Arid Semiarid Research Articles

Analysis of complex ecological system of the Qinghai Lake catchment

青海湖流域是西北半干旱地区一个典型的复合生态系统,它主要由草地、湖泊、沙漠、农田和城镇生态系统复合而成。该系统具有高寒干旱、太阳辐射强,以及交通闭塞、人口少、经济落后等特点,因而抗干扰能力弱、输出水平较低。在气候暖干化条件下,不合理的人类经济活动使该系统暴露出土地沙化、植被退化、湖水位下降、渔业减产和鸟岛生态环境恶化以及潜在的工业污染扩大等一系列的生态环境问题。;Qinghai Lake coitchment,a typical complex ecosystem in the arid-semi arid region of Northwest China,is competed of grass lands, lakes Tdesert,farm lands,cities and towns.The system is characterized by dry and cold alpine,strong solar radiation,traffic inconveniece,a sparse population and backward econom-mic conditions,therefore showing a w-eak capacity of resistance and a lower output.Under warm and dry climatic conditions,the unreasonable human activities cause a series of eco-evironmental degradation,in-eluding land desertization,vegetation deterioration, decline of lake level,decrease in fish catch, ecological degradation in Bird Island and potential industrial pollution.

Sub‐Grid‐Scale Characterization of Channel Lengths for Use in Catchment Modeling

We explored methods for extrapolating mainstream channel lengths of first‐order drainage basins from synoptic data to characterize them for numerical watershed modeling. We analyzed four catchments in a climatologically semiarid arid geologically homogeneous region east of the Cascade Mountains in Washington state. Within each of these catchments, we identified stream channel networks manually from 1:24,000‐scale topographic maps, and from 50‐m resolution digital elevation models using commercially available drainage network extraction methods. A least squares fit of logarithms of mainstream length plotted against basin area established a regression relation to use for predicting mainstream lengths in the smallest subbasins. To test our relation, we compared predicted mainstream lengths with first‐, second‐ and third‐order channel lengths measured from low‐altitude aerial photographs of a representative fourth‐order basin. Our results indicate that relations of mainstream length to basin area derived from coarsely gridded data (e.g., 30 m) cannot be used to characterize stream and basin morphometry in the smallest basins due to the presence of hydrologic and geometric controls (i.e., thresholds) that limit the mainstream channel length and total basin length in first‐, second‐, and third‐order basins. The presence of these thresholds potentially constrains the range over which theoretically self‐similar, or fractal, relationships can be applied to stream‐channel networks.

Variation in Amounts of Epicuticular Wax on Leaves of Prosopis glandulosa

Epicuticular wax weight, leaf dry weight, and area of honey mesquite (Prosopis glandulosa Torr.) leaves were determined periodically during a growing season at six locations in Texas with contrasting climates. Leaf size and wax weight per unit leaf weight and leaf area of individual trees within each population did not differ significantly on any sampling date. Significant variation was observed among population means, both within and across sampling dates, but the population means did not vary by as much as a factor of two. Amounts of epicuticular wax per unit leaf area were least in April and May, increased until July, and remained stable thereafter at most locations. Population means ranged from ca. 4 mg dm-2 in east-central Texas during April and May to a maximum of over 10 mg dm-2 on leaves of trees growing in north-central Texas in October. Honey mesquites growing in arid west Texas and semiarid south Texas had no more wax per unit leaf weight or area than those in humid east-central Texas.