Abstract Peatlands in the Western Boreal Plains act as important water sources in the landscape. Their persistence, despite potential evapotranspiration (PET) often exceeding annual precipitation, is attributed to various water storage mechanisms. One storage element that has been understudied is seasonal ground ice (SGI). This study characterized spring SGI conditions and explored its impacts on available energy, actual evapotranspiration, water table, and near surface soil moisture in a western boreal plains peatland. The majority of SGI melt took place over May 2017. Microtopography had limited impact on melt rates due to wet conditions. SGI melt released 139mm in ice water equivalent (IWE) within the top 30cm of the peat, and weak significant relationships with water table and surface moisture suggest that SGI could be important for maintaining vegetation transpiration during dry springs. Melting SGI decreased available energy causing small reductions in PET (<10mm over the melt period) and appeared to reduce actual evapotranspiration variability but not mean rates, likely due to slow melt rates. This suggests that melting SGI supplies water, allowing evapotranspiration to occur at near potential rates, but reduces the overall rate at which evapotranspiration could occur (PET). The role of SGI may help peatlands in headwater catchments act as a conveyor of water to downstream landscapes during the spring while acting as a supply of water for the peatland. Future work should investigate SGI influences on evapotranspiration under differing peatland types, wet and dry spring conditions, and if the spatial variability of SGI melt leads to spatial variability in evapotranspiration.
Abstract In many areas of Ontario concentrations of nitrate in groundwater at levels above the Ontario drinking water limit of 10 mgL−1 constitute a serious threat to municipal drinking water supplies. In the Region of Waterloo permeable soils and high nitrogen application rates on farmland combine to produce high risk zones in a significant portion of the rural landscape. This study assesses the potential risk of agricultural land use on nitrate contamination in four well fields located west of the city of Waterloo. Secondary data from government documents and consultants’ reports were used to develop GIS layers for soil drainage and nitrogen application rates by land use system. These layers were combined to produce a measure of risk of nitrate groundwater contamination associated with the combined effect of both factors. Results indicate that approximately 45% of the study area is at high risk. Two well fields, one of which was closed because nitrate levels exceeded the Ontario drinking water limit, have nearly 60% of their recharge areas in the high risk category. If this situation is to be improved, programs directed towards changing current nutrient management practices must be instituted. Dans bien des régions de l’Ontario, la concentration de nitrate dans les eaux souterraines dépasse la limite admise par la province pour l’eau potable (10 mg/l) et représente une sérieuse menace pour l’approvisionnement en eau potable des municipalités. Dans la région de Waterloo, la perméabilité du sol et les taux élevés d’application de nitrate sur les terres agricoles se combinent pour faire des secteurs environnants des zones à risque élevé. L’auteur de la présente étude évalue le risque que peut représenter l’exploitation agricole des terres sur la contamination au nitrate de quatre champs de captage situés à l’ouest de Waterloo. Il s’est servi de données secondaires de source gouvernementale et de rapports émis par des consultants pour cerner les couches SIG de drainage et les taux d’application d’azote selon le système d’utilisation des terres. Ces couches se combinent pour produire une mesure du risque de contamination au nitrate des eaux souterraines, sous l’effet des deux facteurs. Les résultats indiquent qu’environ 45 p. 100 des terres étudiées présentent un risque élevé. Deux champs de captage, dont un qu’il a fallu fermer parce que son niveau de nitrate dépassait la limite permise pour l’eau potable en Ontario, s’alimentent dans une proportion de presque 60 p. 100 dans ces zones à risque élevé. Pour remédier à la situation, il faudra mettre en oeuvre des programmes qui encouragent la modification des pratiques actuelles de gestion des nutriants.
Abstract The Western Boreal Plain (WBP) comprises a diverse array of wetland types; however, swamps are understudied in the WBP relative to other wetlands, despite their ubiquity. We apply an ecohydrological and GIS‐based research approach at a fen–swamp complex in the WBP to characterize the ecohydrological properties of the varying wetland types and relate these interactions to the hydrologic function of the watershed. In this study, we evaluate 3 years of hydrological monitoring data, with additional hydrochemical, vegetation and remote sensing data. In our analyses, we identified five land types: fen, flat peat swamp and peat margin swamp (peatlands), mineral swamp and upland. Flat peat swamp was distinguished from fen using Ducks Unlimited criteria, stating fens cannot have trees >10 m in height. Little difference in water table variability, groundwater connectivity, vegetation composition and water chemistry were found between flat peat swamp and fen, suggesting that for all practical purposes, they can be considered a single unit and tree height alone cannot be used to differentiate these peatland types. In contrast, peat margin swamps exhibited lower and more variable water tables and consistent downward hydraulic gradients and comprised a mixture of peatland and upland vegetation. Peat margin swamps, however, exhibited similar porewater pH, electrical conductivity and base cation concentrations as upland, flat peat swamp and fen, suggesting that they are well connected hydrologically. Peat margin swamps were also found to modulate subsurface water movement between fen and upland (via reduced transmissivity from lower water tables) and therefore act as distinct ecohydrological units.
Abstract Peatlands represent over 90% of Canadian wetlands and are the focus of considerable hydrological and biogeochemical research. Research on evapotranspiration (ET) has shown that it can exceed annual precipitation (P) where there are replenishing flood events. Evaporation from open water ponds in boreal peatlands exceeds ET from vegetated riparian zones by about two times, but surrounding forests can shelter small ponds by reducing turbulence. In an open bog, evaporation was modelled by separating the surface into vascular vegetation, hummock moss and hollow moss surfaces, and showed that vascular plants contribute 60-80% of ET, mosses making up the remainder with hummock mosses dominant over hollows. Runoff from peatlands is enhanced by features ranging from headwater swamps, ice-cored peat plateaus, patchy arctic wetlands and even sections of riverine peatlands. Groundwater fluxes can be quite erratic, and depend on transient properties of the peat that depend on moisture content (e.g., unsaturated hydraulic conductivity) to unsteady saturated hydraulic properties (e.g., hydraulic conductivity, specific yield) caused by peat compression and dilation associated with water storage changes. Surface elevation adjustments can result in a more stable depth to water table, increase evaporation losses, increase methane emission, and attenuate pore-water concentration of contaminants. Research on Canadian peatlands has also made significant methodological advances, including measurement of hydraulic properties of living mosses and peat pore-water and pore dimension characteristics. A considerable multi-annual effort has also been made in evaluating carbon dynamics from Canadian peatlands. Summer moisture availability is important to determining carbon fluxes with some peatlands experiencing enhanced productivity following drought (water table drawdown). Sudden changes in water table elevation promote DOC production and export. Methane bubbles confound hydraulic gradients and flows by creating local pockets of pressure, which are then released episodically when the entrapped gas reaches a threshold content. Canadian peatland hydrology continues to be actively researched in lab, field and modelling studies. Les tourbières représentent au-delà de 90 % des milieux humides au Canada et font l'objet d'un nombre considérable de recherches hydrologiques et biogéochimiques. Les recherches sur l'évapotranspiration (ET) ont révélé qu'elle peut dépasser les précipitations annuelles (P) là où se produisent des inondations qui entraînent une réalimentation des cours d'eau. L'évaporation des étangs à ciel ouvert dans les tourbières boréales dépasse d'environ deux fois l'ET des zones riveraines enherbées. Cependant, les forêts environnantes peuvent servir d'abri aux petits étangs en réduisant la turbulence. Dans une tourbière ouverte, l'évaporation a été modélisée grâce à la répartition de la surface en végétation vasculaire, en mousses de buttes et en surfaces de mousses creuses, et le tout a révélé que les plantes vasculaires contribuent de 60 à 80 % de l'ET. Les mousses représentent le reste, les mousses de buttes étant dominantes par rapport aux dépressions. L'écoulement des tourbières se trouve à être accru du fait de diverses caractéristiques, notamment les marécages d'amont, les plateaux palsiques à noyau de glace, les marécages arctiques épars et les sections homogènes des tourbières riveraines. Les flux d'eau souterraine peuvent être très irréguliers et reposent sur les propriétés transitoires de la tourbe qui dépendent de la teneur en humidité (p. ex. conductivité hydraulique en régime insaturé) et des propriétés hydrauliques saturées instables (p. ex. conductivité hydraulique, débit spécifique) causées par la compression et la dilation de la tourbe associées aux changements au niveau de l'emmagasinement des eaux. Les ajustements à l'élévation de surface peuvent résulter en une profondeur plus stable de la surface de la nappe, accroître les pertes par évaporation, augmenter les émissions de méthane et atténuer la concentration des contaminants dans les eaux interstitielles. Les études menées sur les tourbières du Canada ont également permis de réaliser d'importantes percées méthodologiques, notamment la mesure des propriétés hydrauliques des mousses vivantes et de l'eau interstitielle de la tourbe et des caractéristiques dimensionnelles de l'eau interstitielle. Des efforts considérables s'échelonnant sur de nombreuses années ont été déployés pour évaluer la dynamique du carbone des tourbières canadiennes. L'humidité disponible en été est importante pour la détermination des flux de carbone, certaines tourbières connaissant une productivité accrue à la suite d'une sécheresse (rabattement de la nappe phréatique). Des changements soudains dans l'élévation de la surface de la nappe favorisent la production et les exportations de carbone organique dissous. Les bulles de méthane confondent les gradients et les écoulements hydrauliques en créant des poches locales de pression, qui sont par la suite libérées de manière épisodique lorsque les gaz piégés atteignent un certain seuil. L'hydrologie des tourbières au Canada continue de faire l'objet de recherches actives en laboratoire et sur le terrain, sans oublier les études de modélisation.
Abstract In Canada, peatlands are the most common type of wetland, but boundary delineation in peatland complexes has received little attention in the scientific literature. Typically, peatland boundaries are mapped as crisp, absolute features, and the transitional lagg zone—the ecotone found between a raised bog and the surrounding mineral land—is often overlooked. In this study, we aim (1) to advance existing approaches for detecting and locating laggs and lagg boundaries using airborne LiDAR surveys and (2) to describe the spatial distribution of laggs around raised bog peatlands. Two contrasting spatial analytical approaches for lagg detection were tested using five LiDAR‐derived topographic and vegetation indices: topography, vegetation height, topographic wetness index, the standard deviation of the vegetation's height (as a proxy for the complexity of the vegetation's structure), and local indices of elevation variance. Using a dissimilarity approach (edge‐detection, split‐moving window analysis), no one variable accurately depicted both the lagg‐mineral land and bog‐lagg boundaries. Some indicators were better at predicting the bog‐lagg boundary (i.e., vegetation height) and others at finding the lagg‐mineral land boundary (i.e., topography). Dissimilarity analysis reinforces the usefulness of derived variables (e.g., wetness indices) in locating laggs, especially for those with weak topographic and vegetation gradients. When the lagg was confined between the bog and the adjacent upland, it took a linear form, parallel to the peatland's edge and was easier to predict. When the adjacent mineral land was flat or sloping away from the peatland, the lagg was discontinuous and intermittent and more difficult to predict.
