Browsing by Subject "LAKE-SEDIMENTS"

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  • Silvonen, Soila; Niemistö, Juha; Csibrán, Adrián; Jilbert, Tom; Torma, Péter; Krámer, Tamás; Nurminen, Leena; Horppila, Jukka (2021)
    Hypolimnetic withdrawal (HW) is a lake restoration method that is based on the removal of phosphorus (P) along with near-bottom water. While it has often proven to be effective, the method also sets challenges: it is about balancing between effective P removal and maintenance of the thermal stratification of the lake. The success of different HW projects has been reviewed in some studies retrospectively, but scientific literature still lacks studies that use detailed data on the lake biogeochemistry to scale and optimize the method in advance, and to predict the outcomes of the restoration measure. In the current study, we investigated the seasonal biogeochemistry, P stocks and thermal stratification of a eutrophic lake (Lake Kymijarvi/Myllypohja basin, southern Finland) to determine an optimal withdrawal rate, to assess its effects on stratification, and to evaluate the expected success of HW. We found that by adjusting HW with P diffusive fluxes from the sediment (diffusion-adjusted HW), it is possible to remove a notable part of the cycling P without causing major disturbances to the thermal stratification even in a relatively shallow lake. Our results show that HW can have great potential in lake restoration: diffusion-adjusted HW in our study lake could increase the annual P output by 35-46%, shifting the P budget of the lake to negative. We thus propose a novel approach to optimize HW on the basis of the diffusive flux of P from the sediment, with the goal of extracting P continuously at an equivalent rate to the diffusive flux. We finally discuss how this can be achieved more effectively with HW based on a closed-circuit system. (c) 2020 The Authors. Published by Elsevier B.V.
  • Lucke, Bernhard; Roskin, Joel; Vanselow, Kim André; Bruins, Hendrik; Abu-Jaber, Nizar; Deckers, Katleen; Lindauer, Susanne; Porat, Naomi; Reimer, Paula J.; Bäumler, Rupert; Erickson-Gini, Tali; Kouki, Paula (2019)
    Loess accumulated in the Negev desert during the Pleistocene and primary and secondary loess remains cover large parts of the landscape. Holocene loess deposits are however absent. This could be due low accumulation rates, lack of preservation, and higher erosion rates in comparison to the Pleistocene. This study hypothesized that archaeological ruins preserve Holocene dust. We studied soils developed on archaeological hilltop ruins in the Negev and the Petra region and compared them with local soils, paleosols, geological outcrops, and current dust. Seven statistically modeled grain size end-members were identified and demonstrate that the ruin soils in both regions consist of mixtures of local and remote sediment sources that differ from dust compositions deposited during current storms. This discrepancy is attributed to fixation processes connected with sediment-fixing agents such as vegetation, biocrusts, and/or clast pavements associated with vesicular layers. Average dust accretion rates in the ruins are estimated to be similar to 0.14 mm/a, suggesting that similar to 30% of the current dust that can be trapped with dry marble dust collectors has been stored in the ruin soils. Deposition amounts and grain sizes do not significantly correlate with wind intensity. However, precipitation may have contributed to dust accretion. A snowstorm in the Petra region delivered a significantly higher amount of sediment than rain or dry deposition. Snowfall dust had a unique particle size distribution relatively similar to the ruin soils. Wet deposition and snow might catalyze dust deposition and enhance fixation by fostering vegetation and crust formation. More frequent snowfall during the Pleistocene may have been an important mechanism of primary loess deposition in the southern Levant.
  • Lucke, Bernhard; Sandler, Amir; Vanselow, Kim André; Bruins, Hendrik J.; Abu-Jaber, Nizar; Baeumler, Rupert; Porat, Naomi; Kouki, Paula (2019)
    Archaeological structures are often filled with sediments and may serve as effective dust traps. The physical parameters and chemical composition of archaeological soils in hilltop ruins, ancient runoff-collecting terraces, and cleanout spoils of cisterns were determined in the Petra region in southern Jordan and the Northern Negev in Israel. Different types of ruins are characterized by certain soil structures, but could not be distinguished with regard to substrate composition. This reflects a predominance of aeolian processes for primary sedimentation, while fluvial processes seem to only re-distribute aeolian material. In the Petra region, the physical and chemical properties of all archaeological soils show a significant local contribution from associated weathered rocks. Compared to modern settled dust, archaeological soils in Southern Jordan are enriched with various major and trace elements associated with clays and oxide coatings of fine silt particles. This seems connected with preferential fixation of silt and clay by surface crusts, and a role of moisture in sedimentation processes as calcareous silt was found to be deposited in greater amounts when associated with precipitation. In contrast, the contribution of rocks is negligible in the Negev due to greater rock hardness and abundant biological crusts that seal surfaces. Archaeological soils in the Negev are chemically similar to current settled dust, which consists of complex mixtures of local and remote sources, including significant portions of recycled material from paleosols. Archaeological soils are archives of Holocene dust sources and aeolian sedimentation processes, with accretion rates exceeding those of Pleistocene hilltop loess in the Negev. Comparison with Pleistocene paleosols suggests that dust sources did not change significantly, but disappearance of snow could have reduced dust accumulation during the Holocene.
  • Lahtinen, Maria; Oinonen, Markku; Tallavaara, Miikka; Walker, James; Rowley-Conwy, Peter (2017)
    Dates for early cultivation in Finland obtained from pollen analysis and from remains from archaeological sites are compared to changes in population size derived from the summed calendar year probability distributions published by Tallavaara et al. (2010). The results from these two independent proxies correlate strongly with one another, indicating that population size and the advance of farming were closely linked with each other. Moreover, the results show that the adaptation and development of farming in this area was a complex process comprising several stages and with major differences between regions. The most intensive expansion occurred in and after the Iron Age. It is therefore more accurate describe the introduction of farming into the area as a long-lasting process rather than an event.