Spatial and seasonal dynamics of elemental composition and mineralogy of intertidal and subtidal sediments in the Lima estuary (NW Portugal)

In estuaries, the mineral distribution in the top sediment layer results from the combined effect of fluvial and coastal inputs and may present seasonal patterns owing to forcing, e.g., floods, storms, waves, and tides. Our main goal was to study the estuarine sedimentological components, including textural and geochemical parameters, in order to characterize the seasonal and spatial dynamics of subtidal and intertidal sediments in a highly energetic temperate estuary (River Lima, NW Portugal). Subtidal sediments were usually anoxic within the middle estuary and presented higher amounts of clay and silt than intertidal sediments. Oxygen, silicon, carbon, aluminum, and potassium were the most abundant elements. The amount of silicon and carbon was related to the clay and silt content of the sediments. The mineralogical composition of sediments reflected the lithology of the watershed, with the most representative minerals being quartz, microcline (k-alkaloid feldspar), and albite (plagioclase), in line with the results obtained in the elementary characterization. The lower stretches were particularly rich in iron silicates and anatase. No clear seasonal variation was found for sediment elemental and mineralogical compositions. Factor analysis explained 80% of the elemental origin, being 33% related to terrigenous origin, 24% to marine sediments, and 15% to anthropogenic inputs.