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Water Quality Measurements     Central District Highlights

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Water Quality Measurements


Field Data Sheets

Physical Field Parameters


Field measurements are collected for every water body sampled. Dissolved oxygen, pH, specific conductance, and water temperature are measured using a field meter. These measurements are conducted in accordance with DEP Standard Operating Procedures (SOPs). Other observations included with the field measurements are cloud cover, wind direction, wind velocity, and air temperature. Weather conditions and other events that could affect the water quality or result in analytical results that are not representative of a water body (i.e. flooding, heavy rains, drought conditions, etc) are also recorded.



  • Dissolved Oxygen - Oxygen dissolves in water from both atmospheric and biological sources. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement) and as a waste product of photosynthesis. The amount of dissolved oxygen gas is highly dependent on temperature. Dissolved oxygen is essential for aquatic life. Algae blooms, high nutrient levels, and seasonal conditions can result in low or very high levels of dissolved oxygen levels which can result in fish kills, among other things.  

  • pH - This is a measurement of the acidity or alkalinity of water.  Values range between 0 and 14. A low pH (below 7) represents acidic conditions, and a high pH (above 7) represents alkaline conditions. A pH of 7 indicates the water is near neutral conditions. Several factors influence the pH of a water body including acid precipitation, bedrock and soil composition, plant growth, organic material, and possible chemical pollution.

  • Secchi Depth - Secchi depth is measured with a Secchi Disk. Secchi depth measurements are related to turbidity, chlorophyll, and color in that all relate to water clarity.

  • Specific Conductance − Specific conductance is a measure of the ability of a liquid, to conduct electricity. The conductance is a function of the amount and type of ions in the water.


Sample Collection on the St. Johns

Laboratory Analytes

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  • Alkalinity - Alkalinity is a measure of water's capacity to neutralize acids. Alkalinity is important because it keeps the pH of a water body constant in spite of changes due to acid rain or other sources, protecting aquatic life.

  • Ammonia (NH3) - Ammonia is used as a fertilizer. Even very low concentrations of ammonia can be toxic under the certain conditions. As a nutrient, ammonia can contribute to eutrophication of water. An abundance of nutrients in water leads to excess plant growth and eventually to eutrophication.

  • Biochemical Oxygen Demand (BOD-5) − BOD is a test for determining how much oxygen is utilized by microorganisms during a 5 day incubation period. High BOD levels can have detrimental effects on a water body including fish kills.


  • Calcium - Calcium salts and calcium ions occur commonly in nature. Calcium is an important contributor to water hardness. Calcium can reduce the toxicity of many chemical compounds making it very important to aquatic life.

  • Chloride  - Chloride is the most abundant component of seawater. Sources of chloride include human and animal waste and saltwater intrusions. High levels of chloride can harm metallic pipes and inhibit growing plants.

  • Chlorophyll a - Chlorophyll a is a green pigment found in plants. Chlorophyll a measurements are used to estimate phytoplankton biomass. Levels of Chlorophyll a in surface waters naturally fluctuate over time. Consistently high levels are indicators of poor water quality and may be a result of excess nutrient loading.

  • Color - Color is not an indicator of water quality. Some natural metallic ions, plankton, industrial wastes, and weeds are sources that affect the color of water. Water bodies can be naturally tannic, or tea colored, from the presence of tannins.

  • Fecal Coliform - Fecal Coliform bacteria are found in the fecal waste of warm blooded animals. While some of these bacteria are not harmful, they are indicators that pathogens may be present. Analysis results are used to assess the sanitary quality of the water. High levels of fecal coliform bacteria can result in low dissolved oxygen levels.

  • Fluoride - Fluoride may occur naturally in waters or added in controlled amounts. It is commonly found in drinking water as a method of reducing dental carries. Too much fluoride can be harmful to human health. Fluoride in surface water is mainly derived from natural minerals in rocks and soil.

  • Magnesium - Magnesium ions may contribute to water hardness. Varying concentrations of magnesium and calcium in a water body can play a role in the distribution of aquatic life.

  • Nitrate + Nitrite (NO3 + NO2) as N - Nitrate and nitrite are naturally occurring nutrients that contain a nitrogen atom joined to oxygen atoms, with nitrate containing three oxygen atoms and nitrite containing two. Nitrates in water bodies typically originate from fertilizers, septic tanks and animal waste from runoff or seepage into groundwater. Nitrates encourage plant growth. An abundance of nitrates in water leads to excess plant growth and eventually eutrophication of the water if the sources are not addressed.

  • Organic Carbon - Total Organic is one of several measurements of the organic content in water. The presence of organic contaminants in waters may degrade ion exchange capacity or serve as a nutrient source for undesired plant growth.  An abundance of nutrients in water leads to excess plant growth and eventually eutrophication of the water if the sources are not addressed.

  • Orthophosphate (PO4) - As a nutrient, orthophosphate can contribute to eutrophication of water.  An abundance of nutrients in water leads to excess plant growth and eventually to eutrophication. Sources of phosphate include organic and inorganic fertilizers, animal waste, human waste effluent and industrial waste.

  • Potassium (K) - Potassium is important for both plant and human nutrition. Sources include groundwater (mineral dissolution), decomposing plants, and agricultural runoff.

  • Sulfate (SO4) - Sulfate occurs naturally in water with a large range in concentrations. Unnatural sources of sulfate include agricultural, disposal, and industrial waste.

  • Total Dissolved Solids (TDS) - Solids are suspended or dissolved matter in water. TDS measures the combined amount of inorganic and organic substance dissolved in water. It is not a measure of water quality but an indicator of the presence of chemical contaminants.

  • Total Kjeldahl Nitrogen (TKN) − TKN measures the sum of ammonia and organic nitrogen in water. An abundance of nutrients in water leads to excess plant growth and eventually to eutrophication.

  • Total Nitrogen - The sum amount of nitrate, nitrite, ammonia, and organic nitrogen of water. An abundance of nutrients in water leads to excess plant growth and eventually eutrophication of the water if the sources are not addressed.

  • Total Phosphorus - Elemental phosphorus is toxic. In nature, it exists as phosphates.  Phosphates exist in three forms: orthophosphate, metaphosphate, and organically bound phosphate. Total phosphorus is the sum of these concentrations. An abundance of phosphate in a system can result in excess plant growth and eventually to eutrophication if it is the growth-limiting nutrient of that system.

  • Total Suspended Solids - This refers to the amount of solid material suspended in the water. It differs from turbidity in that it provides the actual weight of suspended matter. 

  • Turbidity - Turbidity is a measure of the colloidal suspension of tiny particles and precipitates in spring water. High turbidity water blocks light from penetrating the water which can be harmful to aquatic life.



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Contact List- Watershed Management and Monitoring


Central District Office

Watershed Management and Monitoring Section

3319 Maguire Blvd, Suite 232

Orlando, Florida 32803-3767

phone: 407-897-4100

fax: 850 412-0472


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Last updated: May 31, 2011

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