February 28, 2007
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Global Climate Change Digest
A Guide to Information on Greenhouse Gases and Ozone Depletion
Published July 1988 through June 1999
FROM VOLUME 12, NUMBER 2, FEBRUARY 1999
RESPONSE OF WETLANDS TO CLIMATE CHANGE
Climatic Change devoted a special issue to the topic of Canadian
freshwater wetlands and climate change:
Precambrian Shield Wetlands: Hydrologic Control of the Sources and
Export of Dissolved Organic Matter, Sherry Schiff et al.,Climatic
Change 40 (2), 167-188 (1998).
Stream flow, dissolved organic carbon (DOC), dissolved organic matter
(DOM), C:N ratios, and 14C were measured as water flowed out of forest
wetlands to determine the role of hydrology on DOM in peat porewaters, the
sources and export of DOM, and DOC concentration and export during wet and
dry periods. 14C activity in DOC from wetlands is mostly recently
laid-down carbon, indicating the DOM was exported from shallow,
organic-rich horizons. Stream DOM, however, spanned a range from older
(during dry periods) to modern carbon (during wet conditions), indicating
that it came from lower soil horizons during dry spells and near-surface
horizons during wet spells. Reduced export from wetlands under drier
climatic conditions may produce larger fluctuations in concentrations of
DOC in streams and lower DOM loads to lakes.
Hydrology of Prairie Pothole Wetlands During Drought and Deluge: A
17-Year Study of the Cottonwood Lake Wetland Complex in North Dakota in
the Perspective of Longer Term Measured and Proxy Hydrological Records,
T. C. Winter and D. O. Rosenberry,Climatic Change 40 (2),
Hydrologic measurements during a prolonged drought and for 10 years
before indicated that some prairie pothole wetlands served only to
recharge groundwater under all climate conditions. Persistence of the
wetland during the drought depended largely on what was under it (e.g.,
sand or low-permeability till). Proxy data indicated that the observed
drought was typical of droughts common to the area for the past 500 years.
The current wet period, though, is the wettest for at least 130 and
perhaps 500 years.
Hydrologic Response of a Wetland to Changing Moisture Conditions:
Modeling Effects of Soil Heterogeneity, P. J. Zeeb and H. F. Hemond,Climatic
Change 40 (2), 211-227 (1998).
A highly sensitive piezocone was developed to map wetland soils. It
attains centimeter-scale resolution vertically and meter-scale
horizontally. Wetland response to precipitation, stream stage, and
flooding were measured and the results combined with piezocone data to
parameterize a locale whose subsurface flow was then modeled. The model
was then used to realistically simulate hydrologic processes relevant to
climate change (e.g., water exchange between wetland and stream, porewater
movement to plant root zone, and wetland desaturation).
Uncertainty in Predicting the Effect of Climatic Change on the
Carbon Cycling of the Canadian Peatlands, T. R. Moore, N. T. Roulet,
and J. M. Waddington,Climatic Change 40 (2), 229-245
To aid the development of quantitative models of wetland responses to
climate change, qualitative responses and estimates of associated
uncertainty were derived for five variables (water-table level, CO2
exchange, CH4 emission, DOC export, and carbon storage) for
three types of peatlands (hummock/plateau palsa with dry conditions,
lawn/swamp with moist conditions, and floating mat/pool under wet
conditions) under doubled atmospheric CO2 and warmer
temperatures. The uncertainty is considerable because of the spatial
diversity of wetlands in Canada, their different positions in the
landscape, and the great variation within a single peatland.
Effect of Temperature on Production of CH4 and CO2
from Peat in a Natural and Flooded Boreal Forest Wetland, C.
McKenzie et al., Climatic Change 40 (2), 246-266 (1998).
Peat was collected from flooded and unflooded wetlands and incubated at
different temperatures. Flooding greatly increased methanogenesis, and
methane and CO2 production approximately tripled for each 10°
C rise in temperature. This temperature dependence probably arose from a
link with the metabolic rate of the microbial methanogens. Even deep peats
with 14C ages of 1000 years produced significant amounts of methane. These
results indicate that natural wetlands can be a significant long-term
source of methane.
Northern Canadian Wetlands: Net Ecosystem CO2 Exchange
and Climatic Change, J. M. Waddington, T. J. Griffis, and W. R.
Rouse, Climatic Change 40 (2), 267-275 (1998).
A model of northern Canadian wetlands indicated that the summer water
table would drop 0.14 m and surface peat temperature would increase 2.3°
C in response to a 3° C summer temperature increase and a 1-mm/day
increase in rainfall. Given these changes, net ecosystem CO2
exchange was calculated; the results indicated that fens would become
greater sinks for CO2 and bogs would become a net source of CO2.
If the ecosystems productivity were unchanged by the enhanced CO2,
the model indicated that summer carbon storage by all types of peatland
Gas Production from an Ombrotrophic Bog: Effect of Climate Change on
Microbial Ecology, D. A. Brown, Climatic Change 40
(2), 277-284 (1998).
In bogs that are waterlogged but not flooded, microbes decompose some of
the organic material, forming bubbles of methane and CO2 that
then obstruct hydrologic flow and block nutrients from reaching the
biomass. Investigation of such a bog revealed that any change in the water
table will change its production of greenhouse gases. If the water table
falls, the bog becomes aerobic, and CO2 is given off as the
biomass is metabolized. If the bog is flooded, the trapped bubbles
coalesce and are released to the atmosphere and the rate of degradation of
the biomass will be enhanced.
Holocene Climate and the Development of a Subarctic Peatland near
Inuvik, Northwest Territories, Canada, S. R. Vardy, B. O. Warner,
and Ramon Aravena,Climatic Change 40 (2), 285-313 (1998).
Permafrost peat was analyzed for stratigraphy, bulk density,
organic-matter content, pollen, macrofossil, and stable- isotope
composition. Results indicated that the site had experienced a history
that started with an open-water mineral wetland with aquatic plants that
changed to a fen dominated by mosses and sedges that changed to a peatland
dominated by ombrotrophic vegetation. The last transition in the
vegetation coincided with the end of the early Holocene warm period and
may have been associated with the aggradation of permafrost caused by
climatic cooling and consequent changes in hydrology.
Peatland Initiation During the Holocene in Continental Western
Canada, L. A. Halsey, D. H. Vitt, and I. E. Bauer,Climatic
Change 40 (2), 315-342 (1998).
Basal peat deposits from across western Canada were radiocarbon dated to
reconstruct their formation and spread across the landscape. Peat
formation began 8000 to 9000 years BP in upper-elevation nucleation zones
in Albertas Montane and northern regions. From 6000 to 8000 years
BP, peat formation expanded eastward into Manitoba as summers provided
less insolation as the Arctic front shifted southwesterly, bringing
moisture from the Pacific Ocean to Alberta. After 6000 years BP, the
southeasterly expansion continued, reaching the Peace-Wapiti River basin
and the lower elevations of the Hudson Bay lowlands in the past 3000 to
4000 years. This temporal and spatial distribution of peatland initiation
is corroborated by pollen records.
Potential Effects of Global Warming on Waterfowl Populations
Breeding in the Northern Great Plains, L. G. Sorenson et al.,Climatic
Change 40 (2), 343-369 (1998).
In the northcentral United States, the Palmer Drought Severity Index was
found to be closely correlated with annual counts of May ponds and
breeding-duck populations. Future Index values predicted by two general
circulation models were used to project future pond and duck numbers for
different levels of temperature increase and precipitation decrease. Most
increased-temperature scenarios produced increased drought and decreased
ponds and ducks. Under doubled-CO2 conditions, duck
populations of the area were projected to decline from 5.7 million to 2.1
to 2.7 million, and May ponds would decline from 1.3 million to 0.6 to 0.8
Implications of Global Climate Change for Tourism and Recreation in
Wetland Areas, Geoffrey Wall,Climatic Change 40 (2),
Recreational uses of coastal wetlands may be threatened by rising sea
levels, but inland-water usages may be affected more by precipitation and
subsequent water deficits. Both high and low water levels harm boating and
marina operations. Participants in recreational activities are seen to be
more adaptable to the constraints of climate change than are the
businesses that are tied to locations, facilities, and particular services
by capital investment, specialized expertise, and marketing history.
Assessing the Impact of Climate Change on the Great Lakes Shoreline
Wetlands, L. D. Mortsch,Climatic Change 40 (2),
An assessment of the historical records, sensitivities, and
vulnerabilities indicated that the Great Lakes and their wetlands would
experience hydrologic and ecological changes if climate change produced an
increased frequency and duration of low water levels or highly variable
seasonal water levels. The Great Lakes could display (1) higher winter
water levels because of an early melting of a (reduced) snowpack, (2)
reduced extent and duration of winter ice cover, and (3) lower summer
water levels because of evaporative losses and less runoff. Wetlands would
experience a negative impact on productivity because of increased duration
and intensity of low water levels, imperiling many rare, endangered, or
threatened plants and animals and restricting diversity. Marshes might
dry, but their main vegetation types could colonize newly exposed sites;
swamps and their trees could not adapt as quickly. Some wetland ecosystems
could progress to terrestrial systems. The irregular slope and rocky
substrates of the Precambrian Shield would provide few sites for
colonization along a retreating shoreline.
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