I have a stream where the seasonal maxima oxygen concentrations (i.e. annual max of daily max) preceded measured abundance peak by a few weeks. Of course the abundance measure has it's error. But please ignore that for now and think about whether oxygen production should, in theory peak before, at, of after plant maxima. A plant biomass peak defines the transition from net growth to net decline. Would it be safe to assume net growth is levelling off prior to the peak? Would oxygen production reflect biomass of total plants, biomass only of the growing cells, or the net growth of plant material (e.g. kg dry matter added per square meter per day). The stream oxygen measurements reflect what is happening over the reach upstream on a given day, so think about reach scale biomass/growth as the sum total of individual cells within individual stems.
Thoughts and suggestions welcome, thank you.
As Marek has stated Oxygen production is analogous with the net primary production, to get an picture of the gross primary production of your system requires a measure of Respiration. I would recommend looking at oxygen uptake during the dark phase and subsequently calculating the gross primary production as GPP = NPP + R, for a given time period. Having said that this will be for the total community so will include both plant, animal and microbial biomass.
Good points - thank you.
I have estimates of photosynthesis (g/m3/d at 20C). Reaeration calculated from time lag between solar noon and DOmax. Respiration and photosynthesis calculated using delta method. Is it reasonable to treat that photosynthetic rate as net prim. productivity?
This gives a similar result with max photosynthesis preceding max plant abundance by about two weeks. I get a similar lag with depth-corrected photosynthesis (g/m2/d at 20C, using a time-series of depth), and with P/R and P+R. Within a few days of each other. Probably worth mentioniong that the end of season decline in plant abundance had the most pronounced lag after the decline in photosynthesis (closer to 4 weeks).
Of course I don't have a true measure of plant abundance, and I can write the lag off as an artefact of the methods I used to estimate abundance (%bed cover). If I could measure true population biomass, would that determine net primary productivity given that not all of the plant biomass is actively photosyntheisizing (e.g. shaded, structural or sensecing material)?
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