Salt marshes in the silica budget of the North Sea

• Export of recycled salt marsh DSi to the North Sea is estimated to 3400 t Si a−1.
• DSi export from salt marshes amounts to 0.8% of river export to the North Sea.
• Salt marsh DSi export in the English Channel amounts to 16% of river export in summer.

Local scale studies reported the silica recycling of salt marshes to substantially attenuate the dissolved silica (DSi) limitation in coastal waters during summer. To assess the importance of salt marshes in the silica budget of the North Sea, we extrapolate reported DSi exports by local scale studies to salt marsh areas adjacent to the North Sea. The resulting annual average contribution of salt marshes to the DSi budget of the North Sea is estimated to 0.8% of the annual river DSi export. During summer, this contribution may reach 2.4%. Thus, salt marshes likely impact the annual dissolved silica budget of the North Sea only weakly. However, for regions with favorable geographic conditions of low river DSi exports and large marsh areas, salt marsh DSi exports may substantially contribute to coastal DSi budgets. In the English Channel, salt marsh DSi exports are estimated to 16% of river DSi export in summer. However, the low data density calls for additional field research to improve extrapolations and the evaluation of the contribution of salt marsh DSi export to the coastal DSi budgets.