EFFECTS OF CHANGES IN N LOADING AND WARMING ON NUTRIENT LIMITATION OF PERIPHYTON: AN APPROACH USING QUANTITY AND QUALITY PROXIES

CAROLINA TROCHINE; FLORENCIA CUASSOLO; URSULA STRANDBERG ; ERIK JEPPESEN

Natal

Congreso; Shallow Lakes 2021; 2021

Universidad Federal del Rio Grande do Norte

Periphyton is a key contributor to primary productivity, particularly in environments witha developed littoral area. The growth of lake periphyton is often limited bythe availability of N and P. Limitation of periphyton growth by nutrients maybe further impacted by climate warming. The quality, measured as the fattyacids (FA) composition of periphyton, also differs in aquatic ecosystems underdiffering nutrient and warming conditions. The objective of the present study wasto elucidate how nutrient limitation affects periphyton quantity (measured asChlorophyll-a, Chl-a) and quality (measured as FA), in mesocosms mimickingshallow lakes with contrasting temperatures (climate warming scenarios). Inthese mesocosms the external N-loading was reduced substantially for 1 yearbefore it was again raised to normal high level. We added nutrient diffusionsubstrata (NDS, 2% agar alone or releasing N, P and combined N and P with aGF-F filter on top) to 12 mesocosms on the two occasions (before and afterreturn to the normal high N-loading). In each occasion, the NDS remained in themesocosms for 21 days to allow colonization by periphyton. We then measured periphytonChl-a and FA amounts and composition. The analysis of Chl-a of the first NDSexperiment indicated that the ambient temperature and the +3ºC scenario wereN-limited in the low N-loading scenario. However, the warmest scenario (+4.5ºC)did not show any differential response to the addition of nutrients, eithersingle nutrient limitation or co-limitation. The N limitation was not evidentany more in the second NDS experiment in the high N-loading scenario. The FA profilesof periphyton growing in the NDS before and after the N-loading showeddifferences in physiological important FA as eicosapentaenoic acid (EPA). Weshowed that the quantity and quality of the periphyton changes with N-loadingwith differential effects in the different warming scenarios.