Building a rainforest terrarium and determining where a soil horizon begins are two ecosystem project ideas. Building a rainforest terrarium takes two to three weeks to complete and is a group activity, and it is possible to determine where bits of plants become soil instantly in the soil horizon experiment.
Building a rainforest terrarium requires a see-through container such as a glass fish bowl, sand, potting soil, a tropical plant such as a fern, construction paper and cling wrap. After rinsing out the container, add 1/2 inch of sand to the bottom of the container, followed by 1 1/2 inches of soil. The sand and soil should be spread out separately and evenly. The tropical plant is added next, along with another inch of dirt to secure it. Trim the plant if it sticks out of the top of the container. Fully soak the soil by pouring 2 to 3 cups of water into the container, and place construction paper animals into the container. Secure cling wrap over the opening of the container, place it in partial, direct sunlight, and track growth in the next two to three weeks.
To determine the soil horizon, first consider an environment, and make a hypothesis on how deep plant foliage goes before soil becomes more consistent. Next, push a shovel straight down into the soil without mixing the layers of soil, and then look into the hole. Use a ruler to measure where bits of organic material stop and soil becomes consistent. Repeat the experiment in different settings to learn about different environments.