Reclaiming to Brackish Wetlands in the Alberta Oil Sands: Comparison of Responses to Sodium Concentrations by Carex atherodes and Carex aquatilis

The variation in sodium concentrations in waters of natural fens and marshes on the western Canadian landscape provides a background for choosing the appropriate plants for wetland reclamation. Broad tolerances to salinity are especially important for reclamation trials on saline-rich ‘in-pits’ that were left from open-pit oil sands mining. One such species, Carex aquatilis, has been identified as a key species in early reclamation attempts; however, at the Sandhill Wetland on the Syncrude Canada oil sands lease, this species has aggressively colonized, dominating parts of the wetland and limiting species diversity. A second species, also widespread on natural lake shores and marshes, is Carex atherodes, with field observations suggesting a broad tolerance to salinity. Here, we examine the responses of this species to a series of sodium concentrations and compare these to those of C. aquatilis. In particular, we addressed three questions: (1) How do structural attributes of C. atherodes respond to a series of Na+ concentration treatments? (2) Are different structural responses related to the functional attributes of photosynthesis, stomatal conductance, and/or transpiration rate? (3) How do these responses compare to those of C. aquatilis? We implemented a phytotron experiment to test the responses of these two species to either five or six concentrations of sodium, ranging from 20 to 3000 mg Na+ L−1. In general, structural responses of C. atherodes did not differ between 50 and 789 mg Na+ L−1, while performances of all attributes were reduced at 1407 mg L−1. Physiological attributes had high variation, but also had reduced performances at similar treatment levels. In comparison, a clear threshold was present for structural attributes in Carex aquatilis between 1650 and 2148 mg Na+ L−1, while physiological attributes were reduced between 1035 to 1650 mg Na+ L−1. These responses from C. aquatilis were similar to those previously reported. Na+ concentrations in porewater at the Sandhill Wetland in 2019 reached as high as 1200 mg Na+ L−1, with natural subsaline and sodic sites ranging much higher. Although all of the plants in the treatments remained viable at the end of the experiment, these results indicate that Na+ concentrations above 1500–2000 mg Na+ L−1 may inhibit the growth of these two species and decrease their competitive abilities.

Swampy mesotrophic peatmoss spruce forests of European Russia and Urals

На основе выборки из 130 геоботанических описаний, сделанных авторами в 1995-2019 гг. или взятых из литературы, проведена доминантно-детерминантная классификация топких мезотрофных (Picea abies s.l.) ельников сфагновых, развивающихся при подтоплении либо периодическом затоплении в Европейской России и на Урале. Ценотическое разнообразие этих сообществ определяется спецификой названных процессов в сочетании с климатическими факторами, тогда как роль почвообразующих пород почти не выражена. Выделено 6 ассоциаций с 6 субассоциациями и 2 вариантами, всего 11 синтаксонов (табл. 1). В их числе подтопленные ельники вейниковые сфагновые с господством Calamagrostis purpurea s.l. и Equisetum sylvaticum в травяном ярусе (4 субассоциации в разных подзонах тайги либо долготных секторах), вздутоосоковые с Carex rostrata и C. vesicaria и вахтовые с Menyanthes trifoliata (2 субассоциации). Кроме того, выделены эндемичные для Южного Урала ельники малоцветковоосоковые с C. pauciflora и Rubus chamaemorus, развивающиеся на поверхностном дождевом стоке (2 варианта), приречные северотаежные водноосоковые с Carex aquatilis и затопленные южно- и подтаежные белокрыльниковые с Calla palustris. Для большинства синтаксонов характерны Swampy mesotrophic peatmoss spruce forests, dominated by Picea abies s.l. and originated due to inundation or periodical flooding, have been classified in European Russia and the Urals using the dominant-determinant approach to vegetation. The data set involves 130 relevés made by the authors in 1996-2019 or taken from the published sources. 11 syntaxa are totally recognized (see Table 1). Inundated reedgrass-peatmoss (with the dominance of Calamagrostis purpurea s.l. and Equisetum sylvaticum in the field layer; 4 subassociations in different subzones or longitudinal sectors), sedge-peatmoss (with Carex rostrata and C. vesicaria), and trefoil-peatmoss (with Menyanthes trifoliata; 2 subassociations) spruce forests are recognized. In addition, one can distinguish sedge-cloudberry-peatmoss spruce forests with Carex pauciflora и Rubus chamaemorus in the subalpine belt of the Southern Urals, developing due to surficial rain flow, also riverine northern-boreal sedge-peatmoss forests with Carex aquatilis and flooded southern- and hemiboreal calla-peatmoss spruce forests with Calla palustris. The observed syntaxonomic diversity is governed by inundation/flooding intensity and longevity together with latitudinal zonation and climate continentality, whereas the role of bedrock type influence is minimal. Multi-dominance and mutual replaceability are typical for peatmosses in most of the syntaxa.

Impacts of Wetland Plants on Microbial Community and Methane Metabolisms

Aims Microbial activity in the soil of wetlands is responsible for the emission of more methane to the atmosphere than all other natural sources combined. This microbial activity is heavily impacted by plant roots, which influence the microbial community by exuding organic compounds and by leaking oxygen into an otherwise anoxic environment. This study compared the microbial communities of planted and unplanted wetland soil from an Alaskan bog to elucidate how plant growth influences populations and metabolisms of methanogens and methanotrophs. Methods A common boreal wetland sedge, Carex aquatilis, was grown in the laboratory and DNA samples were sequenced from the rhizosphere, unplanted bulk soil, and a simulated rhizosphere with oxygen input but no organic carbon. Results The abundance of both methanogens and methanotrophs were positively correlated with methane emissions. Among the methanotrophs, both aerobic and anaerobic methane oxidizing microbes were more common in the rhizosphere of mature plants than in unplanted soil, while facultative methanotrophs capable of utilizing either methane or other molecules became relatively less common. Conclusions These trends indicate that roots create an environment which favors highly specialized microbial metabolisms over generalist approaches. One aspect of this specialized microbiome is the presence of both aerobic and anaerobic metabolisms, which indicates that oxygen is present but is a limiting resource controlling competition.

Structural and functional responses of Carex aquatilis to increasing sodium concentrations

Carex aquatilis is a widespread boreal species that is abundant in open fens and marshes. The species has broad natural tolerances to differing water levels and ion concentrations including occurrences in brackish marshes but not sodic wetlands. Sandhill Wetland, constructed on Syncrude Canada Ltd. mineral surface lease in the Athabasca Oil Sands Region, is a research site that was engineered to support a self-sustaining wetland. The site is currently in its eighth year post wet-up and is partially dominated by C. aquatilis. Increasing Na+ concentrations in the porewaters at Sandhill Wetland are an on-going concern for the performance of the existing plant communities. Here we examine the responses of C. aquatilis to an increasing regime of sodium carried out in a greenhouse experiment. We posed three questions for this experiment: (1) is there a threshold response for performance of C. aquatilis to increasing sodium, (2) if so, does it occur in the range of sodium that is present at current reclamation programs, and (3) is C. aquatilis resistant to high concentrations of sodium? Carex aquatilis survived all treatment concentrations of sodium including the highest treatment of 2354 mg L− 1. In general, both structural and functional attributes of C. aquatilis did not differ between the 17 and 1079 mg L− 1 treatments; however, performances of all attributes were reduced in the 2354 mg L− 1 treatment. Belowground biomass had greater decreases compared to aboveground components, including both biomass and photosynthesis. The aboveground decreases in performance were associated with exclusion of sodium from the aboveground components by the belowground components. Reduction in photosynthesis was strongly correlated with reduced stomatal conductance and lower transpiration. Although C. aquatilis demonstrated a wide tolerance to sodium concentrations, a clear threshold was present between 1079 and 2354 mg L− 1. These decreases in performance in our greenhouse trials were at levels currently present at Sandhill Wetland, and careful assessment of sodium concentrations in the near future needs to be continued.

Development of a subarctic peatland linked to slope dynamics at Lac Wiyâshâkimî (Nunavik, Canada)

A palaeoecological study of a subarctic minerotrophic peatland was undertaken to reconstruct the formation of the site as an archive of slope geomorphological processes. The study peatland is located about 400 m from Caribou slope (unofficial name) on Lepage Island, Lac Wiyâshâkimî, Nunavik (northern Québec, Canada). The site is close to the lakeshore and receives runoff directly from Caribou slope and its catchment. Gravity processes have been active on Caribou slope since the deglaciation of the region at approximately 6000 cal. yr BP. These processes may be differentiated in terms of Holocene stages of intensity. The objective of our study was to detect evidence of gravity processes in the peatland and to note their frequency since its establishment using loss-on-ignition testing, macrofossil analysis and radiocarbon dating. Our results indicate that peat began to accumulate over the sandy-gravelly sediments at around 4900 cal. yr BP. Larix Laricina, Carex aquatilis and Carex rostrata were present at this time until 4660 cal. yr BP, at which point these taxa were replaced by aquatic taxa such as Hippuris vulgaris and Daphnia (aquatic invertebrates). The percentage of mineral sediments (sand) remained high during this period, which could be linked to slope activity. After 4660 cal. yr BP, sandy sediments diminished while episodes of aquatic conditions and sand inflow occurred on at least three occasions (at 4660, 3905 and 3130 cal. yr BP). The increase in water flow and the introduction of more medium to fine sand into the peatland could be linked to slope movements and the long-distance runout of debris flow that we observed in the field. Given these factors, conditions at the study site remained wet from the earliest phases until the present. Unlike the subarctic permafrost peatlands in northern Québec, permafrost did not become established at the study site.

Thermo-erosion gullies boost the transition from wet to mesic vegetation

Continuous permafrost zones with well-developed polygonal ice-wedge networks are particularly vulnerable to climate change. Thermo-mechanical erosion can initiate the development of gullies that lead to substantial drainage of adjacent wet habitats. How vegetation responds to this particular disturbance is currently unknown but has the potential to strongly disrupt function and structure of Arctic ecosystems. Focusing on three major gullies of Bylot Island, Nunavut, we aimed at estimating the effects of thermo-erosion processes in shaping plant community changes. Over two years, we explored the influence of environmental factors on plant species richness, abundance and biomass studying 197 polygons that covered the whole transition from intact wet to disturbed and mesic habitats. While gullying decreased soil moisture by 40 % and thaw front depth by 10 cm in breached polygons, we observed a gradual vegetation shift within five to ten years with mesic habitat plant species such as Arctagrostis latifolia and Salix arctica replacing wet habitat dominant Carex aquatilis and Dupontia fisheri. This transition was accompanied by a five time decrease in graminoid above-ground biomass in mesic sites. Our results illustrate that wetlands are highly vulnerable to thermo-erosion processes that may rapidly promote the decrease of food availability for herbivores and reduce methane emissions of Arctic ecosystems.