Creating a Pond Habitat in your School Garden

Submitted by editor on Tue, 03/09/2010 - 15:12

Learning with the Liquid of Life

Photo courtesy of Hamilton Heights Elementary SchoolWater makes life on the planet not just livable, but possible. All organisms are utterly dependent on it for survival. Our bodies are 80 percent water. Water covers three-quarters of the Earth's surface, but only 3 percent of that area is fresh water. The rest is oceanic salt water and more than half of that is in the form of ice.

There are lots of ways to wade into water in schoolyard gardens and habitats: exploring transpiration, experimenting with mulches and other means of conserving water, creating weather stations, restoring wetlands, and assessing the water needs of area wildlife, to name a few. Photo courtesy of Austin Independent School DistrictOne sure route to rousing students' thinking about water is through the creation of a schoolyard or classroom pond. Many teachers have discovered that ponds inspire explorations of the life and chemistry of aquatic ecosystems, along with reading, writing, and quiet reflection.

Even if your school is fortunate to have a "real" pond nearby, "growing" even a small one of their own can deepen students' understanding of the interactions among all the ecosystem's factors and players. Resourceful learners have used all sorts of humble materials to create freshwater habitats, indoors and out. No matter the container — a preformed pond liner, wading pool, plastic storage bin, or aquarium tank — it's the diversity of the habitat that counts rather than the size.

Materials

All Ponds - Container or pond liner, carpenter's level
In-Ground - Tools for excavating hole (shovels, picks), sand
Above-Ground - Cushion for plastic container (e.g., sawdust, mulch, piece of carpet)
Indoor - Sturdy plastic sheeting, light source

Planning Your Pond: Pools of Life

As dynamic ecosystems, ponds feature a constant interaction among living and nonliving elements. To be effective pond stewards, your students should have a basic understanding of these fascinating relationships. Through a class discussion, find out how much they already know about pond habitats, such as the flora and fauna they would expect to see there and what adaptations plants and animals have for living in an aquatic environment. Then find out what questions remain. This can form the basis of your pond inquiry and fuel the construction of your own watery wonder. From there, curious learners can naturally branch into other topics.

To help you plan, here's a (very) short course.

"Players" and Elements	Roles They Play
Pond Microbes	As in healthy garden soil, a rich web of microbes, including bacteria, diatoms, and microscopic animals abound in pond water and mud. Some, like algae, are producers. They photosynthesize, using light energy to manufacture food for themselves and for all other living things, and produce oxygen in the process. Others break down organic matter for other creatures to consume as well as into nutrients useful to plants. These are classified as decomposers. Others are microscopic animals that feed on algae and other microbes, and are considered consumers. Some microbes produce substances that help particles in the water to settle, reducing 'cloudy' conditions. All become fodder for creatures elsewhere in the food web. Algae (pictured at right) are probably the most noticeable of pond microbes because they mass together to form the familiar scum that forms on the water's surface and on submerged objects. Though they aren't scientifically classified as plants, some types photosynthesize.
Plants	Plants are classified as producers. Submerged plants (those growing completely under water), such as elodea and stonewort (Chara), are the pond's greatest source of oxygen. Lacking roots, they are free-floating. They compete with algae for light, carbon dioxide, and nutrients while providing shelter for pond creatures. Floating-leaved plants (leaves lie on top and roots reach the bottom), such as the lilypads at right, take in nutrients through their roots, and provide shading that keeps floating algae in check and helps moderate water temperature. Emergent plants grow along the shore, with their leaves mostly above water. Cattails and sedges are examples. They provide cover and food to insects, birds, and other animals.
Animal	Animals are consumers. Fish and insect larvae require dissolved oxygen and nutrients. Amphibians and many insects spend the juvenile stage of their life cycle submerged. Their waste products, such as ammonia, are absorbed as nutrients by plants. Snails, tadpoles, and other scavengers eat algae, plant debris, and other once-living matter.
Abiotic (non-living) Factors	The sun supplies energy to fuel all living systems on Earth. Gasses (e.g., oxygen, carbon dioxide), are required by plants and animals for photosynthesis and respiration. Minerals and nutrients (e.g., phosphorus, ammonia) are elements necessary for life processes such as metabolism and growth. And, of course, water, without which there wouldn't be a pond! It also makes up most of the volume of plant and animal cells.

Setting the Stage for an Outdoor Pond

In-Ground or Above-Ground?

Pre-formed, rigid plastic or fiberglass liners are designed for in-ground installation, but you can use them as above-ground ponds as well.

Installed, these liners have a life span of 3 to 5 years. Flexible liners of EPDM, butyl rubber, or PVC (some are tear-resistant) last about 20 to 50 years.

In regions where frost penetrates deeply, if you want plants to overwinter, plan to dig your pond or choose a liner that's at least 18 inches deep.

For an above-ground pond, a plastic wading pool, ceramic pot, or other leak-proof container works fine. If you'll place a plastic container on concrete, asphalt, or other hard surface, clear the area of stones and spread a cushioning layer of straw, sawdust, or other material beneath. On a lawn or other soil surface, use a carpenter's level and a spade to create a level spot.

Seeking out and preparing a site will require students to use some math skills, because they'll need to make sure their pond will fit a chosen spot. You might even hold a contest to see who can most closely estimate the volume or perimeter of the finished pond.

Choosing an Outdoor Site

Before scoping out a site, check with your school district administrators to identify any restrictions or safety precautions you should consider. Incorporate their requirements into your list, and set your students on the search for a place that fits the bill.

No trees, please Trees aren't the best of companions for ponds. Not only do they drop debris, which increases nutrients in the water that can result in algae bloom, but their roots can invade in-ground ponds.

On the level If you don't have a level spot, have students consider how to create one, or find an alternative to the original concept (e.g., dig a terrace into a slope and set the pond liner there, use an above-ground container in a corner of the parking lot).

Runoff Even with a level pond, excessive rain or spring meltwater can cause it to overflow. If overflow is likely in your area, design your pond with a high edge, or dig a ditch and install drainage tiles to carry overflow to a storm drain.

Water source Ponds need periodic topping-up compensate for the volume of water lost to evaporation. Make sure you're within reach of a hose or other water source for this purpose. (See more about treated water in the section Stocking Up.)

Light Pond organisms can thrive with just 5 hours of sun daily. For very small in-ground or container-based ponds, make sure they get some shade, preferably during the hottest part of the day, so water temperatures don't fluctuate too much. Students might track the sun's aspect and duration at various sites to determine which is most suitable.

Power If you plan to use a pump or fountain to increase dissolved oxygen or to create a waterfall, be sure there's an appropriately grounded electrical source nearby. (Solar-powered equipment is an option to consider.)

Installing Outdoor Ponds

Preformed Pond Liner

Step 1: Put the pond liner on the ground, and mark an outline around the edge with light-colored sand or flour.

Step 2: The hole should be the same shape as the liner, slightly wider and longer, but not as deep. (When it's done the lip of the pond should stand 2 to 3 inches above the soil level creating a gentle slope so that runoff from rainstorms won't wash debris into the pond.) Remove all rocks and roots, then get in the hole and stomp on the soil to make a firm surface.

Step 3: Spread about 2 inches of sand on the bottom, moisten it, and snug the liner into it.

Step 4: Place a smooth, straight piece of lumber across the length and width of the liner in order to take measurements with the level. Make necessary adjustments to level the pond.

Sept 5: Backfill the hole with soil or sand, tamping it in place until it's about half way up the side of the liner, then fill the pond about half way with water to settle it in place. Continue backfilling as the pond fills with water — try timing these steps to finish simultaneously.

Flexible Pond Liner

Pond suppliers can help you choose the right amount of liner material for your pond based on the dimensions (length, width, depth). Some have online calculators.

Step 1: Use a garden hose, stakes and twine, or sand to mark the outline of your pond. Next, remove the existing surface to a depth of 2 inches and about 12 inches in width around the edge of the pond. Lay a straight, smooth piece of lumber across the length and width of the area and use a carpenter's level to determine whether the edges of the area are even. Add or remove soil as needed to level the edges all around.

Step 2: Remove any objects, such as rocks and roots, that might abrade or penetrate the liner. If you've designed a pond with variable depth, just remember that in cold climates the deepest part of the pool must be at least 18 inches deep so that floating-leaved plants can root in mud that won't freeze. Once you've reached bottom, compact the soil by stomping on it (a bit of dancing fun after all that digging!).

Step 3: Line the bottom of the hole with an inch or two of soft sand. If your liner material doesn't have a bonded underlayer to protect it against abrasion and punctures, lay a piece of carpet or sturdy landscape fabric before placing the rubber liner over the surface of the pond floor.

Step 4: Next, anchor the liner's edges over the banks of the pond with stones or other heavy edging material. Adjust the liner bottom and fill the pond slowly with water, gradually pleating the large creases to stay flat, and adjusting the stones for the liner to settle.

Step 5: Arrange stones around the edges of your pond, and trim any visible lining material.

Stocking Up

By this time, you and your students should know the type of pond you're going to nurture. You may have decided to use only native plants, or perhaps opted for a Japanese design, or a scaled replica of Monet's water garden. Whatever your plans, be sure to consider what to plant around your pond as well. If you'll be harvesting wild plants and creatures, before you start, please read Pick with Caution.)

Add elements in this order:

Mud It's optional, but will seed your pond with lodes of microbes, invite more life forms more quickly, and it gives plants a place to root. Spread one to three inches of regular garden soil (not potting soil!) on the bottom of your container. If you plan to include emergent plants in your pond, heap soil along the edge to create shallows, or in the middle to form an island. Harvest some mud from a local pond, enough to spread about an inch deep across the soil base. To harvest mud, scoop from just the first couple of inches — that's where most of the microbes live. Without mud, algae and other microbes will still show up in your pond, though more slowly. Students may wonder where they've come from, and decide to investigate (for instance, algae spores are adapted to withstand long periods of drought, and they're present in soil and on organic matter).

Safe water Chlorine is designed to kill microbes, so you don't want it in your pond! Fish and some plants can't tolerate it either. If you're filling the pond with treated water, let it sit for a few days to a week to allow the chlorine to evaporate before introducing living things.

Photo courtesy of Larry NauPlants To keep algae growth in balance, plants should eventually cover about three-quarters of the surface of your pond. Whether you bring in native plants from local ponds (see Pick with Caution, below), or purchase them from aquarium or water garden suppliers, it's important to include both submergent and floating-leaved plants.
If you opt not to create a muddy bottom in your pond, you'll have to anchor your floating-leaved plants in pots of soil. Line plastic nursery pots with sheets of newspaper to block drainage holes, then fill with regular garden soil and pot up your plants. If you want to prevent soil from washing out, cover the surface with stones. You can also pot up emergent plants like cattails. Challenge students to devise a way to situate them at a depth that approximates the shallow edge of a pond (e.g., setting them on submerged brick or other heavy platform).

Fish and other creatures As exciting as they are to observe, you should limit the number of fish to what your pond can support. Too many fish release waste (nutrients) that causes algae blooms which, when decaying, remove oxygen that fish need! Some references state that a pond can support 1 inch of fish for every 5 gallons of water without needing extra oxygenation from a pump. Native fish, including goldfish and mosquito fish, can overwinter in ponds that don't freeze completely, so long as there is oxygen exchange (via a hole in the ice, for example. If you live where your pond will freeze, make sure you have a home for your fish for their winter vacation!) Non-native fish, such as koi, require highly oxygenated water, need to be fed daily, tend to eat water plants, and aren't as winter-hardy. Give the water temperature a few days to a week to equilibrate before adding fish.

If you bring in plants and mud from other ponds, you will probably bring in scavengers, such as snails, that eat algae and once-living matter on pond liners and plant stems. You can also buy scavengers at water gardening or aquarium supply stores.

Pick with Caution Never collect or disturb any plant or animal species that may be endangered or protected. Learn your state laws by contacting a natural resources agency. It's a good idea even with non-protected plants to use the following rule of thumb: never collect a plant/creature unless you can see at least six in the area. Also, always get permission from the owner of any property on which you intend to collect plants.

Photo courtesy of Jon SullivanSee what comes In the early stages of a new pond, you'll likely see an explosion of floating green algae. Don't fret. This is part of the natural process in a healthy system. Once other plants are established that provide balance and slow algae growth, the green scum should clear somewhat. Maintaining a variety of water plants and removing dead or dying matter will help. But keep in mind that in a thriving ecosystem, you shouldn't expect to see crystal-clear water. Once things have settled in, your students should keep their eyes peeled for insects, frogs, toads, and other life forms that appear.

Invigorating Indoor Ponds

Lack of an outdoor venue need not hinder your pond quest! Many classes have created thriving wetlands and ponds indoors. What's important is including representatives from each category of the Players Table above.

Photo courtesy of Hamilton Heights Elementary SchoolBefore you begin, have students discuss how an indoor habitat differs from one exposed to the elements and cycles of your climate. They might see value in the ability to control more variables (e.g., no raccoons to feast on the frogs!) and to easily make daily observations. On the other hand, what's lacking indoors that the pond inhabitants need to survive (e.g., a light source)? As students monitor their indoor pond, have them add to the lists of differences between an indoor and outdoor pond.

Containing your pond While some classrooms have ample room for wading-pool-size ponds, a small preformed pond liner (as in the picture at left) or even an aquarium can foster copious inquiries. (Two aquariums side by side create enticing observation opportunities. Try stocking them with different plants and creatures, or one with mud, one without.)

While available space is the most common limiting factor, if you have the room for a sizable pond, check the floor load capacity of your proposed site with your facilities manager. At 8 pounds per gallon, water makes an impact!

Pond-proof the floor If your floor is carpeted, spread a hefty sheet of plastic to catch spills. Remind children that linoleum floors (or the plastic sheet) are slippery when wet, and advise them to avoid splashing as much as possible during observations.

Sunshine, or something like it To oxygenate water, plants need light for photosynthesis. In a room illuminated for most of the day by sun, supplemental light may not be necessary. If light is lacking, an inexpensive fluorescent fixture, with grow lights and a timer, will do the trick. You might have students use a light meter to monitor light intensity, and choose plants that do best in those conditions. Or, they can experiment with various plants to see which will thrive.

Time to stock it Use the guidelines above to stock your pond. Importing some pond mud and some partially decayed organic material will seed your indoor pool with lots of life forms.