Unexpected consequences of bombing. Community level response of epiphytic diatoms to environmental stress in a saline bomb crater pond area

The spatial response of epiphytic diatom communities to environmental stress was studied in a moderately saline wetland area located in the plain of Danube-Tisza Interfluve, Hungary. The area is characterised by World War II bomb crater ponds and can be regarded as an excellent ecological model system where the dispersion of species is slightly limited by distance. To study the effect of environmental variables on the communities, canonical correspondence analysis was applied. Salinity, pH, total suspended solids, total phosphorous and depth proved to be significant environmental drivers in this analysis. The ecological status of the ponds was assessed with Ziemann’s halobity index, as the trophity-depending metric cannot be applied to these habitats (due to the naturally high phosphorus content). Ponds in “good” ecological status significantly differed from those appertaining to water quality category of “not-good” ecological status considering characteristic of natural astatic soda pans (e.g. salinity, pH, ammonium, total phosphorous concentration, nitrogen:phosphorous ratio and turbidity). The differences between epiphytic diatom communities inhabiting the ponds were detected using non-parametric multidimensional scaling. The samples formed three groups according to the types of ponds (“transparent”, “transitional” and “turbid”) based on the width of the macrophyte belt around them. Indicator species related to the ecological status of the ponds and diatom communities contributing to the separation of groups of ponds were identified. One of the indicator species differed from species already described. Light and scanning electron microscopy features and phylogenetic analyses based on three genes (18S and 28S rRNA genes, rbcL) proved that it was a new species of Nitzschia genus, closely related to Nitzschia frustulum and Nitzschia inconspicua. Therefore, description of a new species, Nitzschia reskoi Ács, Duleba, C.E.Wetzel & Ector is proposed. We concluded that the increasing abundance of Nitzschia reskoi was a signal of the degradation of the intermittent saline wetlands.

本研究以匈牙利多瑙河-蒂萨河间平原的一处中度盐碱湿地为研究区域，探究了附生硅藻群落在环境胁迫下的空间响应特征。该区域以二战遗留弹坑形成的池塘为主要地貌特征，可视为优质的生态学模型系统——此处物种的扩散受距离限制程度较低。为探究环境变量对硅藻群落的影响，本研究采用了典范对应分析（Canonical Correspondence Analysis, CCA）。经分析，盐度、pH值、总悬浮颗粒物、总磷及水深为该区域的关键环境驱动因子。由于该生境天然磷含量较高，依赖营养状态的评价指标无法适用于本研究区域，因此本研究采用泽曼嗜盐指数（Ziemann’s halobity index）对池塘的生态状况进行评估。结合天然无稳定水位苏打浅滩的特征（盐度、pH值、铵态氮、总磷浓度、氮磷比及浊度等），生态状况为“良好”的池塘与“非良好”生态状况类别的池塘存在显著差异。本研究采用非度量多维尺度分析（Non-metric Multidimensional Scaling, NMDS）对栖息于不同池塘的附生硅藻群落差异进行检测。根据池塘周边大型植物带的宽度，样本可按照池塘类型划分为“透明型”“过渡型”与“浑浊型”三个群组。本研究鉴定出与池塘生态状况相关的指示物种，以及对池塘群组划分具有贡献的硅藻类群。其中一种指示物种与已发表的物种存在差异。通过光学显微镜、扫描电子显微镜的形态观察，以及基于18S rRNA、28S rRNA及rbcL三个基因的系统发育分析，证实该物种为菱形藻属（*Nitzschia*）一新种，与*Nitzschia frustulum*及*Nitzschia inconspicua*亲缘关系密切。因此，本研究正式描述该新种，命名为*Nitzschia reskoi* Ács, Duleba, C.E.Wetzel & Ector。本研究最终得出结论：*Nitzschia reskoi*的丰度上升可作为间歇性盐碱湿地生态退化的指示信号。