Forms of phosphorus in suspended particulate matter in agriculture-dominated lowland catchments: Iron as phosphorus carrier

Bas van der Grift; Leonard Osté; Paul Schot; Arjen Kratz; Emma van Popta; Martin Wassen; Jasper Griffioen

doi:10.1016/j.scitotenv.2018.02.266

Forms of phosphorus in suspended particulate matter in agriculture-dominated lowland catchments: Iron as phosphorus carrier

Sci Total Environ. 2018 Aug 1:631-632:115-129. doi: 10.1016/j.scitotenv.2018.02.266. Epub 2018 Mar 16.

Authors

Bas van der Grift¹, Leonard Osté², Paul Schot³, Arjen Kratz⁴, Emma van Popta⁴, Martin Wassen³, Jasper Griffioen⁵

Affiliations

¹ Deltares, P.O. Box 85467, 3508 AL Utrecht, The Netherlands. Electronic address: bas.vandergrift@deltares.nl.
² Deltares, P.O. Box 85467, 3508 AL Utrecht, The Netherlands.
³ Copernicus Institute of Sustainable Development, Faculty of Geosciences, Utrecht University, P.O. Box 80115, 3508 TA Utrecht, The Netherlands.
⁴ Deltares, P.O. Box 85467, 3508 AL Utrecht, The Netherlands; Copernicus Institute of Sustainable Development, Faculty of Geosciences, Utrecht University, P.O. Box 80115, 3508 TA Utrecht, The Netherlands.
⁵ Copernicus Institute of Sustainable Development, Faculty of Geosciences, Utrecht University, P.O. Box 80115, 3508 TA Utrecht, The Netherlands; TNO Geological Survey of the Netherlands, P.O. Box 80015, 3508 TA Utrecht, The Netherlands.

PMID: 29524889
DOI: 10.1016/j.scitotenv.2018.02.266

Abstract

The fate and environmental effects of phosphorus (P) in natural waters depend on its chemical forms. The particulate P (PP) concentration is dominant over the dissolved P concentration in agriculture-dominated headwaters in the Netherlands. Routine water quality monitoring programmes do not include the chemical fractionation of PP. To quantify the chemical forms of PP under various conditions in six agriculture-dominated lowland catchments in the Netherlands, a sequential chemical extraction method was applied to suspended particulate matter (SPM) samples collected by centrifugation or filtration. Centrifuge samples had lower values for the sum of the PP fractions compared with the filtration samples due to lower contents from PP fractions other than the Fe-P pool. With an average value of 8.8mgg^-1, internationally high P contents of the SPM were found. Ferric iron-bound P was the most important PP fraction in SPM samples (38-95%; median 74%), followed by organic P (2-38%; median 15%). Exchangeable P ranged from 0.2 to 27%, with a median of 4.4%, Ca-P ranged from 0.1 to 11% with a median of 3.9% and detrital P was present in only a small fraction (0-6%; median 1.1%). Ferric iron-bound P was the dominant PP pool throughout the entire range of watercourses (from headwater ditches to catchment outlets) and in samples taken during winter months as well as those taken during summer months. Furthermore, the PP fraction distribution did not change markedly when flow conditions were altered from low to high discharge. The dominance of the Fe-P pool denotes the presence of Fe(III) precipitates in SPM that originate from exfiltration of anoxic Fe-bearing groundwater. These Fe(III) precipitates are a major fraction of the total SPM concentration (4 to 67% as Fe(OH)₃; median 18%). Although not measured directly, our results suggest that formation of authigenic Fe(III) precipitates causes a rapid transformation of dissolved P in groundwater to PP in surface water. We advise including sequential chemical extraction of SPM monitoring programmes because the composition of particles is critical for P bioavailability, which is a key driving factor for eutrophication.

Keywords: Filtration; Iron hydroxides; Natural water; Phosphate binding; Sequential chemical extraction; Suspended particulate matter.