A new study has found that warming winters may cause an increased downstream exposure to chemicals. Although there is still insufficient data to determine the exact impact on water quality, it is certain that the phenomenon causes an increase in phosphorus and nitrogen levels in both groundwater and surface water.
The study, conducted by six researchers led by University of Kansas’ Erin C Seybold was published in Environmental Research Letter under the title “Winter runoff events pose an unquantified continental-scale risk of high wintertime nutrient export.”
Chemicals usually used for agriculture typically freeze during cold winters. Under normal circumstances, the slow melt of frozen areas in the Spring gives plants a chance to absorb them and prevent excessive accumulation downstream.
However, warming winters mean that this process is becoming quicker and starting sooner. As a result, nutrients are released much quicker and plants are unable to absorb them as they rush downstream contaminating water bodies.
The study focused on the United States, assessing the impact of early thawing and rains. It states: “Runoff from such midwinter events was historically infrequent, but these increasingly common winter flushing events can interact with nutrient-rich landscapes to export large pulses of nutrients from soils to receiving waters, with potentially detrimental, but largely unknown, impacts on downstream water quality.”
The increased levels of these chemicals can cause water contamination, algal overgrowth and may lead to the appearance of hypoxic dead zones: patches of water where conditions are not suitable for animal life leading to fish die-offs or fauna migration.
According to the study, this phenomenon is caused by two anthropogenic factors: climate change and use of phosphorus and nitrogen in agriculture.