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A comprehensive review of Holocene paleoenvironmental data has been prepared, providing the basis for evaluating natural variability in climate and ecosystem dynamics in the northern Columbia River basin. The paleoenvironmental record reveals four major climatic shifts and a number of less well-defined climatic changes throughout the Holocene. The major climate changes are (1) a cool or cold, late-glacial climate at the end of the last glaciation (>11500 cal. year BP), (2) an interval of drought and maximum summer warmth during the early Holocene (ca. 10500 to 8000 cal. year BP), (3) a mid-Holocene trend towards a cooler, more moist climate (ca. 8000 to ca. 4000 cal. year BP), and (4) a relatively stable climate persisting from ca. 4000 cal. year BP until the arrival of European settlers. Air temperatures have warmed by about 1[degrees]C over the past century. Minor climate events that are emerging as global in nature include Little Ice Age (1200-150 BP) conditions, and a late Holocene cool wet period (3500-2500 BP). These are observed in some study sites examined in this paper and may be related to large-scale cycles of 2800-2000 and 1500 years. A discussion of changing atmospheric circulation patterns, and the causes of long-term climatic change are included, together with a discussion of the implications of the paleoenvironmental record for understanding future climate, and the likely response of communities and ecosystems. Key words: climate change, paleoclimate, paleoecology, British Columbia, Washington. Les auteurs ont prepare une revue d'ensemble des donnees paleo environnementales de l'Holocene, constituant ainsi une base pour l'evaluation de la variability naturelle de la dynamique du climat et des ecosystemes, dans le bassin de la riviere Columbia. Les donnees paleo environnementales revelent quatre changements climatiques majeurs et un nombre de modifications du climat moins bien definies, tout an long de l'Holocene. Les changements climatiques majeurs sont (1) un climat de fin de glaciation vers la fin de la derniere glaciation (>11,500 AP) frais on froid); (2) un intervalle de secheresse et de temperatures estivales maximales an cours du debut de l'Holocene (ca. 10,500 a 8,000 AP); (3) une tendance vers un climat plus humide et plus frais vers le milieu de l'Holocene (ca. 8,000 a ca. 4,000 AP); et (4) un climat relativement stable a partir de ca. 3,000 AP jusqu'a l'arrivee des colons europeens. Les temperatures de fair ont rechauffe d'environ 1[degre]C an cours du siecle dernier. Les changements climatiques mineurs de nature globale incluent le Petit age glaciaire (1,200-150 AP) et une periode humide et fraiche en fm de l'Holocene (3,500-2,500 AP). On observe ces phenomenes sur certains sites d'etude mentionnes dans ce travail, et on pent les relier a des cycles a large echelle de 2,800- 2,000 et 1,500 ans. Les auteurs presentent une discussion sur les patrons changeant de la circulation atmospherique, incluant les causes du changement climatique a long terme, ainsi qu'une discussion des implications des donnees paleo environnementales pour comprendre le climat futur, ainsi que les reactions probables des communautes et des ecosystemes. Mots-cles : changement climatique, paleoclimat, paleoecologie, Colombie canadienne, Washington. [Traduit par la Redaction], Introduction Many paleoecological and paleoclimatological studies have been conducted in the Columbia River basin. These studies provide essential background information on the natural variability of climate and ecosystem dynamics, prior [...]

Tidal salt marshes are known to accumulate "blue carbon" at high rates relative to their surface area, which render these systems among the Earth's most efficient carbon (C) sinks. However, the potential for tidal salt marshes to mitigate global warming remains poorly constrained because of the lack of representative sampling of tidal marshes from around the globe, inadequate areal extent estimations, and inappropriate dating methods for accurately estimating C accumulation rates. Here we provide the first estimates of organic C storage and accumulation rates in salt marshes along the Pacific Coast of Canada, within the Clayoquot Sound UNESCO Biosphere Reserve and Pacific Rim National Park Reserve, a region currently underrepresented in global compilations. Within the context of other sites from the Pacific Coast of North America, these young Clayoquot Sound marshes have relatively low C stocks but are accumulating C at rates that are higher than the global average, with pronounced differences between high and low marsh habitats. The average C stock calculated during the past 30 years is 54 ± 5 Mg C ha-1 (mean ± standard error), which accounts for 81 % of the C accumulated to the base of the marsh peat layer (67 ± 9 Mg C ha-1). The total C stock is just under one-third of previous global estimates of salt marsh C stocks, likely due to the shallow depth and young age of the marsh. In contrast, the average C accumulation rate (CAR) (184 ± 50 g C m-2 yr-1 to the base of the peat layer) is higher than both CARs from salt marshes along the Pacific coast (112 ± 12 g C m-2 yr-1) and global estimates (91 ± 7 g C m-2 yr-1). This difference was even more pronounced when we considered individual marsh zones: CARs were significantly greater in high marsh (303 ± 45 g C m-2 yr-1) compared to the low marsh sediments (63 ± 6 g C m -2 yr-1), an observation unique to Clayoquot Sound among NE Pacific Coast marsh studies. We attribute low CARs in the low marsh zones to shallow-rooting vegetation, reduced terrestrial sediment inputs, negative relative sea level rise in the region, and enhanced erosional processes. Per-hectare, CARs in Clayoquot Sound marsh soils are approximately 2-7 times greater than C uptake rates based on net ecosystem productivity in Canadian boreal forests, which highlights their potential importance as C reservoirs and the need to consider their C accumulation capacity as a climate mitigation co-benefit when conserving for other salt marsh ecosystem services. [ABSTRACT FROM AUTHOR]

Tidal salt marshes are known to accumulate "blue carbon" at high rates relative to their surface area and have been put forth as a potential means for enhanced CO2 sequestration. However, estimates of salt marsh carbon accumulation rates are based on a limited number of marshes globally and the estimation of carbon accumulation rates require detailed dating to provide accurate estimates. We address one data gap along the Pacific Coast of Canada by estimating carbon stocks in 34 sediment cores and estimating carbon accumulation rates using 210Pb dating on four cores from seven salt marshes within the Clayoquot Sound UNESCO Biosphere Reserve and Pacific Rim National Park Reserve of Canada (49.2° N, 125.80° W). Carbon stocks averaged 80.6 ± 43.8 megagrams of carbon per hectare (Mg C ha-1) between the seven salt marshes, and carbon accumulation rates averaged 146 ± 102 grams carbon per square meter per year (g C m-2 yr-1). These rates are comparable to those found in salt marshes further south along the Pacific coast of North America (32.5-38.2° N) and at similar latitudes in Eastern Canada and Northern Europe (43.6-55.5° N). The seven Clayoquot Sound salt marshes currently accumulate carbon at a rate of 54.28 Mg C yr-1 over an area of 46.94 ha, 87 % of which occurs in the high marsh zone. On a per-hectare basis, Clayoquot Sound salt marsh soils accumulate carbon at least one order of magnitude more quickly than the average of global boreal forest soils, and approximately two times larger than rates for forests in British Columbia. However, because of their relatively small area, we suggest that their carbon accumulation rate capacity could best be considered as a climate mitigation co-benefit when conserving for other salt marsh ecosystem services. [ABSTRACT FROM AUTHOR]

In central Canada, long fire history reconstructions are rare. In a context where both anthropogenic and climate infliuences on fire regime have changed, Parks Canada has a mandate to maintain ecological integrity. Here we present a fire history derived from fire-scarred jack pine (Pinus banksiana Lamb.) trees growing at their southern distribution limit in Riding Mountain National Park (RMNP). In Lake Katherine Fire Management Unit (LKFMU), a subregion within the park, fire history was reconstructed from archival records, tree-ring records, and charcoal in lake sediment. From about 1450 to 1850 common era (CE) the fire return intervals varied from 37 to 125 years, according to models. During the period 1864-1930 the study area burned frequently (Weibull Mean Fire Intervals between 2.66 and 5.62 years); this period coincided with the end of First Nations occupation and the start of European settlement. Major recruitment pulses were associated with the stand-replacing 1864 and 1894 fires. This period nevertheless corresponded to a reduction in charcoal accumulation. The current fire-free period in LKFMU (1930-today) coincides with RMNP establishment, exclusion of First Nations land use and increased fire suppression. Charcoal accumulation further decreased during this period. In the absence of fire, jack pine exclusion in LKFMU is foreseeable and the use of prescribed burning is advocated to conserve this protected jack pine ecosystem, at the southern margins of its range, and in the face of potential climate change. [ABSTRACT FROM AUTHOR]

Carbon (C) and nitrogen (N) elemental and nitrogen isotopic ratios were determined for bulk organic matter in surface sediments of 11 sockeye salmon (Onchorynchus nerka) nursery lakes in British Columbia, Canada. Chitinous exoskeletons of Bosmina spp. were also picked from the sediments and analyzed for δ15N. The correlation between salmon escapement (spawner abundance) and bulk organic δ15N confirms the importance of marine-derived nitrogen to the study lakes. The relation between sediment δ15N and escapement, however, suggests that simple mixing models may significantly underestimate spawner abundance in nitrogen-limited lakes. In addition, the use of sediment and chitin δ15N and C:N data to characterize lake-specific differences demonstrates that sediment isotope signatures are dependent on attendant nitrogen deficiency. The sediment C:N ratio, on its own, provides a sensitive measure of nutrient status in these lakes. This finding provides an alternate additional interpretation of C:N ratios that may be more appropriate in large lakes where terrestrial contributions to the central basin are insignificant. [ABSTRACT FROM AUTHOR]