Abstract
This review summarises the main ecotonal properties of chalk hyporheic zone (CHZ), using a holistic approach on both structure and functionality of this habitat. The corroborated results suggest that the CHZ represents a typically shallow habitat (approx. 40–50 cm deep), with a homogenous distribution of both fauna and chemistry between heads and tails of riffles (putative down and, respectively, upwelling zones). Despite being groundwater fed, the CHZ is equally influenced by surface waters, chemically and biologically. However, despite its shallowness, the CHZ plays a very important role in nutrients (re)cycling and in the energy flux towards river ecosystems, fuelling benthic food webs with surface-derived macronutrients and subsurface chemosynthetic C. Although groundwater variation influences strongly the river flow during winter, the effects on interstitial fauna dynamic are limited, suggesting the active role of CHZ played in the stochastic events of down/upward migration of fauna across habitats. Overall, the CHZ represents a confined, but critical habitat in the structure and functionality of chalk river ecosystems and fulfils most properties of a true ecotone.
Published Version
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