Effects of climate change and variability on thermal regime and dissolved oxygen resources of oligotrophic lakes in the Adirondack Mountain region

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Abstract An analysis of multi-decadal (1994-2021) temperature and dissolved oxygen profiles revealed a generally consistent pattern of response to climate change and variability among oligotrophic lakes in the Adirondack Mountain region. Regional increases in annual average air temperature (0.34 ± 0.09 oC per decade) were accompanied by warming and thinning of epilimnia, cooling and expansion of hypolimnia, and declining hypolimnetic dissolved oxygen. Lakes in this region are recovering from acidification and we hypothesize that associated increases in dissolved color have caused greater heat trapping in the surface layer and earlier onset of stratification. The combined effects of increasing air temperature and declining water clarity resulted in stronger thermal stratification and greater cumulative oxygen depletion in bottom waters. Lake bathymetry was a key variable determining the sensitivity of lakes to climate effects on oxygen resources. Lakes with thin hypolimnia exhibited low dissolved oxygen concentrations, which were exacerbated by strengthening of vertical temperature gradients and earlier onset of stratification. Photic depths are decreasing faster than mixing depths such that declines in photosynthesis may contribute to lower dissolved oxygen in deeper layers. We predict that with climate warming fewer Adirondack lakes will provide suitable habitat for cold water fisheries such as brook trout due to decreasing hypolimnetic oxygen.

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