The carbon cycle in Long Island Sound
Abstract
Like many coastal waters in heavily populated areas, Long Island Sound (LIS) suffers from hypoxia and anoxia, especially in its western 'Narrows' section near New York City. The prime driver for the oxygen deprivation is considered to be excess algal productivity. Primary productivity has increased strongly as a result of nitrogen inputs from the watershed, and direct input from waste water treatment plants in NY and CT. The EPA mandated a reduction of nitrogen inputs of >50% by 2014 relative to 1990. The NY-CT joint N release was close to that benchmark, but little improvement has been seen in the water quality, although the last few years had summers with relatively small hypoxic areas. We studied sediment cores for C, N, biogenic silica (diatoms), foraminifera, determined δ13C and δ15N on bulk sediment, δ13C-δ18O and Mg/Ca on the foraminifer Elphidium excavatum, and measured the archaeal lipid biomarker TEX86. Temperature records were derived from foraminiferal Mg/Ca and TEX86, paleo-oxygenation from foraminiferal δ13C values. We reconstructed mass accumulation rates (MAR) of foraminifera, C(org) and N as indicators of eutrophication in dated cores (14C, Hg pollutant stratigraphy, 210Pb), and determined the source of organic material from δ13C, C/N and δ15N. We used the abundance of the bacterial spore Clostridium perfringens as an indicator for wastewater N inputs. Eutrophication and hypoxia started in the early 1800s with the strong population growth in the region. The δ15N record shows a discrete shift to heavier values due to sewage release. Sedimentary organic matter in the colonial era was mainly sourced from the marine realm, but by the start of the 20th century terrestrial carbon became dominant. The ratio of marine versus terrestrial carbon inputs shows wide swings, reflecting deforestation and shifts to agricultural land and reforestation in the 20th century. We compare modern nitrogen MARs from marine organic carbon with the estimated N fluxes into the Sound, and scale this to marine nitrogen MARs for the early 1800s, to approximate presumed pre-eutrophication N inputs.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS41C2041V
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCESDE: 4235 Estuarine processes;
- OCEANOGRAPHY: GENERALDE: 4235 Estuarine processes;
- OCEANOGRAPHY: GENERAL