Written by Isabella Oleksy, a 2016-2017 Sustainability Leadership Fellow and Ph.D. student in the Department of Ecosystem Science and Sustainability and Graduate Degree Program in Ecology
It’s a beautiful day. There is not a cloud in the sky, the temperature is perfect, and there is no wind to speak of. You are walking up on what appears to be a crystal clear body of water surrounded by menacing rock formations, towering overhead. This is Sky Pond, an appropriately named waterbody. It is situated at the headwaters of one of the Platte River’s many tributaries. Sky Pond and its surrounding views are the reward for the 5 miles of hiking and 1500 feet of climbing it takes to get here from the trailhead; a reward so sweet that thousands of people make the strenuous round trip each year. As you take a moment to catch your breath while simultaneously having it taken away by what surrounds you, everything stands still, if only for a moment. This place is teeming with life. Depending on the time of year, you may see elk, wildflowers, trout, moose, marmot, big horned sheep, and ill-prepared tourists. Curiosity brings you close to the water’s edge. Upon closer inspection, the crystal clear waters reveal extensive mats of green slime, flowing with the gentle water current. This green slime is everywhere, and it looks like it came straight out of Ghostbusters. You kneel down to take a sample of the green slime. A curious onlooker asks what you are doing, and you look up and quote Dr. Peter Venkman (Bill Murray) himself, “Back off, man, I’m a scientist.” If you’re still following along, this is what I experience on a weekly basis, except I don’t really tell curious onlookers to back off. The scene I am describing is a day in the life of field work in the Loch Vale watershed, and that “green slime” is actually filamentous green algae. I’m trying to figure out why the algae are growing here, because until recently, this sight was more common in a retention pond in Michigan than in a “pristine” alpine lake in the Rockies.
The beauty of the Loch Vale Watershed is no secret. It’s situated in one of the most visited areas of Rocky Mountain National Park, just east of the continental divide. My research is a complement to what my advisor, Dr. Jill Baron, might call her life’s work. In 1983, Dr. Baron established the watershed as a long-term ecological research site with the goal of understanding watershed-scale ecosystem processes and how air pollution and climate-variability affect ecosystem function. At the time, many ecologists were focused on understanding the effects of acid rain. While Loch Vale was not getting hit with acid rain, it was (and still is) getting hit by precipitation carrying particles of nitrogen, sourced from automobile emissions, power plant exhaust, and increasingly even the by-products of industrial agriculture, which are so prominent on the Front Range of the Colorado Rockies.
Nitrogen alone is not exactly a bad thing; it is essential for life. It is the nutrient whose absence is responsible for limiting a plant’s growth. This is precisely why, if you buy into the scourge of the American lawn, you use nitrogen-based fertilizer to make your lawn look greener than the Jones’ next door. The problem is, the Loch Vale watershed and surrounding areas can’t process all of the incoming human-made nitrogen. Mountainous areas are particularly sensitive because there is little plant and forest cover to absorb the excess nitrogen. Since the mid-20th century, mountainous areas in Colorado have been receiving much more nitrogen than is needed for biological uptake. Where does all that excess go? Unfortunately, much of it ends up in surface waters, running downhill into the wetlands, lakes, and streams.
Ecologists and biogeochemists have a range of tools in our toolbox that we can use to answer questions about the natural world. Working in Loch Vale, one of our most valuable tools is in analyzing the high-quality, weekly, long-term measurements of water chemistry and weather data in this watershed. We can ask and answer questions such as does the water chemistry leaving the watershed match the precipitation chemistry entering the watershed (1)? Or, what is the ecological critical load of incoming nitrogen deposition before adverse ecological effects occur (2)? However, how can we assess changes in ecosystem processes for variables that we do not routinely measure? For example, Loch Vale researchers have known for years that surface waters were high in nitrate, but the impacts on aquatic plant life, particularly algae, were not fully understood. For those kinds of questions, we put on our detective hats and pull out our paleo-toolkit.
Paleolimnology is a sub-discipline of limnology (the study of inland waters) that primarily uses lake sediment cores to meticulously reconstruct past environments of inland waters. By analyzing physical, chemical, and biological characteristics of sediment layers deposited in lakes, paleolimnologists can get a glimpse into the past. Sediment core analysis allows us to piece together how lakes are affected by climate on short and long time scales as well as by a numerous other factors such as land-use change (e.g., deforestation), food-web manipulations (e.g., fish introductions), and other human impacts (e.g., acid rain, nitrogen deposition).
The effect of nitrogen deposition on lake algae has been well documented with sediment cores collected across Europe and North America. Most show a pattern very similar to what we have observed in the Colorado Rocky Mountains: for hundreds of years these lakes were home to a diverse flora of diatoms, single-celled algae that spend their life photosynthesizing in the water column and are preserved in sediments when they settle and die because of their strong, silicate shells. Once nitrogen inputs increased, one or two species of diatoms outcompeted the rest and dominate to this day. To our knowledge, no one had observed the green slime until very recently. In Loch Vale, is it new or has it been there all along? Are we still seeing the response of algae to nitrogen or are other factors involved? For my doctoral research, I am further diversifying our paleo-toolkit and looking at not only diatoms, but all algal species, by analyzing a diverse range of algal pigments from layers throughout lake sediment deposits. This technique is useful for reconstructing changes in algal groups through time, especially those that don’t leave us microscopic fossils to count under a microscope, like the green algae we observe today.
Last March, our team of researchers and volunteers embarked on an expedition to The Loch, the subalpine lake in the Loch Vale watershed. With our crew loaded down with sleds and heavy packs full of equipment, what is normally a moderate 2-mile snowshoe hike turned into a strenuous uphill slog. We drilled a hole through the ice over the deepest spot in the lake and dropped a gravity corer into the sediments to obtain a short core of the most recent lake sediments. We used a special device to extrude the mud out of a plastic core tube and sliced the sediments into fine layered intervals for laboratory analysis. In less than a foot of sediment, we captured several hundred years of lake ecological history!
What the sediment core has told us so far is that this prolific growth of slimy green algae is indeed a new phenomenon in The Loch. Recent sediments show strong signs of increased chlorophytes (green algae) and colonial cyanobacteria, with well-preserved but relatively small amounts of those pigments just a few centimeters from the top of the core. Interestingly, The Loch never saw a substantial increase in diatoms, as Sky Pond did, potentially because it is lower in elevation and slightly buffered by the forest surrounding it. While we now can confirm that our recent observations have not occurred within the last several hundred years in this lake, we still do not fully understand why. Luckily for me, my job is to solve this mystery with laboratory and field experiments.
What has changed in the last few decades that might be causing these algal blooms? We know that our surface waters have been warming steadily in the peak of summer, at the rate of about 0.7°C a decade since we began measuring (1). We also know that glaciers, rock glaciers, and permafrost are shrinking and releasing additional nutrients that were previously locked up and frozen (3,4). Could filamentous green algae be appearing because of dust from forest fires and drought? (5) There are a myriad of potential drivers of ecological change in these lakes, and scientists are only beginning to understand how these mountain jewels are changing right before our eyes. Our world is changing rapidly and we don’t fully understand the cost nor the consequences. Luckily, there are people in local, state, and federal government that are seeking partnerships and solutions to minimize the impacts that are within our control, such as air pollution. There are farmers in Colorado who are voluntarily changing their management practices to reduce nitrogen volatilization from their farms. And soon, you too can help us document where these algal blooms are (and are not) occurring across the intermountain West! Simply download WATR2016 from the App Store and document lake conditions as you hike anywhere in the western United States. All submissions will be automatically uploaded to our database on CitSci.org.
(1) Mast, M. A., Clow, D. W., Baron, J. S., & Wetherbee, G. A. (2014). Links between N Deposition and Nitrate Export from a High- Elevation Watershed in the Colorado Front Range. Environmental Science & Technology.
(2) Baron, J. S. (2006). Hindcasting Nitrogen Deposition To Determine an Ecological Critical Load. Ecological Applications, 16(3), 433–439.
(3) Leopold, M., Lewis, G., Dethier, D., Caine, N., & Williams, M. W. (2015). Cryosphere: ice on Niwot Ridge and in the Green Lakes Valley, Colorado Front Range. Plant Ecology & Diversity, 874(March 2015), 1–14. http://doi.org/10.1080/17550874.2014.992489
(4) Barnes, R. T., Williams, M. W., Parman, J. N., Hill, K., & Caine, N. (2014). Thawing glacial and permafrost features contribute to nitrogen export from Green Lakes Valley, Colorado Front Range, USA. Biogeochemistry, 117(2–3), 413–430. http://doi.org/10.1007/s10533-013-9886-5
(5) Neff, J. C., Ballantyne, a. P., Farmer, G. L., Mahowald, N. M., Conroy, J. L., Landry, C. C., Reynolds, R. L. (2008). Increasing eolian dust deposition in the western United States linked to human activity. Nature Geoscience, 1(3), 189–195. http://doi.org/10.1038/ngeo133