=plants =farming =aquaculture
Water hyacinth
is one of the fastest-growing plants, and is generally considered a noxious
weed. It has a number of unusual attributes which are both good and bad.
fast-growing
In nutrient-rich water, with optimized
harvesting, WH can produce ~800 tons/hectare/year of biomass. It's ~95%
water, so that's only ~40 tons of dry mass, but that's comparable to the
biomass production from the fastest-growing grasses with optimal conditions.
That's good if you're trying to grow WH, but it also means WH can spread
quickly and kill native plants.
water content
WH
has a much higher water content than most terrestrial plants. That makes it
harder to transport, but it also means it's easy to squeeze WH for juice or
turn WH into a pumpable slurry.
mats
WH tends to
form mats connected by roots. That means it can obstruct boats and block
water pipes, but it can also make harvesting it easier.
heavy
metals
Because it collects nutrients so aggressively, WH tends
to absorb heavy metals from water. That's bad if you're trying to grow food
in polluted water, but it can be good if you're producing chemicals from
biomass and want to clean up a lake.
protein content
Because it doesn't grow tall, the dry matter of WH has a relatively high
protein content, with less cellulose than grasses. This can be good for
animal feed, but it means the biomass yield per nitrogen is less, and can be
bad for conversion to some chemical products. Cows can eat WH, and WH can
produce more protein per area than any terrestrial plant.
How cheaply could WH be produced?
This paper estimated
$40/ton dry mass in 2008, which is ~$58 with inflation in 2023. That's
somewhat cheaper than any grass can be grown, but somewhat more than some
agricultural byproducts.
That's pretty good, but it assumes that area
on freshwater lakes is available for free. There's a lot of land where crops
can't grow well, and theoretically that could be flooded to grow WH instead,
but apart from environmental concerns, the water requirements would be much
too high to make ponds with desalinated water just to grow WH, perhaps $400
/ dry ton. The evaporation rate of ponds covered by WH is
generally ~2.5x that of open water, and most areas (excluding oceans)
don't have enough water to form a lake.
It's technically possible to
farm water hyacinth on the ocean, by using plastic sheets with floating
edges to separate a layer of desalinated water from seawater, and adding
nutrients separately. The desalination alone is too expensive, and oceans
also have big waves, but this is something I thought about briefly as part
of a possible SF story setting. While it would be expensive, the potential
food production per hectare is much greater than with open seawater.