It's kind of funny- the ideas and thoughts we tend to latch onto in this hobby. I have a few concepts which hare never very far from my mind, and I just keep musing on them.
Muddy bottoms and leaf litter are two of the more interesting elements in the natural aquatic ecosystems of the world.
Okay, at least to a geek like ME! (The guy who loves slogging around stinky mangrove thickets in search of...well, who knows?)
And when the two elements are combined, the result is a milieu which, if applied properly in the aquarium and managed carefully, in my opinion could yield some very interesting discoveries and possible breakthroughs.
This combination of materials is found in a number of interesting habitats, including some of the West African habitats which contain a pretty deep layer of leaves over mud- home to the interesting little Parananochromis species, for example. A discussion I had with Ted Judy a couple of years back about the habitats of these fish, which he's collected and worked with for some time, spurred me to think about how to replicate these types of habitats in our aquariums.
This habitat is somewhat different from many of the Amazonian habitats we touch on a lot here (except for the inundated forest floors, of course), in which a fine layer of white sand is more common, topped off by accumulating leaves. Both seem to foster a surprising diversity of life, on both the microbial and "macro" level.
And of course, you see these areas of mud and sediment topped off with leaves in many brackish habitats, such as estuaries and mangrove swamps. As a result of mangrove leaf drop, these waters are quite productive, and often are a bit turbid and tinted from the decaying botanical materials, even though they are alkaline and slightly salty (often anywhere from 1.003-1.010 SG). The diversity of life forms in these ecosystems is huge.
These are remarkably biodiverse, rich, and very interesting niches to study and attempt to replicate in our aquariums- and that's the realm of our "Estuary" concept and the collection of materials we offer. Much like in our blackwater "practice", the combination of these elements can create a sort of "functional aesthetic" which has lots of implications for developing fascinating aquatic displays.
In addition to being aesthetically interesting, these types of habitats are functionally "right up our alley", right? We operate in that interesting zone where substrate, shoreline, leaves, botanical materials, and wood all interact. And we're developing a good understanding of how to manage these systems long-term in our aquariums.
Now, there are a lot of interesting aspects to running an aquarium with a mix of mud and botanicals. You have the challenge of trying to balance the depth of the sandbed- deep enough for denitrification to occur, but not so deep that it becomes a burden on the biological filtration of the system. I went through this with my recent brackish tank, sort of laughing at myself, because it would be months before the roots of the mangrove propagules I secured to the woodwork would even "touch down" on the substrate...It's just sort of..."there" right now...doing something.
With mud or sediment-heavy substrates, unlike in more "inert" materials like sand and gravels, you have a more rapid dissolution of trace elements and other chemicals into the aquarium environment. And when you factor in the botanical "element" provided by leaves and such, it's that much more interesting to me!
Studies have suggested that, even in very fine sediments, denitrification occurs.
This is interesting, and is a real potential benefit for those of us who have a fascination with fine sediments and mud, because it's been established that you don't need a huge layer of it to reap the benefits it can provide! And then when you add the additional element of a layer of leaves or other botanicals, which provide tannins, humic substances, and areas for algal and fungal growth, I think you have the makings of a very "biologically rich" aquarium.
As far as what substrate materials to use to replicate these habitats, we have several options.
For the brackish habitats, there are commercially-available "mud" products which can be used to compose a substantial amount- if not all- of the substrate in your aquarium, although they can be expensive. You could also use combinations of terrestrial soils (such as used in "dirted" planted tanks) and muds. Obviously, in the pure freshwater environment, you would have a variety of planted tank substrates and inert materials from which to choose, and putting together combinations of various materials would be well worth experimenting with (and kind of fun, if you ask me!).
Now, I think it's pretty important to have good water movement in such a rich environment, not only for the transport of oxygen and dissolution of carbon dioxide, but to keep some materials like detritus, pieces of decomposing leaves, biofilms, and uneaten food in suspension in the water column.
As aquarists, of course, we can provide this with well-placed electronic water pumps, many of which have controllable features that enable you to customize flow patterns to suspend materials, drive current into different levels of the aquarium, etc.
Now, there is a sort of "art" to creating flow without disrupting the leaf litter and blowing sediment all over the aquarium, and there is no real "instruction manual" for this process. I'm afraid that it's a matter of trial and error (and blowing stuff around more than you'd like)!
That being said, the application of water movement in a system such as this is very important, and well worth the additional time it takes to get things set up correctly. I decided to use my fave Eco Tech Marine "Vortech" pumps, set at gentle "Lagoon Random" mode, to do the trick in my brackish aquarium.
And of course, in a biologically-diverse closed system which embraces the use of mud/sediment and leaves/botanicals, you need to monitor water quality and employ good husbandry- on a regular basis. Water changes are always important, as is careful feeding, stocking, and the application of other common-sense aquarium maintenance "best practices." In a self-contained, highly biologically-diverse habitat with a significant quantity of organic materials, lax husbandry is a fatal flaw.
Oh, and plants would be very applicable in the brackish-water habitat. I think that utilizing plants like the much-discussed Cryptocroyne ciliata, which does well in brackish water and loves a rich substrate, would provide multiple benefits for your aquarium, ranging from nutrient utilization/export to aeration of the soil to oxygenation. I think that in the brackish version of a "mixed element" system, plants are very much part of the equation. Or, at the very least, mangrove propagules with their roots naturally "touching down" into the substrate.
But you kind of knew that already, right?
There is so much more to explore with aquariums utilizing mud/sediments and leaves together that this piece is little more that a very "info-lite" introduction just to get you thinking about them. I'd love to see a number of you experimenting with these types of systems as we move into the Spring and Summer once again. It's a dance to really provide some interesting insight into a slightly different aquarium dynamic. And any challenges you face would, in my opinion (and experience) be more than compensated for with the truly interesting discoveries that await.
The reality is, that just like any other specialty system, such "mixed element" systems simply require some more stepped-up or specialized maintenance practices- no more difficult or unusual than any other type of setup. There are dynamics to understand, procedures to refine.
We just have to put in the effort.
I hope that this ridiculously cursory discussion on this concept has at least piqued your interest in learning more about them- and perhaps even thinking about how to incorporate these elements into your next aquarium! Wether it's simply adding some mud to an existing blackwater aquarium, or starting your own brackish water mangrove habitat aquarium, you'll be blazing some less-than-well-trodden trails.
As with some many of the ideas we discuss here, it's pretty much a "ground floor" opportunity to contribute to the growing body of knowledge about this stuff!
Stay intrigued. Stay curious. Stay motivated. Stay diligent...
And Stay Wet.