Back - What are Fens and Bogs

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I Introduction

Fens are strongly enriched peatlands (Johnson 1985) that receive their nutrients from both the atmosphere and mineral substrates (Davis 1992). "A true bog is a peat-containing wetland, a major part of whose growing surface receives no input from underlying or adjacent mineral soils" (Davis and Anderson 1991). Bogs are developed from the accumulation of peat in a fen to a level above that of the minerotrophic waters (Davis 1992). This peat accumulation happens by the natural process of succession (Larsen 1982).

Bogs and fens can be delineated by their general characteristics which include: geographic distribution, abundance, surface topography, peat depth, pH, nutrient source, productivity, decomposition and floristic diversity (Davis and Anderson 1991). Together, these characteristics create a unique ecosystem with many uses.

In the past, information on Maine peatlands has emphasized vegetation rather then surface morphology. (Worley and Sullivan 1980). However, increasing public interest and scientific inquiry has augmented the scientific database considerably during the last 15 - 20 years (Johnson 1985).

Fens are found worldwide in moist locations, and bogs are primarily in boreal moist locations (Davis and Anderson 1991) because of this fens are more numerous than bogs . Bogs are found mostly in boreal moist locations, because they need environmental conditions that "reduce decomposition of organic matter and allow for continued plant (and peat) production on raised surfaces" (Davis and Anderson 1991). Bogs also develop "only where there is sufficient excess precipitation over evapotranspiration through out the year" (Davis 1992). These favorable conditions for bog development place their southern limit for eastern North America in Maine (Davis 1992). Orono bog liesin Maine, within this favorable climate for bog development. Orono bog lies approximately at 45^o52’ latitude and 68^o45’ longitude 9USGS 1974) off of Stillwaater Avenue in Orono, Maine. It is a smaller section of the 2,5500-acre Caribou Bog (Johnson 1985). I will refer to my study area as Orono bag as did Graham (1948). See Map 1 and Map 2 for a map of Caribou Bog and the surrounding area.

II Materials and Methods

In this study I ascertained whether Orono Bog is a true bog, by examining it’s surface topography and peat depth. I also measured pH to evaluate the trophic state at each location. My study site began at the red dot painted in front of telephone pole #153 on Stillwater Ave. in Orono, Maine. The base line established for the study ran approximately northwest to a point 333.45m into the bog. All distances were measured using a pace of 2.61 ft/step. All measurements were taken in the fall of 1992.

The topography of Orono bog was determined by sampling the surface elevation and the peat depth. The elevation was determined using an Engineer's Transit and a Philadelphia Level Rod according to the Engineering field Manual published by the Soil and Water conservation Service (1979). Dr. Davis provided instructions for determining peat depth. This peat depth was then subtracted from the elevation to determine the bottom profile of the bog.

Four pH samples were collected by digging a hole and allowing it to fill with water. I collected the water and stored it at 4^oC until a pH analysis could be performed. The final pH sample was collected from surface water 4.27m along the baseline and then stored like the others. Samples were then analyzed by Dr. Tjepkema (at U-Maine).

III Results

Table 1 and Figure 1 show the results I obtained from my field work at Orono bog. In table 1, the first column shows the station #. The second column shows the distance into the bog from the red mark, which was established as a reference point of 0.00m distance along the baseline and 30.48m elevation. The third column shows the elevation in reference to the red mark. The fourth column shows the thickness of the peat at each location. The last column shows the pH at various locations. Figure 1 sums up the information in visual form.

The exact elevation of the bog surface could not be determined because the closest benchmark had been moved out of its proper position (possibly by soil creep or snow plows), not allowing for accurate enough results. Each distance in table 1 corresponds to a relative elevation determined by a simple surveying from the reference point. Station 1, 4.27m along the baseline declined 0.9m to an elevation of 29.58m. This first slope is the steepest due to the road construction between the reference point and this point. The natural landscape beyond this location begins to rise and appears unaltered by humans. The pH equals 6.00 at this location, taken from a standing pool of water.

At station 2, 9.45m along the baseline the elevation rises slightly to 29.65m. at station 3 the elevation rises to 29.62m, showing an elevation increase of only 2cm. At station 4 the elevation rises to 29.88m, with a peat thickness of 2.13m. The glacio-marine silt clay (gmsc) has at this point a relative elevation of 27.75m. station 5, rises to 29.92m, with a peat depth of 3.05m. The gmsc declines to a relative elevation of 26.87m. The pH equals 5.12. At station 6 the elevation rises to 30.20m, with a peat depth of 3.35m. The relative elevation of the gmsc declines only 2cm to 26.85cm.

Station 7 has an elevation of 30.36m, with a peat depth of 4.11m. The pH at this location equals 4.99. The next location (station 8) has an elevation of 30.21 and a peat depth of 4.57m. The gmsc is at 25.64m. Station nines elevation rises to 30.50m, with a peat depth of 5.75m. The elevation of the gmsc is 24.75m. The elevation then declines slightly at station 11 to an elevation of 30.35m, with a peat depth of 5.79m. The gmsc is at 24.56m. The pH at this station is 3.80.

The elevation begins to rise again at station 12 to 30.52m, with a peat depth of 5.49m. This puts the gmsc at an elevation of 25.03m. Station 13 has an elevation of 30.51m and station 14 had an elevation of 30.38m.

IV Discussion

As stated in the introduction Orono Bog lies in an area where Bogs are known to exist. Because of this I will compare the other features in table 2 to show that Orono bog is a true bog.

Fens are concave or flat and allow water to flow towards their centers, whereas true bogs are raised and allow excess water to flow towards their outer edges (Davis and Anderson 1991) (Davis 1992). As shown in figure 1, Orono Bog rises as you travel into it. A rise of about one meter occurs over a 333.45m distance. After a recent rain storm water, had collected in the outer area of Orono Bog. Thus the surface Topography of Orono Bog is one indicator that Orono Bog may be a true bog.

Fens have shallow peat depths and Bogs have deep peat depths (Davis and Anderson 1991). Over 7m of peat has been found in some bogs (Davis 1992). I found peat as deep 5.79m deep in Orono bog out in stations 10 and 11 of my baseline. The Shallowest peat depth was 2.13m at station 4 (where I began to measure peat depth). This indicates that Orono Bog is a true bog with a fen area and transition zone leading into the bog proper. Deeper peat depths were found in Orono bog by Graham (1948).

After I saw the above data supporting my hypothesis, I needed further information. I next looked into pH. Various sources give different values for the pH of both bogs and fens (See table 3). My samples ranged from 6.0 near the road to 3.80 at station 11. This further supports the theory that Orono bog is a true bog out past station 11 and that a transition zone lies between stations 7 and 11. The area before station 7 is most characteristic of a fen.

Fens receive their nutrients from both the atmosphere and ground water sources. Bogs receive their nutrients from the atmosphere (Davis and Anderson 1991). The nutrient source can be roughly inferred from pH. Bogs lack buffering capacity normally supplied by mineral soil nutrients. Acidic conditions develop from the organic acids that develop from organic decomposition. Fens have more buffering capacity than do bogs because of the dissolved minerals in the ground water flow. This causes them to have a higher pH than that of Bogs. The transition zone between fens and bogs is never clear, but I have approximated that orono bog is oligotrophic from 242.01m and further, but before that point there is a transition zone from minerotrophic to oligotrophic environments.

Bogs have low productivity due to their lack of nutrients, and fens can have high or low productivity due to their ability to use nutrient rich ground waters (Davis 1992). I observed as I went further into the bog that trees and shrubs were reduced in size. Sphagnum also became the dominant species further into the bog. "All bogs possess fen areas around their periphery, where productivity and diversity are greater" (Davis 1992). This also affects the floristic diversity. The more productive areas have more diversity. I observed a greater variety of plants near Stillwater Avenue, though no formal survey of the plants were taken for this study.   Click here to see some great pictures of the plants found in bogs.

V Conclusion

Orono Bog is a true bog due to its surface topography, peat depth and trophic state. I found a definite rise in the surface topography towards the center of the bog. The peat depth was also sufficient for a bog classification and the pH samples showed evidence of oligotrophic conditions in the bog.

The transition zone from fen to bog lies between stations 7 and 11. This area has a rapid increase in peat depth and the surface topography is raised above that of the fen area.

Sources of Error -

These could include using my pace to determine distance instead of a measuring tape. Not surveying to the cupola (summit) of the bog. Also the act of surveying may add some error due to the highly unstable surface. I did try to keep the level steady as possible. It is hard to tell what margin of error this introduced into my calculations for determining elevation.

Future Research-

Future research could examine the pH over a period of time (possibly different seasons) to see if there is a change in the pH of any particular location.

A laser level could also be used to determine the elevation with greater accuracy. The exact elevation of Orono bog can be determined by surveying to a known benchmark. The baseline could also be expanded to include an entire cross section of the bog

A quantitative analysis of the floral diversity, productivity and decomposition rates could have been conducted at this site. (These studies may have been conducted, but I did not research these subjects.)

Thanks for reading my paper, if you enjoyed it please let me know.

Read the references for further information on bogs.

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