Estimation of Phosphorus Bioavailability in the Water Column of the Bronx River, New York

The purpose of this project was to understand fecal microorganism contamination in the Bronx River within New York City and how it is affected by combined sewer overflow (CSO) events. Nine sites along the Bronx River were sampled throughout the summer of 2014 during wet and dry weather conditions. The samples were analyzed for enterococcus fecal indicator bacteria (FIB) concentration. The data revealed that wet weather enterococci concentrations are as 3 to 28 times greater than dry weather concentrations. The highest enterococci concentrations were found where the river enters Bronx County from Westchester County and near a storm water outfall. The positive correlation shown between the amount of rainfall and the FIB concentrations verifies that CSO and storm water discharges are a major source of FIB contamination in the river.

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Anoxic depositional overprinting of 238U/235U in calcite: When do carbonates tell black shale tales?

Geology ◽

10.1130/g48949.1 ◽

2021 ◽

Author(s):

Xinming Chen ◽

Stephen J. Romaniello ◽

Michael McCormick ◽

Alyssa Sherry ◽

Jeff R. Havig ◽

...

Keyword(s):

New York ◽

Water Column ◽

Isotope Geochemistry ◽

Sediment Traps ◽

Depositional Environments ◽

Uranium Isotopes ◽

Carbonate Sediments ◽

Anoxic Water ◽

Green Lake ◽

Bottom Waters

The fidelity of uranium isotopes (δ238U) in marine carbonates as a paleoredox proxy relies on whether carbonates can record and preserve seawater δ238U. Although modern carbonate sediments deposited under oxic conditions have been shown to track seawater δ238U, it remains unknown whether this is true for carbonates deposited under anoxic conditions. This is a crucial question because many ancient carbonates were likely deposited or reworked under anoxic bottom waters. To better understand the behavior of uranium isotopes under this scenario, we investigated U isotope geochemistry in the meromictic Fayetteville Green Lake (FGL; New York, USA), where primary calcite is precipitated from oxic surface waters, sinks past the chemocline, and is deposited under anoxic bottom waters. We observed significant depletions of dissolved U concentration (from 2.7 to 0.9 ppb) and δ238U (from –0.55‰ to –0.96‰) below the chemocline in FGL. Parallel with these depletions, δ238U of sediment traps increased progressively from –0.51‰ to –0.16‰, suggesting that U(VI) reduction was occurring in the anoxic water column. Carbonate sediments deposited under anoxic bottom waters were enriched in U by 6–18× compared to primary calcite. Our data suggest that such significant authigenic U enrichments resulted from U(VI) reduction in the anoxic water column and below the sediment-water interface. The δ238U value in the top 0.25 cm of sediments was –0.29‰ ± 0.10‰, overprinting original δ238U in primary calcite (–0.51‰ ± 0.02‰). Future applications of carbonate δ238U as a paleoredox proxy should consider depositional environments (oxic vs. anoxic) of carbonates.

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