Inferring the occurrence of regime shifts in a shallow lake during the last 250 years based on multiple indicators

GONZÁLEZ SAGRARIO, MARÍA DE LOS ÁNGELES; MUSAZZI, SIMONA; CÓRDOBA, FRANCISCO ELIZALDE; MENDIOLAR, MANUELA; LAMI, ANDREA

ECOLOGICAL INDICATORS

ELSEVIER SCIENCE BV

Año: 2020 vol. 117

1470-160X

Regimeshifts are ecosystem-scale phenomena. In lake studies, most supporting evidenceis frequently based on a single state variable. We examined the sediment recordof the shallow lake Blanca Chica (Argentina) to explore the response ofmultiple proxies belonging to different trophic levels (nutrients, chlorophylland carotenoid pigments, diatoms, Cladocera remains, and Rotifera resting eggs)over the last 250 yr. We explored different ecological indicators to assesschanges consistent with regime shifts. To do so, first we identified the timingof transitional periods on multiple-proxies. Then, we explored (1) the natureof the change (linear versus non-linear dynamics), (2) different indicators ofa shift across the food web: multimodality and resilience indicators (standarddeviation and autocorrelation), and (3) examined the synchronicity of thedetected indicators at multiple-trophic levels. Generalized additive modelsfitted to the ordination scores of the assemblages analyzed revealed two transitions:ca. 1860-1900, and 1915-1990. Ecological indicators of regime shifts revealedthat the first transition is consistent with a threshold state response (changein the ecosystem state manifest as a jump when the driver exceeds a state threshold),and the second one with a critical transition (hysteretic transition in whichthe system change to an alternate stable state). After the first transition lakestructure shifted from littoral to pelagic species dominance (evidenced by Cladocera anddiatom assemblages), and turbidity increased, indicating a rise in lake waterlevel. This transition was non-linear, showed multimodality, and is most likelydriven by an increase in precipitation registered inthe region since 1870. During the second transition,nutrient levels rose, all indicators showed multimodality, non-linear dynamicsand an increase in standard deviation prior to the regime shift. These dynamicsare consistent with a critical transition in response to eutrophication, andcoincides with a post-1920 change in land use. Our results show that several ecologicalindicators of regime shifts need to be examined to perform an accuratediagnosis. We highlight the relevance of a multi-proxy approach including multiple-trophiclevel responses as the appropriate scale of analysis to determine the occurrence,type and dynamics of regime shifts. We also show that resilience indicators andcritical transitions can be detectable in the whole food web and that shallowlakes can undergo different types of regime shifts.