There is a whole, fascinating science to river and stream structure, and with so many implications for understanding how these structures and mechanisms affect fish population, occurrence, behavior, and ecology, it's well worth studying for aquarium interpretation!
Leaf litter beds form in what stream ecologists call "meanders", which are stream structures that form when moving water in a stream erodes the outer banks and widens its "valley", and the inner part of the river has less energy and deposits silt- or in our instance, leaves.
Did you get that part where I mentioned that the lower-energy parts of the water courses tend to accumulate leaves and sediments and stuff?
It's logical, right? And it's also interesting, because, as we know, fishes and their food items tend to aggregate in these areas, and embracing the "theme" of a litter/botanical bed or even wood placement, in the context of a stream structure in the aquarium is kind of cool!
You could build upon, structure, and replace leaves and botanicals in this "framework"- like, indefinitely...sort of like what happens in the "meanders in streams!"
In Nature, the rain and winds also effect the depth and flow rates of many of the waters in this region, with the associated impacts mentioned above, as well as their influence on stream structures, like submerged logs, sandbars, rocks, etc.
Stuff gets redistributed constantly.
Is there an aquarium "analog" for these processes?
We might move a few things around now and again during maintenance, or perhaps current or the fishes themselves act to redistribute and aggregate botanicals and leaves in different spots in our aquairums.
And how we structure the more "permanent" hardscape features in our tanks has a profound influence on how botanical materials can aggregate.
So, rather than covering the whole bottom of your tank with leaves, would it be cool to create some sort of hardscape structure- with driftwood, etc., to retain or keep these items in one place..to create a "framework" for a long-term, organized, specifically-placed litter bed.
The composition of bottom materials and the depth of the channel are always changing in response to the flow in a given stream, affecting the composition and ecology in many ways. I'll probably state this idea more than once in this piece, because it's really important:
Every stream is unique. Although there are standard structural or functional elements common to many streams, each stream is essentially a "custom response" to local ecological, topographical, meteorological, and biological factors.
Permanent streams will often have different volume and material composition (usually finely-packed sands and gravels, with lots of smooth stones) than more intermittent streams, which are the result of inundation caused by rain, etc., or even so-called "ephemeral" streams, often packed with leaves and lighter sediments, which typically occur only immediately after rain events (which means they usually don't have fish in them unless they are washed into them from more permanent watercourses).
The latter two stream types are typically more affected by leaves, botanical debris, branches, and other materials. Like the igarapes ("canoe ways") of Brazil...little channels and rivulets which come and go with the seasonal rains. And then, there's those flooded Igapo forests we obsess over.
In the overall Amazon region (you knew I was sort of headed back that way, right?), it sort of works both ways, with the rivers influencing the surrounding land...and then the land "giving" some of the materials back to the rivers...the extensive lowland areas bordering the river and its tributaries, known as varzeas (“floodplains”), are subject to annual flooding, which helps foster enrichment of the aquatic environment.
Much of them come from trees.
The materials that comprise the tree are known in ecology as "allochthonous material"- something imported into an ecosystem from outside of it. (extra points if you can pronounce the word on the first try...) And of course, in the case of trees, this also includes includes leaves, fruits and seed pods that fall or are washed into the water along with the branches and trunks that topple into the stream.
You know, the stuff we obsess over around here!
Although many streams derive their food base from leaves and organic matter, there is a lot of other material present that contributes to its structure. Think along those lines when scheming your next aquarium. Ask yourself what factors would contribute to the bottom composition of the area you're taking inspiration from.
There seems to be a pervasive mindset within the botanical method aquarium hobby that you need to incorporate a wide variety of botanicals into every aquarium. I would like to go on record right now to state that this is simply untrue. You can use as little or as much diversity of materials as you'd like;
Nature doesn't have a "standard" for this!
It's a "guideline" which I believe vendors have placed into the collective consciousness of the hobby for reasons that are not entirely altruistic. Personally, I will only use a one or two types of botanical materials in a given aquarium. Maybe three, but that's typically it. This mindset was forged by both my aesthetic preferences and my studying of the characteristics of many of the natural habitats which we model our aquariums after.
They simply don't have an unlimited variety of materials present. Rather, the composition of the accumulated materials in most wild aquatic habitats is limited- often based upon the plants in the immediate vicinity, as well as other factors, like currents (when present) and winds. During storms, materials can be re-distributed from outside of the immediate environment, adding to the diversity of accumulation.
In general, one of the ecological roles of streams are to distribute materials throughout the greater ecosystem. Streams have interesting morphologies. It's interesting to consider the structural components of a stream, to get a better picture of how it forms and functions. What are the key components of streams?
Well, there is the top end of a stream, where its flow begins..essentially, its source. The "bottom end" of a stream is known as its "mouth." In between, the stream flows through its main course, also known as a "trunk." Streams gain their water through runoff, the combined input of water from the surface and subsurface.
Streams which flow over stony, open bottoms, free from natural obstacles like tree trunks and such, tend to develop a rich algal turf on their surfaces.
While not something a lot of hobbyists like to see in their tanks (with the exception of Mbuna guys and weirdos like me), algae-covered stones and rocks are entirely natural and appropriate for the bottom of many aquariums! (enter a tank with THAT in the next international aquascaping contest and watch the ensuing judge "freak-out" it causes! )
Grazing fishes, of course, will feed extensively on or among these algal films, and would be logical choices for a stony-bottom-themed aquarium. Like Labeo ("Sharks"), Darter characins, and barbs. When we think about the way natural fish communities are assembled in rivers and streams, it's almost always as a result of adaptations to the physical environment and food resources.
Now, not everyone wants to have algae-covered stones or a mass of decomposing leaves on the bottom of their aquarium. I totally get THAT! However, I think that considering the role that these materials play in the composition of streams and the lives of the fishes which inhabit them is important, and entirely consistent with our goal of creating the most natural, effective aquariums for the animals which we keep.
As a hobbyist, you can employ elements of these natural systems in a variety of aquariums, using any number of readily-available materials to do the job. And, let's face it; pretty much no matter how we 'scape a tank- no matter how much- or how little- thought and effort we put into it, our fishes will ultimately adapt to it.
They'll find the places they are comfortable hiding in. The places they like to forage, sleep and spawn. It doesn't matter if your 'scape consists of carefully selected roots, seed pods, rocks, plants, and driftwood, or simply a couple of clay flower pots and a few pieces of egg crate- your fishes will "make it work."
As aquarists, observing, studying, and understanding the specifics of streams is a fascinating and compelling part of the hobby, because it can give us inspiration to replicate the form and more important- the function- of them in our tanks!
Now, you're also likely aware of the fact that we're crazy about small, shallow bodies of water, right? I mean, almost every fish geek is like "genetically programmed" to find virtually any random body of water irresistible!
Especially little rivulets, pools, creeks, and the aforementioned forest streams. The kinds which have an accumulation of leaves and botanical materials on the bottom. Darker water, submerged branches- all of that stuff...
You know- the kind where you'll find fishes!
Happily, such habitats exist all over the world, leaving us no shortage of inspiring places to attempt to replicate. Like, everywhere you look!
In Africa for example, many of these little streams and pools are home to some of my fave fishes, killifish! This group of fishes is ecologically adapted to life in a variety of unusual habitats, ranging from puddles to small streams to mud holes. However, many varieties occur in those streams in the jungles of Africa.
And many of these little jungle streams are really shallow, cutting gently through accumulations of leaves and forest debris. Many are seasonal. The great killie documenter/collector, Col. Jorgen Scheel, precisely described the water conditions found in their habitat as "...rather hot, shallow, usually stagnant & probably soft & acid."
Ah-ah! We know this territory pretty well, right?
I think we do...and understanding this type of habitat has lots of implications for creating very cool biotope-inspired aquariums.
And why not make 'em for killifish?
So, yeah- we keep talking about "very shallow jungle streams." How shallow? Well, reports I've seen have stated that they're as shallow as 2 inches (5.08cm). That's really shallow. Seriously shallow! And, quite frankly, I'd call that more of a "rivulet" than a stream!
"Virtually still, with a barely perceptible current..." was one description. That kind of makes my case!
What does that mean for those of us who keep small aquariums?
Well, it gives us some inspiration, huh? Ideas for tanks that attempt to replicate and study these compelling shallow environments...
Now, I don't expect you to set up a tank with a water level that's 2 inches deep..And, although it would be pretty cool, for more of us, perhaps a 3.5"-4" (8.89-10.16cm) of depth is something that can work? Yeah. Totally doable. There are some pretty small commercial aquariums that aren't much deeper than 6"-8" (20.32cm).
We could do this with some of the very interesting South American or Asian habitats, too...Shallow tanks, deep leaf litter, and even some botanicals for good measure.
How about a long, low aquarium, like the ADA "60F", which has dimensions of 24"x12"x7" (60x30x18cm)? You would only fill this tank to a depth of around 5 inches ( 12.7cm) at the most. But you'd use a lot of leaves to cover the bottom...
Yeah, to me, one of the most compelling aquatic scenes in Nature is the sight of a stream meandering into the forest.
There is something that calls to me- beckons me to explore, to take not of its intricate details- and to replicate some of its features in an aquarium- sometimes literally, or sometimes,. just taking components that I find compelling and utilizing them.
An important consideration when contemplating such a replication in our tanks is to consider just how these little forests streams form. Typically, they are either a small tributary of a larger stream, with the path carved out by rain or erosion over time. In other situations, they may simply be the result of an overflowing tributary during the rainy season, and as the waters recede later in the year, they evolve into smaller streams meandering through vegetation.
Those little streams fascinate me.
In Brazil, they are known as igarape, derived from the native Brazilian Tupi language. This descriptor incorporates the words "ygara" (canoe) and "ape"(way, passage, or road) which literally translates into "canoe way"- a small body of water which forms a route navigable by canoes.
A literal path through the forest!
These interesting little tributaries areare shaded by trees at the margins, and often cut for many kilometers through dense rain forest. The bottoms of these tributaries- formerly forest floor- are often covered with seed pods, twigs, leaves, and other botanical materials from the vegetation above and surrounding them.
Although igapó forests are characterized by sandy acidic soils that have a low nutrient content, the tributaries that feed them are often found over a fine-grained, whitish sand, so as an aquarist, you a a lot of options for substrate!
In this world of decomposing leaves, submerged logs, twigs, and seed pods, there is a surprising diversity of life forms which call this milieu home. And each one of these organisms has managed to eke out an existence and thrive.
A lot of hobbyists not familiar with our aesthetic tastes will ask what the fascination is with throwing palm fronds and seed pods into our tanks, and I tell them that it's a direct inspiration from Nature! Sure, the look is quite different than what has been proffered as "natural" in recent years- but I'd guarantee that, if you donned a snorkel and waded into one of these habitats, you'd understand exactly what we are trying to represent in our aquariums in seconds!
Streams, rivulets...whatever they're called- they beckon us. Compel us. And challenge us to understand and interpret Nature in exciting new ways in our aquariums.
I think we're starting to see a new emergence of a more "holistic" approach to aquarium keeping...a realization that we've done amazing things so far, keeping fishes and plants in a glass or acrylic box with applied technique and superior husbandry...but that there is room to experiment and push the boundaries even further, by understanding and applying our knowledge of what happens in the real natural environment.
Think differently. Expand your horizons.
Stay curious. Stay creative. Stay brave. Stay studious...
And Stay Wet.