Since the late nineteenth century, channel depths have more than doubled in parts of New York Harbor and the tidal Hudson River, wetlands have been reclaimed and navigational channels widened, and river flow has been regulated. To quantify the effects of these modifications, observations and numerical simulations using historical and modern bathymetry are used to analyze changes in the barotropic dynamics. Model results and water level records for Albany (1868 to present) and New York Harbor (1844 to present) recovered from archives show that the tidal amplitude has more than doubled near the head of tides, whereas increases in the lower estuary have been slight (<10%). Channel deepening has reduced the effective drag in the upper tidal river, shifting the system from hyposynchronous (tide decaying landward) to hypersynchronous (tide amplifying). Similarly, modeling shows that coastal storm effects propagate farther landward, with a 20% increase in amplitude for a major event. In contrast, the decrease in friction with channel deepening has lowered the tidally averaged water level during discharge events, more than compensating for increased surge amplitude. Combined with river regulation that reduced peak discharges, the overall risk of extreme water levels in the upper tidal river decreased after channel construction, reducing the water level for the 10-year recurrence interval event by almost 3 m. Mean water level decreased sharply with channel modifications around 1930, and subsequent decadal variability has depended both on river discharge and sea level rise. Channel construction has only slightly altered tidal and storm surge amplitudes in the lower estuary. Plain Language SummaryDredging for navigation has deepened harbors and estuaries around the world, altering circulation patterns and tidal water levels. In the Hudson River estuary, channel construction for ports in New York Harbor and Albany more than doubled channel depths in some regions. Major dredging began in the late 1800s, so to characterize associated changes in the hydrodynamic conditions, we analyzed archival water level records and navigational charts back to that period. Water level records from Albany show that channel construction reduced the effects of friction such that the tide now amplifies in the upper estuary, more than doubling the tidal amplitude compared with before dredging. The lower friction also allows storm surge from the coast to travel farther landward. However, major flooding in the upper tidal river historically was mainly due to river discharge events, and the deeper channel allows for more effective conveyance of flood waves. Thus, despite the increases in tides and storm surge, the risk of flooding in the upper estuary decreased with construction of the navigational channel. The Hudson provides a well-documented example of how multiple anthropogenic factors can significantly influence physical processes in extensively modified estuaries. Key Points:• Archival records over the past 150 years show that the tidal amplitu...

Tidal wetlands produce long-term soil organic carbon (C) stocks. Thus for carbon accounting purposes, we need accurate and precise information on the magnitude and spatial distribution of those stocks. We assembled and analyzed an unprecedented soil core dataset, and tested three strategies for mapping carbon stocks: applying the average value from the synthesis to mapped tidal wetlands, applying models fit using empirical data and applied using soil, vegetation and salinity maps, and relying on independently generated soil carbon maps. Soil carbon stocks were far lower on average and varied less spatially and with depth than stocks calculated from available soils maps. Further, variation in carbon density was not well-predicted based on climate, salinity, vegetation, or soil classes. Instead, the assembled dataset showed that carbon density across the conterminous united states (CONUS) was normally distributed, with a predictable range of observations. We identified the simplest strategy, applying mean carbon density (27.0 kg C m−3), as the best performing strategy, and conservatively estimated that the top meter of CONUS tidal wetland soil contains 0.72 petagrams C. This strategy could provide standardization in CONUS tidal carbon accounting until such a time as modeling and mapping advancements can quantitatively improve accuracy and precision.

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[1] An observational study was conducted to identify mechanisms of suspended sediment flux and turbidity maintenance in the Delaware River estuary. From March through October 2005, instrumented moorings were deployed to obtain continuous measurements of currents and suspended sediment concentration at sites along the estuarine channel and on flanking subtidal flats. Data time series were analyzed to determine the relative influence of nontidal advection and tidal pumping on residual fluxes of sediment. Results indicate that the estuarine channel is a strongly advective transport environment with residual sediment fluxes driven mostly by gravitational circulation. Tidal pumping is a contributing process of residual sediment flux in the channel near the estuarine null point and turbidity maximum, though the magnitude and direction of pumping vary with river flow and resident sediment inventory in the upper estuary. Sediment pumping in the channel is driven by tidal asymmetries in velocity and particle settling and perhaps by tidal variations in internal mixing in the stratified lower estuary. In contrast to the estuarine channel, residual sediment fluxes over the subtidal flats are weak and dominated by tidal pumping. Landward advective fluxes of sediment in bottom waters of the lower estuarine channel are strongest during neap tides; during large spring tides sediment is mixed high in the water column and the advective flux reverses to seaward under the residual surface outflow. Despite these transient seaward fluxes, the estuary has an enormous capacity to buffer extreme freshwater discharges and suppress export of suspended sediment to Delaware Bay.

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