What would you like to know? OM composition can be studied using molecular techniques on both quantity and quality: chlorophyll-a, fatty acids and stable isotopes are interesting proxies, in combination with total Organic Carbon and total Nitrogen analysis. Breakdown rates can be derived from depth profiles of highly degradable components (e.g. chl-a), community metabolism driven by quantity and quality of fresh OM can be assessed using benthic chambers, measuring Sediment Oxygen Demand, but also measuring vertical oxygen profiles, and vertical nutrient profiles.
You need to decide whether you are interested in biomass production and quality or the underlying soils and sediments. Remember that you are in an intertidal zone, so that leaves and sediment are moved around, although there is usually a net accumulation of sediment. The surface soil layer is usually a mottled yellow-orange colour indicating the presence of some oxygen. However below 10-15 cm, the colour is greenish blue indicating anoxic conditions. The pH is usually