| Abstrakt: |
Paleolimnology studies in tropical reservoirs and urban lakes are relatively scarce. These aquatic ecosystems, however, are subject to a range of environmental impacts, including cultural eutrophication, a process that can be assessed and monitored using paleolimnological methods. Arcellinida (testate lobose amoebae) is a taxonomic group that can be used as a bioindicator in paleolimnological research, though there has been relatively little work with the group in tropical regions. We evaluated how arcellinids responded to environmental changes over a period of 90 years (1920-2010) in Guarapiranga Reservoir, São Paulo, Brazil. We investigated the relationship between arcellinids and several other sediment variables (particle size, total organic carbon content, copper, total nitrogen and total phosphorus concentrations, stable isotope values (d13C and d15N) and diatoms), with a focus on recent trophic state shifts and their relation with biodiversity changes, with respect to both individual species and community structure. We found 25 arcellinid taxa, dominated in abundance by Centropyxis aculeata, Cucurbitella tricuspis, and Difflugia oblonga. Community structure shifted with environmental changes. Multivariate analyses (redundancy analysis—RDA and multivariate linear regression) indicated a relationship between C. aculeata and C. tricuspis and abiotic variables, as well as with diatoms, including a positive correlation between C. tricuspis and Aulacoseira granulata. Stratigraphically constrained cluster analysis (CONISS) indicated the community was characterized by three arcellinid phases: (1) Centropyxis Phase—CTP (1920-1936), (2) Difflugia Phase —DFG (1947-1959), and (3) Cucurbitella tricuspis/Centropyxis Phase—CCB/CTP (1974-2010).The arcellinid phases are temporally coincident with diatom phases and shifts in trophic state conditions identified in previous paleolimnological work. Persistent presence of C. aculeata in all samples reflects the eurytopic character of this species, which was abundant under both oligotrophic and eutrophic conditions. D. oblonga yielded a high bioindicator value (IndVal = 0.841, p = 0.019) for the mesotrophic phase. C. tricuspis is strongly associated with cultural eutrophication (IndVal = 0.815, p = 0.036), and displayed increasing abundance as the reservoir became enriched with nutrients, pointing to a change in trophic state even before diatoms did. Our results shed light on correlations between arcellinids and both abiotic variables and diatoms, thereby improving our understanding of the potential bioindicator value of this group in tropical reservoirs, especially for inferring past trophic state conditions. [ABSTRACT FROM AUTHOR] |
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