Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 81-85). Also available on the World Wide Web.

Investigation into the effects of beaver dams on hyporheic exchange in peat dominated mountainous streams is needed to better understand stream-floodplain connections and improve our overall conceptual model of water storage and flow through riverine valleys. The objective of this study was to determine the influence of instream beaver dams on vertical and lateral hyporheic exchanges. Hyporheic interactions were examined using hydrometric methods to determine both flow pathways and water fluxes for a second-order stream draining a Canadian Rocky Mountain peatland. Investigation was conducted on two instream beaver dams and an undammed reference section for the ice free periods of summers 2006 and 2007 at the Sibbald Reseach Basin located in Kananaskis Country, Alberta, Canada. Lateral hyporheic fluxes dominated over vertical hyporheic fluxes, due to a layer with low saturated hydraulic conductivity (K &sim 10⁻⁷ 10⁻⁹ m/s) just below the streambed throughout most of the study reach. The lateral flow around the north dam (> 0.6 m high) resulted in fluxes that ranged from 0.002 to 0.015 L/s in the near bank environment. These results confirm that hydraulic properties of the substrata are an important factor in the development of hyporheic exchange in stream systems draining peatlands. Results also demonstrate the ability of beaver to connect valley floors to their streams, which maintains seasonally stable water tables and wetland conditions in the riparian zone.

Investigation into the effects of beaver dams on hyporheic exchange in peat dominated mountainous streams is needed to better understand stream-floodplain connections and improve our overall conceptual model of water storage and flow through riverine valleys. The objective of this study was to determine the influence of instream beaver dams on vertical and lateral hyporheic exchanges. Hyporheic interactions were examined using hydrometric methods to determine both flow pathways and water fluxes for a second-order stream draining a Canadian Rocky Mountain peatland. Investigation was conducted on two instream beaver dams and an undammed reference section for the ice free periods of summers 2006 and 2007 at the Sibbald Reseach Basin located in Kananaskis Country, Alberta, Canada. Lateral hyporheic fluxes dominated over vertical hyporheic fluxes, due to a layer with low saturated hydraulic conductivity (K &sim 10⁻⁷ 10⁻⁹ m/s) just below the streambed throughout most of the study reach. The lateral flow around the north dam (> 0.6 m high) resulted in fluxes that ranged from 0.002 to 0.015 L/s in the near bank environment. These results confirm that hydraulic properties of the substrata are an important factor in the development of hyporheic exchange in stream systems draining peatlands. Results also demonstrate the ability of beaver to connect valley floors to their streams, which maintains seasonally stable water tables and wetland conditions in the riparian zone.

Willow bioengineering is an alternative erosion management technique that includes the use of living and inert willow material. It is successfully used across North America, Europe and Asia but, due to lack of public awareness of the technique or concerns about its effectiveness, it is currently used only occasionally in southern Manitoba. To provide insight into possible biological limitations upon the use of willows to prevent erosion a combination of field experiments and observational studies of new bioengineering sites was carried out across southern Manitoba. The results indicate that first year willow cutting survival is likely to be below 50% unless planted within 100cm of fall low water level. Using taller cuttings may improve survival as they develop greater numbers of shoots early in the growing season, but taller cuttings have a greater chance of being cut down or even pulled from the ground by beaver. Flooding had a negative effect of shoot numbers during the first year after planting, although it did not impact survival. In 2012 flood levels were lower at the majority of sites than the long term mean; more extensive flooding may have a more negative effect upon the cuttings. Maximum shoot length was reduced by high water levels, but was improved by cutting proximity to low water later in the summer. More research is needed to better understand the effect of high water levels on long term survival. Combining live willow with erosion blanket helps reduced substrate loss during establishment and also prevented willow bundles from being removed by beaver reducing the potential of project failure.

Mercury (Hg) binds to organic matter (OM) within boreal forest soils. Land disturbances, such as forest harvesting, alter the export of OM and nutrients to nearby streams. This can affect the structure of stream communities and their food webs by changes to basal resource availability, and consumer reliance on these resources. It may also impact the uptake and biomagnification of Hg within streams. Beaver impoundments often co-occur with forestry and can similarly influence Hg in streams. However, their combined effects are unknown. Most research on the effects of forest harvesting on Hg have focused on abiotic factors with little attention given to Hg dynamics in food webs, particularly in Canada’s boreal. This thesis examined the effects of forest harvest on macroinvertebrate communities and leaf litter decomposition (Chapter 2), and on Hg bioaccumulation and biomagnification temporally and regionally across streams (Chapter 3) and upstream and downstream of beaver reservoirs in harvested and non-harvested landscapes (Chapter 4). In Chapter 2, no effects of harvest on leaf litter decomposition were observed, yet results suggested that effects on macroinvertebrate communities within harvested landscapes were site-specific and most severe (i.e., declines in diversity, evenness, and in sensitive taxa) in streams with narrow buffer zones and higher amounts of harvest within their watershed. Chapter 3 showed that Hg concentrations ([Hg]) in macroinvertebrates were elevated in harvested landscapes, likely because of higher [Hg] in food sources, and that streams afforded less protection are at greater risk of increased [Hg] in water and consumers. Chapter 4 revealed that while [Hg] of consumers and biomagnification rates were elevated in harvested landscapes upstream of reservoirs, they did not persist downstream, indicating that effects of reservoirs and harvest were not additive, and were instead site-specific. This thesis provides novel and impactful information on Hg cycling and may assist foresters to develop guidelines to minimize Hg risk to stream ecosystems. / Thesis / Doctor of Philosophy (PhD) / Mercury is a dangerous contaminant that is stored in boreal forest soils, and disturbances to soils, such as forestry activities and beaver dams, can transport it into nearby streams. Mercury is then available for uptake in food webs, leading to high concentrations in fish. Harvesting can affect the number of different species of stream macroinvertebrates, and their assemblages serve as indicators of stream health. This thesis investigated the separate and combined effects of both forest harvesting and beaver dams on mercury in stream food webs and harvesting effects only on macroinvertebrate communities. A stream with extensive watershed harvesting, narrow buffer zones, and a machinery crossing upstream experienced the greatest impacts. Further, mercury levels were higher in food sources and macroinvertebrates in streams with harvest compared to those without. Separately, forestry and beaver dams had some effects on mercury concentrations, but together their effects were not increased.

Šio darbo metu buvo ištirta ir įvertinta buvusių bebrų patvankų vietose ir ant bebrų trobelių susiformavusi augalija, jos pokyčiai laike priklausomai nuo apleistų bebraviečių amžiaus. Taip pat bebrų pievų augalija buvo palyginta su sąlyginai natūralių šlapių pievų augalija. Transformuotų bebrų buveinių fitocenozių tyrimai atlikti 2007 – 2010 metų liepos – rugsėjo mėnesiais palei Sąvalkos upelį (Vilniaus r., Nemenčinės apylinkės, Pailgės km.) esančiose trijose apleistose bebrų ir trijose natūraliose šlapiose pievose, o 21 bebrų trobelės augalija buvo tiriama Vilniaus, Molėtų ir Širvintų rajonuose. Pievose pagal Braun-Blanquet metodiką buvo aprašyti 48 (4 m2 kiekvienas) tiriamieji laukeliai, o ant bebrų trobelių 21 (vid. 10 m2 kiekvienas). Jie leido nustatyti tirtų augimviečių floristinę sudėtį, identifikuoti ir aprašyti augalų bendrijas, nustatyti ekologinius augalų poreikius bei įvertinti apleistų bebrų pievų augalijos pokyčius priklausomai nuo bebraviečių amžiaus. Apleistose bebrų pievose išskirtos 113 induočių augalų rūšių, natūraliose šlapiose pievose – 109, o ant bebrų trobelių 104. Apleistose bebrų pievose formuojasi įvairios augalų bendrijos, tačiau tirtose pievose dažniausios buvo Molinio-Arrhenatheretea elatioris R. Tx. 1937 klasei priklausančios bendrijos. pagal Ellenberg’o skalę vertinti augalų ekologiniai poreikiai apleistose bebravietėse, natūraliose šlapiose pievose ir ant bebrų trobelių iš esmės yra panašūs. Visose tirtose buveinėse vyravo mezofitai. Tačiau yra... [toliau žr. visą tekstą] / The work presents exploration and evaluation of the data on the vegetation which forms on beaver lodges and in abandoned beaver meadows and its alteration in time. Likewise, comparison of the abandoned beaver meadows phytocenoses with the plant communities of naturally flooded meadows is presented. Research on meadows phytocenoses occured in 2007 – 2008, each year explorations were holding from July till August, in Sąvalka stream valleys (East Lithuania). Three abandoned beaver meadows and three naturally flooded meadows were explored. Botanical composition of plants communities was determined using Braun-Blanquet method (Braun-Blanquet, 1964), took 48 squares, each 4 m2, in six meadows and 21 squares on beaver lodges, each 10 m2 , and evaluating all plant species from them. The scale of H. Ellenberg (2001) was used to decide plants species attachment to hydrological regime, soil reaction, and trophical features of abodes. Coefficients of Sörensen and Jaccard (Dombois-Mueller, Ellenberg, 1974) were used to express floristical similarity of communities. In abandoned beaver meadows 109 plant species were identified meanwhile in naturally flooded meadows – 100; 104 plant species were identified on beaver lodges. Various phytocenoses are formed in beaver meadows, however, communities belonging to the Cl. Molinio-Arrhenatheretea elatioris R. Tx. 1937 are the most frequent. In comparison with naturally flooded meadows, phytocenoses of beaver meadows are distinguished by the... [to full text]

Thesis (M.S.)--Oregon State University, 2001. / Typescript (photocopy). Includes bibliographical references (leaves 71-77). Also available online.

North American beavers (Castor canadensis) build dams in stream channels, thus creating impoundments that flood surrounding riparian areas. Due to the widely circulating global pool of mercury in the atmosphere, mercury is deposited onto the landscape both near and far from point sources, including areas occupied by beavers. The organic form of mercury, methylmercury, is a potent neurotoxin with potential to cause harm to both humans and wildlife due to its ability to biomagnify up food chains. Recently flooded areas, such as those resulting from beaver impoundments, create ideal environments for the methylation of mercury. These impoundments can release methylmercury to downstream food webs where there is potential for it to be transferred to higher trophic level organisms. Beaver impoundments can also boost productivity in aquatic systems, so increases in mercury may be accompanied by an increase in nutrients and algal and invertebrate biomass. The findings here describe increased concentrations of methylmercury in water, algae, and invertebrates downstream from in-channel beaver dams in the southern Canadian Rockies. There was, however, no significant increase in nutrients or algal and invertebrate biomass downstream from impoundments. An examination of trophic transfer of mercury in these stream systems reveals that uptake is enhanced at low concentrations. The uptake pathway from water to algae is especially important but is attenuated in higher trophic levels due to a small relative difference in trophic level between predators and prey. The overall rate of trophic transfer in these systems falls within the low end of the typical range, and low baseline concentrations mean that methylmercury is not biomagnifying to dangerous levels in these low-productivity mountain systems. Beavers can provide important ecosystem services such as improving landscape heterogeneity, creation of new habitat for invertebrates and fish and improved angling opportunities, but they also enhance mercury export. Therefore, in systems that are mercury-sensitive such as those with low pH or long-lived, slow-growing predatory fish species, beaver influence should be considered as an important source of methylmercury.

No description available.

Thesis (M.Sc.). / Written for the Dept. of Natural Resource Sciences. Title from title page of PDF (viewed 2009/06/29). Includes bibliographical references.