Chemistry - Why Water Chemistry? Why is this lake so green?...

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Why Water Chemistry? Why is this lake so green?
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of the Dead Zone Dawn Why is there a Dead Zone in the Gulf of Mexico?
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Why Water Chemistry?
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Why Water Chemistry? What is that white stuff in Lake Michigan?
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Dissolved substances Gases oxygen (O 2 ) carbon dioxide (CO 2 ) ammonia (NH 3 ) nitrogen (N 2 ) most abundant gas on earth
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Dissolved substances Ions Major cations (+) potassium (K + ) calcium (Ca +2 ) iron (Fe +2 , Fe +3 ) sodium (Na + ) most abundant cation in seawater magnesium (Mg +2 ) hardness aluminum (Al +3 ) acid rain important nutrients ammonium ( ) NH + 4
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Dissolved substances Ions Major anions (-) chloride (Cl - ) most abundant anion in seawater bicarbonate ( ) HCO - 3 buffering carbonate ( ) CO -2 3 nitrate ( ) NO - 3 important nutrients phosphate ( ) PO -3 4 acid rain sulfate ( ) SO -2 4
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Dissolved substances This may seem obvious but. .. CO 2 CO 2 HCO 3 - gases move between water and atmosphere ions do not NH 3 NH + 4 NH 3
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Dissolved substances Salinity salinity measurement (concentration of all ions together) -conductivity (charged ions promote passage of electrical current) -evaporate water and weigh residue (total dissolved solids: TDS) There isn't a perfect linear relationship between conductivity and total dissolved solids. How come? seawater- 35 g/L (average) parts per thousand (ppt) freshwaters- highly variable (20 - 300 mg/L) parts per million (ppm)
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Dissolved substances Ions Major cations (+) potassium (K + ) calcium (Ca +2 ) iron (Fe +2 , Fe +3 ) sodium (Na + ) magnesium (Mg +2 ) aluminum (Al +3 ) ammonium ( ) NH + 4 atomic weight = 39 atomic weight = 40
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Dissolved substances Salinity Why is seawater salty? The hydrologic cycle gives us a clue
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Dissolved substances Salinity Where would we expect the highest salinities?
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Salinity There is evidence to indicate that the salinity of the oceans has been stable for > 1 billion years. Dissolved substances All during that time, rivers have continued to add dissolved ions to the oceans. How can this be?
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Dissolved substances Hardness "hard" water - high in Ca +2 and Mg +2 "soft" water - low salinity freshwaters -all seawater is hard -some freshwaters are hard "softened" water - replace Ca +2 and Mg +2 with Na + Why "softened" water? cleaner clothes, less crust on plumbing fixtures
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Dissolved substances Hardness Which is better for your health, Na + or Ca +2 in drinking water? Why else should you care about water hardness? Acid Rain
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Dissolved substances Nutrients N, P, C macronutrients (needed in larger amounts) elements that tend to limit plant growth fertilizer ingredients plants take up dissolved inorganic forms, produce organic forms micronutrients (needed in smaller amounts) Co, Cu, Fe, Mn, Zn, etc. -limit aquatic plant growth in most places -limit aquatic plant growth in a few places -some can be toxic at high doses CuSO 4 used as algicide -can be in the form of a gas or ion
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Dissolved substances Dissolved organics (DOC) labile refractory proteins, simple carbs, fats humic acids (absorb UV) -highly "digestible", easily decomposed by bacteria -poorly digestible, not easily decomposed by bacteria
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This note was uploaded on 03/23/2010 for the course ISP 217 taught by Professor Peacor during the Spring '08 term at Michigan State University.

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Chemistry - Why Water Chemistry? Why is this lake so green?...

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