Toilets: Then and Now, Part 10; Excessive Human Wastes in Coastal Waters, Page 3 of 4

(an excess of nutrients flowing from the land to the sea has created serious environmental problems)

What about Cattle, Corn, and Cars?

  • The assault on the waters of the developed world that began with urban sewage systems in the mid-1800s has only escalated since that time.
  • Because nitrogen and phosphorus are essential for human nutrition, the rapidly growing world population consumes and excretes ever larger amounts of both elements.
  • This factor alone almost doubled the release of nutrients from human waste between 1950 and 1985.
  • And not only are there more people on the earth but also the typical diet is becoming ever richer in protein.
  • All this protein contains abundant nitrogen, which just increases the burden on the environment when it is metabolized and finally excreted.
  • As the human population has skyrocketed, so has the number of animals raised for food.
  • The count of livestock—animals that also consume and excrete large amounts of nitrogen and phosphorus—has grown by eighteen percent during the past twenty years.
  • To produce the huge quantities of crops needed to feed both humans and livestock, farmers have been applying increasing amounts of fertilizer to their fields since the 1950s.
  • The main ingredients in these fertilizers are nitrogen and phosphorus. Rain washes these nutrients off the land and into rivers and streams, which then carry them to lakes and oceans.
  • Between 1960 and 1980 the application of nitrogen fertilizer increased more than fivefold, and in the decade that followed, more synthetic fertilizer was spread on land than had been applied throughout the entire previous history of agriculture.
  • Farmers have also been raising increasing quantities of legumes (such as soybeans), which live in partnership with microorganisms that convert nitrogen to nutritive forms.
  • Vast quantities of enriching nitrogen compounds; perhaps equal to half of what is produced as fertilizer, have become available from this source.
  • That there have been widespread changes in the oceans is not surprising

  • The dead zone that forms in the Gulf of Mexico every summer probably results from excess fertilizer washed from farms and carried down the Mississippi.
  • Unfortunately, such nutrient injections may be even more dangerous to coastal waters than to lakes.
  • Research early on showed that phosphorus rather than nitrogen induces aquatic plants to bloom in most freshwater environments.
  • This news was in a sense good for lakes, because phosphorus is more easily managed than nitrogen.
  • Phosphorus is chemically sticky and binds easily to other substances.
  • Thus, it tends to adhere to soil and is less likely than nitrogen to leach out of fertilized fields.
  • Phosphorus can be easily removed from sewage by taking advantage of the same stickiness: during treatment, chemicals are added that bind up the element and then settle out along with other sludge.
  • Largely because of improved phosphorus removal from sewage and a widespread ban on the use of phosphate in products; such as, laundry detergent, the eutrophication of many lakes and rivers has been stopped or greatly reduced.
  • There is increasing evidence that the phytoplankton of most temperate estuaries, bays and other coastal ocean waters respond not so much to phosphorus as to nitrogen.
  • Marine scientists still do not fully understand the reasons for this difference, but the implications are quite profound.
  • Nitrogen washes easily from fertilized fields into streams and rivers; many sewage-treatment plants are not yet configured to remove nitrogen from wastewater; and there is an additional, copious supply of nitrogen to the oceans and the atmosphere.
  • Lightning has always converted a tiny amount of inert nitrogen gas, which makes up seventy-eight percent of air, into soluble compounds that plants can take up in their roots and metabolize.
  • The combustion of fossil fuels has unleashed a torrent of such nitrogen compounds into the atmosphere.
  • When oil, gas and coal burn at high temperatures in engines and electricpower generators, they produce nitrogen oxides.
  • Rain and wind carry these soluble compounds to the earth, further enriching coastal waters already containing large amounts of sewage and agricultural runoff.
  • In all, fossil-fuel combustion accounts for about fifteen percent of the biologically available nitrogen that human activities add to the world every year.
—Information from "Enriching the Sea to Death" by Scott W. Nixon;
as seen in Scientific American, 1998; pages 43-58.

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