Differential stimulation and suppression of phytoplankton growth by ammonium enrichment in eutrophic hardwater lakes over 16 years

Vanessa J. Swarbrick, Gavin L. Simpson, Patricia M. Glibert, Peter R. Leavitt*

*Corresponding author af dette arbejde

Publikation: Bidrag til tidsskrift/Konferencebidrag i tidsskrift /Bidrag til avisTidsskriftartikelForskningpeer review

13 Citationer (Scopus)


Previous research suggests that fertilization of surface waters with chemically reduced nitrogen (N), including ammonium (NH 4 + ), may either enhance or suppress phytoplankton growth. To identify the factors influencing the net effect of NH 4 + , we fertilized natural phytoplankton assemblages from two eutrophic hardwater lakes with growth-saturating concentrations of NH 4 Cl in 241 incubation experiments conducted biweekly May–August during 1996–2011. Phytoplankton biomass (as chlorophyll a) was significantly (p < 0.05) altered in fertilized trials relative to controls after 72 h in 44.8% of experiments, with a marked rise in both spring suppression and summer stimulation of assemblages over 16 yr, as revealed by generalized additive models (GAMs). Binomial GAMs were used to compare contemporaneous changes in physico-chemical (temperature, Secchi depth, pH, nutrients; 19.5% deviance explained) and biological parameters (phytoplankton community composition; 40.0% deviance explained) to results from fertilization experiments. Models revealed that that the likelihood of growth suppression by NH 4 + increased with abundance of diatoms, cryptophytes, and unicellular cyanobacteria, particularly when water temperatures and soluble reactive phosphorus (SRP) concentrations were low. In contrast, phytoplankton was often stimulated by NH 4 + when chlorophytes and non-N 2 -fixing cyanobacteria were abundant, and temperatures and SRP concentrations were high. Progressive intensification of NH 4 + effects over 16 yr reflects changes in both spring (cooler water, increased diatoms and cryptophytes) and summer lake conditions (more chlorophytes, earlier cyanobacteria blooms), suggesting that the seasonal effects of NH 4 + will vary with future climate change and modes of N enrichment.

TidsskriftLimnology and Oceanography
Sider (fra-til)S130-S149
StatusUdgivet - jan. 2019
Udgivet eksterntJa


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