Resolving Sediment Connectivity between Rivers and Estuaries by Tracking Particles with their Microbial Genetic Signature

Sea level rise is not only climbing our coastline and sculpting our saltmarshes, it is also pushing ocean tides far inland where they sweep up rivers and roll across their fringing forests. Treasured for their biodiversity, beauty, and other services they provide society, these freshwater wetlands will evolve from forest to marsh to open water as sea level rises.

The pace of this transition over the coming decades isn’t yet known, and it is likely that even small changes in the interaction between coastal landscapes and their rivers will lead to very different impacts affecting public lands, private property, and environmental management of watersheds and estuaries. Society will be better positioned to adapt to these impacts by preparing in two ways.

First, exploring how the settling of mud, silt, and sand from rivers and estuaries builds the elevation of tidal wetlands, especially wetlands at the farthest upstream reach of tides, will help pinpoint where (and possibly when) major changes to these wetlands will occur. Second, educating coastal populations on why their coastal landscapes are changing and training them to measure and monitor these changes will strengthen local decision-making and empower scientists and coastal managers to more precisely target environmental protections.

This project will measure the immediate source of suspended sediment in the fluvial tidal and saline zones of estuaries, particularly during river floods. These measurements will help answer notoriously challenging questions about the connectivity of rivers with their estuaries, such as “how far do river-borne particles travel into estuaries during river floods, and what proportion of the suspended sediment do these particles comprise in the saline estuary?” The answers will reveal as much about the time scale of particle movements as the spatial scales of river and estuarine influence.

The recent origin of sediment particles will be assessed using high throughput DNA sequencing of the particle-associated microbial community. The advantage of this technique is that sediment particles of identical mineralogy and chemical composition can be traced to their most recent source (freshwater, tidal freshwater, benthic, wetland, saline estuary).

Synoptic surveys of particle-associated microbial DNA along the riverine-estuarine transition of two tributaries of the Chesapeake Bay will be interpreted using results from laboratory incubation and mixing experiments with suspended sediment from various sources and water matrices. The spatial and temporal patterns of sediment mixing will be generalized and applied to predict vulnerability of freshwater tidal wetlands on the US east coast.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.