Mechanisms of Anthropogenic Tidal Marsh Development in the Hudson River

Abstract:

Tidal marshes provide many valuable ecosystem services, including critical species habitat, shoreline buffering from coastal hazards, and filtering of terrestrial runoff. While urban development has frequently resulted in the loss of tidal wetlands, some construction activities have inadvertently resulted in the emergence of new tidal marshes. Prominent examples of such anthropogenic wetlands lie along the shores of the Hudson River, where recent work reveals more than 50% of the system’s wetlands were unintentionally created in the last 150 years due to river engineering and shoreline modifications. Here, we utilize two of these human-induced tidal wetlands to explore the sedimentary and hydrodynamic conditions driving rapid marsh development. Despite their nearly identical geomorphic and catchment characteristics, Tivoli North Bay (TVN) has developed a thriving marsh habitat while Tivoli South Bay (TVS) remains a mudflat. Using a combination of water column measurements, sediment traps, and sediment cores, we present sediment budgets from these two anthropogenically sheltered bays, quantify sediment accumulation rates, and parameterize trapping processes responsible for varied marsh development. This analysis shows that sedimentation rates and trapping efficiency are considerably higher in the marsh habitat of TVN than the mudflat of TVS. Furthermore, sediment contributions from tributaries draining into these two wetlands are comparable to the amounts of sediment being imported to TVN and exported from TVS via tidal exchange. Contrary to previous thought, it appears that both systems are in a steady-state morphology and the mudflat at TVS is unlikely to transition to a marsh system at its current rate of sediment trapping. Continued research will clarify the causes of this divergence and determine the ability of these systems to keep up with sea level rise. With billions of dollars invested in creating and restoring marshes around the country, the results of this project have important implications for these restoration efforts.