Proliferations of benthic mats dominated by anatoxin-producing Microcoleus autumnalis (basionym Phormidium autumnale ) pose an increasing health risk to human and animals worldwide. This study assessed M. autumnalis mats in two in situ experiments undertaken at three spatial scales: (1) reach-scale along a river; (2) reach-scale, focusing on two sites upstream and downstream of a tributary with substantial differences in naturally occurring M. autumnalis ; and (3) patch-scale differences in light intensity. Most studies exploring drivers of proliferation have surveyed natural populations with correlative analyses; these in situ experiments aimed to validate previously hypothesised drivers. In experiment one, M. autumnalis mat area and expansion tended to increase downstream. This longitudinal variation was partially associated with increases in dissolved inorganic nitrogen, fine sediment and associated biologically available phosphorus. M. autumnalis mat area differed markedly at sites above and below the most downstream tributary. A second experiment with additional parameters (metals, grazing and light) was undertaken in this reach. None of the parameters conclusively explained differences in mat area, although numerous metals were identified for further investigation with a controlled experimental approach. These results posit that there are multiple non-linear drivers of M. autumnalis proliferation and their hierarchy of importance varies amongst sites.

中文翻译：

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原位河流实验探索秋季小球藻垫扩展的变异性

以产生类毒素的秋季小球藻（基名 Phormidium fallale）为主的底栖垫的增殖对世界范围内的人类和动物造成越来越大的健康风险。本研究在三个空间尺度上进行的两个原位实验中评估了 M.Autumnalis 垫子：(1) 沿河的到达尺度；(2) 河段尺度，侧重于一条支流的上下游两个站点，自然发生的 M.Autumnalis 存在显着差异；(3) 光强度的斑块尺度差异。大多数探索扩散驱动因素的研究都通过相关分析调查了自然种群；这些原位实验旨在验证先前假设的驱动因素。在实验一中，M.fallalis 垫面积和扩张在下游有增加的趋势。这种纵向变化部分与溶解无机氮、细沉积物和相关生物可利用磷的增加有关。M.fallalis mat 面积在最下游支流上方和下方的位置显着不同。在这个范围内进行了第二个附加参数（金属、放牧和光）的实验。尽管通过受控实验方法确定了许多金属用于进一步研究，但没有一个参数最终解释了垫子面积的差异。这些结果假定 M.Autumnalis 增殖有多种非线性驱动因素，它们的重要性等级因地点而异。在最下游支流上方和下方的地点，秋叶草席面积显着不同。在这个范围内进行了第二个附加参数（金属、放牧和光）的实验。尽管通过受控实验方法确定了许多金属用于进一步研究，但没有一个参数最终解释了垫子面积的差异。这些结果假定 M.Autumnalis 增殖有多种非线性驱动因素，它们的重要性等级因地点而异。在最下游支流上方和下方的地点，秋叶草席面积显着不同。在这个范围内进行了第二个附加参数（金属、放牧和光）的实验。尽管通过受控实验方法确定了许多金属用于进一步研究，但没有一个参数最终解释了垫子面积的差异。这些结果假定 M.Autumnalis 增殖有多种非线性驱动因素，它们的重要性等级因地点而异。