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Photochemistry at the Ocean's Surface: Effects and Interactions of Dissolved Organic Matter with Microplastics

Periodic Reporting for period 1 - POSEIDOMM (Photochemistry at the Ocean's Surface: Effects and Interactions of Dissolved Organic Matter with Microplastics)

Reporting period: 2016-05-01 to 2018-04-30

The Mediterranean Sea is the 6th most polluted sea with plastics, with a comparable concentration to the subtropical oceanic gyres. Microplastics may have a strong impact on marine life and biodiversity, with increased impact on higher trophic levels and eventually on humans. The study of the impact of microplastics on marine systems deals with a plethora of associated effects at local and global scale. There are numerous potential, yet unstudied impacts on fundamental marine ecosystem functions and key processes on which we all depend: do marine microplastics influence climate change?
The objective of POSEIDOMM was to study the interaction of photochemical degradation, microplastic pollutants and natural organic matter cycling in the top oceanic layer. The very top layer of the ocean, the sea-surface microlayer, is a specific interface connecting the atmospheric and the marine systems. It accumulates natural and anthropogenic organic material, with concentrations up to 500 times higher than in the water below. We hypothesize that micro plastics accumulated in this interface layer may modify microbial carbon dynamics, modifying gas exchange, and increasing the production of climate altering gases from the ocean.
Marine litter, and in general, plastic, stems mostly from land-based sources (GESAMP 1991), being in large part (> 80%) of anthropogenic origin. To tackle the problem at its source, POSEIDOMM also teamed up with the international citizen-science initiative FreshWater Watch of the EarthWatch Institute (Oxford, UK). Citizen-scientists and students seasonally monitor the state of the Arno River tributaries (Italy) for ecological parameters and riverbanks litter through a standardized approach allowing for data comparison to similar citizen-sciences project around the globe. By encouraging bottom-up data acquisition and community science, we believe adding a piece of the puzzle towards behavioral change to address the emerging crisis of marine/freshwater litter and preventing parts of the plastic pollution to reach the Tyrrhenian Sea.
"In the first phase (Micro-POSEIDOMM), the organic matter produced by non-axenic pure strains of marine microalgae was employed for experiments under pseudo solar conditions, exploring the photochemical and microbial turnover of organic matter and its interaction with microplastics. The results suggest that the presence of microplastics associated with photo degradation of organic matter may modify the microbial carbon cycling in marine environments, changing the availability of organic substrates for marine biogeochemical cycles.
These dynamics were further explored in larger field ""controlled"" conditions during the second phase (Meso-POSEIDOMM). Between May and June 2017 a field mesocosm experiment was performed at the Cretacosmos facility at the Hellenic Center for Marine Research (HCMR) in Crete, Greece, the only mesocosm facility in a Mediterranean oligotrophic environment (AquaCosm network).Six mesocosms were filled each with 3 cubic meter of coastal seawater from the Cretan Sea, where three replicates served as control and three other replicates were amended with standard microplastics in high concentration. The six mesocosms were maintained at ambient conditions and natural irradiation. In all mesocosms, the bloom development as well as nutrients depletion and remineralization were followed along with other parameters (chlorophyll-a, dissolved organic carbon, CO2 and total alkalinity, chromophoric dissolved organic matter, marine gels, autotrophic and heterotrophic counts, trace-metals binding capacity) both in the underlying water and in the sea-surface microlayer. The experiment led by the POSEIDOMM project involved 4 different research institutions in 3 countries and several participants (University of Siena, University of Florence, HCMR Crete, HCMR Athens and GEOMAR Kiel). Data and sample analysis have been completed, and results will be made available soon in publications/conferences.

A parallel citizen-science research project started in collaboration with high-school students and local municipalities in the Arno River catchment, Italy, and continues beyond the duration of POSEIDOMM. The project “Citizen Observatories project for local aquatic ecosystems monitoring” utilizes the experiences of the international initiative FreshWater Watch (https://freshwaterwatch.thewaterhub.org) of the Earthwatch Institute (Oxford, UK). This community based approach aims at developing public stewardship of aquatic ecosystems through active citizens monitoring local water bodies for water quality and anthropogenic litter presence and composition. Within POSEIDOMM, more than 40 participants (high-school students, citizens, teachers) have been trained in water quality monitoring. Volunteers have adopted a specific site and sampling strategy (that includes a sampling kit) and did regular monitoring and data acquisition for more than 2 years. Regular dissemination/outreach events have taken place, comprising seminars both in schools and within the local community, followed by public training in sampling and monitoring. The activities have raised interest in the local media with coverage in both the newspapers and regional/national and European television. The first results of the outreach actions have been presented at various national and international conferences. Results from the citizen observatory are publicly available online."
Plastic pollution may have unseen and unsuspected effects, directly on the marine ecosystem dynamics. Much of the low-density plastic debris derived from human activity remain on the sea-surface. Thus, they are subject to photochemical degradation, to microbial colonization and degradation, and support biofilm formation.
These linked processes at the ocean's surface may influence ocean-atmosphere dynamics by altering the flux of gases and particles at the air-sea interface, with climate implications.
These ideas have been tested in laboratory (Micro-POSEIDOMM) and field controlled conditions (Meso-POSEIDOMM, mesocosm experiment), and the results so far suggest that plastic accumulation, especially in surface waters, may interfere with the production and consumption of organic material, with implications for the air-sea exchange of gases and the export of organics across the water column.
The problem of plastic pollution needs to be tackled on land. The parallel citizen-science project carried out within POSEIDOMM aimed at promoting public stewardship of local aquatic resources, quantifying the type and quantity of plastic entering our rivers with the aim of reducing the amount of plastic reaching our seas. Efforts to solve the plastic problem require a partnered approach between research institutions, municipalities, educational institutions and citizens that can be achieved through citizen science. Since the starting of the project, POSEIDOMM volunteers have helped removing more than 1500 plastic macro pieces from local waterways preventing them entering the Mediterranean Sea, and performed 152 samplings over 25 sampling sites in the Arno River catchment (Tuscany, Italy). Such project has helped creating an informed community willing and able to participate to environmental management discussion and decisions, with many positive socio-economic impacts at the local level towards higher awareness, participation and public stewardship of aquatic resources.
Hypotheses and research focus of POSEIDOMM