Using GRASS GIS to Model Solar Irradiation on North Carolina Aquatic Habitats with Canopy Data

Sunlight can have a significant impact on freshwater aquatic communities. Using 64‐ bit GRASS, a previously generated 18.2 m resolution forest canopy height grid for the State of North Carolina was used as a base elevation layer for calculation of 18.2 m resolution total irradiance (Watt‐hours/square meter/day) grids for 365 days of the year. Daily calculations were aggregated annually and overlaid on rasterized 1:24,000‐scale USGS hydrology with canopy type and seasonal filters to quantify annual solar irradiation input to streams and rivers in North Carolina. Bare earth calculations of solar irradiation for the aquatic habitats were compared to the canopy filtered calculations. There was substantially less solar irradiation in aquatic habitats under the canopy filtered model. Total solar irradiation for subbasins created from point locations of occurrences of Dwarf wedgemussel (Alasmidonta heterodon) were compared with total solar irradiation for watersheds created from locations with no mussels for the full subbasin, 1 km, and 500 m upstream from the sampling point. There was no significant difference in the amount of total solar irradiation modeled for the subbasins with Dwarf wedgemussel and watersheds with no mussels.     

Atmospheric equilibrium,instability and energy transport at the last glacial maximum

A range of diagnostics from two GCM simulations, one of the present-day climate and one of the last glacial maximum (LGM) is used to gain insight into their different temperature structures and eddy dynamics. There are large local increases in baroclinicity at the LGM, especially in the Atlantic storm track, with large accompanying increases in the low level transient eddy heat flux. However, the differences in the zonal mean are much smaller, and the increases in both baroclinicity and heat flux are confined to low levels. Supplementary experiments with baroclinic wave lifecycles confirm the marked contrast between local and zonal mean behaviour, but do not adequately explain the differences between the zonal mean climates. The total flux of energy across latitude circles in the Northern Hemisphere does not change much during DJF, although its transient component is actually reduced at the LGM (during JJA the transient component is increased). Calculations of total linear eddy diffusivity reveal that changes in the time mean stationary waves are chiefly responsible for the seasonal range of this quantity at the LGM, while they only account for half the seasonal range at the present-day.     

Relative humidity recorded in tree rings: A study along a precipitation gradient in the Olympic Mountains, Washington, USA

Humidity is one of the fundamental variables controlling the energy balance of the climate, and thus its reconstruction represents a significant aspect of paleoclimate studies. We here report a study of oxygen and hydrogen isotopic compositions of tree-ring cellulose along a precipitation gradient in the Olympic Mountains of Washington, USA, to examine whether and how the relative humidity is recorded in the cellulose. According to the physically-based model described in this paper, the relationship between δD and δ¹⁸O of cellulose should have the same slope as that in the relationship between δD and δ¹⁸O in the source water (∼8.8 for the local meteoric water) if there is no systematic variation in the mean relative humidity among study sites and no physiologic differences among trees. However, our isotopic analyses of cellulose yielded a slope of 17.4, significantly greater than the slope of the Local Meteoric Water Line. We show that to produce such a slope, a positive covariation between the relative humidity and the δD and δ¹⁸O in the source water is required across the precipitation gradient. This work suggests that the δD vs. δ¹⁸O relationship in tree rings can be a useful tool for paleohumidity reconstruction.     

Persisting effects of armored military maneuvers on some soils of the Mojave Desert

Soil compaction and substrate modification produced during large-scale armored military maneuvers in the early 1940s were examined in 1981 at seven sites in California’s eastern Mojave Desert Recording penetrometer measurements show that tracks left by a single pass of an M3 “medium” tank have average soil resistance values that are 50% greater than those of the surrounding untracked soil in the upper 20 cm At one site, measurements made along short segments of track that have been visually eliminated by erosion and deposition processes show a 73% increase in penetrometer resistance over adjacent, undisturbed soils Dirt roadways at three former base camp locations could not be penetrated below 5–10 cm because of extreme compaction Soil bulk density was not as sensitive an indicator of soil compaction as was penetrometer resistance Density values in the upper 10 cm of soil are not significantly different between tank tracks and undisturbed soils at most sites, and roadways at two base camps show an average increase in bulk density of only 12% over adjacent soils. Trench excavations across tank tracks show that physical modifications of the substrate can extend vertically beneath a track to a depth of 25 cm and outward from a track’s edge to 50 cm These soil disturbances are probably major factors that encourage accelerated soil erosion throughout the manuever area and also retard or prevent the return of vegetation to pre-disturbance conditions     

The Zymoetz River landslide, British Columbia, Canada: description and dynamic analysis of a rock slide–debris flow

The Zymoetz River landslide is a recent example of an extremely mobile type of landslide known as a rock slide–debris flow. It began as a failure of 900,000 m³ of bedrock, which mobilized an additional 500,000 m³ of surficial material in its path, transforming into a large debris flow that traveled over 4 km from its source. Seasonal snow and meltwater in the proximal part of the path were important factors. A recently developed dynamic model that accounts for material entrainment, DAN3D, was used to back-analyze this event. The two distinct phases of motion were modeled using different basal rheologies: a frictional model in the proximal path and a Voellmy model in the distal path, following the initiation of significant entrainment. Very good agreement between the observed and simulated results was achieved, suggesting that entrainment capabilities are essential for the successful simulation of this type of landslide.     

Quantifying Isotopic Heterogeneity of Candidate Reference Materials at the Picogram Sampling Scale

We propose a method for quantifying the in situ heterogeneity of solid materials at the picogram test portion scale, illustrating its use by investigating the oxygen isotope ratio (¹⁸O^?/¹⁶O^?) of four quartz samples. Using secondary ion mass spectrometry, we could estimate the intrinsic heterogeneity using a large number (~ 100) of closely spaced duplicated measurements. An analysis of variance was then applied to these large data sets to extract the measurement repeatability (typically 0.10–0.15‰, 1s) from the total variability, thereby revealing a variability ranging from 0.18‰ to 2.3‰, which can be attributed to the genuine isotope ratio heterogeneities. A small proportion of outlying values were either rejected manually after inspection, or were accommodated using robust statistics. We also evaluated two distinct approaches for estimating and correcting instrumental drift; the use of a sub‐area of the test material (if shown to have sufficiently low heterogeneity) is judged to be preferable to using a piece of unrelated silicate glass that we believe to be homogeneous. We also compared three approaches for estimating measurement repeatability, from which we show that the ‘duplicate method’ applied to the reference material is preferable to using other methods based either on the drift monitoring material or on assessing residuals of the drift monitoring material after drift correction. Finally, here we propose a strategy for predicting the number of measurements on individual fragments of a material that would be required to achieve a specified target uncertainty.