Rapid organic matter assay of organic matter degradation across depth gradients within marine sediments

Methods to quickly measure organic matter degradation have been well developed for terrestrial and freshwater ecosystems. However, these methods have not been adapted to marine environments. Current methods of assessing organic matter degradation in marine ecosystems are costly, difficult to relate across spatial scales and rarely include sediment depth components to account for redox effects and subsurface macrofaunal activity. We developed a method which is cost effective and time efficient to directly measure rates of organic matter degradation across vertical and horizontal spatial scales in marine sediments. This rapid organic matter assay (ROMA), utilizes a simple design consisting of an acrylic plate with a series of machined wells (0.9 ml) filled with carbon rich substrate. Substrate can be easily adapted to any carbon source by simply modifying the recipe. The plates are deployed with minimal disturbance to the sediment surface and subsurface stratification. Once collected, the resulting change in carbon substrate volume is equated to organic matter degradation. Rapid organic matter assay was shown to be a useful tool in comparing organic matter degradation across sediment redox potentials, habitats within an estuary, and similar habitats across different estuaries. Here, we demonstrate its utility, versatility, and ease of use across a variety of habitats and environments. Rapid organic matter assay is an effective assay for in situ, whole community (micro, meio and macrofauna) organic matter degradation across a myriad of habitats. This supports intensive spatial and temporal analysis that are costly and logistically difficult with current methods. Because it is simple, cost effective, and adaptable, it is an ideal candidate for a standard method to measure organic matter degradation rates in estuaries globally.