multiple-scale indicator for a comprehensive evaluation of ESs should receive more attention.

Classification of riparian woody plant communities along the Thamalakane River in northwestern Botswana.

There is still paucity of information on the species composition of woody species along the Thamalakane River, northern Botswana, which may limit efforts aimed at conserving riparian woodland species. The current study was aimed at classifying the vegetation, and determining the species composition and diversity of the riparian woodland plant communities along the Thamalakane River. It was hypothesized that there will be no different woodland communities along the Thamalakane River. The 71 sampling plots measured 1000m2 (20m × 50m). In each plot,the percentage cover for each species was estimated following the Braun-Blanquet scale. Different woodland communities were determined through Hierarchical Cluster Analysis followed by Indicator Species Analysis. Multi-Response Permutation Procedures (MRPPs) were used to determine whether or not there was a significant separation between the groups. The Kruskal-Wallis test was used to statistically compare the diversity between woodland communities. Five major woodland communities were identified along the Thamalakane River, namely Vachellia tortilis-Gardenia volkensii, Combretum imberbe-Gymnosporia senegalensis, Philenoptera violacea-Garcinia livingstonei, Dichrostachys cinerea-Flueggea virosa and Croton megalobotrys-Colophospermum mopane. There was significant (p <0.05) separation between the plant groups. Species diversity was highest in Dichrostachys cinerea-Flueggea virosa community and lowest in Vachellia tortilis-Gardenia volkensii community. The distribution of woodland species in along Thamalakane river could be influenced by human disturbance, which may override abiotic environmental conditions such as flooding in influencing the composition and distribution of plant species. This calls for proper management initiatives of the riparian vegetation in the study area. Such initiatives may include establishment of exclosures to promote the germination and propagation of the woodland species. Other strategies may include education and awareness creation of the local communities to promote their co-existence with the riparian vegetation.