Jhasmin Duarte Tejerina¹ & Mishel Justiniano Ayllón^1
1Geographical Research Institute (IIGEO), Universidad Mayor de San Andrés (UMSA), Campus de Cota Cota, Calle 26 s/n, La Paz, Bolivia
Pilot Project UNDP/GEF 05-B-05 'Permanent Titicaca Observatory'.

Introduction -Scheonoplectus tatora, commonly known as totora, is an emergent macrophyte, endemic to the Altiplano, key to sustaining the biodiversity of fish, macroinvertebrates and aquatic birds, providing breeding, feeding and refuge habitats. On the other hand, there is abundant literature, based on observations and experiments, which demonstrates that totora contribute naturally to the purification and treatment of wastewater, originating mainly from the city of El Alto.

Objectives - The important role of totora in Titicaca Minor Lake led to the need to know the variation in their spatial distribution during the dry season between two extreme years of maximum and minimum water levels, compared to the current situation of intermediate water levels.

Study strategy – For this purpose, we used Landsat 5 and 8 satellite images as a tool. Our study allows us to assess the combined impacts of climate change and wastewater discharges from the expanding urbanization of El Alto. It allows us, indirectly, to estimate the evolution of the totora purification capacity.

Over the last 4 decades (1979-2019), based on SENAMHI data, we selected the periods of the highest water level of Lake Titicaca, 3,811.28 m asl in April 1986, and the lowest water level, 3,807.39 m asl in September 1996, representing a fluctuation range of 3.89 m. Using satellite remote sensing, we calculated the spatial extents of totora reed beds during these periods and compared them with the current spatial extent calculated in April 2019 with an intermediate level of 3,808.38 m asl. (Fig. 1).

Calculation of totora surfaces in years with extreme events - For the calculation of totora distribution surfaces, we performed a supervised classification on Landsat images of the years 1986, 1996 and 2019. 1986, 1996 and 2019. The results obtained showed that in 1986, the increase in lake level covered the totora reed beds, with a surface area of 3,786 ha (Fig. 2). In 1996, due to the low water level present that year, the surface area increased to 5,818 ha (Fig. 3). Possibly, the larger area of shallow littoral waters allowed the expansion of colonization by totoras. The area of totora reed beds was larger in 1996, it was observed that the maximum occurred at the end of the rainy season, since during the dry season, the stems dried out, turned yellowish and became more scattered.

Comparison with the current extent of totoras in Lago Menor - Using the 2019 Landsat 8 images, we calculated a totora area of 8,419 ha (Fig. 4), even larger than in 1996. This could result from the massive sediment inputs by the rivers of the Katari basin over the last two decades. This period corresponds to the accelerated development of the cities of El Alto and Viacha, plus the intensification of the quarrying of aggregates in the Seke and Seco rivers. The abundant contributions of fine sediment to the littoral sectors and Cohana Bay, combined with the progressive lowering of the lake level, cause the reduction of the depth to ≤ 50 cm, favoring the greater spatial extension of the totoras.