Effects of biochar addition to estuarine sediments

Authors: Gerardo Ojeda Joana Patrício Stefania Mattana Abilio J F N Sobral

Publish Date: 2016/07/01

Volume: 16, Issue: 10, Pages: 2482-2491

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Abstract

Biochar is a carbonrich product able to enhance soil fertility and mitigate CO2 emissions While biochar effects on agriculture are becoming known its impact elsewhere eg on estuarine ecosystems has yet to be assessed The main aim of the present study was to determine the effect of biochar on sediment–water retention CO2 emissions from sedimentary organic carbon decomposition sediment pH and electrical conductivity in aerobic conditions similar to those observed at low tideSediments from the Mondego Estuary Portugal were mixed with pine gasification biochar at different doses 5 10 14  and immersed in water with different salinity values 15 25 30 for 96 h The influence of biochar on water retention the residence time of water and CO2 emissions between −075 and −15 MPa total organic carbon pH and electrical conductivity EC were determined Carbon chemical composition and polycyclic aromatic hydrocarbon PAH concentrations were determined in sediments and biochar Differences between biochar treatments after immersion in different water salinities were analysed using the Kruskal–Wallis testResults showed that biochar was able to a increase sediment–water content in terms of quantity and residence time b decrease CO2 emissions but only with a specific soil–water content and at the highest biochar dose c increase sediment pH at all biochar doses and d increase sediment EC at the highest biochar dose In contrast the percentage of carbon mineralised was not modified Biochar carbon was rich in PAHs and less decomposable than sedimentary carbon The increments observed in sediment pH and EC were unable to change sediment alkaline or saline status according to standard classificationsOur results suggest that the remarkable water adsorption capacity of biochar–sediment mixtures may be considered the main factor in regulating CO2 emission rates from sediments together with high PAH concentrations which probably restrain the organic matter decomposition processThis research was carried out as part of the SOCARRAT project contract AGL200912343 of the Spanish Ministry of Science and Innovation The authors wish to thank the Fundação para a Ciência e Tecnologia—the European Social and National Funds POPH QREN SFRH/BPD/36371/2007 and Universidad Nacional de Colombia at Palmira—Colciencias FP448421382015 for financial support through the postdoctoral grants to G Ojeda We appreciate the study system map Fig 1 designed by Z Teixeira

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