Planning: Can we proceed from existing conditions and with Bug Flows and BF 

results move to more refined foodbase management? This set of projects and 

Bug Flows are not mutually exclusive, are not proposed as alternatives to Bug 

Flows, nor do they need to be ignored so long as Bug Flows are ongoing

What and How? Address specific questions by conducting basic field and some 

laboratory experiments at and near Lees Ferry and the Paria River confluence.

Why? Determine whether and how to scale potential CRE foodbase

enhancement up to the ecosystem scale.

When? Over the course of the next several years, perhaps with the GCMRC 

2020 budget revision, and in concert with the results of a foodbase PEP

Issues: Relationship of questions to Bug Flows results

Integration into GCMRC schedule and budget planning

Consider public visibility and safety issues

(e.g., flotsam and fixed CWD experimentation)

Contingency planning 

(e.g., anomalous flows, vandalism and replication levels) 

Future CRE Foodbase Research and Management 
1. Embeddedness: How do it and flow variation affect foodbase productivity?

2. Power-flushing the benthos: Does flushing benthic substrata reduce BHA

and enhance macroinvertebrate production?

3. Coarse woody debris: Can reintroduction of CWD improve foodbase production?

4. Attractants: Do specific microhabitats differentially attract and support selected BMI?

5. Nutrient dynamics: Whether and how strongly do Lake Powell Reservoir-to-downstream

nutrient dynamics affect CRE aquatic foodbase productivity?

6. EPT population enhancement: Can mainstream EPT populations be enhanced?

7. Epiphytic and macrophyte interactions: Does epiphyton composition vary among

the five common macrophyte taxa and can epiphyton production be enhanced?

8. Desiccation and freezing: What are the impacts and recovery rates of the foodbase

from desiccation and freezing?

Eight Questions and Issues 

That May Warrant More Attention

in CRE Tailwaters Aquatic Foodbase Management
1) Embeddedness

Question: How do embeddedness and flow variation affect CRE 

tailwaters foodbase productivity?

Experiments: Use gravel/cobble basket treatments, floating (constant 

flow) vs below-low-flow anchored in springtime vs fall, and in the 

clearwater mainstream vs below the Paria River confluence 

Replication: 30 reps of each treatment, deploy the baskets for two 

month intervals spring and fall, pulling 6 baskets bi-weekly

Year 2: Use results to test for interaction effects 

Relation to Bug Flows: Determine how embeddedness interacts with 

reduced flow variation to affect benthic macroinvertebrates (BMI).
2) Power-flushing Benthic Sediments

Question: Can flushing benthic substrata reduce benthic and hyporheic 

anoxia and enhance macroinvertebrate production?

Experimental tests: Shallow submerged, 10 m X 5 m power- flushed 

rectangular plots, long axis perpendicular to channel

Replication: 12-15 replicates each in cobble vs sand, with controls, 

sampled bi-weekly for six months in springtime and in fall using 

submersible Hess samplers.

Year 2: Compare and contrast these results with pre- and post-autumn 

and springtime HFE scour

Relation to Bug Flows: Determine how Bug Flows influence 

embeddedness. 
3) Coarse Woody Debris

Question: Cessation of coarse woody debris import and presence has 

been a major dam-related habitat alteration of the CRE. Can 

reintroduction of CWD improve foodbase production?

Experiment: Barked pine logs, floating with both ends anchored, each 

with numerous easily-extractable 0.1 m2sampling blocks, attached to 

shore, extending through the varial zone. Test branch baskets also?

Replication: Deploy 6 reps above vs 6 below the Paria River 

confluence, and monitor/sample bi-weekly; compare against other 

treatments. Test in the Paria River as well.

Year 2: a) Water- logging and decomposition rates of CWD of 

different tree species, if warranted; 

b) CWD movement and deposition using citizen scientist tracking 

of labeled CWD through the river corridor.

Relation to Bug Flows: Determine whether CWD differs from rock. 
4) Attractants

Question: Do other specific microhabitats differentially attract and 

support selected BMIs?

Test: a) Bubbling water: Establish floating shoreline basket samplers 

up on river left at the foot of the Paria Riffle where wave action is 

pronounced, and compare with another set of floating samplers 

placed downstream where wave action is minimal. Measure 

exposure and velocity relatively constant

Replication: 12 samplers in each setting, with pilot tests 

Year 2: Is scaling up feasible with this question?

Relation to Bug Flows: Are specific microhabitats, such as wavewashed boulders preferred for nematoceran oviposition?
5) Nutrient Supplementation

Question: How strongly do Lake Powell Reservoir-to-downstream 

nutrient dynamics affect CRE aquatic foodbase productivity?

Test: a) Standard shallow-submerged clay pot experiment with N 

vs P vs control treatments. Scrape 100 cm2/pot on upstream vs. 

downstream sites on bi-weekly intervals. 

Replication: N=30 replicates of each treatment in springtime and 

in autumn, with deployment upstream, downstream, and in the 

Paria River.

Year 2: Use results to refine nutrient ratio data and test for 

interaction impacts of the two nutrients.

Relation to Bug Flows: Presently monitored and modeled by 

GCMRC, but not experimentally tested with Bug Flows.
6) EPT Population Enhancement

Question: Can CRE EPT populations be enhanced? 

Test: Establish on-shore pool, onshore experimental flowing 

channel, and in-channel floating pool habitats. Pools are 1 m2

X 0.25 m deep. Channels 0.5 m X 5m X 0.1 m deep, velocity 

of ca 0.1 m/sec. 

Replication: 12 reps each, six shaded, the others in full sun, 

upstream, downstream, and in the Paria River. Monitor BMI 

colonization rates bi-weekly in springtime and fall. 

Year Two: Attempt translocation of local Cheumatopsyche osleri

from the Paria River into onshore and in stream channels and 

carefully monitor.

Relation to Bug Flows: Bug flows may demonstrate some EPT 

establishment; this experiment will indicate how the duration 

and timing of steady flows influences EPT colonization.
7) Macrophyte Ecology

Question: Epiphyton are the real source of the CRE aquatic food base, 

but are they distributed equally among five common macrophytes? 

Measurements: a) Describe epiphyton and invertebrate composition 

and diet on Chara, Zannichellia, Oscillatoria, Cladophora, and moss. 

Use field surveys, laboratory, and in situ field experiments to 

determine comparative habitat preferences and competitive status of 

the five primary macrophyte taxa.

Replication: Measure ephiphytic and BMI presence across stage 

elevation on 6 transects above Lees Ferry and 6 below the Paria River 

confluence, and six transects in the Paria River.

Year Two: Experimental manipulation of nutrients and substrata to 

determine if it is possible to shift or enhance epiphyton-rich taxa (i.e., 

Cladophora) distribution.

Relation to Bug Flows: This topic has to do with larval BMI feeding, 

rather than egg desiccation, but may influence BF outcomes. 
8) Desiccation and Freezing Impacts

Question: Desiccation and freezing may exert important impacts 

on near-shore habitats – what are macrophyte and BMI recovery 

rates from such disturbances?

Test: Opportunistically and experimentally test desiccation and 

freeze duration impacts on the five major macrophyte taxa, and 

BMI recolonization rate, using sterilized vs non-sterilized cobbles, 

upstream and downstream, and within the Paria River. Scrape 10 X 

10 cm surface patches. 

Replication: Test colonization rate and exposure impacts on 30 

replicated cobbles of each in each setting. 

Year Two: Use results if preliminary experiments to conduct 

scaled-up research.

Relation to Bug Flows: This experiment may augment BF 

examination of flow fluctuations affect epiphyton and macrophyte

mortality.
Other Questions to be Addressed?

Discussion – Relevance of these ???

Moving forward – A Foodbase Ad Hoc?