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Water Qualtiy: Dissolved Oxygen, pH, Alkalinty Water Qualtiy: Dissolved Oxygen, pH, Alkalinty From Lawson, Boyd.

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Presentation on theme: "Water Qualtiy: Dissolved Oxygen, pH, Alkalinty Water Qualtiy: Dissolved Oxygen, pH, Alkalinty From Lawson, Boyd."— Presentation transcript:

1 Water Qualtiy: Dissolved Oxygen, pH, Alkalinty Water Qualtiy: Dissolved Oxygen, pH, Alkalinty From Lawson, Boyd

2 Chemical Properties: dissolved oxygen along with temperature, dissolved oxygen (DO), is important in metabolic regulation along with temperature, dissolved oxygen (DO), is important in metabolic regulation dissolved oxygen concentration and temp both determine the environmental niche aquaculture organisms occupy dissolved oxygen concentration and temp both determine the environmental niche aquaculture organisms occupy occupation of niches is controlled by a complex set of behavioral and physiological (acclimatorial) activities occupation of niches is controlled by a complex set of behavioral and physiological (acclimatorial) activities acclimation is slow wrt D.O. (hours, weeks) acclimation is slow wrt D.O. (hours, weeks)

3 Chemical Variables: dissolved oxygen although oxygen is rather abundant in the atm (21%), it is only slightly soluble in water (6 mg/L is not much) although oxygen is rather abundant in the atm (21%), it is only slightly soluble in water (6 mg/L is not much) implications to fish/invertebrates? implications to fish/invertebrates? Even metabolic rates of aqua-communities can effect rapid changes in [D.O.] Even metabolic rates of aqua-communities can effect rapid changes in [D.O.] this effect increases with temp (interaction) this effect increases with temp (interaction) solubility decreases with increased temp/sal solubility decreases with increased temp/sal other factors: BP (direct), altitude (indirect), impurities (indirect) other factors: BP (direct), altitude (indirect), impurities (indirect)

4 Oxygen Solubility Curve

5 Chemical Variables: dissolved oxygen factors affecting D.O. consumption: factors affecting D.O. consumption: water temperature (2-3x for every 10 o C) water temperature (2-3x for every 10 o C) environmental (medium) D.O. concentration (determines lower limit) environmental (medium) D.O. 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) post-feeding period, etc. (2x, 1-6 hrs post feeding)

6 Oxygen Consumption vs. Size for Channel Catfish (26 o C) O 2 cons. RateIncrease in (mg/kg/hr)oxygen consumption Fish size (g)NonfedFedfrom feeding (%) , , From Lovell (1989)

7 Chemical Variables: dissolved oxygen What might be considered minimal levels of maintenance of D.O.? What might be considered minimal levels of maintenance of D.O.? hard to determine due to compounding effects (can’t standardize conditions) hard to determine due to compounding effects (can’t standardize conditions) major factor: exposure time major factor: exposure time for most species: for most species: long-term: 1.5 mg/L long-term: 1.5 mg/L medium term: 1.0 mg/L medium term: 1.0 mg/L short-term: 0.3 mg/L short-term: 0.3 mg/L

8 Chemical Variables: dissolved oxygen In general warm-water species are more tolerant of low D.O. concentrations In general warm-water species are more tolerant of low D.O. concentrations Ictalurus punctatus: adults/1.0 mg/L, fingerlings 0.5 mg/L Ictalurus punctatus: adults/1.0 mg/L, fingerlings 0.5 mg/L Procamberus clarkii: adults/2.0 mg/L, juveniles/1.0 mg/L Procamberus clarkii: adults/2.0 mg/L, juveniles/1.0 mg/L Litopenaeus vannamei: adults/ mg/L Litopenaeus vannamei: adults/ mg/L Litopenaeus stylirostris: adults/ mg/L Litopenaeus stylirostris: adults/ mg/L

9 Chemical Variables: dissolved oxygen Many practical aquaculturists will recommend that D.O. concentrations do not drop below 6.0 mg/L Many practical aquaculturists will recommend that D.O. concentrations do not drop below 6.0 mg/L this is an impractical guideline in that this level can seldom be achieved at night this is an impractical guideline in that this level can seldom be achieved at night a more practical guideline might be to maintain D.O. levels around 90% saturation a more practical guideline might be to maintain D.O. levels around 90% saturation no lower than 25% saturation for extended periods no lower than 25% saturation for extended periods

10 Chemical Variables: dissolved oxygen/behavior if D.O. levels in the medium are adequate, fish meet increased demands due to locomotion or post-feeding by increased rate of ventilation or large “gulps” of water if D.O. levels in the medium are adequate, fish meet increased demands due to locomotion or post-feeding by increased rate of ventilation or large “gulps” of water declining D.O.: seek zones of higher D.O., reduce activity (reduced MR), stop consumption of feed declining D.O.: seek zones of higher D.O., reduce activity (reduced MR), stop consumption of feed compensatory point: when D.O. demand cannot be met by behavioral or physiological responses compensatory point: when D.O. demand cannot be met by behavioral or physiological responses

11 Chemical Variables: dissolved oxygen/behavior upon reaching compensatory point: gaping at surface, removal of oxygen from surface upon reaching compensatory point: gaping at surface, removal of oxygen from surface shown in both fish and invertebrates shown in both fish and invertebrates small aquatic animals are more efficient small aquatic animals are more efficient some oxygen provided by glycolysis or anaerobic metabolism, but blood pH drops some oxygen provided by glycolysis or anaerobic metabolism, but blood pH drops pH drop in blood reduces carrying capacity of hemoglobin (hemocyanin?)--> death pH drop in blood reduces carrying capacity of hemoglobin (hemocyanin?)--> death

12 Oxygen/Temperature Interaction Oxygen consumption increases with temperature until a maximum is achieved Oxygen consumption increases with temperature until a maximum is achieved peak consumption rate is maintained over a small temp range peak consumption rate is maintained over a small temp range consumption rate decreases rapidly as temp increases consumption rate decreases rapidly as temp increases lethal temperature finally achieved lethal temperature finally achieved

13 Chemical Variables: dissolved oxygen/sources major producer of D.O. in ponds is primary productivity (up to 80%), diffusion is low (<3%) major producer of D.O. in ponds is primary productivity (up to 80%), diffusion is low (<3%) incoming water can often be deficient depending upon source water conditions incoming water can often be deficient depending upon source water conditions major consumers: primary productivity, aquatic species (density dependent), COD major consumers: primary productivity, aquatic species (density dependent), COD diel fluctuation diel fluctuation indirect relationships (algae, secchi) indirect relationships (algae, secchi)

14 Oxygen Budget

15 Diel Oxygen Fluctuation Typical pattern = oxygen max during late afternoon Typical pattern = oxygen max during late afternoon difference in surface vs. benthic for stratified ponds difference in surface vs. benthic for stratified ponds dry season = faster heating at surface and less variation dry season = faster heating at surface and less variation

16 Influence of Sunlight on Photosynthesis/O 2 Production

17 Photorespiration: predictable

18 Chemical Variables: total alkalinity total alkalinity: the total amount of titratable bases in water expressed as mg/L of equivalent CaCO 3 total alkalinity: the total amount of titratable bases in water expressed as mg/L of equivalent CaCO 3 “alkalinity” is primarily composed of the following ions: CO 3 -, HCO 3 -, hydroxides, ammonium, borates, silicates, phosphates “alkalinity” is primarily composed of the following ions: CO 3 -, HCO 3 -, hydroxides, ammonium, borates, silicates, phosphates alkalinity in ponds is determined by both the quality of the water and bottom muds alkalinity in ponds is determined by both the quality of the water and bottom muds calcium is often added to water to increase its alkalinity, buffer against pH changes calcium is often added to water to increase its alkalinity, buffer against pH changes

19 Chemical Variables: total alkalinity thus, a total alkalinity determination of 200 mg/L would indicate good buffering capacity of a water source thus, a total alkalinity determination of 200 mg/L would indicate good buffering capacity of a water source natural freshwater alkalinity varies between 5 mg/L (soft water) to over 500 mg/L (hard water) natural freshwater alkalinity varies between 5 mg/L (soft water) to over 500 mg/L (hard water) natural seawater is around mg/L natural seawater is around mg/L seldom see pH problems in natural seawater seldom see pH problems in natural seawater water having alkalinity reading of less than 30 mg/L are problematic water having alkalinity reading of less than 30 mg/L are problematic

20 Chemical Variables: total alkalinity total alkalinity level can be associated with several potential problems in aquaculture: total alkalinity level can be associated with several potential problems in aquaculture: < 50 mg/L: copper compounds are more toxic, avoid their use as algicides < 50 mg/L: copper compounds are more toxic, avoid their use as algicides natural waters with less than 40 mg/L alkalinity as CaCO3 have limited biofiltration capacity, pH independent natural waters with less than 40 mg/L alkalinity as CaCO3 have limited biofiltration capacity, pH independent low alkalinity = low CO 2 --> low nat prod low alkalinity = low CO 2 --> low nat prod low alkalinity = high pH low alkalinity = high pH

21 Chemical Variables: total hardness total hardness: total concentration of metal ions expressed in terms of mg/L of equiva- lent CaCO 3 total hardness: total concentration of metal ions expressed in terms of mg/L of equiva- lent CaCO 3 primary ions are Ca 2+ and Mg 2+, also iron and manganese primary ions are Ca 2+ and Mg 2+, also iron and manganese total hardness approximates total alkalinity total hardness approximates total alkalinity calcium is used for bone and exoskeleton formation and absorbed across gills calcium is used for bone and exoskeleton formation and absorbed across gills soft water = molt problems, bone deformities soft water = molt problems, bone deformities

22 Chemical Variables: pH pH: the level or intensity of a substance’s acidic or basic character pH: the level or intensity of a substance’s acidic or basic character pH: the negative logarithm of the hydrogen ion concentration (activity) of a substance pH: the negative logarithm of the hydrogen ion concentration (activity) of a substance pH = -log(1/[H + ]) pH = -log(1/[H + ]) ionization of water is low (1x10 -7 moles of H + /L and 1x10 -7 moles OH - /L) ionization of water is low (1x10 -7 moles of H + /L and 1x10 -7 moles OH - /L) neutral pH = similar levels of H + and OH - neutral pH = similar levels of H + and OH -

23 Chemical Variables: pH at acidic pH levels, the quantity of H+ predominates at acidic pH levels, the quantity of H+ predominates acidic pH = pH 7 acidic pH = pH 7 most natural waters: pH of 5-10, usually 6.5-9; however, there are exceptions most natural waters: pH of 5-10, usually 6.5-9; however, there are exceptions acid rain, pollution acid rain, pollution can change due to atm CO 2, fish respiration can change due to atm CO 2, fish respiration pH of ocean water is stable (carbonate buffering system, later) pH of ocean water is stable (carbonate buffering system, later)

24 Chemical Variables: pH Other sources of change: Other sources of change: decay of organic matter decay of organic matter oxidation of compounds in bottom sediments oxidation of compounds in bottom sediments depletion of CO 2 by phytoplankton on diel basis depletion of CO 2 by phytoplankton on diel basis oxidation of sulfide containing minerals in bottom soils (e.g., oxidation of iron pyrite by sulfide oxidizing bacteria under anaerobic conditions) oxidation of sulfide containing minerals in bottom soils (e.g., oxidation of iron pyrite by sulfide oxidizing bacteria under anaerobic conditions)

25 Chemical Variables: carbon dioxide normal component of all natural waters normal component of all natural waters sources: atmospheric diffusion, respiration of cultured species, biological oxidation of organic compounds sources: atmospheric diffusion, respiration of cultured species, biological oxidation of organic compounds usually transported in the blood as HCO 3 - usually transported in the blood as HCO 3 - converted to CO 2 at the gill interface, diffusion into medium converted to CO 2 at the gill interface, diffusion into medium as the level of CO 2 in the medium increases, the gradient allowing diffusion is less as the level of CO 2 in the medium increases, the gradient allowing diffusion is less

26 Chemical Variables: carbon dioxide this causes blood CO 2 levels to increase, lowering blood pH this causes blood CO 2 levels to increase, lowering blood pH with lower blood pH, carrying capacity of hemoglobin decreases, also binding affinity for oxygen to hemoglobin with lower blood pH, carrying capacity of hemoglobin decreases, also binding affinity for oxygen to hemoglobin this phenomenon is known as the Bohr-Root effect this phenomenon is known as the Bohr-Root effect CO 2 also interferes with oxygen uptake by eggs and larvae CO 2 also interferes with oxygen uptake by eggs and larvae

27 CO 2 Level Affects Hemoglobin Saturation

28 Chemical Variables: carbon dioxide in the marine environment, excesses of CO 2 are mitigated by the carbonate buffering system in the marine environment, excesses of CO 2 are mitigated by the carbonate buffering system CO 2 reacts with water to produce H 2 CO 3, carbonic acid CO 2 reacts with water to produce H 2 CO 3, carbonic acid H 2 CO 3 reacts with CaCO 3 to form HCO 3 - (bicarbonate) and CO 3 2- (carbonate) H 2 CO 3 reacts with CaCO 3 to form HCO 3 - (bicarbonate) and CO 3 2- (carbonate) as CO 2 is used for photosynthesis, the reaction shifts to the left, converting bicarbonates back to CO 2 as CO 2 is used for photosynthesis, the reaction shifts to the left, converting bicarbonates back to CO 2 what large-scale implications does this have? what large-scale implications does this have?

29 The Effect of pH on Carbonate Buffering

30 Chemical Variables: carbon dioxide Concentrations of CO 2 are small, even though it is highly soluble in water Concentrations of CO 2 are small, even though it is highly soluble in water inverse relationship between [CO 2 ] and temperature/salinity inverse relationship between [CO 2 ] and temperature/salinity thus, CO 2 solubility depends upon many factors thus, CO 2 solubility depends upon many factors

31 Chemical Variable: carbon dioxide CO 2 is not particularly toxic to fish or invertebrates, given sufficient D.O. is available CO 2 is not particularly toxic to fish or invertebrates, given sufficient D.O. is available maximum tolerance level appears to be around 50 mg/L for most species maximum tolerance level appears to be around 50 mg/L for most species good working level of around mg/L good working level of around mg/L diel fluctuation opposite to that of D.O. diel fluctuation opposite to that of D.O. higher levels in warmer months of year higher levels in warmer months of year


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