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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2020-372
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-372
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  30 Oct 2020

30 Oct 2020

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This preprint is currently under review for the journal BG.

Complex interactions of in-stream DOM and nutrient spiralling unravelled by Bayesian regression analysis

Matthias Pucher1,2, Peter Flödl3, Daniel Graeber4, Klaus Felsenstein5, Thomas Hein1,2, and Gabriele Weigelhofer1,2 Matthias Pucher et al.
  • 1WasserClusterLunz – Biologische Station GmbH, Lunz am See, Austria
  • 2Institute of Hydrobiology and Aquatic Ecosystem Management, University of Natural Resources and Life Sciences, Vienna, Austria
  • 3Institute of Hydraulic Engineering and River Research, University of Natural Resources and Life Sciences, Vienna, Austria
  • 4Department Aquatic Ecosystem Analysis and Management (ASAM), Helmholtz Centre for Environmental Research – UFZ, Magdeburg, Germany
  • 5Department of Statistics, Vienna University of Technology, Vienna, Austria

Abstract. Uptake and release patterns of dissolved organic matter (DOM) compounds and nutrients are entangled, and the current literature does not provide a consistent picture of the link between DOM composition, nutrient concentrations, and effects on their cycling. We performed two plateau addition experiments for each of five different, realistic, complex DOM leachates in a small stream, heavily enriched in nitrate but not phosphate or DOM due to diffuse agricultural pollution. By including cow and pig dung as well as corn, leaves and nettles leachates, the study used a wide range of different DOM qualities. We measured changes in nutrient concentrations and determined DOM fractions by fluorescence measurements and parallel factor (PARAFAC) decomposition. To assess influences from hydrological transport processes, we used a 1-D hydrodynamic model.

We propose a non-linear Bayesian approach to the nutrient spiralling concept, the Interactions in Nutrient Spirals using BayesIan REgression (INSBIRE) approach. This approach can disentangle complex and interacting biotic and abiotic drivers in nutrient uptake metrics, show their variability and quantify their error distribution. Furthermore, previous knowledge on nutrient spiralling can be included in the model using prior probability distributions. We used INSBIRE to assess interactions of compound-specific DOM and nutrient spiralling metrics the data of our experiment.

The uptake processes of different DOM fractions were linked to each other. We observed stimulating and dampening effects of DOM fractions on each other and the overall DOM uptake. We found saturation effects for dissolved organic carbon (concentration of C, DOC) uptake, as rising concentrations of a DOM fraction dampened its uptake. The degradation of a humic DOM component of terrestrial origin was stimulated by other DOM fractions, pointing to priming effects. We also found an influence of the wetted width on the uptake of soluble reactive phosphorus (SRP) and a microbially derived humic substance, which indicates the importance of the sediment-water interface for P and humic C cycling in the studied stream. Interestingly, we found no interactions between DOM uptake and nitrate or SRP concentrations, or any effect of the added DOM leachates on nitrate uptake, indicating that the increase in DOC concentrations and SRP concentrations were not sufficient to affect the relatively steady nitrate uptake during the experiments.

Overall, we show that bulk DOC is a weak predictor of DOC uptake behaviour for complex DOM leachates and that individual DOM compound uptake, nitrate uptake and SRP uptake are controlled very differently within the same aquatic ecosystem. We also found effects of hydromorphology on the uptake of one humic fluorophore and SRP. We conclude that cycling of different C fractions, their interaction and interactions with N and P uptake in streams is a complex, non-linear problem, which can only be assessed with advanced non-linear approaches, such as we present with INSBIRE.

Matthias Pucher et al.

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Matthias Pucher et al.

Model code and software

MatthiasPucher/INSBIRE: INSBIRE: Interactions in Nutrient Spirals using BayesIan nonlinear REgression Matthias Pucher https://doi.org/10.5281/zenodo.4071852

Matthias Pucher et al.

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Short summary
Dissolved organic matter is an important carbon source in aquatic ecosystems, yet the uptake processes are not totally understood. We found evidence for the release of degradation products, efficiency loss with higher concentrations, stimulating effects and influences from the benthic zone. To conduct this analysis, we included interactions in the equations of the nutrient spiralling concept and solve it by a Bayesian non-linear fitting algorithm.
Dissolved organic matter is an important carbon source in aquatic ecosystems, yet the uptake...
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