Protection and Management Plan for the Millbrook Marsh Nature Center
The soil types occurring on site are depicted in Map 5, based on the Centre County Soil Survey (Braker 1981). A list of hydric soils was developed by the local county office of the Natural Resources Conservation Service (formerly Soil Conservation Service). Along parts of Thompson Run is a swath of Opequon-Hagerstown (OhD, Map 5), a steeply sloping section with rapid runoff rates due to a grade of 15 to 25%. There is high to moderate erosion potential for this area. Depth to bedrock is shallow and there are limestone outcrops throughout.
At the junction of Thompson Run and East College Avenue, as well as most of the land surrounding the corridor of Slab Cabin Run and Bathgate Spring Run, soils consist of a hydric soil, Melvin Silt Loam (Mm, Map 5). Since the slope is merely 0 to 2%, runoff rates are very slow, as are rates of erosion. There is frequent flooding and ponding here, and the water table is seasonally high. This type of soil is commonly found in the flat floodplain of limestone valleys. To the west of Thompson Run, and on parts of the area previously known as Farm 12, is Hagerstown Silt Loam (HaB, Map 5) with a gentle 3 to 8% slope. This soil type and slope is moderately prone to erosion and runoff rates are moderate as well. Sinkholes and clay pans are not unusual for this classification found in valley floors of limestone uplands. Sections of 3 to 8% sloping Hagerstown Silt Loam are found near the Route 322 bypass as well as along the south edge of the site adjacent to East College Avenue. Some of this section, especially the area above the calcareous fen, consists of fill (Federal Highway Administration and Pennsylvania Department of Transportation 1981), seemingly of discarded concrete highway pavement. Based on our analysis of aerial photographs, the fill was deposited circa the late 1960s. It appears that groundwater is filtering through or under the fill, yet continues to support the fen vegetation of Millbrook Marsh. It is probable that the fen could benefit from removal of this fill, and possibly restored to a greater areal extent. Restoration potential will be discussed later.
Directly adjacent to the Route 322 bypass is a portion of Hagerstown Silt Loam with a slope of 8 to 15% (HaC, Map 5), yielding moderate to rapid runoff rates and erosion levels. Clay pans and sinkholes are possible here as well. Also adjacent to the bypass, is Opequon-Hagerstown with a slope of 8 to 15% (OhC, Map 5). The limitations are the same as those for Hagerstown Silt Loam, though in addition, depth to bedrock is shallow. There is a portion of Opequon-Hagerstown with a severe slope of 25 to 90% along the same edge of the site in which runoff is rapid and erosion high. This area has a very shallow depth to bedrock, and here too, clay pans and sinkholes may occur. In the triangular area between Thompson and Slab Cabin Runs is found Dunning Silty Clay Loam with a slope of just 0 to 2% (Du, Map 5). Runoff is very slow and erosion probability is slight except in flood situations. This is a hydric floodplain soil, with potential ponding, frequent flooding, and a high water table. Also in this triangular section, on both sides of Slab Cabin Run, are Lindside Soils with a 0 to 2% slope (Lx, Map 5). Lindside Soils are found often in the flat areas of floodplains in limestone valleys, and typically have hydric soil inclusions. Runoff is slow due to minimal grades and erosion occurs only in flood situations. As with the Melvin Silt Loam, Lindside has a seasonally high water table. One section along the southern edge of Millbrook Marsh is classified as Urban Land (Urb, Map 5), so actual soil identification was not possible. Runoff is rapid and sinkhole formation a possibility.
In general, due to a combination of overland water flow, seasonally high water tables, and flooding regimes of varying duration, much of the site consists of hydric, anaerobic soils. As stated earlier, portions of Millbrook Marsh have maintained relatively intact wetland functions and characteristics despite being drained or covered with fill. The full potential of Millbrook Marsh is not being realized now, but it is not irreparably damaged at this point in time.
On to Wetland Vegetation