June 05, 2017

Aquatic plants in the flooded forests and plains of Amazonia...and in our aquariums!

With a lot of interest in our little botanical stretch of the aquarium hobby being paid to habitats like the Brazilian Igapo and Varzea floodplains/forests, we have a lot of hobbyists ask us which plants are most appropriate for this habitat.

Now, I'll be the first to admit that I am not an expert on aquatic plants by any means, and any discussion on plants which I present is by nature rather superficial and limited. However, I did do a lot of research, read a number of scientific papers, and had some good discussions with those i"n the know" about which aquatic plants are commonly associated with these habitats over the years. I was able to glean some information that might be of use to you in this regard, and with all of the interest, it seems like an appropriate time to be discussing this stuff!

There are literally dozens of species of true aquatic plants that are found in these inundated grasslands and forests, and a number of representative species or genera are commonly kept in aquariums. Most of the aquatic plant life occurs in Varzea and Igapo floodplains, both of which we've talked about before. The Varzea are seasonally-flooded forest areas, which are inundated by pH-neutral "whitewater", and can reach significant depths, whereas the Igapo are generally shallow, blackwater environments with relatively low nutrient content and acidic soils. Varzea forests are extremely rich, which leads to a very rich aquatic ecosystem when inundated, and tend to have greater density of aquatic plants. Várzea forest soils have high nutrient contents because they receive high loads of sediment (from the Andean and pre-Andean regions) from the whitewater rivers nearby.

Igapó forests, on the other hand do not receive this seasonal influx of sediments , which is why they have relatively inorganic nutrient- poor soils. Igapo waters are acidic, with a pH ranging between 4 and 5, and are rich in organic materials- particularly humic and fulvic acids. It is also thought by scientists that the seasonal inundation of the Igapo soils creates anoxic conditions, limiting plant growth in general.

So, we have two contrasting aquatic environments, with widely varying conditions available for the growth of plants. Obviously, the Varzea forests are better conditions for a wider variety of plants, with their less acidic water and higher overall nutrient availability than Igapo, which tend to be representative of a more "classic" blackwater habitat, with far less plant growth and fewer species of fishes.

The other important factor affecting plant growth in these aquatic habitats is light; or specifically, light penetration. This affects diversity of both the terrestrial grasses and aquatic plants present in the waters. In the blackwater Igapo areas, light only penetrates down to depths of 1-2 meters, and many submerged grasses and terrestrial forest plants simply die back from lack of light. And the forest canopy adds to the shading in some areas, further reducing the amounts of light available to plants.

It should hardly be surprising that the diversity of plants, both terrestrial and aquatic, which survive in the inundated season is much greater in the areas of the savannas flooded by clear, nutrient-rich waters. In fact, it was determined in one study that around 900 species of grasses alone occur in the Pantanal (Varzea ) region, with almost 250 of them considered aquatic!

(The flooded Pantanal region. Image by Alicia Yo at the English Language Wikipedia)

Okay, terrestrial grasses are interesting, but they're not something that we typically will be keeping in our aquariums, right? However, the common "Barnyard Grass", Echinochloa, is ubiquitous worldwide and would make a and interesting subject to play with...you know, planting some in rich soils and filling it with water...oh, man, that's the kind of experiment I'm into! Who's on THIS idea?

(Echinochloa- Image by Michael Becker, used under CC BY-SA 3.0)

So, what types of aquatic plants would you expect to find in these habitats? Well, in the here are a few:

Nymphaea, Polygonum, Salviania, and Pistia, and the much-loved Water Hyacinth, Eichhornia crassipes, and yeah, some species of "Amazon Sword Plants", just to name a few.

I've kept Polygonum species before (ironically, in more of a "blackwater" setting) and had great success with them, so a more "clearwater" botanical-style aquarium would no doubt really help them grow like mad!

Floating plants seem to be some of the dominant aquatic species found in both regions, with no shortage of well-known, readily varieties from which to choose. Now, their suitability for aquarium use (as opposed to ponds) is debatable, but there are numerous varieties of Water Hyacinth (Eichhornia) to play with if you're so inclined!

In the Igapo areas, the predominant aquatic plants seem to be Cabomba, Nymphaea, and Utricularia, all of which are commonly kept in aquaria or ponds.

(Nymphaea, image by TC Tao, used under CC BY-SA 3.0)

Utricularia

I have always had a soft spot for Cabomba, being one of the first aquatic plants I've ever kept. So, seeing that it's at home in a blackwater habitat is, well- comforting, lol! It's super adaptable, fast-growing, and easily obtainable...Winner!

There are some other true aquatic plants which are found in these habitats, but the options for species found in the blackwater Igapo systems are fairly limited. In the end, you may find yourself selecting plant species that are more representative of those found in these habitats, as opposed to the exact species, simply because of the need to be practical, and the desire to be creative!

That being said, the idea of incorporating aquatic plants into our botanical-style aquariums (blackwater or otherwise), is irresistible to many, and adds a new dimension to our displays, possibly attracting a wider audience of hobbyists to our little niche!

We've already seen a number of you creating impressive planted blackwater, botanical-style aquariums, and there is so much more potential for experimentation and artistic creativity...and FUN!

And with that, I exit this absolutely-by-no-means-comprehensive look at the aquatic plants of the flooded forests, leaving you with a little bit of information, and hopefully, a lot of inspiration- to try some fun stuff with your blackwater/clearwater, botanical-style aquariums!

Stay creative. Stay excited. Stay experimental. Stay motivated.

And Stay Wet.

Scott Fellman

Tannin Aquatics