Dissolved Oxygen The Good Gas

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

DO: A Soluble Gas H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O O2O2 H2OH2O H2OH2O H2OH2O O2O2 O2O2 O2O2 O2O2 O2O2 H2OH2O O2O2 H2OH2O

Hydrilla Coontail Parrotfeather Submerged Aquatic Vegetation (SAV’s)

Phytoplankton (single cell plants)

Hypoxic Anoxic Normoxic Habitat Classification Based on DO Concentration 0 – 0.2 mg/L 0.2 – 2 mg/L > 2 mg/L

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)

CO 2 : A Soluble Gas Too! H2OH2O H2OH2O H2OH2O H2OH2O O2O2 H2OH2O H2OH2O H2OH2O O2O2 O2O2 O2O2 O2O2 O2O2 H2OH2O O2O2 H2OH2O CO 2

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

Daily Aquatic Oxygen Cycle SunriseNoonSunsetMidnight Dissolved Oxygen SunshineMoonshine

∞ Day ∞ Night Photosynthesis Respiration

∞ Photosynthesis Respiration ∞ Low Respiration High Respiration

∞∞ High Photosynthesis Low Photosynthesis

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

Water Flow Blood Flow Counter Current Flow Blood Flow Water Flow

Blood Flow Water Flow Hi DO Blood Flow Water Flow Low DO Blood Flow Water Flow Med DO

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!!

Abiotic Factors That Affect DO Concentration Temperature Water Clarity Current Velocity (Flow) Wind Cloud Cover

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 Temperature (C) 100% Saturation Lavel

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

Wind Stirs in atmospheric oxygen

Current Velocity The faster water flows, the more atmospheric oxygen is mixed into the water.

Water Clarity Pure water Secchi Disk (cm) Oceanic seawater

Cloud Cover Clouds decrease the amount of sunlight reaching aquatic plants, thus oxygen production is reduced.

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

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

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

Finally!! A single DO measurement provides little information Regular monitoring provides a better picture of the health of a waterway – based on oxygen.