Organic Matter

Organic matter in soil consists of plant and animal tissue in different stages of decomposition. It can be grouped in three major groups, plant residue and living microbial biomass, active soil organic matter (detritus) and stable soil organic matter (humus). The living part of the organic matter consists of a wide variety of microorganisms such as fungi, bacteria, algae, viruses, and protozoa. Larger organisms are also included, such as plant roots, insects, and some animals, all contributing with the processing and mixing of the organic matter into the soil. The fresh residue of the organic matter (active soil) comprises all the recently deceased microorganisms, insects, old plant roots ect... This fraction of the organic matter is the more easily decomposed and serves as food source for a variety of organisms living in the soil. Lastly, the humus, forms the part of organic matter which has been fully decomposed and is not source of food for organisms. It plays an important role nonetheless, holding some essential nutrients for plants, and regulating water retention or drainage in different types of soils ( sandy, clay) contributing to the their structure \citet{2013}
The amount of organic matter on beaches greatly depends on the location. In the northern Baltic sea for instance, great levels of eutrophication contribute to the deposition of algal mats on its shores \citep{Norkko_1996} increasing the organic matter count.
With a surface area of 123 km2 and a mean depth of 3m Roskilde fjord is a long and narrow micro-tidal eutrophic estuary   (Flindt, M.R., 1997. Description of the three shallow estuaries: Mondego River (Portugal), Roskilde Fjord (Denmark) and the Lagoon of Venice
(Italy). Ecological Modelling 102: 17–31.) . In this type of environment, the concentration of organic matter in the litter layer is controlled by the intensity of brief geomorphic processes, while in the topsoil, its accumulation is a slower process influenced by the stationary exposure environment \citep{Nyl_n_2015}. Trends have also shown that higher concentration of organic matter can be associated with more sheltered beaches \citep{Rodil_2007,Incera_2003} which can be true for a system like Roskilde fjord.