PARAMETER IDENTIFICATION IN A TWO‐MULTIPLIER SEDIMENT YIELD MODEL1

ABSTRACT: A process based, distributed runoff erosion model (KINEROS2) was used to examine problems of parameter identification of sediment entrainment equations for small watersheds. Two multipliers were used to reflect the distributed nature of the sediment entrainment parameters: one multiplier for a raindrop induced entrainment parameter, and one multiplier for a flow induced entrainment parameter. The study was conducted in three parts. First, parameter identification was studied for simulated error free data sets where the parameter values were known. Second, the number of data points in the simulated sedigraphs was reduced to reflect the effect of temporal sampling frequency on parameter identification. Finally, event data from a small range‐land watershed were used to examine parameter identifiability when the parameter values are unknown. Results demonstrated that whereas unique multiplier values can be obtained for simulated error free data, unique parameter values could not be obtained for some event data. Unique multiplier values for raindrop induced entrainment and flow induced entrainment were found for events with greater than a two‐year return period (～25 mm) that also had at least 10 mm of rain in ten minutes. It was also found that the three‐minute sampling frequency used for the sediment sampler might be inadequate to identify parameters in some cases.     

长江上游高寒草地生态建设和管理中生态理论的若干质疑

现有的草地管理政策和措施建立在西方经典生态学理论的基础上，并在很大程度上改变了传统管理模式．本文针对长江上游高寒草地生态建设与管理中的问题，结合草地生态学的新进展，从草地生态系统特征、多样性与稳定性、草地承载力、平衡与非平衡等几个方面进行了讨论，旨在能引起今后草地生态建设中加强这些方面的针对性研究，并有效地避免由于理论自身偏差而导致不应有的技术失误．本文的中心观点在于，由于长江上游地区的高寒草地处在环境因子剧烈变化的条件之下，草地的生态过程在很大程度上受制于非生物条件(如气候)，而不是生物因子的相互作用(如放牧)，因此，已有的一些草地生态理论不能完全解释草地动态变化的机理，其适用性受到限制，而任何简单套用理论以及基于这些理论发展的技术和模式都有可能给生态治理和管理带来负面影响．图2参22     

LONG-TERM AQUATIC HABITAT RESTORATION: MAHOGANY CREEK,NEVADA, AS A CASE STUDY1

ABSTRACT: We compared the recovery from abusive grazing of aquatic habitat due to different range management on two geomorphically similar rangeland streams in northwest Nevada. Managers excluded livestock from the Mahogany Creek watershed from 1976 to 1990 while allowing rotation of rest grazing on its tributary Summer Camp Creek. Bank stability, defined as the lack of apparent bank erosion or deposition, improved through the study period on both streams, but periodic grazing and flooding decreased stability more on Summer Camp Creek than flooding alone on Mahogany Creek. Pool quantity and quality on each stream decreased because of coarse woody debris removal and sediment deposition during a drought. Fine stream bottom sediments decreased five years after the removal of livestock, but sedimentation increased during low flows in both streams below road crossings. Tree cover increased 35 percent at both streams. Thus, recovery of stability and cover and decreased sedimentation are compatible with rotation of rest grazing on Summer Camp Creek. Width/depth ratio and gravel/cobble percent did not change because they are inherently stable in this stream type. Management activities such as coarse woody debris removal limited pool recover and road crossings increased sedimentation.