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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

JOURNAL ARTICLES...
RESPONSE OF WETLANDS TO CLIMATE CHANGE

Climatic Change devoted a special issue to the topic of Canadian freshwater wetlands and climate change:

Item #d99feb4

“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.

Item #d99feb5

“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), 189-209 (1998).

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.

Item #d99feb6

“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).

Item #d99feb7

“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 (1998).

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.

Item #d99feb8

“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.

Item #d99feb9

“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 ecosystem’s productivity were unchanged by the enhanced CO₂, the model indicated that summer carbon storage by all types of peatland would decrease.

Item #d99feb10

“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.

Item #d99feb11

“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.

Item #d99feb12

“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 Alberta’s 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.

Item #d99feb13

“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 million.

Item #d99feb14

“Implications of Global Climate Change for Tourism and Recreation in Wetland Areas,” Geoffrey Wall,Climatic Change 40 (2), 371-389 (1998).

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.

Item #d99feb15

“Assessing the Impact of Climate Change on the Great Lakes Shoreline Wetlands,” L. D. Mortsch,Climatic Change 40 (2), 391-416 (1998).

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.