Urban ecosystems and green spaces are paramount to the mental well-being of communities. Lakes and ponds in particular provide a critical venue for recreational opportunities from swimming and fishing in the summer, to ice-skating in the winter, and in some cases provided drinking water to local communities. Because of their proximity to residential and industrial developments, urban ponds are also vulnerable to local sources of pollution such as road and lawn runoff and factory effluent. No pond typifies both the importance and vulnerability of urban ponds better than Providence’s Mashapaug Pond.
Mashapaug Pond has received considerable attention from scientists and local activists throughout the years. For an excellent overview of the sociological importance of the pond as well as information on how local industrial development have affected the pond and community, refer to the Urban Pond Procession website and video archives. For his PhD thesis at Brown University, Bernabo reconstructed vegetation communities around the lake using pollen assemblages in a sediment core. Settlement by Europeans and later industrial development activity are both reflected in changes in the pollen spectra. One of the largest polluters, historically, was the Gorham Silver Company, which likely released considerable heavy metal and organochemicals into the pond and along the shoreline in the late 1800’s. While the silver company has long-closed, scientists wonder about the long-lasting legacy of such pollution. Currently, the RI EPA advises strongly against eating fish from the pond as well as swimming in the pond. Efforts are underway to assess the recovery of the pond post-contamination and to establish baseline criteria for managing the pond in the future.
As part of the efforts surrounding Mashapaug Pond, Brown University undergraduate Sophia Rudin (advisors: Dave Murray, Tim Whitfield), is reconstructing the history of heavy metal pollution using two methods. First, she is comparing metal concentrations in plants collected today with plants collected over 100 years ago and stored in Brown’s Herbarium collection. Secondly, and this is where I come in, she is using lake sediment cores to reconstruct the ecological changes and heavy metal changes that have occurred since the mid-1800’s. Preliminary analysis of the sediment core shows a very obvious heavy metal signature of industrialization, and importantly, a gradual return towards baseline conditions (pre-industrialization sediments had essentially no heavy metals), although baseline conditions have not yet been achieved, and may not ever. Along with the heavy metal changes, there are clear changes in diatom assemblages and primary productivity, which are more likely linked to phosphorus and nitrogen pollution over the same period of industrialization. Investigation is ongoing.
Here are photographs from the sediment coring expedition, which occurred in October, 2016. Sophia Rudin, Dave Murray, and I had an excellent day to core this lake.