Publications by authors named "Steven A Kuehl"

4 Publications

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Anthropogenic impact on the organic carbon sources, transport and distribution in a subtropical semi-enclosed bay.

Sci Total Environ 2021 May 19;767:145047. Epub 2021 Jan 19.

Department of Earth Sciences, The University of Hong Kong, Hong Kong, China.

Suspended particulate organic carbon (POC) and sedimentary total organic carbon (TOC) in coastal areas play critical roles in the global carbon cycle, yet sources and dynamics of coastal POC and TOC have been affected by various anthropogenic activities such as aquaculture, sewage discharge, dam construction and land reclamation. To better understand the anthropogenic impacts on coastal organic carbon, this study was carried out in a representative semi-enclosed bay, Dongshan Bay, Southeast China. Through analyses of stable isotopic compositions of both POC (δC and δN) and TOC (δC and δN), the ratio of total organic carbon vs. total nitrogen (C/N), grain size, Chl-a concentrations and hydrological parameters, our study led to the following main findings: 1) During flood season, the distribution of δC, δC δN and δN values within the bay did not follow the conventional land-sea transition pattern. This distribution pattern indicated more terrestrial organic matter input seaward, which contrasts with the conventional organic matter distribution along the estuarine gradient. 2) Using the organic δC, δN and C/N signatures of different endmembers, we found that the sources of organic matter deposited in the bay were strongly related to anthropogenic activities, including municipal wastewater discharge, aquaculture, land reclamation and sluice-dyke construction. Furthermore, 3) by applying the Grain Size Trend Analysis Model and the previously-estimated residual current directions, we suggested that human activities have not only altered the sources of organic matter to the semi-enclosed bays, but also significantly modified their transportation and deposition patterns, and might influence the ultimate fate of organic matter into and out of Dongshan Bay. The conclusions of this study should be applicable to similar coastal bays around the world.
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http://dx.doi.org/10.1016/j.scitotenv.2021.145047DOI Listing
May 2021

Amazon Sediment Transport and Accumulation Along the Continuum of Mixed Fluvial and Marine Processes.

Ann Rev Mar Sci 2021 01 7;13:501-536. Epub 2020 Jul 7.

School of Oceanography, University of Washington, Seattle, Washington 98195, USA; email:

Sediment transfer from land to ocean begins in coastal settings and, for large rivers such as the Amazon, has dramatic impacts over thousands of kilometers covering diverse environmental conditions. In the relatively natural Amazon tidal river, combinations of fluvial and marine processes transition toward the ocean, affecting the transport and accumulation of sediment in floodplains and tributary mouths. The enormous discharge of Amazon fresh water causes estuarine processes to occur on the continental shelf, where much sediment accumulation creates a large clinoform structure and where additional sediment accumulates along its shoreward boundary in tidal flats and mangrove forests. Some remaining Amazon sediment is transported beyond the region near the river mouth, and fluvial forces on it diminish. Numerous perturbations to Amazon sediment transport and accumulation occur naturally, but human actions will likely dominate future change, and now is the time to document, understand, and mitigate their impacts.
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http://dx.doi.org/10.1146/annurev-marine-010816-060457DOI Listing
January 2021

Changes in sediment and organic carbon accumulation in a highly-disturbed ecosystem: the Sacramento-San Joaquin River Delta (California, USA).

Mar Pollut Bull 2009 5;59(4-7):154-63. Epub 2009 May 5.

Virginia Institute of Marine Science, School of Marine Science, College of William and Mary, P.O. Box 1346, Gloucester Point, VA 23062, USA.

We used the Sacramento-San Joaquin River Delta CA (Delta, hereafter) as a model system for understanding how human activities influence the delivery of sediment and total organic carbon (TOC) over the past 50-60 years. Sediment cores were collected from sites within the Delta representing the Sacramento River (SAC), the San Joaquin River (SJR), and Franks Tract (FT), a flooded agricultural tract. A variety of anthropogenic tracers including (137)Cs, total DDE (Sigma DDE) and brominated diphenyl ether (BDE) congeners were used to quantify sediment accumulation rates. This information was combined with total organic carbon (TOC) profiles to quantify rates of TOC accumulation. Across the three sites, sediment and TOC accumulation rates were four to eight-fold higher prior to 1972. Changes in sediment and TOC accumulation were coincident with completion of several large reservoirs and increased agriculture and urbanization in the Delta watershed. Radiocarbon content of TOC indicated that much of the carbon delivered to the Delta is "pre-aged" reflecting processing in the Delta watershed or during transport to the sites rather than an input of predominantly contemporary carbon (e.g., 900-1400 years BP in surface sediments and 2200 yrs BP and 3610 yrs BP at the base of the SJR and FT cores, respectively). Together, these data suggest that human activities have altered the amount and age of TOC accumulating in the Delta since the 1940s.
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http://dx.doi.org/10.1016/j.marpolbul.2009.03.025DOI Listing
September 2009

Assessment of the historical trace metal contamination of sediments in the Elizabeth River, Virginia.

Mar Pollut Bull 2007 Apr 18;54(4):385-95. Epub 2007 Jan 18.

College of William and Mary, School of Marine Science, Virginia Institute of Marine Science, 1208 Greate Road, Gloucester Point, VA 23062, USA.

Two sediment cores (Southern Branch, PC-1, and Western Branch, WB-2) were taken from the highly industrialized Elizabeth River, Virginia. The concentrations of trace metals cadmium, cobalt, chromium, copper, nickel, lead and zinc, major elements iron, manganese and aluminum, organic carbon content and the specific surface area of the sediments were determined in each of the cores. Down-core variations in metals varied significantly in each core with maximum contamination events occurring at different times in different portions of the river. In PC-1, maximum metal concentrations were seen after the appearance of (137)Cs. In contrast, the highest levels in WB-2 occurred well before the appearance of (137)Cs. Although stricter environmental regulations have caused a decrease in metal concentrations since the 1980s, the concentrations in the surface sediments of many trace metals were elevated to levels 2-5 times higher than the levels at the bottom of the cores in both the Southern and Western Branches of the river.
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http://dx.doi.org/10.1016/j.marpolbul.2006.11.005DOI Listing
April 2007
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