Influence of hydroperiod on aquatic primary productivity between short- and long-hydroperiod Florida Everglades marshes

Abstract:

Everglades National Park (ENP) represents one of the largest wetlands in the United States, where carbon cycling and primary productivity are closely linked to hydroperiod. Only recently has an integrative assessment of the CO₂balance been undertaken in ENP. Previous periphyton and marcrophyte clipping experiments suggest that aquatic primary productivity (APP) is generally low in the Everglades freshwater marsh ecosystems. However, few studies have quantified aquatic metabolism in ENP, which may have significant influence on the entire ecosystem carbon dynamics.

Eddy covariance towers were installed at a long- and short-hydroperiod marsh (Shark River Slough, SRS and Taylor Slough; TS, respectively) within ENP and have been running since 2008 . Net ecosystem exchange of CO₂, H₂O, and energy between the ecosystem and the atmosphere were measured along with meteorological data. To address how interannual and habitat variations in APP influences overall CO₂ flux dynamics, we installed a D-Opto dissolved oxygen sensor (Zebra-Tech LTD) at each site in March of 2011, which allowed us to collect percent dissolved oxygen (DO%), dissolved oxygen concentration (DO ppm), and water temperature (^oC) data at half hourly intervals from March of 2011 until present.

We calculated gross and net aquatic primary productivity (ANPP), and night time aquatic respiration (AR), and compare interannual and inter site variation in APP between SRS and TS from October 2011 through December 2013. Our results reveal that across all three years (2011 – 2013) ANPP and AR were significantly higher at TS. ANPP was 15%, 16%, and 20% higher, and AR was 96%, 55%, and 7% higher at TS than at SRS. These results indicate that APP is contributing to the ecosystem carbon dynamics and differs with hydroperiod. Along with meteorological and data collected at the flux towers, we were also able to relate APP to changes in water level, photosynthetically active radiation and water temperature.

This is the first long term continuous study on water column carbon dynamics in ENP. Currently the Everglades is undergoing hydrological restoration, and further studies will help elucidate how interactions between aquatic abiotic conditions contribute to variations in between site APP, and how APP affects ecosystem level carbon flux dynamics.