Northern Cold Water Lakes Under Global Change

Environmental & Science Education, STEM, Watersheds, Global Change, Climate Change, Earth & Space Science, Earth Systems, Sustainability, Models, Nature of Science.

Ed Hessler

More attention is being paid to large landscape ecology and conservation rather than on single lakes or a small sample. And this involves science with a basis in modeling. An example is a new study led by Dr. Gretchen Hansen of the Department of Fisheries, Wildlife, and Conservation Biology, UMN). It was published in  Ecosphere (2022), an Ecological Society of American Open Access Journal. What follows is f although I've added some subheads.

Why large studies? Managing ecological systems for resilience can increase their capacity to maintain key functions even under global change. Oxygenated cold water(oxythermal) * habitat in lakes is an important ecological resource that is threatened by both climate change and eutrophication. 

Quantifying resilience: Here, we quantify the resilience of oxythermal habitat in ~10,000 glacial lakes in the upper Midwestern United States to climate change and watershed disturbance and classify lakes for conservation prioritization based on their current conditions and resilience. Oxythermal habitat was predicted by lake morphometry, July air temperatures, and watershed land use. 

The introduction includes information on sample size which consisted of 9688 dissolved oxygen profiles from 2168 lakes in Minnesota, Wisconsin, and Michigan collected between 1995 and 2018.

What the current future holds.  Temperatures are projected to increase by mid-century, and the magnitude of warming, its effect on oxythermal habitat, and the uncertainty surrounding that effect varied among lakes. Under mid-century climate conditions, the number of lakes containing suitable coldwater habitat was predicted to decline by 67%, while the number of lakes with unsuitable habitat was predicted to increase by over 200%. Lakes varied in the amount of temperature increase that they could sustain without a resultant change in habitat tier (i.e., their climate resilience). Median climate resilience was 4.3 degrees C, with some lakes capable of remaining in their habitat tier even with temperature increases up to 14 degrees C. Changing watershed land use was predicted to influence oxythermal habitat in 24% of lakes (n=2391). (My underline).

The first prediction is bleak, the consequences dire. The second prediction is more optimistic and points to the role of interventions in the lands surrounding the lakes such as restoration where needed and also to the role of preserves in maintaining suitable oxythermal habitat.. 

 Lake management classes. We classified lakes into seven management classes based on their current oxythermal habitat conditions and the resilience of oxythermal habitat to climate and watershed disturbance. 

Use of study in making management decisions. By quantifying the resilience of lakes and how it is influenced by local action across a multistate region, we can prioritize conservation action across multiple scales to maintain the critical habitat and ecosystem function of glacial lakes.

Methods, results, discussion, including study limitations are freely accessible and while the details may appear daunting, there are some useful summaries provided in charts and maps. To deal with the complexity of these lakes the authors divided the lakes into three tiers noting, " We defined three tiers of oxythermal habitat quality based on observed TDO3and its relationship to cisco presence. Our focus was on all glacial lakes in the region,not just those containing cisco. However, we used cisco as an indicator species for classifying oxythermal habitat as suitable (Tier 1), marginal (Tier 2), and unsuitable (Tier 3). This decision was based on previous research (cited).

*Refers to oxygen and temperature. In the northern midwest cold-water fish are susceptible to climate change because suitable oxygen and temperature habitat is limited in the summertime (see Madeline R. McGee for a discussion.).