Marianne S. V. Douglas

EFFECTS OF CLIMATE CHANGE ON THE FRESHWATERS OF ARCTIC AND SUBARCTIC NORTH AMERICA

Region 2 comprises arctic and subarctic North America and is underlain by continuous or discontinuous permafrost. Its freshwater systems are dominated by a low energy environment and cold region processes. Central northern areas are almost totally influenced by arctic air masses while Pacific air becomes more prominent in the west, Atlantic air in the east and southern air masses at the lower latitudes. Air mass changes will play an important role in precipitation changes associated with climate warming. The snow season in the region is prolonged resulting in long-term storage of water so that the spring flood is often the major hydrological event of the year, even though, annual rainfall usually exceeds annual snowfall. The unique character of ponds and lakes is a result of the long frozen period, which affects nutrient status and gas exchange during the cold season and during thaw. GCM models are in close agreement for this region and predict temperature increases as large as 4°C in summer and 9°C in winter for a 2 × CO2 scenario. Palaeoclimate indicators support the probability that substantial temperature increases have occurred previously during the Holocene. The historical record indicates a temperature increase of > 1°C in parts of the region during the last century. GCM predictions of precipitation change indicate an increase, but there is little agreement amongst the various models on regional disposition or magnitude. Precipitation change is as important as temperature change in determining the water balance. The water balance is critical to every aspect of hydrology and limnology in the far north. Permafrost close to the surface plays a major role in freshwater systems because it often maintains lakes and wetlands above an impermeable frost table, which limits the water storage capabilities of the subsurface. Thawing associated with climate change would, particularly in areas of massive ice, stimulate landscape changes, which can affect every aspect of the environment. The normal spring flooding of ice-jammed north-flowing rivers, such as the Mackenzie, is a major event, which renews the water supply of lakes in delta regions and which determines the availability of habitat for aquatic organisms. Climate warming or river damming and diversion would probably lead to the complete drying of many delta lakes. Climate warming would also change the characteristics of ponds that presently freeze to the bottom and result in fundamental changes in their limnological characteristics. At present, the food chain is rather simple usually culminating in lake trout or arctic char. A lengthening of the growing season and warmer water temperature would affect the chemical, mineral and nutrient status of lakes and most likely have deleterious effects on the food chain. Peatlands are extensive in region 2. They would move northwards at their southern boundaries, and, with sustained drying, many would change form or become inactive. Extensive wetlands and peatlands are an important component of the global carbon budget, and warmer and drier conditions would most likely change them from a sink to a source for atmospheric carbon. There is some evidence that this may be occurring already. Region 2 is very vulnerable to global warming. Its freshwater systems are probably the least studied and most poorly understood in North America. There are clear needs to improve our current knowledge of temperature and precipitation patterns; to model the thermal behaviour of wetlands, lakes and rivers; to understand better the interrelationships of cold region rivers with their basins; to begin studies on the very large lakes in the region; to obtain a firm grasp of the role of northern peatlands in the global carbon cycle; and to link the terrestrial water balance to the thermal and hydrological regime of the polar sea. Overall, there is a strong need for basic research and long-term monitoring.

Crossing the final ecological threshold in high Arctic ponds

A characteristic feature of most Arctic regions is the many shallow ponds that dot the landscape. These surface waters are often hotspots of biodiversity and production for microorganisms, plants, and animals in this otherwise extreme terrestrial environment. However, shallow ponds are also especially susceptible to the effects of climatic changes because of their relatively low water volumes and high surface area to depth ratios. Here, we describe our findings that some high Arctic ponds, which paleolimnological data indicate have been permanent water bodies for millennia, are now completely drying during the polar summer. By comparing recent pond water specific conductance values to similar measurements made in the 1980s, we link the disappearance of the ponds to increased evaporation/precipitation ratios, probably associated with climatic warming. The final ecological threshold for these aquatic ecosystems has now been crossed: complete desiccation.

Marked post-18th century environmental change in high-arctic ecosystems.

Paleolimnological data from three high-arctic ponds on Cape Herschel, Ellesmere Island, Canada, show that diatom assemblages were relatively stable over the last few millennia but then experienced unparalleled changes beginning in the 19th century. The environmental factors causing these assemblage shifts may be related to recent climatic warming. Regardless of the cause, the biota of these isolated and seemingly pristine ponds have changed dramatically in the recent past and any hopes of cataloging natural assemblages may already be fruitless.

Fisheries productivity in the northeastern Pacific Ocean over the past 2,200 years

Historical catch records suggest that climatic variability has had basin-wide effects on the northern Pacific and its fish populations, such as salmon, sardines and anchovies. However, these records are too short to define the nature and frequency of patterns. We reconstructed ∼2,200-year records of sockeye salmon abundance from sediment cores obtained from salmon nursery lakes on Kodiak island, Alaska. Large shifts in abundance, which far exceed the decadal-scale variability recorded during the past 300 years, occurred over the past two millennia. A marked, multi-centennial decline in Alaskan sockeye salmon was apparent from ∼100 BC to AD 800, but salmon were consistently more abundant from AD 1200 to 1900. Over the past two millennia, the abundances of Pacific sardine and Northern anchovy off the California coast, and of Alaskan salmon, show several synchronous patterns of variability. But sardines and anchovies vary out of phase with Alaskan salmon over low frequency, which differs from the pattern detected in historical records. The coherent patterns observed across large regions demonstrate the strong role of climatic forcing in regulating northeastern Pacific fish stocks.

From controversy to consensus: making the case for recent climate change in the Arctic using lake sediments

We live in a constantly changing environment, yet tracking ecological change is often very difficult. Long-term monitoring data are frequently lacking and are especially sparse from Arctic ecosystems, where logistical difficulties limit most monitoring programs. Fortunately, lake and pond sediments contain important archives of past limnological communities that can be used to reconstruct environmental change. Here, we summarize some of the paleolimnological studies that have documented recent climate warming in Arctic lakes and ponds. Several hypotheses have been evaluated to determine if warming, resulting in changes in ice cover and related variables (eg increased habitat availability), was the factor most strongly influencing recent diatom and other biotic changes. Striking and often unprecedented community changes were evident in post-1850 sediments, and could be linked to ecological shifts consistent with warming. Because future temperature increases are predicted to be greatly amplified in polar re...

The Diatoms: Freshwater diatoms as indicators of environmental change in the High Arctic

Introduction High arctic environments have received increased attention over recent years, as polar regions are considered to be especially sensitive to the effects of global climatic and other environmental changes (Walsh, 1991; Rouse et al ., 1997). For example, potential warming from ‘greenhouse gases’ is expected to be accentuated in the High Arctic (Roots, 1989). Other environmental changes, such as increased ultraviolet (UV-B) light penetration and deposition of airborne contaminants, have also been noted recently in high latitude regions (e.g., Landers, 1995). There is considerable potential for using living and fossil diatom assem blages for tracking environmental trends in high arctic regions (Smol & Douglas, 1996). However, to date, relatively few studies have been completed on the taxonomy, ecology, and paleoecology of high arctic, freshwater diatoms, even though lakes and ponds are dominant features of most arctic landscapes. For example, about 18% (by area) of Canadas surface waters are situated north of 60° N (Statistics Canada, 1987), and Sheath (1986) estimates that tundra ponds cover approximately 2% of the Earths surface. The heightened interest in high arctic environments, coupled with increased accessibility (e.g., with helicopter support) of these remote regions, has resulted in a recent surge of interest in arctic diatom research. Moreover, proxy techniques such as palynology and dendroecology have some serious limitations in high arctic regions due to the paucity of higher plants (Gajewski et al ., 1995). Consequently, paleolimnological approaches using diatoms may become especially important for studies of global environmental change.

Long-term environmental change in Arctic and Antarctic lakes

1. Paleolimnological research in polar regions: An introduction. Reinhard Pienitz, Marianne S.V. Douglas and John P. Smol 2. Geochronology of high latitude lake sediments. Alexander P. Wolfe, Gifford H. Miller, Carrie A. Olsen, Steven L. Forman, Peter T. Doran and Sofia U. Holmgren 3. Physical and chemical properties and proxies of high latitude lake sediments. Scott F. Lamoureux and Robert Gilbert 4. Palynology of North American arctic lakes. Konrad Gajewski and Glen M. MacDonald 5. Algal indicators of environmental change in arctic and antarctic lakes and ponds. Marianne S.V. Douglas, Paul B. Hamilton, Reinhard Pienitz and John P. Smol 6. Aquatic invertebrates and high latitude paleolimnology. Ole Bennike, Klaus P. Brodersen, Erik Jeppesen and Ian R. Walker 7. Use of water isotope tracers in high latitude hydrology and paleohydrology. Thomas W.D. Edwards, Brent B. Wolfe, John J. Gibson and Dan Hammarlund 8. Lake sediments as records of arctic and antarctic pollution. Derek C.G. Muir and Neil L. Rose 9. Paleolimnology of the middle and high Canadian Arctic. Alexander P. Wolfe and I. Rod Smith 10. Paleolimnology of the North American Subarctic. Bruce P. Finney, Kathleen Ruhland, John P. Smol and Marie-Andree Fallu 11. Holocene paleolimnology of Greenland and the North Atlantic islands (north of 60 N). N. John Anderson, David B. Ryves, Marianne Grauert and Suzanne McGowan 12. Paleolimnological research from northern Russian Eurasia. Glen M. MacDonald, Thomas W.D. Edwards, Bruce Gervais, Tamsin E. Laing, Michael F.J. Pisaric, David F. Porinchu, Jeffrey A. Snyder, Nadia Solovieva, Pavel Tarasov and Brent B. Wolfe 13. Paleolimnological studies in arctic Fennoscandia and the Kola Peninsula (Russia).Atte Korhola and Jan Weckstrom 14. Paleolimnological studies from the Antarctic and subantarctic islands. Dominic A. Hodgson, Peter T. Doran, Donna Roberts and Andrew McMinn 15. Paleolimnology of extreme cold terrestrial and extraterrestrial environments. Peter T. Doran, John C. Priscu, W. Berry Lyons, Ross D. Powell, Dale T. Andersen and Robert J. Poreda 16. Epilogue: Paleolimnological research from arctic and antarctic regions. Reinhard Pienitz, Marianne S.V. Douglas and John P. Smol

PERIPHYTIC DIATOM ASSEMBLAGES FROM HIGH ARCTIC PONDS1

Epiphytic, epilithic, and surface sediment diatom assemblages were identified and enumerated from 35 study ponds on CapeHerschel (78°37″N, 74°42″W), east‐central Ellesmere Island, Canada. All the sites are shallow (maximum depth <2 m), clear, oligotrophic, and freshwater. The ponds freeze completely for 10 months of the year. Major ion concentrations are relatively similar among the 35 sites, although environmental gradients exist. Over 130 diatom taxa from 28 genera were identified in the periphyton samples. Marked differences in species composition were evident among the ponds. Moreover, many of the diatoms exhibited varying degrees of microhabitat specificity. Variance partitioning by canonical correspondence analysis showed that 26% of the total variance exhibited by diatom species composition could be accounted for by the measured environmental variables (i.e. 10.2% by habitat and 15.8% by water chemistry). Pondwater alkalinity best explained the distribution of taxa, and weighted averaging regression and calibration were used to develop a transfer function to infer pondwater alkalinity from the diatom assemblages. Other important environmental variables included [Na+] for the epilithic and [SiO2] for the epiphytic assemblages.

Seabird-driven shifts in Arctic pond ecosystems.

Migratory animals such as seabirds, salmon and whales can transport large quantities of nutrients across ecosystem boundaries, greatly enriching recipient food webs. As many of these animals biomagnify contaminants, they can also focus pollutants at toxic levels. Seabirds arguably represent the most significant biovectors of nutrients and contaminants from the ocean to the land, given their sheer numbers and global distribution. However, long-term census data on seabirds are rare. Using palaeolimnological proxies, we show that a colony of Arctic seabirds has experienced climate-induced population increases in recent decades. We then document increasing concentrations of contaminants, including polychlorinated biphenyls and cadmium, in pond sediments that are linked to biotransport by seabirds. Our findings suggest that climate-related shifts in global seabird populations will have the unexpected consequence of restructuring coastal ecosystems.

PERIPHYTIC DIATOM ASSEMBLAGES FROM ULTRA-OLIGOTROPHIC AND UV TRANSPARENT LAKES AND PONDS ON VICTORIA ISLAND AND COMPARISONS WITH OTHER DIATOM SURVEYS IN THE CANADIAN ARCTIC1

Periphytic diatoms are potentially powerful indicators of environmental change in climatically‐sensitive high latitude regions. However, only a few studies have examined their taxonomic and ecological characteristics. We identified and enumerated diatom assemblages from sediment, rock, and moss habitats in 34 ultra‐oligotrophic and highly transparent lakes and ponds on Victoria Island, Arctic Canada. The similar limnological characteristics of the sites allowed us to examine the influence of habitat, independent of water chemistry, on the diatom assemblages. As is typical in shallow arctic water bodies, benthic taxa, including species of Achnanthes, Caloneis, Cymbella, Navicula, and Nitzschia, were most widely represented. Minor gradients in our measured environmental variables did not significantly explain any variance in diatom species, but there were marked differences in diatom assemblages among sites. Pond ephemerality seems to explain some diatom variation, because aerophilic taxa such as Achnanthes kryophila Petersen and A. marginulata Grunow were dominant in shallow sites that had undergone appreciable reductions in volume. We identified several taxa that exhibited strong habitat preferences to sediment, moss, or rock substrates and also found significant differences (P < 0.01) in diatom composition among the three habitats. In comparisons with three similar diatom surveys extending over 1200 km of latitude, we determined that surface sediment assemblages differed significantly (P < 0.001) among all regions examined. Diatom species diversity was inversely related to latitude, a result likely explained by differences in the lengths of growing seasons. These data contribute important ecological information on diatom assemblages in arctic regions and will aid in the interpretation of environmental changes in biomonitoring and paleolimnological studies.