Twenty years of catchment monitoring highlights the predominant role of long-term phosphorus balances and soil phosphorus status in affecting phosphorus loss in livestock-intensive regions

Jian Liu; Marianne Bechmann; Hans Olav Eggestad; Anne Falk Øgaard

doi:10.1016/j.scitotenv.2023.165470

Twenty years of catchment monitoring highlights the predominant role of long-term phosphorus balances and soil phosphorus status in affecting phosphorus loss in livestock-intensive regions

Sci Total Environ. 2023 Nov 10:898:165470. doi: 10.1016/j.scitotenv.2023.165470. Epub 2023 Jul 13.

Authors

Jian Liu¹, Marianne Bechmann², Hans Olav Eggestad², Anne Falk Øgaard²

Affiliations

¹ The Norwegian Institute of Bioeconomy Research (NIBIO), P.O. Box 115, 1431, Ås, Norway. Electronic address: jian.liu@nibio.no.
² The Norwegian Institute of Bioeconomy Research (NIBIO), P.O. Box 115, 1431, Ås, Norway.

PMID: 37451443
DOI: 10.1016/j.scitotenv.2023.165470

Abstract

Livestock husbandry has raised enormous environmental concerns around the world, including water quality issues. Yet there is a need to document long-term water quality trends in livestock-intensive regions and reveal the drivers for the trends based on detailed catchment monitoring. Here, we assessed the concentration and load trends of dissolved reactive phosphorus (DRP) in streamwater of a livestock-intensive catchment in southwestern Norway, based on continuous flow measurements and flow-proportional composite water sampling. Precipitation and catchment-level soil P balance were monitored to examine the drivers. At the field level, moreover, the relationship between soil P balance and soil test P (measured using the ammonium lactate extraction method, P-AL) was assessed. Results showed that on average of 20 years 95 % of the P was applied to the catchment during March-August, when 40 % of annual precipitation and 25 % of annual discharge occurred. The low runoff helped reduce P loss following P applications. However, flow-weighted annual mean DRP concentration significantly increased with increasingly cumulative soil P surplus (R² = 0.55, p = 0.0002). With a mean annual P surplus of 8.8 kg ha^-1, the annual mean DRP concentration (range: 49-140 μg L^-1; mean: 80 μg L^-1) and annual DRP load (range: 0.35-1.46 kg ha^-1; mean: 0.65 kg ha^-1) significantly increased over the 20-year monitoring period (p = 0.001 and 0.0003, respectively). At the field level, P-AL concentrations were positively correlated with soil P balances (R² = 0.48, p < 0.0001), confirming the long-term impact of P balances on the risks of P loss. The study highlights the predominant role of long-term P balances in affecting DRP loss in livestock-intensive regions through the effect on soil test P.

Keywords: Animal agriculture; Catchment monitoring; Eutrophication; Phosphorus balance; Soil test phosphorus; Water quality.