Effects of Beaver Dams on Subarctic Wetland Hydrology

Beaver dams are ubiquitous in subarctic wetlands, where runoff in the flat terrain is highly prone to changes as the stream courses are modified by beaver activities. Depending on the state of preservation, stream flow can overtop or funnel through gaps in the dams, leak from the bottom of the dams or seep through the entire structure. Peak and low flows are regulated by these dams to a varying extent. The formation of beaver ponds causes local flooding, while the open water surfaces of the ponds increase water loss from the wetlands. Water spilled from the dams may cause diversion channels to produce complex drainage patterns. Comparing the water balance of basins with and without a beaver dam at its outlet confirms that the dammed basin lost more water to evaporation, suppressed the outflow and increased the basin water storage.

Response of peatland carbon dioxide and methane fluxes to a watertable drawdown experiment

This is the peer reviewed version of the following article: Strack, M. and Waddington J.M. 2007. Response of peatland carbon dioxide and methane fluxes to a water table drawdown experiment. Global Biogeochemical Cycles, 21, GB1007, doi: 10.1029/2006GB002715, which has been published in final form at https://doi.org/10.1029/2006GB002715. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.Northern peatlands play an important role in the global carbon cycle representing a significant stock of soil carbon and a substantial natural source of atmospheric methane (CH4). Peatland carbon cycling is affected by water table position which is predicted to be lowered by climate change. Therefore we compared carbon fluxes along a natural peatland microtopographic gradient (control) to an adjacent microtopographic gradient with an experimentally lowered water table (experimental) during three growing seasons to assess the impact of water table drawdown on peatland-atmosphere carbon exchange. Water table drawdown induced peat subsidence and a change in the vegetation community at the experimental site. This limited differences in carbon dioxide (CO2) exchange between the control and experimental sites resulting in no significant differences between sites after three seasons. However, there was a trend to higher respiration rates and increased productivity in low-lying zones (hollows) and this was coincident with increased vegetation cover at these plots. In general, CH4 efflux was reduced at the experimental site, although CH4 efflux from control and experimental hollows remained similar throughout the study. The differential response of carbon cycling to the water table drawdown along the microtopographic gradient resulted in local topographic high zones (hummocks) experiencing a relative increase in global warming potential (GWP) of 152%, while a 70% reduction in GWP was observed at hollows. Thus the distribution and composition of microtopographic elements, or microforms, within a peatland is important for determining how peatland carbon cycling will respond to climate change.This research was funded by NSERC (Canada) and Canadian Foundation for Climate and Atmospheric Science (CFCAS) grants to J.M.W., NSERC Julie Payette and CGS scholarships to M.S., and a postdoctoral grant from the Academy of Finland (project 12328) and from the Faculty des Sciences de l'Agriculture et de l'Alimentation, Université Laval, to E.T

Dynamics of biogenic gas bubbles in peat and their effects on peatland biogeochemistry

This is the peer reviewed version of the following article: Strack, M., Kellner, E. and Waddington, J.M. 2005. The dynamics of biogenic gas bubbles in peat and their effects on peatland biogeochemistry. Global Biogeochemical Cycles, 19, GB1003, doi: 10.1029/2004GB002330, which has been published in final form at https://doi.org/10.1029/2004GB002330. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.Production and emission of peat gas has attracted great interest because substantial amounts of methane (CH4) are emitted to the atmosphere from peat soils. Many studies indicate supersaturation of CH4 in peat water, implying a high potential for gas bubble formation. However, observations of bubbles in peat are often only qualitatively described, and in most cases the presence of entrapped gas has been largely ignored in peatland studies. On the basis of a review of literature, a conceptual model of entrapped gas dynamics was developed and investigated using field and laboratory measurements at a poor fen in central Quebec. We investigated variations in production and volume of gas and the effect of this gas on trace gas emissions, peat buoyancy, and pore water chemistry during 2002 and 2003. Measurements made with moisture probes and subsurface gas collectors revealed that gas volume varied throughout the growing season in relation to hydrostatic and barometric pressure. Shifts in entrapped gas volume were also coincident with changes in dissolved pore water CH4. The presence of these bubbles has important biogeochemical effects, including the development of localized CH4 diffusion gradients, alteration of local flow paths affecting substrate delivery, peat buoyancy, and the potential episodic release of CH4 via ebullition events. These interactions must be included in peatland models to describe accurately the hydrology and greenhouse gas emissions from these ecosystems and to make predictions about their response to environmental change.This research was supported by Premier’s Research Excellence Award, a NSERC Discovery Grant, and a Canadian Foundation for Climate and Atmospheric Sciences grant to J. M. W. and a NSERC Julie Payette Scholarship and NSERC Canada Graduate Scholarship to M. S

How Does Moss Resist Evaporation? Towards Elucidating Site-Specific Influences on Sphagnum Moss Resistance

While multiple approaches to exist to quantify plant resistance to evaporation, these methods assume that the vegetation is vascular despite many ecosystems, such as peatlands, dominated by a surface cover of mosses. Mosses in peatlands (e.g., Sphagnum species and Brown mosses) conduct water up to the photosynthetic location via capillary forces, in the presence of a moisture potential gradient, brought on by evaporation demand from the atmosphere. If moisture is transported to the evaporating surface to meet atmospheric demand, moss will evaporate at potential rates, and is only limited by available energy. However, as soil moisture declines in the unsaturated zone, the ability to conduct water up to the evaporating surface will also decline, where at a given threshold of evaporative demand and unsaturated hydraulic conductivity, evaporation will decline, and fall below potential rates. While the soil physics theory behind this process has been known for some time, it has proven difficult to parameterise moss resistance to evaporation beyond site specific values, and albeit with a high degree of uncertainty. This work is the beginning of a review of moss resistance values, where the research question being asked is: What is a typical value of moss resistance in a peatland, and how does it vary by species, site, and hydroclimatic setting? This work seeks to constrain peatland moss resistance to better represent peatland evaporative processes in our current landscape-scale ecohydrological models.This research was undertaken thanks, in part, with support from the Global Water Futures Program funded by the Canada First Research Excellence Fund (CFREF

Effect of water table drawdown on northern peatland methane dynamics: Implications for climate change

This is the peer reviewed version of the following article: Strack, M., Waddington, J.M. and Tuittila, E.-S. 2004. The effect of water table drawdown on northern peatland methane emissions: Implications for climate change. Global Biogeochemical Cycles, 18, GB4003, doi: 10.1029/2003GB002209, which has been published in final form at https://doi.org/10.1029/2003GB002209. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.As natural sources of methane (CH4), peatlands play an important role in the global carbon cycle. Climate models predict that evapotranspiration will increase under a 2 x CO2 scenario due to increased temperatures leading to lowered water tables at many northern latitudes. Given that the position of the water table within a peatland can have a large effect on CH4 emissions, climate change may alter the CH4 emissions from peatlands in this area. Research was conducted during 2001–2003 on natural and drained (8 years prior) sites within a poor fen in central Quebec. Flux measurements were made for each site at different microtopographical features that varied in depth to water table and vegetation cover. The quantity of CH4 dissolved in the pore water was measured in the field and the potential of the peat for CH4 production and consumption was determined in the laboratory. Methane emissions and storage were lower in the drained fen. Growing season CH4 emissions at the drained site were 55% lower than the control site, primarily due to significantly reduced fluxes from topographic highs (up to 97% reduction), while the flux from topographically low areas remained high. The maintenance of high fluxes at these hollow sites was related to hydrological and ecological effects of the water table drawdown. The removal of standing water removed a potential zone of CH4 oxidation. It also enabled plant colonization at these locations, leading to an increase in gross ecosystem photosynthesis (GEP). At the hollow sites, seasonal CH4 emissions were significantly correlated to seasonal GEP (R2 = 0.85). These results suggest that the response of northern peatland CH4 dynamics to climate change depends on the antecedent moisture conditions of the site. Moreover, ecological succession can play an important role for determining future CH4 emissions, particularly from wetter sites

Response of vegetation and net ecosystem carbon dioxide exchange at different peatland microforms following water table drawdown

This is the peer reviewed version of the following article: Strack, M., Waller, M.F. and Waddington, J.M. 2006. Sedge succession and peatland methane dynamics: A potential feedback to climate change. Ecosystems, 9, 278-287., which has been published in final form at https://doi.org/10.1029/2005JG000145. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.Northern peatlands are significant stocks of terrestrial soil carbon, and it has been predicted that warmer temperatures and lower water tables resulting from climate change will convert these ecosystems into sources for atmospheric carbon dioxide (CO2). However, these predictions do not consider the potential for hydrologically induced ecological succession or the spatial variability of carbon accumulation rates between different microforms in peatlands. To address these issues, the vegetation community was described, and the rates of gross ecosystem photosynthesis (GEP), ecosystem respiration (Rtot) and net ecosystem CO2 exchange were determined along poor fen microtopographic gradients at a control site and at a site which experienced a water table drawdown of 20 cm 8 years prior to the study (drained). Sampling plots within these sites were classified as microforms of hummocks, lawns, or hollows. The coverage of Sphagnum moss declined on drained hummocks, drained lawns were invaded by sedges, and hollows shifted from open water plots at the control site to Sphagnum-dominated plots with sparse vascular plant cover at the drained site. As a result, Rtot was significantly greater at the drained site at all microforms while maximum rates of GEP declined at drained hummocks and were enhanced at drained lawns and hollows compared to similar control microforms. These results suggest that predictions about the response of northern peatland carbon exchange to climate change must consider the interaction between ecology and hydrology and the differential responses of microforms related to their initial ecohydrological conditions.This research was funded by NSERC (Canada) and Canadian Foundation for Climate and Atmospheric Science (CFCAS) grants to J.M.W., NSERC Julie Payette and CGS scholarships to M.S., and a postdoctoral grant from the Academy of Finland (project 12328) and from the Faculty des Sciences de l'Agriculture et de l'Alimentation, Université Laval, to E.T

Everyday Secrecy:Boundaries of Confidential Gossip

Gossip is an everyday part of organizational life and has been increasingly researched. However, some gossip has a particular character, whereby it is to some degree secret. Drawing on studies of both gossip and secrecy, in this paper we explore this ‘confidential gossip’ via a participant observation case study. This was based on an internship with Quinza, a British media company, and had a covert element which is discussed and justified. Specifically, we show how the boundaries around confidential gossip are marked in organizational interactions. The paper contributes to existing knowledge about organizational gossip by showing the particular significance of secrecy which makes confidential gossip a more potent source of group inclusion and exclusion

The Complete Star Formation History of the Universe

The determination of the star-formation history of the Universe is a key goal of modern cosmology, as it is crucial to our understanding of how structure in the Universe forms and evolves. A picture has built up over recent years, piece-by-piece, by observing young stars in distant galaxies at different times in the past. These studies indicated that the stellar birthrate peaked some 8 billion years ago, and then declined by a factor of around ten to its present value. Here we report on a new study which obtains the complete star formation history by analysing the fossil record of the stellar populations of 96545 nearby galaxies. Broadly, our results support those derived from high-redshift galaxies elsewhere in the Universe. We find, however, that the peak of star formation was more recent - around 5 billion years ago. Our study also shows that the bigger the stellar mass of the galaxy, the earlier the stars were formed. This striking result indicates a very different formation history for high- and low-mass formation.Comment: Accepted by Nature. Press embargo until publishe

Hubble Space Telescope Imaging of Lyman Alpha Emission at z=4.4

We present the highest redshift detections of resolved Lyman alpha emission, using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Lyman alpha emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Lyman alpha photons at high redshift. While our data do not support a positional offset between the Lyman alpha and rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out of the three galaxies are significantly larger in Lyman alpha than in the rest-frame UV continuum. This result is confirmed when comparing object sizes in a stack of all objects in both bands. Additionally, the narrowband flux detected with HST is significantly less than observed in similar filters from the ground. These results together imply that the Lyman alpha emission is not strictly confined to its indigenous star-forming regions. Rather, the Lyman alpha emission is more extended, with the missing HST flux likely existing in a diffuse outer halo. This suggests that the radiative transfer of Lyman alpha photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts.Comment: Submitted to the Astrophysical Journal. 11 pages, 10 figure