How many wetlands occur in the Spring Creek Watershed? This is a typical question arising when considering the water resources of a geographic area. It is also a difficult one to answer. An easier, and perhaps more interesting, question is “How many different types of wetlands occur? In this brief synopsis, we’ll examine both questions, as we explore the abundance and diversity of wetlands in the Spring Creek Watershed.
Climate, geology, topography, and soils are the primary natural drivers that determine the characteristics of a landscape, including wetlands, floodplains, and streams. Spring Creek receives fairly consistent precipitation of about 40 inches each year. Temperatures vary seasonally, but within an expected range, and seldom above 100 or below 0 degrees Fahrenheit. Together with our temperate latitude of about 41 degrees N, precipitation and seasonal temperatures define our climate, and hence, the plant and animal communities of Spring Creek.
Next, let’s consider the geology, which is quite complex, with folded sandstone and shale ridges (Bald Eagle, Tussey, and Nittany mountains). These ridges set the topographic boundaries of the watershed, while fertile limestone valleys fill much of the lower elevations with sand barrens and the limestone walls of the Spring Creek Canyon providing even more geomorphic diversity. The soils, then, reflect these underlying features, ranging from droughty sands, to heavy clays, and most everything in between. This combination of environmental characteristics, plus the impacts of human activity over time determine the nature of wetlands and stream types.
What Types of Wetlands?
The vast majority of wetlands in Spring Creek (> 90%) are associated with streams and their floodplains, so they are classified as riverine (Figure 1). The higher elevation ridges can form saddles, where surface waters can infiltrate into the ground or form surface channels. The result is the formation of springs, sometimes developing into headwater streams with permanent flows (Figure 2), and sometimes seeping out along geologic contact zones where spring seeps and slope wetlands form. These wetlands are usually quite small in area, but contribute to the base flow of headwater streams. If gradients are low, then the flow slows, soils remain saturated, and moss or sedge peat accumulates in bogs and fens. If beavers are present, they can damn headwaters more easily than wider portions of the river downstream, further enlarging wetland extent within the watershed (Brooks et al. 1993, Brooks et al. 2013). Springs and slope wetlands provide habitat for salamanders and aquatic insects, and overwintering areas for turtles. Groundwater is released at a fairly constant temperature (low 50s degrees F), which keeps these areas nearly free of ice and snow during most winters. Turkeys and other resident birds will search these wetlands for food during colder months (Brooks et al. 1993). Thus, wetlands act as a natural buffer to extremes in temperature and precipitation.
Figure 1. Reach of Slab Cabin Run with cross vane structure helping reconnect the stream with the adjacent floodplain (Photo: Robert P. Brooks).
Figure 2. Groundwater supported stream filled with watercress (Bathgate Run, Millbrook Marsh Nature Center; Photo: Robert P. Brooks).
As tributaries intersect with broad limestone valleys, floodplains and their accompanying wetlands expand. Vertical riparian banks are formed where the meandering river channel erodes and cutHow many wetlands occur in the Spring Creek Watershed? This is a typical question arising when considering the water resources of a geographic area. It is also a difficult one to answer. An easier, and perhaps more interesting, question is “How many different types of wetlands occur? In this brief synopsis, we’ll examine both questions, as we explore the abundance and diversity of wetlands in the Spring Creek Watershed.
Climate, geology, topography, and soils are the primary natural drivers that determine the characteristics of a landscape, including wetlands, floodplains, and streams. Spring Creek receives fairly consistent precipitation of about 40 inches each year. Temperatures vary seasonally, but within an expected range, and seldom above 100 or below 0 degrees Fahrenheit. Together with our temperate latitude of about 41 degrees N, precipitation and seasonal temperatures define our climate, and hence, the plant and animal communities of Spring Creek.
Next, let’s consider the geology, which is quite complex, with folded sandstone and shale ridges (Bald Eagle, Tussey, and Nittany mountains). These ridges set the topographic boundaries of the watershed, while fertile limestone valleys fill much of the lower elevations with sand barrens and the limestone walls of the Spring Creek Canyon providing even more geomorphic diversity. The soils, then, reflect these underlying features, ranging from droughty sands, to heavy clays, and most everything in between. This combination of environmental characteristics, plus the impacts of human activity over time determine the nature of wetlands and stream types.
s into the base of ridges. Belted kingfishers and bank swallows prefer to nest in these sandy, vertical banks. Wood turtles can rest in the tangled root masses of silver maples, box elders, or sycamores that line the forested riparian corridors. Muskrats and mink also frequent these habitats, as both are capable of building burrows or dens into the banks. On the inner curve of river meanders, water velocity slows dropping gravel, sand, and sediments to form gently sloping bars where spotted sandpipers can forage, and snakes and turtles can bask.
The Spring Creek Watershed has farm ponds and several small reservoirs, but few lakes. Wherever these waterbodies occur, fringing wetlands can flourish in water depths less than about three feet. Emergent species, such as grasses, sedges, rushes, and broad-leaved forbs, or multi-stemmed shrubs like speckled alder, arrowwood, or dogwoods can form dense stands around the perimeter of these sites.
Small, shallow wetland depressions, commonly know as vernal pools or temporary ponds (Figure 3), are unusually common in the Scotia Barrens area of Spring Creek. Some were formed when depressions developed in the karst landscape, as underground solution channels or streams created cave-like spaces in the calcium-based soils causing the surface to subside. If these depressions become lined with fine sediments and clays, they may be able to hold surface water seasonally. Those that continue to erode can collapse into sinkholes. In portions of the Spring Creek headwaters, notably in the vicinity of Scotia Barrens, people historically prospecting for bog iron, sands, or clays dug shallow pits and left them open. Some of these pits filled with water, thus becoming valuable habitats for pond-dwelling amphibians (spotted salamanders, Jefferson salamanders, wood frogs) (Julian et al. 2013) and aquatic invertebrates (fairy shrimp, caddis flies, aquatic beetles, dragonflies) (Coburn et al. 2008). As the water level falls and eventually dries out as summer progresses, amphibian tadpoles metamorphose into young adults and head for cover in the surrounding forests to mature. Adults often return year after year to their natal pond (pond of their birth) to breed only for a few days. Other isolated depressions can form in floodplains, where the hydraulic forces of a flooding river scour out sediments, but do not create an outlet channel reconnecting to the stream. These floodplain depressions form another type of wetland in Spring Creek, which can host fishes and larger frog species depending on how long the water persists. Both resident and migrating waterfowl and other waterbirds may use these aquatic habitats as well.
Figure 3. Vernal pool (isolated depression) in Scotia Barrens providing habitat for pond-dwelling salamanders and frogs (Photo: Robert P. Brooks).
How Many Wetlands?
When one tries to inventory all the wetlands of Spring Creek, the task becomes quite difficult. Based on the National Wetland Inventory (NWI), there are 247 separately defined wetlands (Figure 4). The NWI, however, is quite outdated for Pennsylvania, being based on interpretation of aerial photographs taken around 1980; over 35 years ago! We know there are more wetlands than this, but a comprehensive inventory has not yet occurred.
Figure 4. Wetland types found throughout the Spring Creek Watershed based on the National Wetland Inventory (Graphic: Corina Fernandez).
There are two major factors that can alter typical patterns of wetland formation in valley floodplains. Karst landscapes form in carbonate valleys, where streams alternately flow aboveground, then belowground, entering solution channels or sinkholes. They are called sinking streams. The other factor is centuries of human activities, including farming, constructing transportation corridors, and urban development that have altered natural river flow patterns through channelization, ditching, riparian bank hardening, and changes in soil infiltration rates. Spring Creek’s valleys have been farmed extensively, removing much of the woody vegetation and influencing hydrologic patterns. Today, forests dominate the ridges and the canyon, with agriculture gradually being replaced by urban development in the valley bottoms (Figure 5). These activities result in increased impervious surfaces leading to higher stormwater runoff. In combination, these factors reduce the presence and extent of wetlands in Spring Creek (Figure 6). Because the ecological health or condition of wetlands is strongly influenced by surrounding land use, we computed several landscape metrics within a 1 km-radius circle around each wetland (Figure 7; from Riparia at Penn State, www.riparia.psu.edu). A publicly available GIS tool will soon be available on the PASDA website (www.pasda.psu.edu) where one can view the NWI wetlands and surrounding landscape stressors on a watershed basis throughout the Commonwealth.
Figure 5. Land use change in the Spring Creek Watershed (1938-2006) (Graphic: Joseph A. Bishop).
Figure 6. Land uses in Spring Creek Watershed create stressors that impact aquatic ecosystems (Graphic: Corina Fernandez).
Figure 7. Landscape Development Intensity and Impervious Surface metrics based on patterns of land uses within 1-km of each known wetland in Spring Creek Watershed. Colored circles indicate the expected health or condition (referred to as ecological integrity) for each wetland based on land use surroundings: green – high, yellow – moderate, red – low. (Graphic by: Corina Fernandez).
From the headwater streams and wetlands formed in the saddles of Tussey and Bald Eagle mountains, to the springs and slopes flowing from geologic contact zones or fractures along mountain slopes and bedrock outcroppings in the valley floors, to the steep walls of Spring Creek Canyon, and the forested floodplains of Spring Creek proper, this watershed harbors a surprising diversity of wetlands. These in turn provide varied habitats that support an amazing mix or wetland- and stream-dependent plants, invertebrates, and wildlife. In addition, we garner substantial benefits from the wetlands of Spring Creek in the form of ecosystem services, such as temporary storage of floodwaters (Figure 8), improved water quality, and water-based recreation.
Figure 8. Floodwaters overtopping banks at the confluence of Slab Cabin Run (left) and Thompson Run (right) within Millbrook Marsh. Storage of floodwaters in Millbrook Marsh reduced damage to downstream communities, structures, and habitats. (Photo: Robert P. Brooks).
Places to View and Explore Wetlands
If you want to see wetlands up close and personal in the Spring Creek Watershed, two areas stand out. At the Millbrook Marsh Nature Center (http://millbrook.crpr.org/), located off Puddintown Road, trails, including a 1,500-foot long wooden boardwalk, take you past the spring-fed Bathgate Run with its dense mats of watercress, and to the confluence of Thompson Run and Slab Cabin Run where emergent plants and wetland shrubs cover the flat surface of the 60-acre marsh. From the bird blind at the eastern end of the boardwalk, you can look east toward College Avenue along the treeline, where a large, natural fen forms. Here, highly alkaline waters seep out of the limestone/dolomite bedrock and mingle with the surface flows of Thompson Run. This rather fragile fen supports rare plant species, but it is inaccessible to most visitors. As this chapter is being written, a small, simulated fen is being built and planted along Bathgate Run near the Nature Center’s buildings. Maybe you can find time to visit this new feature in the coming years as the plants grow and the wetland matures. The second suggested area to visit is the Spring Creek Canyon. Here, the main channel of Spring Creek winds through the shady canyon walls, bordered by extensive floodplain wetlands, and a convenient walking trail accessible from several trailheads. Additional rare plant species find the cool, moist walls suitable as habitat, as do numerous species of amphibians and aquatic invertebrates. Wetlands within the Canyon’s floodplain interact with the spring-fed waters of Spring Creek to produce renown fishing opportunities.
If you are interested in classifying the types of wetlands when you visit them, refer to the simple key at the end of this article. Details about the full classification key can be found in Brooks et al. 2013).
Author: Robert P. Brooks (rpb2@psu.edu)
Brooks is Professor of Geography and Ecology, and Founder and Director of Riparia at the Pennsylvania State University. He is a practicing wetland scientist and wildlife biologist.
Works Cited:
Brooks, R. P., D. A. Devlin, and J. Hassinger (with M. C. Brittingham and G. A. Hoover). 1993. Wetlands and Wildlife. College of Agricultural Sciences, Pennsylvania State University, PA. 55pp.
Brooks, RP, MM Brinson, DH Wardrop, and JA Bishop. 2013. Hydrogeomorphic (HGM) classification, inventory, and reference wetlands. Pages 39-59, Chapter 2 in RP Brooks and DH Wardrop (eds.) Mid-Atlantic Freshwater Wetlands: Advances in science, management, policy, and practice. Springer Science+Business Media, 491+xiv pp.
Coburn, EA, SC Weeks, and SK Reed. 2008. Diversity and ecology of vernal pool invertebrates. Pages 105-126 in AJK Calhoun and PG deMaynadier (eds.), Science and conservation of vernal pools in Northeastern North America. CRC Press, Boca Raton, FL. 363pp.
Julian, JT, GL Rocco, MM Turner, and RP Brooks. 2013. Assessing wetland-riparian amphibian and reptile communities. Pages 313-337, Chapter 9 in RP Brooks and DH Wardrop (eds.) Mid-Atlantic Freshwater Wetlands: Advances in science, management, policy, and practice. Springer Science+Business Media, 491+xiv pp.
Table 1. Key for Classifying inland hydrogeomorphic wetland types in the Mid-Atlantic Region of the U.S. Descriptions and definitions are based on Cowardin et al. (1979), Brinson (1993), Cole et al. (1997, 2006), and this abbreviated key was derived from Brooks et al. (2011) tailored for the Spring Creek watershed (see also Brooks et al. 2013). Classes and subclasses are in bold. Please read footnote before using this wetland classification system.
