Geochemical and geospatial studies of sediment accumulation and carbon burial in the lower Hudson River estuary and its implications for the global carbon cycle

Estuaries are dynamic systems that occur at the land-ocean interface. Urbanized estuaries are not only affected by natural processes, but also impacted by human activities. In this research, a combined geochemical and geospatial research approach was used to examine and quantify sediment accumulation and organic carbon burial in the lower Hudson River estuary.;A pilot study conducted in the Neponset River estuary documented the use of 7Be (half-life, t1/2 = 53 days) as a tracer and clock to examine estuarine sediment processes over monthly-to-seasonal time scales. It provided a long-term record of 7Be atmospheric deposition to the Boston area that can be used to indicate sediment accumulation, bypassing, and erosion in estuarine environments.;Berylium-7 and 131I (t1/2 = 8 days) were used to examine sediment accumulation in the lower Hudson River estuary over monthly-to-seasonal time scales. Comparisons between 7Be sediment inventories and its atmospherically supported depositional inventories indicated a large degree of spatial and temporal variation in sediment accumulation patterns in the lower Hudson River estuary. Iodine-131 sediment penetration depths indicated greater during high flow conditions and it served as a novel tracer for identifying sites affected by municipal wastewater inputs.;Cesium-137 (t1/2 = 30 years) was used to examine sediment accumulation in the lower Hudson River estuary over yearly-to-decadal time scales. Comparisons between 137Cs sediment inventories and its supported inventory indicated a large degree of spatial and temporal variation in sediment accumulation patterns in the lower Hudson River estuary. Measured 137Cs sediment profiles in vibracores indicated three generic types of estuarine sedimentation environments.;Geographic information systems (GIS) and 137Cs were used to quantify organic carbon burial in both the Yangtze River and the lower Hudson River estuaries and documented its implications for the global carbon cycles. Results show that 5-10x1013 gC/yr of carbon may be trapped and buried in the world's 25 largest estuarine systems. Therefore, carbon burial in the sediments of non-steady-state river-estuarine systems and other lower-energy or protected areas at the land-ocean interface should be explicitly considered as a potential new carbon sink in the global carbon budget within the global carbon cycle.