Vulnerability of high-mountain lakes of Sierra Nevada to multiple stressors

CABRERIZO, M.; CARRILLO, P.; VILLAFAÑE, V. E.; MEDINA-SÁNCHEZ, J. M.; HELBLING, E. W.

Santander

Congreso; XVII Congreso de la Asociación Ibérica de Limnología; 2014

Current global change is altering ecosystems and producing changes whose magnitude is not  completely predictable in single-factor studies due to the interaction among multiple stressors. Our objective was to quantify the responses of primary producer communities, with different light histories and acclimation to solar radiation to: (i) double-ambient CO2 concentration, increased in nutrient inputs, fluctuating light regimes and different light qualities on a short-term scale. We carried out a multifactorial experiment during the highest UVR fluxes (mid ice-free period) with natural communities collected from six high-mountain lakes [Río Seco Grande (RS), Río Seco Superior (RSS), La Caldera (LC), Aguas Verdes (AV), Las Yeguas (LY) and Lagunillos de La Virgen (LV)] of Sierra Nevada National Park across UVR-transparency gradient. The experimental design consisted of two radiation treatments [ultraviolet radiation (PAB) versus photosynthetically active radiation(PAR)] , two nutrient enrichment [non-enriched (Nutambient) versus enriched conditions (Nutadded)], two CO2 concentrations [ambient (390 ppm) versus enriched (750 ppm)] and two fluctuating regime [static versus mixed (one rotation from surface to 3 m depth (speed 1m 4 min-1, total 10 cycles). We evaluated the impact of these stressors on primary production (PP) and on excreted organic carbon (EOC) as percentage. A significant single inhibitory UVR effect on PP was found in all lakes. Besides, the combined impact of PABxNutxCO2xMixing on PP produced a synergistic effect, increasing %UVR inhibition on AV and LY, whereas it was antagonistic for RS, RSS, LC and LV, as a result of increase in nutrients, CO2 and a fluctuating regime. Likewise, EOC percentage exhibited a similar response pattern to PP, but with highest values showed in LV, an intermediate UVR-transparency lake, and the lowest in LC, the most transparent lake. These results represent a differential vulnerability of these ecosystems due to their different nutrient concentrations, variations in species composition and UVR-protection levels related with the DOM concentrations.