Palmer M A, Bely A E, Berg K E
Department of Zoology, University of Maryland, 20742, College Park, MD, USA.
Oecologia. 1992 Feb;89(2):182-194. doi: 10.1007/BF00317217.
Recovery following hydrological disturbances is usually rapid for lotic invertebrates. Stream ecologists have assumed that recovery is facilitated by behavioral migrations during floods down into the hyporheic zone (the interstitial spaces of a streambed) to seek temporary refuge from possible erosion (the "hyporheic refuge hypothesis"). We provide the first explicit test of this hypothesis by evaluating three predictions of the hypothesis. We coupled field observations of the response of meiofaunal invertebrates to floods with field and flume experiments. The study site was a sandy-bottom stream in northern Virginia. Prediction 1, that loss of fauna from a streambed during floods should be minimal as long as the depth of scour in the streambed is less than the depth of the hyporheic zone, was not supported for any taxon. For two floods which varied considerably in magnitude, 50-90% of the fauna was lost from the bed despite the fact that the depth of scour (10-30 cm) was significantly less than the total depth of the hyporheic zone (50 cm). Prediction 2, that fauna should move deeper into the bed at higher flows, was supported by field observations during only one of two floods and then only for rotifers. In flume experiments that tested for finer scale behavioral movements, significant vertical migrations were found for copepods and chironomids which moved 1.5-3.5 cm downward as mean velocity (3 cm off bottom) was increased from 5-23 cm/s. Movements down by rotifers were not found in the flume experiments. Prediction 3, that the hyporheic zone is the most important source of colonists to defaunated areas, was supported in part by field experiments. The hyporheic route was not the primary route for any taxon but it was as important for the rotifers and copepods as water column or streambed surface routes. We conclude that, even though smallscale (cm's) migrations into the streambed in response to increased flow may be observed for some taxa and the hyporheic zone may serve as a partial source of colonists following disturbances, movements down are not adequate in preventing significant losses of meiofauna during floods.
对于流水无脊椎动物来说，水文干扰后的恢复通常很快。溪流生态学家认为，洪水期间向下迁移到潜流带（河床的间隙空间）的行为性迁移有助于恢复，以便从可能的侵蚀中寻求临时避难所（“潜流避难所假说”）。我们通过评估该假说的三个预测，首次对这一假说进行了明确的检验。我们将小型无脊椎动物对洪水的反应的现场观察与现场和水槽实验相结合。研究地点是弗吉尼亚州北部一条沙质底部的溪流。预测1，即只要河床冲刷深度小于潜流带深度，洪水期间河床动物的损失就应最小，但对任何分类群都不成立。对于两次规模差异很大的洪水，尽管冲刷深度（10 - 30厘米）明显小于潜流带总深度（50厘米），但仍有50 - 90%的动物从河床中消失。预测2，即动物在更高流量下应向河床更深处移动，仅在两次洪水中的一次现场观察中得到支持，而且仅对轮虫成立。在测试更精细尺度行为移动的水槽实验中，发现桡足类和摇蚊有显著的垂直迁移，随着平均流速（离底部3厘米处）从5 - 23厘米/秒增加，它们向下移动了1.5 - 3.5厘米。在水槽实验中未发现轮虫向下移动。预测3，即潜流带是重新定殖区域最重要的殖民者来源，在一定程度上得到了现场实验的支持。潜流路径不是任何分类群的主要路径，但对轮虫和桡足类来说，它与水柱或河床表面路径一样重要。我们得出结论，尽管对于一些分类群可能会观察到因流量增加而向河床进行的小规模（厘米级）迁移，并且潜流带可能在干扰后作为殖民者的部分来源，但向下迁移不足以防止洪水期间小型动物的大量损失。
