A revised classification of temperate lowland groundwater‐fed headwater streams based on their flora

Abstract

Prolonged drought leads to the temporary simplification or loss of aquatic biological communities, as surface water is progressively reduced or dry phases are extended in intermittent streams. Using surveys of aquatic and semi-aquatic plants, and recording non-aquatic grasses and herbs, we classify the communities within 24 groundwater-fed streams in south England. We examine changes over a 21year period following a 3-year drought. Our classification reveals a simplification of communities driven by a decline in the abundance of obligate aquatic taxa and an increase in the abundance of semi-aquatic taxa. We demonstrate plant community structure as a strong indicator of a site's flow history, including intermittence, but interactions with channel morphology also influence communities and need further investigation. We recommend that future surveys encompass terrestrial, semi-aquatic and aquatic plants, as well as habitat assessments, to improve the understanding of how instream communities change between flowing, ponded and dry phases in intermittent streams.

Drought in intermittent river and ephemeral stream networks

“…Comparisons of stream community responses to drought across reaches with different intermittence regimes have yielded mixed evidence (Bêche et al, 2009; Cañedo‐Argüelles et al, 2020; Herbst et al, 2019; Hill et al, 2019; Rolls et al, 2016; Sarremejane et al, 2020; Sarremejane, Stubbington, et al, 2021; Westwood et al, 2020). Several studies found congruent drought‐induced changes in community composition across streams with different permanence regimes (Bêche et al, 2009; Herbst et al, 2019).…”

Colonisation of terrestrial vegetation in an intermittent river: Diversity responses to seasonal drying

“…In river systems experiencing longer dry phases, semi‐aquatic and terrestrial taxa can colonise a riverbed from channel margins and the riparian zone (Franklin et al, 2008; Holmes, 1999; Stromberg & Merritt, 2016). Where drying is prolonged, plant communities can consist exclusively of terrestrial vegetation rooted in dry riverbeds (Holmes, 1999; Westwood, England, Johns, & Stubbington, 2020). However, little information exists regarding the diversity and composition of terrestrial vegetation inhabiting dry riverbeds, especially in cool, wet temperate (i.e., oceanic climate) regions with previous studies grouping terrestrial plants as ‘terrestrial herbs’ and ‘terrestrial grasses’ (Holmes, 1999; Westwood et al, 2020).…”

“…Despite the many ecosystem functions provided by plant communities, there are no studies considering their colonisation and succession in dry riverbeds of good morphological condition (i.e., no water abstractions and low anthropogenic pressures), and underlain by carboniferous limestone deposits. Past research has focussed on predominantly aquatic plant colonisation in intermittent rivers on chalk and of different ecological statuses (e.g., Westwood et al, 2020; Westwood, Teeuw, Wade, & Holmes, 2006; Westwood, Teeuw, Wade, Holmes, & Guyard, 2006). Exploring the spatial and temporal pattern of terrestrial plant colonisation in dry rivers may aid our understanding of the effects of intermittency in cool, wet temperate regions.…”

“…However, little information exists regarding the diversity and composition of terrestrial vegetation inhabiting dry riverbeds, especially in cool, wet temperate (i.e., oceanic climate) regions with previous studies grouping terrestrial plants as 'terrestrial herbs' and 'terrestrial grasses' (Holmes, 1999;Westwood et al, 2020).…”

Spatial and temporal dynamics of nitrogen exchange in an upwelling reach of a groundwater‐fed river and potential response to perturbations changing rainfall patterns under UK climate change scenarios

“…Alterations to groundwater flows and groundwater quality arising from the climate change are likely to impact on river ecology. For example in rivers associated with chalk aquifers there is evidence that low flows may result in decline of vegetation, such as Ranunculus pseudofluitans , associated with priority habitats (Westwood et al, 2020). We also know that warming may impact biogeochemistry by changing the way rivers couple and transform carbon and nutrients (Hood et al, 2017; Preiner et al, 2020), and work by Kurylyk et al (2014) and Kurylyk et al (2015) suggests that although groundwater‐fed rivers are likely to remain buffered to temperature changes in the regional groundwater, this buffering capacity may decline over time (Leach & Moore, 2019).…”