The study of marine biogeochemical cycles has historically concentrated on natural components, but the growing understanding of the complex relationships among these cycles, especially those impacted by ecosystem eutrophication, soil and water acidification, and climate change, highlights the enormous influence of human activity. Estuaries and lagoons, which are Transitional Water Systems (TWS) that link freshwater and marine habitats, are especially susceptible to these impacts. Natural processes are disturbed by unchecked coastal development, which leads to ecological degradation, habitat destruction, and erosion. Additionally, this development modifies river flows, impacting aquatic species migration and sediment transfer not only from the river to the coastal area but also vice versa. Moreover, soil erosion and silt accumulation are caused by changes in land use brought about by mining, agriculture, and urbanisation, which affect areas downstream and along the shore. The introduction of hazardous chemicals, heavy metals, plastics and excess nutrients by pollution from urban, agricultural, and industrial sources further deteriorates water quality and endangers aquatic life and biogeochemical systems.

To maintain ecosystem balance, ensure nutrient availability, stabilize the climate and protect marine biodiversity, scientists have been studying biogeochemical cycles and the impacts of human activity on these critical processes for over a century. However, stresses on marine ecosystems have increased due to urbanisation, industrialisation, and changes in human lifestyle/existence. The natural dynamics of marine habitats have been further disturbed by coastal development, as well as by modifications to river sediment loads and natural water flow. Acidification, algal blooms and hypoxic zones have also been brought about by the increased use of fossil fuels and agricultural runoff which have added too much carbon, nitrogen and phosphorus to the oceans. These modifications affect the systems that regulate the temperature, disturb marine food webs and endanger biodiversity. To deepen our understanding of these intricate relationships and effectively guide conservation efforts, further research is crucial, particularly given the shifting impacts of human activities. Protecting marine ecosystems requires achieving a balance between environmental conservation and sustainable development. By giving equal importance to conservation and development, we can preserve these essential cycles and secure the health and sustainability of marine habitats for future generations.

Research on this important topic, especially when consolidated into a single journal issue, significantly enhances readability and facilitates the application of findings to societal challenges and considerations. This special issue, published in Frontiers in Marine Sciences, will showcase a diverse collection of papers that engage readers by presenting various perspectives and insights related to the subject. Additionally, it provides high visibility for the authors, allowing their work to reach a broader audience. This strategic approach not only highlights the complexity of the topic but also encourages exploration across different disciplines, reflecting the multifaceted and interconnected nature of the issues at hand. By bringing together a range of studies, this special issue aims to contribute meaningfully to the ongoing dialogue in marine sciences and related fields.

Original and innovative studies on biogeochemical evidence and anthropogenic impacts in vulnerable coastal zones are welcome in, but not limited to the following areas:
1. Changes caused by humans and their effects on marine biogeochemical cycles
2. Effects of coastal development on marine life.
3. Impact of anthropogenic pollution on marine food webs and bioaccumulation
4. Hypoxia, eutrophication and the dynamics of coastal ecosystems
5. Sediment dynamics and human impact on river-ocean connectivity
6. Strategies and measures for tracking biogeochemical health
7. Policies, conservation, and sustainable development in coastal zones
8. Combined methods and modelling for ecosystem management

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Anthropogenic Footprints on Marine Ecosystems: Insights into Biogeochemical Shifts