Teagasc, Environmental Research Centre, Johnstown Castle, Wexford, Co., Wexford, Ireland; School of Biology and Environmental Science, University College Dublin, Dublin 4, Ireland.
Teagasc, Environmental Research Centre, Johnstown Castle, Wexford, Co., Wexford, Ireland.
Sci Total Environ. 2019 Sep 15;683:9-20. doi: 10.1016/j.scitotenv.2019.05.031. Epub 2019 May 7.
Freshwaters worldwide are affected by multiple stressors. Timing of inputs and pathways of delivery can influence the impact stressors have on freshwater communities. In particular, effects of point versus diffuse nutrient inputs on stream macroinvertebrates are poorly understood. Point-source inputs tend to pose a chronic problem, whereas diffuse inputs tend to be acute with short concentration spikes. We manipulated three key agricultural stressors, phosphorus (ambient, chronic, acute), nitrogen (ambient, chronic, acute) and fine sediment (ambient, high), in 112 stream mesocosms (26 days colonisation, 18 days of manipulations) and determined the individual and combined effects of these stressors on stream macroinvertebrate communities (benthos and drift). Chronic nutrient treatments continuously received high concentrations of P and/or N. Acute channels received the same continuous enrichment, but concentrations were doubled during two 3-hour periods (day 6, day 13) to simulate acute nutrient inputs during rainstorms. Sediment was the most pervasive stressor in the benthos, reducing total macroinvertebrate abundance and richness, EPT (mayflies, stoneflies, caddisflies) abundance and richness. By contrast, N or P enrichment did not affect any of the six studied community-level metrics. In the drift assemblage, enrichment effects became more prevalent the longer the experiment went on. Sediment was the dominant driver of drift responses at the beginning of the experiment. After the first acute nutrient pulse, sediment remained the most influential stressor but its effects started to fade. After the second pulse, N became the dominant stressor. In general, impacts of either N or P on the drift were due to chronic exposure, with acute nutrient pulses having no additional effects. Overall, our findings imply that cost-effective management should focus on mitigating sediment inputs first and tackle chronic nutrient inputs second. Freshwater managers should also take into account the length of exposure to high nutrient concentrations, rather than merely the concentrations themselves.
全世界的淡水都受到多种胁迫因素的影响。输入的时间和途径会影响胁迫因素对淡水生物群落的影响。特别是，点源与扩散性养分输入对溪流大型无脊椎动物的影响还不太清楚。点源输入往往会造成慢性问题，而扩散性输入往往是急性的，具有短暂的高浓度峰值。我们在 112 个溪流中操纵了三个关键的农业胁迫因素，即磷（环境、慢性、急性）、氮（环境、慢性、急性）和细沉积物（环境、高），（26 天的殖民化，18 天的处理），并确定了这些胁迫因素对溪流大型无脊椎动物群落（底栖生物和漂流生物）的单独和综合影响。慢性养分处理持续接受高浓度的 P 和/或 N。急性通道接收相同的连续富化，但在两天 3 小时期间（第 6 天，第 13 天）浓度增加一倍，以模拟暴雨期间的急性养分输入。沉积物是底栖生物中最普遍的胁迫因素，减少了总大型无脊椎动物的丰度和丰富度、EPT（蜉蝣、石蝇、毛翅目）的丰度和丰富度。相比之下，N 或 P 富集并没有影响任何六个研究的群落水平指标。在漂流群落中，随着实验的进行，富集效应变得更加普遍。在实验开始时，沉积物是漂流响应的主要驱动因素。第一次急性养分脉冲后，沉积物仍然是最具影响力的胁迫因素，但它的影响开始减弱。第二次脉冲后，N 成为主要的胁迫因素。总的来说，N 或 P 对漂流的影响是由于慢性暴露，急性养分脉冲没有额外的影响。总的来说，我们的研究结果表明，具有成本效益的管理应该首先集中精力减少沉积物的输入，其次是处理慢性养分输入。淡水管理者还应考虑到暴露于高养分浓度的时间长度，而不仅仅是浓度本身。
