The Role of the Beaver on the Physiochemical Characteristics of Aquatic Ecosystems

There are strong and continuous interactions between hydrology, geomorphology, water chemistry and temperature in aquatic ecosystems, and they are all significant factors that influence aquatic organisms, and can be modified by beaver activity.

A) Hydrological Effects of the Beaver:

-Reduction of stream velocity (slows down the flow rate in streams)

-Decreased peak discharge and stream velocity during a run-off event, thereby reducing the potential for erosion

-Reductions in the sediment-carrying capacity of the stream, which causes sediment accumulation, which can protect areas from erosive perturbations

-Increases in the area of riparian habitat, which act as buffers against aquatic contamination

-Recharged groundwater due to elevated water table

-Enhanced water conservation due to decreased run-off efficiency

B) Water Chemistry:

-Beavers may exert considerable influence on the productivity of fresh waters by altering nutrient levels

-Naiman & Melillo (1984) found that beaver ponds stored approximately 1000 times more nitrogen (N) in sediments, per linear metre of stream channel, than riffle areas and that this was solely a function of the amount of sediment accumulated in the different habitats

-Fallen wood from trees killed by inundation and wood used in dams and lodges represent input sources of organic matter that are important to phosphorus and nitrogen dynamics of the aquatic ecosystem and represent a long-term source of nutrients to the pond water and outflow

-The anaerobic zones (without oxygen) in the sediment interstitial waters of beaver ponds may be enriched in dissolved nutrients, which stimulates increased primary production (e.g. higher algae levels were found in streams that housed beaver dams compared to streams without beavers)

-Beavers may play an important role in modifying water chemistry in regions where inputs of strong acids from atmospheric pollution are relatively high

-Smith et al. (1991) found that pH, acid neutralizing capacity (ANC), dissolved organic carbon (DOC), iron (Fe2+) and manganese (Mn2+) values were elevated, while sulphate (SO42–) and ionic forms of aluminium (Aln+) were decreased following passage of water through a beaver impoundment

-Beaver ponds also act as net annual sinks for inlet nitrate (NO3–) and silica (H4SiO4) and a net annual sources of ammonium ions (NH4+)

C) Water Temperature:

-The role of beaver dams on water temperature are somewhat inconclusive, but some patterns have been identified

-Studies have found that beaver dams in large ponds act as thermal buffers, raising downstream water temperatures slightly, and they also decrease daily fluctuations in water temperature to create a more stable environment