New publication from Freshwater Competence Centre: warm and rainy winters double the turbidity of water, suggesting major erosion and nutrient loading
Gypsum treatment of agricultural fields has shown promising results in reducing phosphorus and suspended sediment loads, and therefore also eutrophication of water bodies, like Baltic Sea. However, its efficacy has not been investigated on catchment scale to any wide extent. Therefore, the latest study from Freshwater Competence Centre scientists examined the functionality of the gypsum treatment in an agriculture-dominated boreal catchment in the Archipelago Sea basin in Finland – particularly with the point of view that winters are getting warmer and the amount of precipitation coming in liquid state in the wintertime is increasing as a result of the warming climate.
Image: Bathymetric mapping at Savijoki with ADCP, Elina Kasvi
Text: Annukka Pekkarinen, Elina Kasvi
What did they find out?
The turbidity of the water increased greatly during high winter discharges, compared to other seasons. This suggests that the more frequent freeze-thaw cycles and precipitation coming as rain during the unvegetated period increase erosion and therefore also the particulate phosphorus loads. Basically, when we see more water coming as rain in the winter time, the result is more erosion, muddier waters and more nutrients into the streams and coastline. They are not talking about any small impact either: The turbidity levels during the extremely wet and warm winter of 2020 were twice as high as in the other winter periods with snow-melt-induced peak discharges. Even the heavy summer rains do not increase the turbidity as much, likely due to vegetation and higher evaporation of the water.
What does this mean?
The results of this catchment scale study showed that gypsum treatment faces the same challenges as many other nutrient load reduction measures. The seasonal and climatological variations affect the gypsum performance, and it may happen in an unpredictable manner. As the gypsum treatment operating principle is directly linked to preventing erosion, the combined effect of lack of vegetation and soil frost during winters is causing the most challenging circumstances for gypsum. Regional differences in gypsum response were also observed during the same winter rains, but no clear reason for this was found. The research thus raised many new questions and highlighted the fact that avoiding over-simplified interpretations on the effects of nutrient reduction measures requires catchment scale investigations over years.
Reference:
Kasvi Elina, Saarinen Aino, Kämäri Maria, Porkka Jutta, Alho Petteri, Ekholm Petri,The effect of seasonal variation, flow conditions and erosion forces on suspended matter fluxes from boreal gypsum-treated agricultural fields, CATENA, Volume 243, 2024, 108199, ISSN 0341-8162, https://doi.org/10.1016/j.catena.2024.108199.