The purpose of this earthcache is to provide children (and adults like me who know very little about the geologicl environment) with an opportunity to increase their knowledge-base and, like me, to develop a deeper appreciation for the world we live in. The lessons and related questions are intended to be brief, quick to answer and easy to remember for a lifetime!
This is the third earthcache in Attleboro that will take you to a vernal pool. Why do number 3 you ask? Simply this: each pool has significant difference in size, etiology, and hydroperiod...lending to a more comprehensive learning experience. It's also a 2-stage earthcache: Stage 1 takes you to a short path that leads to the southern end of the pool, stage 2 takes you to the northern end where there is kiosk describing vernal pools and their impact on the ecology and aquatic development.
Definition of Terms:
Vernal pools: (also known as ephemeral pools, autumnal pools, and temporary woodland ponds), are depressions in woodland areas that typically fill with water in the autumn or winter due to rainfall and rising groundwater.
Watershed: an area of land that contains a common set of streams and rivers that all drain into a single larger body of water, such as a larger river, a lake or an ocean. Through our watersheds, pollution is distributed far away from its original source.
Soil Permeability: is the property of the soil to transmit water and air and is one of the most important qualities to consider for fish culture. High permeability will allow fluids to move rapidly through soil.
Transpiration: is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. It is essentially evaporation of water from plant leaves.
Hydroperiod: the length of time that water is present in the pool.
Vernal pools typically remain filled with water through the spring and into summer. They usually dry up completely by the middle or end of summer each year, although some can remain filled for up to a few years. During a study of 65 pools in the Pawcatuck River watershed, it was learned that hydroperiods (Hp) vary widely among pools and even from year to year within the same pool. In 2001, for example the first pools to dry up did so in early July, and 14 pools held water throughout the year. In 2002, which was a drier year, some pools dried up as early as the Middle of May, and nearly all pools were dry by mid-September.
Pool hydroperiod is critically important because it determines which species can breed successfully in a pool. Each species of amphibian has a minimum required hydroperiod – based on the time of egg deposition and the length of the larval period.
As a result of work by Peter Paton of URI and one of his students, Bill Crouch, it is now known how long a pool must hold water if at least 95% of the larvae are to survive to metamorphosis.
Wood frogs, for example, require water until mid-July, or for about 21 weeks, starting on the first of March. Spotted salamanders need water until early October, or for about 31 weeks from the first of March. Most other pool-breeding amphibians fall between these extremes.
If a pool dries up too soon, some or all the larvae will perish. Pools with longer hydroperiods can support more species.
In general, 90 or more consecutive days of water are needed over the winter and spring to allow insect and amphibian larvae to develop. A shallow wetland with a limited watershed in a sunny location is likely to dry up every year and may not provide enough time for salamander and frog larvae to develop. However, a deep wetland with a large watershed in a shaded location may never go dry. Once the water is gone, it may be difficult to identify the area as a vernal pool. Some clues that may alert you to the presence of a seasonally dry pool include: dark stained leaves, caddis fly larvae cases, fingernail clams, aquatic snails, bright green sedges (grass-like plants), and a lack of trees growing in the depression.
To simplify habitat assessment, the URI researchers used Pawcatuck hydroperiod and egg mass data to develop 4 classes that describe a pool’s hydroperiod in most years and reflect its habitat value for amphibians: (Note: the number of weeks for each class is counted starting from March 1 of each year.)
Class 1 (< 20 weeks – drying by mid-July),
Class 2 (20-27 weeks – drying between mid-July and early September),
Class 3 (28-36 weeks – drying between early September and early November), and
Class 4 (37-44 weeks – drying after early November).
Hydroperiod class is useful for predicting pool’s potential amphibian diversity and productivity. For example, Class 3 pools generally have the most species and the most egg masses, while Class 1 pools have fewest species and the fewest egg masses.
The following factors and their relationship to each other influence how often a pool dries up:
- Water depth
- Annual precipitation and evaporation
- Soil permeability
- Watershed size (amount of water that runs into the wetland from surrounding land)
- Amount of sunlight
- Transpiration from trees, shrubs, and plants growing in and around the wetland
Vernal ponds are good for the physical environment as well. They help protect watersheds by capturing and holding water, allowing time for the water to seep into the surface and recharge groundwater supplies. This reduces the amount of water runoff, lessens erosion and decreases the potential for flooding. Vernal ponds also capture sediment, thereby protecting water quality in nearby streams and rivers.
When a vernal pool obtains official certification status in Massachusetts, it is protected under the Wetlands Protection Act (WPA) regulations. The protections under this law often extend to up to 100 feet beyond the pool’s boundaries. Certified pools also receive protection under the following:
- Title 5 of the Massachusetts Environmental Code
- Section 401 of the Federal Clean Water Act
- The Massachusetts Surface Water Quality Standards which relate to Section 401, and
- The Massachusetts Forest Cutting Practices Act.
Documentation for vernal pool certification has three components: evidence of its existence, mapping that identifies its location, and an observation form completed by an interested person.
Geological factors:
Vernal pools are geologic depressions that can form in a variety of ways. According to Pennsylvania Natural Heritage Website, the geological factors include:
Floodplains - when a stream overflows its banks entering the floodplain. Some of the overflow pockets do a good job of retaining water and become vernal pools. If this continues over the years it can lead to the creation of vernal pool habitats in the form of oxbow wetlands.
Glaciers - glaciers created many isolated depressions through freezing, thawing and erosion that fill with rain water and snowmelt. This process is similar, in fact, to the way in which kettles are created.
Sag Ponds - sag ponds form when surface water gathers in depressions formed by easily dissolved bedrock (such as limestone) underneath an impermeable soil layer. Eventually the soil sags and water gathers in the depression.
Pingos – Pingos are formed by freezing and thawing processes on moist mountainous slopes. The upper layers of soil thaw first and slowly slide over the underlying frozen soil. The result is a landscape peppered with crescent-shaped wetlands.
Human Activities - some vernal pools are created deliberately by people who wish to create wildlife habitat or to replace a seasonal wetland that was destroyed. Other pools are inadvertently created during any kind of surface disruption (mining, roadside ditches, agricultural fields, etc.) that creates shallow depressions that hold water long enough to support seasonal pool wildlife.
Please send the CO answers to the following questions in order to earn your smiley for this Earthcache. It will not be necessary to wait for a response from them to log your find. One of the members of the Attleboro Geocachers Alliance will contact you if there are any concerns or questions with your responses.
1. About the pool….
a. What is the approximate width and length of the pool? Include the time of year that you visited the pool area, and how that may have impacted the width/length.
***If the vernal pool has dried up for the season, please answer 1b.***
b. If you arrived during a dry season, what evidence did you observe that verified the existence of a vernal pool?
2. Which geological factor has more than likely contributed to the formation of this vernal pool, and what characteristics did you observe to support your choice?
3. Does this pool have a high or low soil permeability rate, and what evidence do you have to support your decision?
4. Which Hp class best describes this pool, and what evidence do you have to support your decision?
5. (Optional) Take a picture of you with the pool area behind you.