Study on Surface and Internal Humidity of Dunes in the Southwestern Margin of the Taklimakan Desert

Greening on the edge of desert is an effective way to prevent and control desertification. This paper studies the humidity characteristics of sand samples collected from the surface and interior of dunes in the southwestern edge of the Taklimakan Desert, whose geographic coordinates are 39°43’37” – 39°43’41” N, 78°43’02” – 78°43’09” E. The humidity of sand samples at vertical depths under five different surface positions of windward slope bottom, windward slope middle, windward slope top, leeward slope middle and leeward slope bottom was studied. On the surface of the sand at different locations and at the same depth under the surface, the sand humidity is greater closer to the bottom of the slope, for both windward slope and leeward slope. The humidity gradient values on the surface and at different depths on different positions of the dunes are obtained. Finally, recommendations are provided for effective ways to prevent desertification in the desert edge of Kashgar.

Spatial variation in soil physical properties and effects on soil NO3– production on forest hillslopes

<p>Ammonium (NH<sub>4</sub><sup>+</sup>) and nitrate (NO<sub>3</sub><sup>–</sup>) concentrations and production rates in forest soil vary by hillslope position due to variation in ammonia-oxidizing microorganism concentrations, soil chemistry, and surface soil moisture. These spatial distributions have a significant effect on nutrient cycles and streamwater chemistry. Soil moisture conditions significantly restrict microbial activity, influencing the spatial distribution of NO<sub>3</sub><sup>–</sup> concentrations on forest hillslopes. However, studies linking forest hydrological processes to nitrogen cycling are limited. Therefore, we investigated the determinants of spatial variation in soil moisture and evaluated the effects of soil moisture fluctuations on spatial variation in NO<sub>3</sub><sup>–</sup> concentration and production rate.</p><p>The study sites were the Fukuroyamasawa Experimental Watershed (FEW) and Oyasan Experimental Watershed (OEW) in Japan. The two have similar topographies, climates, and tree species. In each watershed, a 100 m transect was set up from the ridge to the base of the slope, and soil moisture sensors were installed at soil depths of 10 cm and 30 cm at both the top and bottom of the slope. We collected surface soil samples at a depth of 10 cm at the top, middle, and bottom of the slopes using 100 cm<sup>3</sup> cores, and measured soil physical properties, particle size distribution, volcanic ash content, chemical properties (pH, NO<sub>3</sub><sup>–</sup>, NH<sub>4</sub><sup>+</sup>, nitrification rate, and mineralization rate), and microbial content (archaeal content). Spatial and temporal changes in soil moisture on the hillslope were calculated using HYDRUS-2D to examine contributing factors of soil moisture.</p><p>At FEW, high NO<sub>3</sub><sup>–</sup> concentrations and nitrification rates were observed only at the slope bottom and middle, and no NO<sub>3</sub><sup>–</sup> concentrations were detected at up slope. By contrast, at OEW, high NO<sub>3</sub><sup>–</sup> concentrations and nitrification rates were observed at all points. NH<sub>4</sub><sup>+</sup> concentrations were similar at all points in both watersheds. At FEW, 10 cm surface soil moisture fluctuated within 25–40% at the slope top but was within 40–50% at the slope bottom. At OEW, surface soil moisture was 30–40% at both the slope top and bottom, with no significant differences according to slope position. It was confirmed that soil moisture was significantly involved in NO<sub>3</sub><sup>– </sup>concentration and nitrification rates. Model simulations showed that the difference in soil moisture fluctuations between FEW and OEW was mainly explained by the spatial variation in soil physical properties. In particular, volcanic ash influenced soil moisture along the entire slope at OEW, resulting in high water retention, but only influenced soil moisture at the slope bottom at FEW. These findings indicate that spatial variability in soil physical properties has a significant effect on soil moisture fluctuation and leads to a spatial distribution of NO<sub>3</sub><sup>–</sup> production.</p>

Behaviour of Lake Baikal amphipods as a part of the night migratory complex in the Kluevka settlement region (south-eastern Baikal)

The night migration complex in the bottom zone of the shallow-water slope on the east coast of southern Lake Baikal near the village of Kluevka was investigated. According to the observations, it was established that the pelagic fish of the suborder Cottoidei and the pelagic amphipodMacrohectopus branickiican sporadically participate in the migration complex. The mass presence of benthic amphipods was highest in the first minute of observations, with more than 250 individuals/freeze-frame, and then stabilized at 43-65 individuals/freeze-frame. The Juday net-collected amphipods comprised only one typically benthic species,Micruropus wohlii platycercus, which is known to be a nocturnal migrant. For the first time, the typically pelagic speciesM. branickii, was observed in the migratory complex over shallow coastal shoal, which species, according to all previous studies, was considered to inhabit only greater depths and to avoid areas with depths of less than 100 m, such as shallow-water slope bottom zones.

Numerical Simulation of Nonlinear Wave Propagation and Breaking Over Constant-Slope Bottom

The numerical simulation of the two-dimensional free-surface flow resulting from the propagation of nonlinear gravity waves over constant-slope bottom is presented. The simulation is based on the numerical solution of the Euler equations subject to the fully nonlinear free-surface boundary conditions and the appropriate bottom, inflow and outflow conditions using a hybrid finite-differences and spectral-method scheme. Wave breaking is accounted for by a surface roller model. The formulation includes a boundary-fitted transformation and is suitable for future extension to incorporate large-eddy and large-wave simulation terms. Results are presented for the simulation of the free-surface flow over two different bottom topographies, with constant slope values of 1:10 and 1:50, and three different inflow wave heights. Over the bottom slope, waves of small wave heights are modified according to linear theory. For nonlinear waves, wavelengths are becoming shorter, the free surface elevation deviates from its initial sinusoidal shape and wave heights increase with decreasing depth. Breaking is observed for the cases with the larger initial wave height and the smaller outflow depth.