Factors controlling the stable isotope composition and C:N ratio of seston and periphyton in shallow lake mesocosms with contrasting nutrient loadings and temperatures

CAROLINA TROCHINE; MARCELO GUERRIERI; LONE LIBORIUSSEN; WILLEMS PRISCILA; TORBEN L. LAURIDSEN; MARTIN SØNDERGAARD; ERIK JEPPESEN

FRESHWATER BIOLOGY (PRINT)

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2017 vol. 62 p. 1596 - 1613

0046-5070

1.             Carbon (C)and nitrogen (N) stable isotope composition (15N:14N, δ15N and 13C:12C,δ13C) have been widely used to elucidate changes inaquatic ecosystem dynamics created by eutrophication and climate warming, oftenhowever, without accounting for seasonal variation. 2.             Here, we aim to determine the factors controlling thestable isotope composition and C:N ratio of seston and periphyton in shallowlakes with contrasting nutrient loadings and climate; for this purpose, wefollowed the monthly stable isotope composition (~1-yr) of seston (SES) and periphyton (PER) in24 mesocosms mimicking shallow lakes with two nutrient treatments (enriched andunenriched) and three temperature scenarios (ambient, +3°C and +5°C). 3.             Nutrient enrichmentand warming had a stronger impact on the δ15Nand δ13C values of seston than on periphyton, and thetemporal isotopic variability of both communities was large. 4.             δ15NPER did not differmarkedly between nutrient treatments,while δ15NSES was lower in the enriched mesocosms, possibly reflecting higher N2-fixation by cyanobacteria. δ15NSES was higherin winter in the heated mesocosms and its dynamics was linked with that of NH4-N, whereas δ15NPERshowed a stronger association with NO3-N. δ15NSESdemonstrated a positive relationship with mean monthly temperature, indicatingless isotope fractionation among autotrophs when production increased.5.             δ13CSES was lowest in the enrichedmesocosms during winter, whereas δ13CPER did not differ betweennutrient treatments. δ13CSES and δ13CPERwere positively related to pH, likely reflecting a pH-induced differentialaccess to dissolved carbon species in the primary producers. The positive δ13C-temperature relationship suggested less fractionation of CO2 and HCO3-and/or larger use of HCO3- at higher temperatures.6.             The C:N ratios varied seasonally and the differencesbetween the enriched and unenriched mesocosms were stronger for seston than forperiphyton. Particularly, the C:NSES ratios did not indicatedeficiencies in N as opposed to the C:NPER ratios, supporting theobserved changes in δ15N and suggesting that seston and periphytonhave access to different sources of nutrients. We did not observe any cleareffect of temperature warming on the C:N ratios.7.             Ourstudy provides evidence of strong seasonality in the isotopic composition andC:N ratios of seston and periphyton across nutrient and temperature levels;also, we identified several factors that are likely to modulate the strengthand variability of stable isotopes values and stoichiometry of sestonic andperiphytic communities under these scenarios.