to shallow breathing In pondsfluctuations are more extremeanalog - PDF document

to Òshallow breathing.Ó In pondsfluctuations are more extreme,analogous to Òdeep breathing.ÓCarbon dioxide problems aretherefore more likely as the thick-ness of the bloom increases.Carbon dioxide problemsmost likely in summerdioxide concentrations are maxi-mum during summer. However,carbon dioxide is rarely a prob-oxygen concentrations are usuallynear the surface as if they wereafter a period of extremely calmand cloudy weather, but quicklyweather returns.be a problem in fish ponds. Warmwater temperatures increase themetabolism of all pond organismsand therefore respiration rates arefeeding rates are high. Theed by large quantities of organicsummer requires large quantitiesof dissolved oxygen and produceslarge quantities of carbon dioxide.During the summer, carbon diox-ide concentrations are lower thanduring winter, but dissolved oxy-gen concentrations are often criti-cally low. Fortunately, summer isare aerated frequently. In additionoxygen, vigorous aeration willdrive off some proportion of thecarbon dioxide produced in thecarbon dioxideCarbon dioxide can be measureddirectly with standard test kits.Alternatively, meas

urement of pHwater. As carbon dioxide isdecline. (Conversely, when carbondioxide is removed during theday, pH will increase.) There areimportant interrelationshipstotal alkalinity. Knowing pH andmeasurements is plagued by diffi-measurement. Litmus paper, dropprobes with meters have beenselection of measurement devicesfor pH is largely a situation infor.Ó For example, pH pens arebrated correctly, and do not com-ture. Some scientific supply hous-es now sell narrow-range litmustechnique is easyAsimple graphical technique fortration is presented in Figure 2.using a standard test kit. Next,determine the pH from a waterline up from the pH value to thecurved line representing the totalhand axis, indicating the free car-across from 20 mg/Lrepresents aproblem. Therefore, using thedifferent total alkalinity (Table 1).In general, water can hold morecarbon dioxide as temperaturedeclines, although differences intemperature are less importantthan differences in total alkalinityperature correction is not neces- Figure 1. The daily cycle of oxygen and carbon dioxide in a fish pond. ide. Figure 4 on page 6 is a blankthat carbon dioxide is

more likelyto be a problem as alkalinityincreases. However, alkalinityprovides Òbuffering capacityÓ todioxide and pH is thereforealkalinity (20 to 50 mg/Lasoptimum fish growth and produc-problems can be evaluated by aand measure the pH. Put an air-stone in the bucket and run airthrough the water for about 30minutes. If the pH increases bymore than one pH unit, then car-bon dioxide may be a problem.Carbon dioxide is an unusual problem in is rarely a cause for concern infish ponds with sufficient alkalini-ty. There are a few specific circum-bon dioxide may be a problem,copper sulfate. Large quantities oforganic material derived fromdead plankton are quickly decom-posed, reducing oxygen andincreasing carbon dioxide. Again,emergency aeration practicesserve the dual role of supplyingoxygen and reducing carbon diox-Under certain circumstances, car-bon dioxide can be a problem inlayers of relatively lighter, Table 1.Critical pH values at a given level of alkalinity.Total alkalinity (mg/L as CaCO3)Carbon dioxide may be a problem at a pH value less than:506.7756.91007.01257.11507.2 Figure 2. Agraphical technique for estimation of c

arbon dioxide concentration. warmer, oxygen-rich water over-laying layers of relatively moredense, cooler, stagnant (and car-bon dioxide rich!) water. In pondswarm and relatively calm weath-er, strong sustained winds or vig-orous aeration can cause ponds toÒroll overÓ and mix deep waterwith surface water, therebyincreasing carbon dioxide concen-tration throughout the water col-umn. During the summer, whena problem, ponds are typicallyaerated through the night.and destratify daily, water cur-rents established by aeration andumn well-mixed and, as a result,carbon dioxide problems rarelyoccur.when fish are held at high density,or crowded in front of aeratorsrise dramatically, the problem canoff some carbon dioxide.Table 2.Liming agents able to remove carbon dioxide from pond waters.Liming AgentChemicalFactorComments formulaQuicklimeCaO3.45-caustic (protect skin and eyes)-potential for high pH-relatively low solubilityHydrated limeCa(OH)4.57-caustic (protect skin and eyes)-potential for high pH-relatively low solubility -relatively inexpensiveSodium carbonateNa6.48-safe-low potential for high pH-relatively high solubility -qu

ick reaction with carbon dioxide a temporary solutionCarbon dioxide can be removedby chemical treatment of pondum carbonate (Table 2). These lim-ing agents chemically react direct-ly with carbon dioxide, resultingin reduced carbon dioxide andincreased alkalinity and pH.cally remove carbon dioxide fromIn order to calculate the amountAlternatively, consult Figure 3 forquicklime treatment requirementsfactor from table xcarbon dioxide concentration xpond area (acres)xaverage depth (ft)=pounds of liming agent to hydrated lime required to treat a10-acre pond with an averageide concentration of 20 mg/Lisor approximately 1.4 tons. Treat-um carbonate would require 5,184pounds or 2.6 tons. Clearly, largequantities of liming materials arerequired to chemically treat a car-bon dioxide problem.At best, treatment with limingagents represents a temporaryconsumed by reaction with lim-treatment of ponds with limingagents does not address the rootcause of a presumed carbon diox-ide problem. In ponds receivinglbs/acre per day) or in whichlowing an algae crash, treatmentaffect the rate of carbon dioxideproduction and thus represents atemporary

, Òband-aidÓ solution.Perhaps a more serious conse-quence of chemical treatment ofcarbon dioxide problems is relat-poorly buffered (low alkalinity)waters following treatment withHigh pH causes a shift towards agreater proportion of the morequently, a well intended applica-ÒtreatÓ what is thought to be acarbon dioxide problem can resultin a very stressful environmentApplication of chemicals to treata carbon dioxide ÒproblemÓ isbenefit. Aeration and mixing arethe most effective availabledissolved oxygen. Vigorous aera-tion accelerates the diffusion of mixing will prevent or minimizeAclear determination of a carbondioxide problem is required priorto any treatment. If a carbon diox-ide problem is suspected, otherbefore attempting any treatment.increases as dissolved oxygenproblem can be traced to some- Figure 3. Agraphical technique for estimation of quicklime required to neutralize carbon dioxide.The work reported in this publication was supported in part by the Southern Regional Aquaculture Center through Grant No.94-38500-0045 fromthe United States Department of Agriculture. Figure 4. Blank graph for use by pond manager