Biomarker evidence for recent turf cultivation in Northeast Brazil (Lagoa do Boqueirão, RN)

Abstract : The first meter of sediment in Lagoa do Boqueirão [Rio Grande do Norte State (RN), Brazil) is characterized by low sedimentation rates over the period 1000 BC-1500 AD and a high sedimentation rate in the top 20 cm, corresponding to the last ten years. Several pentacyclic triterpene methyl ethers (PTMEs) such as taraxer-14-en-3α-ol ME (crusgallin) and arbor-9(11)-en-3β-ol ME (cylindrin) occur in all the samples selected. The major change in sedimentation rate recorded at 20 cm is accompanied by a change in PTME concentration and distribution. Sediments deposited during the period 1000 BC-1500 AD contain PTMEs in low concentration level (1.3 μg/g sed.) that could constitute a geochemical background of the grass that naturally developed in the catchment. High PTME concentrations occur during the period 1996-2000. These result mainly from high concentrations of a compound tentatively assigned as arbor-8-en-3βol ME, a potential diagenetic derivative of cylindrin. The increase corresponds to the beginning of intensive cultivation of Cynodon dactylon and Zoysia japonica (arundoin and cylindrin producers), for the production of turf to cover Brazilian football stadiums and golf practices. The results constitute a novel application of PTMEs to reconstruct land use changes from lake sediment archives.