Gypsum reduces agricultural phosphorus load: preliminary results from a large-scale pilot

Petri Ekholm1*, Markku Ollikainen2, Eliisa Punttila2

 

1 Finnish Environment Institute, P.O.Box 140, 00251 Helsinki, Finland

2 University of Helsinki, P.O.Box 27,00014 Helsingin yliopisto, Finland

* petri.ekholm@environment.fi

 

Eutrophication is the major problem in open and coastal waters of the Baltic Sea. According to the HELCOM’s Baltic Sea Action Plan, Finland has to reduce the load of phosphorus (P) into the Gulf of Finland by 364 t y−1. Municipal and industrial wastewaters being efficiently purified for P, the abatement measures should focus on agricultural diffuse load. Yet, even if all the planned measures were fully implemented, the target would fall about 250 t y−1 short. New approaches for tackling agricultural P load are therefore urgently needed.

We are testing the performance of a novel agri-environmental measure, the surface application gypsum (CaSO4 ∙ 2H2O), in reducing P losses from clayey agricultural fields. In autumn 2016, gypsum was spread (4 t ha−1) on 1550 hectares in the middle reaches of the river Savijoki, south-western Finland. The upper reaches of the river were left as a control area, where gypsum was not used. Runoff in both areas has been intensively monitored before, during and after the gypsum amendment.

In this presentation we will discuss the ability of the measure to decrease dissolved and particulate forms of P, based on data collected during 14 months after the gypsum amendment. In addition, we present the results of extensive ecotoxicological studies, which focussed on a potential side-effect, the impact of increased concentrations of sulfate on riverine fish, mussels and mosses. The results suggest that gypsum has a marked potential in reducing P losses from clayey fields with minimal adverse effects on riverine biota. Future studies will concentrate on evaluating the duration of the gypsum effect, which is related to the gradual leaching of gypsum from soil. The gypsum pilot contributes to the NutriTrade project lead by John Nurminen Foundation and funded by the European Union Central Baltic Program.