Tate Kenneth W, Lancaster Donald L, Lile David F
Rangeland Watershed Specialist, Plant Sciences, University of California, Mail Stop 1, One Shields Avenue, Davis, California 95616-8780, USA.
Environ Monit Assess. 2007 Jan;124(1-3):289-300. doi: 10.1007/s10661-006-9226-5. Epub 2006 Aug 1.
Native trout species, such as the redband trout (Oncorhynchus mykiss), occupy thermally harsh stream habitats in hot, arid rangeland basins of the western United States. Declines in the distribution and abundance of these species has generated interest in understanding how these cold water species survive in these systems, as well as in identifying opportunities to restore these species to their former ranges. The purpose of this study was to assess the potential for thermal stratification to provide thermal refuge for redband trout in stream pools characterized by warm intermittent flow conditions on arid rangelands. We studied vertical thermal stratification in two pools during three summers on Boles Creek located on the Modoc Plateau in extreme northeastern California. Water and air temperature data were collected on a 0.5 h time step from 15-Jun through 15-Sep during 1996, 1997, and 2000 using commercial temperature data-loggers. Water temperature was measured at the top (0.3 m below pool surface) and bottom (0.3 m above pool substrates) of each pool. Vertical thermal stratification occurred within these pools creating conditions as much as 7.6 C cooler and consistently more constant at the bottom of pools compared to pool surface waters. Thermal stratification was dependent upon air temperature with the magnitude of stratification increasing as air temperature increased. The magnitude of thermal stratification varied significantly from year to year, likely reflecting variation in annual weather conditions. The thermal regime in the study pools was often near the upper lethal limit reported for redband trout, but temperatures at the bottom of these pools did offer refuge from lethal temperatures realized near the pool surface. Temperatures at pool bottom were consistently above optimal levels published for redbands.
当地的鳟鱼品种，如红斑鳟（Oncorhynchus mykiss），栖息于美国西部炎热干旱牧场流域中温度条件恶劣的溪流栖息地。这些物种分布范围和数量的减少引发了人们的兴趣，想要了解这些冷水物种如何在这些系统中生存，以及寻找机会将这些物种恢复到它们以前的分布范围。本研究的目的是评估在干旱牧场间歇性温暖水流条件下的溪流池塘中，热分层为红斑鳟提供热庇护所的潜力。我们在加利福尼亚州东北部极端地区莫多克高原的博尔斯溪上的两个池塘中，在三个夏天研究了垂直热分层情况。在1996年、1997年和2000年的6月15日至9月15日期间，使用商用温度数据记录器，以0.5小时的时间步长收集水温和气温数据。在每个池塘的顶部（水面以下0.3米）和底部（池底以上0.3米）测量水温。这些池塘内出现了垂直热分层，与池塘表层水相比，底部水温低达7.6℃，且始终更为稳定。热分层取决于气温，随着气温升高，分层程度增加。热分层的程度年际变化显著，可能反映了年度天气条件的变化。研究池塘中的热状况常常接近报道的红斑鳟的致死温度上限，但这些池塘底部的温度确实为表层附近的致死温度提供了庇护。池塘底部的温度始终高于公布的红斑鳟的最佳水平。
