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Eddy covariance (EC) is one of the most effective ways to directly observe evaporation from a lake surface. However, the deployment of EC systems on lakes is costly and technically challenging which engenders a need for accurate modelling of evaporation from reservoirs for effective management. This study aims to 1) refactor the Canadian Small Lakes Model (CSLM) into modern high-level programming languages in open-source repositories and 2) evaluate evaporation estimates from the CSLM using nine years of EC observations of a pit-lake in Northern Alberta. The CSLM is a 1-D physical lake model simulating a mixing layer and arbitrary thick skin layer which interfaces with the atmosphere and includes a module for ice dynamics. It was developed to interface with the Canadian Global Coupled models as part of the surface classification scheme, and thus utilizes widely accessible forcing data. In this study the CSLM evaporation estimates are also compared to a commonly used bulk transfer method of estimating evaporation. In general, the CSLM had smaller open-water season error (RMSE of 0.70 mm day-1) than the bulk transfer method (RMSE of 0.83 mm day-1). However, if EC data is available, further improvement can be gained by using an Artificial Neural Network to adjust the modelled fluxes (RMSE of 0.51 mm day-1). This final step can be very useful for gap-filling missing data from lake observation networks as there has been recent attention on the limited coverage of direct open water evaporation observations in the literature. [ABSTRACT FROM AUTHOR]

The first three years of net ecosystem exchange of carbon dioxide (NEE) for a wetland constructed on bitumen mine tailings show its progression towards becoming an annual carbon dioxide sink. • A reclaimed wetland was a source of CO 2 for the first 2 years after construction. • In year 3 the wettest region absorbed 77 g C m−2, similar to natural peatlands. • Drier regions remained net CO 2 sources due to greater rates of soil respiration. Northern peatlands contain up to 20% of the ∼3000 Pg of global soil organic carbon. Carbon-rich peatlands cover upwards of 65% of the landscape in northern Canada where resource extraction activities disturb both the carbon pools and the future carbon sequestration capacity of the landscape. Previous estimates of the carbon losses from this disturbance predict a complete loss of the region's peatland carbon pool. Mining industries operating in these sensitive environments have recently begun constructing closure landscapes which are intended to develop carbon cycle processes similar to undisturbed northern peatlands. This study investigates eddy covariance fluxes of carbon dioxide (CO 2) at one of Canada's first fully constructed boreal plains watersheds, the Sandhill Fen Watershed. During the first three years since inception, only the lowland region had an annual net ecosystem exchange of CO 2 (NEE) indicative of increasing CO 2 sink potential. The lowland region was characterized by saturated salvaged peat soils, standing water, thriving communities of Typha and Carex spp. and was a net CO 2 sink of 77 g C m−2 in the third year. At the same time the upland and the midland regions characterized by moist salvaged peat soils and a mix of herbaceous, shrub and planted Picea glauca and Pinus banksiana remained net sources of CO 2. Despite similar rates of gross primary production, ecosystem and plot-level respiration rates in the lowland were significantly lower than in the midland region, likely due to very low reduction potentials within the lowland's saturated soils. With no other significant outflows of carbon, the lowland of the Sandhill Fen Watershed may be in the early stages of organic matter accumulation. Due to limited oxidation of the salvaged peat substrate in the lowland region, wetland reclamation employing these techniques may reduce the disturbance loss of the carbon pool in the boreal plains. [ABSTRACT FROM AUTHOR]

• GEP in reclaimed broadleaf forests is lower than harvested or mature forests. • The moisture retention of the soils also promotes low water use efficiencies. • Large reclamation projects must balance forest growth and downgradient water yields. Reclaiming upland boreal forests as part of post-mining watershed construction in the Athabasca Oil Sands Region (AOSR) requires evaluation criteria as these novel ecosystems develop. Here, we analyzed 55 site-years of eddy covariance observations of constructed forests and soils on formally pit-mined landscapes (9 sites) and contrasted them to 18 site-years of post-harvested ecosystems (3 sites) and 38 site-years of mature Boreal Plains ecosystems (3 sites). After approximately 5 years, the post-harvested sites had fluxes of gross primary productivity (GPP), evapotranspiration (ET), and water use efficiency (WUE) within the variability of the widely studied mature Boreal Plains BERMS FLUXNET sites. However, even after 10 years the constructed forests had significantly lower WUE than the mature sites. High ET fluxes drove low WUE in the constructed upland conifer sites despite similar rates of GEP. Conversely, in the constructed broadleaf forests low GEP, despite similar ET, resulted in low WUE. A climate sensitivity analysis showed that there was little impact of abnormal hot, cold, wet, or dry growing seasons on GEP or evapotranspiration (ET) at the constructed forests. It is presumed that the high moisture retaining properties of the soils used in reclamation produced the low WUE and resilience to dry and hot conditions in constructed forests. Placing moisture retaining soils incorporates a degree of resilience to climate variability but also limits downgradient water yields to low lying wetlands in the relatively dry AOSR climate. This highlights a potential shortcoming of reclamation objectives developed for specific ecosystems when scaling from ecosystem to watershed scale construction. Finally, robust relationships between satellite observed greenness (MODIS EVI and NDVI) and ecosystem scale fluxes highlight how remote sensing-based metrics can be used by land managers to identify regions within landscape units that may be under performing. [ABSTRACT FROM AUTHOR]

Mine reclamation in the Athabasca oil sands region is legally required as companies must reconstruct disturbed landscapes into functioning ecosystems which previously existed in the Boreal landscape. Upland-wetland systems are relatively new in the constructed landscape and only two exist to date. The objective of this work is to understand the key hydrological changes post-management of a constructed peatland watershed and provide insight on the overall system function. Six years of hydrometric data are presented from the Sandhill Fen Watershed (SFW), a 52-ha upland-wetland catchment built on soft tailings with a pump system to provide fresh water, support drainage, and limit salinization. Wet years (seasonal precipitation > evapotranspiration) occurred in 2013, 2016 and 2018 and dry years (seasonal precipitation < evapotranspiration) occurred in 2014, 2015 and 2017 where wet years had large 5-, 10- and 100-year storms which were absent in dry years. Surface conductance and solar radiation explained most of the variation in ET fluxes. Changes in management practices drove many of the observed hydrological changes. Heavy management in 2013 muted water table (WT) responses to climate as inflow and outflow (via pumps) controlled WT response. After 2014, management efforts declined and hydrological exchanges were predominantly vertical, and saturated storage across the wetland increased. As a result, WT variability was tightly coupled to ET regardless of WT position relative to the ground surface, with greater changes related to deeper water tables, suggesting the absence of water conserving feedback mechanisms. Intra-watershed water movement was primarily towards the wetland from recharge areas in the upland swale, whereas surface runoff was rare and only occurred during extreme rain events and spring snowmelt. Peat properties were degraded compared to those observed in undisturbed peatlands, and natural stratification of the peat profile was absent. Results suggest that current conditions are not favorable for fen-peatland development as marsh-like conditions have developed, limiting water conserving functions and the ability to persist long-term in a changing climate. Development of the wetland (top) and upland (bottom) in the Sandhill Fen Watershed from 2013 to 2018. [Display omitted] • Reduced hydrologic management shifted the dominant water fluxes and WT responses to P and ET. • Upland ET > wetland ET, and upland ET increased year-over-year while wetland ET decreased. • WTs primarily coupled to atmospheric forcing indicating absence of water-conserving functions. • Quality of peat material degraded as natural stratification was absent. • Variable WTs, degraded peat, salinity and marsh-like areas are barriers for fen-peatland success. [ABSTRACT FROM AUTHOR]

Currently, post-mining landscape plans in the Athabasca Oil Sand Region include large watersheds terminating in pit lakes. In 2012, Base Mine Lake (BML), was constructed with the aim of demonstrating technologies associated with lake reclamation in the region. This paper examines the first 6.5 years of lake-atmosphere energy and carbon exchange. Energetically, BML behaved similar to other northern lakes, storing large quantities of heat in the spring and releasing it in the fall as sensible and latent heat fluxes. At various times a hydrocarbon sheen formed on the lake, which may have suppressed evaporation. However, simple linear relationships failed to statistically quantify the impacts and more comprehensive modelling of the variability may be required. At daily scales, variability in evaporation was well explained by the product of vapour pressure deficit and wind speed as well as the available energy (R2 = 0.74), while sensible heat was explained by the product of wind speed and the difference in air and surface temperature as well as available energy (R2 = 0.85). Spring CH 4 fluxes were high, particularly around ice melt, with a maximum flux of 3.3 g m−2 day−1. Otherwise fluxes were low, except during irregular periods. The peak flux of these periods occurred following ~58 h of continuously falling pressure, relating cyclone activity to these large periods of methane emissions. Annually, CO 2 and CH 4 fluxes were initially high, with median fluxes of 231 mg CO 2 m−2 h−1 and 23 mg CH 4 m−2 h−1 in 2014. However, the median fluxes reduced quickly and over the least three years of the study (2017 through 2019) the median fluxes declined to 36 mg CO 2 m−2 h−1 and 10 mg CH 4 m−2 h−1. Overall, BML behaves similar to other boreal lake ecosystems with above average carbon fluxes compared to other constructed reservoirs. Relative pressure preceeding peak CH 4 emissions (top). Grey shading indicates the 32 to 68th percentiles (±1 SD), black line is median. Middle panel shows the 2017 CH 4 fluxes (grey), with 24 hour gap filled mean (black), to illustrate the peaks (pink arrows) identified by the detection algorithm. Horizontal dotted line is the 90th percentile of CH 4 fluxes used to set the minimum threshold for the peak detection. The bottom panel is the air pressure over the same period. The 2017 timeseries was selected for this example because it had the most complete CH 4 flux and pressure records. Unlabelled Image • Reclamation activities produced a lake energetically similar to other boreal lakes. • Methane emissions are related to cyclone activity. • Methane emissions are largest in the spring, around changing ice conditions. • Initially carbon emissions are high. • After three years' carbon emissions are comparable to other reservoirs. [ABSTRACT FROM AUTHOR]

Oil sand mining in the boreal planes of Canada has been predicted to release stockpiled carbon from disturbed peatlands and permanently degrade the carbon sequestering capacity of the landscape (Rooney et al. 2012). The Sandhill Fen Watershed (SFW) is a pilot watershed built on soft tailings in an infilled pit mine to reclaim lost peatland services. It was constructed between 2009 and 2012 and is composed of 60 ha of mixed upland and lowland ecosystems. This analysis presents the first six years of carbon cycling using a mix of DOC pore-water samples, eddy covariance techniques and chamber measurements. At first, the lowland region rapidly shifted to an annual sink of CO2, having an annual Net Ecosystem Exchange of 77 g C-CO2 m-2 by the third year, while maintaining comparable rates of GPP to the reclaimed upland regions. Unlike the uplands however, the lowlands had much lower rates of heterotrophic respiration. This suggests that the design of the ecosystem maintained the salvaged peat in sufficiently anoxic conditions to limit decomposition. However, shifts in the vegetation towards marshland associated species altered the seasonality of photosynthesis has resulted in delayed spring uptake and the lowlands returning to an annual net source of carbon to the atmosphere. Methane emissions have continued to be suppressed over all six years despite organic material in anoxic conditions. The suppressed methane is likely due to competition from sulphate- and metal-reducing bacteria. Over the same period, DOC is increasing in the SFW pore water, but with limited outflow pathways to the surrounding landscape, it is likely not a major carbon flux out of the ecosystem. [ABSTRACT FROM AUTHOR]

Plant communities and water chemistry properties were characterized at Sandhill Wetland; an experimental reclamation site constructed above a backfilled open pit mine in northeastern Alberta, Canada. Observations from the reclamation site were compared to 12 mature reference wetlands (10 fens and 2 marshes) to determine the type of natural wetland the site most closely resembles at its current successional stage. From this survey of 20 research plots distributed across Sandhill Wetland, 44 plant species were encountered (35 vascular plants and 9 bryophytes). Using multivariate approaches, diversity indices, and coefficient of conservatism values, results indicate areas with water levels above the soil surface at Sandhill Wetland are most comparable to regional marshes, with Typha latifolia and Carex aquatilis exhibiting the highest cover. Across the wetland periphery where water levels are several centimeters below the soil surface, plant communities were quite dissimilar from the reference sites and dominated by the grass Calamagrostis canadensis. Based on principle components analysis, we show water chemistry at Sandhill Wetland is in a state that is between marshes and saline fens. Sandhill Wetland overall possesses a unique set of structural and chemical features in the sixth year of development. In areas where water levels are above the soil surface there is potential for development into a slightly brackish marsh analogue. The successional trajectory of low water table position areas is somewhat uncertain as the wetland periphery exhibited mixed characteristics resembling those of wet meadow, riparian, and upland environments, which we did not survey. • Sandhill Wetland plant communities resemble regional marshes in some areas • Plants have sorted out into spatially distinct zones due to water level preference • Sodium concentrations have increased annually at Sandhill Wetland since inception • Sodium-tolerant plants are present at Sandhill Wetland, albeit at low abundance • Further monitoring should continue to track potential community shifts [ABSTRACT FROM AUTHOR]