Spatial Ecology of Pre –Euro‐American Fires in a Southern Rocky Mountain Subalpine Forest Landscape

Natural disturbances such as fires have been widely studied, but less is known about their spatial ecology than about other aspects of them. We reconstructed and mapped pre–Euro‐American fire history in a subalpine forest landscape in southeastern Wyoming, and analyzed the fires using GIS. Mean fire interval varies little with topography (elevation, aspect, slope) and is spatially autocorrelated at distances of at least 2 km. Fires often spread downslope, and spread more than expected from the north and south and less than expected from the west, under the influence of particular synoptic climatic conditions. The landscape of 1868 a.d., at the time of Euro‐American settlement, was strongly influenced by fires. However, it contained large patches of connected forest and few high‐contrast edges, unlike the modern landscape, which is fragmented by industrial forestry and roads. The spatial ecology of the natural fire regime may be a useful guide for management.     

High spatial and temporal resolution observations of the ionospheric cusp

The Halley PACE HF radar has been operated in a new mode to provide very high time (10 s) and space (15 km) resolution measurements of the iono-spheric signatures of the cusp and the low-latitude boundary layer. The first data show that the iono-spheric signature of flux transfer events occur up to 300 km equatorward of regions showing the HF characteristics of the ionospheric cusp. Whilst larger flux transfer events are seen, on average, every 7 min, many much smaller and short-duration events have been identified. On one occasion DMSP data have been used to show that at least four flux transfer events are occurring simultaneously at the edge of the cusp over 2 h of MLT. There is strong, but not conclusive evidence, that reconnection at the magnetopause is both intermittent and patchy. These data also suggest that flux transfer events can be a significant contributor to the cross-polar cap potential.     

Hydroxyl temperature and intensity measurements during noctilucent cloud displays

Two Fourier transform spectrometers have been used to investigate the properties of the near-infrared hydroxyl (OH) nightglow emission under high-latitude summertime conditions and any association with noctilucent clouds (NLCs). The measurements were made from Poker Flat Research Range, Alaska (65.1°N, 147.5°W), during August 1986. Simultaneous photographic observations of the northern twilight sky were made from Gulkana, Alaska (62.2°N, 145.5°W), approximately 340 km to the south to establish the presence of NLCs over the spectrometer site. Data exhibiting significant short-term variations in the relative intensity (as much as 50-100%) and rotational temperature (typically 5–15 K) were recorded on six occasions when NLCs were observed. Joint measurements were also obtained on several “cloud-free” nights. No obvious relationship was found linking the mean OH intensity or its variation with the occurrence of NLCs. However, a clear tendency was found for the mean OH temperature to be lower on NLC nights than on cloud-free nights. In particular, a significant fraction of the OH(3-1) band spectra recorded by each instrument (16-57%) exhibited temperatures below \sim154 K on NLC nights compared with <3% on cloud-free nights. This result is qualitatively consistent with current models for ice particle nucleation and growth, but the mean OH temperature on NLC nights (\sim156 K) was significantly higher than would be expected for long-term particle growth in this region. These observations raise questions concerning the expected proximity of the high-latitude, summertime OH layer and the NLC growth region.     

Channel form and processes of the flood-dominated Narmada River,India

The 1300 km long Narmada River flows along a structural lineament, alternating between constricting rocky gorges and rapids, and meandering wide alluvial reaches. Channel forms and processes were studied in a 120 km long section of an alluvial reach. Channel size, shape and bedforms in the Narmada River are related to very large floods which have occurred three times in this century. During such floods the entire 400 m wide channel is utilized and 10–15 m high cliffs on both sides operate as riverbanks. Normally, even the high flows of the south-western monsoon are insufficient to fill the whole channel, and hence their effects are limited to building of discontinuous floodplains between the cliffs and modifying bedforms and bars. A channel-in-channel topography is thus created. The very large floods are also responsible for erosion of the rocky stretches and building of point bars. The river meanders, but its movement is restricted because of (1) rocky gorges and scablands operating as anchor points at intervals, and (2) the presence of high alluvial cliffs which are topped on extremely rare occasions. In spite of being located in a tectonically active zone in a monsoon setting, it is the exceptional high-magnitude floods at irregular intervals which control the form and behaviour of the Narmada River.     

Effects of salinity on the condition and survival of zebra mussels (Dereissena polymorpha)

The objectives of this study were to determine the tolerance of various life stages of zebra mussels to salinity; determine the extent to which acclimation events in estuarine systems, affect tolerance of zebra mussels; and determine the effects of salinity on health or condition of adult zebra mussels. At high temperatures (18–20°C), the condition of zebra mussels is reduced at salinities above 1%.. However, at lower temperatures (3–12°C), the optimum salinity for zebra mussels is 2–4%.. The incipient lethal salinity of post-veligers is near 2%., of larger adults (5–15 mm) between 2%. and 4%., and of veliger larvae near 4.5%.. Zebra mussels are able to acclimate to slowly changing salinities (i.e., 1%. d^?1) such that the time to 50% mortality of a population should be greater than 1 yr at temperatures near 20°C and salinites up to 8%.     

Oxygen isotope exchange between illite and water at 22°C

Oxygen isotope exchange experiments at 22°C have been made on a series of illites displaying a range of perfection of crystallinity and degree of interstratification. Structurally bound oxygen underwent significant non-equilibrium exchange in time periods ranging from 2 to 70 months. Exchange was found to be controlled by accessibility of water to the interlayer cation region.1000 In α appears to be in the general neighborhood of +23.4 at 22°C for the illite-water system; however, it was found that equilibrium fractionation cannot be represented by a single value for structurally and chemically distinct illites.