Evaluations of Estuary Quality

Evaluations of Estuary Quality
By Connie Wood
Fall 97

Summary
The purpose of this paper is to list and describe some the evaluations used to determine the quality of estuaries. Specific tests, locations and standards are given.

Location
The locations are on the Texas Gulf Coast. They include Galveston Bay, San Antonio Bay, Corpus Christi Bay, Laguna Madre and small estuaries found along the Texas coast.

Tests preformed
Tests performed to determine estuary quality are bottom life, light penetration, sediment contaminants, fish pathology, dissolved oxygen levels, pH, temperature, and conductivity.

Measuring Estuary Quality:

Water Temperature
One of the most important measurements of water quality monitoring is water temperature. It has an effect on chemical, physical and biological processes. Some examples of these processes are solubility of compounds, rate of reactions, water density, inversions and mixing, feeding, reproduction and the abundance of organisms. Extended periods of high temperatures may make an aquatic area unsuitable for certain organisms that would be able to live there the rest of the year. Fish larvae and eggs usually require smaller temperature range than adult fish. Generally fish prefer a slow change in temperature rather than a rapid change. As water temperatures decrease, the ability to hold dissolved oxygen increases. One situation of how temperature effects water quality is during the summer as water temperature increases, dissolved oxygen levels decrease, metabolism of aquatic organisms increase, and microorganisms that consume waste organics use oxygen faster. All of these factors put stress on the aquatic system. One indication of poor water quality in estuaries would be a sudden or large increase in water temperature. In a coastal area, an increase of 5 degrees Celsius above the normal level for that season, or an increase of 32 degrees Celsius would indicate a concern.

Light Penetration
Another measurement used to determine estuary quality is light penetration. A Sect disk is one way to measure this characteristic. Light penetration or visibility of the water indicates the presence of things such as particles of silt or algae growth. The color of the water effects the transparency. Sediments suspended in water can block sunlight to submerged plants and carry nutrients, pesticides or other pollutants through the water.

Dissolved Oxygen
Dissolved oxygen is another indicator of estuary water quality. It is usually measured in milligrams per liter or parts per million. Fish, invertebrates, plants and aerobic bacteria require oxygen. Temperature influences DO greatly. Water with a temperature of 31 degrees Celsius will only hold about half as much oxygen as water with a temperature of 1 degree Celsius. The amount of DO in an estuary depends on wind, water flow and thermal upwelling and mixing. It also depends on the type and amount of aquatic plants, algae and phytoplankton that produce oxygen as a by-product of photosynthesis. Hypoxia refers to water with low DO levels and anoxia refers to water with no DO levels. Too many aquatic plants and animals can consume most of the oxygen. Too many aquatic plants or increased alga growth can result form the elevated concentrations of nitrogen and phosphorus in the water. These two nutrients may come from run-off from farms, golf courses, fertilized yards and sewage plant effluent. Since DO is dependent on temperature, standards for DO in estuaries are also tied to temperature measurements. Generally a reading of no less that 5 mg/l is acceptable.

Measuring pH
A measurement of pH is also used to determine estuary water quality. pH is a measure of how acidic or basic a substance is. Coastal areas normally vary from pH 7-8. In general, wetlands, swamps, and other forested areas will have lower pH levels. pH level changes can indicate such conditions as photosynthetic uptake of carbon dioxide or oxygen deficient waters. Heavy rainfall or inflow of contaminants can also change pH levels. Water with pH lower than 5.0 or higher that 9.0 should be investigated. One key indicator of algae bloom is the presence of increased pH and DO levels.

Remote sensing
Another type of monitoring of estuary quality is the use of remote sensing. Remotely sensed data from aircraft and satellites provide information about estuary systems. The Earth Scan Laboratory (ESL) captures satellite images from the Gulf of Mexico, most of the Atlantic, the extreme eastern Pacific, the Northern Caribbean and the land masses from Hudson Bay to northernmost South America. Also included in remote sensing data are images from the Geostationary Operational Environment Satellites (GEOS). This satellite system transmits thermal and visible imagery from most of the Western Hemisphere every thirty minutes. This information is used to monitor and analyze coastal and deep-gulf circulation, coastal sediment transport, storm formation, oil spills, and vegetation conditions.

Additional factors of Estuary quality
Estuaries are places where fresh water from rivers and salt water from oceans mix. Salinity is a major factor affecting the physical makeup of estuaries. The salinity levels decrease as the estuary moves inland and as the volume of freshwater changes.

Conductivity measurements correlate to salinity and the amount other dissolved solid in water. Wastewater discharge and fertilizer runoffs are activities that might change the conductivity of estuary water.

EPA Test results
During the 1991-93 testing periods, EPA rated the following estuary areas for quality. Tests included bottom life condition, DO, light penetration, sediment contaminants and fish pathology. Corpus Christi Bay was rated overall fair with poor conditions for bottom life (59 +- 13%), and light penetration (<10%) (37+/- 13%). DO levels less than 2ppm were rarely observed. Galveston Bay was rated overall poor to fair. Areas of concern were bottom life, light penetration<10%, sediment contaminants and fish pathology. San Antonio Bay was rated overall good to fair. Only bottom life conditions and light penetration were rated poor. Matagorda Bay was rated good overall. Bottom life conditions were rated poor. Laguna Madre was rated good overall. Bottom life was the only poor condition reported there.

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