Characterizing the Pearl and Pascagoula River systems using trace elements and strontium isotope ratios

Water microchemistry combines geologic and hydrologic factors and has been increasingly used to delineate regions within watersheds. These chemical signatures are also incorporated into chronologically layered calcified structures of biological organisms and can be used to retrace species’ life history. Strontium (Sr), barium (Ba), manganese (Mn) and 87Sr/86Sr ratios have been useful for microchemical characterization because of their relationship to underlying substrates, gradients in their relative abundance within watersheds, and large concentration differences between fresh and saline water. In the Pearl and Pascagoula River systems of Mississippi and Louisiana, USA, an understanding of microchemistry would benefit research on the life history of species of management importance, such as the Federally threatened Gulf Sturgeon (Acipenser desotoi). Therefore, Sr, Ba, Mn and 87Sr/86Sr were measured across these watersheds in multiple years using solution inductively coupled-mass spectrometry (ICP-MS) to create or expand watershed microchemistry maps. The relative interannual variability was low (generally < 25%) in both river systems, but was highest in Mn (~42%). The Pearl River system was differentiated into three chemically unique river reaches: the Bogue Chitto River exhibited higher levels of Sr, Ba and 87Sr/86Sr compared to the Upper and Lower Pearl Rivers; 87Sr/86Sr differed among the three regions; and Mn was not statistically different. The Pascagoula River system was differentiated into four main river reaches: the Leaf/Bouie River was chemically unique compared to the other three regions, the Upper Leaf River had similar chemical signatures of all elements compared to the Chickasawhay and the Pascagoula Rivers and the Pascagoula River had significantly higher Ba compared to the Chickasawhay River and lower Mn when compared to the Leaf/Bouie River. These results show microchemistry differentiation of these river systems, which is useful for river and species management, including for mobile species such as the Gulf Sturgeon.