Diatoms of North AmericaWe acknowledge passing through the ancestral homelands of the Nuciu (Ute), Pueblos, Diné (Navajo), Hopitutskwa (Hopi), Nuwuvi (Southern Paiute), Havasu Baaja (Havasupai), Kvav-Kapai (Hualapai), Pipa Aha Macav (Mojave), and Nuwuwu (Chemehuevi) peoples, past and present. We recognize with gratitude the people who have stewarded these lands since time immemorial and the vibrant Native communities who make their home in the Grand Canyon today.
The Colorado River below Glen Canyon Dam is changing in dramatic ways, rapidly. For many decades, water released from the dam was cold (13-15 °C) and concentrations of phosphorus were low (below ~ 5 μg/L). Directly below the dam, river water was clear and transparent (all the sediment having settled at the bottom of Lake Powell), but downstream tributaries brought lots of sediment to keep the river its muddy, colorful self.
But, the southwest has been in a severe drought for the past 22 years, in what is being called the region's worst megadrought since at least the year 800. The water released from the dam is much warmer (19 °C in summer 2022), as Lake Powell decreases and the turbines pull warmer, surface water of the reservoir. Without rain, tributaries like the Paria River at very low base flow for longer periods of the year. Without flowing water, sediments are not transported to the Colorado River and the river stays more transparent.
In 2021, the Colorado River was so clear that prolific Didymosphenia geminata blooms were reported. With its sister taxon, Cymbella mexicana, they covered much of the river bed at 1-2 meters depth. The stalks were attached to rock and boulder substrates, particularly in zones of wave turbulence. The detached stalks were present down the river, floating and gathering in pools between rapids.
As diatom communities in the Colorado River change, researchers want to understand how this relates to other aspects of the ecosystem. How do changes in diatom communities alter the food webs that support native fish? How do diatoms respond to changes in water chemistry resulting from drought?
In 2021 and 2022, we traveled some 225 miles down the river to collect samples of diatoms, with help of over 50 Grand Canyon Youth Partners in Science participants. The GCY program is a collaboration with the US Geological Survey Grand Canyon Monitoring and Research Center, with the goal to "develop monitoring and research programs, and related scientific activities, that evaluate short and long-term impacts of the Glen Canyon Dam on the biological, cultural, and physical resources of the Colorado River Ecosystem.”
Each youth science team learned to make daily measurements of water temperature, pH, specific conductance, and dissolved oxygen concentrations as we floated our way downriver. We looked in places where diatoms live and found frogs. Youth were able to hold a Flannel Mouth Sucker or the native, endangered Humpback Chub to measure their length. Some teams asked about oxygen and - how could oxygen possibly be in the water? (Oxygen dissolves in water!) Others peered at algae with field microscopes, or followed beetles in clear pools using the "cone of wonder". We were creative and playful, and we all learned more about algae, fish, and food webs of the river ecosystem.
