Ian Spooner

A new method for visualizing sediment particle size distributions

Conventional uses of sediment grain size data as a proxy for paleoenvironmental processes are usually restricted to simple statistical descriptions of the particle size distribution (PSD) (e.g., mean, median and mode). These descriptions provide a generalized indication of down-core changes in depositional conditions and processes, but are not sensitive to non-normal or polymodal distributions. In contrast, surface plots of grain size data allow qualitative interpretation of the characteristics of the entire PSD and thus can provide important insights into depositional processes and changing environmental conditions. This method is especially useful for distinguishing multiple sedimentary processes, which can appear as additional modes within the PSD. In general, this approach can be used on sediments from most depositional environments and at any spatial or temporal resolution. In combination with conventional summary statistics, PSD surface plots increase the potential utility of grain size as a paleoenvironmental proxy for identifying changes in clastic and organic depositional processes in lake sequences.

The impact of air mass circulation dynamics on Late Holocene paleoclimate in northwestern North America

Paleoclimate records from northern British Columbia, southwestern Yukon, and adjacent Alaska suggest that Late Holocene climate may have been influenced by specific air mass circulation dynamics. The Aleutian lowpressure index (ALPI) is a measure of sea level pressure fluctuations in the Pacific Northwest associated with the Aleutian low (AL) pressure system. In this study, we show that the AL has a strong influence on historical climate change in the study area and explore the relationships between ALPI polarity and changes in late Holocene paleoclimate records. Analyses of weather station data in the study area indicate positive correlations (r > 0.63) between mean wintertime (December– March) temperature and ALPI values; total wintertime snowfall accumulation and total precipitation show moderate and weak negative correlations, respectively. A Late Holocene increase in exotic western hemlock (Tsuga heterophylla) pollen has been observed in regional paleoclimate studies. A sustained positive ALPI phase during the late Holocene is considered as a causative mechanism. Under such conditions, warm maritime air masses would more frequently penetrate inland, potentially resulting in eastward pollen transfer, enhanced growing conditions at coastal sites, and an increase eastwards in the range limit of these species. This study indicates that apparent conflicts in the timing and magnitude of Late Holocene climate change may be the result of a strong regional climate-forcing mechanism that exhibits both temporal and geographical variation. r 2002 Elsevier Science Ltd and INQUA. All rights reserved.

A multi-proxy holocene record of environmental change fromthe sediments of Skinny Lake, Iskut region, northern British Columbia,Canada

A stratigraphic record from a lake in the Central Plateau Regionof northern British Columbia reveals changes in environment and inferredclimate during the Holocene. Upon deglaciation (ca. 11500 BP), Skinny Lakebecame an embayment of an ice-dammed lake. High clastic sedimentationrates, an unstable landscape, and cool, possibly wet conditions likelypersisted until the early Holocene (ca. 9000 BP). From ca. 9000–8300 BPdeclining lake levels coupled with warm and dry conditions resulted in theformation of a prominent marl bed. A colonizing shrub and herb assemblagepersisted from 9000 BP until about 8300 BP when it was replaced by a spruce(Picea) and subalpine fir (Abieslasiocarpa) forest under slightly cooler and moister conditions. Themiddle Holocene was warmer-than-present, however, decreasingtemperature and increasing precipitation trends characterize the period fromca. 6000 BP–3000 BP. The transition to modern climate at 3000 BP isevident primarily in the lithostratigraphic record and corresponds with theinitiation of the Tiedemann glacial advance (ca. 3300 BP) in thesouth-coastal mountains of British Columbia. A significant change infossil pollen occurs at ca. 2400 BP and is characterised by an increase in pinepollen accompanied by decreases in alder (Alnus), spruceand fir. This also coincides with an increase in west-sourced exoticwestern hemlock (Tsuga heterophylla) and cedar type(Cupressaceae) pollen possibly transported by regional changes in air masscirculation patterns associated with Aleutian Low dynamics. This studydemonstrates that both lithostratigraphic and biotic proxies are helpful inreconstructing the timing and nature of climate change and that each may havevarying sensitivities to a particular type of change.

Spatial Snow Depth Assessment Using LiDAR Transect Samples and Public GIS Data Layers in the Elbow River Watershed, Alberta

This study illustrates the potential to combine LiDAR remote sensing and GIS techniques for the purpose of estimating instantaneous winter snowpack volume within the mountainous Elbow River Watershed (ERW) upstream of Calgary, Alberta. Two LiDAR (Light Detection and Ranging) datasets, one during snow-free and the other during late winter were used to evaluate a procedure for snow depth sampling. These data were also used to classify terrain and canopy cover attributes to enable snow depth estimation in areas that were not directly sampled but for which equivalent land classifications could be derived via other means. The mean snow depth from 1675 field measurements collected coincident with the winter LiDAR survey (late March, 2008) in snow-covered areas only was 0.28 m ( = 0.27 m). The mean LiDAR-based snow depth in snow-covered areas was comparable with the field values at 0.26 m ( = 1.2 m), or 0.18 m when averaged across both snow-covered and snow-free areas. Using field measurements of snow density, a GIS routine was employed to estimate total watershed snow water equivalent (SWE) from ten snow accumulation units (SAUs) using elevation, aspect and canopy cover. The total watershed SWE estimate was 46.0 106 m3. This volume of water can also be expressed as 0.058 m of water depth across the entire basin, or approximately 18% of the total 2008 runoff yield. Further work is needed to improve LiDAR-based snow depth estimation in areas of shallow snowpack where the influence of noise in the data is highest and to optimize the methods of sampling and extrapolation. At the present level of airborne LiDAR sophistication, positional uncertainties in LiDAR data (though small) are such that high confidence in the watershed snowpack volume estimate, would only be achieved during deep snowpack years; which also tend to be the years where accurate data are least required. However, given the availability of LiDAR base maps is ever growing, and the accuracy and costs associated with the technology are constantly improving, this approach to snow depth sampling has the potential to become a useful tool to support headwater snowpack resource assessment in water-stressed regions of Canada.

Colonial Marine Birds Influence Island Soil Chemistry Through Biotransport of Trace Elements

Marine birds are important vectors of nutrient and contaminant transfer from sea to land. In eastern Nova Scotia, Canada, colonial marine birds nest on specific nearshore islands within archipelagoes, and we predicted that soils on islands with bird colonies would have higher concentrations of selected trace elements (notably K, Ca, As, Cd, Cu, Pb, Se, Hg, and Zn) than soils on islands without colonies. In this study, common eider (Somateria mollissima), Leach’s storm petrel (Oceanodroma leucorhoa), black guillemot (Cepphus grylle), double-crested cormorant (Phalacrocorax auritus), great black-backed gull (Larus marinus), and herring gull (Larus argentatus) were considered to be the principal avian vectors for contaminant transfer. Results indicate that soils from islands with bird colonies had unique chemical compositions and commonly displayed elevated concentrations of K, Ca, Cu, Se, and Zn when compared to islands without colonies. Thus, marine birds feeding in the nearby marine zone move pollutants and nutrients from the ocean to nesting islands, potentially influencing habitat quality for coastal terrestrial species.

Geomorphology and Late Wisconsinan sedimentation in the Stikine River Valley, northern British Columbia

Abstract The Stikine River Valley (SRV) contains a thick and well-exposed sequence of Late Wisconsinan glaciolacustrine and glacial sediments. The glaciolacustrine sequences record the development of Glacial Lake Stikine (GLS), an advance-phase glacial lake produced when the advance of Coast Mountain glaciers impeded the westward drainage of the Stikine River. These deposits fine upwards and fill the deeply incised pre-glacial drainage system. The thickness of GLS sediment indicates that a significant time-lag occurred between the advance of alpine ice in the Coast Mountains and regional ice cover at the study region. A deformation till and a melt-out till overlie the glacial lake sediments. The lack of any ice-directional features in the till, and the lack of lodgement till in regions covered by glaciolacustrine sediment may be an indication that thin ice with low basal shear stresses existed within the SRV. Deglaciation in the SRV resulted in the formation of a complex suite of depositional and erosional landforms. Ice persisted as a stagnating, down-wasting valley glacier and both subglacial and ice marginal drainage networks were most likely present. A sedimentary record of the development of a retreat-phase glacial lake is not evident. Catastrophic drainage of a Late-glacial to Holocene basalt- or ice-dammed lake was responsible for extensive erosion that created a scabland near the village of Tahltan.

Bioaccumulation of Lead and Arsenic in Gastropods Inhabiting Salt Marsh Ponds in Coastal Bay of Fundy, Canada

The Cumberland Marsh Region (CMR), located on the coast of the Bay of Fundy, is a major feeding ground for waterfowl and contains significant coastal wetland systems. In this study, concentrations of lead (Pb) and arsenic (As) were assessed in the bottom sediments of various open water wetlands across the CMR, and gastropods were sampled from the same wetlands to assess bioaccumulation of these non-essential trace elements and the potential for transfer to higher trophic level species. It was predicted that gastropods would have higher concentrations of Pb and As from wetlands with higher concentrations of these elements in sediments. Although wetland sediments and gastropods had elevated Pb and As concentrations, in some cases above the Canadian Sediment Quality Guidelines for the protection of aquatic life, there were no significant correlations between sediment and gastropod trace element concentrations. Gastropod to sediment ratios of Pb and As concentrations were highest in the brackish wetlands, but overall, levels were not of toxicological concern. Wetland chemistries and gastropod physiologies are hypothesized to be driving factors in determining the level to which Pb and As will bioaccumulate and merit careful consideration when developing wetland management strategies.

Do rural impoundments in coastal Bay of Fundy, Canada sustain adequate habitat for wildlife?

In Canada and elsewhere in North America, impoundments are created in compensation for historic wetland loss and for habitat loss due to development projects, but these new sites are infrequently evaluated to determine how effectively they function. The Cumberland Marsh Region (CMR), located at the head of the Bay of Fundy, Canada, is of importance to migratory birds and has been subject to 300+ years of anthropogenic alteration, including impoundment creation on diked and drained tidal marsh in the last five decades. Wetland managers have noticed a pervasive decline in impoundment productivity leading to reduced waterbird usage (senescence). To understand factors that promote senescence, we analyzed abiotic and biotic proxies in sediment archives from six freshwater impoundments in two coastal watersheds to assess spatial trends across the CMR within recent decades. Our results demonstrate that impoundment productivity is driven by autochthonous nutrient sources (C/N between 7.7 and 14.4), but biogeochemical conditions can be highly variable among impoundments despite their proximity. Biogeochemical variation among top-of-core sediment samples from each impoundment was generally minimal, and thus we believe that the aging of impoundments has resulted in low productivity and organic matter accumulation due to dike stabilization and declines in nutrient loading. We conclude that these freshwater impoundments (in the CMR and likely other similar settings) are not highly productive, and may not provide abundant forage and optimal wildlife habitat which is expected of these systems; adaptive management strategies and hydrologic rehabilitation merit consideration to enhance ecological functioning. Understanding landscape attributes, hydrologic dynamics, and conditions prior to and after major human alterations should be a priority in future compensation projects.

Late Holocene Records of Changing Moisture Regime from Wetlands in Southwestern Nova Scotia, Canada: Implications for Wetland Conservation and Restoration

Abstract An understanding of the morphological stability and succession of open water and wetland ecosystems in Nova Scotia is a priority for informing the conservation management of critical habitats for a complex of nationally listed, rare, disjunct wetland species. Baltzer Bog and Big Meadow Bog in southwestern Nova Scotia contain stratigraphic records of late Holocene moisture variability. Baltzer Bog is a shrub bog that formed in an elevated, enclosed kettle basin. Excavated sections exposed by peat mining revealed 2 distinct wood-rich horizons that are located above a well-developed soil and wood horizon that yielded a radiocarbon-dated age of 3260 cal. BP from an upright stump. The overlying wood-rich horizons were dated at 1640 and 1045 cal. BP and were overlain by Sphagnum species transitions indicative of increasing wetness. At Big Meadow Bog, a thin wood mat in Sphagnum at 90 cm depth was dated at 1760 cal. BP. These records are broadly correlative with pollen and stratigraphic data from Pleasant River Fen in central Nova Scotia that indicate periods of high and low productivity and a fluctuating water table from 1950 cal. BP until present. Though other high-resolution paleoclimate records from the region indicate that the late Holocene was a time of increasing precipitation and cooler air temperatures, these wetland records demonstrate that in Nova Scotia this time period was characterized by rapid variations in effective moisture and that significant and sustained dry periods likely occurred. This record of late Holocene moisture variability and its influence on habitat structure serves to better establish the potential for long-term residency of threatened and endangered species at wetland sites.

Thin-Skinned Debris Flows in Cape Breton Highlands National Park, Nova Scotia, Canada

Landslides are common in Nova Scotia, particularly within the highly incised river valleys of the Cape Breton Highlands National Park. They have resulted in the modification of habitat and may pose considerable risk as both industrial and recreational use of this area intensifies. Field research focused on the investigation of debris flows that occur on the sides of incised river valleys where colluvium and till overlie grus, saprolite, and bedrock. The debris flows are complex events, which begin as thin translational slides or slumps and quickly evolve into debris flows. They are long and consistently narrow (< 20 m), commonly initiate just below the intersection of the valley wall and the Cape Breton Highlands peneplain, fail on slopes ranging from 27° to 48°, and denude no more than 1.5 m of the surface. Failed slopes are commonly unvegetated, with no observed association with large-scale surface depressions or gullies. Two common stratigraphic relationships on failed slopes are: 1) highly compacted, impermeable clay-rich lodgement till overlain by highly permeable colluvium and 2) impermeable weathered bedrock in the form of saprolite overlain by permeable colluvium. Both contact boundaries act as slip surfaces. Ground water accumulates at the colluvium/till interface within the activation zone producing an effective glide plane for initial translational movement. No specific triggering mechanisms were identified, though failure is likely associated with saturation and loading due to rainfall events and spring snowmelt; root decay and loss of soil strength associated with tree root failure from spruce budworm (Choristoneura fumiferana Clem.) infestation may also be of importance. RESUME Les glissements de terrain sont courants en Nouvelle-Ecosse, en particulier a l’interieur des vallees fluviales fortement encaissees du parc national des Hautes-Terres-du-Cap-Breton. Ils ont entraine la modification de l’habitat et pourraient poser un risque considerable au fur et a mesure que s’intensifie l’utilisation industrielle et recreative de cette region. Des recherches sur le terrain se sont attardees sur l’etude des coulees de debris presentes sur les versants des vallees fluviales encaissees ou le colluvion et le till recouvrent la groise, le saprolite et le substrat rocheux. Les coulees de debris constituent des phenomenes complexes, qui commencent sous forme d’effondrements ou de glissements plans minces et qui evoluent rapidement en coulees de debris. Elles s’etendent en longueur et demeurent constamment etroites (< 20 metres); elles apparaissent en general immediatement en aval du point de rencontre de la paroi de la vallee et de la peneplaine des hautes-terres du cap Breton; elles occasionnent des affaissements des pentes variant entre 27 et 48 degres; et elles decouvrent au maximum 1,5 metre de la surface. Les versants affaisses sont communement depourvus de vegetation et on n’y observe aucune association avec des depressions de surface ni des ravines a grande echelle. Les versants affaisses presentent deux liens stratigraphiques courants : 1) un till de fond riche en argile impermeable et tasse recouvert par un colluvion fortement permeable et 2) un substrat rocheux meteorise impermeable sous forme de saprolite recouvert de colluvion permeable. Les deux limites de contact representent des surfaces de glissement. L’eau souterraine s’accumule dans la zone de contact du colluvion et du till a l’interieur de la zone d’activation, produisant un plan glissant efficace pour le mouvement de translation initial. Aucun mecanisme de declenchement particulier n’a ete decele, meme si l’affaissement est probablement associe a une saturation et a un apport du aux episodes pluvieux et a la fonte des neiges du printemps; la pourriture des racines et la perte de resistance du sol associee a la rupture des racines des arbres causee par une infestation de tordeuses des bourgeons de l’epinette (Choristoneura fumiferana Clem.) pourraient egalement avoir une importance. [Traduit par la redaction]