Can shells of freshwater mussels (Unionidae) be used to estimate low summer discharge of rivers and associated droughts?

This paper examines if shell oxygen isotope ratios of Unio sp. can be used as a proxy of past discharge of the river Meuse. The proxy was developed from a modern dataset for the reference time interval 1997-2007, which showed a logarithmic relationship between discharge and measured water oxygen isotope ratios. To test this relationship for past time intervals, values were measured in the aragonite of the growth increments of four Unio sp. shells; two from a relatively wet period and two from a very dry time interval (1910-1918 and 1969-1977, respectively). Shell records were converted into values using existing water temperature records. Summer values, reconstructed from of 1910-1918, showed a similar range as the summer values for the reference time interval 1997-2007, whilst summer reconstructed values for the time interval 1969-1977 were anomalously high. These high values suggest that the river Meuse experienced severe summer droughts during the latter time interval. Values were then applied to calculate discharge values. It was attempted to estimate discharge from the reconstructed values using the logarithmic relationship between and discharge. A comparison of the calculated summer discharge results with observed discharge data showed that Meuse low-discharge events below a threshold value of 6 m3/s can be detected in the reconstructed ?18Ow records, but true quantification remains problematic.