Water Quality Notes: Dissolved Oxygen1 - Polk.WaterAtlas.org

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Water Quality Notes: Dissolved Oxygen 6causing a change in the current flow in theanode-electrolyte-cathode-meter circuit when themeter is turned on. The probe current (reading)changes proportionally to the amount of O 2diffusingthrough the membrane and reacting at the cathode.The oxygen concentration inside the membrane canbe assumed to be zero since it is readily consumed atthe cathode.Advantages1. Field portable.2. Easy to calibrate and use.3. Can instantaneously and continuously monitorDO concentrations.4. Do not need sampling equipment, bottles, orstorage facilities.Disadvantages1. Difficulties associated with instrumentcalibration and maintenance.2. Relatively expensive. Typical DO meters rangein cost from $600 to $1,500.3. Hydrogen sulfide gases tend to reduce thesensitivity of membrane electrodes. Frequent use inenvironments where these gases are common willrequire more frequent cleaning of electrodes andreplacement of membranes.State Surface Water Quality CriteriaIt is important to recognize that the mostdesirable DO concentrations for one water body maynot be the same as for others. The desiredconcentration range ultimately depends on thedesired use for the water body. The lowest desiredconcentration should support desirable species at thelowest point of the diurnal DO profile (just beforedawn).The Florida Department of EnvironmentalProtection (FDEP) is charged with protecting waterquality within State-owned surface water bodies fortheir respective designated uses. To accomplish thisFigure 3. Typical membrane electrode used for measuringdissolved oxygen. A gas-permeable membrane covers thegold cathode and anode. The electrode is attached to anelectronic meter that gives direct readings in mg/L orpercent saturation.goal, FDEP defined criteria for DO concentrations inState surface water bodies. Table 5 lists thedesignated uses for each surface water classificationgroup. Water quality restrictions are greater fornumerically lower classes of water (i.e. I > II > III >IV >V). Water flowing from a numerically higherclass of water (for example class IV) into a morerestrictive class (i.e. numerically lower class) may berequired to meet standards for the lower class. Alisting of the FDEP guidelines for surface water DOconcentrations is also shown in Table 5.Dissolved Oxygen ManagementOpportunities1. When designing and constructing ponds,maximize the surface area exposed to theatmosphere and limit the depth to facilitateatmospheric transfer and to encourage naturalmixing by wind and wave action.2. While not as environmentally sustainable asnatural atmospheric transfer, blowers andfountains can be used to increase DO levels.3. Minimize input of additional Biological OxygenDemand into aquatic systems. Always follow theinstructions on the herbicide label whencontrolling weeds within an aquatic system. Ifallowed, consider treating large water bodies insections over time to prevent the entire waterbody from becoming anaerobic when the plantmaterial begins to degrade by microbial action.
Water Quality Notes: Dissolved Oxygen 74. Minimize nutrient inputs into the aquaticsystems from surrounding land and drainagesystems to reduce risks of stimulating algalblooms. Limitation of all nutrients may not benecessary since algal blooms are often limited bya single nutrient (typically nitrogen orphosphorus). Determine the limiting nutrient andtarget best management practices that minimizeexport of that nutrient into the aquatic system.References for More InformationAmerican Public Health Association (APHA),American Water Works Association (AWWA), andthe Water Environment Federation (WEF). StandardMethods for Examination of Water and Wastewater.United Book Press, Inc. Baltimore, MD.Avault, Jr. 1996. Fundamentals of Aquaculture.AVA Publishing Co. Inc, Baton Rouge, LA.Bachmann, M., M. Hoyer, and D. Canfield, Jr.1999. Living at the Lake. University of Florida/IFASand The Florida Cooperative Extension Service, P.O.Box 110810, Gainesville, FL 32610-0810.Florida Statute 62-302.530. Criteria for SurfaceWater Classifications.Kotz, J.C. and K.F. Purcell. 1987. Chemistry &Chemical Reactivity. Saunders College Publishing,New York.Merrit, R.W. and K.W. Cummins (eds). 1996.An Introduction to the Aquatic Insects of NorthAmerica, Third Edition. Kendall/Hunt PublishingCo., IW.Timmons, M.B., J.M. Ebeling, F.W. Wheaton,S.T. Summerfelt, and B.J. Vinci. 2002. RecirculatingAquaculture Systems, 2 nd ed. Cayuga Aqua Ventures,Ithaca, N.Y.GlossaryPhotosynthesis - The assimilation of carbondioxide by green plants and by pigmented,photosynthetically active prokaryotes, and itsconversion into carbohydrate, using energy from thesun. This conversion can be described by thefollowing equation:6CO + 12 H O +energy →C H O + 6O + 6H2O2 26 12 6 2Respiration – Metabolic process in whichstored energy is released with the oxidation ofreduced organic carbon compounds. The ultimateby-products of respiration are often carbon dioxide(CO 2) and water (H 2O).Vertebrate - Organism possessing a distinctcartilaginous or bony axial endoskeleton, consistingof a skull and vertebral column.Invertebrate - Animals not possessing a distinctcartilaginous or bony axial endoskeleton.Titration – Procedure used to quantitativelyanalyze the amount of a substance by means of anessentially complete reaction in a solution with areagent of known concentration (Kotz and Purcell,1987).Anode – Within the context ofoxidation-reduction reactions, electrons are producedat the anode (- terminal) where oxidation occurs.Cathode - Within the context ofoxidation-reduction reactions, electrons produced atthe anode move toward the cathode (+ terminal)where reduction occurs.Electrolyte – A substance that dissolves inwater to form an electrically conducting solution(Kotz and Purcell, 1987).Precipitate – An insoluble salt (Kotz andPurcell, 1987).Cutaneous – of, pertaining to, or affecting theskin.Gills – Respiratory organs present in manyaquatic animals. Gills are the structures used totransfer dissolved oxygen from the water into theorganism for aerobic metabolism.Hemoglobin – Component of blood responsiblefor transport of O 2from respiratory gas exchangeorgans to respiring cells and transport of CO 2fromrespiring cells to gas exchange organs.
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