Effects of the Rio Salado Confluence on Benthic Substrate in the Rio Grande Harmony Lu REU 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

Background Flood 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

Background Invertebrate 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.% cobble 2.depth 3.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 microscope Day Site ChironomidaeSimuliidaeTricorythidaeBaetidaeLeptoceridaeHempiteraOdonataCladocera

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): p: 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 key closeness implies similarity

Invertebrate Community Data (Global R): p: Temporal Changes – succession of species over the summer

Correlation between environment and biological communities CorrelationVariables 0.330gravel, vv fine sand + silt 0.330gravel, vv fine sand + silt, v fine sand 0.321gravel, 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

MDS size 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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