Does the morphology of beaver ponds alter downstream ecosystems?

Abstract

Differences among lake morphologies often explain variation in characteristics of lentic ecosystems. Although beaver ponds also vary in morphology, previous studies have not examined the effects of such variation on downstream ecosystems. This study evaluated downstream effects of multiple beaver ponds in the Colorado Rocky Mountains during one low and one high-flow year. Beaver pond morphology was described as the natural log transformed ratio of beaver dam height (which determines hydraulic head) to pond surface area and related to pond spillover phytoplankton and characteristics of the ecosystem downstream (nutrient concentrations, limiting nutrients, periphyton, benthic organic matter (BOM), and benthic invertebrate consumers). Nitrate concentration increased systematically downstream of beaver ponds, but only in the low flow year when groundwater influences predominated. Effects of beaver ponds on soluble reactive phosphorus concentration depended on pond morphology, increasing downstream of small ponds with high dams, but only during the low-flow year. In situ experiments showed that neither beaver activity nor pond morphology predicted periphyton-limiting nutrients downstream. Both periphyton biomass and BOM decreased downstream of small ponds with high dams but pond morphology did not predict abundance of invertebrate grazers or detritus-feeding consumers. While suspension feeding invertebrates increased downstream from small ponds with high dams, variation in chlorophyll a from water spilling over beaver dams did not follow a similar pattern. We conclude that the effects of beaver ponds on downstream nutrients, resources and consumers are rarely systematic, but instead depend on variation in pond morphology and on annual hydrologic variation.

Habitat engineering by beaver benefits aquatic biodiversity and ecosystem processes in agricultural streams

“…The accumulation of fine sediment and organic matter behind beaver dams is closely linked to the reduction in downstream transport and the increased input of felled or dead wood to the channel (Gurnell, 1998). Reported changes in stream or groundwater chemistry below beaver impoundments range from decreases (Correll, Jordan & Weller, 2000;Margolis, Castro & Raesly, 2001b) to increases (Klotz, 1998;Fuller & Peckarsky, 2011) in different fractions of N and P, and are typically related to increased hyporheic exchange due to longer channel residence times (Lautz, Siegel & Bauer, 2006). The reductions in N and P in our study are more substantial than often reported, but were only significant in the summer, consistent with reports by Margolis et al (2001b) and Klotz (2010).…”

Beavers alter stream macroinvertebrate communities in north‐eastern Utah

“…Even studies comparing macroinvertebrate densities between natural pools and lotic reaches have shown site-dependent effects (Herbst et al 2018;Logan and Booker, 1983). Lastly, the beaver dam itself is a habitat with a unique macroinvertebrate assemblage (Clifford, Wiley & Casey, 1993), and beaver ponds can affect macroinvertebrates downstream due to hydrologic changes altering stream temperature and nutrients (Fuller & Peckarsky, 2011a, 2011b. Lastly, the beaver dam itself is a habitat with a unique macroinvertebrate assemblage (Clifford, Wiley & Casey, 1993), and beaver ponds can affect macroinvertebrates downstream due to hydrologic changes altering stream temperature and nutrients (Fuller & Peckarsky, 2011a, 2011b.…”

Impacts of beaver dams on channel hydraulics and substrate characteristics in a mountain stream

“…A majority of results in the literature associated with changes in hydraulic characteristics come from measurements upstream and downstream of dams, which does not allow for direct comparison with our study. Meentemeyer & Butler (1999) Waddington, 1990), increases in sediment storage (Butler & Malanson, 1995Green & Westbrook, 2009), and influences on downstream aquatic ecology (Fuller & Peckarsky, 2011) may also differ.…”

“…Overall, it is evident that beaver dams introduce variability in depth and velocity values between reaches and that the variability cannot be solely attributed to natural differences in channel geometry and slope. These three comparisons also indicate that other impacts related to channel hydraulics, such as improvements in fish habitat heterogeneity (Kemp et al , ), riparian corridor structure and productivity (Westbrook et al , ), alterations in hydrology (Nyssen et al , ; Westbrook et al , ; Woo & Waddington, ), increases in sediment storage (Butler & Malanson, ; Green & Westbrook, ), and influences on downstream aquatic ecology (Fuller & Peckarsky, ) may also differ.…”