This research was published in the INSPIRED: A Publication of the New Hampshire Agricultural Experiment Station (Fall 2024)
Researchers: B. L. Brown, G. E. Moore, H. Mogensen, T. Sims-Harper, J. Gibson, B. Y. Lee, C. Wardinski and G. Jarrett
Microplastics, tiny plastic particles less than 5mm in size, are pervasive pollutants that pose significant risks to aquatic ecosystems and human health. However, there is no quantified baseline of microplastics presence in three key New England estuaries: Great Bay Estuary, Hampton-Seabrook Estuary, and Great Marsh Estuary. Developing a quantified benchmark is an important first step to any future monitoring efforts to inform emerging policies to manage microplastics levels in New England waterways. This benchmark is critical to determining whether mitigation strategies can be effective.
Background and Key Concepts
Microplastics are plastic fragments smaller than 5mm that persist in the environment, affecting both freshwater and saltwater habitats. These tiny particles originate from the degradation of larger plastic items and can come from various sources, including industrial processes, wastewater, and urban runoff.
Estuaries, which are transitional areas between rivers and oceans, play a crucial role in filtering pollutants and providing habitat for a diverse array of species. They support vital economic activities, such as fishing and aquaculture, making the study of microplastic pollution in these areas essential for environmental and public health.
Previous studies have shown that microplastics can accumulate in marine sediments and salt marsh peat, where they pose risks to aquatic organisms and potentially humans through the food chain. These particles can block digestive tracts, alter feeding and reproductive behaviors, and transport harmful chemicals and microorganisms. However, there are limited data on the presence and impact of microplastics in New England's estuarine systems. This study aimed to fill that gap by providing a comprehensive baseline assessment of microplastic levels in three estuaries: Great Bay Estuary (GBE), Hampton-Seabrook Estuary (HSE), and Great Marsh Estuary (GME). Understanding the distribution and types of microplastics in these regions is crucial for developing effective mitigation strategies and protecting both ecosystems and human health.
Methodology
Water samples were collected at each site (Fig. 1) using a combination of plankton nets, manta trawls, and discrete grab samples. In GBE, samples from the water column were obtained through horizontal tows using a 64 μm mesh net, while in HSE and GME surface water samples were collected with a 330 μm mesh manta trawl. Additional bulk water samples were taken in HSE using 1L glass jars. Sediment cores from high and low marsh areas in HSE were collected using a piston coring device, which provided samples representing approximately 35–40 years of sediment accretion.
Key Findings
- Microplastics (MP) are present in over 98% of samples from New England estuaries: Great Bay, Hampton-Seabrook, and Great Marsh.
- Hampton-Seabrook Estuary exhibited significantly higher MP concentrations in surface waters and marsh sediment.
- Seasonal variations show MP levels peaking in summer. Various types were identified, along with rubber and other biogenic materials like chitin, cellulose, aragonite, and calcite.
About the Co-authors
Bonnie Brown, Professor of Biological Sciences
Contact information: Bonnie.Brown@unh.edu, FindScholars profile
Gregg Moore, Associate Professor of Biological Sciences
Contact information: Gregg.Moore@unh.edu, FindScholars profile
Fig. 1. Map of New England (top left) and individual maps of estuarine sites where samples were analyzed for microplastics between 2018–2023. (A) Great Bay Estuary, New Hampshire; (B) Hampton-Seabrook Estuary, New Hampshire; (C) Great Marsh Estuary, Massachusetts.
Samples were analyzed for microplastic content using both confocal microscopy and laser direct infrared spectrometry (LDIR) (Fig. 2). For water samples, the preserved material was filtered, digested to remove organic matter, and stained with Nile Red for fluorescence analysis. Representative samples were then subjected to LDIR to identify and quantify the types of microplastics present.
Sediment samples underwent a similar process, including sieving, density separation, and visual assessment under a microscope. Field blanks and replicates were integrated into the sampling plan to ensure accuracy and to minimize contamination. Statistical analyses, including the Shapiro-Wilk normality test and Kruskal-Wallis test, were performed to assess the variability and significance of microplastic concentrations across different sites and years.
Discussion of Findings
Microplastics were found in over 98% of the samples collected from the three estuaries, with concentrations varying significantly by region, site, and season. The HSE exhibited the highest levels of microplastic pollution (Fig. 3), likely due to its rapid water flushing compared to the other estuaries. Seasonal trends were noted, with microplastic concentrations peaking during the summer months. There was also a wide range of microplastics, including various polymers and biogenic materials such as chitin, rubber, and coal. This diversity highlights the complex nature of microplastic pollution and its potential sources.
Fig. 2. Confocal (left) and Laser Direct Infrared (LDIR) comparison images showing microplastics.
Estuarine marshes play a critical role in collecting microplastics. These marshes act as natural filters, trapping microplastics within their dense vegetation and sediment layers. This trapping mechanism helps reduce the movement of microplastics further into the aquatic system. In the HSE, higher microplastic concentrations were found in marsh sediments compared to water samples, emphasizing the marshes' role in capturing these particles. Understanding how estuarine marshes interact with microplastics can inform the development of conservation strategies aimed at enhancing their natural filtering capacities.
Fig. 3. Microplastics found at eight locations in coastal marsh sediments of Hampton-Seabrook Estuary, each subsampled at high and low marsh elevations.
Strategic Recommendations and Conclusion
To address microplastic pollution effectively, targeted cleanup and prevention strategies should focus on high-risk areas, such as the HSE, which exhibited the highest concentration of microplastics. Using the baseline data from this study, policymakers and industry leaders in waste management, water treatment, aquaculture, and fishing can implement practices to minimize contamination. Additionally, enhancing the natural filtering capacities of estuarine marshes by protecting and restoring these habitats could significantly reduce the movement of microplastics further into the aquatic system.
Future research should prioritize understanding the long-term impacts of microplastics on estuarine ecosystems and human health. Developing improved hydrodynamic models to predict microplastic distribution and identifying sources will be crucial. Engaging in continuous monitoring and integrating findings into policy frameworks will help mitigate the risks posed by these pollutants. Protecting estuarine environments through informed strategies ensures the sustainability and health of these critical ecosystems and the industries they support.
This material is based on work supported by the NH Agricultural Experiment Station through joint funding from the USDA National Institute of Food and Agriculture (under Hatch award number 1023564) and the state of New Hampshire.
