Pesticides and climate change, among the main threats to Mediterranean wetlands

The Mediterranean basin is one of the hot spots on the planet with the greatest concentration of biodiversity. With a high ecological value, it is a provider of a large number of ecosystem services – ecosystem goods and processes that provide essential benefits for society – such as carbon sequestration and oxygen production.

For historical and cultural reasons, these ecosystems have been subjected to a wide variety of anthropogenic pressures. In a bibliographical review, published in the journal Science of the Total Environmentwe have identified the main consequences of human activity on the biodiversity of Mediterranean coastal wetlands.

Man-made or exacerbated threats include the proliferation of invasive species, salinization, and increased temperatures due to climate change.

In France, the excessive concentration of nutrients or eutrophication causes blooms of algae and a decrease in the size of plankton cells.

In Italy, salinization problems lead to the loss of biodiversity in invertebrates, and invasive species prey on native species.

One of the activities that has the greatest impact on the environment is agriculture, mainly through the contribution of excess nutrients or phytosanitary products to the water, including herbicides to combat the growth of weeds, insecticides and fungicides to eradicate conditions caused by fungi.

Rice cultivation in the Albufera of Valencia

Rice is one of the most important crops linked to Mediterranean wetlands, with a strong dependence on water, since rice fields need to remain flooded most of the time.

Specifically, in the Albufera Natural Park in Valencia, this cereal began to be produced intensively in the 18th century. Currently, the park is home to 13,000 hectares of rice fields, which require the massive use of pesticides to maintain sufficient productivity standards in relation to market prices.

In the Albufera, rice is sown in mid-May. Until its harvest at the end of September, a series of events take place characterized by the application of different types of pesticides, especially fungicides, with the aim of eradicating or preventing the different pests that threaten it.

Every time the fields are drained to apply these compounds, the contaminated water is discharged into the Albufera lake through ditches.

Rice field in the Albufera.
Oselfa Faber / Flickr, CC BY-NC-ND

Consequences for aquatic biodiversity

The application of pesticides has a negative impact on aquatic biodiversity, both in the rice fields themselves and in the Albufera lagoon and the irrigation channels of the Natural Park.

In the aforementioned review, we show the main negative effects of pesticides on the species that inhabit these ecosystems.

Fish, for example, suffer from the effects on their nervous system and liver tissue. Bioaccumulation of pesticides has also been observed in the liver and muscle tissue of birds.

On the other hand, in invertebrate communities –insect larvae and crustaceans that form plankton– there has been an increase in species tolerant to pollution and opportunistic species –those that easily adapt to new environmental conditions– to the detriment of the groups of species most sensitive to pollution.

The additional effect of climate change

Another stress factor that affects the biodiversity of Mediterranean wetlands is climate change, since it interferes with the use and presence of pesticides in the environment.

In many cases, increases in temperature cause other processes such as microbial activity to speed up. Microorganisms can increase the degradation of pesticides, but on other occasions they can transform these compounds into others that are more soluble in water, which would increase their toxicity.

A study carried out by the Ecotoxicology Group of the IMDEA Water Institute in collaboration with the Norwegian Institute for Water Research and the IE Business School has evaluated the ecological risk in the rice fields of the Natural Park taking into account different climatic and pesticide application scenarios. . Using computer tools we have made predictions of the impacts of climate change for the years 2050 and 2100.

Sunset in a lagoon.
Lagoon in the Albufera.
Antonio Marín Segovia / Flickr, CC BY-NC-ND

Influence of precipitation and temperature

Part of the results obtained show that the most important negative impacts of climate change are conditioned by extreme precipitation events rather than by the increase in temperature itself.

Through different predictive models we have observed that by 2050 and 2100 rainfall will be less, but will be concentrated in shorter periods of time. This will affect pesticide exposure and increase the ecological risk of many compounds.

When it rains, physical-chemical processes take place that intervene in the degradation of pesticides, such as the reduction of evaporation or the increase in the resuspension of the compounds that were in the sediment, in addition to the washing itself from the plants into the water.

Likewise, specific compounds such as fungicides show a very high ecological risk in any of the climate scenarios, even in cases in which the dose is reduced to half of those currently applied.

Future scenarios: the European Green Deal

These results show the need to adopt measures such as those included in the European Green Pact. Since the increase in temperature and the decrease in precipitation seem irrevocable circumstances, mitigation proposals should focus on reducing the use of pesticides.

Said regulation, in its section “From farm to table”, indicates that by the year 2030 it is intended to reduce the use of pesticides in crops by 50%. This will greatly decrease the ecological risk of many of the compounds currently applied to rice fields.

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