Botanicals and their "environmental impact"- a slightly closer look...

With far more than just a passing interest about tossing leaves and twigs and seed pods into my tanks, I'm a bit obsessed about some of the more "functional" aspects of these materials in the aquatic environment. 

And the reality is that there simply is no real body of work in the hobby upon which to draw for information on this aspect of our craft. Sure, there are the occasional articles about "How to aquascape with seed pods" (Okay, maybe not...) or pieces about selection of wood and stuff (barely)...but almost nothing about how these things affect the closed environment of an aquarium. (Okay, nothing that isn't found in this blog/podcast!)...

Yet, as we all delve deeper and deeper into the dark and seedy (LOL) world of botanicals, it's kind of interesting to learn a few things about them that we might not know. Literally, going just underneath the most basic level of information out there, not being afraid to search more academic stuff, you can find a lot of good information which can help you create and maintain more successful blackwater, botanical-style aquariums.

And a lot of this starts with an understanding of the botanicals themselves, and how they impact the aquatic environments in which they end up. Or, for that matter, understanding the wild aquatic habitats that we are interested in replicating in our aquariums.

And it goes beyond just the amazing aesthetics!

An interesting place to start is to simply review a bit about the very composition of the materials that we play with, like seed pods and leaves and such.

Many seed pods and similar botanicals contain a substance known as lignin. Lignin is defined as a group of organic polymers which are essentially the structural materials which support the tissues of vascular plants. They are common in bark, wood, and yeah- seed pods, providing protection from rotting and structural rigidity.

In other words, they make seed pods kinda tough.

That being said, they are typically broken down by fungi and bacteria in aquatic environments. Inputs of terrestrial materials like leaf litter and seed pods into aquatic habitats can leach dissolved organic carbon (DOC), rich in lignin and cellulose. Factors like light intensity, mineral hardness, and the composition of the aforementioned bacterial /fungal community all affect the degree to which this material is broken down into its constituent parts in this environment.

Hmm...something we've kind of known for a while, right?

So, lignin is a major component of the "stuff" that's leached into our aquatic environments, along with that other big "player"- tannin.

Tannins, according to chemists, are a group of "astringent biomolecules" that bind to and precipitate proteins and other organic compounds. They're in almost every plant around, and are thought to play a role in protecting the plants from predation and potentially aid in their growth. As you might imagine, they are super-abundant in...leaves. In fact, it's thought that tannins comprise as much as 50% of the dry weight of leaves!


And of course, tannins in leaves, wood, soils, and plant materials tend to be highly water soluble, creating our beloved blackwater as they decompose. As the tannins leach into the water, they create that transparent, yet darkly-stained water we love so much!  

In simplified terms, blackwater tends to occur when the rate of "carbon fixation" (photosynthesis) and its partial decay to soluble organic acids exceeds its rate of complete decay to carbon dioxide (oxidation).

Chew on that for a bit...Try to really wrap your head around it...

And sometimes, the research you do on these topics can unlock some interesting tangential information which can be applied to our work in aquairums...

Interesting tidbit of information from science: For those of you weirdos who like using wood, leaves and such in your aquariums, but hate the brown water (yeah, there are a few of you)- you can add baking soda to the water that you soak your wood and such in to accelerate the leaching process, as more alkaline solutions tend to draw out tannic acid from wood than pH neutral or acidic water does. Or you can simply keep using your 8.4 pH tap water! 

"ARMCHAIR SPECULATION": This might be a good answer to why some people can't get the super dark tint they want for the long term...If you have more alkaline water, those tannins are more quickly pulled out. So you might get an initial burst, but the color won't last all that long...

Okay, let's think about the biology of these ecosystems for a bit, and contemplate how some aspects of their composition and function can be applied to our aquariums.

During the rainy season in the tropics, overflowing streams flood the rainforest floor, accumulating materials which the fish communities utilize for food and shelter. And materials which fall from the surrounding trees and banks are major contributors to the productivity of this ecosystem. As the waters recede somewhat, temporary streams flow through these areas.

Interestingly, scientists have found that these streams have very little internal production of food sources for their resident fishes. Rather the food sources come from materials such as plants, fruits, leaves, and pieces of wood which come from the surrounding terrestrial environment.

Oh, and insects.

Lots of insects from the surrounding trees and "shorelines", which fall into the water.

These materials and organisms are known as "allochthonous inputs" in ecology- materials imported into an ecosystem from outside of it. This is rather interesting point. Essentially, it means that these areas, rich habitats that they are, are almost completely influenced by outside materials....

And, as one might expect- as more materials fall from the trees and surrounding dry areas, the greater the abundance of fishes and other aquatic animals which utilize them is found.

And materials will continue to fall into the water and accumulate throughout the periods of inundation, maintaining the richness of the habitat as others decompose or are acted on by the organisms residing in the water.

Not unlike an aquarium, right?

Actually, when you do the research, you find out that the fishes themselves play a significant role in shaping the overall aquatic environment...

Fishes which consume matter found in the substrate (detritivores) and other materials in the substrate (omnivores) also play a fundamental role in the transportation of organic carbon, which is a source of energy for downstream fish communities. Through their foraging activities, these fishes enhance the "downstream transport" and processing of organic material and ensure the proper functioning of the aquatic system and its biological community.

These interdependencies are really complicated- and really interesting!

And it just goes to show you that some of the things we could do in our aquariums (such as utilizing alternative substrate materials, botanicals, tolerating the presence of detritus, and perhaps even utilizing submersion-tolerant terrestrial plants) are strongly reminiscent of what happens in the wild.

Sure, we don't maintain completely "open" systems, but I wonder just how much of the ecology of these fascinating habitats we can replicate in our tanks-and what potential benefits may be realized when we do.

Yes, I think just having a bit more than a superficial understanding of the way botanicals and other materials interact with the aquatic environment, and how we can embrace and replicate these systems in our own aquariums is really important to the hobby. The real message here is to not be afraid of learning about seemingly complex chemical and biological nuances of blackwater systems, and to apply some of this knowledge to our aquatic practice.

It can seem a bit  intimidating at first, perhaps even a bit contrarian to "conventional aquarium practice", but if you force yourself beyond just the basic hobby-oriented material out there on these topics (hint once again: There aren't many!), there is literally a whole world of stuff you can learn about!

And you should. Don't just take the stuff I write/talk about here as the last word on the subject...

And the information you can gain from this process just might have an amazing impact on your aquarium practice; applications that might just lead to some remarkable breakthroughs that will forever change the hobby!

And it all starts with looking under those leaves (both metaphorically AND literally!)

You simply never know what you might find!

Stay inquisitive. Stay curious. Stay open-minded. Stay diligent. Stay obsessed...

And Stay Wet.


Scott Fellman

Tannin Aquatics 







Scott Fellman
Scott Fellman


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