How to Determine Thermal Effects in an Estuary

Identify regional causes of temperature change. All estuaries are prone to natural thermal fluctuations from seasonal weather changes and daily tidal cycles. Aquatic species living in estuaries are well-adapted to transitional temperature changes. However, extreme fluctuations can also come from anthropogenic sources, such as nuclear power plants and terrestrial runoff from urban areas. These fluctuations can be detrimental to the estuarine species. To identify the anthropogenic heat sources, examine the surrounding areas of the estuary. Take temperature measurements at varying depths from multiple locations around the bay. There may be a noticeable natural gradient, such as warmer water from the river outlet area, but there may also be anomalies of warmer temperatures. Note where these anomalies occur and if they are associated with cities or towns. For instance, is there a sewer pipe or street drainage pipe nearby that drains the roads and parking lots? Is there a nuclear power plant in the region? What other drains come from the city?

Prepare a control group and a variable test group of organisms whose natural habitats are estuaries. Additionally, their behaviors should be temperature-dependent. Study a regional estuary to determine the types of species that exhibit these features and choose an appropriate example. For instance, phytoplankton are ideal because their photosynthetic and reproductive habits are dependent on a particular temperature regime. Macrofauna can be used as well for study -- blue crabs from the Chesapeake Bay will only molt when the temperature range is optimal. To prepare the samples, use aquariums appropriately fitted to the fauna being studied. Small organisms, such as plankton, can be observed in small 1- to 5-gallon aquariums, while macrofauna, such as fish or crabs, will need a larger space. Ideally water of the same composition as the estuary should be used, matching salinity, temperature and depth, if possible.

Subject the test group of organisms to extreme fluctuations in temperature by adding heated or cooled water to the test system. This can be done gradually by adding water through the filter system of the aquarium. Adjust the temperature of the externally sourced water to add incremental reductions or additions in temperature; for instance, if the average water temperature of the estuary is 40 degrees Fahrenheit, add water that is 45 degrees, 50 degrees, and so on. Organisms should be exposed for varying periods of time as well. For instance, a short duration of extreme heat may cause reproductive rates to slow. Continued exposure may damage reproductive processes irreversibly and prolonged durations may cause death. The control group should be exposed to normal temperature changes during regular intervals, following natural cycles such as tidal or seasonal fluctuations.

Make note of the temperature fluctuations and the duration of exposure on a spreadsheet or in a notebook. Make a list using headers such as: species, ambient temperature, temperature of external source, duration of exposure and behavioral changes (reproduction, feeding patterns, etc.) . Monitor how the organisms react and change their behavior based on the temperature and length of time they are exposed. As the temperature increases, the amount of dissolved oxygen in the water decreases. This results in decreased photosynthetic capabilities, decreased reproduction and increased metabolism. An increased metabolism in organisms can cause them to eat themselves out of a food source within the ecosystem. If organisms are exposed to prolonged extreme temperatures, a mass die-off can occur.