While reading a paper I had long forgotten about at the recommendation of one of my dissertation committee members, I had several random brain farts going off. To start off, let me put in a basic set of definitions of commonly used (based on Chapin
et al., 2006 and/or Randerson
et al., 2002 unless otherwise specified).
By the way, the Randerson paper was one I read once upon a time and was one of the handful of papers that set me on this path of... not-quite-destruction. It also happens that I took two of J. Randerson's classes when the Ranger wasn't such a dominant part of me and even if I was probably one of his worst students, enough stuck with me to keep me curious enough to continue with school! Anyway, there's a lot of really cool stuff to inspire a lot of random thoughts in both the Randerson and Chapin papers, especially the stuff with temporal and spatial scales each of these terms tend to be more used for.
GPP = gross primary production, ie, the total amount of photosynthesis in the ecosystem
R_auto = autotrophic respiration (ie, respiration by everything that photosynthesizes)
R_het = heterotrophic respiration (ie, not-autotrophic respiration)
NPP = net primary production, GPP - R_auto ie, the total amount of biomass accumulation
NEP = net ecosystem production, GPP - (R_auto + R_het) -- the imbalance between GPP and total ecosystem respiration -- using the Chapin
et al., 2006 definition
NEE = net ecosystem exchange, the net CO2 exchange between ecosystem and atmosphere. This one's a bit of a weird one because it's more of an atmospheric-type thing so unlike all the others, positive is CO2 moving into the atmosphere. The other terms all consider going into the atmosphere to be negative and into the ecosystem positive. This one ONLY looks at CO2 and no other forms of carbon.
NECB = net ecosystem carbon balance, -NEE + R_auto + R_het + F_VOC + F_CH4 + F_DIC + F_DOC + F_PC where VOC = volatile organic carbon, CH4 = methane, DIC = dissolved inorganic carbon, DOC = dissolved organic carbon, PC = net lateral transfer of particulates by processes (animal movement, deposition, erosion, anthropoenic)
NBP, net biome production, is NECB estimated at large temporal/spatial scales
While a lot of the terms may look very much the same, they do have their subtle differences. As an eddy covariance type, I think more of NEE, the net ecosystem exchange because the eddy flux towers measure CO2 exchange. Oh I might have another post later on on eddy covariance... if my brain survives the finale of the Test of High Academics on Tuesday. I also do occasionally mess around with NPP because it's another relatively easy one to measure: use the growth increments because it is the difference between the total photosynthesis (C uptake by plant) and the respiration (C loss from the plant to make it function for stuff like maintenance, root ion uptake, growth)
Anyway, on to the brain farts. With all these different terms taking into account different things or focusing on a particular form of carbon, I still ponder over a couple of things. First is with NECB and the carbon sequestration hot topic. If we go by the definition of NECB, should we just put as much of our carbon as possible into non-destructible forms of carbon that won't decompose or burn? That way we can cut the respiration fluxes and volatiles. Of course, I haven't fully thought this out because it's a random brain fart but what if we put all of our carbon into say, bike frames and carbon arrow shafting and other relatively indestructible goodies? Would that help keep the carbon out of the atmosphere?
The second brain fart on my mind is with NEE. By the definitions I've seen, it's the net CO2 exchange, although in most cases it applies to plant-soil-atmosphere interaction and at relatively small temporal and spatial scales. Should there be a bigger-scale version of it like with NBP for NECB... or are the large number of terms getting too unwieldy? Then there's the whole thought of anthropogenic CO2 (and no, we're not talking about farts... which by the way are largely CH4 but have some CO2 in them) and how that fits into the scheme of things with NEE, especially a scaled-up version. Again, not a fully thought out thought but just something starting to bubble in my brain. There are some pretty good discussions about NEE out there, can't remember off the top.
There's more but I'm tired. Maybe more later if I feel up to it. If not, well, enjoy!
