Spatial and temporal analysis of rare earth elements in the Neuse River, North Carolina

Rare earth elements (REEs) found in bottom sediment and dissolved river load samples serve as excellent monitors of continental weathering processes within a basin. However, the extent of REE variation along a river's profile is poorly understood due to the influences several physical and chemical parameters have upon shale-normalized (i.e., PAAS) REE concentrations. In this investigation, we report on analyses of REE concentrations of bulk bed sediment and dissolved river load samples to better understand the transport of river-born REE collected at 5 sampling stations along the Neuse River, North Carolina. The gauge height, pH, turbidity, dissolved oxygen, nitrate concentration and water temperature are recorded at each sampling location. The underlying geology is also noted. These factors collectively influence REE weathering. PAAS-normalized REE patterns of dissolved water loads vary spatially among the 5 different sampling stations and exhibit station-station temporal variation as well as overall river variation. Our results show that REE patterns in dissolved river loads are similar across the length of the river with the exception of gadolinium (Gd) spikes. Further work is necessary to determine the nature of these spikes and their possible sources. These findings may indicate that the overall influence of underlying basin rock does not significantly alter REE patterns along the profile of a river, but rather suggest that a homogenized pattern occurs as a result of mixing.