Reports: UNI849438-UNI8: Organic Carbon Sources and Accumulation Rates Along a Regional Transect of Meromictic Lakes, Maine

Brad Hubeny, PhD , Salem State University

This project utilizes modern lakes in Maine to study organic depositional processes that are applicable to the study of lacustrine petroleum source rocks.  Specifically, the research is designed to quantify the sources of particulate organic matter in the water column, diagenetic alteration of the organic matter during deposition, and regional patterns of organic matter fluxes to the sediment surface over time. 

Undergraduate research training has been a significant aspect of this project.  Grant funds provided financial support for four undergraduate summer research assistants.  Six senior theses were produced stemming from this project, four focused on sediment core studies, one focused on sediment trap analysis, and the final addressing particulate organic matter filtered from the lake. 

The six students who conducted senior theses associated with this PRF project are all using their experiences to assist in the next step of their careers.  One student has started a Ph.D. program at URI’s Graduate School of Oceanography and two students are currently in the application process for M.S. program in sedimentology and geophysics.  One student is currently working as a mud logger for Chesapeake Drilling, another is actively serving in the Air Force, and finally we have a student applying for public school teaching positions.  Each of these students is better prepared for their current roles after experiencing original scientific research first-hand. 

The work generated from this grant has been instrumental in gaining additional funding for related studies from both the National Science Foundation and internal Salem State University sources.   In 2011, the PI was awarded a Major Research Instrumentation grant from NSF (EAR-1126128) to acquire an analytical system for stable carbon isotope and elemental analyses, as were used as proxies with the PRF work.  The lab is now able to utilize this new elemental analyzer/isotope ratio mass spectrometer (EA/IRMS) in-house which expands research and training opportunities at Salem State.  In 2010 Hubeny was awarded a collaborative research grant through the Paleo Perspectives on Climate Change program of NSF (EAR-1003449).  Hubeny is expanding on his PRF work in Maine to conduct similar investigations of organic matter deposition in Icelandic meromictic lakes through sediment trap and core work.  Finally, funding has been obtained through the Salem State University Research Committee to obtain a sediment freeze corer to use in this PRF work, as well as to help defray other analytical costs of the project. 

A manuscript was published in the Proceedings of the National Academy of Sciences in 2011 that was partially funded by the grant.  An additional manuscript based on preliminary method development for the PRF grant is currently in peer review for publication in The Holocene.  The PI is currently synthesizing the results of student theses and other analyses, and plans to submit a manuscript in summer 2012 that assesses the regional coherency of organic matter deposition in three Maine lakes over the Holocene epoch.  These ponds include Tea Pond, Conroy Lake, and Pineo Pond, and represent the western-mountain, northern, and downeast regions of the state.    

Students have presented their research findings from this project at professional meetings.  A total of seven abstracts have been published at Geological Society of America national (2010) and Northeast Regional meetings (2011, 2012).

Over 75 meters of sediment core have been collected during the 2009-10 field seasons and are being analyzed to answer the research questions posed.  The samples are archived on campus and will provide the PI with material for future senior theses associated with organic matter deposition in Maine lakes at a number of time scales.  Additionally, new equipment such as core storage reefers, a Stratabox acoustic sub-bottom profiler, sediment traps, and a sediment freeze corer are important for the professional growth of this new investigator. 

            At the present time, we have made significant progress on each of the three research questions posed:

  1. Filtered water samples have enabled the quantification of the geochemical signature of particulate organic matter (POM) from modern lakes in Maine.  Stable carbon and carbon/nitrogen elemental data suggest mixing that the POM in the study lakes are a composite of lacustrine algae and terrestrial C3 plants. Surface sediments from these same lakes have similar stable carbon ratios to the POM, but display enrichment in the C/N ratio. This observation is likely due to early diagenetic loss of nitrogen during the sedimentation process. 
  2. Sediment traps were deployed and recovered from three study lakes during the 2009-10 year.  These funnel-type sediment traps have amplified the sedimentation signal, enabling us to analyzed each sample at <monthly resolution.  These samples have been processed, and carbon and nitrogen isotopic analyses have confirmed the similar nature of the material sedimenting out of the water column and the POM found in the upper water column.
  3. Sediment core samples are being utilized to examine variability in organic matter origin and fluxes over the late Holocene.  Low frequency variability in organic matter deposition in Tea Pond and Conroy Lake (hundreds of kilometers apart) are coherent, suggesting regional influences on the production and preservation of organic matter in these meromictic lakes.  Ongoing work is utilizing the annually-laminated sediments and additional radiocarbon dates to better constrain the age models, allowing for the examination of higher frequency coherency in the region.  In addition, sub-bottom geophysical data are permitting facies analysis in conjunction with the core studies to provide a more complete understanding of the lacustrine depositional processes.
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