land already converted to farming land, the implications of our farming practices for the environment cannot be ignored[sc:1]. Unsustainable land development happens in many ways as analysed in Greentumble’s article “How does unsustainable land development happen?”; but it is not just our land that gets affected. The marine environment bears the brunt of it with close to 500 dead zones being created covering more than 245,000 km² globally, equivalent to the UK’s surface[sc:2].
The good news is that just like when one thing in our environment is out of balance, another part of it will suffer, when something is improved then there is a positive ripple effect in other areas. So, just as the potential of crop rotations systems and practices has emerged as a remedy to the devastating effects of monoculture farming for our land, crop biodiversity can bring about positive effects for our aquatic ecosystems. As indicated in “Advantages and disadvantages of monoculture farming”, if farmers were to introduce a system of crop rotation which essentially increases the varieties of crops planted, this would improve the quality of the soil, the resilience of the plot in terms of fighting off pests and increase agricultural yields. The underlying principle in crop rotation, which is crop biodiversity, can have very positive impacts for our seas and water in terms of reversing the impacts and spread of ocean dead zones.
Crop biodiversity is already recognised as essential for combatting climate change, safeguarding biodiversity as well as ensuring food security and combatting poverty[sc:3]. This is reflected in the fact that the UN Sustainable Development Goals explicitly reference the importance of “maintain[ing] the genetic diversity of seeds, cultivated plants and farmed and domesticated animals and their related wild species, including through soundly managed and diversified seed and plant banks at the national, regional and international levels” as a means of ending hunger, achieving food security and improved nutrition[sc:4].
But the Louisiana State University in the United States conducted some research which suggests that crop biodiversity can also have some very positive externalities for our seas, rivers and lakes[sc:5]. The researchers identified a link between the diversity of crops grown in farmlands and the pollution created in lakes and rivers: when crop diversity was high, less dissolved nitrogen was found in nearby watersheds. This is particularly important as nitrogen from fertilisers ends up in aquatic ecosystems where it increases the level of dissolved nitrate. The increased nitrate leads to the growth of algae, which uses up the available oxygen in the water stifling other marine life and creating dead zones that cannot support life.
In their research paper, the authors looked at how nitrate levels in watersheds had changed since 1900’s. The results were staggering particularly when compared to areas where agriculture is taking place. Since 1906, the average aquatic nitrate concentration increased by a factor of three in the US and by a factor of ten in the Iowa, Des Moines, and Minnesota Rivers, all of which are located in or close to agricultural areas. In stark contrast, areas where farming is scarce or absent, there was no perceptible change in dissolved nitrogen concentrations since the early 1900s.
The researchers also observed that in areas with higher crop biodiversity, there was less dissolved nitrate. While the explanation of this phenomenon is difficult to discern, it has nonetheless led them to believe that the nitrate impacts observed in other areas might be reversible. Specific policy changes, including crop rotation, would be needed to achieve this[sc:6].