Temporal variability of carbon and nutrient burial, sediment accretion, and mass accumulation over the past century in a carbonate platform mangrove forest of the Florida Everglades

Abstract

The objective of this research was to measure temporal variability in accretion and mass sedimentation rates (including organic carbon (OC), total nitrogen (TN), and total phosphorous (TP)) from the past century in a mangrove forest on the Shark River in Everglades National Park, USA. The 210 Pb Constant Rate of Supply model was applied to six soil cores to calculate annual rates over the most recent 10, 50, and 100 year time spans. Our results show that rates integrated over longer timeframes are lower than those for shorter, recent periods of observation. Additionally, the substantial spatial variability between cores over the 10 year period is diminished over the 100 year record, raising two important implications. First, a multiple-decade assessment of soil accretion and OC burial provides a more conservative estimate and is likely to be most relevant for forecasting these rates relative to long-term processes of sea level rise and climate change mitigation. Second, a small number of sampling locations are better able to account for spatial variability over the longer periods than for the shorter periods. The site average 100 year OC burial rate, 123 ± 19 (standard deviation) g m À2 yr À1 , is low compared with global mangrove values. High TN and TP burial rates in recent decades may lead to increased soil carbon remineralization, contributing to the low carbon burial rates. Finally, the strong correlation between OC burial and accretion across this site signals the substantial contribution of OC to soil building in addition to the ecosystem service of CO 2 sequestration.

Carbon Sequestration and Sedimentation in Mangrove Swamps Influenced by Hydrogeomorphic Conditions and Urbanization in Southwest Florida

“…The sites with discernible 137 Cs peaks registered accretion rates on the order of 2.85 to 7.34 mm¨year´1. Accretion rates calculated from 137 Cs peaks and 210 Pb in our study are well within the range of vertical accretion reported for mangrove forests [11,24,57,58]. For all sites, accretion rates calculated with 210 Pb were considerably lower than the rates calculated with 137 Cs peak activity.…”

“…The mangroves on some of Florida's coastline actually experience and survive occasional frosts that are rare in subtropical regions. In the Florida Everglades, 100 km east of our study site, Breithaupt et al [58] found similar rates of carbon sequestration (123˘19 g-C m´2¨year´1) rates comparable to our reference tidal creek, which averaged 113˘19 g-C m´2¨year´1. Their study represented a relative homogenous landscape and similar hydrogeomorphic conditions (coring sites were spaced within 200 m) while ours represented a gradient of hydrologic energies in differing hydrogeomorphic environments.…”

Dissolved carbon biogeochemistry and export in mangrove-dominated rivers of the Florida Everglades

“…Another method of estimating forest lateral carbon export utilizes the difference between measurements of net ecosystem-atmosphere CO 2 exchange (NEE) above the mangrove forest surrounding Shark River (267 ± 15 mmol m −2 yr −1 in 2004; (Barr et al, 2012) (Breithaupt et al, 2014) measured at the same location (FCE LTER site SRS6) in this forest. The difference between NEE and NECB (40 ± 17 mmol m −2 d −1 ) provides an estimate of the annual rate of forest carbon export to Shark River on a daily basis (Chapin et al, 2006).…”

Linking Organic Matter Dynamics to Management, Restoration, and Climate in the Florida Everglades

“…Changes in flow and salinity associated with rising sea levels throughout the estuarine extent of ENP ) and altered freshwater delivery will influence the ecotone, as well as the freshwater and saltwater regions. Shifting surface water flows are predicted to alter landscape topography (USACE, 1999;Science Coordination Team, 2003;), vegetation communities , biogeochemical cycling (Reddy et al, 2010;, and carbon sequestration capacity (Jimenez et al 2012;Breithaupt et al 2014;. It is therefore essential to understand how OM currently responds to hydrology in order to predict how changes in these factors may affect the carbon cycle in the future, particularly in response to landscape-scale factors like restoration and climate change (Middleton and Souter, 2016).…”

“…Better understanding of the potentially complex relationship between inundation and DOC export is therefore crucial for low-relief coastal systems like mangrove forests, where ecosystem sustainability is based on accretion keeping pace with sea-level rise (McKee, 2011). Mangrove accretion is primarily dependent on primary productivity (Cahoon & Lynch, 1997) and correlates to organic C burial rates, which are below global averages for the Shark River (Breithaupt et al 2014). Thus, potential DOC losses from mangrove peats due to the combined effects of increased salinity and inundation could increase the vulnerability of the coastal mangrove fringe to submergence.…”