Seasonal and spatial distributions of grain size and organic matter content across an intertidal area at St. Lawrence Estuary, Canada

Grain size distribution and organic matter content (loss on ignition) of surface scrape sediments were analyzed in summer 2016, autumn 2017, and summer 2018 at Nazareth tidal flat and marsh located west of Rimouski on the southern shore of Lower St. Lawrence Estuary (Canada). Surface sediment samples for analysis of grain size and organic matter content were collected at each site within 1 m radius of CSM measurements using a spatula to scrape the top 2-3 cm of sediments. The combustible organic matter content (loss on ignition, LOI) of the surface sediments was determined after: (1) drying at 60°C for 24 h until no weight change occurred; (2) placing in oven at 450°C for 16 h. For grain size analysis, the coarse and the fine grain size distributions were processed with Gradistat (Blott and Pye, 2001) to compute median grain size (d50), mean grain size, and sorting using the geometric moment method. The sorting is calculated similarly to a standard deviation. Cross-shore transect B was sampled in November 2017 for which, the data is presented here. The data for summer 2016, summer 2017, and summer 2018 was published in the context of annual variations in sediment biostabilization (Waqas et al., 2019, doi:10.1594/PANGAEA.911771)