Project F update: 

Lead decomposition, bat monitoring, aquatic insects 

*This information is preliminary and 

is subject to revision. It is being 

provided to meet the need for timely 

best science. The information is 

provided on the condition that 

neither the U.S. Geological Survey 

nor the U.S. Government shall be 

held liable for any damages 

resulting from the authorized or 

unauthorized use of the information. 

1-US Geological Survey, 

Southwest Biological Science 

Center, Grand Canyon 

Monitoring and Research 

Center, Flagstaff, AZ 

2-US Geological Survey, 

Alaska Cooperative Fish and 

Wildlife Research Unit, 

Fairbanks, AK 

Ted Kennedy1, Eric Scholl1, Anya Metcalfe1, Jeff Muehlbauer2, 

Charles Yackulic1, Morgan Ford1, Cheyenne Szydlo1 U.S. Department of the Interior 

U.S. Geological Survey 
Outline 

 Leaf decomposition study (9 slides) 

 Bat monitoring update (3 slides) 

 Light trap update (3 slides) 

Leaves decomposing 

in a stream 

Community science bat monitoring Community science insect monitoring 
-

 

 

 

Decomposition Study Background: 

• Decomposition of organic matter 

represents a fundamental ecosystem 

process in rivers 

• Changes in decomposition alter how 

energy and nutrients move through 

aquatic and riparian food webs 

Food webs of the Colorado 

River circa 2006 2009. 

From Kennedy and others, 

2014 USGS Fact Sheet 
 

 

 

Decomposition Study Background:

Drivers of decomposition are rapidly 

changing in the Colorado River 

 

From Scholl and others, in press, Ecosphere 

Biological invasion Biocontrol Water nutrients Temperature 

Objective: Compare the breakdown of cottonwood, willow, and saltcedar to a 

1998 experiment (Pomeroy et al. 2000) that was conducted in context of: 

-cooler temperatures 

-lower mudsnail density 

-saltcedar litter not affect by biocontrol beetles 

-higher phosphorus concentrations 
 

 

 

Water 

temperature 

Leaf 

chemistry

(% nitrogen) 

Water 

phosphorus 

1998: cool 

2022: warm 

Mudsnails 

1998: low 

2022: high 

1998: low 

2022: high 

1998: high 

2022: low 

67% decrease 

Prediction: Saltcedar decomposition 

will show strongest response owing 

to warming and higher leaf nutrient 

content associated with herbivory 

Saltcedar 

Herbivory by Tamarix beetles leads to early 

senescence of leaves before nutrient translocation. 

Cottonwood Willow 
 

 

 

Experimental Approach: 

• Constructed 105 total leaf packs 

(4g of litter/pack) 

• Packs at Lees Ferry, collected 5 

replicates per litter type on days 1, 

2, 7, 24, 46, 84, 142 (April 4th 

– Aug 

24th 2022) 

• Dried, weighed, and ashed all litter 

shortly after retrieval to estimate 

mass loss throughout experiment 

• Removed, counted, 

measured, and 

identified all 

invertebrates 
Results: Saltcedar decomposition rate more than 

doubled between 1998 and 2022 

1998 

2022 

k = decay rate 

From Scholl and others, in press, Ecosphere 
 

Results: Interaction between 

warmer temps and higher 

quality litter (10X higher N 

content) likely led to largest 

response in saltcedar 

 

Beetle herbivory causes 

premature litterfall before 

nutrients are translocated 

during senescence 

From Scholl and others, In Press, Ecosphere 
 

 

 

Results: Minor changes in other leaf types despite warmer 

temperatures likely driven by lower phosphorus concentrations 

1998 

2022 

Water phosphorus declines 

1998 to 2022 

Total P 63% 

SRP 69%

From Scholl and others, In Press, Ecosphere 
 

 

 

Results: Mudsnails were the dominant invertebrate across all 

dates and leaf types (compared to worms in 1998)...still unclear 

if they influenced decomposition in our study 

NZ mudsnail 

From Scholl and others, In Press, Ecosphere 
 

Conclusions: 

• Drivers of decomposition are changing in the Colorado River 

• Warmer temperatures likely interacted with higher litter quality to 

accelerate saltcedar decomposition 

• Declines in water phosphorus may have offset effects of warming on 

cottonwood and willow decomposition 

• Future work is needed to examine: 1) mudsnail impacts (diff. mesh 

size) and 2) patterns of decomposition farther downstream 
 

 

Modeled bat activity 2017-2023 

Community science data (Echometers) 

N um er ous ba t-hu m a n en cou n ter s i n 2023, 

bu t w a s ther e m or e ba t a cti v i ty ? N o. 

* 

Mixed effects model run using BRMS, includes Year, Month, and Site as random effects and offsets for sampling duration 

Post-hoc Tukey test found no significant differences between years (confidence level 0.95, alpha=0.05) 

*Sampling effort in 2020 was reduced and did not include spring 

Metcalfe et al. 2023 

Provisional data, subject to change. 
Provisional data, subject to change. 

H ow do S M 4 a n d E chom eter T ou ch da ta com pa r e? 

EchoMeter 

Strength: real-time display 

is great for comm. science 

Weakness: modest 

microphone range, sensor 

saturation 

SongMeter4

Strength: large microphone 

range, not easily saturated 

Weakness: black box, no 

real time viewing (guides 

hated it) 

Study design: community 

scientists deployed both units 

simultaneously for 1hr. 

Metcalfe et al. In prep. Trade -offsin designing a participatory acoustic study of bats: 

User engagement and data quality comparison of SongMeter4 and Echometer. 

Result: More bat activity 

detected using SM4 than 

EchoMeters. 

Result: 1.6 more bat species 

per sampling event using 

SM4s than EchoMeters 
 

A pr i l 2023: S i x n ew s ta ti on a r y ba t detector s depl oy ed i n G R C A 

Above Kwagunt rapid Below Emerald rapid 

S M 4B AT -FS 

USGS sites NPS sites Sites chosen based on high and low 

nodes of insect availability, NABat 

priority, and NPS site compatibility Recording took place dusk:dawn 

twice a week (Sundays and 

Thursdays) 

Site name RM Side 

Below Tatahatso 38.9 R 

Above Kwagunt 56.2 L 

Science Camp 63.8 R 

Below Emerald 104.8 R 

184-mile – below Lava 184 L 

Fall Canyon 213 R 

Site RM Side 

North Canyon 20.8 R 

Malgosa Canyon 58 R 

Bright Angel Creek 88 R 

Kanab Creek 144 R 

Parashant Canyon 199 R 

Surprise Canyon 248.7 R 

275 Mile Marsh 275 R 
 

 

2023 Light Traps 

Freshwaters Illustrated 

2023 Community Scientists 

Collector #samples Collector #samples 

GCY 60 WilliamsK 23 

RatayR 51 KennedyT 17 

FadeleyB 47 MansfieldL 16 

LouvierM 43 AllenK 14 

RoussisO 43 MetcalfeA 14 

LokeyE 42 SellerP 14 

BurchR 38 SiemionG 14 

KristjonsdottirS 37 SzydloC 9 

LowryM 35 TownsendJ 8 

SeabaughC 35 CatlettJ 6 

TankersleyG 35 PettyJ 6 

MagnificoS 32 PalmquistE 4 

GantertJ 27 StalveyA 3 

Thank you guides, GCY, and others!! 

Kennedy and others 2016, Bioscience In a nutshell 

Community science monitoring started in 2012 

~700 samples of adult aquatic insects per year 

Robust dataset for quantifying insect population response to Bug Flows 
 

2023 Caveats 

 ~29% of samples processed (200 out of 680) 

 However, samples randomly selected for processing and models 

account for variation in sampling effort across years 

Unpublished data, subject to change, 

do not cite. 
 

Result 

 2023 

 55% decrease in midges 

 77% decrease in caddisflies 

 Statistics 

Very strong model support for positive 

Bug Flow effect 

Bug Flow model v. model w/o Bug Flow effect 

 Midges, deltaAIC: 27.5 

 Caddisflies: deltAIC: 35.1 

Note: deltaAIC >2 considered strong support 

Estimates of annual average from mixed effects model 

Provisional data, subject to change. 

17 
From Scholl and others, In Press, Ecosphere 

Provisional data, subject to change. Provisional data, subject to change. 

Conclusions 

 Drivers of decomposition are changing, but in 2022 low phosphorus likely 

offset warm temperatures except in case of saltcedar 

 Community science bat monitoring being supplemented by fixed site 

monitoring in coordination with GRCA 

 Preliminary result: strong model support for Bug Flow effect on aquatic 

insects