Detritus is nearly benign once it even touches the top of the sand, but is quickly rendered completely benign by the microfauna and bacteria in the surface layers. They were wrong about this in the early days and has since changed with more studies that have come out. The issue with stirring up the sand is that you flip flop the oxic and anoix areas and also can bury creatures that live in the oxic zone and expose creatures that live in the anoxic causing die off. The detritus stir up is unfortunate and messy, but it has nothing organic to contribute to creating nitrate. The ecosystem disturbance is the issue - both the die off and the lower processing ability. Let's assume that you did disturb the ecosystem and it was no longer functioning at 100%... "normal" nitrate would not be able to be processed and would rise, right? This happens to many people, but the sand bed did not "release" any nitrate, it just was unable to do the job that it was once doing. The oxic and anoxic areas repopulate and this usually sorts it's self out, but it takes some time.
The people who use shallow sand beds keep the stirred up so that the anoix areas can never develop. This does not cause any issues since no ecosystem was disturbed.
The idea of detritus releasing nitrates is one of the things that dates the WWM FAQ a bit... yes, the nitrates will creep up, but not from the detritus, as explained above. Also, you will read them mention that nitrate (or phosphate) will go to "zero" - this is not completely true as we are able to measure today. You have to remember that when WWM was in the prime, test kits were horrible and most test kits showed nitrate under 2 as zero - or "clear." What they mean when they say "zero" is that they are undetectable on a test kit. Most nitrate test kits are no better today, but we do have better phosphate test kits and also IC.
Even with all of these issue, WWM is still THE BEST resource for reefing knowledge that is out there. It is free of advertiser self-serving "studies," fanboydom or any kind of bias. These were just guys who knew their stuff and wanted to help. Also, if they ever found out that they were not correct, they were not too proud to correct themselves.
**Tangent, a bit... people did start to realize that detritus would "gum up the works" and not allow good areas of fauna and bacterial development when the benign detritus built up too much. This led to folks starting to vacuum some of their sand after 4-5 years. They went slow, like 15-20% every six months. You sometimes even have to add new sand as the lower pH in the sandbed can melt some. Not everybody did this, but it did not hurt anything as long as not too much was done at once. I vacuum about 25% of my sand a year now that my tanks are quite old. It is fun to see the conchs, cucumbers and worms flock to the freshly vacuumed area to see what I disturbed that are now able to reach.
