Effects of a Large Irrigation Reservoir on Aquatic and Riparian Plants: A History of Survival and Loss

Abstract

Dammed rivers have unnatural stream flows, disrupted sediment dynamics, and rearranged geomorphologic settings. Consequently, fluvial biota experiences disturbed functioning in the novel ecosystems. The case study is the large irrigation reservoir Alqueva in Guadiana River, Southern Iberia. The study area was divided into three zones: upstream and downstream of the dam and reservoir. For each zone, species composition and land use and land cover (LULC) were compared before and after the Alqueva Dam implementation. Data consist of aquatic and riparian flora composition obtained from 46 surveys and the area (%) of 12 classes of LULC obtained in 90 riverine sampling units through the analysis of historical and contemporary imagery. There was an overall decrease of several endemic species and on the riparian shrublands and aquatic stands, although differences in the proportion of functional groups were not significant. Nevertheless, compositional diversity shows a significant decline in the upstream zone while landscape diversity shows an accentuated reduction in the reservoir area and downstream of the dam, which is likely related to the loss of the rocky habitats of the ‘old’ Guadiana River and the homogenization of the riverscape due to the irrigation intensification. The mitigation of these critical changes should be site-specific and should rely on the knowledge of the interactions between surrounding lands, ecological, biogeomorphologic, and hydrological components of the fluvial ecosystems.

Water Quality Assessment of a Hydro-Agricultural Reservoir in a Mediterranean Region (Case Study—Lage Reservoir in Southern Portugal)

“…It is part of the Guadiana basin with a total storage capacity of 4150 hm 3 [19]. It was built to be a strategic water reserve that would allow the reinforcement of water capacity, the supply to populations (drinking water), the irrigation of crops, and the production of electricity (hydroelectric production) [20]. With the construction of the Alqueva Multipurpose Development Project (AMDP), three subsystems for irrigation (Alqueva, Ardila, and Pedrógão) constituting the Alqueva Global Irrigation System (AGIS) were created [21].…”

Impounding Reservoirs, Benefits and Risks: A Review of Environmental and Technical Aspects of Construction and Operation

“…The main conclusion of this review is that priority should be given to implementing sustainable planning and technological solutions to build facilities whose social benefits will largely outweigh any environmental losses. These should be subject to the most effective possible compensation [69][70][71][72][73][74][75][76][77][78][79][80][81][82][83]. The need for ex ante impact assessments is emphasised, but also for studies to be repeated after a longer period of reservoir operation [69].…”

“…It is not insignificant to maintain baseflows (biological) on the outflow from the reservoir. The construction of large facilities of strategic importance for the whole country or region will always involve environmental impacts; however, studies of the large Alqueva reservoir have shown that many other factors have been superimposed on changes to the vegetation structure in its catchment, and that the recovery of important assemblages of endemic species is possible by adopting ecological-restoration solutions [73]. Such a measure has been implemented in the case of the Three Gorges Reservoir catchment, where there has been a change in microclimate favourable to the spread of vegetation [74].…”

Assessing the Connectivity of Riparian Forests across a Gradient of Human Disturbance: The Potential of Copernicus “Riparian Zones” in Two Hydroregions

“…Although riparian zones are highly dynamic ecosystems, relevant changes in the riparian woody strata usually require more than 5 years to be significantly detectable with the image resolution that was used in the current study. Other riparian woody vegetation analyses have been successfully conducted with similar temporal mismatch among images and field data [47]. As for differences in the spatial resolution, due to the coarser resolution used to develop the ARZ model, riparian patches appear larger, more homogeneous and less numerous, while with the MRZ layer, representative of the ground-truth, patches are smaller, more heterogeneous and in higher number (Figure 4).…”