In addition, in 2003, Ruttenberg studied the major global biospheric fluxes of P, which found that the annual rate of uptake by marine biota is a magnitude higher than in the terrestrial plants due to a much slower cycling in the latter. Flux by erosion is estimated between 19 and 30 Mt P annually. According to Smil (2000; 2007) erosion and runoff of P have increased by at least a factor 2 since the pre-industrial era. The one-directional flow of P towards the ocean can be inferred from the return flow of only 0.3 Mt P which returns to land with fisheries.