Difference between revisions of "The Bugflow Experiment"

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[[File:2024Bugflows.png|thumb|center|500px| 2025 Annual Reporting Meeting ]]
 
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*The abundance of adult caddisflies increased riverwide in two of three years that Bug Flows were conducted compared to the pre-Bug Flow baseline from 2012-2017. Caddisflies have been rare in Grand Canyon and improving conditions for them was a primary objective of the experiment. However, this caddisfly increase is correlated with low suspended sediment levels in these same years, complicating this response. Continued experimentation with Bug Flows may be warranted based on these results.
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! <h2 style="margin:0; background:#cedff2; font-size:120%; font-weight:bold; border:1px solid #a3b0bf; text-align:left; color:#000; padding:0.2em 0.4em;"> Primary causal mechanism </h2>
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*Contrary to predictions, no increases in the abundance or changes in distribution in midges were observed across multiple long-term datasets. Modeling suggested that a ~30% increase in non-biting midges riverwide, a common type of aquatic insect, might be realized if Bug Flows was successful.  
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*More adult aquatic insects emerged from the Colorado River riverwide during steady weekend Bug Flows compared to weekday fluctuating releases, suggesting that low steady flows improve conditions for adult insects, an unanticipated benefit.
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*Bug Flows increased algae production by 38% in Marble and Grand Canyon, resulting in an additional 100 metric tons of algae-carbon to sustain food webs. The increase in algae production during Bug Flows was energetically substantial and likely supported increased invertebrate and fish production given that production at these levels is food limited.
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*The types of prey eaten by rainbow trout in Glen Canyon varied by flow treatment but overall energy intake was unchanged. Anglers captured more rainbow trout on average during Bug Flows than regular weekday fluctuating flows.
  
 
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Revision as of 12:01, 18 June 2025
https://www.usbr.gov/uc/progact/amp/twg/2022-01-13-twg-meeting/20220113-AnnualReportingMeeting-ProjectF-AquaticEcologyFoodBaseMonitoring-508-UCRO.pdf

What is the “Macroinvertebrate Production Flow (MPF)" or "Bug Flow" experiment?
This would be an experimental release at Glen Canyon Dam to see if short-duration steady releases might increase the diversity and production of aquatic insects below Glen Canyon Dam. This experiment is included in the Preferred Alternative of the LTEMP DEIS. These “macroinvertebrate production flows” would occur from May to August and would maintain releases on the weekends to a level equal to the minimum release made during the week. This would allow aquatic insects two days a week throughout the river corridor to be able to lay their eggs at a stage where they would not be at risk of being dewatered or desiccated. The experiment would include monitoring to evaluate if the flows did increase the diversity and production of aquatic insects. The experiment was designed to test the hypothesis put forward in Kennedy's 2016 BioScience Paper while minimizing impacts to the hydropower resource at Glen Canyon Dam by having the steady flows on the weekend. This results in a transfer of water from the weekend to the weekdays increasing the daily minimums and maximums and the range of fluctuation during the week. Western believes that this experiment will result in only a small decrease in the energy value, but a modest increase in the capacity value of hydropower produced at Glen Canyon Dam.

Bugflows were implemented May-August in 2018, 2019, 2020, and 2022.

EPT.jpg
EPT as Biologic Indicators of Stream Condition
Chara.jpg
Algae and Aquatic Macrophytes
Macroinvertebrates.jpg
Aquatic Macroinvertebrates

Hypothesis

Daily flow fluctuations dry (desiccate) and kill eggs laid in the evening along the shorelines resulting in population level declines in the abundance and diversity of aquatic macroinvertebrates (midges and EPT) below Glen Canyon Dam.

  • In areas where evening egg laying is out of sync with the daily hydropower wave (Glen Canyon, Upper and Lower Granite Gorge), we should be able to detect increased egg laying and egg survival during the low weekend flow.
  • Increased egg survival should translate into increased larval and adult insect abundance and diversity.
BioScience Paper
https://www.usbr.gov/uc/progact/amp/twg/2018-01-25-twg-meeting/AR10.pdf

How will we know if Bugflows are successful?

  • See a smoothing of the spatial pattern in midges in Grand Canyon
  • Increase in midges throughout Glen and Grand Canyons
  • Increase in caddisflies (and other EPT) throughout Glen and Grand Canyons


Observations

2025 Annual Reporting Meeting
  • The abundance of adult caddisflies increased riverwide in two of three years that Bug Flows were conducted compared to the pre-Bug Flow baseline from 2012-2017. Caddisflies have been rare in Grand Canyon and improving conditions for them was a primary objective of the experiment. However, this caddisfly increase is correlated with low suspended sediment levels in these same years, complicating this response. Continued experimentation with Bug Flows may be warranted based on these results.
  • Contrary to predictions, no increases in the abundance or changes in distribution in midges were observed across multiple long-term datasets. Modeling suggested that a ~30% increase in non-biting midges riverwide, a common type of aquatic insect, might be realized if Bug Flows was successful.
  • More adult aquatic insects emerged from the Colorado River riverwide during steady weekend Bug Flows compared to weekday fluctuating releases, suggesting that low steady flows improve conditions for adult insects, an unanticipated benefit.
  • Bug Flows increased algae production by 38% in Marble and Grand Canyon, resulting in an additional 100 metric tons of algae-carbon to sustain food webs. The increase in algae production during Bug Flows was energetically substantial and likely supported increased invertebrate and fish production given that production at these levels is food limited.
  • The types of prey eaten by rainbow trout in Glen Canyon varied by flow treatment but overall energy intake was unchanged. Anglers captured more rainbow trout on average during Bug Flows than regular weekday fluctuating flows.

How are Bugflows monitored?


LTEMP descriptions

The Bugflow Experiment: (Chapter 2 LTEMP EIS, Page 71)

A more diverse and productive aquatic food base could benefit a variety of priority resources, including native fish (including the endangered humpback chub), the rainbow trout fishery, and other riparian species that occur in Glen, Marble, and Grand Canyons. Mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera), collectively referred to as EPT, are important components of a healthy aquatic food base, but they are notably absent from the Glen and Marble Canyon reaches and very low in abundance and diversity in the Grand Canyon. GCMRC has hypothesized that EPT taxa are recruitment limited, because daily flow fluctuations to meet hydropower demand cause high egg mortality, and the absence of EPT has an adverse effect on the carrying capacity and condition of the trout fishery and native fish communities. EPT are thought to be recruitment limited because Glen Canyon Dam fluctuations create a large varial (intermittently wetted) zone along shorelines. Because the Colorado River in Glen, Marble, and Grand Canyons is canyon-bound and the tributaries that join the river all have comparatively low flow, the size of the varial zone does not appreciably decrease with distance downstream. Thus, although water temperature regimes become more naturalized with distance downstream, the effect that daily flow fluctuations to meet hydropower demand have on the stability of shoreline habitat does not attenuate much with distance from the dam.

This hypothesis attributes the absence of EPT and the poor health of the invertebrate assemblage to the width of the varial zone, similar to earlier investigations (Blinn et al. 1995), but focuses on the effects unstable shorelines have on the eggs of these species. This hypothesis assumes that egg-laying by EPT occurs principally along shorelines. According to the hypothesis, EPT taxa downstream of Glen Canyon Dam are recruitment limited, because daily flow fluctuations to meet hydropower demand negatively affect habitat quality along the shorelines where egg laying is assumed to occur.

To test this hypothesis, macroinvertebrate production flows would be provided every weekend from May through August (34 days total). The flow on weekends would be held steady at the minimum flow for that month, which would ensure that the insect eggs laid during weekends would remain submerged throughout larval development. If the hypothesis is true, there would be an increase in insect production due to the reproductive success of insects that laid eggs during weekends. No change in monthly volumes, ramping rates, or the maximum daily range in flow during weekdays would be required for this experiment. To offset the smaller water releases that would occur during weekends within a given month, larger releases would need to occur during the weekdays within a given month.

Implementation of macroinvertebrate production flows would consider resource condition assessments and resource concerns using the processes described in Sections 2.2.4.3 and 2.2.4.4. These flows may not be tested when there appears to be the potential for unacceptable impacts on the resources listed in Section 2.2.4.3.

Effects of the tests would be evaluated using observation to determine the location where insect eggs are deposited and the emergence rates of species. Depending on the outcome of the tests, the experiment could be discontinued if there were unacceptable effects on other resources. There is also the possibility that implementation would result in confounding interactions with TMF experiments, and this will be discussed during the communication and consultation process as described in Section 2.2.4.4.

Target two to three replicates (Table 2-9, Page 2-54).

LTEMP Biological Assessment, pages 30-41

Low steady weekend flows (“Macroinvertebrate Production Flows”) would be conducted to test whether the flows would increase insect abundance. On an experimental basis, for example, flows would be held low and steady for two days per week (weekends) from May through August to attempt to improve the productivity of the aquatic food base, and increase the diversity and abundance of mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera), which are collectively referred to as EPT.


Information and Links

Drift and Food Availability Studies

Resources that might be affected

  • Foodbase: abundance, diversity, availability (drift)
  • Hydropower: value, capacity
  • Trout and native fisheries: production, condition
  • Lees Ferry fishery: access, economics
  • Boater safety: Glen Canyon, downstream
  • Sediment transport: beaches

Financial costs of the experiment

  • The cost of the 2018 Bugflow Experiment was $165,000 [1]
  • The cost of the 2019 Bugflow Experiment was $327,000 [2]
  • The cost of the 2020 Bugflow Experiment was $941,000 (3)

The three-year (2018-2020) total of doing the Bugflow Experiment is $1,433,000

  • The cost estimate for doing a Bugflow Experiment in 2021 (which wasn't implemented) was $1,021,000
  • The cost of the 2022 Bugflow Experiment was $1,154,000 [3]

Possible confounding factors

  • Tributary inflows make mainstem flows anything but "steady" through Grand Canyon
  • Changes in nutrients, turbidity, and temperature are also thought to be strong drivers of macroinvertebrate production
  • Bugflows may have a compounding affect on production that may not be seen for many bug generations (months to years)

Papers and Presentations

2023

2022

2021

2020

2019

2018

2016

Other Stuff

Example of an experimental Macroinvertebrate Production Flow (MPF) hydrograph

Modeling Assumptions:

  • Macroinvertebrate Production Flows (MPFs) would occur every weekend from May - Aug (34 days, we scheduled July to have the 5th weekend because that how it works out in 2016)
  • Weekend flow = minimum flow for the month = weekday minimum flow (see weekly hydrographs on the monthly tabs)
  • Hybrid Public Draft monthly volume, ramp rates, or daily change parameters
  • Moved weekend water to weekday releases
  • Energy prices used in this modeling are for a Saturday, Sunday, and a weekday for May, June, July, and August 2016. These are the energy prices Argonne used in the LTEMP modeling for 2016.

Hybrid Public Draft 8.23 MAF volumes:

  • May = 632
  • June = 663
  • July = 749
  • August = 800

Ramp rates: 4,000 up and 2,500 down

Daily change:

  • May = 9
  • June = 10
  • July = 10
  • August = 10

Minimum release: 5,000 cfs
Maximum release: 25,000 cfs

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