The synergistic effects of climatic and anthropogenic factors on the sustainability of coastal ecosystems

Abstract:

Coastal marshes are effective nature-based defenses of coastal cities against the effects of storms; vice versa, hurricanes pose significant and complex impacts on coastal marshes. The literature on the impacts of hurricanes on coastal marshes was highly case-specific and can be contracting. Understanding the impact of hurricanes on coastal marshes is a topic of increasing importance under the changing climate and with the ever-growing coastal population. To find out the general pattern of the impacts of hurricanes on marshes, this study examines the impacts of multiple hurricanes on coastal marshes in Mississippi River delta, one of the world’s five largest river deltas that exposed to frequent hurricane impacts. We use long-term satellite data archives (Landsat 1984-2014 and MODIS 2005-2015) and coast-wide field-based environmental data (1978-2018) to examine the impacts of three major hurricanes, i.e., Katrina (2005), Gustav (2008), and Isaac (2012), on the coastal marshes in Louisiana, USA. We found that the hurricanes immediately caused large reductions in the marshes’ biomass and area, followed by general recoveries in the next one to two years. The most severe damage was always found in the intermediate and brackish marshes of the Breton Sound basin, where the water nitrogen concentration was significantly higher (P < 0.05). Excess nutrients can reduce marsh root growth and degrade the root mat. This result suggests that the long-term nutrient enrichment from the diverted Mississippi River water may have increased the marshes’ susceptibility to hurricanes. The study highlights the profound synergistic effects of climatic and anthropogenic factors on coastal ecosystem sustainability and has strong implications for coastal management coping with a changing climate.