We don't really have a lot of data on P. aquatica at this point, but the literature would seem to suggest it is a bit more stable in alkaloid profile than P. arundinacea (though assuredly it will likely vary quite a bit between locations/climates and other conditions).
The literature reports common aquatica being approximately .1-.2% alkaloids with DMT as the main alkaloid, but with 5-MEO-DMT present in fairly significant quantities, and traces of bufotenine; there is not much information on the presence of other alkaloids such as gramine and hordenine, or whatever else may be present. So one would be advised to proceed with caution in bioassay.
As a source of DMT wild aquatica grasss is not really ideal, wild grasses have their own blend of alkaloids and "spirit" if you will, they are their own
teachers with their own lessons. If you are interested in furthering our understanding of these these medicines and willing to step into fairly untread territory effectively guinea pigging yourself in the name of science, we need all the volunteers we can get in that area and your efforts would be greatly appreciated by the entheogen using community at large; if however you are simply looking for a good source of DMT, go the acacia route or look into the known strains of phalaris and pass on the wild grass.