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Chemical Variables: Total Alkalinity Total Alkalinity: the total amount of titratable bases in water expressed as mg/L of equivalent CaCO 3. Alkalinity.

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Presentation on theme: "Chemical Variables: Total Alkalinity Total Alkalinity: the total amount of titratable bases in water expressed as mg/L of equivalent CaCO 3. Alkalinity."— Presentation transcript:


2 Chemical Variables: Total Alkalinity 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 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.

3 Total Alkalinity Total alkalinity = 200 mg/L. Good buffering capacity of a water source. Freshwater 5 mg/L (soft water) to 500 mg/L (hard water). Seawater ~ 115-120 mg/L. Seldom see pH problems in natural seawater. Alkalinity < 30 mg/L? Problem?

4 Total Alkalinity Total Alkalinity (TA) level can be associated with several potential problems in aquaculture: If TA< 50 mg/L: copper compounds are more toxic. avoid their use as algicides (copper sulfate) Natural waters with less than 40 mg/L alkalinity as CaCO3 have limited biofiltration capacity. pH independent (What does this mean?) Low alkalinity = low CO 2 --> low natural productivity Low alkalinity equals low pH.

5 Total Hardness 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. Total Hardness approximates total alkalinity. Calcium is used for bone and exoskeleton formation and absorbed across gills. Soft water = molt problems. bone deformities.... or minimally...clogged pipes!

6 CONVERSION OF WATER HARDNESS UNITS Water Hardness Unit Definition Internatio nal recomme nded mmol/liter Physical measures mval/liter America & states PPM English o e French o f German o dH 100mg CaCO 3 per 1000 ml water 28 mg CaO or 50 mg CaCO 3 per 1000 ml water 1 part CaCO 3 per million = 1 mg CaCO 3 per 1000 ml water 1 grainCaCO 3 per gallon= 14.3 mg CaCO 3 per 1000 ml water 10 mg/ CaCO 3 per 1000 ml water 10 mg/CaO per 1000 ml water 1 mmol/litre 1 mval/litre 1 PPM 1 O e 1 O f 1 O dH 1 0.5 0.01 0.1429 0.10 0.1786 2 1 0.02 0.285 0.20 0.357 100 50 1 14.29 10.00 17.86 7.0 3.5 0.070 1 0.700 1.250 10.00 5.00 0.10 1.429 1 1.786 5.6 2.8 0.056 0.7999 0.5599 1

7 DEGREE OF HARDNESS EXPRESION SOFT:< 1.6 mmol/l = 160 PPM = 9 o dH SLIGHTLY HARD: 1.6-3.2 mmol/l = 160-320 PPM = 9-18 o dH HARD: 3.2-4.6 mmol/l = 320-460 PPM = 18-26 o dH VERY HARD: ABOVE 4.6 mmol/l = ABOVE 460 PPM = ABOVE 26 o dH

8 Chemical Variables: pH pH: the level or intensity of a substances acidic or basic character. pH: the negative logarithm of the hydrogen ion concentration (activity) of a substance. pH = -log(1/[H + ]). 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 -


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

11 Chemical Variables: pH Other sources of change: Decay of organic matter. Oxidation of compounds in bottom sediments. 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).

12 Chemical Variables: Carbon Dioxide Normal component of all natural waters. Sources: atmospheric diffusion. respiration of cultured species. biological oxidation of organic compounds. Usually transported in the blood as HCO 3 - 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.

13 Chemical Variables: Carbon Dioxide 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. This phenomenon is known as the Bohr-Root effect. CO 2 also interferes with oxygen uptake by eggs and larvae.

14 CO 2 Level Affects Hemoglobin Saturation

15 Chemical Variables: carbon dioxide 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. 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. What large-scale implications does this have?


17 The Effect of pH on Carbonate Buffering


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

20 Chemical Variable: Carbon Dioxide 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. Good working level of around 15-20 mg/L. Diel fluctuation opposite to that of D.O. Higher levels in warmer months of year.

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