Data from: A new paradigm for biomonitoring - An example building on the Danish Stream Plant Index

Despite intensive efforts for more than a decade to develop Water Framework-compliant assessment systems, shortcomings continue to appear. In particular, the lack of reference conditions has hindered the development of assessment systems capturing the heart of the WFD – that ecological status should be set as the deviation from the natural, undisturbed condition. Recently, the Danish Stream Plant Index (DSPI) was developed. This system contrasts existing systems in that it builds on an expert interpretation of the normative definitions of ecological status classes in the WFD without taking pressure-impact relationships into account.
Here, we substantiate the approach taken in the development of DSPI and examine if the DSPI class decreases with increasing level of anthropogenic stress and, additionally, if the deviation from the natural undisturbed condition increases with decreasing DSPI class sensu WFD using trait composition of plant assemblages from Danish streams around year 1900 as a reference. We furthermore examine the trait composition of the vegetation in sites classified into different DSPI status classes to explore if predictable patterns exist that can be used to identify the ultimate cause(s) of failure to meet ecological goals and help guide the selection of appropriate mitigation measures.
We observed that DSPI declined with several parameters indicative of environmental stress in Danish streams and, furthermore, that the deviation from the natural undisturbed condition regarding the trait composition of plant communities declined with increasing DSPI, implying that the trait composition of plant communities in the high DSPI status class was most similar to those occurring in Danish streams around year 1900. We also found that trait characteristics capable of disentangling important stressors in Danish streams varied consistently among sites classified into different DSPI classes.
Based on our findings, we call for new thinking. We suggest that more effort should be directed at describing reference conditions and interpreting the normative definitions of good, moderate, poor and bad instead of focusing solely on developing assessment systems using pressure-impact frameworks. We find this particularly important with respect to streams since these are seldom impacted by only a single stressor.

尽管十余年来学界为开发符合水框架指令（Water Framework Directive, WFD）要求的水生生态评估系统投入了大量精力，但相关缺陷仍持续显现。其中，参考基准条件的缺失尤为关键，它阻碍了直击WFD核心的评估系统开发——WFD的核心要义在于，生态状态应基于与自然未受干扰状态的偏差来界定。
近期，丹麦溪流植物指数（Danish Stream Plant Index, DSPI）得以开发。与现有评估系统不同，该指数的构建基于专家对WFD中生态状态等级规范性定义的解读，并未纳入压力-影响关系（pressure-impact relationships）的考量范畴。
本研究旨在佐证DSPI的开发思路，并以1900年左右丹麦溪流植物群落的性状组成作为参考基准，开展两项验证分析：其一，DSPI等级是否会随人为干扰程度的升高而降低；其二，按照WFD的定义，当DSPI等级降低时，群落与自然未受干扰状态的偏差是否会相应增大。此外，本研究还对归入不同DSPI状态等级的采样位点的植被性状组成进行分析，以探索是否存在可识别的规律，用于明确未达生态目标的根本成因，并为合理选择生态修复措施提供指导。
研究结果显示，丹麦溪流中的DSPI分值随多项表征环境干扰的参数升高而降低；同时，植物群落性状组成与自然未受干扰状态的偏差，随DSPI等级升高而减小，这意味着高DSPI状态等级位点的植物群落性状组成，与1900年左右丹麦溪流的原生群落最为相似。此外，本研究还发现，能够区分丹麦溪流主要干扰因子的性状特征，在不同DSPI等级的采样位点间呈现出一致的变化规律。
基于上述研究结果，我们呼吁学界更新研究思路：应投入更多精力用于描述参考基准条件，并解读WFD中“良好”“中等”“较差”“极差”生态状态的规范性定义，而非仅专注于基于压力-影响框架开发评估系统。这一点对于溪流生态系统尤为重要，因为溪流几乎不会仅受单一干扰因子的影响。