饲养场与牲畜防护林的基本设计标准

饲养场与牲畜防护林的基本设计标准ＤａｖｉｄＬ．Ｈｉｎｔｚ饲养场与牲畜防护林的主要目的是为了防止风害与吹雪，在冷天它的背风面防护区可以为牲畜提供广大的御寒场所。经验表明，合理的设计能使饲养场防护林发挥它应有的作用，牲畜能够得到保护并获得最大效益；与此相...     

进军“蓝色经济”

我国一位著名经济学家曾断言“蓝色经济”将成为我国重要的经济增长极。作为依山傍海的赣榆人民,在经历了大办农业之后,开始了向海水养殖和海洋捕捞的模式转变,海洋经济快速发展,至2002年,全县海洋渔业产值已占农业总产值的44％,沿海经济总量支撑全县的“半壁江山”。     

Simulating a lake as a high-conductivity variably saturated porous medium

One approach for simulating ground water–lake interactions is to incorporate the lake into the ground water solution domain as a high-conductivity region. Previous studies have developed this approach using fully saturated models. This study extends this approach to variably saturated models, so that ground water–lake interactions may be more easily simulated with commonly used or public domain variably saturated codes that do not explicitly support coupled lake–water balance modeling. General guidelines are developed for the choices of saturated hydraulic conductivity and moisture retention and relative permeability curves for the lake region. When applied to an example ground water–lake system, model results are very similar to those from a model in which the lake is represented as a specified head boundary continuously updated by a lake mass balance. The high-conductivity region approach is most suitable for relatively simple geometries and lakes with slower and smaller fluctuations when the overall flow pattern and system fluxes, rather than the detailed flow pattern around the intersection of the lake and land surfaces, are of interest.     

Persistence of petroleum hydrocarbon contamination in sediments of the canals in Venice,Italy: 1995 and 1998

Total hydrocarbon and selected polycyclic aromatic hydrocarbon (PAH) levels were examined in sediments collected from known problematic areas in the canals of Venice, Italy, in 1995 and 1998. Hydrocarbon concentrations were greatest in the interior canals, moderate in the partially enclosed locations and lowest in the open-water sites. Total hydrocarbon and PAH concentrations declined from 1995 to 1998. Ancillary data suggest that this decline may have been in response to the elimination of many industrial activities in the lagoon and to initiating an aggressive canal dredging program. The distributions of individual components were generally similar both years regardless of the total PAH concentration or the location of sample collected. PAH alkyl homolog distributions suggest that atmospheric deposition of petrochemical combustion products is the main source of PAHs to Venice's sediments. In some cases however, the presence of low levels of the two-ring naphthalene homologous series indicate additional low-level inputs of fresh oil.