September 18, 2020

Love, life...leaf litter...

Okay, the title of this piece is kind of ridiculous, but the point of it is really simple: We love the idea of using leaf liter in aquariums. Pretty much everything that we work with in the botanical-style aquarium world is based on leaf litter!

So, like, what's the big deal?

What are the implications for leaf litter in our aquariums? They're as functional as they are "aesthetic" in our world. Decomposing leaves recruit biofilms, serve as "fuel" for the growth of fungi and microorganisms...which, in turn, provide supplemental food for our fishes.

And of course, we have to consider the impact of these materials on water quality

Dead, dried leaves such as those we favor don’t have nearly the impact on water quality, in terms of nitrate, as fresh leaves would. I’ve routinely seen undetectable nitrate levels in aquariums loaded with botanicals. This is largely because dead, dried leaves have depleted the vast majority of stored sugars and other compounds which lead to the production of nitrogenous substances in the confines of the aquarium.

To understand this more fully, let’s look at what happens when a leaf dies and falls into the water in the first place.

At some point, the leaves of deciduous trees (trees which shed leaves annually) stop photosynthesizing in their structures, and other metabolic processes within the leaves themselves begin to shut down, which triggers a process in which the leaves essentially “pass off” valuable nitrogen and other compounds to storage tissues throughout the tree for utilization. Ultimately, the dying leaves “seal” themselves off from the tree with a layer of spongy tissue at the base of the stalk, and the dry skeleton falls off the tree.

As we know by now, when these leaves fall into the water, or are immersed following the seasonal rains, they form a valuable substrate for fungi to break down the remaining intact leaf structures. And the fungi population helps contribute to the bacterial population which creates the now-famous biofilms, which consist of sugars, vitamins, and various proteins which many fishes in both their juvenile and adult phases utilize for supplemental nutrition.

And of course, as the fishes eliminate their waste in metabolic products, this contributes further to the aquatic food chain. And yeah, it all starts with a dried up leaf!

Hence, leaving leaves in to fully decay in your aquarium likely reaches a point when the detritus is essentially inert, consisting of the skeletonize sections of leaf tissue which can decay no further. Dead leaves contain largely inert forms of polysaccharides, and are reach in structures like lignin and cellulose, all of which are utilized by various microorganisms and fungi within the "food chain."

Utilizing leaf litter in our aquariums opens up all sorts of possibilities for interesting experiments. You can go with just a few leaves- or really go crazy with a deep bed of leaf litter in your tank!

I periodically discuss the idea of creating a really deep litter bed in an aquarium, to more accurately replicate some of the litter beds found in South America, Asia, Africa, and elsewhere. By "deep", I'm talking 6"- 12" (15.24cm-30.48cm). Yes, there are deeper litter beds in these areas (several feet in depth); however, for practical aquarium display purposes, I think the rational "upper limit" is likely more like the 12" (30.48cm) range.

Or, is it?

Now, there is certainly a difference between the "theoretical" and the "practical", but I can't help but think that there is something beneficial about such a deep leaf litter bed...perhaps stuff we haven't imagined, because we're too busy talking about all of the possible "downsides" of the idea.

And it's intriguing for me to contemplate how to make such an idea work. I mean, it isn't really all that much different than what many of us do now...the main difference being that we'd use MORE of the same materials.

In researching the idea of executing such a deep litter bed, I thought about what would be the main considerations when attempting to create one in an aquarium. In no particular order, here are just a few of the main concerns I have:

-The ratio of "leaves to water" in a given aquarium could be quite significant. I mean, what size aquarium do I go with? I'm also curious about the impact on the water quality and oxygen levels with that much decomposing materials "in play."

On the other hand, starting from scratch with a new system and cycling it with "bacteria in a bottle" products and/or "seeded" substrate materials would no doubt at least "kick start" the biological filtration before fishes ever enter the equation.

And, although the mass of leaves would be considered "bioload", I can't help but wonder if it would also function as a "nutrient processing" facility, much in the same way a deep sand bed does in a reef aquarium? I mean, with that much "media" surface area, could this be the case? Like, denitrification by "deep leaf litter bed!"

Maybe?

And what about the impact on pH- something aquarists debate constantly?

There have been researchers of natural leaf-litter banks who contemplate that processes which produce the low pH levels associated with these beds (sometimes down to 2.8-3.5pH!) are not caused entirely by humic acids which are frequently assumed to be the major contributor -and are not strong enough acids to produce such a low pH.

A possibility suggested by researchers is that fermentation deep within the litter banks is releasing strong organic acids such as acetic acid...Could this happen in the confines of a closed aquarium?

I'm honestly not sure, but I suppose anything is possible, right? On the other hand, as we've talked about repeatedly, even in water with little to no carbonate hardness, pH impact is likely not strong enough to drop pH into those crazy low ranges. And, with substrates present in most tanks, there is probably some degree of buffering which occurs as well.

So, what about the "biology part?"

Well, let's contemplate, for a few minutes, the role leaf litter plays in natural aquatic ecosystems.

Suffice it to say, the leaf litter bed is a surprisingly dynamic, and one might even say "rich" little benthic biotope, contained within the otherwise "impoverished" waters. And, as we've discussed before on these pages, it should come as no surprise that a large and surprisingly diverse assemblage of fishes make their homes within and closely adjacent to, these litter beds. These are little "food oasis" in areas otherwise relatively devoid of food.

The fishes are not there just to look at the pretty leaves!

Many blackwater rivers are often called "impoverished" by scientists, in terms of plankton production. They show little seasonal fluctuations in algal and bacterial populations. This is a fact borne out by many years of study by science. However, "impoverished" doesn't mean "devoid" of life. And in many cases, these populations of food organisms do vary from time to time- and the fish along with them.

As we’ve discussed repeatedly over the past couple of years, there are so many benefits to painting leaf litter in the aquarium in some capacity. Wether it’s for water conditioning, supplemental food, a home for speciality fishes, or simply for a cool-looking display. Simply overcoming our ingrained aesthetic preferences and accepting the decomposing leaves as a natural, transitory, and altogether unique habitat to cherish in the aquarium opens up so many incredible possibilities!