Browsing by Author "Wissel, Holger"

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    Challenging the Atacama desert: Agronomic and water conditions for pre-Hispanic maize agriculture in hyper arid environments inferred by 518O isotopes
    (2024) Vidal-Elgueta, Ale; Luecke, Andreas; Perez, M. Fernanda; Wissel, Holger; Maldonado, Antonio; Uribe, Mauricio
    During the Formative Period (ca.2400-950 years BP), pre-Hispanic farmers in Pampa del Tamarugal developed a complex agricultural system in the hyper-arid Atacama Desert in Tarapaca, northern Chile. This system involved numerous agricultural fields congregated near the Tarapaca Valley's perennial stream and the Guatacondo ravine's ephemeral stream. Well-established villages such as Caserones, Pircas, Ramaditas, and Guatacondo accompanied these developments. However, the importance of understanding the water sources has been neglected despite the efforts to understand the relationships between pre-Hispanic agriculture and their living environment. Thus, we presumed the use of local water sources without a clear understanding of their exploitation methods or the associated technological implications. Furthermore, there is limited research on groundwater use in Tarapaca. This research aims to understand water sources used in the cultivation of maize (Zea mays) using 518O isotope values obtained from pre-Hispanic maize kernels in Tarapaca. We compared these values with published 518O values of water sources and applied a generalized linear model (GLM) with a Gaussian distribution, performing a Tukey's post hoc test for multiple comparisons of means with heteroscedasticity-consistent covariance estimation. The best-fit model was identified using a stepwise model selection procedure based on the Bayesian information criterion (BIC). Our results indicate that mean 518O values of organic matter from maize kernels range from 24.73 %o to 31.65 %o. The best performing model on 518O only included Group (BIC=298.2) as the explanatory variable as Period, Site, and Weight had no effects. These findings point towards a significant statistical relationship between the 518O values of organic matter derived from maize kernels and the specific geographic regions they originate from. These values also show an enrichment of 518O isotope in Tarapaca samples, except for Pica 8. These results indicate diverse agricultural strategies that utilized different water sources including perennial flow in the Tarapaca River, ephemeral runoff at Guatacondo, and groundwater in the Pampa del Tamarugal. Also, due to the enrichment of 518O, we suggest that the circular structures found among the fields were used as water reservoirs leading to the observed enrichment of 518O isotope values. We discuss the role of ancient agriculture technology in water management, the role of maize, cultural strategies, and the relationships with their environment. In conclusion, pre-Hispanic farmers managed limited water sources successfully despite intermittent drought for hundreds of years until the 1970 s, when agriculture was abandoned due to multiple factors.
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    Evaluating the isotopic composition of leaf organic compounds in fog-dependent Tillandsia landbeckii across the coastal Atacama Desert: Implications for hydroclimate reconstructions at the dry limit
    (2024) Jaeschke, Andrea; Boehm, Christoph; Schween, Jan H.; Schefuss, Enno; Koch, Marcus A.; Latorre, Claudio; Contreras, Sergio; Rethemeyer, Janet; Wissel, Holger; Luecke, Andreas
    Fog is an important component of the coastal climate of northern Chile and southern Peru. Moisture and nutrients from fog maintain highly endemic vegetation (lomas) as well as unique Tillandsia landbeckii ecosystems that thrive at elevations of ca. 900-1200 m asl. Although this epiphytic CAM bromeliad is well adapted to the extreme climate, declining Tillandsia stocks observed over the past decades question the long-term survival with ongoing climate change. Here, we aim at better understanding the hydroclimatic signal encoded in the leaf organic compounds of Tillandsia landbeckii across the Atacama Desert's coastal mountain range (ca. 18-21 degrees S). First, we investigate spatiotemporal patterns of fog occurrence and related moisture sources available for the plants applying a new satellite -based fog -detection approach. We then use stable carbon, oxygen and hydrogen ( delta 13 C, delta 18 O, delta D) isotope analysis of leaf wax n -alkanes and cellulose to identify photosynthetic pathway as well as environmental and physiological processes that shape the isotopic composition in Tillandsia landbeckii . We find that leaf wax n -alkanes and cellulose reflect the balance of climatic and physiological drivers differently. While n - alkane delta D values more closely follow changes in precipitation delta D, evaporative enrichment seems to have a dominant influence on cellulose delta 18 O values. Cellulose delta D values are highly enriched compared to n -alkane delta D values, likely reflecting a predominant metabolic imprint on delta D. delta 13 C signatures in the organic compounds are valid proxies for CAM activity. Our results prove the general applicability of the isotopic biomarkers for reconstructing environmental change in the coastal Atacama Desert. This approach can be extended globally to west -coast deserts that share fog as a major source of moisture.