What Colin Reynolds could tell us about nutrient limitation, N:P ratios and eutrophication control
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COLIN S. REYNOLDS’ LEGACY
Review Paper
What Colin Reynolds could tell us about nutrient limitation, N:P ratios and eutrophication control Ingrid Chorus
. Elly Spijkerman
Received: 13 March 2020 / Revised: 27 July 2020 / Accepted: 2 August 2020 The Author(s) 2020
Abstract Colin Reynolds exquisitely consolidated our understanding of driving forces shaping phytoplankton communities and those setting the upper limit to biomass yield, with limitation typically shifting from light in winter to phosphorus in spring. Nonetheless, co-limitation is frequently postulated from enhanced growth responses to enrichments with both N and P or from N:P ranging around the Redfield ratio, concluding a need to reduce both N and P in order to mitigate eutrophication. Here, we review the current understanding of limitation through N and P and of co-limitation. We conclude that Reynolds is still correct: (i) Liebig’s law of the minimum holds and reducing P is sufficient, provided concentrations achieved are low enough; (ii) analyses of nutrient
Guest editors: Judit Padisa´k, J. Alex Elliott, Martin T. Dokulil & Luigi Naselli-Flores / New, old and evergreen frontiers in freshwater phytoplankton ecology: the legacy of Colin S. Reynolds Ingrid Chorus, formerly Department of Drinking Water and Swimming Pool Hygiene, Federal Environment Agency, Berlin, Germany I. Chorus (&) Department of Drinking Water and Swimming Pool Hygiene, Federal Environment Agency, Berlin, Germany e-mail: [email protected] E. Spijkerman Department of Ecology and Ecosystem Modelling, University of Potsdam, Potsdam, Germany
limitation need to exclude evidently non-limiting situations, i.e. where soluble P exceeds 3–10 lg/l, dissolved N exceeds 100–130 lg/l and total P and N support high biomass levels with self-shading causing light limitation; (iii) additionally decreasing N to limiting concentrations may be useful in specific situations (e.g. shallow waterbodies with high internal P and pronounced denitrification); (iv) management decisions require local, situation-specific assessments. The value of research on stoichiometry and colimitation lies in promoting our understanding of phytoplankton ecophysiology and community ecology. Keywords Phytoplankton Nitrogen limitation Redfield ratio Co-limitation Enrichment experiments
Introduction Now almost 30 years ago, in his classical paper on ‘‘What Vollenweider couldn’t tell us’’, Colin Reynolds pointed out the importance of distinguishing between limitation of nutrient uptake rates, growth rates and the capacity for biomass formation. In order to effectively control eutrophication, he emphasised the practical ‘‘need for a consensus view of aquatic ecosystem functioning that is implicitly correct’’,
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Hydrobiologia
which at the time he assessed as ‘‘far from being the case’’ (Reynolds, 1992, p. 5). Some of the issues he listed as controversial may in part be resolved or better understood by now, i.e. the relative relevance of bottom-up versus top-down
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