HUMAN IMPACTS TO URBANIZED ESTUARIES

Shorelines have been heavily modified over the last few centuries, such that today it is difficult to find a coastal system that has not experienced some sort of significant anthropogenic alteration. New York Harbor and the 250 km Hudson River estuary serve as a prominent example of one such modified system, where human activities have dramatically altered flood regimes, tidal propagation, and important biophysical structures such as oyster reefs and tidal marshes. Dredging has more than doubled water depths and coastal armoring and infrastructure has straightened shorelines. Consequent losses of wetlands and estuarine ecosystems have spurred calls to restore the system back to more natural conditions at costs in the billions of US dollars . However, until recently it has been unclear how all of the above-mentioned historical modifications initially impacted the estuary, and in turn, if such calls for restorations will have the intended effect.

Most modern instrumentation post-date early human modifications to estuaries; however, historical archives and sedimentary records provide perspective on pre-modified shoreline morphology and hydrodynamic processes. Numerical simulations using pre- and post- modifications provide further insight. Here we provide prominent examples of such research and focused to anthropogenic alterations on the Hudson River estuary including: 1) the impacts of 17^th-18^th century oyster reef removal on shoreline erosion and wave-induced flooding, 2) dredging influences on tides, salinity and extreme high water levels, 3) effects of dams on sediment delivery, and finally 4) assessments of tidal wetland development in response to shoreline development. New York City is the largest coastal megacity in the Western Hemisphere; as such, impacts to its estuary and harbor warrant focus. However, we argue that many of our findings extend to other urbanized estuaries and coastlines and are in turn globally relevant.