“With Earth Day coming up this Saturday, Coupeville Middle School student Issaak Einterz says he’s already learned something about the natural world.In nature, everything fits together, he said. As part of a special Earth Day science project Einterz and his classmates are also finding that when human beings try to recreate some of those natural systems, the fit isn’t always as good.Our first system broke and leaked, said Bronwyn Russell, 13, who along with Einterz and other project partners Meghan Tucker, and Alisha Evola has been trying to perfect a man-made, living environmental system out of old soda bottles, plastic tubing, caulk, aluminum foil and an air pump.This week, the team’s latest model of a self-contained wetland appears to be working pretty well as it moves dirty contaminated water through a series of natural filters, such as water plants, bacteria and soils to become a livable environment for tadpoles, snails and fish.We’re trying to make it as clean as it can be without chemicals, Russell said.Several student teams from Terry Welch’s Coupeville Middle School science classes will present and explain their working wetland projects at the Greenbank Farm Saturday as part of Earth Day festivities. Welch said the students have faced numerous setbacks and failures trying to get their systems to work properly, but most have stuck with it.I’m proud of the kids, seeing how diligent they’ve been, she said.Student Sharlie Blouin, part of another team, said man-made systems based on nature could have real-life applications.There are sewer treatments that use a lot of electricity and stuff. We’re trying to see if we can use a little bit of electricity and natural plants and animals to do the same thing, she said.Success is measured regularly.So far, none of our fish are dead, said one of Blouin’s partners, Alex Platt. And the water is getting clearer every day.Student Amanda Sterling said designing natural filters may come easy to Mother Nature, but it takes good planning for the average middle-schooler.There’s a layer of dirt and a layer of sand and a layer of gravel, she said. It’s not just plain mud.The students have been working with their systems for a couple of months and are now starting to introduce new experiments, such as raising the water temperature, that might also occur in nature.We want to know if the fish will do better in a warmer or colder environment, said Sterling. She admitted that some of the design changes they’re making are more practical than scientific, however.We added a lid, she said, so the snail doesn’t get out.”