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As dynamic ecosystems, ponds feature a constant interaction among living and nonliving elements. To be effective pond stewards, your class 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, and 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, such as those suggested in Curriculum Connections. To help you plan, here's a (very) short course.
In-Ground
or Above-Ground? 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.
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 to make up for volume 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 available, but tends to be expensive.) 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 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 continues to fill with water — try to time these steps to finish simultaneously. Flexible
Pond Liner Step 1. Use a garden hose, stakes and twine, or sand to mark the outline of your pond. Next, remove the sod 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 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 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 an inch or so deep across the
soil. 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.
Plants. 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,
above), or purchase them from aquarium
or water garden suppliers, it's important to include both submergent
and floating-leaved
plants. 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.
See
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 keen
observers should keep their eyes peeled for
insects, frogs, toads, and other life forms that appear. Invigorating
Indoor Ponds
Before 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 with it, will seed your indoor pool with lots of life forms.
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Classroom Project Background Setting the Stage for an Outdoor Pond
And
Around it Goes: The Water Cycle
Water Habitat Tools from the Gardening with Kids Store Dipping Into a Pond's Ecosystem Filtered Learning: Middle Schoolers Take the Plunge NEW! Guide for School Garden Entrepreneurs
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Choosing
an Outdoor Site
Step
3. Spread about 2 inches of sand on the bottom, moisten it,
and snug the liner into it. 
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!).
