62. What is the difference between primary production and algal biomass - be ver
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62. What is the difference between primary production and algal biomass - be very specific about what they How do we measure primary production practically? Why do we incubate a dark and a light bottles at measure? different depths to measure p production? How do we compare primary productivity on land question) rimary productivity? How can we calculate nutrient assimilation from primary with that in the ocean? (10 points - 2 points ea Why do and 2 points for the final question) n what we mean by gross productivity, net productivity, the compensation depth and the critical depth? es the depth of the mixed layer affect primary productivity? (10 points - 2 points for each definition 64. Describe the depth profiles for the concentrations of the dissolved nutrients nitrate and silicate in the o (shapes and concentrations). Why are they shaped the way they are in surface water (upper 100 to 200m), at mid depths (-200-1000m), and in deep waters ( 1000m)? Would you expect the profile of dissolved phosphate to look like that of silicate or nitrate, and why? Why are the concentrations of all nutrients in deep waters of the Pacific Ocean higher than those in the deep Atlantic? (10 points) pen oceanExplanation / Answer
62. Primary production is defined as the rate at which solar energy is converted to chemical energy. Some part of the converted energy, i.e. the net primary production (NPP), is utilized for the growth of the body of an organism. This growth is represented as algal biomass in units of kg/m2 while the NPP is measured in units of g/m2/year.
Primary production is measured by doing experiments using three sets of bottles - initial (I), light (L), and dark (D). Dissolved oxygen (DO) concentration is measured in each of the bottles which contain water samples from a particular depth. The difference in DO obtained from two bottles give the values of Gross primary production (L - D), net primary production (L -I).
Incubation in light and dark bottles is done at different depths because of the decrease in the amount of sunlight that is received from the surface to the deeper layers of the water column.
The nutrient assimilation can be estimated using the Redfield ratio which enables the quantification of C, N, and P as they are commonly present in the ratio of 106:16:1.
In general, land fixes more carbon and produces more biomass than oceans due to an abundance of sunlight but the ocean produces more oxygen through respiration as it has a vast spatial extent compared to land. So, net primary production per unit area is more on land compared to an ocean.
63. Net Primary Production (NPP) = Gross Primary Production (GPP) - Respiration
The part of the converted solar energy that is used for growth of plant's body is quantified as NPP. The remaining part of the converted energy is used for respiration. The summation of the two parts yields GPP.
The depth at which photosynthetic production of organic compounds offsets the breakdown of such compounds due to respiration is known as the compensation depth.
The depth above which the growth rates of phytoplankton become equal to the decay rates of phytoplankton is known as the critical depth.
64. Dissolved nitrate and silicate concentrations generally decrease with depth in the open ocean. At the surface, the nutrients are consumed by microorganisms such as phytoplankton for building their shells and metabolic activity. At mid-depth, the water masses undergo denitrification due to bacterial consumption. At deeper depths, the productivity decreases due to a decrease in photosynthesis and the nutrients increase in concentration.
The dissolved phosphate concentration would look similar to that of nitrates and silicates, as the consumption rates due to the presence of organisms would remain similar.
The concentration of all nutrients in deep waters of the Pacific are higher than those in Atlantic due to the large-scale circulation of global oceans. The downwelling of waters in the North Atlantic results in a long residence time of the waters in the deep Pacific. The waters retain the high nutrient characteristics until upwelling at the surface of the Pacific Ocean and the subsequent discharge to the Indian Ocean.
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