General Lake Chemistry-Part II

In photosynthesis, aquatic plants and algae use the energy from the sunlight, carbon dioxide, nutrients and water to produce organic compounds like sugar, water and oxygen. This relationship between bioloby and chemistry is constantly regulated by a check and balance feedback system. The sun's energy is stored in sugar as chemical energy. The photosynthetic uptake of carbon to form sugar is called "primary production." The oxygen produced during photosynthesis is the primary source of dissolved oxygen in the water and of oxygen in the atmosphere. Before plants and animals can utilize the chemical energy produced by photosynthesis, it must be transfformed by respiration. Respiration consumes oxygen and releases carbon dioxide back into the water.

In productive stratified layered lakes, photosynthesis dominates the epilimnion, or upper laryer of water. The excess organic matter produced in the well-lit euphotic zone eventually sinks down through the water to the sediments where respiration dominates. A significant difference often exists between the oxygen-rich euphotic zone and the unerlying, oxygen-poor aphotic zone. The presence or absence of oxygen has significant effects on the important oxidation-reduction chemisty.

Chemical reactions in which electrons are transferred from one to another are known as oxidation-reduction reactions. The presence of oxygen promotes oxidation (a gain in electrons, Fe++ to Fe+++) because of free electrons are available. In the absence of oxygen, abundant free electrons promote chemically reducing conditions. Such reaction affect substantially the state of many chemicals found in lake water. For instance, oxidized sulfur as sulfate (SO4-) is reduced to sulfide, as in hydrogen sulfide (H2S) in lake sediments. The resulting hydrogen sulfide gas, when released from the water, is characterized by the smell of "rotten eggs." This is known as fall "turnover."

Both parts of your chemistry primer are pretty interesting reading Bonefish. Lot of H2S coming out of those spillways these days as many lakes get drawn down to winter pool.

Good stuff Bonefish. I thought I was reading my Limnology text book.

I always had trouble with redox equations. Oxygen must be gaining the electron to fill it's outer orbital while the Fe Iron gave up an electron to get an extra positive charge. That means it lost one of it's electrons to the Oxygen atom.

Next week lets cover the Carbon cycle in lakes. Then we can work on pH changes in the shallows caused by increase of Oxygen and Decrease of CO2 during the daytime and and Increase in CO2 and Decrease of Oxygen during the night time hours.

Putting all this good information to work in helping figure out where the fish hang out is hard work. I think I need a beer. Oh wait it's too early for a beer. Guess a cup of decaf will do for now.

Just kidding with you mate. I enjoy reading the stuff you post.




[quote=Bonefish;307438]In photosynthesis, aquatic plants and algae use the energy from the sunlight, carbon dioxide, nutrients and water to produce organic compounds like sugar, water and oxygen. This relationship between biology and chemistry is constantly regulated by a check and balance feedback system. The sun's energy is stored in sugar as chemical energy. The photosynthetic uptake of carbon to form sugar is called "primary production." The oxygen produced during photosynthesis is the primary source of dissolved oxygen in the water and of oxygen in the atmosphere. Before plants and animals can utilize the chemical energy produced by photosynthesis, it must be transformed by respiration. Respiration consumes oxygen and releases carbon dioxide back into the water.

In productive stratified layered lakes, photosynthesis dominates the epilimnion, or upper layer of water. The excess organic matter produced in the well-lit euphotic zone eventually sinks down through the water to the sediments where respiration dominates. A significant difference often exists between the oxygen-rich euphotic zone and the underlying, oxygen-poor aphotic zone. The presence or absence of oxygen has significant effects on the important oxidation-reduction chemistry.

Chemical reactions in which electrons are transferred from one to another are known as oxidation-reduction reactions. The presence of oxygen promotes oxidation (a gain in electrons, Fe++ to Fe+++) because of free electrons are available. In the absence of oxygen, abundant free electrons promote chemically reducing conditions. Such reaction affect substantially the state of many chemicals found in lake water. For instance, oxidized sulfur as sulfate (SO4-) is reduced to sulfide, as in hydrogen sulfide (H2S) in lake sediments. The resulting hydrogen sulfide gas, when released from the water, is characterized by the smell of "rotten eggs." This is known as fall "turnover."[/quote]

Last year I drove by one of the large pits located in my area. There was a low area where the roadway went down about 100 ft from the rest of the area and that's where the strip pit was located. There were pits on both side of the road where they had mined coal.

I could smell the sulfur in the air. The H2S was just hanging in the air in this valley. I knew right away that the lakes were turning over. A few days later the smell was gone. But it was very strong. But one can detect H2S in the ppm range with the human nose. It must have been a calm day that day.

These pits are very deep and they stratify during the summer months.

They turned over last year some time in the fall. Can't remember when but it was warm last fall until later in the fall. Global warming gives us longer warmer falls than we had in the past.

[quote=Devils Horse;307489]Both parts of your chemistry primer are pretty interesting reading Bonefish. Lot of H2S coming out of those spillways these days as many lakes get drawn down to winter pool.[/quote]