Although the ideal situation would be to not let excess nutrients in the rivers to begin with {and I endorse efforts get us to that place}, we have to implement programs to remove what still gets in now.
I believe that the most effective way to remove excess nutrients from our rivers is to grow plants . . . but wait, there is a catch. The only way that growing plants will effectively remove nutrients, is if you harvest what you grow. Otherwise, many of the nutrients will simply process back through the system and remain in the river. Even more important is that if you don’t harvest plant material, it will die, and the decomposition process will steal crucial amounts of oxygen from the water.
So, I am here to suggest some of the most cost effective ways to remove excess nutrients from rivers by growing and harvesting plants.
First of all, let me say this – the fact that you are harvesting plants is one of the key components of making your program cost effective – by adding value to what you are doing. If all you did was grow and harvest plants to remove nutrients, your program would be cost prohibitive, and would not make economic sense. However, when you are able to produce and harvest a product that has commercial value, it becomes far easier to justify the expense of removing nutrients from the water.
Plant # 1 – Duckweed: There are several reasons why duckweed is an excellent crop to grow to remove nutrients from our rivers. Research has shown that duckweed is an excellent nutrient sink, taking up large amounts of both nitrogen and phosphorus. Duckweed is also very fast growing, able to double it’s mass in as little as two or three days. The fact that it floats and is not rooted on the bottom is what provides for some creative and cost effective ways for it to be harvested. As long as there is a drop in elevation, duckweed can be captured in a screen, while water flows past. It is even possible to use the current of the river to power a spiral water pump that would remove duckweed (with some water), and pump it to a higher location where the crop would be captured, while the water would drain back to the river. Duckweed would be an excellent choice for removing remaining nutrients from discharge water at sewage treatment facilities. All that would be needed would be a staging pond or canal to slow the flow, and then the duckweed could be easily harvested where the water exits and flows on to the river. There already are many existing ponds and lagoons that have nutrient rich water emptying into our local rivers that could be used to grow and harvest duckweed. These could be utilized to clean our water before we go about constructing ponds or lagoons at sites that don’t have them {that would be phase II}. Duckweed is an excellent animal feed that is richer in protein than soybeans. It also makes an outstanding compost material and could be used for urban agriculture. There are many creative ways to take advantage of this opportunity. The important things is to start the conversation.
Another plant that would be easy to grow and harvest is the one that grows along the shores of the Great Miami River{Hygrophila?}. This plant dies off in the winter and therefore would need to be harvested just before this happens. This plant would also make an outstanding material for composting and could be used to help create rich urban farmland. You don’t have to grow it(no planting, weeding, watering, or fertilizing), all you have to do is harvest it. And although it would be more costly than growing alternative crops on land, you get the added benefit of removing nutrients from the river bed. It is the dual win that makes this worth considering.
Remember – the only way that growing plants will effectively remove nutreints from our rivers is if you harvest what you grow. The only way that growing and harvesting plants as a means of removing nutreints will be cost effective is if you can add or create value for what is harvested. Urban ag and growing local are two hot topics right now, and if you can combine their popularity with a means of cleaning our rivers, you will have a feasable solution to a serious problem.
The next thing we need to look at is how we can utilize the current and power of the river to collect and remove many of the leaves that end up in the water . . . but that’s another story.
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