ecology

Chemical Variables of natural Waters: Dissolved Oxygen, pH, Alkalinity

Niño A. Crisolo Discussant

Chemical Properties: Chemical Properties: dissolved oxygendissolved oxygen

along with temperature, dissolved oxygen along with temperature, dissolved oxygen (DO), is important in metabolic regulation(DO), is important in metabolic regulation

dissolved oxygen concentration and temp dissolved oxygen concentration and temp both determine the environmental niche both determine the environmental niche aquaculture organisms occupyaquaculture organisms occupy

occupation of niches is controlled by a occupation of niches is controlled by a complex set of behavioral and complex set of behavioral and physiological (acclimatorial) activities physiological (acclimatorial) activities

acclimation is slow wrt D.O. (hours, weeks) acclimation is slow wrt D.O. (hours, weeks)

Chemical Variables: Chemical Variables: dissolved oxygendissolved oxygen

although oxygen is rather abundant in the atm although oxygen is rather abundant in the atm (21%), it is only slightly soluble in water (6 (21%), it is only slightly soluble in water (6 mg/L is not much)mg/L is not much)

implications to fish/invertebrates?implications to fish/invertebrates? Even metabolic rates of aqua-communities can Even metabolic rates of aqua-communities can

effect rapid changes in [D.O.]effect rapid changes in [D.O.] this effect increases with temp (interaction) this effect increases with temp (interaction) solubilitysolubility decreasesdecreases with with increasedincreased temp/saltemp/sal other factors: BP (direct), altitude (indirect), other factors: BP (direct), altitude (indirect),

impurities (indirect)impurities (indirect)

Oxygen Solubility CurveOxygen Solubility Curve

Chemical Variables: Chemical Variables: dissolved dissolved oxygenoxygen

factors affecting D.O. consumption:factors affecting D.O. consumption:water temperature (2-3x for every 10water temperature (2-3x for every 10ooC)C)environmental (medium) D.O. environmental (medium) D.O.

concentration (determines lower limit)concentration (determines lower limit)fish size (Rc greater for small vs. large)fish size (Rc greater for small vs. large)level of activity (resting vs. forced)level of activity (resting vs. forced)post-feeding period, etc. (2x, 1-6 hrs post-feeding period, etc. (2x, 1-6 hrs

post feeding)post feeding)

Oxygen Consumption vs. Oxygen Consumption vs. SizeSize

for Channel Catfish (26for Channel Catfish (26ooC)C)

O2 cons. Rate Increase in

(mg/kg/hr) oxygen consumption

Fish size (g) Nonfed Fed from feeding (%)

2.5 880 1,230 40

100 400 620 55

500 320 440 38

1,000 250 400 60

From Lovell (1989)


What might be considered What might be considered minimal levels of minimal levels of maintenance of D.O.?maintenance of D.O.?

hard to determine due to hard to determine due to compounding effects (can’t compounding effects (can’t standardize conditions)standardize conditions)

major factor: exposure timemajor factor: exposure time for most species:for most species:

long-term: 1.5 mg/Llong-term: 1.5 mg/L medium term: 1.0 mg/Lmedium term: 1.0 mg/L short-term: 0.3 mg/L short-term: 0.3 mg/L


In general warm-water species are more In general warm-water species are more tolerant of low D.O. concentrationstolerant of low D.O. concentrations

Ictalurus punctatusIctalurus punctatus: adults/1.0 mg/L, : adults/1.0 mg/L, fingerlings 0.5 mg/Lfingerlings 0.5 mg/L

Procamberus clarkiiProcamberus clarkii: : adults/2.0 mg/L, adults/2.0 mg/L, juveniles/1.0 mg/L juveniles/1.0 mg/L

Litopenaeus vannameiLitopenaeus vannamei: adults/0.5-0.8 mg/L: adults/0.5-0.8 mg/L Litopenaeus stylirostrisLitopenaeus stylirostris: adults/1.2-1.4 mg/L: adults/1.2-1.4 mg/L


Many practical aquaculturists will Many practical aquaculturists will recommend that D.O. concentrations do not recommend that D.O. concentrations do not drop below 6.0 mg/Ldrop below 6.0 mg/L

this is an impractical guideline in that this this is an impractical guideline in that this level can seldom be achieved at nightlevel can seldom be achieved at night

a more practical guideline might be to a more practical guideline might be to maintain D.O. levels around 90% saturationmaintain D.O. levels around 90% saturation

no lower than 25% saturation for extended no lower than 25% saturation for extended periodsperiods

Chemical Variables: Chemical Variables: dissolved oxygen/behaviordissolved oxygen/behavior

if D.O. levels in the medium are adequate, if D.O. levels in the medium are adequate, fish meet increased demands due to fish meet increased demands due to locomotion or post-feeding by increased locomotion or post-feeding by increased rate of ventilation or large “gulps” of waterrate of ventilation or large “gulps” of water

declining D.O.: seek zones of higher D.O., declining D.O.: seek zones of higher D.O., reduce activity (reduced MR), stop reduce activity (reduced MR), stop consumption of feedconsumption of feed

compensatory pointcompensatory point: when D.O. demand : when D.O. demand cannot be met by behavioral or cannot be met by behavioral or physiological responsesphysiological responses

Chemical Variables: Chemical Variables: dissolved oxygen/behaviordissolved oxygen/behavior

upon reaching compensatory point: gaping upon reaching compensatory point: gaping at surface, removal of oxygen from surfaceat surface, removal of oxygen from surface

shown in both fish and invertebratesshown in both fish and invertebrates small aquatic animals are more efficientsmall aquatic animals are more efficient some oxygen provided by glycolysis or some oxygen provided by glycolysis or

anaerobic metabolism, but blood pH dropsanaerobic metabolism, but blood pH drops pH drop in blood reduces carrying capacity of pH drop in blood reduces carrying capacity of

hemoglobin (hemocyanin?)--> deathhemoglobin (hemocyanin?)--> death

Oxygen/Temperature Oxygen/Temperature InteractionInteraction

Oxygen consumption Oxygen consumption increases with temperature increases with temperature until a maximum is until a maximum is achievedachieved

peak consumption rate is peak consumption rate is maintained over a small maintained over a small temp rangetemp range

consumption rate decreases consumption rate decreases rapidly as temp increasesrapidly as temp increases

lethal temperature finally lethal temperature finally achievedachieved

Chemical Variables: Chemical Variables: dissolved oxygen/sourcesdissolved oxygen/sources major producer of D.O. in ponds is major producer of D.O. in ponds is

primary productivity (up to 80%), primary productivity (up to 80%), diffusion is low (<3%)diffusion is low (<3%)

incoming water can often be deficient incoming water can often be deficient depending upon source water conditionsdepending upon source water conditions

major consumers: primary productivity, major consumers: primary productivity, aquatic species (density dependent), CODaquatic species (density dependent), COD

diel fluctuation diel fluctuation indirect relationships (algae, secchi) indirect relationships (algae, secchi)

Oxygen BudgetOxygen Budget

I nput O2 (kg/ha) % of total Photosynthesis 4,130 76.9 I nflowing water 94 1.7 Aeration 99 1.8 Diff usion 1,050 19.6 Total 5,373 100.0 Output Overflow, drainage 32 0.6 Phyto respiration 3,090 57.5 Benthic respiration 1,040 19.4 Fish/ shrimp resp. 1,210 22.5

Total 5,372 100.0

Dissolved Oxygen Dissolved Oxygen FluctuationFluctuation

Typical pattern = Typical pattern = oxygen max during oxygen max during late afternoonlate afternoon

difference in difference in surface vs. benthic surface vs. benthic for stratified pondsfor stratified ponds

dry season = faster dry season = faster heating at surface heating at surface and less variation and less variation

Influence of Sunlight on Influence of Sunlight on Photosynthesis/OPhotosynthesis/O22

ProductionProduction

Photorespiration: Photorespiration: predictablepredictable

Chemical Variables: Chemical Variables: total total alkalinityalkalinity

total alkalinitytotal alkalinity: the total amount of : the total amount of titratable bases in water expressed as mg/L titratable bases in water expressed as mg/L of equivalent CaCOof equivalent CaCO33

“ “alkalinity” is primarily composed of the alkalinity” is primarily composed of the following ions: COfollowing ions: CO33

--, HCO, HCO33--, hydroxides, , hydroxides,

ammonium, borates, silicates, phosphatesammonium, borates, silicates, phosphates alkalinity in ponds is determined by both the alkalinity in ponds is determined by both the

quality of the water and bottom mudsquality of the water and bottom muds calcium is often added to water to increase calcium is often added to water to increase

its alkalinity, buffer against pH changesits alkalinity, buffer against pH changes


thus, a total alkalinity determination of 200 thus, a total alkalinity determination of 200 mg/L would indicate good buffering capacity mg/L would indicate good buffering capacity of a water sourceof a water source

natural freshwater alkalinity varies between natural freshwater alkalinity varies between 5 mg/L (soft water) to over 500 mg/L (hard 5 mg/L (soft water) to over 500 mg/L (hard water)water)

natural seawater is around 115-120 mg/Lnatural seawater is around 115-120 mg/L seldom see pH problems in natural seawaterseldom see pH problems in natural seawater water having alkalinity reading of less than water having alkalinity reading of less than

30 mg/L are problematic30 mg/L are problematic


total alkalinity level can be associated with total alkalinity level can be associated with several potential problems in aquaculture:several potential problems in aquaculture:

< 50 mg/L: copper compounds are more < 50 mg/L: copper compounds are more toxic, avoid their use as algicidestoxic, avoid their use as algicides

natural waters with less than 40 mg/L natural waters with less than 40 mg/L alkalinity as CaCO3 have limited alkalinity as CaCO3 have limited biofiltration capacity, pH independentbiofiltration capacity, pH independent

low alkalinity = low COlow alkalinity = low CO22 --> low nat prod --> low nat prod low alkalinity = high pHlow alkalinity = high pH

Chemical Variables: Chemical Variables: total total hardnesshardness

total hardnesstotal hardness: total concentration of : total concentration of metal ions expressed in terms of mg/L of metal ions expressed in terms of mg/L of equivalent CaCOequiva- lent CaCO33

primary ions are Caprimary ions are Ca2+2+ and Mg and Mg2+2+, also iron and , also iron and manganesemanganese

total hardness approximates total alkalinitytotal hardness approximates total alkalinity calcium is used for bone and exoskeleton calcium is used for bone and exoskeleton

formation and absorbed across gillsformation and absorbed across gills soft water = molt problems, bone soft water = molt problems, bone

deformitiesdeformities

Chemical Variables: Chemical Variables: pHpH

pH: the level or intensity of a substance’s pH: the level or intensity of a substance’s acidic or basic characteracidic or basic character

pHpH: the negative logarithm of the : the negative logarithm of the hydrogen ion concentration (activity) of a hydrogen ion concentration (activity) of a substancesubstance

pH = -log(1/[HpH = -log(1/[H++])]) ionization of water is low (1x10ionization of water is low (1x10-7-7 moles of moles of

HH++/L and 1x10/L and 1x10-7-7 moles OH moles OH--/L)/L) neutral pH = similar levels of Hneutral pH = similar levels of H++ and OH and OH--

Chemical Variables: Chemical Variables: pHpH at acidic pH levels, the quantity of H+ at acidic pH levels, the quantity of H+

predominatespredominates acidic pH = pH < 7, basic = pH >7acidic pH = pH < 7, basic = pH >7 most natural waters: pH of 5-10, usually most natural waters: pH of 5-10, usually

6.5-9; however, there are exceptions6.5-9; however, there are exceptions acid rain, pollutionacid rain, pollution can change due to atm COcan change due to atm CO2,2, fish respiration fish respiration pH of ocean water is stable (carbonate pH of ocean water is stable (carbonate

buffering system, later)buffering system, later)

Chemical Variables: Chemical Variables: pHpH

Other sources of change:Other sources of change:decay of organic matterdecay of organic matteroxidation of compounds in bottom oxidation of compounds in bottom

sedimentssedimentsdepletion of COdepletion of CO22 by phytoplankton on diel by phytoplankton on diel

basisbasisoxidation of sulfide containing minerals in oxidation of sulfide containing minerals in

bottom soils (e.g., oxidation of iron pyrite bottom soils (e.g., oxidation of iron pyrite by sulfide oxidizing bacteria under by sulfide oxidizing bacteria under anaerobic conditions)anaerobic conditions)

Chemical Variables: Chemical Variables: carbon dioxidecarbon dioxide

normal component of all natural watersnormal component of all natural waters sourcessources: atmospheric diffusion, respiration : atmospheric diffusion, respiration

of cultured species, biological oxidation of of cultured species, biological oxidation of organic compoundsorganic compounds

usually transported in the blood as HCOusually transported in the blood as HCO33--

converted to COconverted to CO22 at the gill interface, at the gill interface, diffusion into mediumdiffusion into medium

as the level of COas the level of CO22 in the medium increases, in the medium increases, the gradient allowing diffusion is lessthe gradient allowing diffusion is less


this causes blood COthis causes blood CO22 levels to increase, levels to increase, lowering blood pHlowering blood pH

with lower blood pH, carrying capacity of with lower blood pH, carrying capacity of hemoglobin decreases, also binding hemoglobin decreases, also binding affinity for oxygen to hemoglobinaffinity for oxygen to hemoglobin

this phenomenon is known as the this phenomenon is known as the Bohr-Bohr-Root effectRoot effect

COCO22 also interferes with oxygen uptake also interferes with oxygen uptake by eggs and larvae by eggs and larvae

COCO22 Level Affects Level Affects Hemoglobin SaturationHemoglobin Saturation


in the marine environment, excesses of COin the marine environment, excesses of CO2 2 are are mitigated by the mitigated by the carbonate buffering systemcarbonate buffering system

COCO22 reacts with water to produce H reacts with water to produce H22COCO33, carbonic , carbonic acidacid

HH22COCO3 3 reacts with CaCOreacts with CaCO3 3 to form HCOto form HCO33--

(bicarbonate) and CO(bicarbonate) and CO332-2- (carbonate) (carbonate)

as COas CO22 is used for photosynthesis, the reaction is used for photosynthesis, the reaction shifts to the left, converting bicarbonates back to shifts to the left, converting bicarbonates back to COCO22

what large-scale implications does this have?what large-scale implications does this have?

The Effect of pH on The Effect of pH on Carbonate BufferingCarbonate Buffering


Concentrations of COConcentrations of CO22 are small, even though are small, even though it is highly soluble in it is highly soluble in waterwater

inverse relationship inverse relationship between [CObetween [CO22] and ] and temperature/salinitytemperature/salinity

thus, COthus, CO22 solubility solubility depends upon many depends upon many factorsfactors

Chemical Variable: Chemical Variable: carbon carbon dioxidedioxide

COCO22 is not particularly toxic to fish or is not particularly toxic to fish or invertebrates, given sufficient D.O. is invertebrates, given sufficient D.O. is availableavailable

maximum tolerance level appears to be maximum tolerance level appears to be around 50 mg/L for most speciesaround 50 mg/L for most species

good working level of around 15-20 mg/Lgood working level of around 15-20 mg/L diel fluctuation opposite to that of D.O.diel fluctuation opposite to that of D.O. higher levels in warmer months of yearhigher levels in warmer months of year

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