Beaver Ponds Research Articles

Large multi-decade beaver ponding changes in the subarctic Hudson Bay Lowlands, Canada observed using satellite remote sensing

Beavers strongly impact hydrology and ecosystems through their widespread dam building that creates ponds and wetlands. Monitoring the relative abundance of beavers and their waterbodies is needed to assess these effects and factors influencing population levels. However, the ability to do this over vast, remote regions is limited with conventional aerial or field-based surveying. To address this challenge, we developed a satellite remote sensing method to track beaver ponding changes over multiple decades and applied it to a 5127 km2 region of the coastal Hudson Bay Lowlands in Manitoba, Canada. Annual, sub-pixel surface water mapping using 30 m resolution Landsat satellite data, combined with a spatial database of beaver dams, permitted the mapping of 37 year (1985–2021) beaver ponding dynamics. We identified 1714 beaver dams and 1085 beaver pond complexes covering 31 km2, indicating that beavers have an important influence on stream hydrology in this high subarctic landscape. The total area of ponding decreased by 53% from 1986–1989 and by 80% by 1995, and then gradually recovered to initial levels by 2015. The early, steep drop in beaver ponding corresponded to a 13% decline in regional surface water area, while a similar wetness decline during 2015–2018 resulted in little change in beaver ponding. We suggest that strong beaver ponding dynamics were likely caused by the interaction between streamflow levels and beaver populations living near their northern range limit and cold tolerance. The pond mapping method can be applied to other regions if the long-term distribution of beaver dams is known, and ponds are large enough to be identified using a Landsat sub-pixel approach.

Short-term dynamics of beaver dam flow states

Beavers (Castor canadensis and C. fiber) build dams that modify catchment and pond water balances, and it has been suggested that they can be a nature-based solution for reducing flood hydrographs, enhancing low flow hydrographs and restoring hydrological functioning of degraded streams. How water moves through a beaver dam is determined by its flow state (e.g., overflow, underflow). However, current conceptual models only consider flow state as changing over the beaver site occupation-abandonment cycle. To assess whether flow state changes at shorter timescales and identify possible triggers (e.g., rainfall, animals), we integrated camera trap imagery, machine learning, water level measurements, and hydrometeorological data at beaver dams in a montane peatland in the Canadian Rocky Mountains. Contrary to current models, we found that flow states changed frequently, changing a maximum 12 times during the 139-day study period, but that changes had limited synchronicity amongst the dams in the same stream. More than two-thirds of the changes coincided with rainfall events. We observed no changes in flow state in response to beaver activity or wildlife crossings perhaps due to the camera positioning. Our findings augment the long-term oriented framework, which links changes to the occupancy cycle of a beaver pond and frequent and hydrological-driven changes. To develop realistic predictions of hydrological impacts of beaver dams, ecohydrological models should update their representation of the influence of beaver dams to include short-term dynamism of flow states and potential triggers. Our study advances the understanding of the important, yet understudied, role of beaver dams in stream restoration and climate change initiatives.

Beaver dam analogs did not improve beaver translocation outcomes in a desert river

Stream restoration programs employ beaver‐related restoration techniques, including beaver translocations and installation of beaver dam analogs (BDA), to create complex in‐stream habitat. We investigated whether BDA installations improved the probability of translocated beavers surviving and colonizing a section of a degraded desert river. We translocated beavers fitted with tracking devices to the Price River, Utah, United States, for 2 years before and after BDAs were installed. We monitored survival and site fidelity of beavers to estimate apparent survival (φ), using model selection to evaluate models with BDA, flow, and other factors hypothesized to relate to apparent survival. We found similar apparent survival 8 weeks post‐release of pre‐BDA (φ = 0.50 ± 0.08 SE) and post‐BDA beavers (φ = 0.41 ± 0.06 SE). There were 15 predator‐caused mortalities and 39 beavers emigrated out of the study site. Top models indicated apparent survival was negatively related to mean flow. Of the 70 BDAs constructed, beaver activity was detected on only two structures and the number of intact natural dams decreased due to monsoon floods. Our results suggest BDAs may not improve survival and site fidelity of translocated beavers in desert river systems. Instead, the dynamic flow of desert rivers and negative relationship between flow and apparent survival suggest the timing of release may be an important consideration for successful beaver translocation. Additional research is needed to understand how habitat, food availability, individual behavior, and resident conspecifics influence beaver translocation success.

Does restoring apex predators to food webs restore ecosystems? Large carnivores in Yellowstone as a model system

AbstractModification of food webs is a frequent cause of shifts in ecosystem states that resist reversal when the food web is restored to its original condition. We used the restoration of the large carnivore guild including gray wolves (Canis lupis), cougars (Felis concolor), and grizzly bears (Ursus arctos horribilis) to the northern range of Yellowstone National Park as a model system to understand how ecosystems might resist reconfiguration after the restoration of apex predators to the food web. The absence of wolves, cougars, and grizzly bears for nearly a century from the northern range was the primary cause of dramatic changes in riparian plant communities. Willows (Salix spp.) were suppressed in height by intense browsing by the dominant herbivore, elk (Cervus canadensis). The loss of activity by beavers (Castor canadensis) coincided with the loss of tall willows. We hypothesized that intense elk browsing interrupted the mutualism between willow and beavers: ecosystem engineering by beavers was a critical component of willow habitat and tall willows were a critical component of habitat for beavers. This interruption made riparian communities resilient to the disturbance caused by the restoration of apex predators. We hypothesized further that reductions in elk browsing attributable to reductions in elk population size were not sufficient to prevent the suppression of willow growth. To test these hypotheses, we conducted a 20‐year, factorial experiment that crossed simulated beaver dams with the exclusion of browsing. We found that willows grew to heights expected for restored communities only in the presence of dams and reduced browsing. Willows experiencing ambient conditions remained well below this expectation. We found no difference in heights or growth rates of willows in experimental controls and willows in 21 randomly chosen sites, confirming that the results of the experiment were representative of range‐wide conditions. A reorganized community of large herbivores was implicated in the suppression of willow growth. We conclude that the restoration of large carnivores to the food web failed to restore riparian plant communities on Yellowstone's northern range, supporting the hypothesis that this ecosystem is in an alternative stable state caused primarily by the extirpation of apex predators during the early 20th century.

Ontogeny of a threatened freshwater minnow: Implications for conservation

AbstractInvestigating the ontogeny of threatened freshwater fishes is vital for designing future conservation actions that will increase the potential of species' persistence. This study provides a detailed description of the early life stages of a threatened freshwater fish species, the Evrotas minnow Pelasgus laconicus, which occupies aquatic ecosystems with extreme seasonal hydrological variation. The study of the embryonic and juvenile stages was conducted in vivo using light microscopy from eggs obtained from acclimatized wild spawners at 20 ± 1°C. Fertilized eggs were spherical and transparent with a mean diameter of 1.24 ± 0.06 mm and the average length of free embryos at hatching was 3.85 mm NL (notochord length). The main morphological changes observed are related to the absorption of the yolk, the increase and distribution of the melanophores and the sequential development of the fins. In conclusion, the Evrotas minnow was identified as a multiple spawner, exhibiting a protracted reproductive period (March to August), a particularly short egg‐hatching period (5–6 days), a short free embryo stage and a rapid onset of exogenous feeding (2 days). The conservation implications of our study, such as safety stock creation, population reintroduction, conservation of fish refugia and breeding habitats and beaver dam analogues, are discussed.

Сопоставление эффективности использования современных геодезических методов в изучении последствий бобровой деятельности на малых реках

Multiple increase in the beaver population on the East European Plain has led to the appearance of a large number of beaver dams and ponds on small rivers. At present, the problem of regulating small rivers in this region remains poorly studied due to the above circumstances. This study presents the results of a comparison of modern geodetic methods obtained using an electronic total station, GNSS equipment and UAVs. The small river Morkvashinka, flowing along the northern tip of the Volga Upland, was chosen as the object of the study. The spatial coordinates and altitudes measured by the GNSS receiver generally agree well with the tacheometric survey data. The height difference is 0.5 cm (standard deviation – 0.07). However, the main disadvantage of an electronic total station, which limits its use for surveying linearly elongated objects and small river valleys, is the lack of direct visibility of the objects being photographed from the device due to the highly dissected territory, the tortuosity of the river and dense vegetation. Using orthophoto and digital terrain models obtained from unmanned aerial vehicles, it is not always possible to accurately determine the border of the coastline, as well as the absolute heights of the dam, floodplain, terraces, water edge, channel marks (pond depth) due to dense vegetation. However, the river bed and floodplain, beaver dams and ponds are clearly visible on them.

An overview of the current state of the beaver’s environmental activity

A review of scientific publications devoted to the study of the impact of beaver foraging and construction activities on the plant communities of small rivers in different natural zones has been conducted. Based on the analysis of publications devoted to the study of the beaver's environmental activity, its key role in the successional processes of phytocenoses of riverine biotopes in all natural zones within the native and acquired range is noted. The stages of succession transformations initiated by the beaver's vital activity are considered. The degree of succession transformations depends, first of all, on the density of populations and their stages of maturity. The successions are highly intensive, multidirectional and do not reach the final stage, but are concentrated in the floodplains of small rivers and streams, in the coastal strip of other reservoirs. The vital activity of beavers determines the floristic, faunal, and ecologicaltopological diversity of coastal biogeocenoses. An increase in the proportion of groups of aquatic and wetland plant species was noted, and an increase in biological diversity was revealed in the beaver pond backup zone, regardless of zonal factors. However, being strongly transformed, the coastal vegetation remains zonally conditioned, does not become azonal.

Beaver-related restoration: An opportunity for sandy lowland streams in a human-dominated landscape

The expansion of beavers into human-dominated landscapes can help improve the ecological status of degraded streams. This study aimed to assess the changes in the ecological status of a degraded sandy-bottom stream under the influence of processes generated by the activity of a European beaver. We assumed that the processes in the beaver dam-and-pond complex significantly improved the physical, chemical, and bacteriological properties of water and improved the ecological status of a small lowland stream in a human-dominated landscape. To achieve these objectives, water for quality assessment, benthic invertebrates, and fish samples were collected, and the forms of land use and the natural values of the stream were analysed. In the upstream zone of the sandy-bottom stream flowing in a human-dominated landscape, the inflow of pollutants caused a significant reduction in water quality. The amount of nutrients was high and the amount of dissolved oxygen was low. Similarly, the number of meso- and psychrophilic bacteria was significantly higher than in the reference stream. The building activity of beavers initiated a series of positive environmental changes, and beaver ponds improved the self-purification of water in a polluted stream. In the lower part of the studied stream, after the stream passed through the beaver wetland system, the water quality improved, which was indicated by a significant improvement in physicochemical, microbiological, and biotic indicators, that is based on macrozoobenthos and fish. By constructing dams, beavers flooded large areas and created habitats for plant and animal species associated with wetlands, including amphibians, birds, and mammals. The improvement of the ecological status of the stream, combined with the preservation and restoration of wetland habitats in the catchment area, enables the use of ecosystem services provided by the streams in the human-dominated landscape and their surroundings.

Emergence of Amphibious Insects from an Old Beaver Pond in the Upper Khoper Valley under Conditions of the Forest Steppe

Emergence of Amphibious Insects from an Old Beaver Pond in the Upper Khoper Valley under Conditions of the Forest Steppe

Intermittent Prairie Streams in the Northern Great Plains: A Case of an Undervalued Ecosystem

Small (<15 m wide), intermittent prairie streams in western South Dakota, a semiarid part of the northern United States, are undervalued ecosystems because they do not exemplify the values of classic, flowing streams. However, they are valuable as wildlife corridors, aquatic habitat for drought-adapted species, and support of local grazing economies. We surveyed 90 streams in 2018–2019, collecting data on geomorphic, water chemistry, and biological properties, focusing on vegetation and grazing impacts. We developed an approach for categorizing streams by landscape position and flow regime to facilitate appropriate land management and stream restoration actions. The result was a published landowner guide to provide information on low-tech riparian management and restoration options of the four stream types we categorized. The headwaters streams and woody draws with drainage areas <26 km2 are the most abundant types and exemplify the issues described above. Large rivers, despite drainage areas exceeding 260 km2 can go dry. Management issues include invasive plant species, lack of woody riparian establishment, poor water quality, overgrazing, channel incision, and water stress from climate change. The most cost-effective management practices involve rotational grazing and practices that reduce cattle impacts. More recently, beaver dam analogs have been installed and beaver reintroduction is being considered along with reestablishment of native bison herds in place of cattle. Intermittent prairie streams present an excellent case study of an undervalued ecosystem, illustrating the challenges and opportunities of such systems. Engagement of grazing landowners can improve stewardship of these systems.

The positive response of small terrestrial and semi-aquatic mammals to beaver damming

Ecosystem engineers, such as the Eurasian beaver, Castor fiber, transform habitats, thereby creating favourable conditions for other species and increasing biodiversity. Multiple studies have revealed that beaver ponds are valuable habitats for invertebrates and vertebrates, including other mammals, but the impact of watercourse damming on the fauna of small terrestrial rodents and shrews has not yet been documented. We tested the hypothesis that the presence of beaver dams and consequent flooding enrich the small mammal assemblage both quantitatively and qualitatively. We live-trapped small mammals at nine beaver-modified sites on 300-metre transects alongside dammed watercourses, starting from the dam through to the pond to the sections with unmodified lotic conditions. The abundance and species richness of trapped small mammals were highest near the dams and declined with distance. Additionally, five out of 12 trapped species significantly decreased their abundance with linear distance along the shoreline from the dam and none revealed the opposite trend. Four species were more abundant on plots subjected to beaver-related inundation (especially Sorex minutus and Micromys minutus), while none were present solely on uninundated plots. Among the semi-aquatic species, two water shrews benefited from beaver activity in different ways. Neomys milleri occurred only in flooded sections, while N. fodiens preferred unmodified sections, but was the most numerous species closer to the dams, as per known patterns of competitive displacement observed in Central Europe. An important factor affecting small mammals, the herbaceous layer cover, appeared to be interdependent with damming. We provide the first unequivocal evidence that the presence of beaver dams facilitate the abundance and diversity of small mammals, presumably due to increased food abundance, availability of shelter and habitat connectivity. Beaver-created wetlands may act as potential refuges for species most susceptible to the consequences of anthropogenic climate change.

Population dynamics of the threatened Oregon spotted frog before and after drought mitigation

AbstractAmphibians are among the most sensitive taxa to climate change, and species inhabiting arid and semiarid landscapes at the extremes of their range are especially vulnerable to drought. The Jack Creek, Oregon, USA, population of Oregon spotted frogs (Rana pretiosa) faces unique challenges because it occupies the highest elevation site in the species' extant range and one that has been transformed by loss of American beavers (Castor canadensis), which historically maintained open water. We evaluated the effects of drought mitigation (addition of excavated ponds) on relationships between local and regional water availability, inactive legacy beaver dams, and Oregon spotted frog population dynamics in the Jack Creek system. We conducted egg mass surveys and capture‐mark‐recapture sampling at a treatment reach with excavated ponds and 3 reference reaches over 13 years; surveys spanned a period before and after pond excavation at the treatment and 1 primary comparison reference reach. We analyzed data using a combination of robust design capture‐mark‐recapture estimators and generalized linear mixed models to characterize population dynamics. Adult Oregon spotted frog survival was approximately 19.5% higher at the treatment reach than the primary reference reach during the study period. Annual survival was most strongly associated with late summer vegetation greenness, a proxy for water availability, and males had higher survival than females. Among the 4 study reaches, the treatment reach consistently had higher late summer vegetation greenness, and the hydrology functioned more independently of regional precipitation patterns relative to the reference reaches; however, these dynamics were not linked to pond excavation. Breeding was concentrated in 2 legacy beaver ponds that were deepened by excavation during the study compared to an unexcavated beaver pond, 2 excavated ponds without legacy beaver dams, and 9 reference ponds. These results point to the benefit of enhancing existing beaver structures and indicate that management actions aimed at maintaining surface water for breeding in spring and saturated soils and ponded water for adults in late summer would benefit this unique population of Oregon spotted frogs in the face of drought.

Pro-ecological and conservation activities are not always beneficial to nature: a case study of two lowland streams in Central Europe

Since 1990 and in particular, after the implementation of the Water Frame Directive, many positive effects of pro-ecological projects are evident; unfortunately, examples of adverse effects have also been observed. This study aims to indicate how some ill-considered actions, called “pro-ecological”, may lead to habitat degradation and the disappearance of valuable hydrobiont species. Two watercourses, representing the lowland gravel stream and sandy stream type, were selected for the study. Literature indicated that in the past, these watercourses were characterized by an excellent ecological status and the presence of valuable rheophilic fauna and flora. Environmental parameters were recorded, macroinvertebrates and ichthyofauna were sampled and analyzed, and finally, indexes were calculated. The results were compared with literature data. In the course of studies conducted in 2011–2015, drastic habitat deterioration and extensive changes in the species structure of ichthyofauna and aquatic invertebrates were observed. Changes in the Smolnica stream have been caused by the three retention basins constructed in 2000, along the lower and middle course; while in Kiszewko, however, the factor for habitat deterioration was connected with the excessive expansion of the Eurasian beaver (Castor fiber), which created a beaver pond 20 m in width, with impoundment elevations of up to 2 m.

Comparing Sediment Microbial Communities of Arctic Beaver Ponds to Tundra Lakes and Streams

AbstractIn recent decades the habitat of North American beaver (Castor canadensis) has expanded from boreal forests into Arctic tundra ecosystems. Beaver ponds in Arctic watersheds are known to alter stream biogeochemistry, which is likely coupled with changes in the activity and composition of microbial communities inhabiting beaver pond sediments. We investigated bacterial, archaeal, and fungal communities in beaver pond sediments along tundra streams in northwestern Alaska (AK), USA and compared them to those of tundra lakes and streams in north‐central Alaska that are unimpacted by beavers. β‐glucosidase activity assays indicated higher cellulose degradation potential in beaver ponds than in unimpacted streams and lakes within a watershed absent of beavers. Beta diversity analyses showed that dominant lineages of bacteria and archaea in beaver ponds differed from those in tundra lakes and streams, but dominant fungal lineages did not differ between these sample types. Beaver pond sediments displayed lower relative abundances of Crenarchaeota and Euryarchaeota archaea and of bacteria from typically anaerobic taxonomic groups, suggesting differences in rates of fermentative organic matter (OM) breakdown, syntrophy, and methane generation. Beaver ponds also displayed low relative abundances of Chytridiomycota (putative non‐symbiotic) fungi and high relative abundances of ectomycorrhizal (plant symbionts) Basidiomycota fungi, suggesting differences in the occurrence of plant and fungi mutualistic interactions. Beaver ponds also featured microbes with taxonomic identities typically associated with the cycling of nitrogen and sulfur compounds in higher relative abundances than tundra lakes and streams. These findings help clarify the microbiological implications of beavers expanding into high latitude regions.

Channel Gradient as a Factor in the Distribution of Beaver Dams and Ponds on Small Rivers: A Case Study in the Northern Extremity of the Volga Upland, the East European Plain

A very noticeable increase in the beaver population (mainly the Eurasian beaver (Castor fiber L.)) in the East European Plain since the end of the 20th century through reintroduction contributed to the emergence of a large number of beaver dams and ponds, which resulted in the transformation of the channels and the hydrological regime of small rivers. In this paper, for the first time in the Middle Volga region, regularities in the distribution of beaver dams and ponds on small rivers were revealed based on a topographic survey of the river channel, regulated by beaver activity in recent decades. The materials of the paper were obtained during field (geodetic) work in August and September of 2022 in the valleys of two small rivers typical for the north of the Volga Upland, Morkváshinka River (16.6 km) and Morkváshka River (7.8 km), with subsequent statistical processing. According to the results obtained, all the dams we encountered were located in the sections of their channels with relatively small (up to 1%) and medium (1–3%) average gradients. In the upper reaches of the rivers, the expansion of beaver activity is limited to the large gradients of their channels. Along the entire length, there is an alternation of sectors with a “natural” (not regulated by beavers) channel and a cascade of beaver ponds. Drained (at the time of the survey) sectors without dams, as well as those with preserved and destroyed dams, were also identified on the Morkváshinka River. On the whole, 26–48% of the length of the studied rivers has been transformed by beaver activity. The average number of dams per kilometer of the watercourse is 3.7–5.1. The most favorable channel gradients for beaver activity are 3.6–16.6 m/km, or 0.36–1.66%. The average gradient of the channel, above which no beaver dams and related ponds were found in these rivers, is 30 m/km, or 3%. An increase in the channel gradient upstream of the rivers is reflected in the size of beaver dams and ponds. The beaver dams and ponds are slightly larger in the sections of the rivers with a relatively small average gradient than in the sections with a medium average gradient of the channel.

Do beaver ponds increase methane emissions along Arctic tundra streams?

Beaver engineering in the Arctic tundra induces hydrologic and geomorphic changes that are favorable to methane (CH4) production. Beaver-mediated methane emissions are driven by inundation of existing vegetation, conversion from lotic to lentic systems, accumulation of organic rich sediments, elevated water tables, anaerobic conditions, and thawing permafrost. Ground-based measurements of CH4 emissions from beaver ponds in permafrost landscapes are scarce, but hyperspectral remote sensing data (AVIRIS-NG) permit mapping of ‘hotspots’ thought to represent locations of high CH4 emission. We surveyed a 429.5 km2 area in Northwestern Alaska using hyperspectral airborne imaging spectroscopy at ∼5 m pixel resolution (14.7 million observations) to examine spatial relationships between CH4 hotspots and 118 beaver ponds. AVIRIS-NG CH4 hotspots covered 0.539% (2.3 km2) of the study area, and were concentrated within 30 m of waterbodies. Comparing beaver ponds to all non-beaver waterbodies (including waterbodies >450 m from beaver-affected water), we found significantly greater CH4 hotspot occurrences around beaver ponds, extending to a distance of 60 m. We found a 51% greater CH4 hotspot occurrence ratio around beaver ponds relative to nearby non-beaver waterbodies. Dammed lake outlets showed no significant differences in CH4 hotspot ratios compared to non-beaver lakes, likely due to little change in inundation extent. The enhancement in AVIRIS-NG CH4 hotspots adjacent to beaver ponds is an example of a new disturbance regime, wrought by an ecosystem engineer, accelerating the effects of climate change in the Arctic. As beavers continue to expand into the Arctic and reshape lowland ecosystems, we expect continued wetland creation, permafrost thaw and alteration of the Arctic carbon cycle, as well as myriad physical and biological changes.

Beavers ecosystem altering: Influence of beaver dams on aquatic invertebrates in newly created beavers ponds and small mountain river

Beaver-created ponds constitute an important element of small water retention in forest catchments and preserving biodiversity as breeding sites for vertebrates and invertebrates. In many areas, these habitats disappear as a result of drainage melioration, drainage formed from agricultural and developmental needs, and liquidation by littering and backfilling. This study was carried out from 2017 to 2019 to understand the transformations of river valley as a result of the beaver activity in the context of newly created ponds and mountain stream and to assess the changes and biodiversity. Beavers modified in-stream habitat by constructing dams, thus creating a series of interconnected dam ponds. Organic matter retention was higher in beaver ponds relative to unmodified river section. In beaver ponds, the invertebrate aquatic assemblages was highly variable. A total of 56 taxa were identified, and significant seasonal variability of benthos assemblages. The values of diversity indices confirmed the instability of benthos assemblage in beaver ponds (variability of species amongst years and sites), which may be related to the short period of their existence. Lotic macroinvertebrate assemblages were common in the beaver-modified section of stream, with some lentic taxa also being present. The unmodified section of stream had more abundant collectors- gatherers and predators and no filter feeders, while scrapers were more abundant in modified section. The environmental variables which significantly influenced invertebrate occurrence were pH, nitrates, iron and the content of organic matter. The results contribute to ecological characteristics of these aquatic environments, and enable determining their functioning in forest areas.

Mapping Beaver Dams with Machine Learning

A new model deploys a neural network to spot beavers’ engineering exploits in aerial and satellite imagery, an approach that should aid studies of ecosystem and landscape change.

Hyporheic exchange in an urban beaver pond mediates high nutrient groundwater inflow and pond productivity

The rebound of beaver populations across North America has resulted in new understanding of how their alteration of stream channels affects hydrology and biogeochemical cycling, but their increased impact on urban areas has not been well investigated. Urban beaver ponds have the potential to slow and retain runoff, reconnect surrounding floodplains, and reduce nutrients. Where management allows, beaver ponds may partially ameliorate water quality problems in urban streams and enhance the ecological function of the broader riparian zone. In this study we measured water chemistry in surface (over ten months) and hyporheic (over three months) waters, including nitrate, ammonium, and dissolved organic carbon (DOC), to assess the impact of urban beaver dams on water quality. Pond water is sourced from groundwater, with anoxic conditions in the surface water at the top of the pond that become increasingly oxic moving longitudinally through the pond. Large diel dissolved oxygen swings in the pond indicate high sestonic productivity. There are distinct hyporheic geochemical signatures above and below the dam as well as across the dam indicating the dam is driving downwelling above the dam and upwelling below. Hyporheic ammonium concentrations and surface nitrate concentrations are high above the dam and decrease below the dam, showing that shifting oxic conditions drive nitrogen speciation. The δ15N and δ18O values of nitrate point to diffuse sewage leaks as the main source of nutrients to the pond instead of overland runoff. In addition, surface waters have lower δ15N and δ18O of nitrate and DOC concentrations than groundwaters, indicating denitrification may drive the decrease in nitrate concentration. With increasing presence of beaver in urban streams, surface water-groundwater interactions through urban beaver dams have the potential to remediate urban sources of nutrients from ponds.

Impacts of a beaver dam analogue complex on streambed vertical hydraulic gradients in a 1.2‐km stream reach in Wyoming, USA

AbstractBeaver dam analogues (BDAs) have seen growing use as restoration structures across the western United States. This study investigates the patterns in streambed upwelling and downwelling along a 1.2‐km stream reach in Red Canyon Creek (RCC), Wyoming before and after the installation of 31 new BDAs and the upgrade of four existing BDAs in July 2021. Over 100 mini‐piezometers were used to measure upwelling and downwelling in low‐flow, summer periods as quantified by vertical hydraulic gradient (VHG). Both before and after BDA installation, the stream reach was dominated by downwelling patterns, suggesting that RCC was a net losing stream during this summer period, with and without BDAs. While there were spatial variations in VHG before BDA installation, this variation was not dependent on stream depth, water surface concavity, sediment characteristics, and position relative to meanders, suggesting that unobservable subsurface properties may be a control on VHG or that there are attributes that were not captured due to the 10‐m spacing of mini‐piezometers. After BDA installation, VHGs were primarily related to the magnitude of the elevation gradient across the BDA. VHGs were highest near the BDAs and diminished once moving more than a few metres from the BDAs. When VHGs were averaged over the full reach length, BDAs appeared to slightly enhance net stream loss, albeit we could not control for possible seasonal differences in water table gradient during the observtion period.