Celina Campbell

Pollen preservation: Experimental wet‐dry cycles in saline and desalinated sediments

Abstract Experimental degradation of pollen by repeated wet‐dry cycles in saline and desalinated sediments show differences in preservation between taxa and between salinity environments. In desalinated sediment, from which the salts were removed artificially, pollen is rapidly degraded, with a significant net loss of pollen after ten wet‐dry cycles. Picea pollen, which remains identifiable even when heavily damaged, suffers greater breakage in desalinated sediments. Artemisia pollen is rapidly rendered unidentifiable by degradation of the sculptural elements in both saline and desalinated sediments. In comparison to desalinated sediments, saline sediments appear to contain less damaged pollen. Growing salt crystals may envelop the pollen grains and stabilize them against mechanical breakage otherwise incurred by flexing of the pollen wall during desiccation. Caution should be exercised when analyzing sediments subject to wet‐dry cycles, and laboratory procedures modified if necessary to avoid desiccation...

Spatial patterning of net primary production in wetlands of continental western Canada

Abstract Net primary production in wetlands of continental western Canada (Alberta, Saskatchewan, Manitoba) is mapped and summarized by wetland type and ecoregion. The region contains 405 300 km2 of wetlands, with peatlands representing 90.1% of all wetlands. Based on a regional synthesis of published values of net primary production, shrubby swamp and marsh wetlands produce more biomass annually through the process of net primary production than peatlands. Different peatland types appear to sequester similar amounts of plant biomass on an annual basis, with the exception of permafrost bogs that sequester less. Wetland net primary production for the region is calculated as 2.1 ¥ 1014 g yr-1 of plant biomass, with 73.5% sequestered in peatlands. This is equivalent to 9.95 ¥ 1013 g yr-1 of carbon. Provincially this carbon is partitioned into 50% for Manitoba, 30% for Alberta, and 20% for Saskatchewan. Over the last 1000 years, an average of only 5% of this biomass (and carbon) accumulate as peat, with most lost through the process of decomposition. When the annual amount of carbon that accumulates as peat is compared to the amount emitted provincially as anthropogenic greenhouse gases, wetlands present in each of the provinces accumulate 4% (Alberta), 8% (Saskatchewan), and 62% (Manitoba) of the emitted carbon annually. Wetlands in continental western Canada are a significant, active biosphere carbon sink following accumulation patterns of the last one thousand years. Future changes, particularly in fire frequency or intensity, may alter this accumulation pattern.

A first estimate of organic carbon storage in Holocene lake sediments in Alberta, Canada

This paper reports a first estimate of the Holocene lake sediment carbon pool in Alberta, Canada. The organic matter content of lake sediment does not appear to depend strongly on lake size or other limnological parameters, allowing a simple first estimate in which we assume all Alberta lake sediment to have the same organic matter content. Alberta lake sediments sequester about 15 g C m-2 yr-1, for a provincial total of 0.23 Tg C yr-1, or 2.3 Pg C over the Holocene. Alberta lakes may represent as much as 1/1700 of total global, annual permanent carbon sequestration.

Late Holocene vegetation and fire history at the southern boreal forest margin in Alberta, Canada

Abstract A transect of three shallow ponds across the Aspen Parkland/Boreal Forest transition in Elk Island National Park, Alberta, Canada, shows changes in late Holocene vegetation and disturbance dynamics, and consequent carbon storage, in response to climate change and to recent anthropogenesis. Pollen and charcoal analyses reveal unexpected changes in fire regime. Although there is the expected decline in fire activity during the historic period, presumed due to agricultural clearance around the park, there is also a prehistoric fluctuation in fire regime at one of the sites. Pollen evidence suggests that the fluctuations in fire regime may be due to changes in hydrology. Declining groundwater levels during the Medieval Warm Period allowed the replacement of substantial areas of shrub birch (Betula glandulosa) with the less fire-prone aspen (Populus tremuloides) causing a decline in fire frequency and/or severity, while increasing carbon storage on the landscape. This is counter to the intuitive increase in fire activity with warmer and drier climate. Canadian national parks are currently managed under a ‘natural processes and conditions’ paradigm; the changes in conditions and consequent changes in processes evident due to the relatively minor climatic fluctuations of the Little Ice Age and Medieval Warm Period shown here suggest a need to revisit this paradigm in consideration of future anthropogenic climate change.

The late Holocene paleohydrology of Pine Lake, Alberta: a multiproxy investigation

This paper reports on a high-resolution, multi-proxy, late-Holocene study from a lake in the Aspen Parkland of southern Alberta, Canada. A sediment core spanning the last 4000+ yrs from Pine Lake was analyzed for charcoal, granulometry, grain roundness, tephra content, geochemistry, mineralogy and pollen. This multi-proxy record indicates: (1) increasing anoxia causing a shift in S deposition from gypsum to pyrite due to increasing moisture availability in the late Holocene; (2) a decrease in Mg flux into the lake due to the development of the aspen forest, which reduced water flow through the Mg-rich shallow sand aquifer; the aspen forest expansion was in turn induced by the extirpation of plains bison prior to settlement; and (3) a change in the upland fire regime from frequent low-biomass grass fires to less frequent but higher biomass under-story fires, also as a result of the expansion of the aspen forest. Not only are the different proxies sensitive to different rates and magnitudes of change, they also show different sensitivities to different types of hydrological change: the mineralogy and geochemistry are sensitive to changes in water level and redox potential, and to changes in the relative strengths of the aquifers feeding the lake, while the granulometry is sensitive to total hydrological balance. Thus, apparently contradictory proxy results should be viewed as complementary.

Postglacial evolution of a fine-grained alluvial fan in the northern Great Plains, Canada

Abstract This paper reports on the first subsurface core taken from an alluvial fan in the interior plains of western Canada. Sedimentary structures, grain size, grain roundness, loss on ignition, charcoal abundance, bulk authigenic geochemistry, colour, mineralogy and microscopic charcoal identifications show that a fine-grained fan developed through a succession of depositional environments. Within each environment, sediment erosion, transportation and deposition processes were conditioned by changing dominant partial area contributions and complex geomorphic responses. Neither the rate nor the processes of aggradation have been constant through time. Succession from one depositional environment to another involved the crossing of geomorphic thresholds. While climate may have affected sediment yield and therefore the timing of threshold crossings, the basic sequence was controlled by aggradation alone. The sensitivity of this site to climate change is thus overwhelmed by internal processes.