Long Island Sound sediment sources

Figure 7.10 Correlation between ratios of measured 234Th versus expected (based on overlying water source from 238U) sediment inventories in Long Island Sound (USA). This shows that the measured inventory was greater than expected for shallow stations relative to deep stations. (Modified from Sun et al., 1994.)...

Sawhney, B. L., and Frink, C. R. (1979). Clay minerals as indicators of sediment source in tidal estuaries of Long Island Sound. Clays, Clay Miner, (in press). 

If the sources of supply, initial and boundary conditions, and the transport and deposition mechanisms are adequately defined, the resultant distribution of marine sediment can be deduced. This can be done qualitatively for Long Island Sound some of the results can be put in quantitative form. 

As Fig. 11 shows, there is some variability in the integrated trace-element contents of cores from central Long Island Sound. These sediments are not located near intense sources of trace metals nor are there major grain-size differences. As we will show later, the differences in both metal concentrations and inventories can be related primarily to the intensity and depth of biological mixing of the sediment column. 

This estimate is compared to the specific activity of likely sources (upland and marine) in Table XIII. It appears that neither material scoured from the mud-water interface of Long Island Sound nor material eroded from the upland surface is an allowable source, since only material from beneath these surfaces is of sufficiently low activity. It is relatively difficult to effect deep (18-20 cm) erosion of submarine sediment in Long Island Sound, but common for upland soil to erode deeply, especially when land is disturbed by agriculture or construction. This indicates that the source of low-specific-activity inorganic matter is the eroding subsurface material of the watershed. 

Rapid erosion of the cliffs on the north shore of Long Island over the past 90 yr has been deduced from comparison of old and new maps (D. S. Davies, E. W. Axelrod, and J. S. O Connor, undated report. Marine Sciences Research Center, State University of New York, Stony Brook, New York). Because the areas of greatest erosion are quite localized and the composition of the material making up the cliffs has not been systematically sampled, a reliable estimate of the amount of silt-clay sediment entering the Sound from this source cannot be made now. There is a strong possibility that it is significant but nevertheless smaller than the river input. 

---