Maret Terry R, Konrad Christopher P, Tranmer Andrew W
J Am Water Resour Assoc. 2010 Jun;46(3):498-513. doi: 10.1111/j.1752-1688.2010.00430.x.
The influence of environmental factors on biotic responses to nutrients was examined in three diverse agricultural regions of the United States. Seventy wadeable sites were selected along an agricultural land use gradient while minimizing natural variation within each region. Nutrients, habitat, algae, macroinvertebrates, and macrophyte cover were sampled during a single summer low-flow period in 2006 or 2007. Continuous stream stage and water temperature were collected at each site for 30 days prior to sampling. Wide ranges of concentrations were found for total nitrogen (TN) (0.07-9.61 mg/l) and total phosphorus (TP) (<0.004-0.361 mg/l), but biotic responses including periphytic and sestonic chlorophyll a (RCHL and SCHL, respectively), and percent of stream bed with aquatic macrophyte (AQM) growth were not strongly related to concentrations of TN or TP. Pearson's coefficient of determination (R(2)) for nutrients and biotic measures across all sites ranged from 0.08 to 0.32 and generally were not higher within each region. The biotic measures (RCHL, SCHL, and AQM) were combined in an index to evaluate eutrophic status across sites that could have different biotic responses to nutrient enrichment. Stepwise multiple regression identified TN, percent canopy, median riffle depth, and daily percent change in stage as significant factors for the eutrophic index (R(2) = 0.50, p < 0.001). A TN threshold of 0.48 mg/l was identified where eutrophic index scores became less responsive to increasing TN concentrations, for all sites. Multiple plant growth indicators should be used when evaluating eutrophication, especially when streams contain an abundance of macrophytes.
在美国三个不同的农业地区，研究了环境因素对生物对养分响应的影响。沿着农业土地利用梯度选择了70个可涉水区域，同时尽量减少每个区域内的自然变化。在2006年或2007年夏季的一个低流量时期，对养分、栖息地、藻类、大型无脊椎动物和大型植物覆盖情况进行了采样。在采样前30天，在每个采样点收集连续的水位和水温数据。总氮（TN）（0.07 - 9.61毫克/升）和总磷（TP）（<0.004 - 0.361毫克/升）的浓度范围很广，但包括附生和悬浮叶绿素a（分别为RCHL和SCHL）以及有水生大型植物（AQM）生长的河床百分比在内的生物响应与TN或TP的浓度没有强烈关联。所有采样点养分与生物指标的皮尔逊决定系数（R²）在0.08至0.32之间，且在每个区域内一般都不更高。将生物指标（RCHL、SCHL和AQM）合并成一个指数，以评估不同生物对养分富集可能有不同响应的各采样点的富营养化状况。逐步多元回归确定TN、树冠覆盖率百分比、中位浅滩深度和水位的每日变化百分比是富营养化指数的显著因素（R² = 0.50，p < 0.001）。确定了所有采样点TN阈值为0.48毫克/升，此时富营养化指数得分对TN浓度增加的响应变得不那么敏感。在评估富营养化时，应使用多种植物生长指标，尤其是当溪流中含有大量大型植物时。
