Texas Bayous
COOFREO at Offatt's Bayou
(Coastal Ocean Observatory for Research, Education and Outreach)
We are endeavoring to establish an ecological, microbial, environmental observatory in
Offatt's Bayou. It is a regular spot for people to go fishing, boating and picnicking,
and it supports diverse fish and bird flora. Offatt's Bayou is a small inlet within the
larger ecologically and commercially important Galveston Bay Watershed.
With urbanization in the last 100 years, the bayou has been dredged extensively. A
sewage treatment facility resides on its shores to service the many nearby residents,
as well as several large scale local attractions. The "black hole" in the centre of the
bayou formed as a result of dredging activities, is so called, because it is persistently
hypoxic (low dissolved oxygen levels) and in the summer, anoxic (no dissolved oxygen).
This "mini dead zone" is in our own backyard provides a system for addressing concerns
associated with larger dead zones around the world as well as allowing us to address questions
on eutrophication, algal blooms (some harmful), fish kills, microbial processes, biogeochemistry
and elemental cycling (particularly C and N), etc..
A number of studies have been conducted in Offatt's bayou by scientists and students in
recent years and many more are ongoing. Some of those conducted by students in my
laboratory are summarized below. Folks at Texas Parks and Wildlife (Dickinson Office)
have been working with us on these projects, providing resources and invaluable
information. Winston Denton has been our greatest supporter !
Offatt's Bayou is nearby to the Texas A&M in Galveston campus, with easy boat and
facilities access. Undergraduate students taking my courses go on field trips in this
system to gain hands on field experience with boating, scientific instruments, sample
collecting and analysis (Marine Botany (MARB 408) and Scientific Methods (MARB 300).
Those taking Marine Methods (MARS 489) also use this as a field site for their course
work.
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Current and Recent Projects
Undergraduate Honors Scholar Program by Allison Skinner (2005-2007).
Belly-up in the bayou, who's the culprit ? Physical, chemical and biological parameters of Offatt's Bayou, Galveston, Texas during summers 2005 and 2006.
Offatt's Bayou was created by the City of Galveston as a borrow pit for landfill during
the first part of this century. The bayou is approximately 4.8km long with a maximum
width of 1km, with an average depth of approximately 5m. Offatts Bayou is an important
nursery and habitat for many finfish and shellfish. It also serves as an important
recreational area for nearby residents and visitors. The low mixing environment of
Offatts Bayou (due to its relatively deep basin and small mouth), makes it a good study
area for understanding the causes and effects of hypoxia and phytoplankton blooms, both
of which may be significant factors in the cause of the near annual fish kills. Physical,
chemical and biological parameters were measured twice weekly over the course of two summers.
A fish kill occurred in the summer of 2005, however none transpired during the summer of 2006.
This allows for interesting comparisons between the two summers; possibly pointing to the cause
of the observed fish kill in 2005.
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Master's Thesis by Linda Roehrborn (December 2006).
Seasonal analysis of abiotic factors impacting phytoplankton assemblages in Offatt's Bayou, Galveston, Texas
The aim of this investigation in Offatt's Bayou was to quantify natural shifts in distributions
and abundances of algal groups and to examine spatiotemporal patterns of abiotic and biotic
characteristics of the water column over a one year period (December 2004 to November 2005).
Water column hydrological data and surface water samples were collected at eleven stations
throughout the Offatt's Bayou embayment on a regular basis (2 to 4 times per month), along
with phytoplankton tows on a monthly basis. Phytoplankton biomass and community composition
were examined for significant relationships to seasonal variations in water temperature,
salinity, dissolved oxygen concentrations and pH levels.
Spatial patterns of phytoplankton abundance generally reflected the degree of circulation in
Offatt's Bayou with higher abundances observed in the restricted areas and lower abundances in
the well mixed regions. Temporally, diatom blooms were prominent during autumn, winter,
and spring which were seasons characterized by cooler water temperatures, less light
penetration and availability, increased dissolved oxygen concentrations and reduced
salinities than those observed in summer. The most dominant diatoms were Guinardia
delicatula, Ditylum brightwelli, Rhizosolenia setigera, Dactyliosolen fragillissimus
and numerous Chaetoceros species. During summer, the haptophyte, Corymbellus aureus
dominated the bayou, with highest standing crops at the circulation restricted stations
in Lake Madeline. The bloom of this haptophyte produced large volumes of extracellular \
material which along with the lowered dissolved oxygen concentrations in the water column
, likely caused a fish kill. Fry (1000's) and adult (100's) menhaden (Brevoortia patronus),
stripped mullet (<50) (Mugil cephalus) and a ribbon fish (Trichiurus lepturus) were among the dead.
While the results of this study revealed that temperature, dissolved oxygen and pH were
the critical controlling factors (p < 0.05) on phytoplankton biomass and diversity, it
was clear that phytoplankton dynamics in Offatt's Bayou must be also viewed within the
broader context of additional parameters such as salinity, stratification, zooplankton
grazing, nutrient fluxes and wind effects. Long term monitoring of Offatts Bayou is
essential for tracking, recording and assessing various human impacts to phytoplankton
distribution, abundance, and productivity, as well as impacts to higher trophic levels
such as fish and humans.
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Undergraduate Directed Studies Program (MARB 485) by Brad Grimmit (2004).
Offatt's Bayou biodiversity study: Phytoplankton, benthos and fish survey.Offatt's Bayou is home to a surprising biodiversity of plants and animals considering its eutrophication status, the discharge of a sewage effluent plant into its waters, a major island attraction on its shores and high density of urbanization. A semester long study was conducted to assess the phytoplankton, benthic and fish populations in this system.
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Dickinson Bayou Watershed Partnership
The watershed is heavily developed with three cities on its borders: Dickinson, Santa Fe
and League City. Low intensity residential and mixed commercial developments are the
predominant land uses. High intensity developments and business districts are found
adjacent to and at the intersections of the major thoroughfares. Overall, bacteria and
nutrient concerns and/or impairments are found throughout the Dickinson Bayou Tidal watershed
and occur with high frequency in some areas. Sources for both nutrients and bacteria are
usually associated with municipal rather than industrial activities. Elevated bacteria levels
likely stem from intermittent municipal collection system overflows, failing septic systems,
pet waste, naturally occurring wildlife and avian populations found throughout the watershed and
ranchettes that include raising large animals such as cows and horses. Nutrients can come from the
above sources as well as fertilizers applied to lawns. In-stream levels of bacteria and
nutrients are usually higher after rainfall events that result in storm water run-off.
The Dickinson Bayou Watershed Partnership is a group of scientists and resource managers from
universities and state agencies, concerned citizens working together to come up with a strategic plan
for maintaining and long term, improving the overall heath of this system.
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