Together, macroalgal tissue biochemical nitrogen indices (N-indices) and macroalgal abundance can be used as bioindicators of N-enrichment in estuaries. In this study, we examine the extent and rates of response of Ulva bioindicators during rapid N-enrichment perturbations in the eutrophic Avon-Heathcote Estuary (AHE) (Christchurch, New Zealand). With the diversion of the city’s wastewater discharge away from the estuary in March 2010, a ~ 90% reduction in the estuary’s N-concentration was expected. In turn, this was expected to reduce macroalgal biomass and improve the overall trophic condition of the estuary. We surveyed Ulva bioindicators over a five-year period spanning the diversion. There was a rapid (within one year) transition away from eutrophic condition reflected in N-indices (tissue-chlorophyll, -free amino acids, -N and -δ¹⁵N) following wastewater diversion, towards values corresponding with ‘cleaner’ water quality. This was accompanied by large reductions in Ulva percent cover, based on seasonal surveys conducted from 2001 to 2014. However, two large earthquakes in February and June 2011 caused a breakdown of the city’s wastewater infrastructure, resulting in overflows of untreated sewage into the estuary between February and November 2011. The re-enrichment of N and changes in N-sources (treated versus untreated sewage) were rapidly reflected in Ulva bioindicators, notably δ¹⁵N. Following repair of infrastructure, Ulva bioindicators again reverted towards a less eutrophic state. Overall, bioindicators were sensitive to changes in N-availability and N-source, and useful for identifying the position of algal populations on a eutrophic-to-oligotrophic gradient. These attributes demonstrated their utility as adjuncts to water quality monitoring and algal biomass surveys.

中文翻译：

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废水转移和地震扰动后潮汐泻湖富营养化恢复的大型藻类生物指标

大型藻类组织的生化氮指数（N指数）和大型藻类的丰度可以一起用作河口N富集的生物指标。在这项研究中，我们研究了富营养化的雅芳-希斯科特河口（AHE）（新西兰基督城）在快速N富集扰动期间Ulva生物指示剂的反应程度和反应速率。随着2010年3月该市废水排放量从河口转移出去，预计河口的N浓度将减少约90％。反过来，这有望减少大型藻类生物量并改善河口的总体营养状况。我们调查了Ulva跨越转移的五年内的生物指标。有一个快速（一年以内）从过渡反映在N-指数（组织叶绿素，-free氨基酸，-N和-δ富营养状态远¹⁵ N）以下的废水分流，向与“清洁”水质的相应值。根据2001年至2014年进行的季节性调查，这同时伴随着Ulva百分比覆盖率的大幅降低。然而，2011年2月和2011年6月的两次大地震导致该城市的废水基础设施崩溃，导致未经处理的污水溢入河口。 2011年2月和2011年11月。Ulva迅速体现了氮的重新富集和氮源的变化（处理后的污水与未处理的污水）生物指标，特别是δ ¹⁵ N.继基础设施修复，石莼生物指标再次恢复向少富营养状态。总体而言，生物指示剂对氮素有效性和氮源的变化敏感，对于确定藻类种群在富营养化至富营养化梯度上的位置很有用。这些属性证明了它们作为水质监测和藻类生物量调查的辅助工具的用途。