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.

Hyporheic flow influences both biogeochemical cycling in streambeds as well as streambed ecology. Some biogeochemical processes may be temperature dependent; therefore, heat transport associated with hyporheic flow may be an important influence on such cycles. I separately and experimentally assessed the effects of hyporheic flow due to bed topography on thermal dynamics in the sediment using a custom, tilting flume with temperature controls. Diel temperature cycles of 6° C were imposed in the flume and propagation of temperature signals into the sediment was examined for different bed morphologies (plane bed, pool-riffle-pool, and rippled bed), channel flow rates, and sediment grain sizes. Temperature fields in the sediment were monitored using an array of embedded thermistors, and this data was used to identify zones of upwelling and downwelling within the hyporheic zone. Results suggest that bedforms do induce substantially deeper downwelling upstream and downstream of the bedforms, with upwelling near the crest. This in turn leads to substantial advective heat transport and distinct thermal patterns in the sediment. Variation in permeability and channel flow rates further affects the magnitude of this advective transport. These results corroborate existing theoretical models of coupled hyporheic exchange and heat transport under bedforms. Hyporheic flow therefore affects thermal patchiness in sediment, which may in turn exert a control on biogeochemical reaction rates, and form thermal refugia for fauna. / text

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 42-46). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references (leaves 76-82). Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2005. / Printout. Includes bibliographical references (leaves 141-148). Also available via the World Wide Web.

Metabolic and biogeochemical processes in hyporheic zones may depend on inputs of coarse particulate organic matter. Our research focused on how differing quantity and quality of organic matter affects metabolism and nutrient retention in the hyporheic zone of a low-order Appalachian stream. We hypothesized that hyporheic metabolic rates should increase with organic matter additions because the biotic activity is limited by organic matter availability. Four sets (n=4 amendments/set) of plots were established on a tributary of Hugh White Creek, NC. Sediment was extracted and was either supplemented with leaves, wood, or plastic strips, or sediments remained unamended sediments. Following augmentation sediments were reimbedded and approximately three months later sediment was removed from each plot. Aerobic and anaerobic metabolism were measured as the change in O2, and CO2 in recirculating microcosms. At the same time, we monitored other possible terminal electron accepting processes and changes in nutrients. Aerobic metabolism was low in all treatments and respiratory quotients calculated for all treatments indicated that metabolism was dominated by anaerobic processes. Anaerobic and total (combined aerobic and anaerobic) respiration rates were significantly greater (P < 0.05) in plots treated with leaf organic matter compared to controls. Nutrient retention (NO3-N, NH4-N, and DOC) was enhanced in augmented treatments. Measured losses of dissolved organic carbon accounted for 50% total carbon liberated by respiration in amended sediments, whereas in unamended sediments loss of DOC represented only 7% of measured respiration. Augmentation with greater quality organic matter stimulated respiration in hyporheic sediments. Anaerobic processes dominated metabolic rates in both control and amended sediments. Enhanced metabolic rates increased retention of many solutes indicating that energy flow and nutrient dynamics in the subsurface of streams may depend upon the quantity and quality of imported carbon. / Master of Science

Valley Creek, an urbanized stream in Southeastern Pennsylvania, has undergone changes typical of streams in urbanized areas, such as bank erosion, channel redirection, and habitat disruption. One area of disruption that has been little studied is the hyporheic zone, the top layer of the streambed where stream water exchanges with subsurface water and chemical transformations occur. The hyporheic zone of an 18 m reach of Valley Creek in Ecology Park was characterized using a tracer test coupled with a hydrogeophysical survey. Nested wells screened at depths of 20, 35, 50, and 65 cm were placed at four locations along the center of the stream to monitor the passage of the salt tracer through the hyporheic zone. Results from well sampling were compared with time-lapse Electrical Resistivity Tomography (ERT) monitoring of the stream tracer. The streambed was also characterized using temperature probes to calculate the stream water-groundwater flux and freeze core samples to characterize heterogeneities in streambed sediment. Models were created using MODFLOW, MATLAB, and EARTH IMAGER 2-D to understand differences between Ecology Park and Crabby Creek, a tributary within the Valley Creek watershed, where similar studies were performed in 2009 and 2010. Hyporheic exchange and ERT applicability differed between the two study sites. At Ecology Park, tracer was detected only in the 20 cm wells at nests 2 and 4 during the injection period. Noise in the falling limbs of the tracer test breakthrough curves made it difficult to determine whether tracer lingered in the hyporheic zone using well data. ERT surveys were unable to detect tracer lingering after the injection period. At Crabby Creek, tracer was present in all shallow wells, and lingering tracer was detected in the hyporheic zone using ERT during the post-injection period. ERT surveys at Ecology Park were less effective than at Crabby Creek for two reasons: the presence of groundwater discharge (which inhibited hyporheic exchange) and increased stream water depth at Ecology Park. Temperature modeling of heat flux data revealed groundwater discharge at three locations. MODFLOW models predicted that this discharge would diminish the length and residence time of subsurface flow paths. Groundwater discharge likely increased along the contact between the hydraulically conductive Elbrook Formation and the less conductive Ledger Formation. Models created with MATLAB and Earth-Imager 2-D showed ERT sensitivity to tracer in the hyporheic zone depended on stream thickness. With increased water depth, more current propagated through the stream, which reduced sensitivity to changes in the hyporheic zone. A sensitivity analysis showed that the resistivity change in the hyporheic zone at Ecology Park (average water depth 0.36 m) would have to exceed 30% to be detectable, which was greater than the induced change during the tracer test. Deeper water also amplified the confounding effect of changes in the background conductivity of the stream water, though time-lapse ERT detected no lingering tracer even after correcting for this drift. Studies performed at Crabby Creek were able to map lingering tracer in the hyporheic zone because the site had a thin water layer (0.1 m), a large percentage increase of conductivity during the tracer test, and no groundwater discharge. Conversely, at Ecology Park groundwater discharge inhibited hyporheic exchange, and imaging sensitivity was reduced by the thicker water layer, demonstrating the limitations of ERT for hyporheic zone characterization. The modified inversion routines used here demonstrated that, with accurate stream conductivity and depth measurements, ERT can be used in some streams as a method for hyporheic characterization by incorporating site-specific conditions. / Geology

Dynamic exchange of water across the stream-riparian zone interface is important in increasing stream water transit time through basins and enhancing redox-sensitive biogeochemical reactions that influence downstream water quality and ecosystem health. Such exchange may be enhanced by beaver dams, which are common throughout low order streams in North America, Europe, and Argentina. Lateral exchanges of water and nitrogen (N) were observed along a beaver dammed, third-order stream draining a 1.3 km2 Canadian Rocky Mountain valley bottom capped in peat. Measurements of hydraulic heads and chloride concentrations from a network of 80 water table wells were used to identify areas of stream water and groundwater mixing in the riparian area, and their spatiotemporal dynamics in summer 2008. Beaver were found to be the greatest factor affecting lateral movement of channel water into the riparian area. Channel water flowed laterally into the riparian area upstream of the dams and back to the channel downstream of the dams. The hyporheic zone expanded by ¡Ü1.5 m in the un-dammed reaches, but upwards of 7.5 m or more when dams were present. High contributions of stream water were found far out in the riparian area where dams were not immediately present within the stream reach, suggesting that upstream dams directed stream water into the riparian area where it travelled down valley before returning to the stream. This suggests that multiple dams create hyporheic flow paths at multiple scales. Potential mass flux calculations show the riparian area immediately downstream of the beaver dam was a source of N and dissolved organic carbon (DOC) to the stream, and a sink along the rest of the reach. Cold spots of N and DOC availability were also found along the beaver-driven flow paths in the riparian area adjacent to the dam. This pattern likely developed due to flushing of nutrients along the beaver driven hyporheic flow vectors. This work enhances our understanding of stream-aquifer exchange and N dynamics in riparian areas, and the effects of beaver on these processes.

Dynamic exchange of water across the stream-riparian zone interface is important in increasing stream water transit time through basins and enhancing redox-sensitive biogeochemical reactions that influence downstream water quality and ecosystem health. Such exchange may be enhanced by beaver dams, which are common throughout low order streams in North America, Europe, and Argentina. Lateral exchanges of water and nitrogen (N) were observed along a beaver dammed, third-order stream draining a 1.3 km2 Canadian Rocky Mountain valley bottom capped in peat. Measurements of hydraulic heads and chloride concentrations from a network of 80 water table wells were used to identify areas of stream water and groundwater mixing in the riparian area, and their spatiotemporal dynamics in summer 2008. Beaver were found to be the greatest factor affecting lateral movement of channel water into the riparian area. Channel water flowed laterally into the riparian area upstream of the dams and back to the channel downstream of the dams. The hyporheic zone expanded by ¡Ü1.5 m in the un-dammed reaches, but upwards of 7.5 m or more when dams were present. High contributions of stream water were found far out in the riparian area where dams were not immediately present within the stream reach, suggesting that upstream dams directed stream water into the riparian area where it travelled down valley before returning to the stream. This suggests that multiple dams create hyporheic flow paths at multiple scales. Potential mass flux calculations show the riparian area immediately downstream of the beaver dam was a source of N and dissolved organic carbon (DOC) to the stream, and a sink along the rest of the reach. Cold spots of N and DOC availability were also found along the beaver-driven flow paths in the riparian area adjacent to the dam. This pattern likely developed due to flushing of nutrients along the beaver driven hyporheic flow vectors. This work enhances our understanding of stream-aquifer exchange and N dynamics in riparian areas, and the effects of beaver on these processes.