Soy and pollution: a hodgepodge of local circumstances

"Gray water” is the amount of water that is required to wash off the chemicals produced by agriculture in an area. These chemicals include toxic pesticides  and high levels of fertilizers which can be fatal for the local wildlife. 

Many studies have been carried out in order to assess the impact of rising gray water footprint, so I began to wonder:

what role does soybean agriculture play in the gray water cycle?   

Soybean agriculture produces a smaller gray-water footprint than cereals, wheat and corn so it could be regarded as a viable substitute to reduce local freshwater pollution. 

However, in order to understand the impact that an increase in soybean production would have on habitats at a global scale, further debate should be undertaken establish to how different ecosystems react to pollutants. 

In this blog post I explore whether and why fertilizers have a negative effect on the surrounding environment but will also discuss the spatial variability of such implications. This discussion is placed within the framework suggested by Will Steffen, which considers biogeochemical cycles as critical planetary boundaries:

Will believes that nitrogen's levels are so high 

they are posing a threat to human society

Nitrogen 

The nitrogen cycle is a biogeochemical cycle which converts nitrogen through biological and physical processes such as fixation and ammonification. This cycle is of focal importance to ecosystems as it drives the rates of production and decomposition of plants.

In freshwater ecosystems, the levels of nitrogen are one of the controls of production and if increasing levels of nitrogen are introduced in the form of fertilizers, the rate of nitrification changes. Nitrification is the process that creates nitrate through the oxidation of ammonia and nitrite. 

Or more simply... 

When fertilizers such as ammonium nitrate enter groundwater, they lead to an increase in nutrients and production and an increase in algae production in an ecosystem leads to the depletion of oxygen and light leading to degradation. 

Phosphorus

Fertilizers also contain phosphorus, which is considered to be the main driver of eutrophication. Unlike nitrogen, phosphorus is almost only sourced to be used in agriculture so its effects on ecosystems can be directly correlated to such activities. 

Just the same as nitrogen, when phosphorus is introduced to an habitat at a higher rate than normal nutrients availability increases and algae develop. Thus, biodiversity inevitably decline because species have to compete for light and oxygen leading to concerns over the planetary boundary of phosphorus.  

Phosphorus is necessary in the production of soybeans and 7% of its total global consumption is due to this crop alone. Despite mentioning that soybean has a lower gray-water footprint per ton of product than other crops, it doesn't mean that it doesn’t have negative implications on a local or even global scale. It is also fundamental to consider how different soils in different countries will react to the introduction of phosphorus based fertilizers.

Spatial Heterogeneity

Riskin compares the environmental consequences of such fertilizers from soybean agriculture across its 3 main exporters (US, Brazil and Argentina), highlighting the spatial heterogeneity of their impacts.

In Argentina the balance of phosphorus in soils is surprisingly neutral. The addition of fertilizers from soybean agriculture to a previously poor soil solved a deficit in phosphorus and is yet to cause any evidence of eutrophication in the nearby freshwater ecosystems. Hence, the local and regional implications of the agricultural gray-water footprint are very low due the inherent nature of the underlying soil. However, a future increase in fertilizers consumption could lead to a tip in the current equilibrium and to the on-set of regional eutrophication.     

 The Mississippi Basin in Iowa also presents overall neutral levels of phosphorus. However, this is not enough to stop individual ponds from being threatened by the surplus in phosphorus produced by soybean agriculture in the surrounding. 

As soon as levels approach zero, a concern for pollution management should rise at high decision-making levels because preventing phosphorus quantities from rising is easier than treating already affected sites.

In some cases, it is simply impossible to minimize the input of fertilizers without compromising the entire crop production and potentially the local or national economy, but this does not necessarily mean that the local ecosystems will suffer. 

For instance, brazilian deep soils have the capacity to bind high levels of phosphorus reducing the risk of eutrophication that would otherwise be expected.

What solution should I suggest?

There is no single or perfect solution to the implication of increasing nutrients and eutrophication in freshwater ecosystems but an accurate analysis of local responses the agricultural land-use suggests that some areas are more beneficial to sustainable production than others. 

Regardless of the quantitative global gray-water footprint of soybeans agriculture, it is fundamental to assess the local hodgepodge of responses accepting the high diversity of implications.

In conclusion, Riskin suggests that agriculture expansion should be concentrated in the tropics where the soils will be able to best respond to the surplus of nutrients. However this raises a very alarming question:

 Should we sacrifice our tropical rainforest for agriculture expansion because that’s our most sustainable choice?   

Let me know what you think in the comment section below or tweet me!