Extracellular enzyme activities of estuarine mudflats in French Guiana in relation with environmental factors across spatial and seasonal scales

摘要

The main aim of this study was to investigate the dynamic of extracellular enzyme activities within estuarine intertidal mudflats and to explore their potential environmental driving factors. Estuarine slikkes of the main rivers of French Guiana were sampled during two annual contrasted hydro-climatic seasons (wet and dry) over a two-year period (n = 38). The spatio-temporal variability of four enzyme activities (alkaline phosphomonoesterase, arylsulfatase, beta-glucosidase, urease) was assessed and physico-chemical analyses (dry bulk density, salinity, pH, carbon, nitrogen and sulfur content) of sediments were carried out. Results showed that the hydro-sedimentary specificities of each estuary, combined with the alternation of hydro-climatic seasons, had a strong influence on sediment physico-chemical characteristics. They revealed a gradient of mudflats under mainly continental versus marine influence. Mudflats under mainly continental influence were characterized by oli-gohaline pore-waters, more acidic pH and relatively high organic matter content, and conversely for slikkes under mainly marine influence. Crossing of physico-chemical and functional data showed that the main factor associated with enzyme activities was the total nitrogen content. To a lesser extent, pH and organic carbon content were also related to enzyme activities, but these relationships could not be generalized to all enzymes. Moreover, relationships between enzyme activities and physico-chemical variables were not dependent on the mudflat types, except for the beta-glucosidase which showed higher activity under mainly marine influence. Finally, relationships between enzyme activities and physico-chemical variables were not dependent on the seasons, except for alkaline phosphomonoesterase and urease activity, which showed opposite patterns according to seasons.