Climate Change And Coastal Agriculture
When the threat comes from the seas
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I’m not a great fan of salty food myself, but I think it is safe to say that salt should be present only in the last stage of the life cycle of a crop, which is on the dinner table, and in any case definitely not on the field where it is grown. However, despite the claims of climate change deniers, there is a vast scientific evidence that one of the major threats posed by climate change, is the sea level rise, which is already affecting the livelihood of coastal communities of several areas of the World along with their farming systems.
in the Northeast, the average rate of sea level rise is 3 mm per year, and faster in the mid-Atlantic where land is also sinking. […] Many acres of farmland are lost every year because they are becoming too wet and salty to grow crops
Not only heat waves and droughts impact agriculture production as a direct detrimental effect of climate change, but also “salt waves” are posing a considerable threat to rural coastal communities.
Saltwater intrusion
The sea level rise induced by the melting of the glaciers, impacts crop production in coastal agriculture systems, due to a process called saltwater intrusion.
Saltwater intrusion can occur under two circumstances:
- Every time there is a large storm or a high tide, which are both naturally occuring phenoma but they have been greatly exacerbated by climate change in the recent decades, saltwater spreads through freshwater because the sea water overtops areas which are low in elevation
- Every time there is an infiltration of saltwater into a freshwater acquifer, which raises the groundwater table underneath the soil surface
Regardless of how saltwater intrusion takes place, the final result is having salt on your lettuce way before time.
Of course, the closest to the sea the crops are grown and the lower the land elevation is, the higher the effects of salt intrusion. In South-East Asia, the rice cropping systems of Bangladesh have been experiencing a considerable decrease in yield, directly correlated with the higher soil salinity, caused by climate change - induced salt intrusion. As a result, the extra challenge of securing a proper crop production, contributes to harshen the already fragile livelihood conditions of coastal farming communities, in the poorest regions of the World.
Why is salt such a big of a deal for a plant?
Salinity is involved in several metabolic and physiological changes, which vary according to the severity and the duration of the salinity stress.
So, similarly to us, neither plants fancy saltwater, but what does exactly happen if I offer a plant a salty drink?
First of all, the plant will have a hard time trying to take up both the soil nutrients and water, due to the negative soil solution osmotic potential (a measure of how strong the soil retain water and nutrients from the suction power of the roots).Think of it as an arm wrestling match between the soil and the roots: the higher the salt concentration in the soil, the stronger the soil is in keeping the nutrients and water steady in place.
The plant, who can’t take up water from the soil eventually figures that it is better to close the stomata (exactly what you do when you spray deodorant under your armpits, to close the pores and not sweat), to prevent losing water. However, this is not a long-term successful strategy since the plant needs to have the stomata open for respiration (thankfully we humans have the nose for that).
The issues for the plant don’t end there though. The water that the plant does manage to take up is toxic: being salty, it contains ions like Na+ and Cl- which destroy photosynthetic components like enzymes, carotenoids and chlorophyll. This results in stunted growth and wilting.
So, that’s what happens to a plant when you “treat it” with saltwater. You can now see why it is not in the best conditions to provide a proper yield.
What to do then?
Farmers can do a few things in order to prevent their fields to be overly contaminated with saltwater.
- Use irrigation water to dilute the salts in the soil and push them down to deeper layers where crops’ roots are not present
- Grow salt resistance crops
- Grow cover crops which help to leach salt down throught he soil
- Add gypsum to reduce excess salt in the soil
- Adopt conversation strategies such as including riparian buffer strips on field margins to improve water quality, by using non-cash crops to take up the salt
However neither of these are long term solutions, since they are just temporary and don’t solve the problem at its roots. Since the permanent solution of salt intrusion would be the ending of sea level rise, it is clear that farmers and agricultural scientists can only do much to reduce the effects of salinity in the fields.
Tracking salinity changes overtime and identifying the areas which are more at risk of salt intrusion will be key in the years to come, to allow farmers to take preventative measures in time.
Otherwise, we will all save money on table salt in the future.
