Early-warning bio-indicators of Lake Titicaca eutrophication
Lake Titicaca, the largest freshwater lake in South America (8,400 km2), and highest of the Great Lakes (3.810 m asl), despites of its climate, combines all the ingredients to exacerbate eutrophication: being tropical (16ºS), impacted by a strong global warming (twice the Earth average) and multiple urban, industrial, mining, and agricultural contaminations. This was revealed in 2015 by the first documented large-scale green-algae bloom. As part of the IRD-UMSA cooperation, we coordinate two pilot projects funded by UNDP: ‘OLT – Lake Titicaca permanent Observatory’ (PI: X. Lazzaro, D. Achá & J. Nuñez) and ‘BIOREM – Phytoremediation of Lake Titicaca areas of Huatajata and Cohana bay and cultural/economic revaluation of Totora’ (PI: D. Achá & G. Sarret), plus two IRD-UMSA JEAI: ‘FERRIA - Flow–Ecology Relationships Research and Interdisciplinary Applications’ (PI: C. Molina & M. Pouilly), and ‘TITICACA – TracIng the TrIgger mechanisms of eutrophiCAtion and ContAmination of andean aquatic ecosystems (Bolivia)’ (PI: D. Achá & S. Guédron).
The Bolivian Environment Act Nº 1333 (MDSMA 1992) concerns the prevention and control of water pollution, and differentiates four water classes (A-D) according to aptitudes of uses. To include the concept of ecological state and health level of Lake Titicaca, we propose using the European Water Framework Directive (EU WFD), which considers the functional structure of biological communities, habitat, and physico-chemistry.
To dynamically map eutrophication, we search for strong low-cost, effective, and quick bioindicators. We focus on the interactions between the shallow Minor Lake and the Katari watershed tributaries transporting wastewaters from the urban, industrial, and agricultural areas of El Alto (1.2-million inhabitants, 2º Bolivian city). To anticipate undesirable extreme events, such as phytoplankton efflorescences (blooms), we need to implement an early warning system. Our results will guide the Bolivian Environment and Water Ministry (MMAyA) to implement measures for sustainable long-term ecosystem conservation and restoration, and resources management.
We implemented innovative leading tools: i.e., satellite and drone remote sensing, in situ validation using multiparameter probes and a spectroradiometer, and real-time transmission high-frequency meteorological (5 min) and water quality (30 min) monitoring using an automatic HydroMet buoy, operated by a team of young trained interdisciplinary Bolivian partners, faculties and students. Through one-day campaigns (2-3/month), we monitor some classical EU WFD eutrophication indicators in stations along eutrophication gradients, using probes, analytical and microscope procedures: i.e., PAR-UV light extinction coefficients, nutrients (NO3, NH4, PO4, TN, TP), temperature, conductivity, pH/ORP, DO, turbidity, phytoplankton chlorophyll-a and cyanobacteria phycocyanin (both in situ and remotely from Landsat and Sentinel satellites), fDOM, community taxonomic and morphology-based functional composition of phytoplankton, periphyton on emergent Totora, zooplankton, plus lake-scale Totora distribution (1979 to present); occasionally bacterial H2S emission, and ∂C/∂N stable isotope ratios. We are currently developing a promising monitoring approach combining phytoplankton counts, in vivo chlorophyll-a fluorescence and HPLC photosynthetic pigments, to validate satellite chlorophyll-a and phycocyanin estimates. Using the littoral and buoy weather stations, we generate continuous data on air temperature, barometric pressure, wind speed/direction, humidity, rain/snow, and visible solar radiation.
Phytoplankton efflorescences result from excessive nutrient load and/or reduced zooplankton grazing. Shallow lakes may alternate between clear (macrophytes dominance) and turbid (phytoplankton dominance) stable states. Aquatic macrophytes shift between submerged, emerged, and floating communities along gradients of increasing eutrophication. The community architecture (topology) of planktonic and benthic microalgae respond differentially as well. Phytoplankton, periphyton, zooplankton, and microbes are naturally occurring bioindicators that reflect the environment health, detect and resist to ecological changes, and the presence of pollutants. Such knowledge is requiered for Lake Titicaca and other Andes lakes.
This project aims at extracting those patterns, at the interfaces between the Katari basin tributaries, Cohana bay, and Titicaca Lago Menor (central and northern regions), comparing the three main eutrophication gradients. Multivariate analyses will be performed between the topology of those communities, physico-chemistry, river flows, and weather conditions, to identify key response variables and bioindicator organisms, focusing on green algae, cyanobacteria, their pigments and toxins, and herbivorous zooplankton. License and Master students of UMSA Ecology (IE) and Geography (IIGEO) Institutes will collaboratively perform field woks, laboratory analyses (nutrients, pigments, plankton counts), and data analyses, under supervision by UMSA and BOREA researchers:
(1) 2019 seasonal transition: Use the already obtained measurements and samples (one year by July 2020 between campaigns and buoy monitoring), along the western Suriqui branch in Cohana bay (see map).
(2) 2020 seasonal transition: As soon as field works will be approved again, reorganize new campaigns to collect/analyze data and samples, along the southern Chojasivi branch in Cohana bay and the northern Cumana bay in Lago Menor.
To share the results in the context of the Lake Titicaca Observatory (OLT), a (virtual) workshop will be presented, and a collaborative manuscript prepared.
- Darío Achá, IE/UMSA, La Paz : Partenaire UMSA + étudiants IE impliqués dans pilote PNUD BIOREM
- Javier Nuñez IIGEO/UMSA, La Paz : Partenaire UMSA+ étudiants IIGEO impliqués dans pilote PNUD OLT
- Carlos Molina IE/UMSA, La Paz : Partenaire UMSA