15 Terrestrial records of hydroclimate variability from the Pleistocene through the Common Era

Landscapes respond to climatic variability, extreme hydrologic events, and long-term environmental change, informing water resource management. We invite terrestrial proxies of hydroclimate from perspectives in paleoclimatology, geomorphology, or hydrology. Submissions from early-career scientists are encouraged.

Monday, 9 March 2026
1:30 PM - 3:30 PM
RCC, 105

Environmental change at Lake Ypacaraí: urbanization impacts a sub-tropical floodplain lake in Paraguay

Paper number: 15-3
Program: Technical Sessions
Time: 2:05 PM – 2:20 PM

Authors

Abstract

Intense eutrophication of shallow sub-tropical lakes imposes substantial challenges for aquatic conservation across the Global South. Lake Ypacaraí is the largest natural lake by area in Paraguay, where much of the topography is defined by the lowlands shaped by the Paraguay and Paraná Rivers. Lake Ypacaraí is shallow, polymictic, and hydrologically connected to the Paraguay River, flowing out through the Salado River. The lake’s watershed includes in the western basin suburbs of the national capital, Asunción, and its shoreline development is extensive. Urbanization of this watershed, coupled with minimal regulation and environmental oversight, has led to excess nutrient inputs and harmful algal blooms, rendering the lake a significant public health hazard and degrading ecosystem services associated with tourism and water supply. The Ypacaraí Graben is composed of Quaternary sediments, and its boundary has Ordovician to Early Cretaceous sedimentary rocks of the Asunción Rift. Yet to date, no sedimentary datasets are available to characterize this depositional system and to provide a retrospective environmental assessment. Similarly, the long-term hydroclimate and ecological history archived in the basin are unexplored. The bathymetry showed a relatively flat-bottomed lake with a maximum depth of 2.8 m, and the water quality parameters at ~43 cm below the water surface averaged 279 µS cm-1 conductivity, pH ~7.6, and 93.4% dissolved oxygen. Preliminary results from surface sediment samples indicated considerable concentrations of organic matter, with an average total organic carbon of ~8.0 wt. %. δ15N values were < 0 ‰ along the populated northeastern margin and the northern end of the lake, indicating likely cyanobacterial growth near San Bernardino and the Salado River outlet. Short sediment cores (< 1 m) recovered from the northern and southern ends of the lake exhibited a pattern of homogeneous black-to-gray lacustrine muds underlain by dense clayey silt, suggesting an altered depositional environment in the recent past. Magnetic susceptibility increased to ~2 SI x 10-5 towards the bottom of the cores, except for the northernmost cores. Our ongoing research seeks to expand limnogeological and chronological datasets for Lake Ypacaraí, establishing it as the first comprehensive record of human-landscape interactions in Paraguay.

Geological Society of America Abstracts with Programs. Vol. 58, No. 1

doi: 10.1130/abs/2026SE-411891

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