What Colin Reynolds could tell us about nutrient limitation, N:P ratios and eutrophication control

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 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.

Abiotic factors driving cyanobacterial biomass and composition under perennial bloom conditions in tropical latitudes

“…Indeed, TP represents the total pool of phosphorous in the water, and the greater is the pool, the greater is the phytoplankton biomass sustained. High TP values here, however, do not exclude the possibility that other factors such as light or grazers might be limiting the carrying capacity (Reynolds, 1992(Reynolds, , 2006Chorus & Spijkerman, 2020). Indeed, that Chl-a/TP values were mostly \ 1 in this study indicates that factors other than TP were likely limiting phytoplankton biomass (Reynolds, 1992;Chorus & Spijkerman, 2020).…”

“…Results also indicate that nutrients were not limiting phytoplankton biomass based on nutrient concentrations as well as the Chl-a/TP ratio. Specifically, nutrients were always above concentrations considered limiting for phytoplankton uptake (3-10 lg l -1 SRP or 100-130 lg l -1 DIN) (Reynolds, 2006;Chorus & Spijkerman, 2020) with TDN more than tenfold higher than TDP. Yet, considering that nitrogen was always above the saturation threshold for phytoplankton nutrient uptake rate, TP was likely determining the carrying capacity of the system.…”

“…The R-index result was compared to all abiotic variables measured (Zeu, Zmax, TP, TDP, TN, TDN, TSS, VSS, and FSS) to identify the difference in environmental conditions where Microcystis or Raphidiopsis populations dominate. The Chl-a/TP ratio indicates phytoplankton resource efficiency, values equal to 1:1 indicating maximal resource use efficiency which phytoplankton can make use of the carrying capacity, while the ratio can increase at low values of TP or higher values of Chl-a under light limitation conditions (Reynolds, 1992;Chorus & Spijkerman, 2020).…”

Occurrence of a single-species cyanobacterial bloom in a lake in Cyprus: monitoring and treatment with hydrogen peroxide-releasing granules

“…Overall, approaches that were based on ocean dynamics were found to have poor fitting on the trophic status of the lake in contrast with more recent approaches that were intended for fresh waterbodies. This stresses the need of better understanding nutrient dynamics in lakes and the development of holistic approaches based on the different physicochemical characteristics of each waterbody, taking into consideration also other limiting factors that may affect trophic status, such as light intensity and temperature [32]. High correlation of nutrient levels and trophic status indicates the need of monitoring for the early detection of (toxic) cyanobacterial blooms when a high nutrient load is documented.…”

First report on the occurrence of a single species cyanobacterial bloom in a lake in Cyprus: Monitoring and treatment with hydrogen peroxide releasing granules

“…Overall, approaches that were based on ocean dynamics were found to have poor tting on the trophic status of the lake in contrast with more recent approaches that were intendent for fresh waterbodies. This stresses the need of better understanding the nutrient dynamics in lakes and the development of holistic approaches based on the different physicochemical characteristics of each waterbody, taking into consideration also other limiting factors that may affect trophic status such as light and temperature [38]. Nutrients and trophic status of each waterbody are highly correlated, indicating that when a high nutrient load is documented, algal and cyanobacterial monitoring is essential for the early detection of (toxic) blooms.…”