THE PHOSPHORUS PARADOX: GLOBAL CHANGE AND FRESHWATERS

Steve Carpenter, U.W. Madison Limnology, discussed how global change is drive by agriculture since it is the largest use of land, source of climate changing gases, consumer use of freshwater and polluter of freshwater.  Almost 40% of the land surface area has been converted for agriculture.  Agriculture is the key for solving problems posed by global environmental change.  Phosphorus links agriculture to water quality around the world.  The main concern about phosphorus pollution is algae blooms.  Around the world, there are several ways phosphorus gets into the lakes such as human sewage and animal manure.  In Wisconsin and other wealthier parts of the world it is caused by runoff driven by rain, fertilizer containing phosphorus and manure.  Freshwater is very sensitive to phosphorus.  Phosphorus is over applied in many regions especially the corn belt of the United States and China.  A planetary boundary is human developed boundary for how much of a pollutant an area is willing to tolerate.  There are global standards for how much phosphorus people are willing to accept in water.  We are out of the range of planetary boundaries in phosphorus.  Phosphorus is an essential nutrient and agriculture is the way we get phosphorus into people but we are using too much.  Phosphorus is highly localized in its availability on earth.  About 80-90% of the world’s phosphorus is in Morocco and Western Sahara.  Phosphorus demand is projected to rise. Human population is expected to increase to 9 billion so we will need to double our food production.  A global phosphorus shortage in 2007-2008 affected food supplies and started an era of steeply rising prices.  Since that time, prices have somewhat flattened out.  In the United States, watersheds have excessive phosphorus levels.  Phosphorus inputs are mineral phosphorus taken from mines, crop, livestock and industrial products.  The outputs are export accumulations in soil, bio-fuel, farm losses, processing losses and consumption in diets.  The exports exceed the imports mostly in exported food, 8% is consumed by people and more than half is added to the environment and is wasted.  For the past 80 years, Wisconsin has been the leader in managing the phosphorus cycle.  In the 1930’s, Charles Van Hise realized that phosphorus was essential for crops and that we were losing a lot.  He was an advocate on phosphorus conservation.   Phosphorus severity is an opportunity for phosphorus conservation that improves water quality.  Phosphorus conservation can occur by adjusting application of fertilizer to crop needs, recycle human waste more efficiently, recycle manure more efficiently, decrease food waste, and reallocate crops to human food instead of bio-fuel, livestock feed and other non-food applications.  In summary, phosphorus is essential for life; too much phosphorus causes toxic blooms, fish kills, loss of recreation value and high costs of water treatment; we know how to manage phosphorus better; we need to align phosphorus economics with needs for food production, human health and the environment; and growing demand for phosphorus is an opportunity.