Computer Science – Sound
Scientific paper
Aug 1998
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998e%26psl.160..403y&link_type=abstract
Earth and Planetary Science Letters, vol. 160, Issue 3-4, pp.403-418
Computer Science
Sound
3
Cadmium, Manganese, Hudson River, Estuaries, Seasonal Variations
Scientific paper
Surface waters collected along the salinity gradient of the Hudson River estuary in four cruises between 1995 and 1997 were size-fractionated into particulate (>0.45 m), `dissolved' (<0.45 m), colloidal (10 kDa, 0.45 m) and low molecular weight (<10 kDa) phases. Dissolved Cd concentrations (range: 0.11-1.19 nM) in surface waters of the estuary appear to have decreased fourfold (from an average of 2.36 to 0.61 nM) over a 23-year period, since the initial analysis of samples collected in the 1970s by Klinkhammer and Bender [Estuar. Coastal Shelf Sci. 12 (1981) 629-643]. This interannual decline reflects improvement in sewage treatment and the elimination of industrial Cd sources to the Hudson River estuary. In contrast, dissolved Mn levels (range: 0.033-1.46 M) have remained relatively constant over the same period of time, suggesting that anthropogenic sources have very limited impact on Mn concentrations in the estuary. The concentrations of both Cd and Mn appeared to strongly depend on the season and/or river discharge. The highest concentrations were detected under low freshwater discharge, implying that limited hydraulic flushing allows a build-up of metals in the water column. Although the decline in Cd levels within the estuary reflects a reduction in the magnitude of anthropogenic inputs, mass balance estimates indicated that current sources of Cd to the estuary include sewage discharges (in the lower estuary around Manhattan) and diagenetic remobilization from industrial Cd deposited in sediments nearly 2 decades ago (in the upper estuary near Foundry Cove). Moreover, under low river discharge, the sources considered in our model (sewage, riverine input, atmospheric deposition, and benthic fluxes) could account for no more than 60% of the Cd exported from the lower estuary to the ocean. This suggests that undefined sources such as ground water and inputs from other watersheds (e.g., Long Island Sound and Newark Bay) may potentially influence the water quality of the New York Harbor. The size-fractionated metal concentrations indicated that most of the traditionally defined `dissolved' Cd and Mn consisted of <10 kDa molecular weight species. High molecular weight colloidal species of Mn accounted for about 50% of the dissolved fraction at the riverine end-member and <5% at intermediate and high salinities. Colloidal Cd accounted for <6% of the dissolved phase throughout the estuary. Unlike the non-conservative excess (relative to ideal dilution of river water and seawater) of dissolved Mn observed along the estuary, high molecular weight colloidal Mn appeared to be removed at the head of the estuary. The small contribution of colloidal Cd and Mn to the `dissolved' phase suggests that remobilization from suspended particulate phases and/or from sediments occurs through the formation of small molecular weight species.
Sañudo-Wilhelmy Sergio A.
Yang Min
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