Spatial analysis of the recovery of submerged aquatic vegetation in the Hudson river estuary following the 2011-2012 hurricane seasons

Abstract

Submerged aquatic vegetation (SAV) is a critical habitat found in estuarine ecosystems throughout the world. SAV performs a multitude of ecosystem functions ranging from water quality improvement to habitat for macroinvertebrates and juvenile fish, and acts as a significant contributor to dissolved oxygen throughout the estuarine system. In the Hudson River Estuary (HRE), native SAV beds have been greatly reduced or altered by threats such as sedimentation, water quality issues, and the spread of invasive aquatic plants, as well as by disturbance from natural events such as large-scale storms. In 2011 and 2012, three hurricanes made landfall in the northeastern United States, having a tremendous impact on the Hudson River and the Hudson Valley region as a whole. SAV in the estuary was impacted by both storm surge as well as significant sediment deposition from the river's tributaries. However, in the wake of these events, there is uncertainty about the spatial patterns of SAV loss and recovery, and how these patterns are affected by the hydrology and physical characteristics of the river. Therefore, my study seeks to address this knowledge gap by investigating the impacts of these storms on SAV spatial patterns and the influence of SAV proximity to shoreline, tidal wetlands, and persistent "colony" SAV beds. I investigated these effects by analyzing overall (whole system) SAV recovery, the spatial patterns of recovery, and the correlation of recovery to prior SAV coverage and proximity to these features. Analysis was done using three years of remotely-sensed SAV GIS data, and was done at three different spatial scales. SAV coverages were determined at each scale for all three years and areal-change and percentage-change were calculated. Distance to the three aforementioned features was calculated for the fine-scale analysis. The results suggest that there was significant SAV loss river-wide between 2007 and 2014, followed by significant recovery between 2014 and 2016. Loss between 2007 and 2014 was greatest in the most upstream approximately 100 km of the river, likely a result of proximity to the Mohawk River, a major tributary and large sediment source during the storms. SAV recovery showed a similar pattern, occurring most in these upstream reaches. Distance from shoreline, tidal wetlands, and persistent SAV beds had varying impacts on SAV loss and recovery. The findings of this study help to elucidate both the potential impacts on the magnitude and patterns of vegetation loss following a large storm event and subsequent sediment flux, as well as the recovery potential of this vegetation during 'normal' years. Such information can help inform future biological studies of the HRE and watershed management decision-making.