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Restoring Western Headwater Streams with Low-Tech Process-Based Methods: A Review of the Science and Case Study Results, Challenges and Opportunities
This report reviews published research and unpublished case study information on the effects ofrestoring incised and degraded headwater streams in western states with low-tech processbased restoration methods (LTPBR). LTPBR is a subset of process-based restoration (PBR) that seeks to re-establish natural stream processes by reconnecting incised streams with their floodplains and adjacent wetlands so that more frequent inundation of the floodplain occurs. Projects involve the use of simple, temporary, hand-built wood and rock structures that mimic
natural beaver structures, acting as speed bumps that capture sediments to aggrade the stream. LTPBR approaches are substantially less expensive than form-based stream restoration approaches that employ heavy equipment.i This approach is appealing in part because low project costs enable implementation at a scale that can respond to the extent of floodplain alteration, which is estimated at 45% of headwaters streams in Colorado. ii Negative effects of disconnected floodplains include lower groundwater tables, lower summer base flows,
warmer water temperatures, and substantial loss of riparian habitat.
Within the State of Maryland, the potential water quality benefits of beaver are not recognized as contributing to regulatory-mandated pollution reductions. Therefore, jurisdictions lack a regulatory incentive to either encourage beaver colonization or manage and protect existing beaver habitat. Such an incentive is important, as conflicts between human and beaver habitat regularly arise. While beaver habitat often increases the groundwater table and the wetted extent of a stream system, this is not always welcomed by homeowners and can result in beaver being trapped out, with beaver dams dismantled. If beaver ponds were a recognized BMP to improve water quality, it would assist local jurisdictions with the development of beaver habitat conservation programs via easements and adaptive management. Rather than living on top of nature and replicating nature’s original ecosystem engineers with significant amounts of tax dollars, citizens could live with nature allowing tax dollars to go further, and implement more ecological restoration.
The fluxes and concentrations of materials from two contiguous second-order watersheds in the Coastal Plain of Maryland, U.S.A. were measured for six years prior to and six years subsequent to the formation of a 1.25 ha beaver pond near the bottom of one of the watersheds. The watersheds have a clay aquiclude and were equipped with V-notch weirs and continuous volume-integrating water samplers. The beaver pond reduced annual discharge of water, total-N, total-P, dissolved silicate, TOC, and TSS by 8, 18, 21, 32, 28, and 27%, respectively. Most of the total-N reduction was due to increased retention of nitrate in the winter and spring and TON in the winter and summer. Most of the total-P reduction was the result of retention of both TPi and TOP in the winter and summer. Dissolved silicate retention peaked in the spring, while TOC and TSS retention peaked in the winter. Prior to the formation of the beaver pond, concentrations of TON, TPi, TOP, TOC, and TSS had highly significant correlations with stream discharge, especially in the winter, but subsequent to the pond there was little or no relationship between these concentrations and stream discharge. However, concentrations of nitrate in the spring and ammonium in the summer were highly correlated with stream discharge both before and after the formation of the beaver pond and regressions of discharge versus concentrations of these nutrients explained more of the variation in concentrations after the formation of the pond.
Hydrologic extremes dominate chemical exports from riparian zones and dictate water quality in major river systems. Yet, changes in land use and ecosystem services alongside growing climate variability are altering hydrologic extremes and their coupled impacts on riverine water quality. In the western U.S., warming temperatures and intensified aridification are increasingly paired with the expanding range of the American beaver—and their dams, which transform hydrologic and biogeochemical cycles in riparian systems. Here, we show that beaver dams overshadow climatic hydrologic extremes in their effects on water residence time and oxygen and nitrogen fluxes in the riparian subsurface. In a mountainous watershed in Colorado, U.S.A., we find that the increase in riparian hydraulic gradients imposed by a beaver dam is 10.7–13.3 times greater than seasonal hydrologic extremes. The massive hydraulic gradient increases hyporheic nitrate removal by 44.2% relative to seasonal extremes alone. A drier, hotter climate in the western U.S. will further expand the range of beavers and magnify their impacts on watershed hydrology and biogeochemistry, illustrating that ecosystem feedbacks to climate change will alter water quality in river systems.
Rivers and streams, when fully connected to their floodplains, are naturally resilient systems that are increasingly part of the conversation on nature-based climate solutions. Reconnecting waterways to their floodplains improves water quality and quantity, supports biodiversity and sensitive species conservation, increases flood, drought and fire resiliency, and bolsters carbon sequestration. But, while the importance of river restoration is clear, beaver-based restoration—for example, strategic coexistence, relocation, and mimicry—remains an underutilized strategy despite ample data demonstrating its efficacy. Climate-driven disturbances are actively pushing streams into increasingly degraded states, and the window of opportunity for restoration will not stay open forever. Therefore, now is the perfect time to apply the science of beaver-based low-tech process-based stream restoration to support building climate resilience across the landscape. Not every stream will be a good candidate for beaver-based restoration, but we have the tools to know which ones are. Let us use them.
A Review of Two Novel Water-Tight Beaver Dam Analogs (WTBDA) to Restore Eroded Seasonal Creeks in Drain Tile Zones to Permanent Beaver Wetlands
Reducing nutrient runoff in streams is an important task to reduce algae blooms and associated environmental damage in large waterbodies. Beaver Dam Analogs (WTBDA) are an means to address this problem. These Water Tight Beaver Dam Analogs (WTBDA) present a novel approach to this technique that also aim to restore eroded seasonal creeks to perennial wetlands.
Published in Chesapeake Bay Magazine in March 2021, the article highlights various industry professionals who attended BeaverCON 2020. Professionals in stream restoration, water control devices, and environmental journalism were interviewed for this article, discussing successes related to coexisting with beavers. Several important beaver-related studies are mentioned.
A synthesis of scientific literature and our current level of: 1) understanding of the relationship between habitat quantity and quality and salmon production, 2) quantify the improvements in salmon production and survival that can be expected with different restoration actions, and 3) use models to help identify habitat factors limiting production and quantify population-level responses to restoration.
Study on how beavers alter freshwater ecosystems and increase aquatic production to determine how these changes influence the magnitude and lateral dispersal of aquatic nutrients into terrestrial ecosystems
Beaver activity (i.e., damming of streamflow) holds significant potential to impact water quality, specifically in-stream nutrient processing.
A review by the University of Southampton of how the reintroduction of beaver will affect fish in Scotalnd
Review of research about the positive and negative effects of beaver towards fish
Study on how beaver dams affect coastal marshes and their Phosphorus and pH levels
This study quantifies the impacts of beaver on stream hydrologic and temperature regimes, and highlights the importance of understanding the spatial and temporal scales of those impacts. We explored the impacts of beaver dams on hydrologic and temperature regimes at different spatial and temporal scales within a mountain stream in northern Utah over a 3-year period spanning pre- and post-beaver colonization.
The Effect of Beaver (Castor canadensis) Dam Removal on Total phosphorus Concentration in Taylor Creek and Wetland, South Lake Tahoe, California
The presence of beaver ponds in Taylor Creek could improve water quality by reducing the phosphorus load entering Lake Tahoe.
In-depth report on how beaver could provide benefits to local residents and visitors well into the millions of dollars per year in Utah.
A 44 minute Baltimore Sun podcast by Dan Rodricks on beavers and their impact. He interviews beaver experts Frances Backhouse, Mike Callahan, and Scott McGill on the history, present management and future of beavers in North America. Recorded in Feb. 2, 2018