Looking under the leaves...extracting some useful blackwater knowledge!

As we 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 you might not know. Literally, diving just underneath the surface, 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.

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 broken down by fungi and bacteria in aquatic environments...Here's a thought to consider: Inputs of terrestrial materials like leaf litter and seed pods can leach dissolved organic carbon, rich in lignin and cellulose.  Factors like light, mineral hardness, and the bacterial community 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, 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).

These waters tend to be home to much, lower populations of insects and microorganisms as a result of the presence of tannins, but, as we've discussed before, they still host abundant life and different kinds of "food webs" to support the resident fishes and aquatic fauna which reside in them.

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...

As we know from my repeated rantings here, blackwater aquatic systems tend to have low conductivity and low levels of dissolved solids. Or, more precisely, a low content of suspended sediments, but a high content of dissolved organic matter. Soils and detritus provide the fuel for the aquatic eco systems in these rivers, such as the podzols that we've discussed here before.

And fishes, of course, actually play a part in the process of "evolving" the blackwater ecosystem. 

And, in "iagapos "(those seasonally flooded forest areas which lead to blackwater environments), these soils are conducive to good terrestrial plant growth. Fishes which reside in these habitats feed off of the materials, like fruits and seeds, which fall from the trees, or otherwise end up in the water during periods of inundation.

Interestingly, seed dispersal by fish (a process known technically as "ichthyochory") is thought to play an important role in the maintenance of the diversity of trees in these seasonally inundated forests along the main rivers of the Amazon! 

That's another interesting little tidbit of information! The terrestrial environment has significant impact on the aquatic habitat. And, in this area, aquatic life influences the land!  

That makes sense, right?

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, and perhaps even submersion-tolerant terrestrial plants) are strongly reminiscent of what happens in the wild. Sure, we typically 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?

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. The real message here is to not be afraid of learning about seemingly complex chemical and biological nuances of blackwater systems.

It can seem a bit  intimidating at first, but if you force yourself beyond just the basic hobby-oriented material out there on these topics (hint: there aren't many!), there is a whole world of stuff you can learn about!

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

And it all starts with looking under those leaves! You never know what you might find!

Stay curious. Stay undaunted. Stay diligent. Stay open-minded...

And Stay Wet.


Scott Fellman

Tannin Aquatics 







Scott Fellman
Scott Fellman


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