Table 4.2. Distribution of Total Organic Carbon in Galveston Bay. 
Location 
High Values 
(percent) 
West Bay 
1.6 
East Bay 
1.8 
Galveston Bay 
1.9 
Trinity Bay 
2.4 
Buffalo Bayou/ 
Houston Ship Channel 
3.9 
Offatt Bayou 
4.0 
Galveston Channel 
5.7 
Source: (1) 
in bottom sediments. Highest concentrations of TOC occur in bay-center muds, and lowest in bay- 
margin sands. Upper bay concentrations (Trinity Bay) are greater than those found in the lower bays 
(West Bay, East Bay), as shown in Table 4.2. The highest concentrations of TOC, however, occur in 
channels characterized by deeper-water, wave-protected, and oxygen-deficient bottom sediments 
that locally serve as sinks for the accumulation of organic-rich muds (1). High concentrations are 
widely distributed in Trinity Bay, particularly near its head. The Trinity River and bay-head delta are 
probably the primary sources of the carbon. The Trinity River valley contains floodplain swamps and 
marshes that export organic carbon during floods. There is widespread concern that construction of 
the Wallisville dam near the mouth of the Trinity River will affect the transport of vital nutrients to 
the bay. More than 95 percent of carbon, nitrogen and phosphorus input to Galveston Bay arrives 
with freshwater inflow (2). The Trinity River alone provides half of all freshwater inflow to Galveston 
Bay. 
Eutrophication is an excess of dissolved nutrient concentrations in a body of water that produces 
a noticeable change in water quality that may range from simple discoloration to catastrophic events, 
such as fish kills. A whole host of intermediate eutrophication effects, such as changes in species 
composition of food organisms or "dead water" depleted of oxygen, may result. Historically, 
Galveston Bay has contained elevated concentrations of nutrients derived from discharges and non¬ 
point sources (3). Concentrations greater than National Academy of Science guidelines were accom¬ 
panied by severe oxygen depletion in the Houston Ship Channel (84 percent), Galveston Bay (12 
percent). Trinity Bay (4 percent), and West Bay (4 percent of the time), when judged against a 5 mg/ 
1 criterion (4). Light limitation from silt or suspended sediment may hamper plant growth in the 
vicinity of nutrient inputs. Freshwater inflows are responsible for the major portions of nutrient 
inputs to Galveston Bay (5) and light limitation apparently reduces the importance of phytoplankton 
in regions of the estuary that are turbid. 
Recent evaluation of nutrient loading by the Texas Water Commission (6) clearly showed a 
reduction of nutrient loading of nitrogen and phosphorus from 1976 to 1983, compared to the years 
1969 to 1975. The mean concentration of ammonia-N decreased from 0.154 to 0.079 mg/1, and ortho¬ 
phosphorus decreased from 0.463 to 0.293 mg/1. BOD reductions were also observed that produced 
high oxygen concentrations in previously impacted areas. Even though Galveston Bay waters have 
recently had smaller nutrient concentrations than previously measured in the 60s and 70s, their 
deleterious effects have not been eliminated since many non-point sources are not controlled (e.g., 
agricultural fertilization). Accidental or deliberate discharges are also often significant in small areas 
for short periods, as when sewage and sludge released into White Oak Bayou killed thousands of fish 
by oxygen depletion in September 1987. 
Sediments in waterways near industrial facilities generally have levels of heavy metals (arsenic, 
cadmium, copper, lead, mercury, nickel, tin and zinc) that exceed background levels for that 
waterway. Resuspension and redistribution of these contaminated sediments by ship traffic, tidal or 
wave action, and dredging operations are reasons to be concerned about the impact of heavy metals 
on the natural resources in Galveston Bay. Many of these heavy metals are bioaccumulated from the 
sediment by benthic infauna and epifaunas and some plant species. A number of factors, such as pH, 
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