Anthropogenic impacts on the geochemical cycling of nutrients and trace metals within intertidal ecosystems

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The relationship between ecosystem function and community structure is complex and dynamic. My long term research program is directed at understanding  the mechanisms underlying this complex interplay and how this interplay between ecosystem structure and function changes as we modify our environment. Threats now facing our aquatic ecosystems include a changing climate and pollution, the latter of which the increasing presence of plastics pollution, macro and micro has become arguably one of the greatest concerns of this century. Understanding how these anthropogenic contaminants alter ecosystem structure and function and the role they play in the transfer of toxic compounds such as trace metals, through food webs is urgently needed such that preventative and remediative actions to protect these ecosystems can be put in place. Traditionally, sediments have been characterized as being composed of different geochemical attributes such as organic matter and silt that act as sorption sites for metals that have been released into aquatic environments.  Recent research has indicated that plastics also serve as trace metal sorption sites and as such provide an as yet quantified source and hence entry of toxic metals to benthic food webs.  It is also now recognized that plastics that enter into aquatic ecosystems age through photodegradation. Such aging alters the biophysical properties of the plastics from their virgin state. Hence an important aspect of understanding the mechanisms of how plastics are affecting trace metal cycles within intertidal sediments is to incorporate the dynamic nature of the plastic itself, i.e., environmentally aged plastics versus unaged. My objectives for the next 5 year funding cycle are to; 1) Characterize and determine the distribution of  microplastics within several intertidal regions with different sediment geochemical attributes and  compare the sorption of trace metals (cadmium, lead, zinc, copper) by microplastics of different polymers types and ages, among the intertidal regions, 2) through the application of the radiotracer 109Cd, to determine if the accumulation of cadmium by the bivalves Nuttallia obscurata and Protothacia staminea, from microplastics is dependent on polymer type and shape and 3)determine the role of feeding ecology, i.e., rates of ingestion, retention and egestion in influencing the recovery of microplastics from the bivalves N. obscurata and P. stamenia.  Outcomes of my research programme will add to our knowledge base as to how plastics are impacting our aquatic ecosystems, specifically with respect to the movement of trace metals through food webs. This is turn will improve our ability to predict the risks to both ecosystems and humans, that plastics may present as acting as vectors for the entry of toxic metals into intertidal food webs.