TY - JOUR A1 - Sarkar, Saswati A1 - Wilkes, Heinz A1 - Prasad, Sushma A1 - Brauer, Achim A1 - Riedel, Nils A1 - Stebich, Martina A1 - Basavaiah, Nathani A1 - Sachse, Dirk T1 - Spatial heterogeneity in lipid biomarker distributions in the catchment and sediments of a crater lake in central India JF - Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry N2 - The basin-scale spatial variability in lipid biomarker proxies in lacustrine sediments, which are established tools for studying continental environmental change, has rarely been examined. It is often implicitly assumed that a lake sediment core provides an average integral of catchment sources. Here we evaluated the distribution of lipid biomarkers in a modern ecosystem and compared it with the sedimentary record. We analyzed lipid biomarkers in terrestrial and aquatic organisms and in lake surface sediments from 17 locations within the saline-alkaline Lonar crater lake in central India. Terrestrial vegetation and lake surface sediments were characterized by relatively high average chain length (ACL) index values (29.6-32.8) of leaf wax n-alkanes, consistent with suggestions that plants in drier and warmer climates produce longer chain alkyl lipids than plants in cooler and humid areas. A heterogeneous spatial distribution of ACL values in lake surface sediments was found: at locations away from the shore, the values were highest (31 or more), possibly indicating different sources and/or transport of terrestrial biomarkers. In floating, benthic microbial mats and surface sediment, n-heptadecane, carotenoids, diploptene, phytol and tetrahymanol occurred in large amounts. Interestingly, these biomarkers of a unique bacterial community were found in substantially higher concentrations in nearshore sediment samples. We suggest that human influence and subsequent nutrient supply resulted in increased primary productivity, leading to an unusually high concentration of tetrahymanol in the nearshore sediments. In summary, the data showed that substantial heterogeneity existed within the lake, but leaf wax n-alkanes in a core from the center of the lake represented an integral of catchment conditions. However, lake level fluctuation may potentially affect aquatic lipid biomarker distributions in lacustrine sediments, in addition to source changes. Y1 - 2014 U6 - https://doi.org/10.1016/j.orggeochem.2013.11.009 SN - 0146-6380 VL - 66 SP - 125 EP - 136 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Basavaiah, Nathani A1 - Wiesner, M. G. A1 - Anoop, Ambili A1 - Menzel, P. A1 - Nowaczyk, Norbert R. A1 - Deenadayalan, K. A1 - Brauer, Achim A1 - Gaye, Birgit A1 - Naumann, R. A1 - Riedel, N. A1 - Stebich, M. A1 - Prasad, Sushma T1 - Physicochemical analyses of surface sediments from the Lonar Lake, central India - implications for palaeoenvironmental reconstruction JF - Fundamental and applied limnology : official journal of the International Association of Theoretical and Applied Limnology N2 - We report the results of our investigations on the catchment area, surface sediments, and hydrology of the monsoonal Lonar Lake, central India. Our results indicate that the lake is currently stratified with an anoxic bottom layer, and there is a spatial heterogeneity in the sensitivity of sediment parameters to different environmental processes. In the shallow (0-5 m) near shore oxic-suboxic environments the lithogenic and terrestrial organic content is high and spatially variable, and the organics show degradation in the oxic part. Due to aerial exposure resulting from lake level changes of at least 3m, the evaporitic carbonates are not completely preserved. In the deep water (>5 m) anoxic environment the lithogenics are uniformly distributed and the delta C-13 is an indicator not only for aquatic vs. terrestrial plants but also of lake pH and salinity. The isotopic composition of the evaporites is dependent not only on the isotopic composition of source water (monsoon rainfall and stream inflow) and evaporation, but is also influenced by proximity to the isotopically depleted stream inflow. We conclude that in the deep water environment lithogenic content, and isotopic composition of organic matter can be used for palaeoenvironmental reconstruction. KW - isotopes KW - lonar lake KW - modern surface sediments KW - magnetic parameters KW - monsoon KW - palaeoenvironmental proxies Y1 - 2014 U6 - https://doi.org/10.1127/1863-9135/2014/0515 SN - 1863-9135 VL - 184 IS - 1 SP - 51 EP - 68 PB - Schweizerbart CY - Stuttgart ER - TY - JOUR A1 - Merz, Bruno A1 - Aerts, Jeroen C. J. H. A1 - Arnbjerg-Nielsen, Karsten A1 - Baldi, M. A1 - Becker, Andrew C. A1 - Bichet, A. A1 - Bloeschl, G. A1 - Bouwer, Laurens M. A1 - Brauer, Achim A1 - Cioffi, F. A1 - Delgado, Jose Miguel Martins A1 - Gocht, M. A1 - Guzzetti, F. A1 - Harrigan, S. A1 - Hirschboeck, K. A1 - Kilsby, C. A1 - Kron, W. A1 - Kwon, H. -H. A1 - Lall, U. A1 - Merz, R. A1 - Nissen, K. A1 - Salvatti, P. A1 - Swierczynski, Tina A1 - Ulbrich, U. A1 - Viglione, A. A1 - Ward, P. J. A1 - Weiler, M. A1 - Wilhelm, B. A1 - Nied, Manuela T1 - Floods and climate: emerging perspectives for flood risk assessment and management JF - Natural hazards and earth system sciences N2 - Flood estimation and flood management have traditionally been the domain of hydrologists, water resources engineers and statisticians, and disciplinary approaches abound. Dominant views have been shaped; one example is the catchment perspective: floods are formed and influenced by the interaction of local, catchment-specific characteristics, such as meteorology, topography and geology. These traditional views have been beneficial, but they have a narrow framing. In this paper we contrast traditional views with broader perspectives that are emerging from an improved understanding of the climatic context of floods. We come to the following conclusions: (1) extending the traditional system boundaries (local catchment, recent decades, hydrological/hydraulic processes) opens up exciting possibilities for better understanding and improved tools for flood risk assessment and management. (2) Statistical approaches in flood estimation need to be complemented by the search for the causal mechanisms and dominant processes in the atmosphere, catchment and river system that leave their fingerprints on flood characteristics. (3) Natural climate variability leads to time-varying flood characteristics, and this variation may be partially quantifiable and predictable, with the perspective of dynamic, climate-informed flood risk management. (4) Efforts are needed to fully account for factors that contribute to changes in all three risk components (hazard, exposure, vulnerability) and to better understand the interactions between society and floods. (5) Given the global scale and societal importance, we call for the organization of an international multidisciplinary collaboration and data-sharing initiative to further understand the links between climate and flooding and to advance flood research. Y1 - 2014 U6 - https://doi.org/10.5194/nhess-14-1921-2014 SN - 1561-8633 VL - 14 IS - 7 SP - 1921 EP - 1942 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Rach, Oliver A1 - Brauer, Achim A1 - Wilkes, Heinz A1 - Sachse, Dirk T1 - Delayed hydrological response to Greenland cooling at the onset of the Younger Dryas in western Europe JF - Nature geoscience N2 - The general warming trend of the last deglaciation was interrupted by the Younger Dryas, a period of abrupt cooling and widespread environmental change(1-10). Ice core records suggest the abrupt cooling began 12,846 years ago in Greenland(10), about 170 years before the significant environmental and vegetation change in western Europe(7) classically defined as the Younger Dryas. However, this difference in timing falls within age model uncertainties. Here we use the hydrogen isotope composition of lipid biomarkers from precisely dated varved sediments from Lake Meerfelder Maar to reconstruct hydroclimate over western Europe. We observe a decrease in the hydrogen isotope values of both aquatic and terrestrial lipids 12,850 years ago, indicating cooling climate in this region synchronous with the abrupt cooling in Greenland. A second drop occurs 170 years later, mainly in the hydrogen isotope record of aquatic lipids but to a lesser extent in the terrestrial lipids, which we attribute to aridification, as well as a change in moisture source and pathway. We thus confirm that there was indeed a lag between cooling and substantial hydrologic and environmental change in western Europe. We suggest the delay is related to the expansion of sea ice in the North Atlantic Ocean and the subsequent southward migration of the westerly wind system(9). We further suggest that these hydrological changes amplified environmental change in western Europe at the onset of the Younger Dryas. Y1 - 2014 U6 - https://doi.org/10.1038/NGEO2053 SN - 1752-0894 SN - 1752-0908 VL - 7 IS - 2 SP - 109 EP - 112 PB - Nature Publ. Group CY - New York ER - TY - JOUR A1 - Wolff, Christian Michael A1 - Kristen-Jenny, Iris A1 - Schettler, Georg A1 - Plessen, Birgit A1 - Meyer, Hanno A1 - Dulski, Peter A1 - Naumann, Rudolf A1 - Brauer, Achim A1 - Verschuren, Dirk A1 - Haug, Gerald H. T1 - Modern seasonality in Lake Challa (Kenya/Tanzania) and its sedimentary documentation in recent lake sediments JF - Limnology and oceanography N2 - From November 2006 to January 2010, a sediment trap that was cleared monthly was deployed in Lake Challa, a deep stratified freshwater lake on the eastern slope of Mt. Kilimanjaro in southern Kenya. Geochemical data from sediment trap samples were compared with a broad range of limnological and meteorological parameters to characterize the effect of single parameters on productivity and sedimentation processes in the crater basin. During the southern hemisphere summer (November-March), when the water temperature is high and the lake is biologically productive (nondiatom algae), calcite predominated in the sediment trap samples. During the "long rain" season (March-May) a small amount of organic matter and lithogenic material caused by rainfall appeared. This was followed by the cool and windy months of the southern hemisphere winter (June-October) when diatoms were the main component, indicating a diatom bloom initiated by improvement of nutrient availability related to upwelling processes. The sediment trap data support the hypothesis that the light-dark lamination couplets, which are abundant in Lake Challa cores, reflect seasonal delivery to the sediments of diatom-rich particulates during the windy months and diatom-poor material during the wet season. However, interannual and spatial variability in upwelling and productivity patterns, as well as El Nino-Southern Oscillation (ENSO)-related rainfall and drought cycles, exert a strong influence on the magnitude and geochemical composition of particle export to the hypolimnion of Lake Challa. Y1 - 2014 U6 - https://doi.org/10.4319/lo.2014.59.5.1621 SN - 0024-3590 SN - 1939-5590 VL - 59 IS - 5 SP - 1621 EP - 1636 PB - Wiley CY - Waco ER -