Comparison of Benthic Invertebrate Communities Upstream and Downstream of Proposed Culvert Installations in Alabama

Amy C. GillUSGS, Alabama Water Science Center

Problem

Concerns have arisen concerning the use of culverts at highway crossings of streams. The primary concerns are the culvert’s impact on:

• Stream Geomorphology• Suspended Sediment Concentrations• Turbidity• Stream Biology/Ecology

Study Design

ALDOT and USGS are conducting a scientific investigation to determine the impacts of culverts on streams.• Evaluate 8 to 10 proposed culvert

construction sites.• Before, during, and post

construction• Coastal Plain sites• Basins having little to no

anthropogenic influence (stable streams) are targeted.

• Data will be used to improve culvert installation, if possible.

Site Selection

Eight sites located in Lamar, Tuscaloosa, Bibb, Russell, Choctaw, and Clarke Counties.

•Drainage areas range from

0.39 to 16.4 mi2

•Channel slopes range from

9 to 65 ft./mi

•Channel widths range from

12 to 35 ft.

Stream Ecology Site

Potential Effects of Poor Culvert Design or Placement

• Barriers to animal passage

• Fish

• Invertebrates

• Loss of riparian and instream habitat complexity

•Reduced downstream movement of large woody debris

•Scouring due to increased velocities

•Thermal differences

•Increased algal growth in response to loss of riparian cover

•Shifts in invertebrate communities to scrapers and grazers

Benthic Macroinvertebrates

• Sampled as indicator of stream biological/ecological health• Important for food chain • Indicator for measuring sedimentation impact• Both population and diversity important• Site specific – upstream vs. downstream

comparison• For pre-construction and post-construction sampling periods

• Collect & identify benthic invertebrates at cross-sections above and below the culvert.• Use functional feeding group information to

look at community changes caused by existence of the culvert

• Spring/summer collections before and after culvert construction

Approach

Methods

•Visual survey of available instream habitats both upstream & downstream.•Collection of invertebrates by netting, scraping, brushing from the richest habitats available.

Methods

• 500-micron mesh nets and sieves• Composite sample into 5 gallon

buckets• Reduced sample volume as much as

possible by inspection and removal of larger woody debris

• Attempt to keep upstream and downstream sampling efforts comparable • Same number of woody snags,

length of root/bank, etc.• Similar amount of sampling time

USGS National Water Quality Laboratory Biological Unit

100-counts of invertebrates were identified from each sample by the USGS National Water Quality Laboratory in Denver, Colorado

• The Invertebrate Data Analysis System – IDAS

• Summarizes invertebrate data

• Calculates sample metrics

• Self-archives settings and stores output in Excel files

• Comparison of upstream and downstream reaches at each site

• Are differences observed at all or some of the sites?

Analysis

• Abundance – numbers of individuals• Total Numbers of Taxa• EPT Taxa – Ephemeroptera, Plecoptera,

Trichoptera• Tolerance to impaired water quality• Functional Feeding Groups • Similarity Indices

Community Metrics

Oakmulgee

Oakmulgee

Northington Branch

Northington Branch

Tributary to Cahaba

Tributary to Cahaba

• Most sites have relatively pollution intolerant communities, good abundance and taxa richness values.

• Upstream and downstream samples did not reflect nearly identical communities like we had expected.

• Feeding group structure seems to show promise as a way to identify changes in the site pairs.

Preliminary Findings

• Continue working with this data to see if we can find better ways to see differences and similarities.• Summarize taxa in different ways

(ambiguous taxa, metrics at a different taxonomic level)

• Look at the changes in this data along with geomorphology and sediment transport data.

• Prepare to do post-construction sampling using what we have already learned about these sites.

Next Steps

Questions?