Research papersEffects of land use on the hydrologic regime, vegetation, and hydraulic conductivity of peatlands in the central Peruvian Andes
Introduction
Research on South America's Andean wetlands has traditionally focused on the vegetation (Squeo et al., 2006) and its importance for livestock grazing and agriculture (Sawyer, 2008). More recently, interest in conservation and ecosystem services has stimulated the development of maps (Chimner et al., 2019) to quantify carbon stocks because many Andean wetlands are peat accumulating (Planas-Clarke et al., 2020). Research in a few areas has attempted to document a hydrologic connection between glaciers, streams, groundwater, and wetlands (Baraer et al., 2012, Vuille et al., 2018). However, there has been little detailed research on the hydrological drivers shaping these wetlands and maintaining their ecological condition (Cooper et al., 2019, Cooper et al., 2010). Understanding the hydrologic processes that support them and the factors that can disturb them is critical for managing and restoring these vital ecosystems (Millar et al., 2018, Price et al., 2005). Research is needed to evaluate the role of land uses on hydrologic processes such as water table depth and dynamics, soil hydraulic conductivity, rainfall water table dynamics, and vegetation composition and its production.
The Puna region extending along the Andes from central Peru to northern Chile and Argentina is arid, with a long dry season and sparse grassland or desert vegetation in the uplands. Peatlands, regionally termed 'bofedales' (Cooper et al., 2010, Squeo et al., 2006), are conspicuous landscape elements. Bofedales provide many critical environmental services, including pasture for livestock, natural biodiversity, and carbon storage (Benavides et al., 2013). Like other peatland types, bofedales form organic soils when net primary production (NPP) exceeds ecosystem respiration (ER), and net ecosystem productivity (NEP) is positive on a long-term basis (Rydin and Jeglum, 2015). Future increased air temperature and evapotranspiration are predicted to affect peatland carbon dynamics more in tropical than high latitude regions due to the longer warm season (Gallego-Sala et al., 2018). The rainy season could also be shortened, and precipitation events may be more intense with higher runoff and reduced soil infiltration and groundwater recharge (Westra et al., 2014).
Bofedales in the Puna region are groundwater-fed fens (Cooper et al., 2019, Cooper et al., 2010) with vegetation dominated by cushion-forming plant species in the genera Distichia and Oxychloe (family Juncaceae) (Ruthsatz, 2012). The nearly 12 months-long growing season, rapidly growing plants, and groundwater stability supports some of the highest peat accumulation rates known for any mountain region in the late-Holocene (Hribljan et al., 2015). Alteration of the vegetation composition or its production, or groundwater recharge, storage, flow, and water table depth can reduce NPP and increase ER, resulting in an annual net loss of organic matter (Millar et al., 2017). In addition, intensive year-round livestock grazing can reduce, and in many instances kill, the dominant cushion plants that are replaced by species more resistant to grazing (Cooper et al., 2015). These changes can modify the peat soil's physical characteristics, influencing its structure and functioning as natural systems with the capacity to capture and store carbon and provide pasture (Cochi Machaca et al., 2018, Schimelpfenig et al., 2014).
The upper layers of peat soils are composed of partially decomposed plant matter, live roots, and rhizomes and typically have high porosity and hydraulic conductivity (K) (Baird et al., 2004). The number and type of pores controlling soil K depend on plant inputs and organic matter accumulation and decomposition rates (McCarter et al., 2020). A deeper water table created by ditching or climate changes can dry upper soil horizons increasing decomposition rates and reducing the percentage of large pores resulting in altered groundwater flow patterns (Rezanezhad et al., 2016). The high Andes have a long history of human land use and management, particularly in peatlands used by pastoralist communities (Domic et al., 2018). Heavy livestock grazing can modify the vegetation, break up peatland soils and compress the peat (McCarter et al., 2020). This increases soil density reducing porosity and K affecting hydrological functioning (Price et al., 2003).
In this paper, we identify linkages between land uses, vegetation composition, hydrologic regime, and soil hydraulic properties in three peatlands with different land-use histories in the central Peruvian Andes. We focus on the mechanism of land use driven changes in bofedal vegetation and water table changes and the alteration of peat soil hydraulic conductivity. We hypothesized that the study peatlands had similar vegetation, hydrologic regime, landforms, and soil before the initiation of intensive livestock grazing and land management practices since the colonization period (Domic et al., 2018). We tested this hypothesis by addressing the following questions: (1) do the study sites have similar hydraulic conductivities in deep soils indicating similar organic matter inputs and peat formation processes in the past? (2) Is the current vegetation composition correlated with current land uses and water table dynamics? (3) Do shallow soils in the three study sites have distinct soil K related to their current and recent differences in land use, vegetation, and hydrological regime?
Section snippets
Methods
This research was conducted in three peatlands in central Peru's Nor Yauyos – Cochas Landscape Reserve (Fig. 1). The peatlands Huachipampa and Piticocha are on the western side of the Central Cordillera in the upper Cañete River basin in Lima Region. This area drains to the Pacific Ocean and exhibits a well-defined rainy season from December to April when ∼ 85% of the total annual precipitation occurs, with an interannual mean of 720 mm/year (Rau et al., 2017). Moyobamba is in the upper Cochas
Water table and flow patterns
A strong seasonal pattern of WT depth occurred in all three study sites (Fig. 2). The shallowest WT occurred during the wet season averaging 0.09, 0.29, and 0.28 m bgl at Moyobamba, Piticocha, and Huachipampa. The deepest WT occurred in the dry season, May through November, with average depths of 0.46, 0.51, and 0.39 m bgl for the three sites. Logger-based WT readings at HUA-12, PIT-11, and MOY-18 had similar patterns, with the WT rising during the rainy season and deepening during the dry
Origin and modern trajectories of central Andes peatlands
The similar deep soil K values, ground surface cushion and pool microtopography, and dominance of Distichia muscoides in areas with stable water availability, suggest that the three sites had a common origin, similar to other peatlands in the Peruvian Puna (Skrzypek et al., 2011). We recently collected peat cores 3–10 m long from Huachipampa, Piticocha, and seven other peatlands in the Cañete Basin headwaters, and preliminary analyses indicate that the peat is relatively homogeneous and
Conclusion
Groundwater inflow from adjacent hillslope aquifers was the principal water source for the three study peatlands. Its variability was reflected in different water-table dynamics, hydraulic conductivities, and vertical hydraulic gradients between sites. Nevertheless, similar K of the deeper peat layers, combined with a common Distichia muscoides - created cushion and pool microtopography, suggests a common origin for the three sites even though Distichia is dominant today only in areas with the
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
Nor Yauyos – Cochas Landscape Reserve Patronage (PRPNYC) supported this research through the “Nor Yauyos – Cochas wetlands hydrology” project (Agreement PRPNYC-CORBIDI/2016-2020). The authors wish to thank Pedro Lerner, Carmela Landeo, Niskar Peña, Ángela Baldoceda, and Danilo Ávila for their help with funding, fieldwork, data recording, and logistics. The data analysis and preliminary versions of this manuscript were financially supported by a Peruvian National Science and Technology Council
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