We talk a lot about the processes which occur when leaves and other botanicals are added to the aquarium. And this is interesting, not only from an aesthetic standpoint, but from a functional/operational standpoint. We add a lot of biological material to our tanks in the form of leaves and botanicals- perfectly analogous to the process of allochonous input- material is something imported into an ecosystem from outside of it. Exactly what happens in the tropical streams and rivers that some of us obsess over.
There's been a fair amount of research and speculation by both scientists and hobbyists about the processes which occur when terrestrial materials enter aquatic environments. As hobbyists, we have a unique opportunity to observe firsthand the impact and affects of this material in our own aquariums. I love this aspect of our "practice", as it creates really interesting possibilities to embrace and create more naturally-functioning systems.
There are implications for both the biology and chemistry of the aquatic habitats when leaves and other botanical materials enter them.
A lab study I came upon found out that, when leaves are saturated in water, biofilm is at it's peak when other nutrients (i.e.; nitrate, phosphate, etc.) tested at their lowest limits. This is interesting to me, because it seems that, in our botanical-style, blackwater aquariums, biofilms tend to occur early on, when one would assume that these compounds are at their highest concentrations, right? And biofilms are essentially the byproduct of bacterial colonization, meaning that there must be a lot of "food" if there is a lot of biofilm, right?
Oh, and here is another interesting observation:
When leaves fall into streams, field studies have shown that their nitrogen content typically will increase. Way is this important? Scientists see this as evidence of microbial colonization, which is correlated by a measured increase in oxygen consumption. This is interesting, as the rare "disasters" that we see in our tanks (when we do see them, of course, which fortunately isn't very often)- are usually caused by the hobbyist adding a large quantity of leaves at once, resulting in the fishes gasping at the surface- oxygen depletion?
Makes sense, right?
These are interesting clues about the process of decomposition of leaves when they enter into our aquatic ecosystems. They have implications for our use of botanicals and the way we manage our aquariums. I think that the simple fact that pH and oxygen tend to go down quickly when leaves are initially submerged in water during lab tests gives us an idea as to what to expect. A lot of the initial environmental changes will happen rather rapidly, and then stabilize over time. Which of course, leads me to conclude that the development of sufficient populations of organisms to process the incoming botanical load is a critical part of the establishment of one of our aquariums.
Fungal populations are as important in the process of breaking down leaves and botanical materials in water as are higher organisms, like insects and crustaceans, which function as "shredders." So the “shredders” – the animals which feed upon the materials that fall into the streams, process this stuff into what scientists call “fine particulate organic matter.” And that's where fungi and other microorganisms make use of the leaves and materials, processing them into fine sediments. Allochthonous material can also include dissolved organic matter (DOM) carried into streams and re-distributed by water movement.
And the process happens quickly. In experiments carried out in tropical rainforests in Venezuela, decomposition rates were really fast, with 50% of leaf mass loss in less than 10 days! Interesting, but is it tremendously surprising to us as botanical-style aquarium enthusiasts? I mean, we see leaves begin to soften and break down in a matter of a couple of weeks- with complete breakdown happening typically in a month or so for many leaves. And biofilms, fungi, and algae are still found in significant quantities throughout the process.
So, what's this all mean? What are the implications for aquariums?
I think it means that we need to continue to foster the biological diversity of animals in our aquariums- embracing life at all levels- from bacteria to fungi to crustaceans to worms, and ultimately, our fishes...All forming the basis of a closed ecosystem, and perhaps a food web of sorts for our little worlds. It's a very interesting concept- a fascinating field for research for aquarists, and we all have the opportunity to participate in this on a most intimate level!
Now, I understand that this is an aggregation of a lot of facts coming from different directions, being interpreted for our purposes. However, these interesting tidbits of knowledge are things that we can utilize to better understand the actual function of our aquariums, for the benefit of the life forms which reside in them.
Stay fascinated. Stay engaged. Stay curious. Stay observant. Stay diligent...
And Stay Wet.