Globally benthic invertebrate biotic indices are widely used to assess stream health. In New Zealand, the response of biotic indices to high nitrate-nitrogen (hereafter nitrate) concentrations has not been rigorously tested. We conducted a field survey of benthic invertebrates in 41 lowland intensively farmed Canterbury streams representing a wide nitrate gradient (0.4–11.3 mg/l) to determine if biotic indices respond in a predictable manner to increasing nitrate (e.g. show a subsidy stress response). Our results show commonly used biotic indices were not able to detect any effects of high nitrate. We found homogenous and tolerant benthic invertebrate communities dominated and suggest the lack of any detected effects may be because taxa sensitive to nutrients have already been lost from these systems. Therefore, we recommend caution is needed when using biotic indices in lowland agricultural streams where nutrients may be high.

全球底栖无脊椎动物生物指数被广泛用于评估河流健康。在新西兰，生物指数对高硝酸盐氮（以下简称硝酸盐）浓度的反应尚未经过严格测试。我们对代表宽硝酸盐梯度 (0.4-11.3 毫克/升) 的 41 条低地集约化养殖坎特伯雷河流中的底栖无脊椎动物进行了实地调查，以确定生物指数是否以可预测的方式对硝酸盐增加做出反应（例如显示补贴压力反应）。我们的结果表明，常用的生物指数无法检测到高硝酸盐的任何影​​响。我们发现同质和耐受的底栖无脊椎动物群落占主导地位，并表明缺乏任何检测到的影响可能是因为对营养物质敏感的分类群已经从这些系统中消失了。所以，