Editor's note: As we move deeper into the botanical style aquarium world, more minds are opened. More new tanks are started. More new ideas are executed on. And yet, the real "boss" in charge of the whole operation is Nature. She dictates the pace, the evolution, the success of all that we do. And understanding what happens in Nature can most definitely effect what happens in our aquariums. In this guest piece by our beloved freelance biology nerd/philosopher, Johnny Archer, he touches on the emerging love affair we have with aquatics plants, and how they grow in blackwater habitats- in his own unique style, of course!
In my last article, I stated that the "Nature Aquarium" as the hobby embraces it is a lie, because nature is, well- "dirtier." I want to expand on some of those points of that article and talk more about aquatic plants in nature and how botanicals and plants have a very close relationship. For this article, I’m going to put things in categories, knowing full well that Mother Nature hates that and likes to jumble things up a bit. The perfect example of this is:
Scientist: Species cannot interbreed with one another!
Mother Nature: You sure about that?
Mother Nature: Just have a look at Neanderthal DNA
Scientist: Okay, what am I looking for?
Mother Nature: (Points at a part of Neanderthal DNA then points at the Homo sapiens DNA)
Scientist: Wait how did their DNA get into ours?
Mother Nature: How do you think it got there?
Scientist: No No, That cannot be right, we outsmarted them, cause we were more clever, but that doesn’t explain the DNA…… Which must mean……we…….” intermingled”.
Mother Nature: You weren’t smarted just more….. “kinky”
Scientist: I think I’m going to puke
When talking biology, putting things into categories is just asking to be wrong, but I will for this article because spectrums are harder to write about. Aquatic plants grow in 3 environments; in the water, in the splash zone and on the banks or floodplains. Let’s start with the first environment, the water.
Aquatic plants in the water
The first thing to say about plants growing in water is that it’s a terrible idea. The properties of water make it really difficult. Plants need light for photosynthesis, but water absorbs light really quickly. After roughly 20m in clear water, most light will be absorbed and its just blue light remaining at 20m. Red light gets absorbed within 5 meters. These values plummet as soon as you add tannins or any particulates like mud. So plants are already handicapping themselves with light for photosynthesis before I even talk about gasses.
Water holds very very little gas compared to say… Air. Blue whales are the largest creature to ever roam our planet and there is a very good reason why they have held onto their lungs rather than ditched them for gills. Their oxygen demand is soo huge for their exothermic bodies to keep warm in the ocean, water just doesn’t hold enough oxygen to satisfy their needs. One of the reasons Whale sharks can grow so large is that they are endothermic (get most of their heat from the water) so their oxygen demand is a lot smaller. Okay back to plants. Plants not only require oxygen but also carbon dioxide, and this is the limiting gas. For most plants there just isn’t enough CO2 in the water to satisfy their growth rates, and therefore they will die off.
Then there’s the issue of Nitrogen, Potassium and Phosphorus (NPK) aka macronutrients. In the terrestrial world, there are Nitrogen-fixing bacteria in soil that can use Nitrogen gas from the atmosphere and can convert it into Nitrogen compounds such as protein. Bodies of water generally require an external input of NPK from another habitat which we refer to as allochthonous material. The perfect example of this allochthonous material is from botanicals and excretions from animals that find their way from terrestrial to the aquatic environment. Which means the nutrients aren’t necessarily available to the plants in the water.
Then there is the physicality of flowing water. Aquatic plants are fragile and although they can cope with a good water flow they struggle with water at high velocity. If you’re thinking, aren’t they the same thing? Well no they are not. To give you an example a pressure washer has an extremely high velocity that can clean thick mud off a car a but has a very low flow rate. Compared with my local river which has a large flow rate but doesn’t have enough velocity to knock a duck off its feet. Aquatic plants are only able to survive where the water flow and velocity are small enough that fine particulates are able to settle like sand, silt and dead leaves. So the plants have somewhere to plant their roots.
Further up river where it's more rock and pebbles than sand, when the river floods, the river bed can become mobile as the water will pick up stones, boulders and even trees trunks and take them downstream. If you struggle to imagine what this would look like imagine the bolder scene in “Raiders of The Lost Ark”- then imagine Indiana Jones having roots instead of legs (ouch). I think you could now imagine a plant in a flooded river.
When I lay it out like this I’m surprised that any plant could survive this environment. But where there is a will, Mother Nature has a way. So the first plants that can survive are of the annoying single-celled variety, Algae. Algae have a much lower demand on all of these aspects than plants which is why it can be a bloody bugger to get rid of the darn stuff and will grow in almost all known wet environments where there is light.
Mother Nature may have found a way, but not many, the only true aquatic genera(e.i spend 100% of the lives in water) I could think of is Elodea, Egeria, Cabomba, and Vallisneria all of which live in the water fully submerged only flowering above the water line. Aponogetons also grow in water naturally but every dry season go retreat back into a tuber to conserve energy until the water level rises then they sprout new leaves, so I’m going to count them. There is also Water Lilies and floating plants (only 9 species of floating plant In our hobby) which in my eyes cheat with having their leaves above the water to be in the oxygen and carbon dioxide rich air.
So it's not just me saying water is terrible for growing plants. The clear lack of plant genera speaks for itself. All other “Aquatic” plants actually have dual citizenship spending most of their lives above water (emergent) then spending their holidays underwater (submerged) when the river & lakes floods. SO if you struggle with growing plants underwater, don’t beat yourself up because most plants have the exact same problem.
All the true aquatic plants live in slow-moving water where their roots are deeply planted in thick soil! If your thinking, "So what, most plants need soil- what's the big deal here?" What do you think the soil is made out of? Heres a boring definition for you:
“The upper layer of earth in which plants grow, a black or dark brown material typically consisting of a mixture of organic remains, clay, and rock particles.”- Google
The key here is "organic remains", which most importantly for us is from material such as botanicals. All you composters out there will know that you can compost anything organic from tree bark, leaves, fruits, potatoes peelings and even cardboard. Plants grow on the fallen botanicals, literally.
Blackwater is the river, composting botanicals
Blackwater is not perfectly suitable for many submerged plants, the tannin-rich water will block out too much light and will have little to no soil substrate (there are exceptions to this though). Blackwater habitats are the start of a crucial part of the nutrient cycle in rivers. Blackwater habitats compost the organic matter into organic remains by the use of bacteria, fungi, invertebrates and fish- all of which help with composting the botanicals into nutrient-rich soil. When the river floods, it will pick up the smallest particles and transport them downstream to where they will be deposited and will build up soils in the lower reaches of the river.
One could say without botanicals, plants couldn’t live. NO, I will say that all aquatic plants need botanicals, like fish need water. (Preach, brother! -S.F.)
Epiphytes in the splash zones
Epiphytes are plants that grow on any surface like rocks & wood and get their nutrients from the air rain and water so they don’t need soil. Damn it!! I spoke too soon. Okay, this is embarrassing, I knew I should not have dealt with absolutes in biology. Okay okay, I think I’m just going to sweep these plants under the rug…….don't mind me, nothing to see here.
Okay, there is actually an argument here. Epiphytes will absorb any nutrients within the water column Some of those nutrients may have leached out of the soil into the water that then gets splashed on to the plant. You could say botanicals do play a part here. To be honest this argument is soo weak that I’m just going to move on.
Aquatic plants on the forest floor.
Ah ha, I’m going to finish my argument strongly here! The forest floor is of particular interest to me as an Aquascaper, as this is where a lot of “aquatic” plants live most of the time. Which is why biotope enthusiast will bite your head off if they see Echniodorus sp. (Amazon Swords) in a Discus set up, as Echnidorus are found on the forest floor, not the main river channel where Discus come from. Aquatic plants love being on the forest floor, where their roots are firmly rooted into the rich organic soils topped off with leaf litter and their leaves, if the air soaking up as much CO2 as they can desire. Some of those plants will live on or close to the river bank where their roots are always submerged in the water so that they don’t dry out.
The soil in rainforests has built up over millions of years, and it can support the biggest plant ecosystems on the planet. And most of the soil comes from the likes of botanicals that have been broken down on the forest floor by thousands of different species which rely on leaf litter to support their lives, like fungi or Leafcutter Ants.
During floods, the “Aquatic” plants cannot run away, so they have to adapt, but thankfully they have everything they need. A highly nutritious soil for their nutrients- the remains of leaf litter for decomposition to produce carbon dioxide, which makes up for the reduced dissolved CO2 from the rich air. They also change their leaf morphology so they can uptake the gasses easier underwater water.
I hope you can now see that botanicals aren’t just for blackwater aquariums. They help build up soils in the rainforest, in the rivers and lakes so that aquatic plants can thrive. So to say that botanicals have no place in the "Nature Aquarium" is a lot like saying water has no place in the river.
Having botanicals in your planted aquarium is just what happens in nature.
Until next time- get those hands dirty and keep those fingers green.