Letter: Dump waste at sea

From Dave Schoeman and A. J. Smit, School of Biological and Conservation Sciences, University of KwaZulu-Natal

P. G. Whittaker points out that by discarding organic waste in either landfills or the marine environment we might be missing opportunities to increase the rate of plant growth under scenarios of higher atmospheric CO₂ levels (20 May, p 27). While this sentiment is commendable, the proposed solution of concentrating this potential productivity boon on land is misplaced.

First, the author correctly asserts that much of humanity’s organic waste is pumped into the sea and that this is largely “not available to plant growth”. However, the latter part of this statement is misleading because plants are not the only photosynthetic organisms capable of transforming “waste” into usable organic matter. In fact, photosynthetic marine protists, known collectively as algae and comprising not only seaweeds but also phytoplankton, are extremely efficient at doing just this. In the process, these organisms contribute substantially to the global carbon cycle, possibly more so than terrestrial plants. In this sense, nutrients disposed of at sea are not wasted, although they may well be misdirected.

Second, the deserts and forests identified as possible receptacles for excess nutrients are natural ecosystems in their own right. Deliberately enhancing organic growth in either system is therefore not ecologically desirable, unless all of the consequences are fully understood and accepted.

Although we clearly need more creative methods of waste disposal, ecosystems are being and always will be affected by excess nutrients regardless of where they are dumped. Without careful thought, these “discarded” nutrients could ultimately pose as much of an environmental problem as greenhouse gases.

Durban, South Africa