Lake Transparency: A Window into Decadal Variations in Dissolved Organic Carbon Concentrations in Lakes of Acadia National Park, Maine

Abstract

A 40-year time series of Secchi depth observations from approximately 25 lakes in Acadia National Park, Maine, USA, evidences large variations in transparency between lakes but relatively little seasonal cycle within lakes. However, there are significant coherent patterns over the time series, suggesting that large-scale processes are responsible. It has been suggested that variations in colored dissolved organic matter (CDOM) are primarily responsible for the variations in transparency, both between lakes and over time and further that CDOM is a robust optical proxy for dissolved organic carbon (DOC). Here we present a forward model of Secchi depth as a function of DOC based upon first principals and bio-optical relationships. Inverting the model to estimate DOC concentration from Secchi depth observations compared well with the measured DOC concentrations collected since 1995 (RMS error < 1.3 mg C l⁻¹). This inverse model allows the time series of DOC to be extended back to the mid-1970s when only Secchi depth observations were collected, and thus provides a means for investigating lake response to climate forcing, changing atmospheric chemistry and watershed characteristics, including land cover and land use.

Collin Roesler and Charles Culbertson

Charlie and Collin met in 1996 at a dinner party in Connecticut hosted by Pieter Visscher from the University of Connecticut. It was love at first site but they lived over 3000 miles apart, Charlie in California and Collin in Connecticut. It was their common interest in aquatic systems and microorganisms that made their life together possible. Charlie and his mentor, Ron Oremland at USGS, Menlo Park, CA, had worked extensively in Mono Lake, California. They had discovered a strange photosynthetic eukaryote that made its living under extreme conditions of low light and oxygen, and high pH and salinity. Ron turned over the project for them to find the story of this organism in the years of field data that had been collected. This allowed Collin to live for a few months in California to work with Charlie at USGS. When it became clear that more work was needed to understand the environmental tolerances of the organism, Ron enabled Charlie to move to Connecticut for a few months to conduct experiments in Collin’s lab at the University of Connecticut. Collin’s student Stacey Etheridge (now DeGrasse, and another member of the dual-career club) participated in these experiments with them. Putting the field and lab work together resulted in their first joint publication (Roesler, Collin S., Charles W. Culbertson, Stacey M. Etheridge, Ralf Goericke, Ronald P. Kiene, Laurence G. Miller, and Ronald S. Oremland. “Distribution, production, and ecophysiology of Picocystis strain ML in Mono Lake, California.” Limnology and Oceanography 47, no. 2 (2002): 440–452). They joke that Mono Lake is one of the unique places that could have brought together an oceanographer and a limnological microbial ecologist.

After 3 years of across the country courtship, they made the decision to leave all their friends, two amazing jobs (permanent position at USGS and tenure-track position at the University of Connecticut), sell two beautiful houses, and move to coastal Maine. Collin was recruited to Bigelow Laboratory for Ocean Sciences by Barney Balch (who, as another member of the dual-career club, assured them that “miracles happen in Maine”) and Charlie eventually was able to transfer to the USGS Water Science Center in Augusta. Collin has since moved to Bowdoin College, where she teaches oceanography. So miracles do happen in Maine! They have good jobs which provide lots of interesting science discussions. They live with their beautiful twins, Jack and Maeva, on a lovely farm on the Sheepscot River, where the ocean and the freshwater co-mingle.