Stromberg Juliet C, Lite Sharon J, Rychener Tyler J, Levick Lainie R, Dixon Mark D, Watts Joseph M
School of Life Sciences, Arizona State University, Tempe, AZ, USA.
Environ Monit Assess. 2006 Apr;115(1-3):145-73. doi: 10.1007/s10661-006-6549-1. Epub 2006 Apr 28.
A portion of Arizona's San Pedro River is managed as a National Riparian Conservation Area but is potentially affected by ground-water withdrawals beyond the conservation area borders. We applied an assessment model to the Conservation Area as a basis for monitoring long-term changes in riparian ecosystem condition resulting from changes in river water availability, and collected multi-year data on a subset of the most sensitive bioindicators. The assessment model is based on nine vegetation bioindicators that are sensitive to changes in surface water or ground water. Site index scores allow for placement into one of three condition classes, each reflecting particular ranges for site hydrology and vegetation structure. We collected the bioindicator data at 26 sites distributed among 14 reaches that had similar stream flow hydrology (spatial flow intermittency) and geomorphology (channel sinuosity, flood-plain width). Overall, 39% of the riparian corridor fell within condition class 3 (the wettest condition), 55% in condition class 2, and 6% in the driest condition class. Condition class 3 reaches have high cover of herbaceous wetland plants (e.g., Juncus and Schoenoplectus spp.) along the perennial stream channel and dense, multi-aged Populus-Salix woodlands in the flood plain, sustained by shallow ground water in the stream alluvium. In condition class 2, intermittent stream flows result in low cover of streamside wetland herbs, but Populus-Salix remain abundant in the flood plain. Perennial wetland plants are absent from condition class 1, reflecting highly intermittent stream flows; the flood plain is vegetated by Tamarixa small tree that tolerates the deep and fluctuating ground water levels that typify this reach type. Abundance of herbaceous wetland plants and growth rate of Salix gooddingii varied between years with different stream flow rates, indicating utility of these measures for tracking short-term responses to hydrologic change. Repeat measurement of all bioindicators will indicate long-term trends in hydro-vegetational condition.
亚利桑那州圣佩德罗河的一部分被管理为国家河岸保护区，但可能受到保护区边界以外的地下水抽取的影响。我们将一个评估模型应用于该保护区，作为监测河岸生态系统状况因河水可利用量变化而产生的长期变化的基础，并收集了关于一组最敏感生物指标的多年数据。该评估模型基于九个对地表水或地下水变化敏感的植被生物指标。场地指数得分允许将其归入三个状况类别之一，每个类别反映场地水文和植被结构的特定范围。我们在分布于14个河段的26个地点收集了生物指标数据，这些河段具有相似的水流水文特征（空间水流间歇性）和地貌特征（河道弯曲度、泛滥平原宽度）。总体而言，39%的河岸走廊属于状况类别3（最湿润状况），55%属于状况类别2，6%属于最干燥状况类别。状况类别3的河段在常年溪流河道沿线有高覆盖度的草本湿地植物（如灯心草属和蔺草属植物），在泛滥平原有密集的、多年龄的杨属-柳属林地，由溪流冲积层中的浅层地下水维持。在状况类别2中，间歇性水流导致溪边湿地草本植物覆盖度低，但杨属-柳属植物在泛滥平原仍然丰富。状况类别1中没有多年生湿地植物，反映出水流高度间歇性；泛滥平原由柽柳属小树植被覆盖，这些小树能耐受该河段典型的深层且波动的地下水位。草本湿地植物的丰度和古丁柳的生长速率在不同年份随不同的溪流流速而变化，表明这些指标可用于追踪对水文变化的短期响应。对所有生物指标的重复测量将表明水文植被状况的长期趋势。
