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This study provides the first detailed estimate of riverine organic carbon fluxes in British rivers, as well as highlighting major gaps in organic carbon data in national archives. Existing data on organic carbon and suspended solids concentrations collected between 1989 and 1993, during routine monitoring by the River Purification Boards (RPBs) in Scotland and the National River Authorities (NRAs) in England and Wales, were used with annual mean flows to estimate fluxes of dissolved and particulate organic carbon (DOC and POC) in British rivers. Riverine DOC exports during 1993 varied from 7·7–103·5 kg ha−1 year−1, with a median flux of 31·9 kg ha−1 year−1 in the 85 rivers for which data were available. There was a trend for DOC fluxes to increase from the south and east to the north and west. A predictive model based on mean soil carbon storage in 17 catchments, together with regional precipitation totals, explained 94% of the variation in the riverine DOC exports in 1993. This model was used to predict riverine DOC fluxes in regions where no organic carbon data were available. Calculated and predicted fluxes were combined to produce an estimate for exports of DOC to tidal waters in British rivers during 1993 of 0·68±0·07 Mt. Of this total, rivers in Scotland accounted for 53%, England 38% and Wales 9%. Scottish blanket peats would appear to be the largest single source of DOC exports in British rivers. An additional 0·20 Mt of organic carbon were estimated to have been exported in particulate form in 1993, approximately two–thirds of which was contributed by English rivers. It is suggested that riverine losses of organic carbon have the potential to affect the long-term dynamics of terrestrial organic carbon pools in Britain and that rivers may regulate increases in soil carbon pools brought about by climate change. © 1997 by John Wiley & Sons, Ltd. 相似文献
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KIM AARIS-SØRENSEN RONNIE LILJEGREN 《Boreas: An International Journal of Quaternary Research》2004,33(1):61-73
This article presents new data on the Late Pleistocene giant deer, Megaloceros giganteus (Blumenbach), describing its distribution in time and space, geographical and sexual variation and general biology. Twenty‐three south Scandinavian fossils found in situ in lacustrine sediments or redeposited in glaciofluvial material form the basis of this investigation. Fourteen C dates show that the giant deer inhabited southern Scandinavia in the ice‐free late Middle Weichselian from c. 40000 to 28000 BP (the Sandnes Interstadial) and again in the Late Weichselian from c. 12000 to 10700 BP (Older Dryas, Allerød and early Younger Dryas Chronozones), corresponding to a calibrated range from c. 14300 to 12400 cal. yr BP. Osteometric analyses show that the Scandinavian giant deer belonged to the upper size range of the lateglacial Irish population and that a marked sexual dimorphism existed, the males being 10–11% larger than the females. Investigations furthermore point at an antler cycle similar to that among extant northern cervids, and subsequently at a rutting season in autumn. The skeletal remains also prove the occurrence of twin delivery and the possibility of reaching an ontogenetic age of at least 23 years. During both occurrences the Scandinavian giant deer population was part of the northernmost distribution of the species in Europe and the palaeogeographical settings and palaeoenvironmental conditions of the two periods show striking similarities. Clearly, the giant deer were able to colonize and survive in a landscape dominated by grasses and sedges with scattered shrubs and dwarf shrubs. They came as close as 200–250 km to the ice front and their distribution included coastal areas along a cold sea with drifting icebergs. They were present in the area at least from March until November. However, the pure arctic conditions created during the early phase of the Younger Dryas event led to a new local extinction around 10700 14C yr BP. This was the beginning of a total Eurasian extinction which, at least in Europe, was completed before the Pleistocene/Holocene transition. 相似文献
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PATRICK J. MULHOLLAND G. RONNIE BEST CHARLES C. COUTANT GEORGE M. HORNBERGER JUDY L. MEYER PETER J. ROBINSON JOHN R. STENBERG R. EUGENE TURNER FRANCISCO VERA-HERRERA ROBERT G. WETZEL 《水文研究》1997,11(8):949-970
The south-eastern United States and Gulf Coast of Mexico is physiographically diverse, although dominated by a broad coastal plain. Much of the region has a humid, warm temperate climate with little seasonality in precipitation but strong seasonality in runoff owing to high rates of summer evapotranspiration. The climate of southern Florida and eastern Mexico is subtropical with a distinct summer wet season and winter dry season. Regional climate models suggest that climate change resulting from a doubling of the pre-industrial levels of atmospheric CO2 may increase annual air temperatures by 3–4°C. Changes in precipitation are highly uncertain, but the most probable scenario shows higher levels over all but the northern, interior portions of the region, with increases primarily occurring in summer and occurring as more intense or clustered storms. Despite the increases in precipitation, runoff is likely to decline over much of the region owing to increases in evapotranspiration exceeding increases in precipitation. Only in Florida and the Gulf Coast areas of the US and Mexico are precipitation increases likely to exceed evapotranspiration increases, producing an increase in runoff. However, increases in storm intensity and clustering are likely to result in more extreme hydrographs, with larger peaks in flow but lower baseflows and longer periods of drought. The ecological effects of climate change on freshwaters of the region include: (1) a general increase in rates of primary production, organic matter decomposition and nutrient cycling as a result of higher temperatures and longer growing seasons: (2) reduction in habitat for cool water species, particularly fish and macroinvertebrates in Appalachian streams; (3) reduction in water quality and in suitable habitat in summer owing to lower baseflows and intensification of the temperature–dissolved oxygen squeeze in many rivers and reservoirs; (4) reduction in organic matter storage and loss of organisms during more intense flushing events in some streams and wetlands; (5) shorter periods of inundation of riparian wetlands and greater drying of wetland soils, particularly in northern and inland areas; (6) expansion of subtropical species northwards, including several non-native nuisance species currently confined to southern Florida; (7) expansion of wetlands in Florida and coastal Mexico, but increase in eutrophication of Florida lakes as a result of greater runoff from urban and agricultural areas; and (8) changes in the flushing rate of estuaries that would alter their salinity regimes, stratification and water quality as well as influence productivity in the Gulf of Mexico. Many of the expected climate change effects will exacerbate current anthropogenic stresses on the region's freshwater systems, including increasing demands for water, increasing waste heat loadings and land use changes that alter the quantity and quality of runoff to streams and reservoirs. Research is needed especially in several critical areas: long-term monitoring of key hydrological, chemical and biological properties (particularly water balances in small, forested catchments and temperature-sensitive species); experimental studies of the effects of warming on organisms and ecosystem processes under realistic conditions (e.g. in situ heating experiments); studies of the effects of natural hydrological variation on biological communities; and assessment of the effects of water management activities on organisms and ecosystem processes, including development and testing of management and restoration strategies designed to counteract changes in climate. © 1997 John Wiley & Sons, Ltd. 相似文献
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