Transverse and linear dunes in an Upper Pleistocene marine sequence, Corinth Basin, Greece

A range of large-scale dunes of oolitic calcarenite composition are exposed in the Corinth Basin of central Greece. These transverse dunes and a very large linear dune (> 15 m high) lie within an Upper Pleistocene, transgressive marine sequence. Tidal flow, accelerated by constriction through a narrow, fault-bounded seaway, is interpreted to have generated the current velocities necessary to produce the dunes. Marine facies in the Upper Pleistocene sequence include beach to offshore conglomerates and sandstones with wave-modified sedimentary structures and herringbone cross-stratification. An offshore facies association comprises variably bioturbated siltstones and sandstones with a varied marine fauna that includes thermophile species such as scleractinian corals and Strombus bubonius. Oolitic sandstone facies also occur. Oolitic sands were apparently produced in shoal environments subject to tidal (and wave) action, and transported by dominant southerly currents over the southern part of the basin. Oolites accumulated in a linear dune 2.7 km long and 15–20 m high and in three-dimensional transverse dunes up to 10 m high having a variety of compound and simple internal geometries. The isolated, WSW-ENE-trending linear form exhibits angle of repose sedimentary dips (up to 35°) of avalanche sets on its SE flank and sets typically with dips of 15–20° to the NW. Internal high-angle discontinuities are developed in the SE-dipping lee face. It is proposed that a dominant north-to-south flow crossed over the crest obliquely, resulting in both net erosional and depositional processes on the lee flank. A subordinate (?tidal) current may have locally and or periodically crossed the dune crest in a westwards direction. A string of transverse dunes, which were located adjacent to a fault/marine terrace scarp, is interpreted to have originally coalesced to form the linear dune. The distribution of transverse and linear dunes together with the palaeogeographical reconstruction suggest that a marine connection periodically existed across the Corinth Isthmus during the Late Pleistocene due to a combination of active faulting and glacio-eustatic highstands of sea level.     

Nitrogen fluxes in a high elevation colorado rocky mountain basin

Measured, calculated and simulated values were combined to develop an annual nitrogen budget for Loch Vale Watershed (LVWS) in the Colorado Front Range. Nine-year average wet nitrogen deposition values were 1·6 (s=0·36) kg NO₃-N ha⁻¹, and 1·0 (s=0·3) kg NH₄-N ha⁻¹. Assuming dry nitrogen deposition to be half that of measured wet deposition, this high elevation watershed receives 3·9 kg N ha⁻¹. Although deposition values fluctuated with precipitation, measured stream nitrogen outputs were less variable. Of the total N input to the watershed (3·9 kg N ha⁻¹ wet plus dry deposition), 49% of the total N input was immobilized. Stream losses were 2·0 kg N ha⁻¹ (1125 kg measured dissolved inorganic N in 1992, 1–2 kg calculated dissolved organic N, plus an average of 203 kg algal N from the entire 660 ha watershed). Tundra and aquatic algae were the largest reservoirs for incoming N, at approximately 18% and 15% of the total 2574 kg N deposition, respectively. Rocky areas and forest stored the remaining 11% and 5%, respectively. Fully 80% of N losses from the watershed came from the 68% of LVWS that is alpine. © 1997 John Wiley & Sons, Ltd.     

ASSESSMENT OF CLIMATE CHANGE AND FRESHWATER ECOSYSTEMS OF THE ROCKY MOUNTAINS,USA AND CANADA

The Rocky Mountains in the USA and Canada encompass the interior cordillera of western North America, from the southern Yukon to northern New Mexico. Annual weather patterns are cold in winter and mild in summer. Precipitation has high seasonal and interannual variation and may differ by an order of magnitude between geographically close locales, depending on slope, aspect and local climatic and orographic conditions. The region's hydrology is characterized by the accumulation of winter snow, spring snowmelt and autumnal baseflows. During the 2–3-month ‘spring runoff’ period, rivers frequently discharge > 70% of their annual water budget and have instantaneous discharges 10–100 times mean low flow. Complex weather patterns characterized by high spatial and temporal variability make predictions of future conditions tenuous. However, general patterns are identifiable; northern and western portions of the region are dominated by maritime weather patterns from the North Pacific, central areas and eastern slopes are dominated by continental air masses and southern portions receive seasonally variable atmospheric circulation from the Pacific and the Gulf of Mexico. Significant interannual variations occur in these general patterns, possibly related to ENSO (El Niño–Southern Oscillation) forcing. Changes in precipitation and temperature regimes or patterns have significant potential effects on the distribution and abundance of plants and animals. For example, elevation of the timber-line is principally a function of temperature. Palaeolimnological investigations have shown significant shifts in phyto- and zoo-plankton populations as alpine lakes shift between being above or below the timber-line. Likewise, streamside vegetation has a significant effect on stream ecosystem structure and function. Changes in stream temperature regimes result in significant changes in community composition as a consequence of bioenergetic factors. Stenothermic species could be extirpated as appropriate thermal criteria disappear. Warming temperatures may geographically isolate cold water stream fishes in increasingly confined headwaters. The heat budgets of large lakes may be affected resulting in a change of state between dimictic and warm monomictic character. Uncertainties associated with prediction are increased by the planting of fish in historically fishless, high mountain lakes and the introduction of non-native species of fishes and invertebrates into often previously simple food-webs of large valley bottom lakes and streams. Many of the streams and rivers suffer from the anthropogenic effects of abstraction and regulation. Likewise, many of the large lakes receive nutrient loads from a growing human population. We concluded that: (1) regional climate models are required to resolve adequately the complexities of the high gradient landscapes; (2) extensive wilderness preserves and national park lands, so prevalent in the Rocky Mountain Region, provide sensitive areas for differentiation of anthropogenic effects from climate effects; and (3) future research should encompass both short-term intensive studies and long-term monitoring studies developed within comprehensive experimental arrays of streams and lakes specifically designed to address the issue of anthropogenic versus climatic effects. © 1997 John Wiley & Sons, Ltd.