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Ecosystem engineers: Biofilms and the ontogeny of glacier floodplain ecosystems

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Abstract The term “ecosystem engineering” emerged in the 1990s and is commonly used to refer to the activities of larger organisms like beavers and trees in rivers and streams. The focus on larger organisms may be motivated by their more visible effects on the environment. However, while it may be intuitive to suggest that the bigger the organism the bigger its potential engineering effects, there may be microscale organisms who through their number rather than their size can act simultaneously to result in significant impacts. This paper considers biofilms as a candidate ecosystem engineer. It is well known that biofilms play an important role in enriching the sediment matrix of nutrients and in stabilizing sediments. Biofilms may be critical in increasing the habitability of the benthic substratum. In this paper, we consider their potential role in the ontogeny of ecosystems in recently deglaciated terrain. We show how by changing sediment stoichiometry, decreasing sediment erodibility, and reducing surface sediment permeability they may promote primary succession on lateral, incised terraces, which are less perturbed compared with the main active floodplain. This article is categorized under: Water and Life > Nature of Freshwater Ecosystems Science of Water > Water and Environmental Change
Biofilm development stages. From planktonic phase, microbes deposit and attach on the surface and start producing extracellular polymeric substances (EPS). With the secretion of EPS substances, the biofilm enters its growth stage and microcolonies are formed. When the biofilm matures, it may reach a “mushroom” structure where slough of biofilm will later be affected by erosion forces and dispersal. This dispersal stage will link together local communities and form biofilm metacommunities
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Floodplain ontogeny. (a) Floodplain at time to biofilm is no longer developed; (b) Floodplain at time t1 biofilm is developing and coalescing in bigger colonies in abandoned channels, commonly on terraces; (c) floodplain at time t2. There is vegetation where there were biofilms; (d) floodplain at time t3. Biofilms develop in the new abandoned channels; (e) floodplain at time t4. New branches are now disconnected; (f) floodplain at time t5. There is vegetation where were biofilms; (g) floodplain at time t6. Vegetation has colonized more floodplain space
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(a) Biofilm formation in a stream on a terrace in the Val d'Otemma, Valais, Switzerland; (b) a biofilm mat that has formed in a stream in the Val d'Otemma supplied with hillslope‐sourced groundwater showing successional colonization of the channel margin by vegetation. The stream is on a terrace about 1 m above the morphodynamically active channel. Note to the right there are stable bar surfaces, also on the terrace, but largely void of primary production due to severe moisture limitations related to well‐drained glaciogenic sediments
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(a) Ideal model where disturbances do not occur during biofilm development leading to an exponential increase of habitability; (b) conceptual model of the variation in habitability in relation with stream discharge (Q) in the active floodplain. The black dashed line is the discharge (Q), the solid red line is the habitability, the blue dashed line represents the case in which habitability is increased during the winter time; (c) Conceptual model of the variation in habitability in relation with stream discharge (Q) in the abandoned channels
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The Valsorey floodplain (Valais, Switzerland) in October 2018. The floodplain shows clearly primary succession patterns, which are confined to terraces (red lines mark the edges) on both sides of the river that are not reworked by the main braidplain (a,b). Well‐developed and visible biofilm communities tend to be restricted to channels located on terraces (c) because disturbances are not too frequent to destroy the mats
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Transport frequency in an Alpine braided system showing the frequency of disturbances for 15 surveys of a river over a 21‐day period (after Bakker et al., ). The x‐and y‐scales are given in meters
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Science of Water > Water and Environmental Change
Water and Life > Nature of Freshwater Ecosystems

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