Long Term Climate Variability and Lake Water Chemistry

The 25-year record of water chemistry at the Arctic LTER site has documented a doubling of the average alkalinity or acid neutralizing capacity of Toolik Lake (figure 5.14). This change in alkalinity is balanced primarily by changes in calcium and

Year

Figure 5.14 The annual July average alkalinity (1 m depth) in Toolik Lake, Alaska.

Year

Figure 5.14 The annual July average alkalinity (1 m depth) in Toolik Lake, Alaska.

magnesium. There are no corresponding changes in the chemistry or amount of the precipitation that would account for these changes. One suggestion is that dust from the road is causing the changes. However, similar changes in alkalinity have been found in streams and lakes quite distant from the road.

The most reasonable explanation is that the lake alkalinity is an indicator of changes in soil chemistry and groundwater chemistry. These same changes are also found in the stream waters. It is possible that small increases in thaw depth expose new soil material to weathering, material that has been frozen for millennia. Another possibility is that new material is weathering because the active layer has thickened in riparian zones where more water is flowing. Given the large year-to-year variations in thaw depth, these processes are difficult to sort out, but, there can be no doubt that the air and permafrost temperatures have warmed over the past 15 years in northern Alaska (see previous discussion in the section "Variability of climate and related physical factors").

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