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Published bySolomon Barrett Modified over 9 years ago
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Dissolved Oxygen The Good Gas
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Photosynthesis: Your one-stop shop for all of your oxygen needs! Carbon Dioxide (from air) Water (from ground) Oxygen (to air) Carbohydrate (plant material) Solar energy + 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2 Happy Rays of Sunshine
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DO: A Soluble Gas H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O O2O2 H2OH2O H2OH2O H2OH2O O2O2 O2O2 O2O2 O2O2 O2O2 H2OH2O O2O2 H2OH2O
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Hydrilla Coontail Parrotfeather Submerged Aquatic Vegetation (SAV’s)
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Phytoplankton (single cell plants)
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Hypoxic Anoxic Normoxic Habitat Classification Based on DO Concentration 0 – 0.2 mg/L 0.2 – 2 mg/L > 2 mg/L
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Respiration: How we, the animals, use oxygen (and plants too!) C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O + energy (in form of ATP) Carbohydrate + Oxygen Carbon Dioxide + Water + Energy Oxygen in Carbon Dioxide out Previous Meal Carbohydrate in Energy out Water out (later)
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CO 2 : A Soluble Gas Too! H2OH2O H2OH2O H2OH2O H2OH2O O2O2 H2OH2O H2OH2O H2OH2O O2O2 O2O2 O2O2 O2O2 O2O2 H2OH2O O2O2 H2OH2O CO 2
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C 6 H 12 O 6 Solar Energy Heat Energy Biomass (g/m 2 /yr) O2O2 Chemical Energy (ATP) Photosynthesis Respiration Biological Production and Consumption of Oxygen
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Daily Aquatic Oxygen Cycle SunriseNoonSunsetMidnight Dissolved Oxygen SunshineMoonshine
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∞ Day ∞ Night Photosynthesis Respiration
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∞ Photosynthesis Respiration ∞ Low Respiration High Respiration
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∞∞ High Photosynthesis Low Photosynthesis
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SunriseNoonSunsetMidnight CO 2 +H 2 O H 2 CO 3 H + +HCO 3 - 2H + +CO 3 - An increase in CO 2 causes an increase in H + pH SunshineMoonshine pH Level
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5 10 6 9 7 8 7 7 7 7 Water Flow Blood Flow Counter Current Flow 5 6 6 7 7 8 8 9 9 10 Blood Flow Water Flow
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5 6 6 7 7 8 8 9 9 10 Blood Flow Water Flow Hi DO 1 2 2 2 2 2 2 2 2 2 Blood Flow Water Flow Low DO 5 6 6 6 6 6 6 6 6 6 Blood Flow Water Flow Med DO
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Decomposition – Not good for DO Decomposer organisms (mainly bacteria) consume oxygen –Sometimes consume oxygen faster than plants can produce it, even during the middle of the day! A sudden increase in organic matter (think leaf litter) can create a spike in decomposition activity – especially if it is hot –Hurricanes not only add organic matter to our waterways, but also stir up the sediment. –Can cause fish kills!!
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Abiotic Factors That Affect DO Concentration Temperature Water Clarity Current Velocity (Flow) Wind Cloud Cover
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Temperature The warmer water is, the less DO it can hold –Think about opening a coke bottle after it sat a few hours on the dash of your car in August. Excess DO evaporates into the atmosphere! 100% DO Saturation 0 2 4 6 8 10 12 14 16 18 20 05101520253035 Temperature (C) 100% Saturation Lavel
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Oxygen > 100% Saturation Oxygen < 100% Saturation Oxygen diffuses out of water column Oxygen diffuses into water column Water Column Atmosphere Oxygen Can Diffuse Out of or Into the Water Column
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Wind Stirs in atmospheric oxygen
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Current Velocity The faster water flows, the more atmospheric oxygen is mixed into the water.
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Water Clarity Pure water Secchi Disk (cm) Oceanic seawater
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Cloud Cover Clouds decrease the amount of sunlight reaching aquatic plants, thus oxygen production is reduced.
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Why Measure DO? Indicator of primary production (growth of plant material) –More plants = more animals that eat plants = more animals that eat animals that eat plants = happy Cajuns! Most aquatic animals can not live in water without sufficient oxygen
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Measuring DO Winkler method – a titration method –Not very practical in the field –Great to calibrate probes Electronic Probes – easy to use, but needs to be calibrated on a regular basis –Usually accurate to 0.2 mg/L YSI 550A DO Meter w/12' cable
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Putting It All Together Most aquatic DO is biologically produced through photosynthesis Respiration / Decomposition rates can affect DO concentration DO concentration typically cycles with the photoperiod Temperature, Wind, Current Velocity, Water Clarity, and Cloud Cover can indirectly affect oxygen concentration
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Finally!! A single DO measurement provides little information Regular monitoring provides a better picture of the health of a waterway – based on oxygen.
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