Little Lagoon Preservation Society

Little Lagoon Water Quality

It is important to understand the term "water quality". Often we can look at aspects of our waters and correctly conclude the water quality is good or bad.  If the water is murky, has a foul smell to it and it is difficult to find fish or crabs or shrimp one might conclude there is a problem.  Presence of harmful chemicals, bacteria, and algae are more difficult to realize and often require scientific measurement and investigation.  A often used definition of water quality is:

Water quality is the ability of a water body to sustainably support all beneficial uses.

A list of beneficial uses for Little Lagoon would not include providing drinking water but importantly, would include providing sustainable habitat for fish, shrimp, crabs, worms, clams, and numerous other, large to microscopic in size, plants and animals.  Harvest of certain Lagoon species for food use is a popular beneficial use.  Recreational activities such as fishing, crabbing, shrimping, swimming, sailing, power boating or just enjoying a day on the seashore are other popular Lagoon beneficial uses.  

If we use the phrase "water quality in the Lagoon is good", we infer that harmful substances have not compromised beneficial uses of the Lagoon and attributes needed for sustaining those beneficial uses (oxygen, salinity, turbidity, nutrients) are present in the right quantities.  For that reason Little Lagoon Preservation Society volunteers and University Researchers have partnered to measure water quality parameters and conduct scientific research. 

Following is a list of water quality parameters and respective definitions for those parameters which we measure and collect every two weeks since 2007: 

Dissolved Oxygen- The element oxygen is common in water as a component of the compound water.  That "bound" oxygen is generally not available for respiration.  Dissolved, available for respiration, oxygen should be present in minute quantities for a healthy life sustaining aquatic ecosystem.  The amount of dissolved oxygen in water varies with temperature and water movement.  Cold fast moving water generally contains higher dissolved oxygen levels than hot stagnant water.  We measure dissolved oxygen (DO) in parts per million and a DO of 3 ppm is considered minimal for sustaining marine life where as a dissolved oxygen level of 5 ppm is often considered good.  Measured with automated probe.   

Salinity- A measurement of dissolved salts in water, usually in parts per thousand (ppt).  Lagoon waters are generally salty although salinity gradients and stratifications exist within the lagoon with fresh water surface and groundwater sources located at the east and west ends and a salt water source at Lagoon Pass and intermittently at Ivan Pass.  Salinity is important as certain plants and animals can only tolerate a small range of salinities whereas others can survive and flourish in salinities ranging from fresh to near Gulf of Mexico salinities.  For example, many might think that the reason oysters do not flourish in the Lagoon is Dennis and folks like him have eaten them all.  Reality is although the oyster can flourish in the lagoon saline lagoon waters we don't find them colonizing lagoon bottoms because salinities are perfect for the predatory oyster drill to live there also.  Measured with automated probe.     

Ph- Refers to the acidity or alkalinity of water.  A pH of 7 is neutral.  Higher than 7 numbers indicate alkalinity and lower than 7 numbers indicate acidity.  Species vary depending on the pH of water.  Measured with automated probe.

Water Temperature-Water temperature has a direct influence on the amount of dissolved oxygen water can contain as well as the rate of photosynthesis and aquatic organism growth.  For example, during extreme summer temperatures, phytoplankton growth slows and cyano bacteria growth accelerates.  Weather is the principal influence on water temperature though surface runoff and ground water discharges can moderate water temperatures in areas of high volume input.  Measured with automated probe.

Turbidity- A measure of water clarity or suspended particulate matter in the water.  We measure turbidity in lagoon waters with a device called a Secchi dish.  The Secchi is disk shaped and painted alternating black and white.  The dish is lowered into the water and the distance at which the Secchi "disappears" from view is a measure of the distance light can penetrate those waters.  High turbidity waters can result in increased water temperatures and reduce light penetration.    

Chlorophyll A- By measuring the pigment chlorophyll a in Lagoon waters we can calculate the biomass or amount of algae present in lagoon waters.  A high chlorophyll a reading often indicates a phytoplankton bloom.  Analytical lab measurement.

Total Nitrogen- Nitrogen is the most abundant element in the air we breathe.  It is essential to plant and animal life and is recycled continuously.  Total nitrogen consists of organic nitrogen when combined with carbon, and inorganic nitrogen when combined with hydrogen or oxygen.  Too much nitrogen in lagoon waters can cause "over fertilization" and phytoplankton can grow wildly, leading to a bloom and possible reduced oxygen levels.  Nitrogen sources include, fertilizer run off, leaking septic tanks and sewers, manure and other animal wastes (including birds and fish), and car exhausts.  Analytical lab measurement.    

Total Phosphorus- Phosphorus is another element essential for plant and animal growth.  Total phosphorus is a measure of several phosphorus compounds known as phosphates.  Sources of phosphate, include fertilizer run off, leaking septic tanks and sewers, animal wastes (including birds and fish), phosphate rocks and minerals, and detergents.  Too much phosphorus in lagoon waters can also lead to "over fertilization" and stimulate phytoplankton blooms.  Lagoon bottom sediments are very rich in phosphate.  Analytical lab measurement.         

Phytoplankton Composition and Abundance- Phytoplankton are drifting or wandering microscopic plants, often consisting of single cells, chains or filaments.  They obtain energy necessary for food product/photosynthesis from the sun and live in the "photic" or "light zone" of the Gulf and environments like the lagoon.  Phytoplankton form the base of most oceanic and freshwater food webs, produce much of the oxygen in our atmosphere, and fix carbon during growth.  We count and record species of phytoplankton-diatoms, dinoflagellates, and cyanobacteria.   Counts are recorded as cells per liter of water and counts exceeding 100,000 cells per liter can signify a bloom event.  We are especially interested in cataloging and studying bloom formers and toxin producers. 

Bacteria- Fecal coliform bacteria in Lagoon waters indicate that the water has been contaminated by fecal matter from man or animals (eg.birds).  We measure those types of potentially harmful bacteria in lagoon waters by growing cultures from lagoon water samples in agar plates in a constant temperature environment.  We then count and calculate the number of colonies in a known volume of water, and maintain those counts in a data base for use by researchers.  We are concerned with some readings exceeding regulatory standards and researchers are investigating possible sources.   










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