Megacities and large urban agglomerations in the coastal zone: interactions between atmosphere, land, and marine ecosystems

Abstract

Megacities are not only important drivers for socio-economic development but also sources of environmental challenges. Many megacities and large urban agglomerations are located in the coastal zone where land, atmosphere, and ocean meet, posing multiple environmental challenges which we consider here. The atmospheric flow around megacities is complicated by urban heat island effects and topographic flows and sea breezes and influences air pollution and human health. The outflow of polluted air over the ocean perturbs biogeochemical processes. Contaminant inputs can damage downstream coastal zone ecosystem function and resources including fisheries, induce harmful algal blooms and feedback to the atmosphere via marine emissions. The scale of influence of megacities in the coastal zone is hundreds to thousands of kilometers in the atmosphere and tens to hundreds of kilometers in the ocean. We list research needs to further our understanding of coastal megacities with the ultimate aim to improve their environmental management.

Fig. 1

Schematic depiction of the main processes and feedbacks in MCCZ. Details see text. OC organic carbon, BC black carbon, VOC volatile organic compounds, org-X organic halogens compounds

Fig. 2

Schematic of the multiphase reactions leading to the production of ClNO₂ at night. During daytime ClNO₂ can lead to O₃ formation and contribute to the reduction of the lifetime of the greenhouse gas CH₄. For details see boxed text and Osthoff et al. (2008). Figure modified from von Glasow (2008)

Fig. 3

An exceptional plankton bloom with cell densities high enough (≤10⁶ L⁻¹) to cause discolored water in the marina of Syracuse Harbor, Sicily on the Mediterranean coast. The bloom comprised the toxin-producing dinoflagellates Alexandrium minutum and Lingiulodinium polyedrum (Photo courtesy Mariagrazia Giocobbe). Harmful blooms of this nature will become more common as we continue to modify the coast to our own purpose