How to Make Closed Aquatic Ecosystem Jars

Observing real life ecosystems is a great way for students to build ecological content knowledge and a way for them to use the scientific practices needed to investigate natural systems. Making closed aquatic ecosystems is a great, cost effective, way for students to understand and appreciate ecosystems in our very own back yard! This can be an ongoing study where they journal their observations and use the Scientific Method to ask questions, make hypotheses and record what they observe.

What you will need:

Clear jar with lid (best to boil and sterilize prior to collecting your sample)
Fresh water source (pond, creek, puddles, etc..)

How to make your closed aquatic ecosystem:

First scoop about 1 inch of substrate (sand/dirt) from the fresh water source's bed
Find a few nice rocks to put in the bottom
Find some leaf litter and a couple of sticks to add.
Fill 3/4 of the way with water
Add some aquatic plants found in the area (we used Pennywort) and make sure they stick out of the water some. The plants will provide food and oxygen for your ecosystem.
Close your lid (it will look mucky and gross at first, don't worry it will all settle and be surprisingly clear!)

Once you have your jar put together you can place it in a room that receives daytime sunlight. I don't suggest putting it in direct sunlight as this may trigger an algae bloom and this could be detrimental to your ecosystem. If you have a classroom with a window a good spot would be on a desk or shelf nearby.

Things to ask and talk about:

How their jar is similar to the Earth? You may get responses like, "They both have limited space" "It has inside and outside" "It has air"
What are they finding as they are making them? They may find different types of plants,rocks,and animals (I encourage you to use google to identify them. If they don't know already, show them how to use this resource.) Students will dive deep into the world around them while creating these jars. They will love getting their hands dirty, exploring different textures, noticing how the water flow affects the environment's shape and growth, notice where the small fish like to hang out, notice crayfish holes on the creek side. They may encounter caddisfly larvae casings when they look under rocks, one time we were lucky enough to encounter a Mountain Brook Lamprey, it was an amazing thing to see and learn about their life cycle. Do not add animals like fish. Small containers have a lower bioload capacity, and larger animals always produce much more bioload. This will throw off the nitrogen cycle and crash your ecosystem, also it isn't humane. Be prepared to explore and answer a lot of questions. Remember, if you are unsure please make it clear that you don't know, and suggest looking it up when they get back to the classroom. It is great to model curiosity and that it's okay to say you don't know something!
How do the plants help the animals? The plants take carbon dioxide (CO2) out of the air and, by a process called photosynthesis, use the energy from sunlight to take those carbons and string them together to make sugars (plant food), releasing the oxygen (O2) as a waste product. Every environment produces waste, but certain bacteria can break down the harmful waste products and detoxify the ecosystem. This is what makes it self sustaining. The plants take carbon dioxide (CO2) out of the air and, by a process called photosynthesis, use the energy from sunlight to take those carbons and string them together to make sugars (plant food), releasing the oxygen (O2) as a waste product.
How do the animals help the plants? The animals use oxygen as part of the process of metabolism (releasing energy from food). Animals also consume the plants (or other animals) and produce wastes that bacteria break down into the nutrients the plants can reuse.
What kind of relationship to the plants and animals have? In the right balance, they help each other survive because they each produce what the other needs, and they each use up what the other doesn't need. They work together providing what they both need, this is a mutualistic relationship.
What happens to the water? Plants and animals consume the water, however it gets excreted, purified, and reused.
What happens if plants and animals die? They are broken down by If you organisms like bacteria and fungi, and the chemicals that were part of their bodies are recycled back into new living things.
What are the two things that aren't in the bottle essential for this to work? Heat and light (from the sun)
Does your jar have a water cycle? Yes, the water gets sucked up by the plant's roots, and then gets transpired from the leaves, into condensation that drips back down into the bottom.