By Brad Hubeny
Department of Geology

Brad Hubeny, Department of Geology

“How do we know that environmental concerns like global warming and pollution should be taken seriously? All of these changes could just be natural, right?” asked Steve, an outspoken student in my Physical Geology class.

These questions led to a lively class discussion centered on the fact that humans have only kept detailed records of environmental or climate conditions for the past few centuries. Therefore, it is difficult to understand baseline conditions and whether or not humans have altered their environment. Geologists, however, have the power to overcome this limitation by studying proxy records of environmental change that are preserved in natural archives, such as sediment, ice, and trees.

My research focuses on interpreting sediment records preserved at the bottom of lakes, marshes, and estuaries to reconstruct past environmental and climate variability. Locally, I study Sluice Pond in Lynn. This location is an excellent environmental archive, and serves as a dynamic laboratory for geology majors to conduct research and prepare for their professional lives. Sluice Pond is just one of a number of field sites that geologists at Salem State College’s Center for Environmental Science Research are studying to advance our understanding of human influence on Earth systems.

Sluice Pond is unique and it has intrigued me since I came to Salem in 2006.  Because of its small size and extreme depth (18.9m [62 feet]), the pond accumulates sediments largely undisturbed by organisms. As a result, physical and chemical properties of the sediment provide an excellent archive of changing environmental and climate conditions in the area.

Figure 1

During the Fall of 2007 James Randall (Junior geology major) and I used geophysical equipment to map out the sediment thickness and characteristics of Sluice Pond. As part of his independent study that he published last year¹, James determined that approximately 5 meters (16.5 feet) of mud has accumulated in the pond since glacial ice retreated from the area (Figure 1). Since the North Shore has been ice-free for approximately 17,000 years, this means that every 0.3m (1 foot) of sediment that we study represents about 1,000 years.

Nicole Ritch

Nicole Ritch (Class of 2008; currently employed by a local environmental consulting firm) researched the pond’s sediments for her senior research project last fall and published an environmental history for the area last spring.² She utilized a sediment core that we obtained to reconstruct an environmental history using the basic geologic principle of superposition, which tells us that older sediments are buried by younger sediments . Since the bottom of her core sample contained glacial sediment, we know the sediment spans the last 17,000 years. The full sediment chronology will be refined using radiocarbon analyses this summer (2009) thanks to a recently awarded SSC Summer Research Grant.

In her thesis, Nicole was able to reconstruct variability in past organic productivity and inputs of land-based sediment. Changes in organic productivity are fairly pronounced and show much variability (Figure 3)

Since organic productivity is influenced primarily by climatic changes (e.g., temperature, light availability, nutrients carried by wind, and precipitation), such a record is likely associated with regional shifts in climate. For instance, about halfway down the core there is a pronounced decrease in productivity. This period of low productivity could conceivably be linked to a Northern Hemisphere cooling event that is known to have occurred 8,200 years ago.

Magnetic susceptibility, which is closely coupled with erosion rates and runoff in the watershed, reveals that there has been long-term variability in the input of land-based sediments to the Sluice Pond (Figure 4). The spike in magnetic material in the top 10 cm (4 inches) of the core is accompanied by an increase in lead concentrations. The common increases are likely due to the onset of the Industrial Revolution and significant atmospheric pollution.

Emily Crescenzi (Junior geology major) is interested in advancing our understanding of human influences on the environment. As part of her upcoming senior thesis, she is planning to analyze the upper portion of

Sluice Pond sediments for a number of trace metals in 0.5 cm slices. This high-resolution study will allow her to compare the metals pollution record to local and regional industrial activity.

In addition to students conducting original research on Sluice Pond, many others are gaining valuable scientific experience. Many geology majors volunteer to assist with the field and laboratory research, and gain valuable experience in scientific procedures commonly used in environmental lake studies. A number of these students pursue similar senior research projects, and go on to employment in the environmental field.

Sluice Pond provides an excellent and unique record of environmental and climate variability that contributes to the environmental discipline, and serves as a natural outdoor laboratory for SSC geologists training to work in the environmental field.  

I acknowledge the dean of Arts and Sciences, the provost, the Graduate School, the Sluice Pond Association, and the Lynn Fish & Game Protective Association for assistance. Thanks are extended to field and laboratory colleagues who are making this work possible, including students: Nicole Ritch, James Randall, Cam Morissette, ML Crispo, Emily Cresenzi, Maria Catalano, Courtnie Ciapciak, Alan Frueh, and Alison Santos; and collaborators: Jason Sorenson (USGS), Neil Tibert (University of Mary Washington), Doug Allen (Salem State), Lisa Doner (Plymouth State University), Tim Shanahan (Woods Hole Oceanographic Institute), and Brad Moran (University of Rhode Island).

1 Randall, J., J.B. Hubeny, and N. Tibert. 2008. “Sluice Pond geophysical sub-bottom survey, Lynn, Massachusetts.” GSA Abstracts with Programs 40(2).

2 Ritch, N., and J.B. Hubeny. 2008. “Analysis of core sediments gathered from Sluice Pond (Lynn, MA) indicate post-glacial environmental conditions.” GSA Abstracts with Programs 40(2).

This article is part of ASpect’s February 2009 issue, The Cutting Edge in Research and Teaching.