| 1. |
- Catalán, Núria, 1985-, et al.
(författare)
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Effects of beaver impoundments on dissolved organic matter quality and biodegradability in boreal riverine systems
- 2017
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Ingår i: Hydrobiologia. - : Springer Science and Business Media LLC. - 0018-8158 .- 1573-5117. ; 793:1, s. 135-148
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Tidskriftsartikel (refereegranskat)abstract
- Beaver impoundments modify the structure of river reaches and lead to changes in ecosystem function and biogeochemical processes. Here, we assessed the changes in dissolved organic matter (DOM) quality and the biodegradation patterns in a set of beaver systems across Sweden. As the effect of beaver impoundments might be transient and local, we compared DOM quality and biodegradability of both pond and upstream sections of differentially aged beaver systems. Newly established dams shifted the sources and DOM biodegradability patterns. In particular, humic-like DOM, most likely leached from surrounding soils, characterized upstream sections of new beaver impoundments. In contrast, autochthonous and processed compounds, with both higher biodegradation rates and a broader spectrum of reactivities, differentiated DOM in ponds. DOM in recently established ponds seemed to be more humic and less processed compared to older ponds, but system idiosyncrasies determined by catchment particularities influenced this ageing effect.
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| 2. |
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| 3. |
- Ecke, Frauke, et al.
(författare)
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Meta-analysis of environmental effects of beaver in relation to artificial dams
- 2017
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 12
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Forskningsöversikt (refereegranskat)abstract
- Globally, artificial river impoundment, nutrient enrichment and biodiversity loss impair freshwater ecosystem integrity. Concurrently, beavers, ecosystem engineers recognized for their ability to construct dams and create ponds, are colonizing sites across the Holarctic after widespread extirpation in the 19th century, including areas outside their historical range. This has the potential to profoundly alter hydrology, hydrochemistry and aquatic ecology in both newly colonized and recolonized areas. To further our knowledge of the effects of beaver dams on aquatic environments, we extracted 1366 effect sizes from 89 studies on the impoundment of streams and lakes. Effects were assessed for 16 factors related to hydrogeomorphology, biogeochemistry, ecosystem functioning and biodiversity. Beaver dams affected concentrations of organic carbon in water, mercury in water and biota, sediment conditions and hydrological properties. There were no overall adverse effects caused by beaver dams or ponds on salmonid fish. Age was an important determinant of effect magnitude. While young ponds were a source of phosphorus, there was a tendency for phosphorus retention in older systems. Young ponds were a source methylmercury in water, but old ponds were not. To provide additional context, we also evaluated similarities and differences between environmental effects of beaver-constructed and artificial dams (767 effect sizes from 75 studies). Both are comparable in terms of effects on, for example, biodiversity, but have contrasting effects on nutrient retention and mercury. These results are important for assessing the role of beavers in enhancing and/or degrading ecological integrity in changing Holarctic freshwater systems.
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| 4. |
- Herrero Ortega, Sonia, et al.
(författare)
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High methylmercury formation in ponds fueled by fresh humic and algal derived organic matter
- 2018
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Ingår i: Limnology and Oceanography. - : Wiley. - 0024-3590 .- 1939-5590. ; 63, s. S44-S53
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Tidskriftsartikel (refereegranskat)abstract
- Neurotoxic methylmercury causes adverse effects to ecosystem viability and human health. Previous studies have revealed that ponding alters natural organic matter (NOM) composition and increase methylmercury concentrations in rivers, especially in the first years after flooding. Here, we investigate the influence of NOM composition (i.e., sources and degradation status) on mercury methylation rate constants in nine boreal beaver ponds of different ages across Sweden. We show that increased methylmercury concentrations in surface waters is a consequence of enhanced mercury methylation in the pond sediments. Moreover, our results reveal that during the first years after the initial flooding, mercury methylation rates are fueled by the amount of fresh humic substances released from the flooded soils and by an increased production of algal-derived NOM triggered by enhanced nutrient availability. Our findings indicate that impoundment-induced changes in NOM composition control mercury methylation processes, causing the raise in MeHg levels in ponds.
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| 5. |
- Levanoni, Oded, et al.
(författare)
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Are beavers a solution to the freshwater biodiversity crisis?
- 2019
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Ingår i: Diversity and Distributions. - : Wiley. - 1366-9516 .- 1472-4642. ; 25, s. 1763-1772
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Tidskriftsartikel (refereegranskat)abstract
- Aim To determine whether reintroduced beavers, as an example of native herbivorous megafauna, can increase freshwater biodiversity at the landscape scale and to compare effects on two contrasting taxonomic groups. Location South-central Sweden. Methods We collected data on plant and water beetle composition and supporting environmental variables from 20 closely located wetlands, half created from the damming of streams by beavers-beaver ponds (BP), and half by other, mainly natural (e.g. topographic, river migration) means-other wetlands (OW). Differences in species composition and plant growth strategy (i.e. competitor, stress tolerator or ruderal) between wetland types were assessed using multivariate analyses. Results The species pool of both taxonomic groups was higher in BP than OW (plants + 17%; beetles + 15%). For both groups, the number of species unique to BP was 50% higher than those unique to OW. Plant and beetle compositions differed significantly between wetlands, most strongly for plants, while rarity scores showed no difference, and the incidence of invasive species was negligible. Plant composition was mostly influenced by open water, bare ground and woody debris in BP, and plant cover, height and leaf litter in OW. This was consistent with the characterization of BP vegetation by ruderal plants and OW by competitors and stress tolerators. A significant residual effect of wetland type on plant, but not beetle composition, suggests that beavers exert important direct effects on some biota (e.g. via herbivory) independent of the indirect effects they exert via environmental change. Main conclusions Beaver-created ponds support novel biodiversity that is not merely a subset of that found elsewhere in the same landscape. As such, re-establishing beaver populations where they are native should benefit freshwater biodiversity, but effects may be context and taxon specific. Beavers alone cannot solve the freshwater biodiversity crisis, but recognizing the widespread importance of herbivorous megafauna in maintaining heterogeneity and creating novel habitat will be a positive step.
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| 6. |
- Levanoni, Oded
(författare)
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Ecological and biogeochemical implications of the recovery of Eurasian beavers
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In pre-industrial times beavers, ecosystem engineers, inhabited most of the Holarctic. Intensive exploitation over the last millennium, particularly in Europe during the 18th and 19th centuries, led to a dramatic decline in beaver populations. By the end of the 19th century the Eurasian beaver (Castor fiber) was at the verge of extirpation in many regions of Eurasia. However, during the 20th century, changes in management policy and reintroductions have resulted in a fast recovery of the species. Presently, Eurasian beavers are colonizing large parts of their former distribution range, and their population is still growing. Once again, beaver engineering and its outcomes are becoming prominent features of many streams in the boreal landscapes. The goal of this thesis was to investigate how the reintroduction and population recovery of Eurasian beavers might affect ecosystem functioning at local and landscape scales. The work was based on measurements from 12 beaver systems of various colonization histories (pioneer and recolonized) in Swedish boreal forests. Based on water chemistry measurements together with field and lab experiments, I evaluated the effect of beavers on processes of mercury methylation, litter decomposition, and the growth and respiration of benthic biofilms. I also investigated how beavers alter the nutrient limitation of biofilm activity. To assess the environmental effects of the reintroduction of beavers at the landscape scale, this empirical approach was complemented by a meta-analysis of 76 published studies on a total of 16 environmental factors. The results showed that beavers increased MeHg concentrations, decreased algal biomass accrual, and sometimes increased litter decomposition rates downstream compared to upstream beaver systems. However, distinct contrasting patterns were observed in pioneer and recolonized systems: While all the above effects were prominent in pioneer systems, they were moderate or absent in recolonized systems. Albeit algal accrual and community respiration were nutrient limited, beaver systems had no effect on the degree of limitation. Based on the meta-analysis, this thesis demonstrates that, when compared to a reference site, beavers can potentially affect all studied factors. The meta-analysis also identified gaps in knowledge regarding the dependency of beaver effects on different stages of age and colonization history. In conclusion, this thesis highlights: a) the importance of incorporating the successional stage and the colonization history of beaver systems when considering the effects of reintroducing beavers into stream ecosystems; and b) the lack of knowledge regarding these issues.
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| 7. |
- Levanoni, Oded, et al.
(författare)
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Impact of Beaver Pond Colonization History on Methylmercury Concentrations in Surface Water
- 2015
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 49, s. 12679–12687-
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Tidskriftsartikel (refereegranskat)abstract
- Elevated concentrations of methylmercury (MeHg) in freshwater ecosystems are of major environmental concern in large parts of the northern hemisphere. Beaver ponds have been identified as a potentially important source of MeHg. The role of beavers might be especially pronounced in large parts of Europe, where beaver populations have expanded rapidly following near-extirpation. This study evaluates the role of the age and colonization history (encompassing patterns of use and reuse) of ponds constructed by the Eurasian beaver Castor fiber in regulating MeHg concentrations in Swedish streams. In 12 beaver systems located in three regions, we quantified MeHg concentrations together with other relevant parameters on five occasions per year in 2012-2013. Five were pioneer systems, inundated for the first time since beaver extirpation, and seven were recolonized, with dams reconstructed by newly recolonizing beavers. MeHg concentrations in pioneer but not in recolonized beaver systems were up to 3.5 fold higher downstream than upstream of the ponds, and varied between seasons and years. Our results show that pioneer inundation by beavers can increase MeHg concentrations in streams, but that this effect is negligible when dams are reconstructed on previously used ponds. We therefore expect that the recovery and expansion of beavers in the boreal system will only have a transitional effect on MeHg in the environment.
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| 8. |
- Levanoni, Oded, et al.
(författare)
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Rewilding wetlands: beaver as agents of within-habitat heterogeneity and the responses of contrasting biota
- 2018
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Ingår i: Philosophical Transactions B: Biological Sciences. - : The Royal Society. - 0962-8436 .- 1471-2970. ; 373
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Tidskriftsartikel (refereegranskat)abstract
- Ecosystem engineers can increase biodiversity by creating novel habitat supporting species that would otherwise be absent. Their more routine activities further influence the biota occupying engineered habitats. Beavers are well-known for transforming ecosystems through dam building and are therefore increasingly being used for habitat restoration, adaptation to climate extremes and in long-term rewilding. Abandoned beaver ponds (BP) develop into meadows or forested wetlands that differ fundamentally from other terrestrial habitats and thus increase landscape diversity. Active BP, by contrast, are superficially similar to other non-engineered shallow wetlands, but ongoing use and maintenance might affect how BP contribute to aquatic biodiversity. We explored the 'within-habitat' effect of an ecosystem engineer by comparing active BP in southern Sweden with coexisting other wetlands (OW), using sedentary (plants) and mobile (water beetles) organisms as indicators. BP differed predictably from OW in environmental characteristics and were more heterogeneous. BP supported more plant species at plot (+15%) and site (+33%) scales, and plant beta diversity, based on turnover between plots, was 17% higher than in OW, contributing to a significantly larger species pool in BP (+17%). Beetles were not differentiated between BP and OW based on diversity measures but were 26% more abundant in BP. Independent of habitat creation beaver are thus significant agents of within-habitat heterogeneity that differentiates BP from other standing water habitat; as an integral component of the rewilding of wetlands re-establishing beaver should benefit aquatic biodiversity across multiple scales.
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