"Nature Guide Journal"

1 November 2001

Bluebill Lake had become "Bluebill Meadow."  In preparing to take a group to visit Coos Bay Area ponds last month, I discovered most of our local ponds have dried up.  Not too surprising for autumn on the west coast; not surprising at all for a drought year.

Bluebill Lake is technically a large pond.  While both lakes and ponds both have slower water flow than the streams and rivers that feed them, they are different from one another.

A key characteristic of ponds is that they are shallow enough for sufficient light to support green plants along the entire bottom.  The shallowness of ponds also make them susceptible to drying up completely during severe drought.

Rooted water-plants and bottom-dwelling plants grow throughout a pond, and a pond's entire shoreline is typically lined with wetland plants.  The bottom and edges of most ponds are muddy and soft:  Ponds' shallow depth and usual small size don't generate heavy waves to scour the mud from the shoreline.

Bodies of shallow water warm and cool relatively quickly, causing rather extreme differences in day- and night-time temperatures in a pond.  Sunlight penetrating to the bottom warms up the water, decreasing the amount of dissolved oxygen the water can hold.  The level of dissolved oxygen is a critical factor for life in water.

By definition, lakes are too deep—in at least some places—for bottom-dwelling plants.  Lake shorelines are more often bare than those of ponds, since the larger lakes allow greater wave development than generally found in ponds.

Overall water temperature is more constant in lakes than in ponds, although thermoclines (significant boundaries between layers of warmer surface waters and cooler deep waters) usually develop in temperate zone lakes.  In regions with drastic differences in seasonal temperatures, those layers are mixed over the year as the mean air temperatures fluctuate with the seasons.

Shallow, quiet arms of lakes, such as those found along the western edge of Lower Empire Lake in the Coos Bay Area, often function like ponds.  And, a lake may become a pond as it fills with sediment over it's lifetime.

In keys and guidebooks—as well as real life—"ponds" and "wetlands" overlap.  The ponds' shallow, soft shoreline usually produces a marsh or swamp habitat; deep regions of a marsh usually function as a pond.

Both pond-water and sunlit lake-water harbor huge numbers of microscopic plants that thrive on dissolved nutrients.  Lakes, like ponds, have life cycles that eventually end with gradual filling with sediment and the related succession to marsh, to meadow, to shrubland, to forest.  Lakes tend to live longer because they're deeper.

We ended up visiting Bluebill Meadow after visiting Weyerhaeuser Pond on our pond tour, drawn by the lush wetland-plant community thriving on the exposed pond bottom.  With luck, plenty of winter rain will return Bluebill "Lake" by spring.

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(For related information, see plant communities and frogs.)

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Wavecrest Discoveries can craft your personal discovery of this delightful part of our world by customizing one of our distinctive guided excursions.   Our walks, tours, and special activities are wonderful ways to explore this fascinating region—and are the perfect entertainment for guests.