Phosphorus has been entering water bodies for thousands of years

The over-fertilization of lakes started thousands of years ago. Phosphorus inputs to lakes in central Europe increased noticeably at the beginning of the Bronze Age, about 4,000 years ago, according to a new study led by the University of Bern.

However, these early changes were nothing compared to what came later, as the Swiss National Science Foundation (SNSF), which sponsored the study, announced on Friday.

According to the study, industrialization and the use of phosphorus fertilizers in agriculture have increased annual global phosphorus inputs sixfold compared to pre-industrial times, from about 240,000 tons per year to about 1.5 million tons per year today. Over the past 12,000 years, 2.7 billion tons of phosphorus have been deposited in lake sediments worldwide.

Although humans are known to have fundamentally changed the global phosphorus cycle, our understanding of when and how humans affected the cycle is limited, the researchers wrote in the study published in the journal Global and Planetary Change.

The international research team examined sediment layers from 108 lakes around the world. The layers of the examined drill cores extended up to 12,000 years old.

While people in Central Europe arguably intervened in material cycles as early as the Bronze Age, this only occurred later in other regions. In China about 2000 years ago, in North America about 400 years ago. This is related to the later onset of population growth and land use intensification in these regions, as the SNF explained.

According to the release, excessive phosphorus inputs into lakes cause water bodies to contain too many nutrients, which can lead to excessive algae growth, fish kills and a decline in aquatic biodiversity. At the same time, phosphorus is lacking as a nutrient in agriculture when it enters lake sediments. Without phosphorus in the soil, plants cannot grow. That is why phosphorus is added to depleted soils in the form of fertilizer.

(jam/sda)