The use of heavy metal concentrations and dendrochronology in the reconstruction of sediment accumulation, Ma a Panew River Valley, southern Poland

Heavy metal concentrations were investigated in overbank sediments of the Mala Panew River, southern Poland. Samples were collected from seven vertical profiles located within channel infills of a 20th century floodplain at three sites, each up to 50 m wide. In each profile, 15–24 samples were collected and analysed for Ba, Cd, Cu, Pb, and Zn. Sequential extraction of these elements was carried out in the 0.063-mm fraction of selected samples. Additionally, the age of the oldest trees growing close to the profiles has been used to estimate the initiation of sediment accumulation there. Ba, Cu, and Pb, which occur mostly in less mobile, moderately reducible, and residual fractions, were used for sediment dating. Zn and Cd, which in 50–75% occur in the mobile exchangeable fraction, were not suitable for dating. Correlation of Ba, Cu, and Pb concentrations in vertical profiles with changes in the load of effluents discharged to the river showed abrupt changes in the thickness of the strongly polluted sediments across the floodplains. A comparison of the relative changes between heavy metal peaks in sediments of similar age in the different profiles suggests a variable rate of downward metal migration. In general, none of the heavy metals investigated seems to have been mobilised within the stratigraphic layers above the water table. In layers located at stratigraphically lower levels, the Zn and Cd peaks seem to migrate several centimetres to several decimetres down in the profile. In profiles inundated for several weeks every year, Zn and Cd, as well as the relatively less mobile Ba, Cu, and Pb, have migrated downward by several decimetres. The investigation shows that frequent fluctuations of the water table have blurred the original depositional metal patterns of metal concentrations within a period of less than 40 years.     

A 1500-year record of climatic and environmental change in ElkLake, Clearwater County, Minnesota II: geochemistry, mineralogy, and stableisotopes

Most of the sediment components that have accumulated in ElkLake, Clearwater County, northwestern Minnesota, over the past 1500 years areauthigenic or biogenic (CaCO₃, biogenic SiO₂, organicmatter, iron and manganese oxyhydroxides, and iron phosphate) and are deliveredto the sediment–water interface on a seasonal schedule where they are preservedas distinct annual laminae (varves). The annual biogeochemical cycles of thesecomponents are causally linked through the carbon pump, and are recapitulatedin longer-term cycles, most prominently with a periodicity of about 400 years.Organic carbon is fixed in the epilimnion by photosynthetic removal ofCO₂, which also increases the pH, triggering the precipitation ofCaCO₃. The respiration and degradation of fixed organic carbon inthe hypolimnion consumes dissolved oxygen, produces CO₂, and lowersthe pH so that the hypolimnion becomes anoxic and undersaturated with respectto CaCO₃ during the summer. Some of the CaCO₃ produced inthe epilimnion is dissolved in the anoxic, lower pH hypolimnion and sediments.The amount of CaCO₃ that is ultimately incorporated into thesediments is a function of how much is produced in the epilimnion and how muchis consumed in the hypolimnion and the sediments. Iron, manganese, andphosphate accumulate in the anoxic hypolimnion throughout the summer.Sediment-trap studies show that at fall overturn, when iron-, manganese-, andphosphate-rich bottom waters mix with carbonate- and oxygen-rich surfacewaters, precipitation of iron and manganese oxyhydroxides, iron phosphate, andmanganese carbonate begins and continues into the winter months.Detrital clastic material in the sediments of Elk Lake depositedover the last 1500 years is a minor component (<10% by weight) that ismostly wind-borne (eolian). Detailed analyses of the last 1500 years of the ElkLake sediment record show distinct cycles in eolian clastic variables (e.g.aluminum, sodium, potassium, titanium, and quartz), with a periodicity of about400 years. The 400-yr cycle in eolian clastic material does not correspond tothe 400-yr cycles in redox-sensitive authigenic components, suggesting that theclastic component is responding to external forcing (wind) whereas theauthigenic components are responding to internal forcing (productivity),although both may ultimately be forced by climate change. Variations in theoxygen and carbon isotopic composition of CaCO₃ are small but appearto reflect small variations in ground water influx that are also driven byexternal forcing.     

A 140-year record of recent changes in aquatic productivity in a remote,tropical alpine lake in the Rwenzori Mountain National Park,Uganda

Environmental change in many tropical, alpine habitats remains poorly resolved due to an absence of proximate and sustained observations. In the Rwenzori Mountains of East Africa, glaciers have receded rapidly over the last century, and here we assess the impact of this recession through palaeolimnological analyses of a 45 cm sediment core (Buju3) from Lake Bujuku which is closest to the ice-fields and partly supplied by melt water in-flows. ²¹⁰Pb and ¹³⁷Cs suggest that Buju3 has an average sedimentation rate of 2.9 mm year⁻¹ and the base of the core can be dated to 1864 ± 20 years. Contemporary diatom taxa found in the lake are dominated by Tabellaria flocculosa and Synedra spp., but also include Achnanthes minutissima and Fragilaria pinnata. However, the diatom flora for Buju3 is less diverse and dominated by small, tychoplanktonic species of Fragilaria. Over the period associated with glacial recession, organic carbon isotope analysis (δ¹³C) suggests a small but distinct increase in within-lake productivity, which increases in rate since the mid 1970s up to the present day, in line with a shift towards increased algal productivity (as highlighted by C/N ratios). However, the diatom and pollen records appear rather insensitive to changes in glacier recession since the late 19th century.     

A late Holocene record of land-use history,soil erosion,lake trophy and lake-level fluctuations at Bjäresjösjön (south Sweden)

Land-use history, soil erosion, lake trophy and lake-level fluctuations during the last 3000 years were reconstructed through a multidisciplinary palaeolimnological study (pollen, plant macrofossils, diatoms, physical and chemical analysis, magnetic measurements and radiometric methods) of a small eutrophic lake in southern Sweden (Bjäresjösjön, Scania). There are striking responses in diatom, chemical, sediment yield and magnetic records to land-use changes documented by pollen analysis or historical sources, and to lake-level changes identified from sedimentary changes. Our multidisciplinary approach assists interpretation of the processes controlling long-term changes and separation of the effects of different factors (land-use changes, lake-level fluctuations) on individual biostratigraphical records. Climate has controlled processes in the lake indirectly, through lake-level fluctuations, from the Late Bronze Age to the Viking Age (700 BC-AD 800). Since the Viking Age, land-use controlled most of the changes observed in the lake's development and soil erosion processes. Major changes in lake development occurred during the last 200 years, due to a drastic increase in soil erosion and water eutrophication during a period of agricultural modernization.     

Host specificity, nutrient and water dynamics of the mistletoe Viscum rotundifolium and its potential host species in the Kalahari of South Africa

The mechanisms underpinning local host specificity in mistletoes remain elusive. We determined the degree of host specificity in the mistletoe Viscum rotundifolium at Pniel Estates, near Kimberley, South Africa. We found that V. rotundifolium parasitises only Ehretia rigida and Ziziphus mucronata at this site. Both commonly parasitised host species were not the most abundant trees, were not the tallest trees, and did not have the highest water or nutrient content of trees in the area, although these factors are good predictors for mistletoe parasitism. Mistletoe seeds deposited on branches of E. rigida and Z. mucronata have a greater chance of attachment and subsequent survival, compared with those seeds deposited on co-occurring Acacia and other potential host species. The mistletoes had higher water potential than their host trees and by doing so they can passively maintain the flow of nutrients. In addition, the mistletoes had a N:Ca ratio >1, indicating active uptake from host phloem. Thus, this mistletoe species uses both passive and active uptake, which may be a selective advantage in a nutrient-poor environment or on a nutrient-deficient host species.