宁夏东北部典型荒漠草原植物群落与土壤养分特征

以宁夏东北部荒漠草原为研究区,采用野外样方调查、采样和室内植物鉴定、土壤样品测定等方法,探析研究区内植物群落物种组成与土壤养分特征,以及植物多样性指数与土壤养分的相关关系,以期为中国荒漠治理、生物资源保护与可持续性利用提供依据。结果显示:(1)研究区植物共86种,隶属61属21科,其中禾本科(18种)、豆科(16种)、菊科(13种)和藜科(11种)植物占总物种数的67.44%;(2)研究区土壤总体上呈碱性,pH值平均为8.81,全氮、全磷、有机质的质量分数(0-10 cm土层)分别为0.07-0.54、0.16-0.51、0.51-6.24 g·kg^-1;(3)研究区植物多样性指数中的Margalef丰富度指数和Shannon-Wiener多样性指数与土壤pH值呈显著负相关,与其他土壤养分的相关关系未达到显著水平,其他植物多样性指数与土壤养分的关系均未达到显著水平。研究表明,宁夏东北部荒漠草原植物种类少,禾本科、豆科植物优势明显,土壤养分条件差,土壤全氮、全磷、有机质对植物多样性指数的影响不大。     

基于水量平衡的流域生态耗水量计算——以海河为例

论文提出一个基于水量平衡的流域生态耗水量的计算方法。以海河流域为例,利用流域多年年降雨、入海水量、引黄水量、地下水超采水量、工业用水量、农业用水量、生活用水量、工业废污水排放量和生活污水排放量等资料,得出1956～1998年流域生态耗水量的多年变化。计算结果显示,虽然流域在1956～1998年的43年间环境发生明显变化,然而流域生态耗水总量没有呈明显的上升或下降趋势。最后通过对比研究,给出了论文提出的算法与基于当地水资源的算法结果的物理解释。     

植物生理模型用于森林水文气候效应的研究

论文阐述了植物生理数学模型在对森林的水文气候效应的研究中所能起和应起的作用。从树木的多年生习性和宜林山地的复杂地形等因素论证植物生理数学模型对制订造林优化方案、乔灌草关系等方面所起的作用。论述了植物生理模型与土壤模型、微气象之间结合的必要性。     

ESTIMATING DRAINAGE AREA ON STEEP UNIFORM SLOPES1

ABSTRACT: A study was conducted to derive a simple procedure for estimating the tributary drainage area that may potentially develop at the base of a uniformly graded, steep slope. Data were extracted from a nil development flume study in which 112 rills and their tributary drainage areas were documented. The tributary drainage area for each rill was correlated to the slope length and the slope gradient. The findings are considered applicable to planar, convex, and divergent slopes with lengths of up to 130 m. Field verification is needed to extend the applicability of the relation.     

REVISITING THE DEGREE-DAY METHOD FOR SNOWMELT COMPUTATIONS1

ABSTRACT: The simple, empirical degree-day approach for calculating snowmelt and runoff from mountain basins has been in use for more than 60 years. It is frequently suggested that the degree-day method be replaced by the more physically-based energy balance approach. The degree-day approach, however, maintains its popularity, applicability, and effectiveness. It is shown that the degree-day method is reliable for computing total snowmelt depths for periods of a week to the entire snowmelt season. It can also be used for daily snowmelt depths when utilized in connection with an adequate snowmelt runoff model for computing the basin runoff. The degree-day ratio is shown to vary seasonally as opposed to being constant as is often assumed. Additionally, in order to evaluate the degree-day ratio correctly, the changing snow cover extent in a basin during the snowmelt season must be taken into account. It is also possible to combine the degree-day approach with a radiation component so that short time interval (<24 hours) computations of snowmelt depth can be made. When snowmelt input is transformed to basin output (runoff) by a snowmelt runoff model, there is little difference between the degree-day approach and a radiation-based approach. This is fortuitous because the physically-based energy balance models will not soon displace the degree-day methods because of their excessive data requirements.     

RECOVERY OF “LOST” STORM WATER FROM LOCAL WASH BEDS1

ABSTRACT: Most of the precipitation that falls is unused because it never reaches a stream or recharges an underground supply. This storm water evaporates and is transpired and consumed by plants. Described below are pertinent legal principles and the concept for a small-scale system to capture and store some of this “lost” storm water from the subflow of small gravelly washes that are not part of or connected with a stream system. The subsurface flow is interrupted by an elastomer faced earthen barrier (dam) and stored in a gravel bed. Both the barrier and the gravel storage bed are situated below the surface of the wash bed. If the gravel bed is not underlain by a natural substratum that is relatively impervious, it is either placed on a liner of suitable compacted clay or is underlain with an elastomeric membrane to limit the downward infiltration and loss of the stored water. A system may be used to capture and store sub-flow after surface flow has ceased and during periods of drought; to supply household and irrigation water; to exercise Winters Doctrine rights; and to replace small dams and surface impoundments by underground storage of the captured water to ensure a more reliable and sanitary supply for livestock and wildlife. A system is most effective in desert regions where (or when) both stream and ground water are unavailable; where rainfall is infrequent, but in storms resulting in rapid runoff; and where land surface topography and morphology coincide to form sites that permit the productive use of a system. A system should not be installed without sound legal and hydrological advice. Careful engineering is essential to the safe and proper design of a system, especially its subsurface barrier.     

GENERALIZED LOW-FLOW FREQUENCY RELATIONSHIPS FOR UNGAGED SITES IN MASSACHUSETTS1

ABSTRACT: Regional hydrologic procedures such as generalized least squares regression and streamflow record augmentation have been advocated for obtaining estimates of both flood-flow and low-flow statistics at ungaged sites. While such procedures are extremely useful in regional flood-flow studies, no evaluation of their merit in regional low-flow estimation has been made using actual streamflow data. This study develops generalized regional regression equations for estimating the d-day, T-year low-flow discharge, Q_{d, t}, at ungaged sites in Massachusetts where d = 3, 7, 14, and 30 days. A two-parameter lognormal distribution is fit to sequences of annual minimum d-day low-flows and the estimated parameters of the lognormal distribution are then related to two drainage basin characteristics: drainage area and relief. The resulting models are general, simple to use, and about as precise as most previous models that only provide estimates of a single statistic such as Q_7,10. Comparisons are provided of the impact of using ordinary least squares regression, generalized least squares regression, and streamflow record augmentation procedures to fit regional low-flow frequency models in Massachusetts.     

AQUATIC HABITAT CONDITION INDEX,STREAM TYPE,AND LWESTOCK BANK DAMAGE IN NORTHERN NEVADA1

ABSTRACT: The quality of stream habitat varies for a variety of natural and anthropogenic reasons not identified by a condition index. However, many people use condition indices to indicate management needs or even direction. To better sort natural from livestock influences, stream types and levels of ungulate bank damage were regulated to estimates of aquatic habitat condition index and stream width parameters in a large existing stream inventory data base. Pool/riffle ratio, pool structure, stream bottom materials, soil stability, and vegetation type varied significantly with stream type. Pool/riffle ratio, soil and vegetation stability varied significantly with ungulate bank damage level. Soil and vegetation stability were highly cross-correlated. Riparian area width did not vary significantly with either stream type or ungulate bank damage. Variation among stream types indicates that riparian management and monitoring should be stream type and reach specific.     

EVALUATION OF STORMSEWER CONTROL ALGORITHMS USING A TRANSIENT MIXED FLOW MODEL1

ABSTRACT: a hydraulic transient model that is capable of simultaneously modeling open channel and pressurized flows is used to study active control of a deep tunnel stormwater collection system. The simultaneous occurrence of open channel flow and pressurized flow is termed mixed flow. This paper demonstrates the application of a mixed flow hydraulic model to the development of an active control scheme. It is shown that dynamic conditions can exist in a storm sewer system even under moderate inflow conditions and that these conditions, particularly at the time of full system pressurization, can influence the operation of the dynamic control, so that accurate hydraulic modeling is essential to proper control formulation.     

ANNUAL EVAPOTRANSPIRATION OF NATWE VEGETATION IN A MEDITERRANEAN-TYPE CLIMATE1

ABSTRACT: Annual evapotranspiration from a watershed (ETws) is a function of annual precipitation (P) and fraction of the watershed covered by shrubs and trees (C). Other characteristics are not significant in explaining variance of ETws. A rational equation, ETws = (1-C) ETg + CETst, wherein ETg is the ET of herbaceous cover and ETst is the ET of shrubs and trees, is proposed. The equation has been calibrated for ET and P in inches for the watershed of Lake Cachuma on the Santa Ynez River. This equation, ETmax = 2.14(1-C)P^0.647+ 4.53 C^1.76 P^0.68, is recommended for estimating maximum annual ET demand for conceptual models. Where C is not known, the upper limit of ET = f (P) may be approximated by use of 0.65 for C. The equation has been derived for large unmanaged watersheds. Applicability for evaluation of contemporary multiple purpose vegetation management should be determined by studies of the hydrology of small openings in shrub and tree cover.