Does Flood Pulsing Act as a Switch to Store or Release Sediment-Bound Carbon in Seasonal Floodplain Lakes? : Case Study from the Colombian Orinoco-Llanos and the Brazilian Pantanal

Abstract

Wetlands have been identified as key elements of global carbon budgets. Today, due to increasing anthropogenic carbon emissions, the carbon storage capacity of these ecosystems has become of global interest. The focus of this research was to determine the storage capacity and mechanisms of carbon sequestration of Neotropical seasonal shallow lakes (SSLs), assessing their flood pulse, biomass, geomorphology and sediment composition. We applied a standardized and extensive sampling to five SSLs from the Colombian Orinoco-Llanos and five from the Brazilian Pantanal, during both flooded and non-flooded seasons. We found that sediment organic carbon (SOC) storage capacity in SSLs is significantly driven by the number of flooded days (p-value = 0.0057) rather than by their biomass production. The Orinoco-Llanos and Pantanal lakes differ in morphology, and thus in their inundation patterns. SSLs of the Orinoco-Llanos are more concave, having a significantly higher number of flooded days/year than SSLs from Pantanal. These hydrologic differences affect SOC storage, resulting in a significantly higher SOC storage in SSLs from Orinoco-Llanos than in Pantanal. A synopsis of data from both regions suggests the existence of a critical threshold between “non-flooded season losses” and “non-flooded season storage” of SOC in SSLs in a range of 225–275 flooded days/year.