Impact of Shrimp Ponds on Mangrove Blue Carbon Stocks in Ecuador

Abstract

Mangrove forests play an important role in mitigating climate change but are threatened by aquaculture expansion. The inclusion of mangroves in climate change mitigation strategies requires measuring of carbon stocks and the emissions caused by land use change over time. This study provides a synthesis of carbon stocks in mangrove and shrimp ponds in the Gulf of Guayaquil. In this study area, we identified 134,064 ha of mangrove forest and 153,950 ha of shrimp farms. Two mangrove strata were identified according to their height and basal area: medium-statured mangrove (lower height and basal area) and tall mangrove (greater height and basal area). These strata showed statistical differences in aboveground carbon stocks. In both strata, the most abundant mangrove species was Rhizophora mangle. For both strata, trees had a maximum height (>30 m), and their density was greater than 827 ha−1. Total ecosystem level carbon stocks (measured to 1 m soil depth) were 320.9 Mg C ha−1 in medium-statured mangroves and 419.4 Mg C ha−1 in tall mangroves. The differences are attributable to higher basal area, soil organic carbon concentrations and salinity, tidal range, origin of allochthonous material, and herbivory patterns. Mangrove soils represented >80% of the total ecosystem carbon. Ecosystem carbon stocks were lower (81.9 Mg C ha−1) in the shrimp farms, 50% less than in undisturbed mangroves. Our results highlight mangroves as tropical ecosystems with extremely high carbon storage; therefore, they play an important role in mitigating climate change. This research provides a better understanding of how carbon stocks in this gulf are found and can be used for design strategies to protect global natural carbon sinks.

Low Carbon Emission Shrimp Farming Development Model

“…The linkages between shrimp farms area, carbon emissions and climate change are shown in Figure 1. The carbon stock of mangrove ecosystems converted to aquaculture areas decreased to 81.9 Mg C ha -1 or 50% of the natural mangrove carbon stock (Merecí-Guamán et al, 2021). Kauffman et al (2017) concluded that shrimp farming by converting mangroves and extensive technology (productivity of about 250 kg ha -1 ) in the Mahakam Delta caused emissions of 1,603 kg CO2-equivalent for every 1 kg of shrimp produced.…”

Water and Sediment Quality Changes in Mangrove Systems with Shrimp Farms in the Northern Ecuadorean Coast

“…Nitrogen is associated with deforestation processes and the removal of previous soils when shrimp ponds were built. The decrease of OM in shrimp ponds and mangroves receiving shrimp effluents has been described for Brazil [14], Saudi Arabia [88] and southern Ecuador [89], and the increase of carbon in mangroves by shrimp effluents has been described in China [90]; changes in the composition of mangrove sediments receiving shrimp farm effluents decrease the diversity of the bacterial microbiome [91].…”

Impacts of Climate Change on Blue Carbon Stocks and Fluxes in Mangrove Forests

“…Mangrove forests have the largest organic carbon (C ORG ) stocks of any of earth's ecosystems, with a global mean total forest stock of 692.8 ± 23.1 (±1 SE) Mg C ORG ha −1 (updated from [8] with [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]). Soil standing stocks average 516.4 ± 19.8 Mg C ORG ha −1 over the upper 1 m depth, accounting for 74% of total ecosystem standing stocks.…”

“…These large amounts of C ORG reflect rapid rates of soil accumulation on the forest floor, sustained accumulation over long time periods, and high rates of primary productivity. In contrast, global mean aboveground and belowground mangrove biomass average 105.8 ± 4.2 Mg C ORG ha −1 (±1 SE) and 68 Mg C ORG ha −1 , respectively, as updated from Alongi [8] with new data [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28], which underscores the dominance of the soil component.…”