User:KirstenBiefeld/Lake Titicaca

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Introduction

Lake Titicaca is settled on the northern section of the Altiplano, a high plateau nestled in the Andean mountains between Peru and Bolivia. Because of its size, in terms of both its depth and vastness, it is known as the highest navigable lake in the world at an altitude of 3,812 m (12,507 ft) at 16°S latitude. The lake is also an important aspect for humidity of the arid Altiplano water system, as it constitutes about 99% of the total surface water in the region. The lake Titicaca Basin is considered the largest freshwater body in South America, with length of around 190 km (118 miles) and about 80 km (~50 miles) at its widest point. The lake serves around 1,000,000 people who live both on the islands and the surrounding shorelines of the lake.

Limnological Background

Lake Titicaca is a warm, monomictic lake characterized with an endorheic basin. The lake mostly retains water, with its only outflow river, the Desaguadero River, accounting for less than five percent of its water losses. This closed drainage system allows the lake to act similar to a closed ecosystem, making it subject to strong evaporation. Because the loss of water is mainly through evaporation, there is a high level of dissolved solids in the lake, and its total dissolved salt content is close to one gram per liter, with a retention time of sixty-three years.

Map of Lake Titicaca

The Lake is divided into two basins. The smaller basin is Lago Pequeño (also known as Huiñaimarca), with a depth of 40m. The other, larger basin, is Lago Grande (also known as Lago Chucuito), with a maximum depth of 285m. The geographic location and the altitude of the lake subjects it to several different climatic conditions. Being in the Andean mountain range causes a climate of low air humidity, low temperatures, and high intensity of light), however there are tropical climatic conditions as well. The lake is located at a transition area between a desert fringe of the Pacific coast to the west, and the Amazonian Forest to the east.

The lake is stratified in the summer and fall seasons (November – May). During this period of stratification, there is only a small difference of the temperatures between the epilimnion (12.0-15.7°C) and the hypolimnion (11.1°C). The lake has been recorded to have a 40 m thick epilimnion in March with surface temperatures averaging 10-14°C; this layer deeps further to at least 100m by the end of July. During winter (June – September), the lake is almost isothermal as it stays around 11.1 to 11.2°C especially near the end of July.

Lake Titicaca is a part of the TDPS hydrological system a large watershed that also includes other water systems such as the Desaguadero River, Lake Poopó, and the Coipasa Salt Flat system. Lake Titicaca is connected to Lake Poopó via the Desaguadero River and water flows into this outlet in a north to south direction. Due to the inherent aridity of the region and increased irrigation upstream, Lake Titicaca promotes further salty flow into Lake Poopó. When Lake Poopó overflows at sporadic intervals, the excess spills into the other saltpans in the region, specifically the Coipasa Saltpan.

Climate Change Implications

Guaqui, a village on the shores of Lake Titicaca in La Paz, Bolivia

There is predicted to be a significant long-time warming in the Altiplano region, which will increase the rate of evapotranspiration. The TDPS system is characterized by having 70% of its total annual precipitation in its summer-time months, along with extreme climatic variability in the form of droughts and heavy precipitation. The warming climate is estimated to decrease in influx of moisture that is typically suppled from the Amazon and the Atlantic Ocean, decreasing incoming precipitation by 10-30% in 2070 and 2099.

Historically, the water levels of Lake Titicaca have a fluctuation range of 5 m. Around 80% of this fluctuation is explained by climatic variability, while the remaining 20% is from irrigation. Current climate models for the tropical Andes region are projecting an intense warming rate of 4-5°C by 2100. A study by Escurra et al. (2014) notes that the surrounding endorheic basins around Lake Titicaca have a higher potential evapotranspiration (ETP) than precipitation, which may lead to water scarcity for the local communities. High variability in precipitation levels also have lead to droughts or food shortages due to yield reductions in agriculture. Agricultural irrigation, especially along the Desaguadero River, and along with increasing temperatures and evaporation, has lead to multiple periods where Lake Poopó has dried up. In November 2016, Bolivia declared a drought in the entire country. It was most severe in the communities living in valleys and mountainous regions, and drinking water rationing has become commonplace. With warming climatic conditions along with decreasing precipitation events, droughts and dry spells are likely to worsen in the future.

Lake Research

The Peruvian Government established the Proyecto Especial del Lago Titicaca (PELT) (now known as Proyecto Especial Binacional Lago Titicaca) or the Special Project of Lake Titicaca in 1985 to carry out investigations both on the lake and in the region around it. Their main aim is to manage and conserve the natural resources, the hydrological infrastructure, and other factors if the lake that would affect agriculture development. PELT then became the executive arm of the Autoridad Autonoma del Lago Titicaca (ALT), or the Autonomous Authority for Lake Titicaca (now known as Autoridad Binacional Autonoma del Sistema Hidrico del Lago Titicaca, Rio Desaguadero, Lago Poopó y Salar de Coipasa). This organization is a jointly financed project between the government of Bolivia and Peru. They overall aim to increase access to water, sanitation and hygiene for local communities. They are also attempting to further developing an integrated water resource management system and protect and restore the local ecosystem, as well as helping the area to become resilient and adapt to future climate changes. One example of a project that they worked on had been dredging parts of the Desaguadero river to help manage the risk of flooding. They found that the water table had to be kept between 3,808 and 3,811 m.a.s.l. (meters above sea level). PELT has shared data that shows this goal has been consistently met, even when there was a high potential flooding risk in 2001.

Further experimentation was taken in 1997 with the Regional Technical Co-operation Project (RLA/8022), which was developed by the International Atomic Energy Agency, accompanied by ALT and PELT. They worked to improve current knowledge on Lake Titicaca's evaporation precipitation distribution, its lake-atmosphere interactions, and its lake dynamics with the chemical and isotopic balance and vertical mixing rate. Gonfiantini et al. (2002) found that there were significant differences in chemical and isotopic composition between the three main regions of the lake, Lago Mayor and the eastern and western basins of Lago Menor. They found the lake itself to be high in heavy isotopes and dissolved compounds in comparison to the inflow waters. This inconsistency is from the level of evaporation that occurs in the area. Lago Mayor is well mixed vertically and horizontally for both isotopic and chemical measurements, due to its size. The isotopic and chemical composition of Puno Bay is similar to that of Lago Mayor, which would suggest a good exchange of water between the two basins. However, the watershed has faced mining activities that have lead to mercury and heavy metal contamination. Human activity and a lake of proper water waste and sanitization systems have also lead to bacterial and antibiotic contaminations in the region as well. Nearly all those living on the lake islands are not connected to either a sanitation or freshwater network.

Children play outside school in the community of Maquilaya, Bolivia. The beautiful scenery with Lake Titicaca in the background masks the fact that water can be scarce here and food hard to grow. (Photo: David Stephenson)

Lake Titicaca is the largest freshwater lake in South America, and it serves one of the poorest areas of Peru and Bolivia. However, the water of Lake Titicaca is marginally brackish, and cannot be directly consumed with having a salinity range from 5.2-5.5 ppt (parts per thousand, or g/L). Researchers such as Raed Bashitialshaaer are looking into designing a reverse osmosis plant on Lake Titicaca. The lake has potential for these desalination designs, as it often has low temperature and salt concentration. The Bashitialshaaer study (2020) is also looking to power these reverse osmosis plants through the use of solar energy technology. This source of renewable energy would also help save on implementation costs and aid in the general electricity shortage in the area. Other initiatives are taking place to address other growing concerns of the lake.

A study by Duquesne et al. (2021) is working to create a model to determine risk of future algal blooms to help management of the TPDS watershed. In 2015, Lake Titicaca had its first devastating algal bloom in the shallower Lago Menor basin. As the climate is projected to warm further and contamination of the lake increases with population growth, algal blooms are expected to increase in frequency. The model simulates the topography of the lake, as well as the time-space dynamics of four variables: nitrogen-based nutrients, phytoplankton, zooplankton and detritus levels. The group was able to validate their model to effectively represent the limnological behaviors of Lake Titicaca, and see it as a valuable source in creating threshold values for nitrogen discharge to control future algal bloom events.