Abstract
Seasonality and crab activity affects the nutrients and physicochemical parameters in mangrove soils, thus, affecting the emissions of greenhouse gases, such as nitrous oxide (N2O). Climate change may intensify rainfall and/or enhance droughts, affecting mangroves and associated biota. Crabs are natural soil bioturbators responsible for soil aeration and turnover. We evaluated the effect of Ucides cordatus crab on N2O emissions from mangrove soils under a semiarid climate in Northeastern Brazil. Soil and gas samples were collected over the rainy and dry seasons in crab-naturally-bioturbated and crab-exclusion mangrove plots. We measured the soil’s pH, redox potential, and the total contents of carbon, nitrogen, and sulfur. We found higher N2O emissions in the crab-exclusion sites compared to the bioturbated sites, as well as higher N2O emissions in the rainy season compared to the dry season. The fluxes of N2O (µg m−2 h−1) were 47.3 ± 9.7 and 8.9 ± 0.5 for the crab-exclusion sites, and 36.5 ± 7.8 and 4.5 ± 2.1 for the bioturbated sites (wet and dry seasons, respectively). The soil turning over by macrofauna led to lower N2O fluxes in natural crab-bioturbated areas, and seasonality was the environmental factor that contributed the most to the changes in N2O emissions. Broadly, anthropic activities and seasonality influence nitrogen fate, N2O emissions, and ecological services in coastal ecosystems.
Highlights
Severe droughts and stronger storms are the future scenarios of global climate change, which may threaten innumerable ecosystems [1,2,3], including mangroves
Our study highlighted the influence of anthropic activities and seasonal changes on the emissions of nitrous oxide (N2 O) from mangrove soils, contributing to climate change effects
Lower N2 O fluxes in natural crab-bioturbated areas are due to constant soil oxidation by macrofauna, whereas higher N2 O fluxes in crab-exclusion mangrove areas are due to wet/anaerobic soil conditions that favor denitrification
Summary
Severe droughts and stronger storms are the future scenarios of global climate change, which may threaten innumerable ecosystems [1,2,3], including mangroves. Mangrove ecosystems contain the most carbon-rich soils on the planet [4,5], characterized by fluctuations in the soil redox conditions due to tidal flooding [6,7,8]. Mangrove forests are one of the most important coastal carbon (C). Sci. 2020, 10, 2215 sinks, contributing to the mitigation of climate change by sequestering and storing significant amounts of carbon, known as blue carbon [9,10,11,12]. Mangrove macrofauna (especially the crab species) are known drivers for changing the soil’s physicochemical conditions in intertidal environments and can directly affect greenhouse gas emissions, such as nitrous oxide (N2 O) [13,14,15]. The Ucides cordatus crabs are one of the most important bioturbators of mangrove soils, turning over and inducing the natural recycling of nutrients and organic matter [17,18]
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