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Now that we’ve defined our topic, why do we care about it? Well, ask any farmer in Kona about priorities and they’ll inform you that soil and irrigation can be the two trickiest parts of farming (ok, after the beetle bore of course).

“What are some watershed concerns?” you may ask. Frequently, watersheds will be wider at higher elevation and narrow as they progress down the mountain. This leads to a bottlenecking effect that gives the water added force and velocity—look out erosion, here we come! Watershed erosion doesn’t just steal the soil in its path, but valuable phosphorus as well, which it then dumps into bays and disrupts their nutrient balance. Bays can become stressed and oxygen-depleted by this unwanted addition (look up eutrophication for more on this).
Fun fact: Nearly half of watershed water comes from the dew on trees up mauka! Cut down our forests and we cut down our water supply.

So how do we utilize our watersheds? A geological answer would be to make man-made basin dams. These are little valleys that can be dug in watersheds to give the water a resting place and capture flowing silt. These are not always easy or cheap to construct. A more accessible option is utilizing your ground cover. You know that tall grass you hate? The stuff you fight with a weed-wacker only to watch it pop back up next rain? Well you can take solace in knowing it is great for stemming watershed flow and capturing nutrients that would’ve otherwise run off into the bay. If this doesn’t appeal to you, here’s a general rule of thumb: The more ground cover you have (be it grass, trees or weeds), the more soil and nutrients you will capture.

Quick tip: If you’re going to use fertilizer, try a slow-release one or use less fertilizer more frequently. This technique help keep the nutrients on your farm and out of the ocean.

Our trip then took us to the suburbs of South Kona where we learned about hard surface run-off (i.e., streets and parking lots). These man-made watersheds absorb nothing and can funnel oils and other pollutants directly into the bay. There are wells located around the district, which capture some of this run-off, but most have no filters. As a result, these wells slowly fill until they overflow and the pollutants continue on their way. To quote Bobby Kennedy, these wells are a “taxpayer pollution subsidy.” It is important that we rally as a community to impose filters and standards on these wells. Simply hiding the pollutants does not solve the problem.

Glass half full: Next time you’re driving down Mamalahoa and complain that there’s no shoulder, remind yourself that narrower streets=less run off. The less hard surface we have, the healthier our island and its bays will be.

At the tale end of our adventure, we stopped by Manini Bay to look at where all this run off ends up. Does the bay look lovely to you? Well, it has been on the EPA’s impaired environments list for over ten years. We took a quick salinity sample at my favorite snorkel spot and found that the water was 25 parts salt per thousand, rather than the standard 32 parts. That is a nearly 25% salinity deprivation.

Head scratcher: Ever wonder where all the rivers are? On this island rainwater is quickly absorbed by the lava rock where it frequently finds lava tubes to funnel it to the bay. So unless you find a huge underground tube you’ll have to skip the white water rafting here.

It isn’t all bad news. Much of what we discovered on our trip is relatively new science. Being aware of our surroundings is the beginning. Recognize that your plants, trees and yes, even the tall, miserable grass we all hate can each serve a purpose in keeping the balance of our island.

Aloha from One Island!
Ryley Erhardt