Ecological Overlay for the Trinity River for support of Development of ...

Executive Summary
This report summarizes available ecological information on the Trinity River and provides an
“Ecological Overlay” document for future development of instream flow recommendations for
the Trinity River. This summary report includes graphical representations and tabular
information revealing key relationships between flow variation and the ecological indicators.
This also include a species occurrence matrix indicating, when available, the location of various
fish and aquatic species within the basin by river mile, TCEQ waterbody code, HUC code and
latitude and longitude. This was developed in coordination with San Jacinto River Authority and
other investigators in Texas who are conducting similar studies. Supporting graphical and
tabular data are included and attached both in hard copy format and are available in digital
format from the Trinity River Authority and/or Texas Water Development Board
Data used in the preparation was extracted from various sources including published peer
reviewed articles, agency reports, federal aid progress reports, conference proceedings, and
regional, state and federal environmental databases. The focus of this study was on development
of ecological information on the occurrence and relationship of instream living resources and
hydrology. However, an attempt was made to evaluate the concentrations and fluctuation of
important water quality variables (water temperature, conductivity, dissolved oxygen, selected
nutrients and suspended solids) in relation to flow. In addition we reviewed pertinent literature
and data and generated estimates of downstream loading of suspended solids and nutrients to the
lower river and estuary. These loads were evaluated for potential impacts on geomorphology and
aquatic life.
We found that historically degraded water quality (anoxia, hypoxia and fish kills) had reduced or
eliminated aquatic communities in the upper basin below Dallas Fort Worth. Today although
many segments are still listed for violations of dissolved oxygen criteria, fish communities have
recovered. One of the primary factors limiting full recovery of riverine/fluvial specialist fish
species and reintroduction of highly migratory fishes is the high number of dams and reservoirs
in the Trinity River basin which have fragmented the river and reduced connectivity. Based on
recent studies the Trinity River watershed was classified as the most fragmented watershed in
Texas. In addition, this network of reservoirs affects the ability of the river to transport nutrients
and sediment to downstream areas. The cumulative extent of this impact is however unknown.
The lowest reservoir on the river, Lake Livingston, has since its construction reduced sediment
and nutrient loading to the lower river and/or Galveston Bay. The impacts of sediment
reductions are however localized below the dam and do not appear to be affecting Galveston Bay
due to the sediment load regeneration below the dam. Nitrogen and phosphorus loads have also
been reduced below Lake Livingston in comparison to inputs from the upper watershed.
However the phosphorus deficit has slowly been reduced in recent years. The effects of nutrient
load reduction are unknown. During the period after dam construction chlorophyll-a levels
declined rapidly in Galveston Bay. However, there are few pre-dam data and during this period
point source loading sources in the lower basin were also reduced.
Two major products produced from this study include a species occurrence matrix which utilized
data compiled from surveys of the literature including agency reports, and summarization of
ecological relationships of candidate “focal species” previously suggested by TPWD. These
focal species were compared, based on their life history attributes, to other members of the fish
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Environmental Institute of Houston
November 17, 2009
Trinity River Basin
Biological Overlay