Sediment carbon storage increases in tropical, oligotrophic, high mountain lakes
Introduction
Earth is subject to ever-increasing transformations by humans (global change), which have accelerated during the second half of the twentieth century (Steffen et al., 2005). Lakes are amongst the most valuable sensors of global change impacts on the environment, particularly high mountain lakes. These lakes are located on the largest and highest mountains and volcanoes on the planet, and their basins, derived from orogenic processes (Catalan et al., 1993; Catalan and Camarero, 1991), are remote and usually embedded in areas of high natural value, where global change impacts are usually low (MOLAR Water Chemistry Group, 1999; Catalan and Donato Rondón, 2016). High mountain lakes have cold climates, poorly developed soils, and limited vegetation coverage (Sommaruga, 2001; Granados et al., 2006). Their main water supply is derived from atmospheric sources, either directly as precipitation (rain, snow, and hail) or indirectly through runoff and thaw. High mountain lakes usually hold cold waters (3−10 °C) with high oxygen saturation, poor mineralization, low nutrient concentrations (oligotrophic), and medium to low alkalinity (e.g., Battarbee et al., 2002a,b).
High mountain lakes are particularly sensitive to environmental changes and can be used as early alert systems (sentinels) of anthropogenic changes at local and regional scales, including global warming trends and long-distance transport of airborne particles (e.g., Adrian et al., 2009; Schindler, 2009). Because high mountain lakes worldwide share many characteristics, they are considered among the most comparable ecosystems across the world, allowing for comparisons between temperate and tropical regions (Catalan and Donato Rondón, 2016). Most high mountain lakes studies have been performed in temperate zones, while less information has come from tropical areas (Payne, 1986). Data for available tropical high mountain lakes have come mainly from the Andes (Aguilera et al., 2013), the Himalayas (Löffler, 1964), Africa (Eggermont et al., 2007; Fetahi et al., 2011; Rietti-Shati et al., 2000), and Central and South America (Löffler, 1972; Rivera et al., 2005; Widmer et al., 1975).
Although temperate and tropical high mountain lakes share many characteristics, they also present important contrasts, mainly due to differences in solar radiation (Lewis, 1996). For example, tropical high mountain lakes show higher minimum water temperatures, and their winter ice covers (common in temperate high mountain lakes) are thin or absent in the tropics (Löffler, 1964). Moreover, allochthonous organic carbon loads in temperate zones are usually low, whereas in tropical areas, they tend to be higher (Buytaert et al., 2006; Catalan and Donato Rondón, 2016) due to the high mountain vegetation above the timberline (i.e., “paramo”). Nevertheless, very few studies exist on the dynamics of organic carbon in the water column and sediments of tropical high mountain lakes (e.g., Gunkel, 2003).
The dynamics of organic carbon in lakes has received increasing attention recently (e.g., Heathcote et al., 2015; Mendonça et al., 2017) because burial in sediments removes organic carbon from the short-term biosphere-atmosphere carbon cycle. This burial contributes to reducing greenhouse gas emissions from natural systems and thus lessens climate change, one of the main ecosystem services provided by inland water bodies (Cole et al., 2007). However, the magnitude of organic carbon burial in inland waters is not well constrained, and information on tropical high mountain lakes is practically noneexistent. Moreover, human activities may affect the role of inland waters in global carbon cycling and climate forcing in ways that go unnoticed due to the remoteness of high mountain lakes and the lack of the long-term information needed to evaluate organic carbon burial trends.
Mexico has only two perennial high mountain lakes, El Sol and La Luna, both located inside the crater of the Nevado de Toluca volcano in Central Mexico, which is one of the most intensely industrialized and urbanized areas in the country (including the industrial city of Toluca and the megalopolis Mexico City). Despite the protected status of the Nevado de Toluca volcano, urbanization, illegal logging, and open-pit mining are amongst the several anthropogenic threats affecting the ecosystem services provided by the lakes. The deposition of soils eroded from the surroundings and dust transported over long distances (originated from Toluca and Mexico City; Ibarra-Morales et al., 2020) are important sources of contamination for these lakes.
Direct human impacts on the lakes have also threatened these ecosystems, such as the introduction of exotic fish (rainbow trout) during the 1950s, sport diving activities, an increasing flow of tourists visiting the lakes, and even intense subaquatic activities related to archaeological research since the 1960s (e.g., Guzmán Peredo, 1991; Luna et al., 2009; Vigliani and Junco, 2013). Changes in the diatom and planktonic cladocerans assemblages in the paleolimnological records of both lakes occurred within the timeframe of the introduction of rainbow trout (Cuna et al., 2014; Zawisza et al., 2017).
In this work, our main goal was to understand how organic carbon burial and the trophic status of both high mountain lakes have been affected by local and regional anthropogenic activities. For this purpose, we addressed the following research questions: (1) How have the water’s primary productivity and turbidity changed during the past 18 years? (2) How have organic carbon and chlorophyll-a concentrations in the surface sediments evolved in this period? (3) What are the residence times of total suspended solids and organic carbon in both lakes? (4) Have organic carbon burial rate trends changed during the past 100 years?
Our central hypothesis was that land-use changes in the surroundings of the lakes and other anthropogenic regional activities (e.g., urban and industrial development), mostly occurring since the 1950s, have affected sedimentation, productivity, and organic carbon burial in the lakes. Specifically, we expected these anthropogenic activities to cause (1) reduced water quality (higher turbidity and total suspended solids) and higher productivity (higher chlorophyll-a concentrations); (2) higher organic carbon and chlorophyll-a concentrations in surface sediments, reflecting changes in productivity and suspended matter in the water column; (3) higher residence times of total suspended solids and organic carbon in El Sol Lake, given its surface/volume ratio; and (4) larger organic carbon burial rates in both lakes caused by these trends.
To answer the research questions and test the proposed hypothesis, our approach was to evaluate the temporal changes in the (a) water quality and trophic status of the lakes using data derived from monthly monitoring of the water column and surface sediments during three periods within the past 18 years (2000−2001, 2006−2007, and 2017−2018), as well as (b) organic carbon burial rates within the past ∼100 years, from 210Pb-dated sediment cores.
Section snippets
Study area
El Sol and La Luna crater lakes (19°06′N, 99°45′W) at 4200 m a.s.l. are part of the Nevado de Toluca volcano (Fig. 1), a Pleistocene age andesitic–dacitic stratovolcano (García-Palomo et al., 2002; Bloomfield and Valastro, 1974). The Nevado de Toluca volcano has a cold alpine climate (“páramo” type), with average monthly mean air temperatures ranging from 2.8 °C in February to 5.8 °C in April (SMN-CONAGUA, 2017). The mean annual rainfall is 1244 mm, mainly between June and September, and ranges
Water transparency
The Secchi disk depth (ZSD) in La Luna was total, and the lake’s bottom could be clearly seen during the three sampling periods. Conversely, the Secchi disk depth in El Sol ranged from 22 to 69 % of the maximum depth (SI-Table 1). The Secchi disk depth in El Sol was 4.6 ± 1.0 m in 2000−2001, 5.3 ± 1.0 m in 2006−2007, and 4.1 ± 0.3 m in 2017−2018. The Secchi disk depths in 2000−2001 and 2006−2007 were statistically similar (p > 0.05), whereas the Secchi disk depths in 2017−2018 were lower (p <
Water column
The relatively high organic carbon content of surface soils around the lakes (2.6 ± 0.8 % and 13.6 ± 1.5 % in El Sol and La Luna, respectively; Ruiz-Fernández, unpublished data) suggests that the sources of allochthonous organic materials in high mountain lakes are mostly the surrounding soils and vegetation. However, the TSS composition showed that allochthonous materials make a relatively minor contribution (<10 %) compared to autochthonous sources, although this contribution is slightly
Conclusions
In conclusion, studying the temporal variations of environmental data from El Sol and La Luna lakes allowed us to answer the proposed research questions:
- (1)
Within the past 18 years, turbidity in El Sol Lake increased (lower Secchi disk depth, higher total suspended solids), but we observed no changes in productivity (comparable chlorophyll–a concentrations). No significant temporal changes were observed in La Luna Lake, and the water column Secchi disk depth, total suspended solids, and
Declaration of Competing Interest
The authors report no declarations of interest.
Acknowledgements
This work had financial support from the Fondo Sectorial de Investigación Ambiental SEMARNAT-CONACYT 2015 through project 262970, the Universidad Nacional Autónoma de México DGAPA/PAPIIT through projects IN105009 and ES209301, and Programa de Investigación en Cambio Climático (PINCC 2012-2014). The Comisión Estatal de Parques Naturales y de la Fauna (CEPANAF, Secretaría de Ecología, Gobierno del Estado de México) provided the permit for scientific research at the Área de Protección de Flora y
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2022, Quaternary Science ReviewsCitation Excerpt :In addition, increasing water temperatures and high oxygen exposition of the sediments contribute to increase TOC mineralization and CO2 production (Sobek et al., 2009; Gudasz et al., 2010; Marotta et al., 2014; Beaulieu et al., 2019). Moreover, TOC deposition is influenced by variations regarding the deposition of terrigenous components due to changes in the landscape (Anderson et al., 2013; Alcocer et al., 2020). Values of TN and TOC observed in Balma Lake core varied across the sections and drop-down events observed in levels L5, L15 and L25 could be related to decreasing temperatures due to climate changes which occurred in the late Holocene.
Sedimentary organic carbon and nutrient distributions in an endorheic lake in semiarid area of the Mongolian Plateau
2021, Journal of Environmental ManagementCitation Excerpt :For lakes located in populated areas, anthropogenic pollution is often a key factor in the degradation of water and sediment quality (Schoettle and Friedman, 1973; Smith et al., 1999; Havens and Karl, 2003; Moore et al., 2003; Jin et al., 2005; Khim et al., 2005; Ni et al., 2011; de Anda et al., 2019; Murphy and Sprague, 2019; Wen et al., 2020; Tiwari et al., 2021). Furthermore, lakes are significantly influenced by the surrounding environment, and the water and sediment quality is determined by the natural sources in the water basins, especially for an endorheic lake, which is often located in scarcely populated areas (Einola et al., 2011; Xu et al., 2013; Xie et al., 2015; van't Hoff et al., 2017; Alcocer et al., 2020). In an early study, Schoettle and Friedman (1973) examined the sedimentary organic carbon distribution in a lake in North America and found that the spatial heterogeneity of sedimentary organic carbon is related to the environmental conditions in the water basin.
Organic carbon burial in a large, deep alpine lake (southwest China) in response to changes in climate, land use and nutrient supply over the past ~100 years
2021, CatenaCitation Excerpt :Over the past century, OC accumulation rates in lakes are estimated on average to have increased ~2–3 fold (Heathcote et al., 2015; Wang et al., 2018; Anderson et al., 2020). Sediment OC burial is influenced by multiple and complex processes, which include: (a) nutrient inputs, which stimulate primary productivity (Anderson et al., 2013; Dietz et al., 2015; Gallant et al., 2020); (b) temperature and oxygen, where warmer water temperatures and longer oxygen exposure contribute to increased OC mineralization and CO2 production (Sobek et al., 2009; Gudasz et al., 2010; Marotta et al., 2014; Beaulieu et al., 2019), however in deeper lakes, warming may strengthen stratification and increase oxygen depletion in bottom waters and thus enhance OC preservation (Radbourne et al., 2017); and (c) changes in the delivery of terrestrial matter to lakes in response to landscape changes (Anderson et al., 2013; Alcocer et al., 2020). Most studies on sediment OC burial have focused on smaller, shallower lakes in boreal and northern temperate zones (e.g., Sobek et al., 2009; Gudasz et al., 2010; Anderson et al., 2014, 2020; Heathcote et al., 2015), but less attention has thus far been given to deeper lakes particularly in subtropical alpine zones.