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71.
72.
Frank A. Ward Ari M. Michelsen Leeann DeMouche 《Journal of the American Water Resources Association》2007,43(1):237-253
Abstract: The Rio Grande basin shares problems faced by many arid regions of the world: growing and competing demands for water and river flows and uses that are vulnerable to drought and climate change. In recent years legislation, administrative action, and other measures have emerged to encourage private investment in efficient agricultural water use. Nevertheless, several institutional barriers discourage irrigators from investing in water conservation measures. This article examines barriers to agricultural water conservation in the Rio Grande basin and identifies challenges and opportunities for promoting it. Several barriers to water conservation are identified: clouded titles, water transfer restrictions, illusory water savings, insecure rights to conserved water, shared carry‐over storage, interstate compacts, conservation attitudes, land tenure arrangements, and an uncertain duty of water. Based on data on water use and crop production costs, price is found to be a major factor influencing water conservation. A low water price discourages water conservation even if other institutions promote it. A high price of water encourages conservation even in the presence of other discouraging factors. In conclusion, water‐conserving policies can be more effectively implemented where water institutions and programs are designed to be compatible with water’s underlying economic scarcity. 相似文献
73.
Non-native brook trout have become widely established in North European streams. We combined evidence from an artificial-stream
experiment and drainage-scale field surveys to examine whether brook trout suppressed the growth of the native brown trout
(age 0 to age 2). Our experimental results demonstrated that brown trout were unaffected by the presence of brook trout but
that brook trout showed reduced growth in the presence of brown trout. However, the growth reduction only appeared in the
experimental setting, indicating that the reduced spatial constraint of the experimental system may have forced the fish to
unnaturally intense interactions. Indeed, in the field, no effect of either species on the growth of the putative competitor
was detected. These results caution against uncritical acceptance of findings from small-scale experiments because they rarely
scale up to more complex field situations. This and earlier work suggest that the establishment of brook trout in North European
streams has taken place mainly because of the availability of unoccupied (or underutilized) niche space, rather than as a
result of species trait combinations or interspecific competition per se.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献