Water, soil, weather, fishes...

Have you very thought about how water reaches all of the wild aquatic systems of the world? I mean, it's got to get there some way, right? So, how does it reach the ponds, lakes, streams, and rivers and forest floors of the world?

Well, some simply falls into the body of water directly from the sky, and that's that. Some is a result of other overflowing streams and rivers (like, ya' know- those flooded Igapo forests we talk about!). Inputs of precipitation falling over the area of an aquatic habitat are transferred to the habitat via a number of different pathways.

It's surprisingly complicated.

There's like a whole field of science devoted to studying this process! It's called Hydrology, and it's incredibly interesting...As fish geeks, we're probably already acquainted with this field of study, at least tangentially! 

So, water comes from a variety of sources, reaching a myriad of ecological niches. However, not all of the water has such an easy journey on its way into our favorite aquatic habitat!

Even in the case of rainwater, some of it simply lands on tree leaves in the surrounding area and evaporates. This is a process scientists call "interception", and accounts for the fact that not all water makes it to the ground. Water that does reach the ground enters the soil through a process called infiltration. slowly percolating down to soil areas known as the "saturated zone"- and as you'd imagine, this is where the fun really begins! (to a soil geologist, at least!)

The soil properties control the infiltration capacity; these include things like soil permeability, the presence of vegetation and plant roots, and how much water is already in the soil. Through what is known as "ground water flow", ultimately, the water finds it way into our favorite aquatic habitats. It's important to note that soil texture ( the relative proportion of sand, silt and clay particles within the mix) affects infiltration rates. 

Sandy soils like the "podzols", common to forested areas of South America that we've talked about have higher permeability than some clay-based soils. In some really arid areas a "crust" can form on the soil surface, decreasing the permeability. And of course, the thickness of the soil directly affects how much water the soil can actually absorb.

And, in many cases, the substrate composition and its relationship with water has direct impact on the life forms which inhabit these aquatic systems. In the case of some habitats, like vernal pools, which are filled with water seasonally, the substrate is of critical importance to the aquatic life forms which reside there.

Let's talk killies for a second!  One study of the much-loved African genus Nothobranchius indicated that the soils are "the primary drivers of habitat suitability" for these fish, and that the eggs can only survive the embryonic period and develop in specific soil types containing alkaline clay minerals, known as "smectites", which create the proper soil conditions for this in desiccated pool substrates.

The resulting "mud-rich" substrate in these pools has a low degree of permeability, which enables water to remain in a given vernal pool even after the surrounding water table may have receded! And, of course, a lot of decaying materials, like plant parts and leaf litter is present in the water, which would impact the pH and other characteristics of the aquatic habitat.

Interestingly, it is known by ecologists that the water in these pools may stay alkaline despite all of this stuff, because of the buffering capacity of the alkaline clay present in the sediments!

And, to literally "cap it off"- if this impermeable layer were not present, the vernal pools would desiccate too rapidly to permit the critical early phases of embryonic development of the Nothobranchius eggs to occur.

Yes, these fishes are tied intimately to their aquatic environment.

(Image by Andrew Bogott, used under CC BY-S.A. 4.0)

The fascinating concept of embryonic diapause ( a form of prolonged, yet reversible developmental arrest) is well-known to scientists and lovers of annual killies. The occurrence and length of time of diapause varies from species to species, yet is considered by scientists to be an evolutionary adaptation and ecological trait in various populations of Nothobranchius, tied directly into the characteristics of the ephemeral habitats in which these fish reside!

So, yeah- the relationship between water and soil is actually a remarkably complex one, with biological implications that we probably haven't thought about very much as hobbyists. Studying how water gets to the aquatic habitats- how it creates them- is a critical key to understanding the needs, behaviors, and adaptations of our fishes!

During that journey into the (aquatic) habitats, materials like humic substances, minerals, etc. will be absorbed into the water from the surrounding soil. Yeah...that's the interesting part: The surrounding geography and geology have as much to do with the ultimate water characteristics as anything else! Like so many things in Nature, everything is somehow interrelated!

Once again, bringing it all back to a more practical aquarium point of view, I can't help but wonder if working with different types of substrate materials (soils, sands, etc.) in our "makeup water" containers could yield some similar effects to those we see when we steep leaves and botanicals in the water. Could the right combination of soils in both our makeup water containers and even in the aquarium create even more realistic water conditions for our fishes and aquatic plants?

One can only wonder...

It makes a ton of sense.

We're seeing more and more specialized "aquatic soils" for plants which are designed to simulate some of the natural habitats in which they are found. Well, fishes are typically found in those habitats, too, right?

Why should the plants have all the fun?

Wouldn't it make sense to utilize some of these specialty substrates, or substrates comprised of some of these components in tanks which feature fishes and not just plants (or even devoid of plants?). What potential benefits for our fishes could be gained by using these more "technical" aquatic plant substrates in our fish-centric botanical-style blackwater aquariums? 

We're sure as hell going to try to find out! The "Nature Base" line of specialized premium substrates is going to debut soon, and we think it just might change the way we think about substrates in the hobby.

Like, we're busy designing aquatic displays around the substrate, and its form and function...

Stay tuned for way more on this later this summer!

And one more thing to erstwhile copycats of the Tannin brand, of which there have been a few:

"In order to be irreplaceable, one must always be different..." - Coco Chanel

Like I've alluded to previously- it's gonna get real weird real soon. Too many vendors are getting into the botanical game, slinging leaves and pods and just sort of "commoditizing" the whole thing- and that's a sure sign that it's time for Tannin to push beyond...Let's just say that we're going to go WAY beyond, in ways we're pretty confident that no one else in the hobby/industry has- and leave it at that for now... 

Oaky, commercial plug and micro-rant/warning aside, let's dive back in to the topic at hand...

With water finding its way into the streams, rivers and other areas from so many sources, there is probably so much we can learn from finding out more about the surrounding areas  themselves, and how water ultimately makes it into the bodies of water we are so obsessed with. This is an area of study in the hobby that's really wide open for advancement, IMHO.

The possibilities are endless here!

In a blackwater environment, the color is a visual indicator of an influx of dissolved materials that contribute to the "richness" of the environment. Indeed, a blackwater environment is typically described as an aquatic system in which vegetation decays, creating  tannins that leach into the water, making a transparent, acidic water that is darkly stained, resembling tea.

Despite the appearance, as a general rule, blackwater rivers are lower in nutrients than clear rivers. They have very low concentrations of major ions, such as sodium, magnesium, potassium, and calcium, and lower conductivity and typically low levels of dissolved solids. Think about what that means for just a second, and about the many factors that influence the water characteristics of these unique habitats.

Wouldn't it be interesting, when contemplating more natural biotope/biotype aquariums, to study and take into consideration the surrounding geology and physical characteristics of the habitat?  

As we know now, the influence of factors like soil, and the presence of terrestrial materials like seed pods, leaves, and branches play a huge role in the chemical composition and appearance-of the water. It's really no different in the aquarium, right? Tannins from wood and botanical materials will leach into the water, providing the characteristic "tint" that we've become so accustomed to in our little niche.

Studying the characteristics of the igapo and varzea forests of Amazonia is just a start...these are the "textbook" examples of geologic influence on the aquatic environment- something that we can really run with in our biotopic interpretations of this habitat.

Yes, I also have this irresistible curiosity about the potential of botanical-influenced substrates to foster denitrification. With the diverse assemblage of microorganisms and a continuous food source of decomposing botanicals "in house", I can't help but think that such "living substrates" create a surprisingly diverse and utilitarian biological support system for our aquariums.

I think that the idea of an "enriched substrate" will become an integral part of the overall ecosystems that we create. Considering the substrate as both an aesthetic AND functional component- even in "non-planted" aquariums, opens up a whole new area of aquarium "exploration."

And its impact on water is already an obsession to many of us, right?

I envision that the future of mainstream aquarium practice may include creating such a substrate as simply part of "what we do." Adding a mix of botanical materials, live bacterial and small organism cultures, and even some "detritus" from healthy aquatic systems may become how we establish systems.

It's not some amazing "revolution"- it's simply an evolution of practices that we've been playing with peripherally for decades in the hobby.

It's all about what happens when water, soil, weather, and fishes interact.

Stay excited. Stay fascinated. Stay studious. Stay brave. Stay creative. Stay diligent...

And Stay Wet.


Scott Fellman

Tannin Aquatics 

Scott Fellman
Scott Fellman


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