National Wetland Condition Assessment and National Estimates of Soil Carbon Storage

Dr. Amanda M. Nahlik (PESD), by invitation, is attending an interagency Inland Wetland Greenhouse Gas Inventory Workshop in Washington, D.C.  The workshop will provide an overview of the context, current inventory and status of inland wetlands, ongoing Federal and non-Federal data and research efforts, and also discuss the development of a roadmap for improving greenhouse gas estimates from inland wetlands in the Greenhouse Gas Inventory.  Dr. Nahlik will be presenting “National Wetland Condition Assessment (NWCA) and National Estimates of Soil Carbon Wetlands” as part of the workshop.

Impact/Purpose

Wetland soils contain some of the highest stores of soil carbon in the biosphere.  However, there is little understanding of the quantity and distribution of carbon stored in US wetlands, or how these stocks change over time.  In this oral presentation at the Annual International Meeting of the Society of Wetland Scientists (SWS), Siobhan Fennessy (Kenyon College), Amanda Nahlik (EPA/ORD/CPHEA/PESD), Karen Blocksom (EPA/ORD/CPHEA/PESD), and Michael Dumelle (EPA/ORD/CPHEA/PESD) evaluate the change in carbon storage in wetland soils over five years.  To do this, they used data from the 2011 and 2016 US EPA National Wetland Condition Assessment (NWCA).  They evaluated carbon storage and carbon density in approximately 1000 sites in both 2011 and 2016, which represent about 38 million hectares of targeted wetland area across the contiguous US.  Results show that carbon storage and carbon density decreased in wetlands across the US, particularly in deeper soil layers (within 30-60 cm and 60-90 cm) between 2011 and 2016.  The mechanisms driving decreased carbon storage have yet to be explored, but carbon data from 2011 (Nahlik & Fennessy, 2016, NatComm:13835) showed that increased human disturbance was correlated with lower carbon storage in deep soil layers (>60 cm); one hypothesis that will be explored is that the change in carbon storage in resampled sites in 2016 is due to human disturbance.  Other drivers, such as draught or increased ambient temperatures, will also be explored.  These data provide the first empirical, unbiased estimates of carbon storage change in wetlands across the US, especially at soil depths greater than 30 cm.  Because of the probabilistic design from which these data were collected, the consistency used to collect these data in the field, and the repeated data collection on a five-year schedule, this is an important dataset for many efforts being conducted across the US.  This effort exemplifies the power of collecting national data using the NARS approach, and the results of this research further support indicator development efforts by USEPA for future NWCA surveys.  The data we discuss here are necessary to effectively identify patterns of carbon storage and begin to investigate mechanisms that drive change in carbon storage – critical information if we are to implement policies related to climate protection targeted to where they can have the most positive effect.

Citation

Nahlik, A. National Wetland Condition Assessment and National Estimates of Soil Carbon Storage. Building a roadmap to integrating inland wetlands into the U.S. National Greenhouse Gas Inventory, D.C., DC, July 16 - 17, 2024.