Freshwater pearl mussels as stream water stable isotope recorders (MUSES)

径流的同位素记录对于提高我们对水文、生态、地球化学和大气过程的理解和建模至关重要，但其全部潜力的利用受到短时间序列和截断时间序列的阻碍。在这里，我们提出了一个创新的贡献流同位素记录的局限性的问题：使用淡水双壳类作为长期的溪流水delta 18 O记录器。我们已经做了试点工作，通过分析软体动物壳三角洲18 O数据（从10项研究汇编），跨越纬度序列的18个采样点的16个流周围的地球仪。我们发现降水，溪水和淡水软体动物的同位素签名之间有很强的联系-溪水和软体动物都表现出强烈的降水信号阻尼。我们对淡水贻贝的探索性工作开辟了一条道路，我们现在打算遵循几十年的河流水三角洲18 O重建。首先，我们将测试的推测，即流水温度-作为一个先决条件，重建流水δ 18 O从壳δ 18 O-可以推断出（a）壳生长速率，（B）壳的微观结构性能和/或（c）元素的贻贝壳的化学性质。其次，我们将基准IRMS和西姆斯和测试他们的完全兼容性和互补性方面的软体动物壳δ 18 O测量精度。虽然IRMS是测量软体动物壳中δ 18 O的标准工具，但西姆斯可以以高测量精度将δ 18 O数据扩展到后期个体发育壳部分。第三，我们将依赖于测量的几十年降水量delta 18 O数据和重建delta 18 O信号在溪流从三个研究集水区在卢森堡，瑞典和德国测试我们的假设，基岩地质控制长期敏感性的集水区的水文响应气候变化。为了检验我们的假设，我们将依赖于年轻水（Fyw）的比例与流量增加之间的机械关系-这表明快速流动路径对更高流量的比例贡献增加。在我们研究的具有不同自然地理特征和气候的集水区中，我们假设Fyw的放电敏感性（即，Fyw和流量之间关系的线性斜率）对降水和随后的河水δ 18 O信号的潜在年代际变化没有反应。

Isotope records of streamflow are pivotal for improving our understanding and modelling of hydrological, ecological, biogeochemical and atmospheric processes – yet the use of their full potential is hindered by short and truncated time series. Here we propose an innovative contribution to the problem of stream isotope record limitations: the use of freshwater bivalves as long-term stream water delta18O recorders. We have done pilot work by analysing mollusc shell delta18O data (compiled from 10 studies), spanning a latitudinal sequence of 18 sampling sites on 16 streams around the globe. We found strong links between isotope signatures in precipitation, stream water and freshwater molluscs – both stream water and mollusc showing a strong damping of the precipitation signal. Our exploratory work on freshwater mussels has blazed a trail that we now intend to follow for multi-decadal stream water delta18O reconstructions. First, we will test the conjecture that stream water temperature – as a prerequisite for reconstructing stream water delta18O from shell delta18O – can be inferred from (a) shell growth rate, (b) shell microstructural properties and/or (c) element chemical properties of the mussel shell. Second, we will benchmark IRMS and SIMS and test their full compatibility and complementarity in terms of mollusc shell delta18O measurement accuracy. While IRMS is a standard tool for measuring delta18O in mollusc shells, SIMS may extend – with high measurement accuracy – delta18O data to later ontogenetic shell portions. Third, we will rely on measured multi-decadal precipitation delta18O data and the reconstructed delta18O signals in stream water from three study catchments in Luxembourg, Sweden and Germany for testing our hypothesis that bedrock geology controls the long-term sensitivity of a catchment’s hydrological response to climate change. For testing our hypothesis, we will rely on the mechanistic relationship between the fraction of young water (Fyw) increasing with discharge – indicating an increase in the proportional contribution of rapid flow paths towards higher flows. In our study catchments with distinct physiographic characteristics and climates, we hypothesise the discharge sensitivity of Fyw (i.e., the linear slope of the relationship between Fyw and discharge) to be unresponsive to a potential inter-decadal variability in precipitation and subsequent stream water delta18O signals.