Research areas

My research interests are primarily focused on the biogeochemistry and microbial ecology of coastal marine sediments inhabited by burrowing invertebrates and rooted macrophytes. I am currently involved in the following projects:

Infaunal stimulation of organic matter degradation in marine sediments. It is well known that benthic infauna is capable of stimulating the microbial decay of organic matter in sediments. However, the underlying mechanisms for this stimulation are not clearly elucidated. The questions I seek to answer in this respect are: 1. Do infaunal animals stimulate microbial activity directly by grazing or competing with them? 2. Do infaunal animals speed up microbial processes in deep sediment layers indirectly by introducing efficient electron acceptors, such as oxygen, via irrigation activities? 3. Do infaunal animals stimulate microbial activity indirectly by changing the diffusion geometry in anoxic sediment when they create a mosaic of sediment-water interfaces? Species of the common polychaete genus Nereis are excellent model organisms for this purpose. The massive colonization in recent years of the invasive polychaete Marenzelleria viridis in our coastal sediments has raised a number of new and important questions: 1. Vil this new species outcompete native species, such as Nereis diversicolor? 2. How does this new species affect the sediment biogeochemistry? I attempt to answer these questions in the years to come.

Anaerobic mineralization of carbon and nitrogen in marine sediment. Consortia of bacteria mediate anaerobic degradation of organic matter in marine sediments. Hydrolyzing bacteria splits large molecules into smaller organic units, which are degraded to organic monomers (e.g. amino acids) and short chain organic acids (e.g. acetate) by fermenting bacteria. Finally, the anaerobic respirers mineralize these small molecules to carbon dioxide and inorganic nutrients. My questions here are then: 1. Which organisms and processes are responsible for the release of carbon dioxide and ammonium during microbial degradation of organic matter in anoxic sediment? 2. How fast can the microbial community adapt to changes in the composition and quality of organic supplies? I attempt to solve these questions by the use of anaerobic sediment incubations.

Partitioning of microbial respiration processes in bioturbated and rooted intertidal sediments. The terminal microbial respiration in sediments may occur with oxygen, manganese, iron, nitrate and sulfate as electron acceptors. Much work has been done to quantify each of these respiration processes and to determine the partitioning between them in oceanic sediments. Much less is known about these processes in highly disturbed intertidal sediments, such as Spartina marshes and mangrove forests. My objectives for this work is to determine the role of burrowing animals (various crab species) and roots (eelgrass, cordgrass and mangrove trees) for the rates and partitioning of processes, while attempting to answer the following questions: 1. How do animals and roots control the vertical distribution of respiration with the various electron acceptors? 2. What is the temporal variability in the distribution of respiration processes and how is that related to animal and root activity?

In the project, REELGRASS, our aim is to explain why eelgrass is not recovering and recolonizing areas where is was present in the past. The conditions with respect to water quality should not any more hinder such recolonization. My contribution to the project is to determine the if benthic animals hampers the recolonization by grazing on roots and seeds, or if these animals actually facilitate recruitning of eelgrass by oxidizing the sediment.

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