A Natural History of Millbrook Marsh,
A Wetland In An Urbanizing Setting


The 36 ha Millbrook Marsh, an exceptional collection of habitat types in an urbanizing area, consists of riparian zones, palustrine emergent wetland, palustrine scrub-shrub wetland, calcareous fen, early successional upland brush and forest, and pasture and farmland interspersed with woody hedgerows. It provides habitat for abundant flora and fauna, including many wetland species, and offers an outstanding educational opportunity to the community. The new Millbrook Marsh Nature Center encompasses 25 ha of the marsh and the remaining 11 ha are privately owned.

This paper is a compilation, synthesis and analysis of documents and research regarding the natural history of Millbrook Marsh, historically and up to the present. Information was gathered from interviews, published and unpublished papers, reports and data and personal observation.

Disturbance levels within the marsh range from minimal to severe. Some impacts upon it have ceased while others have increased. Sewage treatment plant effluent had tremendous impact upon the streams until 1983. Population growth, projected to be more than 26% over the next 20 years in the surrounding region, is causing increases in proximity to development and in stormwater. Stormwater, with its typical contaminants, is now one of the major detrimental forces acting upon numerous biotic and abiotic components of the marsh. Millbrook Marsh contains a full range of hydrological regimes from persistent saturation to dry upland areas. Two "Cold Water Fish" classified streams, Thompson Run and Slab Cabin Run, traverse and converge within the site. The morphology of Thompson and Slab Cabin Run are significantly affected by large amounts of stormwater origination in the surrounding areas that include residential, commercial, agriculture, and University land use. Bathgate Spring Run, fed by two springs off site, travels through the Nature Center area. Bathgate and the many small springs are the most consistent in discharge throughout the year, while the discharge of Slab Cabin Run varies significantly during dry seasons. The discharge of Thompson Spring seems to have decreased gradually yet significantly over the past 60 years. The geological conditions of the area result in the high water table and numerous springs. The limestone bedrock causes the alkaline conditions necessary to support the plant community of the calcareous fen. Almost 2/3 of the part emergent, part shrub fen was covered with urban fill during the late 1960s, yet it remains one of the largest in Pennsylvania.

There are at least 155 plant species in Millbrook Marsh, including the entire range from obligate wetland to upland species as well as some of special concern. Non-native invasive vegetation is another major detriment to Millbrook Marsh. Non-native plant species have increased from 20% in 1980 to 32% in 1997. A very significant increase in upland non-native shrub species has occurred in the past 50 years, with most of the change occurring in the past 10 to 15 years.

The fauna observed within Millbrook Marsh includes invertebrates and all vertebrate groups. Stream macroinvertebrate communities reflect moderate degradation due to stormwater input. Fish species richness has declined, but most species lost were warm water fish. Bird species richness is to date, including 16 wetland species. Of the 12 mammal species observed, 5 are wetland dependent.

Recommendations for Millbrook Marsh address the problems related to stormwater and invasive, non-native vegetation. Stabilization of streambanks is necessary for restoration and to prevent further degradation, as is reduction of stormwater quantity and improvement of stormwater quality. Initial baseline inventories are needed for reptiles, amphibians and mammals, as well as additional inventories in sections of the marsh that have not been formally studied. Continued research within the calcareous fen could result in recommendation for restoration. Water quality monitoring should include testing for typical stormwater contaminants, as well as inventories of stream and soil macroinvertebrates. A periodic monitoring schedule should be established to determine changes in the marsh and to determine actions that will prevent further degradation.

To obtain the greatest benefits of Millbrook Marsh, it should be protected, restored, and managed in conjunction with public access and education. With this initial Natural History of Millbrook Marsh and the Protection and Management Plan for Millbrook Marsh (Brooks et al. 1998), the wonderful variety of flora, fauna and habitats that is Millbrook Marsh can thrive and continue to be a place of inspiration, discovery, and preservation.

To Acknowledgements