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Factors controlling the stable isotope composition and C:N ratio of seston and periphyton in shallow lake mesocosms with contrasting nutrient loadings and temperatures
Author(s) -
Trochine Carolina,
Guerrieri Marcelo,
Liboriussen Lone,
Willems Priscila,
Lauridsen Torben L.,
Søndergaard Martin,
Jeppesen Erik
Publication year - 2017
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/fwb.12971
Subject(s) - seston , periphyton , mesocosm , nutrient , eutrophication , stable isotope ratio , ecology , environmental chemistry , phytoplankton , environmental science , zoology , chemistry , biology , physics , quantum mechanics
Summary Carbon (C) and nitrogen (N) stable isotope composition ( 15 N: 14 N, δ 15 N and 13 C: 12 C, δ 13 C) have been widely used to elucidate changes in aquatic ecosystem dynamics created by eutrophication and climate warming, often, however, without accounting for seasonal variation. Here, we aim to determine the factors controlling the stable isotope composition and C:N ratio of seston and periphyton in shallow lakes with contrasting nutrient loadings and climate; for this purpose, we followed the monthly stable isotope composition ( c . 1 year) of seston (SES) and periphyton (PER) in 24 mesocosms mimicking shallow lakes with two nutrient treatments (enriched and unenriched) and three temperature scenarios (ambient, +3 and +5°C). Nutrient enrichment and warming had a stronger impact on the δ 15 N and δ 13 C values of seston than on periphyton, and the temporal isotopic variability in both communities was large. δ 15 N PER did not differ markedly between nutrient treatments, whereas δ 15 N SES was lower in the enriched mesocosms, possibly reflecting higher N 2 ‐fixation by cyanobacteria. δ 15 N SES was higher in winter in the heated mesocosms and its dynamics was linked with that of NH 4 ‐N, whereas δ 15 N PER showed a stronger association with NO 3 ‐N. δ 15 N SES demonstrated a positive relationship with mean monthly temperature, indicating less isotope fractionation among autotrophs when production increased. δ 13 C SES was lowest in the enriched mesocosms during winter, whereas δ 13 C PER did not differ between nutrient treatments. δ 13 C SES and δ 13 C PER were positively related to pH, likely reflecting a pH‐induced differential access to dissolved carbon species in the primary producers. The positive δ 13 C‐temperature relationship suggested less fractionation of CO 2 and HCO 3 − and/or larger use of HCO 3 − at higher temperatures. The C:N ratios varied seasonally and the differences between the enriched and unenriched mesocosms were stronger for seston than for periphyton. Particularly, the C:N SES ratios did not indicate deficiencies in N as opposed to the C:N PER ratios, supporting the observed changes in δ 15 N and suggesting that seston and periphyton have access to different sources of nutrients. We did not observe any clear effect of temperature warming on the C:N ratios. Our study provides evidence of strong seasonality in the isotopic composition and C:N ratios of seston and periphyton across nutrient and temperature levels; also, we identified several factors that are likely to modulate the strength and variability in stable isotopes values and stoichiometry of sestonic and periphytic communities under these scenarios.