Citizen Science Light Trapping in Grand Canyon

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Aquatic insects are commonly used to gauge the health of stream and river ecosystems, yet collecting enough samples to adequately characterize a river segment as long as the Colorado River through Grand Canyon (> 250 miles) would be essentially impossible using traditional sampling methods. Since 2012, our group has been collaborating with river guides, private boaters, and educational groups to deploy light traps to collect adult aquatic insects in this river segment. These citizen scientists have generated an impressive quantity of samples and data, which are yielding fundamentally new insights into the Colorado River ecosystem. Listen to a short podcast about these citizen scientists and the aquatic insects of Grand Canyon: https://www.usgs.gov/media/audio/outstanding-field-ep-2-citizen-science-your-data-action.

Three participants in the Grand Canyon Youth Program looking at a light trap at night near the Colorado River in Grand Canyon

Grand Canyon Youth collecting a light trap sample for adult aquatic insects, Grand Canyon, Arizona (15 July 2013). (Credit: USGS/Freshwaters Illustrated.)

Background & Importance

Aquatic insects are a key component of the aquatic and terrestrial food web in and around rivers. Understanding their abundance and distributions over time and space is important to understanding the health of an ecosystem. However, sampling aquatic insects on a large scale, over long periods of time, is impossible for typical research groups of only a few people. However, working cooperatively with people who are on the river every day (professional river guides and private boaters), our group has been able to collect samples throughout 250+ miles of Grand Canyon, throughout the year. The dataset, based on light traps set at the river’s edge every evening that collect adult aquatic insects, currently contains several thousand samples and several million insects. This citizen science effort allows us to ask and answer questions about the Colorado River in Grand Canyon that are truly unprecedented in scale, such as how hydropower releases from Glen Canyon Dam affect aquatic insect populations, how the phenology (seasonal timing) of aquatic insects varies by species and with distance downstream from the Dam, and how aquatic insect populations vary from year-to-year throughout the entire Grand Canyon.

General Methods

Every night in camp, citizen scientists set out a light trap at the river’s edge for one hour at dusk. Traps consist of a fluorescent black light placed on top of a plastic pan containing ethanol. At the end of the hour, the sample is poured into a bottle, and eventually brought back to the lab where its contents are counted and identified by USGS personnel. 

Important Results

Several people on a raft going through muddy rapids.

Grand Canyon Youth trip on the Colorado River, Grand Canyon, Arizona. (Credit: USGS/Freshwaters Illustrated.)

Our results demonstrate that the abundance and diversity of aquatic insects in the Colorado River is constrained by hydropower production at Glen Canyon Dam. Hydropower production at Glen Canyon Dam causes large hourly changes in river discharge, and these discharge waves create an artificial intertidal zone along river margins that is present >250 miles downstream where the Colorado River enters its next reservoir, Lake Mead.  Our citizen science data show that at places in the Grand Canyon where the Colorado River experiences daily low flows at dusk, aquatic insects are over 3 times more abundant compared to places where the daily high flows happen at dusk. Using a series of other experiments and modeling (outlined in a paper in the journal BioScience, listed below), we show that differential mortality of insect eggs laid along river margins is the underlying cause of these differences in adult insect abundance. These results inform the design of environmental flow experiments that should mitigate mortality of aquatic insect eggs while still allowing for the production of renewable hydropower that society needs.

Future Directions

Citizen science light trapping is ongoing. Send an e-mail to citizen_science@usgs.gov if you are interested in becoming a citizen scientist! This tool will be used to help monitor changes in the Colorado River ecosystem in Grand Canyon, and will be critical in understanding how any changes in flow releases from Glen Canyon Dam may be affecting the aquatic insect community that supports the entire food web of this ecosystem.

 

Full moon appearing over red rocks in Grand Canyon.

Moonrise in Grand Canyon, Arizona (24 June 2013). (Credit: USGS/Freshwaters Illustrated.)

 

Small, green adult fly on the Colorado River, Grand Canyon.

Adult fly on the Colorado River, Grand Canyon, Arizona (15 July 2013). (Credit: USGS/Freshwaters Illustrated.)