October 04, 2023

The botanical method aquarium niche is a bit weird, isn't it? Collectively, companies in our space tend to speculate a lot.

We make claims.

And we make recommendations..

And at best, they’re subjective guesses. Based upon our personal experince and perhaps the experiences of others.

Yet, wherever you turn in the botanical method aquarium world, speculation and generalizations are, well- rampant. How much tannin or other compounds are in a given botanical is, without very specific bioassays and highly specialized equipment- simply a guess on our part.

There is absolutely no proof or quantification of these assertions that is grounded in hard facts or rigorous, scientific research. I think about it a lot..For us to make recommendations based on concentrations of various compounds in a given botanical is simply irresponsible and not grounded in fact.

There is a lot of speculation. So-called "experts" in our area of specialization have, in all likelihood, done little beyond use the materials avialbel to us in aquairums. I'm not aware of anyone in our niche who runs a lab, or has performed disciplined scientific analysis on any of the materials that we as a hobby use every day.

This is not an "indictment" or secret reveal about our industry...it's just the way things are.

One of the things that we assert the most is "how much tannins" are in a given material. Okay...What is this based upon?

Generally, it's based upon the admittedly superficial observations that we make as hobbyists and "power users" of botanical materials. There are not awhole lot of other, more insightful observations that we CAN make, right?

Sure, we could tell you that, based upon our experience, a given wood type or seed pod will color the water a darker color than another.. but what does that mean, really?

Not that much.

I mean color of the water is absolutely not an indication of anything- other than the fact that tint producing types of tannins are present. It doesn’t tell you what the pH, dKH, or TDS of the water.. let alone, how much of what tannins are present…

Now, sure, it’s arguably correct that “tannins” are present in many botanical materials. However, the degree to which the tannins present in a given botanical or leaf can influence water chemistry is really speculative. Quite honestly, other than staining the water a distinctive brown color, it’s actually not entirely known by science what other influences that specific tannins impart to water.

So, to be quite honest, when we make general statements like “contains a lot of tannins” or “can lower pH”, many times we’re simply “spitballing…” Guessing. Assuming.

Now, don't get me wrong. I'm not trying to trash the many responsible, experienced vendors in our space. I am, however, attempting to make the point that a large part of what we assert about the materials we work with and sell is, well- speculative.

We make claims.

And we make recommendations..

I think the main thing which keeps the idea from really developing more in the hobby- knowing exactly how much of what to add to our tanks, specifically to achieve "x" effect- is that we as hobbyists simply don't have the means to test for many of the compounds which may affect the aquarium habitat.

At this point, it's really as much of an "art" as it is a "science", and more superficial observation- at least in our aquariums- is probably almost ("almost...") as useful as laboratory testing is in the wild. Even simply observing the effects upon our fishes caused by environmental changes, etc. is useful to some extent.

At least at the present time, we're largely limited to making these sort of "superficial" observations about stuff like the color a specific botanical can impart into the water, etc. It's a good start, I suppose.

Of course, not everything we can gain from this is superficial...some botanical materials actually do have scientifically confirmed impacts on the aquarium environment.

In the case of catappa leaves, for example, we can at least infer that there are some substances (flavonoids, like kaempferol and quercetin, a number of tannins, like punicalin and punicalagin, as well as a suite of saponins and phytosterols) imparted into the water from the leaves- which do have scientifically documented affects on fish health and vitality.

So, there's that.

The one area that we are not speculating or guessing is the ecology part. How botanical materials interact with the aquatic environment to form an ecosystem of organisms. And the most fundamental, most important "driver" of the whole thing is the process of decomposition.

Decomposition is how Nature processes botanical materials for use by the greater aquatic ecosystem. It's the first part of the recycling of nutrients that were used by the plant from which the botanical material came from. When a botanical decays, it is broken down and converted into more simple organic forms, which become food for all kinds of organisms at the base of the ecosystem.

In aquatic ecosystems, much of the initial breakdown of botanical materials is conducted by detritivores- specifically, fishes, aquatic insects and invertebrates, which serve to begin the process by feeding upon the tissues of the seed pod or leaf, while other species utilize the "waste products" which are produced during this process for their nutrition.

In these habitats, such as streams and flooded forests, a variety of species work in tandem with each other, with various organisms carrying out different stages of the decomposition process.

And it all is broken down into three distinct phases identified by ecologists.

It goes something like this:

A leaf falls into the water.

After it's submerged, some of the "solutes" (substances which dissolve in liquids- in this instance, sugars, carbohydrates, tannins, etc.) in the leaf tissues rather quickly. Interestingly, this "leaching stage" is known by science to be more of an artifact of lab work (or, in our case, aquarium work!) which utilizes dried leaves, as opposed to fresh ones.

Fresh leaves tend to leach these materials over time during the breakdown/decomposition process. It makes sense, because freshly fallen or disturbed leaves will have almost their full compliment of chlorophyll, sugars, and other compounds present in the tissues. (Hmm, a case for experimenting with "fresh" leaves? Perhaps? We've toyed with the idea before. Maybe we'll re-visit it?)

Cool experiments aside, this is yet another reason why it's not a bad idea to prep your leaves, because it will help quickly leach out many of the remaining sugars and such which could degrade water quality a bit in closed systems.

The second stage of the process is called the "conditioning phase", in which microbial colonization on the leaf takes place. They begin to consume some of the tissues of the leaf- at least, softening it up a bit and making it more palatable for the aforementioned detritivores. This is, IMHO, the most important part of the process. It's the "main event"- the part which we as hobbyists embrace, because it leads to the development of a large population of organisms which, in addition to processing and exporting nutrients, also serve as supplemental food for our fishes!

The last phase, "fragmentation", is exactly what it sounds like- the physical breakdown of the leaf by various organisms, ranging from small crustaceans and shrimp to fungi- and even fishes, collectively known as "shredders." It has been suggested by some ecologists that microbes might be more important than "shredders" in tropical streams.

Fauna composition differs between habitats, yet most studies I've found will tell you that Chironomidae ( insect larvae-think Bloodworms!) are the most abundant in many streams, pools, flooded forests, and "riffles" in the initial period of leaf breakdown!

The botanical material is broken down into various products utilized by a variety of life forms. The particles are then distributed downstream by the current and are available for consumption by a variety of organisms which comprise aquatic food webs.

Six primary breakdown products are considered in the decomposition process: bacterial, fungal and shredder biomass; dissolved organic matter; fine-particulate organic matter; and inorganic mineralization products such as CO₂, NH₄⁺ and PO₄³^-.

An interesting fact: In tropical streams, a high decomposition rate of terrestrial materials has been correlated to high fungal activity...these organisms accomplish a LOT!

Interestingly, scientists have noted that the leaves of many tropical plant species tend to have higher concentrations of secondary compounds and more recalcitrant compounds than do leaves of temperate species. Why do you suppose this is?

Also, some researchers hypothesized that high concentrations of secondary compounds (like tannins) in many tropical species inhibit leaf breakdown rates in tropical streams...that may be why you see leaf litter beds that last for many years and become known features in streams and river tributaries!

There's a whole lot of stuff going on in the litter beds of the world, huh?

Of course, fungal colonization of wood and botanicals is but one stage of a long process, which occurs in Nature and our aquariums. And, for many hobbyists, once we see those first signs of fungal growths or biofilms, the majority of us tend to reach for the algae scraper or brush and remove as much of it as possible- immediately! And of course, this provides some "aesthetic relief" for some period of time- but it comes right back...because botanical materials will provide a continuous source of food and colonization sites for fungal growths!

And the idea of "circumventing" this stuff is appealing to many, but the reality is that you're actually interrupting the process. It's not a "phase" that your botanical method aquarium goes through. Rather, it's how the aquarium functions on a continuous basis. Siphon the stuff out- and it comes right back. Nature abhors a vacuum, and new growths will return to fill the void, thus prolonging the process.

Why fight it?

Alteration of the botanicals durning the decomposition process 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.

All of these organisms work together- in essence, supporting each other via the processes which they engage in.

And, decomposition is a dynamic, fascinating process- part of why we find the idea of a natural, botanical-method system so compelling. Many of the organisms- from microbes to micro crustaceans to fungi- are almost never seen except by the most observant and keen-eyed hobbyist...but they're there- doing what they've done for eons.

They work slowly and methodically over weeks and months, converting the botanical material into forms that are more readily assimilated by themselves and other aquatic organisms.

The real cycle of life!

The ultimate result is the transformation to 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..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 the smallest organisms: Microbes (bacteria, fungi, and protozoa, specifically)!

Interestingly, in some wild aquatic habitats, such as the famous Peat swamps of Southeast Asia, the decomposition of leaves which fall into these waters is remarkably slow. In fact, ecologists have observed that the leaves typically do not break down.

Why?

It's commonly believed that these low nutrient waters, which are high in tannins, and highly acidic, seem to impede microbial activity. This is seemingly at odds with the understanding that passive leaching of dissolved organic compounds (DOC) from leaf litter has been found to be a major source of energy in tropical stream habitats, fueling the microbial food chains which we are so fascinated by.

No doubt the water parameters have something to do with this. These are unique habitats. Here are a few stats from the peat swamps in which some studies on leaf decomposition were conducted:

Water temperature: 25C/77F-32C/89F

pH: 2.6-3.8

TDS: 89-134mg/l

Nitrate: <0.-0.2mg/l

Dissolved oxygen: 1.8-16mg/l

In the studies, leaves of native species found along the swamps submerged in the waters of the swamps lost very little biomass, which other leaves from trees did break down more substantially. This tends to rule out the generally-held theory that ecologists have which postulates that the slow decomposition rate in the peat swamps is due to the extreme conditions. Rather, as mentioned above, it's believed that the resistance to decomposition is due to the physical and chemical properties of the leaves which are found right along the swamps.

(image by Marcel Silvius)

The reason? Well, think about it.

Leaf litter in tropical peat swamp forests builds up into peat many feet deep over thousands of years, and thus impedes nutrient cycling. And when you think about it, inputs of nutrients into most peat swamps come solely from rainfall, because rivers and streams in the region don't always flow into the swamps. In such nutrient poor, highly acidic conditions, it is more beneficial for plants to protect their leaves, rather than to replace them when subjected to elements like wind, and herbivore damage (mostly by insects) with new growth.

And interestingly, bacteria and fungi are known to be responsible for leaf breakdown in the peat swamps, because ecologists typically don't encounter aquatic invertebrates in the peat swamp which are known to ingest leaf material!

Our friends, the fungi!

Yeah, those guys again. Yet, there just one group of a diverse biome of organisms which contribute to the function of our botanical method aquariums.

By studying and encouraging the growth of this diversity of organisms, and creating a multi-faceted microcosm of life in our tanks, I believe that we are contributing to an exciting progression of the art and science of aquarium keeping!

I'm fascinated by the "mental adjustments" that we need to make to accept the aesthetic and the processes of natural decay, fungal growth, the appearance of biofilms, and how these life forms affect what's occurring in the aquarium.

It's all a complex synergy of life and aesthetic.