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71.17° W
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41.8
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/
CorgLOI%<1
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>4
Shoreline from RIGIS
0 1 2 3 40.5Kilometers
Brown University Narragansett Bay Sediment Project
Corg% in surficial sediments
Total Carbon and NitrogenCarbon and nitrogen concentrations for all three cores begin to increase in the mid- to late- 1800s around the time that anthropogenic lead deposition began. Each profile shows a significant increase in the late 1800s that corresponds with rapid population growth and construction of the Providence sewer system. From these profiles, we can see the evo-lution of the modern productivity gradient, with high to low productivity from North to South. This data also supports the hypothesis that ocean water was the main source of nu-trients to the Bay before the mid-1800s; baseline C and N levels for core 3 are much lower than cores 8 and 17, which may be because this location received less ocean water than the other two. Overall, these records offer strong evidence for anthropogenic eutrophica-tion in the 20th century.
Carbon to Nitrogen RatioThe C/N records for both cores 3 and 8 show an abrupt increase around the time of in-dustrial lead deposition, followed by a gradual decrease to today. This suggests that the
relative contribution of marine organic matter has steadily increased since the mid 1800s, which may correspond to higher algae growth and eutrophic conditions. The core 17 C/N profile is much more steady with a slight decrease in the top 20cm, which may also corre-spond to an increase in algae growth.
Carbon and Nitrogen IsotopesPreliminary nitrogen isotope data for core 8 shows an increase in the top 15cm of the core, roughly the past 30-50 years. This may be caused by increased ammonia discharge from NB wastewater treatment facilities since 1980 upgrades to secondary treatment. A higher ammonia content in the water column may also increase plant production and further en-hance eutrophication, since it can be used more readily than other nitrogen forms.
The carbon isotope profile for core 8 forms an interesting contrast to the C/N record. δ13C results have much more noise prior to lead deposition than C/N, but their profiles roughly mirror one another at about 1850. These results suggest that the contribution of terrestrial organic matter increased abruptly around 1850, but has steadily decreased since then.
Narragansett Bay History and Eutrophication Policy Timeline
1740-1780: RI plantations reach their peak (Hubeny et al. 2008)
1850-1880: Farms decline in Rhode Island, while large scale industrial production begins (Hubeny et al. 2008)
1871: The Providence public water supply opens. Soon after, the Provi-dence sewer system opens (Oczkowski et al. 2008, Nixon et al. 2008)
1890: The Field’s Point wastewater treatment facility (largest in the state) is constructed; nitrogen inputs to the Bay are increasing rapidly (King et al. 2008)
Mid-1900s: N inputs to Upper Bay reach plateau (Vadeboncoeur et al. 2010)
1972: Congress passes the Clean Water Act, which creates the infrastruc-ture for all water pollution monitoring and enforcement. Sewage treat-ment plants around the US upgrade to full secondary treatment, while the Fields Point plant begins to fail
Early 1980s: Fields Point and Bucklin Point WWTFs receive repairs and upgrade to secondary treatment
1998: EPA launches National Strategy for Development of Regional Nutri-ent Criteria, and in subsequent years creates nutrient criteria guidance manuals to help states set nutrient standards
2004: The RI State Assembly passes legislation ordering a 50% reduc-tion in nitrogen inputs from wastewater treatment facilities through up-grades to tertiary treatment
Today: Some RI wastewater treatment facilities have upgraded to ter-tiary treatment to meet reduction goals, but many including Fields Point have not. However, by completing these upgrades, reducing atmospheric deposition of N, and reducing fertilizer use, it may be possible to signifi-cantly lower nitrogen inputs to the Bay (Vadeboncoeur et al. 2010)
Narragansett Bay History and Eutrophication Policy Timeline
An Historical Analysis of Primary Productivity in Narragansett Bay Sediment CoresDevon Y. Cupery and Warren L. Prell
Department of Geological Sciences and the Center for Environmental Studies, Brown University
Eutrophication is defined as an increase in the supply of organic matter to an aquatic ecosystem, often caused by ex-cess nutrients from wastewater treatment facilities, fertilizers, and farm waste (Nixon 2009). These nutrients stimulate algae growth, and as this plant matter decomposes, bacteria con-sume dissolved oxygen in the water. This leaves less for other aquatic organisms and can cause large fish kills and significant economic damage to the fishing industry.
A decade ago, Narragansett Bay experienced a number of serious fish kills, including the 2003 Greenwich Bay fish kill where over one million fish died. Rhode Island lawmak-ers moved to address eutrophication in 2004 and mandated a 50% reduction in nitrogen output from treatment centers, the major source of nutrients to the Bay. In addition, the EPA has taken steps in recent years to promote development of nutri-ent criteria for US water bodies. These nutrient management actions create a need for better historical understanding of nutrient cycles and primary productivity in Narragansett Bay. This research will further scientific understanding of the Bay’s response to changes in nutrient inputs, and may help scien-tists and policy makers predict how the Bay will respond to future nitrogen reductions.
Introduction
Sediment CoresOver the course of this undergradu-ate thesis project, I will analyze 8-10 sediment cores collected from points along Narragansett Bay’s productivity gradient to understand historical pat-terns in aquatic plant growth. Here I am presenting results from three of these cores that represent the upper, mid, and lower parts of the Bay. Each sediment core is 0.5-1.5 meters in length, which offers up to 500 years of history. Cores are collected from a small boat using manual push piston cores that are 7.5-10 cm in diameter.
Measurements of Productivity and ChangeIn the coming months I plan to analyze these 8-10 sediment cores for five indicators: carbon and nitrogen concentrations, their stable isotopes δ15N and δ13C, and the carbon to nitrogen ratio (C/N). Here I display carbon and nitrogen concentration data as well as the C/N for three cores, plus δ15N and δ13C for one core. Total carbon and nitrogen approximate marine primary productivity, nitrogen isotopes describe sources of nitrogen in the Bay and how it is processed in the water column, and both the C/N ratio and carbon isotopes are used to describe the amount of organic matter from land versus water.
Analysis and DatingTotal carbon and nitrogen in the sediment cores are measured using a CE Instruments Model NC2100 elemental analyzer, and δ15N and δ13C are evaluated with a Thermo Delta V Plus isotope ratio mass spectrometer. In addition, each core is run on a GEOTEK core logger and Innov-X Systems Alpha 4000 Handheld XRF, which records den-sity and magnetic susceptibility of the core. These measurements help to assess the core’s quality and provide a preliminary dating framework. In order to create a more precise age model, we will date selected cores in an external lab using radioisotope analyses of Pb-210, Cs-137, and C-14, as well as the onset of Ambrosia (ragweed) and Rumex pollen.
Methods
Q: How has primary productivity in Narragansett Bay changed with increases in anthropogenic nutrient loading, and how does this response vary throughout the Bay?
H: Narragansett Bay’s sedimentary record will reflect post-industrial human influences on carbon and nitrogen cycles that correspond to eutrophication of the Bay. These signals will be strongest in the upper bay, close to wastewater treatment
facilities that supply much of the Bay’s nitrogen.
Question and Hypothesis
References Hamburg, S.P., Pryor, D., Vadeboncoeur, M.A. “Nitrogen Inputs to Narragansett Bay: An Historical Perspec-tive.” Ecosystem-Based Management: Narragansett Bay in the 21st Century. Eds. Desbonnet A., Costa-Pierce B.A. New York: Springer, 2008. Springer, Berlin, pp. pp 177–210.
Hubeny, J. B., King, J. W., and Cantwell, M., 2008, “Anthropogenic influences on estuarine sedimentation and ecology: examples from the varved sediments of the Pettaquamscutt River Estuary,” Rhode Island, J Paleolim-nol, DOI 10.1007/s10933-008-9226-2
King J., Hubeny J.B., Gibson C., Laliberte E., Ford K., Cantwell M. et al. “Anthropogenic Eutrophication of Nar-ragansett Bay: Evidence from Dated Sediment Cores.” Ecosystem-Based Management: Narragansett Bay in the 21st Century. Eds. Desbonnet A., Costa-Pierce B.A. New York: Springer, 2008. pp 211–232.
Nixon, Scott W., 2009, “Eutrophication and the Macroscope,” Hydrobiologia, Vol. 629, No. 1.
Nixon, S., Buckley, B., Granger, S., Harris, L., Oczkowski, A., Fulweiler, R., Cole, L. “Nitrogen and Phosphorus Inputs to Narragansett Bay: Past, Present, and Future.” Ecosystem-Based Management: Narragansett Bay in the 21st Century. Eds. Desbonnet A., Costa-Pierce B.A. New York: Springer, 2008. pp 101–175.
Vadeboncoeur, M. A., Pryor, D. Hamburg, S.H., 2010, “Modeled Nitrogen Loading to Narragansett Bay: 1850-2015,” Estuaries and Coasts, DOI 10.1007/s12237-010-9320-3.
AcknowledgementsMany thanks to the Brown Environmental Fellows Program, which is supported by The Henry David Thoreau Foundation, The Silverton Foundation through a grant to the Swearer Center for Public Service, the Environmental Change Initiative, and the Center for Environmental Studies.
I am also grateful for guidance from mentors Tim Herbert, Chris Deacutis and Don Pryor, and to David Murray, Joe Orchardo, Alex Chuman, Maria Dunlavey, Caitrin Watson, and Lolly Lim for lab and field work assistance.
For further information, please contact me at [email protected].
Total modeled nitrogen inputs to Narragansett Bay since 1850. Figure from Vadeboncoeur et al. 2010
N > > > S
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Discussion
Fellow expeditioners Luke Rohde and Dan Lowry digging a piston core into the mud
Innov-X Systems Handheld XRF CE Instruments Model NC2100 Elemental Analyzer
