Of all the processes which we are fascinated with around here, none is mentioned more frequently- or with as much reverence- as the process of decomposition. Yeah, you're actually hearing about a fish geek celebrating this- finding something compelling, fascinating, and fundamental about stuff breaking down in our tanks.
I respect this process! And you should, too!
Decomposition, to refresh your memory, is the process by which organic materials are broken down into more simple organic matter. For our purposes, we are primarily interested in the breakdown of plant matter, ie; botanicals and leaves. It is in part responsible for some of the unique habitats that we love so much-and an inspiration for some unique aquariums with previously unappreciated aesthetics!
When leaves enter tropical streams and other bodies of water, fungal colonization causes leaves to increase nitrogen content (because of fungal biomass) and leaf maceration. This is known by aquatic ecologists to be evidence of microbial colonization. There are many different stages in the process, starting with the leaching of materials from the cells of the botanicals during initial submersion, in which soluble carbon compounds are liberated in the process. A rapid release of phosphorus accompanies this leaching.
Of course, the process ultimately leads to physical breakdown and/or fragmentation of the leaves and botanicals into smaller "pieces", which possess larger amounts of surface area for microbial attachment. Extensive ecological studies done by scientists specifically in regard to leaf litter have yielded a lot of information about this process.
The fungi known as aquatic hyphomycetes produce enzymes which cause leaf maceration, and in as little as 2 to 3 weeks, as much as 15% of the decomposing leaf biomass in many aquatic habitats is processed by fungi, according to one study I found.
In experiments carried out by aquatic ecologists in tropical forests in Venezuela, decomposition rates were really fast, with 50% of leaf mass loss in streams occurring in less than 10 days!
The ultimate result is the transformation of what ecologists call "coarse particulate organic matter" (C.P.O.M.) into "fine particulate organic matter" (F.P.O.M.), which may constitute an important food source for other organisms we call “deposit feeders” (aquatic animals that feed on small pieces of organic matter that have drifted down through the water and settled on the substrate) and “filter feeders” (animals that feed by straining suspended organic matter and small food particles from water).
And yeah, insect larvae, fishes and shrimp help with this process by grazing among or feeding directly upon the decomposing botanical materials...We've talked about that quite recently, right? So-called "shredder" invertebrates (shrimps, etc.) are also involved in the physical aspects of leaf litter breakdown.
There's a lot of supplemental food production that goes on in leaf litter beds and other aggregations of decomposing botanical materials. It's yet another reason why we feel that aquariums fostering significant beds of leaves and botanicals offer many advantages for the fishes which reside in them!
The biggest allies we have in the process of decomposition of our botanicals in the aquarium are microbes (bacteria, fungi, and protozoa, specifically). Ecologists will tell you that during the early decay phase of botanicals/leaves, the leaching of water-soluble substances plays a key role in the loss of the physical mass of these materials.
Alteration of the botanicals is done chemically via this microbial action; ultimately, the components of the botanicals/leaves (lignin, cellulose, etc.) are broken down near completely. In aquatic environments, photosynthetic production of oxygen ceases in plants, and organic matter and nutrients are released back into the aquatic environment.
Fungal colonization facilitates the access of invertebrates to the energy trapped in deciduous leaves and other botanical materials found in tropical streams. Bacteria and fungi that decompose decaying plant material in turn consume dissolved oxygen for respiration during the process.
This is why adding too much botanical material too rapidly to an aquarium can create problems for the fishes! A rapid decrease in dissolved oxygen in a small body of water can be disastrous; or, at the very least, leave fishes gasping at the surface! And of course, that's why we tell you to deploy massive patience and to go slowly when adding botanicals to an established aquarium...
So, we've just discussed a lot of interesting material about how the process of decomposition of botanical materials occurs in tropical streams and of course, in our aquariums. Now, we likely won't have the diversity/density of invertebrates and other organisms in our aquariums to handle this process that we find in wild habitats, but the process can happen nonetheless. Perhaps, we have a greater ratio of fungi or bacteria to "shredders" in aquariums than occurs in the wild (just a supposition), but it's something worth thinking about.
The idea of decomposing "stuff" in our aquariums certainly runs a bit contrary to what we've been indoctrinated about in our hobby work for generations. I mean, one of the many reasons that we perform regular water exchanges and siphon out "detritus" from out tanks is to remove potential sources of "pollution" from our tanks.
And here I am, asking you to not only "leave them be" -but to encourage their accumulation and foster the development and prosperity of the organisms which "work" them.
Now, again, I have to at least ask the rather long question, "Are these things (detritus; decomposing materials) really problematic for a well-managed aquarium? Or, do they constitute an essential component of a closed aquatic ecosystem...One which can actually provide some benefits (ie; supplemental nutrition) for the resident fishes and the community of life forms which support them?"
Many of us have already made a mental shift which accepts the transient, subtle beauty of decomposing botanical materials, tinted water, biofilms, and the like, so it goes without saying that taking it a little further and allowing these materials to completely breakdown to serve as the substrate for our aquatic ecodivesity is simply the next iteration in the management of blackwater/brackish botanical-style aquariums.
It's something that we as aquarists need to simply explore more.
I can envision systems created to optimize the breakdown and accumulation of botanicals, with targeted water-column flow, use of more coarse (or fine) mechanical filtration media, moderated lighting to discourage excessive algal growth, and even careful selection of hardscape materials, such as Mangrove root tangles, driftwood, etc. to encourage these materials to settle in and among them, as occurs in Nature.
Yeah- aquariums set up specifically to optimize and foster these natural processes!
Letting our minds wander a bit, and accepting and encouraging this stuff, rather than freaking the fuck out every time we see a gram of detritus in our tanks will go a long way towards fostering new discoveries, "best practices"- and maybe even breakthroughs!
So, yeah- there IS a lot to consider when utilizing botanical materials in your aquarium. It's far, far beyond the idea of just "dumping and praying" that has been an unfortunate "model" for how to utilize them in our aquariums for many years. It's more than just aesthetics alone...the "functional aesthetic" mindset- accepting the look and the biological processes which occur when terrestrial materials break down in our tanks is a fundamental shift in thinking.
Much respect to the decomposers- our friends!
By studying the process of decomposition in Nature and in our aquariums, I believe that we are contributing to an exciting progression of the art and science of aquarium keeping!
And everyone's contributions are welcome!
Stay fascinated. Stay diligent. Stay unfazed. Stay creative. Stay excited...
And Stay Wet.