Effects of the Rio Salado Confluence on Benthic Substrate

in the Rio Grande

Harmony LuREU Project

Summer 2010

Background

River Continuum Concept

to Network Hypothesis- gradient of change from

headwaters to mouth of hydrological properties

- biological communities also change to match the local conditions

- discontinuities in these gradients occur, instead view the river as a network

BackgroundFlood events in an intermittent stream

Research Questions

• Are there observable effects from the confluence of an intermittent stream, the Rio Salado, on the main channel, the Rio Grande?

• Do these effects alter the local habitat?

Possible lasting effects of an intermittent tributary

- focus on substrate variation in the main channel water energy determines particle carriage/deposition tributary carries sediment into main channel

- benthic substrate important habitat characteristic

Background

Rio Grande– major water source for agriculture,

domestic use, natural habitats (riparian areas)

– also is a habitat itself for many species– sandy-bottomed with wide floodplain

BackgroundInvertebrate communities are useful

biological indicators in freshwater- commonly studied- many are sedentary and provide

assessment of localized effects- are important parts of river communities

Research Site

Sevilleta National Wildlife Refuge

Research Site

Procedure 1– mapping

• 11 transects from the west bank to the east bank

• 4 samples along each transect

• at each site, 3 measurements:1. % cobble2. depth3. sediment sample taken

for texture analysis

Procedure 2– invertebrate sampling

• 2 sets of samples taken (Day 1: June 4+6, Day 2: June 23)

• 7 sites along the west bank• Data from each site (3

types):– sediment texture– water characteristics– invertebrate community

Invertebrate Sampling Sites

Procedure – invert collection

• Invertebrate sampling:- sediment core sampling

4 cores of the top 1 cm of benthic substrate

• samples preserved in 70% ethanol

Procedure – sample analysis• Sediment

– hydrometer soil texture analysis used to assess % composition

• Invertebrate– invertebrates separated

from debris/sediment– identified to Order or

Family using dissecting microscopeDay Site Chironomidae Simuliidae Tricorythidae Baetidae Leptoceridae Hempitera Odonata Cladocera

1 1 5 12 0 0 0 0 0 01 2 3 7 0 0 1 0 0 01 3 11 14 0 3 0 0 0 01 4 17 653 0 0 0 0 0 0

Results and Discussion

• Confluence map• Invertebrate community• Environmental influence on

invertebrate community• Lasting effects of the confluence

Confluence Depth Map

Rio Salado

Confluence Cobble Cover Map

Rio Salado

bubble size indicates % cobble cover

Invertebrate Data

Invertebrate Community Data

(Global R): 0.536p: 0.001

Similarity of communities – positioning around confluence

Multidimensional Scaling (MDS)

• multivariate – can look at community as a whole• each site’s community data viewed as a matrix• calculated a similarity between all of the matrices• plot similarity in multidimensional space• compress to 2D plot with meaningless axis

Bottom line:relative distance is keycloseness implies similarity

Invertebrate Community Data

(Global R): 0.536p: 0.001

Temporal Changes – succession of species over the summer

Correlation between environment and biological

communities

Correlation Variables

0.330 gravel, vv fine sand + silt

0.330 gravel, vv fine sand + silt,v fine sand

0.321 gravel, vv fine sand + silt

- water characteristics: showed very small variation between sites- sediment texture: much higher variation between sites- BEST analysis: compares environmental information (soil texture) to biological information (community)

- % gravel and % vv fine sand + silt explain most of the variation in biological communities

MDSsize indicates relative % gravel

size indicates relative % vv fine sand + silt

Confluence Sand Map

Rio Salado

bubble size indicates % sand (by mass)

Confluence Gravel Map

Rio Salado

bubble size indicates % gravel (by mass)

Rio Salado

Confluence vv fine sand and silt Map

bubble size indicates % (by mass)gravel

silt

vv fine sand

Matching up to observations

Rio Salado

Conclusions• Invertebrate communities changed through

time• Variation in invertebrate communities could

be correlated with substrate qualities• The main channel around the confluence

shows high variation in substrate quality• Patterns of substrate quality match

observations of tributary inputs• Implications that tributary has lasting

influence on habitat quality of main channel

Further Research

• Intermittent streams as sources of disturbance that change throughout the year

• Interannual variation of precipitation and flow rates of intermittent tributaries

• Variability in the benthic substrate of the Rio Grande overall (temporal and spatial)

Acknowledgements

Ayesha Burdett, Jennifer Johnson

Sevilleta LTER REU 2010 students (Christopher Shepard, Shayla Burnett, Amanda Labrado, Ricardo Duran, Cynthia Malone, Ileana Betancourt, Melissa Shaginoff, Mitch Nakai, Natasha Ribeiro, Amanda Liebrecht, Antonio Nevarez, Elida Iniguez)

Brenda Nieto

National Science Foundation

Sevilleta National Wildlife Refuge & LTER

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Questions?