Operationalizing coastal wetland ecosystem services for enhanced decision making and resilience

Abstract

The overarching goal of this dissertation is to operationalize the concept of ecosystem services to enhance coastal wetland resilience and resource management and decision making. Research herein helps to operationalize ecosystem services for science-based decision making, particularly in the context of wetland mitigation and restoration. In the northern Gulf of Mexico, the subtropical black mangrove, Avicennia germinans, is expanding its range northward into temperate salt marshes dominated by smooth cordgrass, Spartina alterniflora. The northern expansion of mangroves in this region is attributed to increasing temperatures and decreases in the frequency and duration of freezes. With a 2°C to 4°C increase in mean annual minimum temperature, 95-100% of salt marshes in Texas and Louisiana could be vulnerable to displacement by mangroves by the year 2100. A shift in dominance from salt marsh to mangrove habitat could alter ecosystem functions, affecting the supply and resiliency of ecosystem services. A meta-analysis was conducted to examine the variability in carbon storage between marshes and mangroves along the northern Gulf of Mexico and to identify data gaps and research needs in the region. Data were categorized as aboveground biomass, belowground biomass, and soil carbon. There is an abundance of published data on the carbon storage capacity of salt marshes in this region. However, there are less data available on the carbon storage capacity of mangroves, especially for belowground biomass. Results suggest that all compartments of salt marsh carbon storage are significantly different from one another, with the majority of carbon stored in soil carbon and belowground biomass, respectively. Due to lack of mangrove data, only the soil carbon compartment of salt marshes and mangroves were compared and were found to not be significantly different from each other. Data collected in Texas were extracted from the meta-analysis dataset and applied to a case study within the Mission-Aransas National Estuarine Research Reserve, TX. Scenarios were developed to assess potential changes in carbon storage assuming a transition from salt marsh- to mangrove-dominated habitat. Due to greater carbon storage potential in mangrove aboveground biomass, scenarios suggest an increase in aboveground carbon storage capacity, which relates to increased storm protection and climate mitigation. Belowground biomass and soil carbon data were limited, especially for mangroves, but data available from outside the study area were used to make predictions about potential changes within the system. Data gaps and research needs were also highlighted as part of this research. A wetland policy assessment was conducted that elucidated the need for enhanced wetland compensatory mitigation in Texas. This work provides guidance on potential changes to Texas coastal wetland permitting programs for improved protection of coastal wetland functions and ecosystem services. Conceptual models were developed that connect the replacement of wetland functions to specific ecosystem services. The connection between public interest review factors and ecosystem services was also highlighted. Recommendations regarding the need for the development of educational materials to assist individuals involved in the compensatory mitigation process were provided.