Shallow lake water quality
monitoring, Denali

Shallow Lake Monitoring Status and Trends: Denali

In a recent study, high altitude aerial photographs taken in 1980 were compared with landsat TM satellite images from 2007 for two index sites in the northwest corner of Denali National Park & Preserve. Lakes in the Minchumina basin lowlands (MBL) and the Eolian lowlands (EL) were analyzed to track changes in their size, abundance, and distribution. When the Minchumina basin lowland images from 1980 & 2007 were compared, there appeared to be little change. The story was quite different for the Eolian lowlands.

Change in the Eolian lowlands was dramatic. In 27 years, a full 26% of the lakes had shrunk markedly. Another 19% were no longer lakes, but had turned into wet meadows. What had happened?

Changes in lake surface area in Denali are likely influenced by climate, soil composition, and the depth and prevalence of permafrost. The soils underlying the lakes of the Minchumina basin lowlands are largely made up of a thick, spongy layer of peat (as deep as 22”) underlain with frozen silt loam. The Eolian lowlands consist of a very different suite of soils, largely composed of sand with patchy areas of permafrost. This sandy ground is likely the key factor contributing to the rapid change witnessed in the Eolian lowlands.

Particles of silt have the capacity to hold water at fairly high levels. Since the Minchumina basin lowlands are entirely contained by soil underlain with dense, frozen silt, the lakes in this region have seen little change during the past two decades. Not so with the Eolian lowlands and the reason is sand. The sandy soil of the Eolian lowlands is very porous. Quite simply, many of the lakes in this area are leaky, losing their water to the ground below.