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What is a resaca?

Resacas are old river channels of the Rio Grande that once conveyed (transported) flood waters away from the river during times of high flow.  Today, resacas are often referred to simply as ox-bows; however, this is technically incorrect.  The geomorphological processes involved in ox-bow formation are very different from the formation processes associated with resacas.  In fact, many resacas have numerous ox-bows along their path – just like the Rio Grande.  The technically correct term for a resaca is a “distributary” of the Rio Grande or a “historic secondary channel” of the river.

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A water body’s pH tells us the acidity or alkalinity of the water, which affects many chemical and biological processes.  A range of 6.5-8.5 is adequate for most aquatic organisms, although it is not uncommon to find pH values even approaching 10 during certain times of the day or year.  For example, resacas tend to have a pH above 8.  A pH outside the normal range may cause physiological stress to organisms and may even affect reproductive processes.

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Dissolved Oxygen

Dissolved oxygen refers to the amount of oxygen that a body of water contains.  It is often referred to simply as DO.  DO can tell us a lot about how suitable a water body is for sustaining aquatic life.  All aquatic organisms need DO to breath, and when the concentration of DO drops, fish, invertebrates and zooplankton will suffer and either move out of the area if possible, or even die if they cannot leave.  In essence, if DO is too low, these organisms may suffocate.

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Refers to the ability of water to pass an electrical current.  This value directly relates to the amount of salts dissolved in the water, and as such, is closely related to another value called “salinity.” Conductivity is typically higher in areas nearer the coastline, is higher in areas with clay soils or bedrock that tend to dissolve into ionic components that enter the water, and are highest in drier areas with high rates of evaporation.

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Turbidity refers to the clarity of a body or sample of water.  The higher the turbidity, the less clear the water is said to be.  The lower the turbidity, the clearer the water.  Turbidity can be increased by the presence of suspended materials such as sediment or soil particles (usually clay or silt), plankton or algae, and even small particles of organic material.

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Just like air temperature is important for humans and other animals, water temperature is important to all aquatic organisms from microbes to fish.  Water temperature affects the rates of biological and chemical processes of all organisms in the water.  It also affects the dissolved oxygen content of the water (DO  gets lower as temperature increases).  The temperature of the water can also affect the sensitivity of organisms to pollution and diseases.

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Escherichia coli test

E. coli is a species of fecal coliform bacteria. This bacteria is used as an indicator test to tell us if a body of water has been contaminated with sewage or fecal matter from humans and other warm-blooded animals.  It is primarily used to determine if a body of water is safe for human consumption, swimming, boating and other forms of direct and/or indirect contact by humans.  This test does not have direct implications to the aquatic system outside of humans.  As such, this test is more related to the safety of water bodies with regards to public health than ecological testing.

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Benthic Macroinvertebrates Monitoring

This test refers to the abundance and type of invertebrate species found in the bottom layers of water bodies – usually in the mud or sediment.  Examples of benthic species include worms, crustaceans, mollusks and aquatic insects.  Benthic, or bottom, species are as much a part of the aquatic ecosystem as are fishes, plankton, aquatic plants, and aquatic reptiles such as turtles, snakes and alligators.  These groups of organisms are called biological communities.

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Decomposition Assay

Decomposition refers to the decay of plant material like leaf litter in the water.  This process is carried out mainly by microscopic organisms, called decomposers, which include many species of fungi and bacteria.  It is a very important ecosystem process.

The speed of decay (or decomposition rate) is affected by human-caused disturbances, and can be used as a sensitive indicator of ecosystem health.  For example, decomposition slowdown can indicate toxic pollutants in the water, whereas an acceleration of decomposition may indicate a persistent increase in nutrients.

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Resaca Data

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