Crossing the final ecological threshold in high Arctic ponds

Abstract

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.

Fig. 1.

Map showing the location of Cape Herschel (*) on the east coast of Ellesmere Island. Locations and further details regarding the ponds are described in ref. .

Fig. 2.

Photographs of the Cape Herschel ponds, showing the marked changes in water levels and associated ecological effects. (A) Photograph of Camp Pond taken on July 14, 1979 (photo courtesy of W. Blake, Jr). The water levels are so high that some of the surrounding land is also flooded with small pools. (B) Camp Pond on Aug. 24, 1987, at the end of the field season, when the winter snows had already returned to Cape Herschel. Note that the pond, even this late in the field season, is still a large, permanent body of water. (C) Camp Pond on July 12, 2006, just hours before it dried completely. (D) The aquatic invertebrates (with the fairy shrimp, B. paludosa, as the last survivors) concentrated in the remaining puddle left in Camp Pond, the day before it desiccated totally. (E) One of the basins of Cape Herschel Lagoon on Aug. 17, 1987. Although late in the field season, the pond was still a large, permanent body of water. (F) The desiccated basin of Cape Herschel Lagoon on July 16, 2006. (G) Standing in the middle of Beach Ridge Pond. in July 2006; the sediments are now cracked because of drying. (H) As shown by the accumulation of the orange jewel lichen (Xanthoria elegans), which thrives on nutrients from guano, this large boulder in the middle of Beach Ridge Pond used to be a resting place for aquatic birds, which would use the boulder as a refuge from land predators such as foxes. (I) Willow Pond on Aug. 21, 1987 (i.e., already very late in the field season) showing the wet, hummocky wetland in the foreground. (J) The identical area near Willow Pond on July 18, 2006 (i.e., early in the field season), demonstrating that the former wetland is now so dry that it is easily ignited.

Fig. 3.

Comparison of specific conductance values (as a proxy for evaporation/ precipitation; E/P) for July 14 (or as close to that date as possible) from the 24 lower peninsula ponds on Cape Herschel, measured in the three earliest field seasons (1983, 1984, and 1986), compared with measurements for the last three field seasons (2001, 2004, and 2006). Each point represents one of the Cape Herschel study sites; filled circles represent sites mentioned in the text and only these sites are labeled. If a point falls on the 1:1 line, no change in average water conductance has occurred since the 1980s. If the site points are above the 1:1 line, specific conductance has increased since the 1980s. From this analysis, it is clear that all ponds have increased in conductance since the 1980s, except one site (Pond 32), which is the lowest elevation pond on the Cape and is still receiving snowmelt via several streams in July from the two plateaus. Larger and deeper sites, such as Elison Lake, show smaller changes, as expected.