Miriam Steinitz-Kannan

A ∼6100 14C yr record of El Niño activity from the Galápagos Islands

Lithostratigrahic and mineralogic analyses of sediments from hypersaline Bainbridge Crater Lake, Galápagos Islands, provide evidence of past El Niño frequency and intensity. Laminated sediments indicate that at least 435 moderate to very strong El Niño events have occurred since 6100 14C yr BP (∼7130 cal yr BP), and that frequency and intensity of events increased at about 3000 14C yr BP (∼3100 cal yr BP). El Niño activity was present between 6100 and 4000 14C yr BP (∼4600 cal yr BP) but infrequent. The Bainbridge record indicates that there has been considerable millennial-scale variability in El Niño since the mid-Holocene.

Impacts of climate variability and human colonization on the vegetation of the Galápagos Islands.

A high-resolution (2-9 year sampling interval) fossil pollen record from the Galápagos Islands, which spans the last 2690 years, reveals considerable ecosystem stability. Vegetation changes associated with independently derived histories of El Niño Southern Oscillation variability provided evidence of shifts in the relative abundance of individual species rather than immigration or extinction. Droughts associated with the Medieval Climate Anomaly induced rapid ecological change that was followed by a reversion to the previous state. The paleoecological data suggested nonneutral responses to climatic forcing in this ecosystem prior to the period of human influence. Human impacts on the islands are evident in the record. A marked decline in long-term codominants of the pollen record, Alternanthera and Acalypha, produced a flora without modern analogue before 1930. Intensified animal husbandry after ca. 1930 may have induced the local extinction of Acalypha and Alternanthera. Reductions in populations of grazing animals in the 1970s and 1980s did not result in the return of the native flora, but in invasions by exotic species. After ca. 1970 the trajectory of habitat change accelerated, continuously moving the ecosystem away from the observed range of variability in the previous 2690 years toward a novel ecosystem. The last 40 years of the record also suggest unprecedented transport of lowland pollen to the uplands, consistent with intensified convection and warmer wet seasons.

Lake regionalization and diatom metacommunity structuring in tropical South America

Abstract Lakes and their topological distribution across Earths surface impose ecological and evolutionary constraints on aquatic metacommunities. In this study, we group similar lake ecosystems as metacommunity units influencing diatom community structure. We assembled a database of 195 lakes from the tropical Andes and adjacent lowlands (8°N–30°S and 58–79°W) with associated environmental predictors to examine diatom metacommunity patterns at two different levels: taxon and functional (deconstructed species matrix by ecological guilds). We also derived spatial variables that inherently assessed the relative role of dispersal. Using complementary multivariate statistical techniques (principal component analysis, cluster analysis, nonmetric multidimensional scaling, Procrustes, variance partitioning), we examined diatom–environment relationships among different lake habitats (sediment surface, periphyton, and plankton) and partitioned community variation to evaluate the influence of niche‐ and dispersal‐based assembly processes in diatom metacommunity structure across lake clusters. The results showed a significant association between geographic clusters of lakes based on gradients of climate and landscape configuration and diatom assemblages. Six lake clusters distributed along a latitudinal gradient were identified as functional metacommunity units for diatom communities. Variance partitioning revealed that dispersal mechanisms were a major contributor to diatom metacommunity structure, but in a highly context‐dependent fashion across lake clusters. In the Andean Altiplano and adjacent lowlands of Bolivia, diatom metacommunities are niche assembled but constrained by either dispersal limitation or mass effects, resulting from area, environmental heterogeneity, and ecological guild relationships. Topographic heterogeneity played an important role in structuring planktic diatom metacommunities. We emphasize the value of a guild‐based metacommunity model linked to dispersal for elucidating mechanisms underlying latitudinal gradients in distribution. Our findings reveal the importance of shifts in ecological drivers across climatic and physiographically distinct lake clusters, providing a basis for comparison of broad‐scale community gradients in lake‐rich regions elsewhere. This may help guide future research to explore evolutionary constraints on the rich Neotropical benthic diatom species pool.

Appendix C. Figures showing the inferred pattern of sediment accumulation in cores EJ-N-1 and EJ-2 raised from El Junco crater lake.

Figures showing the inferred pattern of sediment accumulation in cores EJ-N-1 and EJ-2 raised from El Junco crater lake.

Effects of Environmental Factors on the Growth of Algae for Biofuel Production in a Household-Based Alternative Energy System

The efficiency and cost effectiveness of using algae to create biofuel has been much debated in recent years. A household-based biofuel system that uses sewage as a medium in which to grow mixed algae cultures is a possible solution to decreasing the production and transportation costs of biofuel. Aside from the manufacturing issues involved, it is important to determine what variables most affect the growth of algae and the production of biofuel. This study presents the results of an ANOVA-based set of experiments that evaluate the effect of several variables on algae growth in wastewater. While much work remains to be done, these results will help determine the optimal environmental conditions for a household-based biofuel system that utilizes mixed algae cultures.Copyright