Effects of ultrasonic cleaning on the amino acid geochemistry of foraminifera tests

Although investigations into amino acid geochemistry of foraminifera have included the use of ultrasonic cleaners as part of their cleaning procedure, there apparently has been no attempt to determine what effects this procedure may have on the observed chemical changes. This paper presents the results of a time study showing the effects of cleaning on ten protein amino acids and the non-protein alloisoleucine. The data suggest that there are three loosely defined groups which all ultimately undergo an exponential decrease in concentration, but which vary within the initial 45 min of treatment: Group I, stable; Group II, constantly decreasing; Group III, showing slight increases. The observed effects suggest that studies based on amino acid enantiomeric ratios probably are the least affected by procedural errors introduced by ultrasonification.     

Crater size-shape profiles for the moon and mercury: Terrain effects and interplanetary comparisons

New crater size-shape data were compiled for 221 fresh lunar craters and 152 youthful mercurian craters. Terraces and central peaks develop initially in fresh craters on the Moon in the 0–10 km diameter interval. Above a diameter of 65 km all craters are terraced and have central peaks. Swirl floor texture is most common in craters in the size range 20–30 km, but it occurs less frequently as terraces become a dominant feature of crater interiors. For the Moon there is a correlation between crater shape and geomorphic terrain type. For example, craters on the maria are more complex in terms of central peak and terrace detail at any given crater diameter than are craters in the highlands. These crater data suggest that there are significant differences in substrate and/or target properties between maria and highlands. Size-shape profiles for Mercury show that central peak and terrace onset is in the 10–20 km diameter interval; all craters are terraced at 65 km, and all have central peaks at 45 km. The crater data for Mercury show no clear cut terrain correlation. Comparison of lunar and mercurian data indicates that both central peaks and terraces are more abundant in craters in the diameter range 5–75 km on Mercury. Differences in crater shape between Mercury and the Moon may be due to differences in planetary gravitational acceleration (gMercury=2.3gMoon). Also differences between Mercury and the Moon in target and substrate and in modal impact velocity may contribute to affect crater shape.     

Coastal wetland subsidence arising from local hydrologic manipulations

Twenty-three estimates of soil subsidence rates arising under the influence of local hydrologic changes from flap-gates, weirs, dikes, and culverts in tidal wetlands were compared to 75 examples of subsidence in drained agricultural wetlands. The induced subsidence rates from these hydrologic modifications in tidal wetlands can continue for more than 100 years, and range between 1.67 to 0.10 cm yr⁻¹ within 1 to 155 years after the hydrologic modifications commence. These subsidence rates are lower than in freshwater wetlands drained for agricultural purposes, decline with age, and are significant in comparison to the rates of global sea level rise or the average soil accretion rates. The elevation change resulting from local hydrologic manipulations is significant with respect to the narrow range of flood tolerances of salt marsh plants, especially in microtidal environments.     

Sensitivity analysis of seismic hazard for the northwestern portion of the state of Gujarat, India

We test the sensitivity of seismic hazard to three fault source models for the northwestern portion of Gujarat, India. The models incorporate different characteristic earthquake magnitudes on three faults with individual recurrence intervals of either 800 or 1600 years. These recurrence intervals imply that large earthquakes occur on one of these faults every 266–533 years, similar to the rate of historic large earthquakes in this region during the past two centuries and for earthquakes in intraplate environments like the New Madrid region in the central United States. If one assumes a recurrence interval of 800 years for large earthquakes on each of three local faults, the peak ground accelerations (PGA; horizontal) and 1-Hz spectral acceleration ground motions (5% damping) are greater than 1 g over a broad region for a 2% probability of exceedance in 50 years' hazard level. These probabilistic PGAs at this hazard level are similar to median deterministic ground motions. The PGAs for 10% in 50 years' hazard level are considerably lower, generally ranging between 0.2 g and 0.7 g across northwestern Gujarat. Ground motions calculated from our models that consider fault interevent times of 800 years are considerably higher than other published models even though they imply similar recurrence intervals. These higher ground motions are mainly caused by the application of intraplate attenuation relations, which account for less severe attenuation of seismic waves when compared to the crustal interplate relations used in these previous studies. For sites in Bhuj and Ahmedabad, magnitude (M) 7 3/4 earthquakes contribute most to the PGA and the 0.2- and 1-s spectral acceleration ground motion maps at the two considered hazard levels.     

Competition as a barrier to establishment of a native perennial grass (Elymus elymoides) in alien annual grass (Bromus tectorum) communities

The alien grass Bromus tectorum dominates stable annual-plant communities that have replaced native shrub-perennial grass communities over much of the semi-arid western United States. We conducted field competition experiments between B. tectorum and a native grass, Elymus elymoides, on two sites to determine the effects of B. tectorum competition on perennial grasses, and the role of B. tectorum competition in the stability of B. tectorum-dominated communities. B. tectorum competition acting on seedling-stage E. elymoides plants greatly reduced first-year relative growth rates and biomass which, in turn, reduced second-year survival, biomass, and flowering. However, B. tectorum competition acting on older E. elymoides plants had much less effect, which may help to explain why intact perennial-plant communities are resistant to B. tectorum invasion. At the drier site, direct effects of B. tectorum competition were less, but competition and drier habitat combined to produce greater E. elymoides mortality.     

Diatom-based interpretation of sediment banding in an urbanized lake

Sediment stratigraphy and diatom succession were studied in an 80.5-cm core taken from the deepest part of Third Sister Lake, a small kettle hole in a recently urbanized landscape of southeastern Michigan. Alternating light clay and dark organic bands documented sporadic inputs of clay from outside the basin during rain events, rather than annual laminations. Urban construction activity also disrupted the inflow stream bed and facilitated transport of clay into the lake to generate non-rhythmic banding in the lake's deep hole. Diatom analysis revealed dramatic changes in predominant taxa with sediment depth verifying the non-annual nature of the sediment bands. Observation of halophilic diatom taxa also documented effects of human activity such as road salting on this small, urban lake.     

Nature’s pulsing paradigm

While the steady state is often seen as the final result of development in nature, a more realistic concept may be that nature pulses regularly to make a pulsing steady stata—a new paradigm gaining acceptance in ecology and many other fields. In this paper we compare tidal salt marshes, tidal freshwater marshes, and seasonally flooded fresh-water wetlands as examples of pulsed ecosystems. Despite marked differences in species composition, biodiversity, and community structure, these wetland types are functionally similar because of the common denominator of water flow pulses. Often a period of high production alternates with a period of rapid consumption in these fluctuating water-level systems, a biotic pulsing to which many life histories, such as that of the wood stork, are adapted. Pulsing of medium frequency and amplitude often provides an energy subsidy for the community thus enhancing its productivity. The energy of large-scale pulses such as storms are usually dissipated in natural ecosystems with little harm to the biotic network; however, when seawalls, dikes, or stabilized sand dunes are constructed to confront these strong pulses, the whole ecosystem (and associated human structures) may be severly damaged when the barriers fail because too much of the storm energy is concentrated on them. The relationship between biologically mediated internal pulsing, such as plant-herbivore or predator-prey cycles, and physical external pulsing is discussed not only in wetlands but in other ecosystem types as well. An intriguing hypothesis is that ecosystem performance and species survival are enhanced when external and internal pulses are coupled. We suggest that if pulsing is general, then what is sustainable in ecosystems, is a repeating oscillation that is often poised on the edge of chaos.