Water Quality and Aquaculture

Choose 2 Bodies of water n One that you think has poor water quality n One that you think has excellent water quality n Why did you choose them

What Factors are Important n Dissolved Oxygen n Temperature and Stratification n pH n Alkalinity n Hardness n Nitrogen Compounds n Salinity n Carbon Dioxide n Turbidity

Dissolved Oxygen n Why is it import? –Fish respiration –Bacteria respiration n Generally the first limiting factor in aquaculture production n What % of the air is Oxygen? n What % of the water?

Where Does the Oxygen in the Water Come From? n 90% comes from photosynthesis n 6CO 2 + 6H 2 O + energy = C 6 H 12 O 6 +6O 2 n 10% comes from the air water interface n Diffusion –movement from an area of high concentration to an area of low concentration

Where Does the Oxygen Go? n Respiration n Oxidation n C 6 H 12 O 6 +6O 2 --> 6CO 2 + 6H 2 O + energy n Sugar + Oxygen = Carbondioxide + water + energy

How do different levels of DO effect aquaculture organisms?

How does temperature affect the amount of DO?

Can the water have too much dissolved oxygen? n Yes, it’s called supersaturation –this means that at times the water may contain more than it can physically hold. –Caused by oxygen being added faster than it can be released from the pond –can actually poison fish and other animals in the pond

When might supersaturation occur? n When a pond has a dense algae bloom and there is hot sunny weather. n At the base of a waterfall.

How does the oxygen get depleted? n Excessive oxygen demand n Net loss of oxygen n Algal bloom die-off n Turn over

Carbon Dioxide & Oxygen Budget

Oxygen Gains and Losses n Photosynthesis by phytoplankton n Diffusion n Plankton respiration n Fish respiration n Respiration by organisms in the mud n Diffusion n 5 to 20 ppm n 1 to 5 ppm n 5 to 15 ppm n 2 to 6 ppm n 1 to 3 ppm n 1 to 5 ppm Gains Losses

Example budget n Day 1 –am DO of 6 ppm n bloom adds 10 ppm n windy, diffusion adds 10 ppm n Respiration by plants and animals in the mud 9ppm n Fish respiration 3ppm n Diffusion out of pond 2 ppm n 6ppm n +10 ppm n = 26 ppm n - 9 ppm n - 3 ppm n - 2 ppm n = 7 ppm

Example budget - Day 2 n 7 ppm to start n + 10 ppm photosynthesis n + 1 ppm diffusion - calm day n = 18 ppm available n - 9 ppm respiration of phytoplankton and organisms in the mud n - 3 ppm fish respiration n - 2 ppm diffusion n 4 ppm left on the morning of day 3

What would happen if the weather stayed the same?

In most cases, a system’s ability to add dissolved oxygen to water will become the first limiting factor in a system’s fish carrying capacity.

How will the density of the algae bloom affect the DO?

Depth vs Oxygen

Stay in the Zone n The most productive zone in lakes, oceans and other bodies of water is called the n This zone ends at the point where there is less than 1% of the incident light.