Year-end Sale % OFF 
Abstract
Riparian tree species, growing under different conditions of water availability, can adapt their physiology to maximise their survival chances. Rivers in South Africa may flow perennially, seasonally or ephemerally (episodically). Different riparian species are adapted to survive under each of these different flow regimes by making use of surface, ground, soil, rainwater, or some combination of these. These water sources are available to varying degrees, depending on local climatic, hydrological, geohydrological and geomorphological conditions. This paper tests physiological differences among trees along rivers with varying flow regimes. In this study 3 parameters were selected and tested, namely wood density, specific leaf area and water use efficiency through stable carbon isotope measurements. All three parameters are quick, simple and cheap to determine and as such their value for standard-procedure river monitoring programmes or environmental flow requirement procedures was tested. Acacia erioloba is an arid-adapted riparian tree along the ephemeral Kuiseb (Namibia) and Kuruman (South Africa) Rivers that shows decreasing specific leaf area and increasing wood density correlating with deeper groundwater levels. Intraspecific changes for specific leaf area and carbon isotope values were demonstrated for Acacia mellifera and Croton gratissimus at varying distances from the active channel of the seasonal Mokolo River (South Africa). No significant differences in physiology were noted for Salix mucronata, Brabejum stellatifolium and Metrosideros angustifolia, growing along the perennial Molenaars and Sanddrifskloof Rivers (South Africa) under reduced flow conditions. Only the measurement of specific leaf area recurrently showed that significant physiological differences for trees occurred along rivers of the drier flow regime spectrum (seasonal and ephemeral). As such, this physiological measurement may be a valuable indicator for water stress, while the other measurements might provide more conclusive results if a larger sampling size were used. Specific leaf area, in conjunction with other carefully picked water stress measurement methods, could be considered for monitoring programmes during environmental flow assessments, river health monitoring exercises and restoration projects. This would be particularly valuable in rivers without permanent flow, where there is little species-specific knowledge and where current monitoring methods are unsuited.Keywords: ecophysiology, stable δ13C isotopes, wood density, specific leaf area, EFAs, river flow regimes, trees
Highlights
Aquatic and riparian community structure of rivers are primarily shaped by a river’s flow regime (Jacobson, 1997; O’Keeffe, 2000) as the life histories of riparian plants are intimately tied to a river’s natural flow regime (Meritt et al, 2009)
Despite promising trends observed in Specific leaf area (SLA) and δ13C, none of these were significant; SLA was significantly correlated with groundwater levels (Fig. 1)
Three ecophysiological methods were used to measure the responses of various riparian trees to changes in water availability under 3 different flow regimes
Summary
Aquatic and riparian community structure of rivers are primarily shaped by a river’s flow regime (Jacobson, 1997; O’Keeffe, 2000) as the life histories of riparian plants are intimately tied to a river’s natural flow regime (Meritt et al, 2009). River flow influences other environmental attributes important for riparian plant growth, such as groundwater recharge, nutrient deposition, sediment transport and substrate deposition (Merritt et al, 2009). These cause-and-effect relationships must be understood in order to successfully specify environmental water requirements (EWRs) that will sustain riparian communities (Merritt et al, 2009). This is especially important where water availability is reduced due to climate change, human abstraction or diversion of flow (Stromberg and Patten, 1990; Tabacchi et al, 2000; Hou et al, 2007; Merritt et al, 2009)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
