Particulate organic carbon formation and phosphorus/iron supply ratios along pH and trophic gradients in lakes

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Globally, lake sediments store a very large amount of carbon. The presence of algal remains in sediments such as pigments, cell walls, etc indicates that sediment carbon is partially derived from algae. However, evidence shows that algal carbon is readily mineralized by the microbial community so it appears that there must be a major non-biological source of sediment carbon. During the last grant cycle, work in my laboratory demonstrated that irradiation of acidic stream waters with artificial sunlight resulted in formation of particulate organic carbon (POC) from dissolved organic carbon (DOC) and that formation of particulate iron played a major role, probably because DOC adheres to the surface of newly formed particulate iron. We hypothesize that this mechanism plays a major role in transferring DOC to sediments. The first part of this proposal seeks to extend this work by examining the extent of POC formation in acidic and non-acidic waters in the absence of UVB.