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Primary Productivity. Primary Productivity. The flow of energy through any ecosystem starts with the fixation of sunlight by plants and other autotrophic organisms. In this way the plant accumulates energy and this energy is called primary production .
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Primary Productivity • The flow of energy through any ecosystem starts with the fixation of sunlight by plants and other autotrophic organisms. • In this way the plant accumulates energy and this energy is called primary production. • The rate at which this energy accumulates is called primary productivity. • The total energy accumulated is gross primary production. However, since plants use some of this energy themselves, it is not all available for the food web.
Net Primary Productivity • The difference between what is accumulated and what is available for the food web is called net primary production expressed kcal or g/m2/y. • This is measured by sequentially measuring growth of the biomass over time by marking the plants somehow, or measuring a total at the end of the growing season. • Alternatively you can measure oxygen production or CO2 consumption both of which equal grams C produced. • In general, swamps and marshes have the highest primary production of all the world's ecosystems.
Productivity • Primary productivity is a term used to describe the rate at which plants and other photosynthetic organisms produce organic compounds in an ecosystem. There are two aspects of primary productivity: • •Gross productivity = the entire photosynthetic production of organic compounds in an ecosystem. • •Net productivity = the organic materials that remain after photosynthetic organisms in the ecosystem have used some of these compounds for their cellular energy needs (cellular respiration).
Dissolved Oxygen • Since oxygen is one of the most easily measured products of both photosynthesis and respiration, a good way to gauge primary productivity in an aquatic ecosystem is to measure dissolved oxygen.
Gross Productivity • We can measure net productivity directly by measuring oxygen production in the light, when photosynthesis is occurring. • We can also measure respiration without photosynthesis by measuring O2 consumption in the dark, when photosynthesis does not occur. • Net productivity = Gross productivity – Respiration
In an aquatic environment, oxygen availability is influenced by a variety of chemical and physical factors. Factors Affecting Oxygen
Factors Affecting Dissolved Oxygen • •Temperature: As water becomes warmer, its ability to hold oxygen decreases. • •Photosynthetic activity: In bright light, aquatic plants are able to produce more oxygen. • •Decomposition activity: As organic material decays, microbial processes consume oxygen. • •Mixing and turbulence: Wave action, waterfalls, and rapids all aerate water and increase the oxygen concentration. • •Salinity: As water becomes more salty, its ability to hold oxygen decreases.
Dissolved Oxygen vs. Light • In this portion of the laboratory you monitor the effect of varying light levels on dissolved oxygen in an algae-rich water culture. • The amount of light available for photosynthesis drops off sharply with increasing depth in an aquatic environment. You will model this condition by wrapping water-sample bottles with increasing layers of screen.
Eutrophication • Eutrophication occurs when large quantities of nutrients such as nitrates and phosphates enter an aquatic environment. • Sources of these nutrients include animal wastes, agricultural runoff, and sewage
An algae bloom occurs as the algae accumulates into dense, visible patches near the surface of the water, prohibiting light from penetrating deeper areas of lake or stream
At this point, oxygen-demanding bacteria take over the ecosystem, decomposing the algae and using up dissolved oxygen in the process. These bacteria increase the biological oxygen demand (BOD) of the ecosystem B.O.D.
Biological Magnification • Certain harmful substances, usually ones not found in nature but introduced by man, may get into plants and/or animals. These poisonous substances may not be broken down in the body or excreted easily, efficiently and quickly. Instead, they accumulate in the tissues, and as the living organism eats more, the concentration of these substances increases and they pass from one trophic level to the next.
