In the 20th century mainly the two nutrients nitrogen and phosphorus were prominently major constituents in agricultural fertilizer and enabled agriculture to increase its productivity and the world’s population to grow more than six-fold. We obtain nitrogen from the air, but we must mine phosphorus. Readily, available global supplies of phosphorus may start running out by the end of this century. At the midst of the 21st century around the global population will grow to around ten billion people (“the global ten billion people issue”). So a shortage of phosphorus looms with as consequences food shortages and famine. We suggest a new approach to extract P from the oceans for reuse on our terrestrial areas by accumulation them in “seaweed plantations” in the shallow seas and continental shelf of our 5-7 major large river systems at our globe and harvesting these macro algae before they disappear as inorganic phosphate for hundred thousand of years “out of the loop” in the infinite oceanic abyssal plain at 6 km depth. In this study we used the North Sea/Rhine system as an example which can be applied especially in S.E. Asia were it is expected that half of the world population will live in the nearby future in extreme mega-cities.
Vincent van Ginneken, Evert de Vries, Tim Wijgerde