Busy Beavers
The Turbidity Signature Of Ecosystem Engineers At Work
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https://doi.org/10.1002/hyp.70661 <-- shared paper
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H/T @Alan Puttock | Lecturer in Applied Nature Based Solutions (Water) Geography at the University of Exeter. Ecohydrology, NbS, Natural Flood Management, Hydrological Extremes, Beavers, Species Reintroduction and Landscape Restoration.
“Beavers are the quintessential ecosystem engineers. In slow-flowing streams, they create complex wetlands with ponds by building dams and canals that can positively impact biodiversity, hydrology and water quality. These activities can interchangeably capture or release sediment along the watercourse. To date this has not been quantified at the resolution of rainfall events or beaver activity. This study used 15-min frequency, sustained monitoring upstream and downstream of a newly establishing beaver wetland to measure episodic changes in water turbidity at an event resolution. Monitoring showed no significant differences between upstream and downstream turbidity over 160 days when the first pair of beavers, known not to be building dams or canals, were resident. Shortly after introduction of another beaver pair, however, dam building, burrows and canal excavations were quickly observed, resulting in the creation of a complex beaver wetland between 2021 and 2024. Monitoring over 375 days during this period showed significant differences. Downstream turbidity was significantly higher overall than upstream: 13.1 Nephelometric Turbidity Units (NTU) compared to 4.2 NTU. Stochastic spikes in downstream turbidity during the study period not recorded upstream were associated with dam building and burrowing. Overall, there was no significant difference in turbidity loads, which was at least partially explained by a reduction in discharge downstream, particularly in higher flows, during the dam building period. This demonstrates a complex system with the trapping of influent sediment, the storing of water and the periodic release of beaver wetland sediment leading to net balance in loads. These results help provide context for other studies which have used temporally discrete sampling campaigns rather than continuous high-frequency monitoring. They provide a unique insight into the downstream impacts of a rapidly developing beaver wetland over its first three and a half years in a landscape that hasn’t had beavers for over 400 years…
[The authors] present[ed] results from high-frequency turbidity monitoring above and below a developing beaver wetland. Following the introduction of a hydromorphologically active beaver pair, that quickly built dams, canals and burrows, overall water turbidity became significantly higher downstream than upstream. There was no significant difference in turbidity loads. During the period of dam building, stream water level was significantly reduced downstream of the developing beaver wetland complex. The reduction in discharge partially explained the increase in turbidity despite no significant change in loads. A detailed timeline of turbidity measurements with rainfall events revealed this effect was overlain by stochastic peaks in downstream turbidity coinciding with beaver excavation and dam building activity. The conceptual model proposed comprises: a general increase in turbidity with catchment rainfall-stage response; a reduction in non-baseflow level downstream with the activation of increased water storage and flow pathways; the episodic release of sediment from beaver activity directly as burrowing and excavation and indirectly as new flow pathways are activated; the balancing of load by the settling and storage of solids.
This work has revealed that in enabling the well-published range of ecosystem services attributed to them, beavers produce a unique and dynamic turbidity signature in the streams they inhabit.
This study compared high-frequency turbidity measurements at the inflow and outflow of one establishing beaver wetland in a fenced enclosure. Future work can build on these results using similar high-frequency monitoring in beaver wetlands encompassing a range of maturity states and catchment characteristics as well as trialling approaches such as turbidity hysteresis to explore in more detail transport dynamics…”
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