RELATIONSHIPS OF BENTHIC MACROINVERTEBRATE COMMUNITY
STRUCTURE WITH HABITAT AND CONTAMINANT CONCENTRATIONS IN
THE
TEXAS TRINITY RIVER
Marisha R. Frazier, J.L. Slye, Ph.D. and J.H. Kennedy, Ph.D.
McNair Scholars Program; Honors College
Department of Biological Sciences, College of Arts and Sciences
University of North Texas
Denton, Texas
ABSTRACT
The upper Trinity River in the Dallas-Fort Worth area, dominated by wastewater treatment plant effluent, is heavily relied upon for municipal drinking water. Increasing water supply needs are a major issue in this rapidly
urbanized, effluent-dominated watershed. Benthic macroinvertebrates, dominated in our study area by small worms and juvenile aquatic insects, live in direct association with sediment, contaminants, and colonizing
microbiota (biofilms). They are an integral part of the trophic transfer of energy through the aquatic food web. Historical studies conclude that many reaches support a diverse benthic community structure with declines
in diversity and biofilm richness downstream of WWTPs. By quantifying legacy contaminants from water and depositional sediment, this study attempts to understand contaminants that have the capacity to alter the
biota downstream of urbanization and WWTP effluent. The specific objectives of this study are to identify benthic genera and quantify 1) habitat parameters, such as sediment size 2) sediment total organic carbon and
contaminant concentration, and 3) water contaminant concentrations. Understanding the dynamics of WWTP effluent and contaminants is crucial to the development of conservation strategies to minimize impacts to
river ecosystems and maximize their potential for human use.
BACKGROUND
Characterization of the Trinity River
The Trinity River located in the Dallas –Fort Worth
Metroplex (DFW) is comprised of three main forks. The
river is the most highly industrialized and populated
watershed in Texas.
In the past 100 years, the Trinity River has been
severely impacted by human activities within its
watershed. In 1925 the Trinity River Sanitary Survey
compared the river to the River Styx, the Greek
mythological river of death.
•The upper Trinity River is dominated by wastewater
treatment plant (WWTP) effluent. Major improvements
to wastewater plant technology has resulted in
increased water quality in the river.
Bioassessments and Benthic Macroinvertebrates
Benthic macroinvertebrates are invertebrates less
than 0.5mm in length that live on the bottom of aquatic
systems.
Benthic macroinvertebrate distributions are influenced
by habitat factors, such as substrate type and water
quality. They have a long history of being used in bioassessments to evaluate the ecological health of
streams and rivers (Cairns and Pratt 1993).
 A 1987- 88 study of the benthos conducted by the
University of North Texas concluded that the Trinity
River water quality supported a diverse benthic
community structure (Dickson et al. 1988). A follow up
study in 2005 measured continued improvements in
water quality (JL Slye et al. 2010).
METHODS
PRELIMINARY RESULTS
•A total 210 individuals were collected from eight samples.
Sample site locations
•Elm Fork downstream of Lake Lewisville - LLELA
•Mainstem downstream of Dallas and Dallas Central WWTP (S. Dallas)
Collection Methods
•Four replicate Ponar grabs (with a sample area of 152 mm2) were taken
from each sampling location.
•Samples were collected and preserved with 10% formalin and transferred to
70% ethanol in the lab.
•Samples were processed to remove excess silt, and the organisms were
found using a dissection microscope.
•Oligochaeta and Chironomidae were mounted on microscope slides using
Eupural mounting media.
•Specimens were identified to genus/species (except for nematodes, bivalves,
and gastropods).
Sediment Analysis
•A soil hydrometer method was used to measure the percentage of silt and
clay in the inorganic fraction of sediment.
•Sieve shaker was used to measure substrate particles larger than silt.
Statistical Methods
test was measured at α-level = 0.05
•Independent t-test
•Preliminary data shows more 90% of the total number of
individuals collected belonged to eleven taxa, representing
the chironomids (95%) and Oligochaeta (4%)
•Overall, the most abundant chironomid genera were
Cryptochironomus, Polypedilum, Dicrotendipes, and
Paracladopelma
•Tubificinae was the dominant Oligochaeta subfamily found in
this study.
•Chironominae , subfamily of Chironomidae, was more
abundant than either Tanypodinae or Orthocladinae at both
sites.
•A decline in chironomid genera richness was seen for SDAL
(site 08) which is located within the DFW metroplex area.
•The average number of macroinvertebrates collected ranged
from a maximum of 75 individuals per replication at the SDAL
(site 08) to a minimum of 15 individuals per replication
collected at the reference site LLELA (site 02; Fig 3)
Benthic Macroinvertebrate Metrics
•Abundance
•Richness
•Diversity
•Evenness
Depositional Sediment Contaminants
Figure 3. Average abundance, richness, diversity, and evenness
Chironomidae for LLELA and South Dallas. No statistical significant
differences were detected (t-test a-level 0.05).
Figure 1. Dallas-Fort Worth Metropolitan map, showing sampling
locations, including four major wastewater treatment plants.
Photos by JLSlye.
DISCUSSION
•It is established that sediment type is a main factor
influencing benthic macroinvertebrate distributions. Benthic
macroinvertebrates, dominated in our study area by small
worms and juvenile aquatic insects, live in direct association
with sediment, contaminants, and colonizing microbiota
(biofilms).
•Historical studies conclude that many reaches support a
diverse benthic community structure with declines in diversity
and biofilm richness downstream of WWTPs.
• By quantifying legacy contaminants from water and
depositional sediment, this study attempts to understand
contaminants that have the capacity to alter the biota
downstream of urbanization and WWTP effluent.
• To determine the role of sediment biofilm fatty acids, we
must first understand the influence of sediment particle size
on the benthic community structure.
OBJECTIVES/HYPOTHESIS
The objectives of this current study are to:
• Characterize the benthic macroinvertebrate community
of the upstream reference location (LLELA) and the
downstream urbanized location (South Dallas).
•Characterize habitat parameters to understand what
environmental variables are related to the benthic
macroinvertebrate abundance and richness.
•Quantify a set of contaminants (DDT, PCBs, atrazine,
chlordane, chloropyrifos, triclosan, and methyl triclosan)
from surface water and sediment.
•Quantify biofilm fatty acid methyl esters (FAME) and
bacterial fatty acid methyl esters (BAME) to assess if a
more diverse biofilm structure is related to benthic
macroinvertebrate abundance and richness.
•Assess if contaminant levels are related to FAME and
BAME metrics; and determine if certain BAMEs are
present with higher concentrations of anti-microbials
(triclosan and methyl triclosan)
•The hypothesis that was tested for this study was:
H0 : There is a relationship among benthic
macroinvertebrate community structure metrics (i.e.
abundance and richness of Chironomidae and
Oligochaeta taxa) and contaminant concentration.
Photo credit:: University of North Texas
ACKNOWLEDGMENTS
Warren Burggren, Ph.D., Provost and Vice President for Academic Affairs
Gloria Cox, Ph.D., Dean, Honors College
Susan Eve, Ph.D., Assistant Dean, Honors College
Diana Elrod, Ph.D., McNair Director, McNair Scholars Program
Rosa Fonseca, McNair Adivsor
Rebekah Samaniego, Technical Editor
Benthic Ecology Laboratory Students
REFERENCES/WORKS CITED
•Cairns J Jr, Pratt JR. 1993. A history of biological monitoring using benthic
macroinvertebrates. In: Freshwater Biomonitoring and Benthic
Macroinvertebrates. Chapman and Hall, New York, NY, USA. pp10 - 27.
•Dickson KL, Waller WT, Kennedy JH, Arnold WR, Desmond WP, Dyer SD, Hall
JF, Knight JT, Malas D, Martinez ML, Matzner SL. 1989. A water quality and
ecological survey of the Trinity River. Report to City of Dallas Water Utitlies by
Institute of Applied Sciences, University of North Texas, and Graduate Program
in Environmental Sciences, University of Texas at Dallas, TX, USA. 339pp.
•Slye J L, Kennedy J H, Johnson DR, Atkinson SF, Dyer SD, Ciarlo M, Price
BB. 2011. Relationships between benthic macroinvertebrate community
structure and geospatial habitat, in-stream water chemistry, and surfactants in
the effluent-dominated Trinity River, Texas, USA. Environmental Toxicology &
Chemistry, 30(5), 1127-1138.