Algal indicators sediments

Algal indicators. Individual marker compounds indicative of sediment contributions from algae (Figure 2) may occur in both marine and lacustrine environments, although their... 

J.P. Smol, B.F. Camming (2000). Tracking long-term changes in climate using algal indicators in lake sediments. J. Phycol, 36,986-1011. 

Figure 9. A, At the base of sediment cores (30-50 cm) from 48 lakes ratios of C SMat nearly equal the ratio found in seston (indicated by the line labeled mean algal C S). A simplistic explanation is that most of the S is derived from seston, and that C and S are mineralized and lost from sediments at similar rates. B, Within the same cores for which data were available, ratios of C S oni tend to be lower than the ratio in seston (19 of 28 points lie below the line). Together, the figures suggest that much of the mineralized S is retained within the sediments. Figure 7 suggests that such retention is dependent on the avail-ability of iron. References are given in Figure 1.

For the removal of Zn from the water column by sedimentation, both algal material and manganese oxides are likely to be important carrier phases. The Zn sedimentation rates show maxima from June to August, at the time of the maximum sedimentation of P (indicating the sedimentation of algal material), and in December, in line with the sedimentation of manganese oxides (86). 

There is no indication of a release of Zn from the sediments during the development of anoxia, unlike the release of phosphate and dissolved silicate. Zn bound to algal material may be dissolved upon mineralization of this material and Zn bound to manganese oxides upon dissolution of manganese oxides. It appears, however, that Zn is efficiently retained in the sediments, probably through bonding to other less soluble particles, such as iron oxides and silica parts of diatoms. In the presence of sulfide, Zn is probably retained in association with sulfide-containing particles. 

The fate of trace ELEMENTS in a eutrophic lake is strongly linked to biological processes, as has been demonstrated for the oceans (1-3). Photo-svnthetic production of algae and the subsequent sedimentation of algal material affect the removal of metal ions to the sediments (4). High sedimentation rates in eutrophic lakes indicate efficient mechanisms for elimination of metal ions. As a result, low concentrations of trace metals are found in the water column. 

High precursor concentrations, coupled with an abundance of phenolic materials, suggest that humification should be readily observable in estuaries. There are indications that humification may occur in the dissolved phase, particularly if algal exudates are abundant. Macrophytic debris may be an important site for humification. Sediment humification processes have been suggested on the basis of downcore increases in high-molecular-weight DOC, along with stable isotope data. However, the actual or relative importance of all these sites of humification in estuaries has yet to be demonstrated. 

NMR spectra of humin from three major types of depositional environments, aerobic soils, peats, and marine sediments, show significant variations that delineate structural compositions. In aerobic soils, the spectra of humin show the presence of polysaccharides and aromatic structures most likely derived from the lignin of vascular plants. However, another major component of humin is one that contains paraffinic carbons and is thought to be derived from algal or microbial sources. Hydrolysis of the humin effectively removes polysaccharides, but the paraffinic structures survive, indicating that they are not proteinaceous in nature. The spectra of humin differ dramatically from that of their respective humic acids, suggesting that humin is not a clay-humic acid complex. 

P.R. Leavitt, D. Hodgson (2001). Sedimentary pigments. In J.P. Smol, H.J.B. Birks, W.M. Last (Eds), Tracking Environmental Change using Lake Sediments Volume 3 Terrestrial, Algal, and Siliceous Indicators (pp. 295-325). Kluwer, The Netherlands. 

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