CNP patterns at catchment scales 

(DOI 10.1088/1748-9326/acc3b1)

Background

The inputs of macro-nutrients (carbon (C), nitrogen (N) and phosphorous (P)) to freshwater ecosystems have been increasing throughout the last decades¹. These ecosystems often connect terrestrial and marine environments and their biogeochemistry can play an important role in mediating macro-nutrient exports. As this mediation is influenced by macro-nutrient stoichiometry², we see the need to understand what controls C:N:P patterns across freshwater ecosystems. Because those patterns are commonly studied on small scale communal levels, less is known about their behavior on catchment scales.

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¹Vitousek et al., „Human Alteration of the Global Nitrogen Cycle“.
²Graeber et al., „Bioavailable DOC“.

Objective

The main objective of this group is to identify the drivers of C:N:P ratios in freshwater ecosystems.

Research questions / hypotheses

We hypothesize that observed macro-nutrient stoichiometric ratios are the result of different biogeochmical and hydrological processes, such as nutrient mobilization and assimilation by algae, plants and bacteria. We speculate that some catchments have more stable (homeostatic) and some more variable (heteroscatic) stoichiometric ratios. As a first step, we want to classify catchments regarding those patterns and try to link them with catchment specific properties, such as land-use, soil type, vegetation or nutrient input.

Data & Methods

We use concurrently measured low-frequency records of dissolved organic carbon (DOC), Nitrate-N (NO3-N) and soluble reactive phosphorus (SRP) from around 200 German catchments along multiple phyiscal and socio-economical gradients. We use ternary plots (see figure) to visualize and classify the DOC:NO3-N:SRP ratios of those catchments and search for common patterns along/ across the above mentioned gradients. Ternary plots offer the visualization of all three macro-nutrients at a time, and also allow us to compare the ratios of catchments to those ideal for different biological groups, such as bacteria (data from Vrede et al.³, shown in the figure).

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³ Vrede et al., „Elemental Composition (C, N, P) and Cell Volume of Exponentially Growing and Nutrient-Limited Bacterioplankton“.

Update October 2022

(currently under review at Environmental Research Letters)

Stoichiometry on the edge - Humans induce strong imbalances of reactive C:N:P ratios in streams

Alexander Wachholz¹, Joni Dehaspe^2,3, Pia Ebeling², Rohini Kumar⁴, Andreas Musolff², Felipe Saavedra⁵, Carolin Winter², Soohyun Yang¹, Daniel Graeber^1
1Department of Aquatic Ecosystem Analysis and Management, Helmholtz-Centre for Environmental
Research (UFZ), Magdeburg, Germany
²Department of Hydrogeology, Helmholtz-Centre for Environmental Research (UFZ), Leipzip, Germany
³Unit Environmental Modeling, Flemish Institute for Technological Research NV- VITO, Mol, Belgium
⁴Department for Computational Hydrosystems, Helmholtz-Centre for Environmental Research (UFZ),
Leipzig, Germany
⁵Department of Catchment Hydrology, Helmholtz-Centre for Environmental Research (UFZ), Halle,
Germany

Abstract

Anthropogenic nutrient inputs led to severe degradation of surface water resources, affecting aquatic ecosystem health and functioning. Ecosystem functions such as nutrient cycling and ecosystem metabolism are not only affected by the over-abundance of a single macronutrient but also by the stoichiometry of the reactive molecular forms of dissolved organic carbon (rOC), nitrogen (rN), and phosphorus (rP). So far, studies mainly considered only single macronutrients or used stoichiometric ratios such as N:P or C:N independent from each other. We argue that a mutual assessment of reactive nutrient ratios rOC:rN:rP relative to organismic demands enables us to refine the definition of nutrient depletion versus excess and to understand their linkages to catchment-internal biogeochemical and hydrological processes. Here we show that the majority (93 %) of the studied 574 German catchments show a depletion or co-depletion in rOC and rP, illustrating the ubiquity of excess N in anthropogenically influenced landscapes (Figure 1). We found an emerging spatial pattern of depletion classes linked to the interplay of agricultural sources and subsurface denitrification for rN and topographic controls of rOC (Figure 1). We classified catchments into stoichio-static and stochio-dynamic catchments based on their degree of intra-annual variability of rOC:rN:rP ratios (not shown). Stoichio-static catchments (36% of all catchments) tend to have higher rN median concentrations, lower temporal rN variability and generally low rOC medians (not shown).
Our results demonstrate the severe extent of imbalances in rOC:rN:rP ratios in German rivers due to human activities. This likely affects the inland-water nutrient retention efficiency, their level of eutrophication, and their role in the global carbon cycle. Thus, it calls for a more holistic catchment and aquatic ecosystem management integrating rOC:rN:rP stoichiometry as a fundamental principle.

Update March 2023

Stoichiometry on the edge - Humans induce strong imbalances of reactive C:N:P ratios in streams

https://iopscience.iop.org/article/10.1088/1748-9326/acc3b1

Alexander Wachholz¹, Joni Dehaspe², Pia Ebeling³, Rohini Kumar⁴, Andreas Musolff³, Felipe Saavedra⁵, Carolin Winter⁶, Soohyun Yang¹, Daniel Graeber⁷

GERMANY

⁶Helmholtz-Zentrum für Umweltforschung UFZ, Permoserstr 15, Leipzig, Sachsen, 04318, GERMANY

⁷Department of Aquatic Ecosystem Analysis, Helmholtz-Centre for Environmental Research - UFZ, Brückstraße 3a 39114 Magdeburg, Magdeburg, Sachsen-Anhalt, 39114, GERMANY

Participants

Felipe Saavedra

Joni Dehaspe

Alexander Wachholz

Carolin Winter

Rohini Kumar

Soohyun Yang

Andreas Musolff

Daniel Graeber

Pia Ebeling

Graeber, Daniel, Youngdoung Tenzin, Marc Stutter, Gabriele Weigelhofer, Tom Shatwell, Wolf von Tümpling, Jörg Tittel, Alexander Wachholz, und Dietrich Borchardt. „Bioavailable DOC: Reactive Nutrient Ratios Control Heterotrophic Nutrient Assimilation—An Experimental Proof of the Macronutrient-Access Hypothesis“. Biogeochemistry, 8. Juni 2021. https://doi.org/10.1007/s10533-021-00809-4

Vitousek, Peter M., John D. Aber, Robert W. Howarth, Gene E. Likens, Pamela A. Matson, David W. Schindler, William H. Schlesinger, und David G. Tilman. „Human Alteration of the Global Nitrogen Cycle: Sources  and Consequences“. Ecological Applications 7, Nr. 3 (1997): 737–50. https://doi.org/10.1890 /1051-0761(1997)007[0737:HAOTGN]2.0.CO;2.

Vrede, Katarina, Mikal Heldal, Svein Norland, und Gunnar Bratbak. „Elemental Composition (C, N, P) and Cell Volume of Exponentially Growing and Nutrient-Limited Bacterioplankton“. Applied and Environmental Microbiology 68, Nr. 6 (1. Juni 2002): 2965–71. https://doi.org/10.1128/AEM.68.6.2965-2971.2002.