Comparison of metals in eelgrass (Zostera marina L.) and the environment across the North Pacific Ocean: Environmental processes drive source delivery

Seagrass beds play a critical role in biodiversity maintenance, serving as nursery habitats for fisheries, and aiding in carbon and sediment sequestration in the ecosystem. These habitats receive dissolved and particulate material inputs, like nutrients and heavy metals, affecting both plant health and the ecosystem. Eelgrass (Zostera marina L.), sediments, and water were randomly collected at twenty sites along the temperate North Pacific coasts of Asia and North America to assess heavy metals concentrations (Cr, Cu, Zn, Cd, and Pb). This aimed to understand heavy metal distribution and accumulation patterns in eelgrass tissues, revealing crucial factors influencing metal accumulation. The sampling included various areas, from pristine marine reserves to human-influenced zones, covering industrial, agricultural, and aquaculture regions, enabling a thorough analysis. This study's uniqueness lies in comparing heavy metal distributions in eelgrass tissues with sediments, uncovering unique accumulation patterns. Aboveground eelgrass tissues mainly accumulated Cd, Zn, and Cu, while belowground tissues stored Cr and Pb. Aboveground eelgrass tissues proved reliable in indicating Cd and Pb concentrations in sediments. However, the correlation between Cu, Zn, and Cr in eelgrass tissues and environmental concentrations seemed less direct, requiring further investigation into factors affecting metal accumulation in seagrass. Human activities are probable major contributors to heavy metal presence in Asian marine environments, whereas oceanographic processes serve as primary metal sources in North American Pacific estuaries. Critical discoveries emphasize the necessity for ongoing research on phytotoxic thresholds and in-depth studies on the complex connections between seagrass physiology and environmental metal concentrations. Understanding these dynamics is crucial for evaluating the broader impact of heavy metal pollution on coastal ecosystems and developing effective conservation measures.

Impact/Purpose

Seagrass beds provide critical ecosystems services and are a sentinel indicator species for estuarine health.  We measured the heavy metals concentration in eelgrass (Zostera marina), sediment and water from twenty sampling sites along the North Pacific Coasts of Asia and North America.  This international collaboration is the first work that we are aware of comparing metals concentrations in eelgrass from China, Korea and the USA.  Metal concentrations were temporally variable and organ specific.  Our work suggests that eelgrass may be a useful indicator of Cd concentrations in the sediment.  Further, we highlight the importance of both anthropogenic and natural (e.g. upwelling and parent rock weathering) sources of metals to these systems.  This baseline data will be important to future ecological risk assessments of heavy metals in seagrass beds.

Citation

Xu, S., J. Kaldy, X. Zhang, S. Yue, Z. Suonan, AND Y. Zhou. Comparison of metals in eelgrass (Zostera marina L.) and the environment across the North Pacific Ocean: Environmental processes drive source delivery. Elsevier Science Ltd, New York, NY, 343:123096, (2024). [DOI: 10.1016/j.envpol.2023.123096]

DOI: Comparison of metals in eelgrass (Zostera marina L.) and the environment across the North Pacific Ocean: Environmental processes drive source delivery