By Micah Moen
[birds chirping, water flowing] [music] Plants require several things to grow.
Most of us know that they need things like water, sunlight, and CO2, but plants also need a variety of nutrients as well: things like nitrogen and phosphorus. Usually, plants will get all the required nutrients from the soil through their roots. But, when the soil is bad, or there’s been a lot of erosion or leaching, farmers–or even just people trying to make their lawns green–will put down something called “fertilizer.” What makes fertilizer so “fertile” is that it’s been enriched with these nutrients that the plants need–again, mostly fixed nitrogen and phosphorus. But plants aren’t the best at soaking up every last nutrient in the soil, and it’s also hard to gauge just how much fertilizer a field needs, as soil quality can vary drastically over short distances. To be safe, farmers will usually apply excess fertilizer to a given plot of land. Better safe than sorry, y’know? But, instead of staying in the soil for years, most of the excess nutrients will be carried away by the rain or other forms of irrigation. These nutrients mix with the water and find their way into bodies of water–like ponds, lakes, reservoirs, and even the oceans sometimes. With all these nutrients added, the algae, phytoplankton, and even plants in the water do the same thing the crops in the field do: they grow. Well, actually they *explode* in numbers. This is called an “algal bloom,” and entire lakes can become covered in layers of plant growth like this. To some, this might seem like a good thing. Plants are good for the environment, right? Well… not always. First off, this floating layer of algae forms basically an impenetrable roof on the water, not allowing sunlight through to the bottom of the lake. Without the presence of sunlight, all plants below the surface cannot partake in photosynthesis– You know–metabolize, make glucose, live, that sort of stuff? But, not even this is the bad part of it all. Many plants can store enough energy in their bodies to wait out these conditions. The real problem comes when all the nutrients are used up and the water can no longer support so much life. When this happens, the excess algae, phytoplankton, and plants die off and sink to the bottom of the body of water. Here, bacteria and other decomposers feast on the dead bodies in a chemical process of decay which consumes oxygen. Now, in a usual ecosystem the amount of dead matter is relatively constant, so oxygen levels stay relatively constant as well. But, when a bloom occurs, far more organic matter is ready to decompose, and so nearly all the oxygen in the water is used in the process of decomposition, and none is left for the animals living in the water. Without this, animals that use the dissolved oxygen to breathe (so, things like fish), can actually suffocate. This causes even more death, leading to more decomposition and more oxygen usage. Basically, at this point, a positive feedback loop has been created. It can take a body of water a very long time to recover, though each one is different, and recovery depends on a lot of things, like: how many nutrients leaked into the water, how big the body of water is, what organisms are present there, and so on. When this happens in lakes, native species can be suppressed and allow invasives to come in while the environment is still disturbed. If this happens in the ocean, the lack of oxygen can cause corals to bleach and possibly even die. All around, this can greatly damage many ecosystems and leads to a decrease in biodiversity globally. Nutrient-rich runoff can also be caused by things like clear-cutting (which releases the nutrients which were kept in the soil by the plants) or also by things like animal farms (where nutrient-rich waste materials can leak into local bodies of water). And that’s eutrophication, simply put! I hope you enjoyed the video and maybe think twice before using fertilizer or clearing a forest. If you want more people to see this video, give it a like, and if you want to see more videos like this, subscribe to this channel. I’ll be back next week with another one… Thanks! 🙂