Inorganic geochemical analysis of sediment has played a central role in palaeolimnology since its establishment as a research field. This chapter outlines methods that can be applied, explores the issues affecting reliability of interpretations, and refers readers to the appropriate literature. A distinction is made between inorganic geochemical palaeolimnology and inorganic geochemistry in general. While sharing many techniques and information sources, the two subjects differ fundamentally in purpose. Inorganic geochemistry aims to understand the chemical properties of the natural world, and the behaviour of chemical substances within it. Geochemical palaeolimnology uses such information to describe and quantify the environment. Furthermore, whereas palaeolimnological analysis is about lake, catchment or even landscape scale processes, geochemistry often considers minute scales. This contrast in scale has lead to conflicting interpretations. Geochemists working with laboratory experiments, and studying speciation and small-scale mobility, emphasize complexity. Palaeolimnologists, on the other hand, tend to look at large scale phenomena, and often find consistent patterns, even where a full geochemical understanding is lacking. The two disciplines should not be seen as separate. Inorganic geochemistry feeds into geochemical palaeolimnology because it is important to have a good understanding of the behaviour of the elements being measured. Conversely, palaeolimnological data can help to constrain geochemical models. Nevertheless, the contrasts in purpose and scale must be kept firmly in mind. A further distinction is made between organic and inorganic methods. For many inorganic elements, behaviour is highly dependent upon organic substances, and the two topics cannot be treated in isolation. Rather, inorganic methods must include a basic evaluation of organic components.

Inorganic Geochemical Methods in Palaeolimnology

ON poor, acidified soils in The Netherlands, an increasing number of great tits, Parus major, and other forest passerines, produce eggs with thin and porous shells1. Here we show that the egg-shell defects, and the related high incidence of clutch desertion and empty nests, are caused by calcium deficiency, that snail shells are the main calcium source for the laying female, but that snails are scarce on poor soils. Similar laying irregularities in birds are reported from acidified regions elsewhere in Europe2–4. We provide evidence that snails declined by a decrease in soil calcium on poor soils. Acid deposition is the main cause for decreasing calcium levels in such soils5–7. To our knowledge, this is the first experimental evidence for calcium limitation in wild birds and it reveals a previously overlooked mechanism by which acidification affects higher trophic levels of the forest ecosystem.

Poor reproduction in forest passerines from decline of snail abundance on acidified soils

This paper reviews the major sources and transport characteristics of heavy metals in the hydrological cycle. It is demonstrated that heavy metal releases to the environment have changed from 19th and early 20th century production-related activities to consumption-oriented factors in more recent times. The relative roles of particle size, sorption and desorption processes, partitioning and the chemical speciation of heavy metals on fine sediments are identified to understand the likely fate of heavy metals released into fluvial systems. It is argued that the spatial and temporal distribution of heavy metals in the river corridor depends not only on an understanding of metal solubility and speciation, but also on an understanding of sediment dynamics which control, for example, floodplain alluviation and the accumulation of metals in the bottom sediments of contaminated rivers, lakes and reservoirs. Existing long- and short-term records are examined to identify the current state of knowledge about the factors which affect heavy metal releases into aquatic environments. With limited exceptions, it is shown that few long-term studies of trends in heavy metal transport are available although, for some major rivers, limited data on trends in metal concentration exists. Palaeolimnological reconstruction techniques, based on an analysis of lake and reservoir sediments, are identified as a possible means of supplementing monitored records of heavy metal transport. Although numerous studies have suggested that trends in atmospheric contamination, mining and urbanization may be identified in the bottom sediment record, other research has shown that the radionuclide-based chronology and the heavy metal distribution within the sediment are more likely to be a function of post-depositional remobilization than the history of metal loading to the basin. Despite these limitations, it is shown that the incorporation of reservoir bottom sediment analysis into a heavy metal research programme, based in river corridors of Midland England, provides an opportunity to identify and quantify the relative contribution of point and non-point contributions to the heavy metal budget and to relate trends in metal contamination to specific periods of catchment disturbance.

Heavy metals in the hydrological cycle: Trends and explanation

Diatom microfossils preserved in lake sediments can be used to provide evidence for lake acidification. Unlike documentary methods of historical reconstruction, the sediment record is potentially useful at all sites, it is usually continuous and it can be extended backwards in time as desired. Cores can be taken with little disturbance, by freezing in situ if necessary, and sediments deposited since about 1800 A.D. can be dated using $^{210}$ Pb analysis. The strong relationship between diatom occurrence and water pH allows pH to be reconstructed with a standard error of between ca. 0.25 and 0.5 pH unit using either an index system or multiple regression analysis. Although there is evidence that long term acidification is a natural process for lakes in areas of resistant base-poor bedrock, diatom analyses from NW European and North American sites shows that rapid acidification has taken place within the last 150 years. The first major sign of acidification is the loss of planktonic diatoms at pH values between about 5.5 and 5.8. Acidification below pH 5.5 leads to the decline of species typical of circumneutral water, such as Achnanthes microcephala Kutz. Cymbella gracilis (Rabh). Cleve and Anomoeoneis vitrea (Grun). Ross, and the expansion of acidophilous taxa such as Tabellaria flocculosa (Roth.) Kutz. and Eunotia veneris (Kutz.) O. Muller. Acidobiontic species become common at pH values less than 5.5 and as the pH drops to 4.5 these taxa begin to replace acidophilous taxa in the assemblage. Tabellaria binalis (Ehr.) Grun. is probably the most faithful member of this group. Diatom analysis for four acid lakes in Galloway, SW Scotland show that the beginning of acidification has varied from 1840 (Loch Enoch) to 1925 (Loch Grannoch) and that pH has declined by between ca. 0.5 units (Loch Dee) and ca. 1.2 pH units (Loch Grannoch) in these lakes. Since lakes without afforested catchments have been acidified and lakes with afforested catchments were acidified before afforestation it can be concluded that afforestation is not responsible for acidification in this region.

Diatom analysis and the acidification of lakes

The distribution of fallout 137cs and 210pb in undisturbed and cultivated soils

137Cs and 210Pb dating of sediments from soft-water lakes in New England (U.S.A.) and Scandinavia, a failure of 137Cs dating

Empirical field evidence for changing chemical processes in soils caused by atmospheric deposition of pollutants consists of: (1) Long-term water quality data including total dissolved solids, concentrations of specific metals (e.g. Ca), and conductivity; (2) Cation exchange capacity and base saturation values for soils located on precipitation pH gradients; (3) Lysimeter studies; and (4) Chemical analysis of organic soils on precipitation pH and metal gradients. For well-drained organic soils, as precipitation pH decreases, metals are differentially leached at an accelerated rate (Mn > Ca > Mg ≥ Zn > Cd and Na > Al). Experimental field and laboratory lysimeter studies on soil columns yield similar results, with increases in leaching rates for soil solutions with pH = 3 up to 100 × values for soil solutions with pH = 5. Nearly 100% of the Pb from precipitation is accumulating in the organic soil layer or sediments. Zn is accumulating in soils and sediments where the pH’s of precipitation, soil solutions, and surface waters are generally above 5 to 5.5. At lower pH values Zn and other chemically similar elements are desorbed/leached (net) at an accelerated rate.

Modern and Paleolimnological Evidence for Accelerated Leaching and Metal Accumulation in Soils in New England, Caused by Atmospheric Deposition

The forest floor at high elevation spruce-fir sites from southern Vermont, U.S. to the Gaspe Peninsula, Quebec, Canada was sampled and analyzed in 1979 and re-sampled and analyzed in 1996 to study temporal changes in the impacts of atmospheric pollutants. We determined organic matter mass, pH, and concentrations of Al, Ca, Fe, K, Mg, Na, Cd, Cu, Hg, Pb, and Zn for the litter (L = fresh litter plus Oi horizon) and fermentation plus humic horizons (F+H) (= Oe plus Oa horizons) of the forest floor. There were no trends for Al or Fe concentrations in the 1979 or 1996 L along the transect. Several sites had significantly lower Al and Fe values in 1996 than in 1979, likely indicating less mineral soil in the 1996 samples. The 1996 concentrations of Ca in L increased along the transect from 0.22% dry weight (dw) in Vermont to 0.60% dw in Quebec. Concentrations of Mg in L were relatively constant along the transect. Neither Ca nor Mg changed at sites from 1979 to 1996, indicating unchanged base status. Concentrations of Cd did not vary spatially along the transect but decreased at all sites from 1979 to 1996. Cu and Zn did not vary spatially or with time. In 1979, the concentration of Hg in L ranged between 150 and 300 μg kg−1 dw, with no spatial gradient. By 1996, Hg concentrations were 25 to 50% lower in L, with decreases generally proportional to the concentration in 1979. The concentration of Pb in 1979 L decreased significantly from 200 mg kg−1 dw in southern Vermont to 60 mg kg−1 dw in Quebec. By 1996, the Pb concentration in L ranged between 32 and 66 mg kg−1 dw with no spatial trend along the transect. Decreases in Pb concentrations at sites were proportional to the absolute value in 1979. The concentrations of Cd, Hg, and Pb have declined in litter from 1979 to 1996, indicating a decline in atmospheric deposition. Higher Hg and Pb accumulation rates to the southwest are suggested for the past as indicated by (F+H) concentrations and inventories of Hg and Pb. The decline of Pb in L is consistent with the decreased use of leaded gasoline starting in the 1970s; the declines in Cd and Hg probably reflect lower emissions over the same period. Declining concentrations of Cd, Hg, and Pb in L parallel those documented in recent lake and peat sediments in the northeastern United States.

Denis W. Hanson

Papers

137Cs and 210Pb dating of sediments from soft-water lakes in New England (U.S.A.) and Scandinavia, a failure of 137Cs dating

Modern and Paleolimnological Evidence for Accelerated Leaching and Metal Accumulation in Soils in New England, Caused by Atmospheric Deposition

Changes in Concentrations of Major Elements and Trace Metals in Northeastern U.S.-Canadian Sub-Alpine Forest Floors