Sediments historical records

Birch, L., Hanselmann, K., Bachofen, R., 1996. Heavy metal conservation in lake Cadagno sediments historical records of anthropogenic emissions in a meromictic alpine lake. Wat. Res. 30, 679-687. 

Between 1890 and 1902, the sedimentation rate identified as Region II of figure 3 averaged 1800 g m"2 yr-1 or 0.83 cm yr-1, i.e., greater than 10 times the pre-cultural rate. Historical records and photographs show that by 1895 most of the land comprising the watershed had been logged and the suburbs of Seattle had reached the lake shore. This rapid land development in the watershed occurred about the turn of the century. 

In this article we plan to focus on two aspects (i) the transport of radionuclides to the ocean floor and the processes which govern their distribution in deep-sea sediments and (ii) the application of deep-sea sediments to retrieve historical records of large scale phenomena, e.g. long term changes in the rate of production of nuclides by cosmic rays. Even while discussing these aspects, our emphasis will be mainly on the processes rather than on the details of the chronometric method. 

The advent of new techniques to collect undisturbed sediment cores, with well preserved sediment - water interface has brought into sharper focus the various deep sea sedimentary processes, their rates and their effects on the preserved records. As mentioned earlier, recent studies have shown that the record contained in sediments is not a direct reflection of the delivery pattern of a substance to the ocean floor as has so far been assumed the record is modified as a result of several complex physical, chemical and biological processes. Therefore, information on the temporal variations in the tracer input to oceans, if sought, has to be deciphered from the sediment-residuum. In the following we consider one specific example of retrieval of information from the sediment pile the application of deep sea sediments to obtain historical records of cosmic ray intensity variations. 

Figure 9. Calculated attenuation factors for various values of T (period in the sinusoidal cosmic ray intensity variations) and A (the total rate constant). See section on deep-sea sediments and historical records for discussion.

Historic records show how devastating intensive monsoon storms can be in the Middle Mountains. In 1993 a storm that produced 540 mm of rainfall over a 24 h period and with rainfall intensities exceeding 70 mm h hit the Kulekhani watershed [7-9]. This resulted in hundreds of landslides and a sediment load of up to 500 T ha per storm in the watershed (Fig. 1). This not only destroyed large tracks... 

The stability of PAH is also apparent when one examines sediment samples taken in such a way as to preserve the historical record (11). This can be done by carefully coring sediments, particularly at anoxic locations where there is little bioturba-tion, segmenting the core into 2-4 cm sections, and analyzing each section for PAH quantitatively. An example of such data is shown in Figure 5 this represents a core from the Pettaquamscutt River in Rhode Island, a highly anoxic basin (12). The total PAH concentration ranges from 14,000 ppb near the sediment surface to... 

Figure 1.1 Historical records of the sales/production volumes of (a) DDT and (b) PCBs, and the similarity of these time-varying trends to the accumulation rates of these chemicals in the sediments of Lake Ontario (from Eisenreich et al., 1989).

Czuczwa JM, Hites RA (1985) Historical record of polychlorinated dioxins, furans in Lake Huron sediments. In Keith LH, Rappe C, Choudhary G (eds) Chlorinated dioxins and dibenzofurans in the total environment II. Butterworth, Toronto p 59... 

Liu, M., Baugh, P.J., Hutchinson, S.M., Yu, L., Xu, S., 2000. Historical record and sources of polycyclic aromatic hydrocarbons in core sediments from the Yangtze Estuary, China. Environ. Pollut. 110, 357-365. 

Astle JW, Gobas FAPC, Siu WY, et al. 1987. Lake sediments as historic records of atmospheric contamination by organic chemicals. Adv Chem Ser 216 57-77. 

Flessa, K.W., Constantine, K.J., and Cushman, M.K. (1977) Sedimentation rates in a coastal marsh determined from historical records. Ches. Bay Sci. 18, 172-176. 

Czuczwa JM, Niessen F, Hites RA (1985), Chemosphere 14 1175-1179.. .Historical record of polychlorinated dibenzo-p-dioxins and dibenzofurans in Swiss lake sediments"... 

A number of recent trend studies are summarised below. Settled sediments from lakes and undisturbed (preferably anoxic) sediments represent a historical record of contaminant... 

Gocht T., Moldenhauer K.-M., and Puttmann W. (2001) Historical record of polycyclic aromatic hydrocarbons (PAH) and heavy metals in floodplain sediments from the Rhine River (Hessisches Ried, Germany). Appi Geochem. 16, 1707-1721. 

Thomas M., Petit D., and Lamberts L. (1984) Pond sediments as historical record of heavy metals fallout. Water Air Soil Pollut. 23, 51-59. 

In a lake, as bottom sediment is deposited, it preserves a historical record of chemical and biological conditions in the lake basin. Remains of aquatic organisms, pollen from the adjoining land, and chemicals sorbed to sediment particles all reflect past conditions. The sediment record is sequential in the absence of events that mix the sediment, deeper sediments are older. If it is possible to determine the date at which a particular layer of the sediment was deposited, the chemical and biological information contained in that layer can be assigned to a particular time in history. 

It is important to recognise that there is a fundamental difference between determining chemical/physical baselines and biological ones. In general, there exists within the ice, soil or sediments a historical record of chemical changes from which it may be possible to assess the natural temporal variability. Rarely is this possible... 

Anthropogenic inputs to intertidal environments are often direct, through point-source waste disposal, but they are also indirect, from riverine, marine and/or atmospheric sources. Trace metals are partitioned between each component of the intertidal sediment-water system they are found in solution ( bulk water or interstitial water) and associated with suspended and deposited sediments. This chapter is concerned with the biogeochemistry of trace metals in deposited intertidal sediments. Two main sections follow in the first, an overview of surface sediments and sediment depth profiles is presented, and in the second, a case study is given of the historic record of Zn from saltmarsh sediments in the Severn Estuary, UK. 

Trace metal concentrations in intertidal sediment depth profiles will no doubt continue to provide useful historic records of pollution in the future. In particular, dated profiles that take into account sediment characteristics and diagenetic processes (where appropriate) are of value. Future studies will perhaps be more process-oriented, e.g. by combining pore-water analysis with solid phase data and through a detailed investigation of the nature and significance of the organic matter present. 

Finally, it is important not to assume that the historic record for other trace metals in the same sediment core will be so straightforward. Detailed examination of depth-related phase associations for each metal is always essential and additional data, e.g. on pore-water chemistry and the amount and nature of organic matter present can be advantageous. 

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