Barely a day has gone by since the COVID-19 pandemic without river pollution being a news headline. Most of the headlines focus on the issues of excess effluent entering rivers. While a serious issue, this is not the only source of river pollution, nor is there a lot of detail about what river pollutants actually are, what their effects are and what safe levels would be.
What is it and where does it come from?
Potassium is a naturally occurring element critical for biological processes, required for photosynthesis in plants and muscle function among other things in animals. It is one of the three essential macronutrients for life, alongside nitrogen and phosphorus. The least common cation in river water, it is typically released from silicate minerals like potassium feldspar and mica with the biggest fluxes from leaching and erosion of dissolved potassium present in soils and groundwater regions with potassium-rich geology.
Fertilisers containing potassium are also widely used in farming and excessive concentrations in irrigation water can disrupt soil nutrient balance and affect plant health. Domestic and industrial effluents from wastewater and sewage often contain potassium compounds, including industrial processes that release potassium salts into waterways. It is these human activities that are the main drivers of increased potassium levels in rivers.
Ballast Quay, Wivenhoe by Chris Holifield
What is the problem?
Although potassium is essential for ecosystems, imbalances or excess concentrations can disrupt river chemistry and affect aquatic life; elevated potassium levels often indicate a broader nutrient pollution, contributing to water quality decline and ecosystem stress.
Unlike nitrogen and phosphorus, potassium is rarely the limiting nutrient for algae growth, meaning it doesn’t directly trigger algal blooms or ‘dead zones’ in the same way, and much of the potassium entering rivers is quickly absorbed by soils and plants, reducing its immediate impact in comparison to other nutrients.
The problems potassium does pose in rivers is in altering the water chemistry. Elevated potassium levels can change the ionic balance of rivers, which can affect the solubility of other nutrients and metals, influencing overall water quality. High potassium concentrations can also be toxic to some freshwater organisms, particularly invertebrates and fish, interfering with their cellular ion regulation. There has also been evidence from major rivers across the world, such as the Yangtze and Amazon, that suggests increased potassium loads caused by human activity are contributing to long-term shifts in river health.
In summary, although potassium pollution doesn’t usually result in the dramatic effects of algal blooms, it can still cause harm to aquatic ecosystems by altering water chemistry and stressing wildlife. Its presence often points to wider nutrient pollution from agriculture and wastewater, making it an important indicator of river health.
