Sources, characterization and transport of sediment bound phosphorus in small agricultural streams

Last changed: 07 May 2021
High water flow in a stream with agriculture on one side and forest on the other. Photo.

A research project on phosphorus and eutrophication with focus on sediments in streams

Introduction

A significant proportion of the total Phosphorus (P) load in streams and rivers is transported in particulate form associated with fluvial suspended sediments and it is well established that different P forms and fractions have dissimilar effects on eutrophication and degradation of surface water quality. Hence, new information on organic P and humic-metal P fluxes, storage, mobilization and bioavailability within agricultural streams on a temporal and spatial scale appropriate for catchment scale management policies is a promising way forward for surface water eutrophication control. However, few studies have specifically characterized and quantified organic P and humic-metal P species within streambed sediments and fewer still their reactivity and bioavailability, especially in fluvial suspended sediments.

Our project (which involves research teams in three countries) will generate new knowledge on the stability and bioavailability of organic P and humic bound P species needed for assessments of in stream primary production and degradation of water quality.

The key output for the Swedish part of the project will be developing molecular level process understanding into more realistic representations of biogeochemical transformations in agricultural catchments, which can be included in catchment-scale models.

Methods

Sampling campaigns will focus on some of the 21 well-monitored small agricultural catchments (2–35 km2) in Sweden with 25+ years water quality data. Intensive monitoring at 8 of the catchments includes flow-proportional stream water sampling, analysis of groundwater quality, yearly crop management surveys and soil characterization. Fluvial and streambed sediment will be sampled using modified in-stream sediment traps in a geologically contrasting subset of these 8 catchments.

Aqueous nutrient concentrations, along with their chemical speciation will be measured. Fluvial and streambed sediment organic P and humic-metal P will be analysed using chemical extractions, as well as 31P NMR for greater resolution of organic P species, high resolution spectroscopic (µ and bulk XANES, µ-XRD, Mössbauer) and imaging techniques (TEM-EDS). Spatial and temporal bioavailability of nano-particulate P (both inorganic and organic) in suspended and streambed sediments will be assessed directly using extra-cellular enzymatic hydrolysis experiments.

Results from the sampling campaigns and speciation analysis will be used to better constrain parameterization of process-based catchment-scale models of surface water P transport. As well as learning and applying state of the art techniques for assessing P speciation and availability, the PhD student at SLU will develop the modelling capabilities needed for incorporating state of the art chemical analyses in the interpretation and prediction of effects of low flow and episodic flood events on export of suspended and streambed sediment bound P from agricultural catchments. The focus of modelling efforts will be on three parts:

  1. Capturing the spatial variability in the mobilization and delivery of the suspended sediment from terrestrial systems to ditches and streams with consideration taken to topography, soils' erodibility, vegetation cover and soil management practices
  2. Refinement of models to explain and predict the temporal and spatial variations in P content and speciation suspended sediments as a function of erosion rates, enrichment ratios and P content in parent material
  3. Development of mathematical formulations describing the fluvial sediment exchanges of P (with a focus on organic phosphorus and humic matter bound P) needed to better constrain predictive P exchange and transport models for agricultural catchments

Funding and participants

The project is funded by Formas and will be a part of JPI Eutro-Sed project involving three main partners: SLU, Trinity College Dublin, and the Canadian Light Source at University of Saskatchewan (UoS). The Swedish work will be carried out as a PhD project. The position is full-time and will be granted for a period of four years, starting in summer 2017.

Results

Read more about results from the project in these articles:


Contact
Page editor: vattenmiljo-webb@slu.se