Managed Flood Effects on Beaver Pond Habitat in a Desert Riverine Ecosystem, Bill Williams River, Arizona USA

Abstract

The ecological effects of beaver in warm-desert streams are poorly documented, but potentially significant. For example, stream water and sediment budgets may be affected by increased evaporative losses and sediment retention in beaver ponds. We measured physical attributes of beaver pond and adjacent lotic habitats on a regulated Sonoran Desert stream, the Bill Williams River, after ≥11 flood-free months in Spring 2007 and Spring 2008. Neither a predicted warming of surface water as it passed through a pond nor a reduction in dissolved oxygen in ponds was consistently observed, but bed sediment sorted to finest in ponds as expected. We observed a river segment-scale downstream rise in daily minimum stream temperature that may have been influenced by the series of~100 beaver ponds present. Channel cross-sections surveyed before and after an experimental flood (peak flow 65 m 3 /s) showed net aggradation on nine of 13 cross-sections through ponds and three of seven through lotic reaches. Our results indicate that beaver affect riverine processes in warm deserts much as they do in other biomes. However, effects may be magnified in deserts through the potential for beaver to alter the stream thermal regime and water budget.

Ecology, management, and conservation implications of North American beaver(Castor canadensis)in dryland streams

“…Water temperatures in a south‐east Oregon stream were consistently slightly warmer within beaver ponds than in neighbouring unimpounded reaches (Talabere, ), but in the cool tailwaters below Alamo Dam on the Bill Williams River (AZ), Andersen et al . () found no consistent trend in water temperature within beaver ponds. It is interesting that both Lowry () and Pollock et al .…”

“…Studies monitoring beaver reintroductions in drylands have reported that beaver ponds maintained perennial standing water (see 'Geomorphology' above), but no data are available to evaluate downstream effects on discharge. In addition, construction of beaver ponds may affect stream water budgets by changing evaporative processes (Andersen et al, 2011). Research is needed to quantify the relationships between beaver dams and hydrologic processes in dryland streams.…”

“…Evidence for thermal effects of beaver dams in dryland streams is mixed. Water temperatures in a south-east Oregon stream were consistently slightly warmer within beaver ponds than in neighbouring unimpounded reaches (Talabere, 2002), but in the cool tailwaters below Alamo Dam on the Bill Williams River (AZ), Andersen et al (2011) found no consistent trend in water temperature within beaver ponds. It is interesting that both Lowry (1993) and Pollock et al (2007) observed relatively cooler water temperature immediately below beaver dams in central Oregon, presumably an effect of groundwater upwelling.…”

Vulnerability of riparian ecosystems to elevated CO2 and climate change in arid and semiarid western North America

“…Floods can damage or destroy beaver dams (Andersen & Shafroth, 2010), so larger flood magnitudes on monsoon rivers and in the northwestern United States also may reduce beaver abundance. Changes in beaver populations in turn could affect local and downstream communities, as beavers are formidable herbivores and beaver dams increase lentic habitat and reduce sediment flux (Andersen et al, 2011).…”

Assessing long‐term fish responses and short‐term solutions to flow regulation in a dryland river basin

“…flow duration, rate of increase to maximum discharge, maximum discharge rate) relate to beaver dam failure. Currently, our ability to make specific management recommendations for instituting flow events in systems with beaver populations is limited, indicating that further work is needed to understand the impact of experimental flood events on beaver dam failure Andersen et al 2011).…”