4.3 Implications on hydrological ecosystem services
Páramo soils have a fundamental role on the hydrological cycle and the provision of ecosystem services in Andean communities (WWF, 2006), particularly for streamflow buffering (Patiño et al., 2021) . However, agricultural activities impair soil properties that sustain these services (Avellaneda-Torres et al., 2018; Dorel et al., 2000).
The present study confirms the implications of land use change on the hydrophysical properties of páramo soils for the understudied dry páramo. Agricultural activities in páramo areas affect the pore distribution in the soil (Daza-Torres et al., 2014), significantly reducing macroporosity and increasing water infiltration velocity, runoff and erosion (Hernández et al., 2009). Likewise, these activities reduce macroporosity which could favor the breakage of aggregates and increase the dispersion of clays (Jaramillo, 2002), blocking pores and limiting water retention capacity (Dorel et al., 2000). This has been evidenced by several authors that report a higher decline in the soil water retention capacity at high suctions, linked with the permanent wilting point and soil microporosity (Agudelo-Cárdenas, 2016; Camargo-García, Dossman, Rodríguez, Arias, & Galvis-Quintero, 2012; Daza-Torres et al., 2014; Farley et al., 2004; Quichimbo et al., 2012).
The removal of natural vegetation and the direct exposure of the soil to the environmental high-Andean conditions oxidize the SOM, which together with the scant input of biomass from crops, is insufficient to restore the natural soil conditions (Daza-Torres et al., 2014). The frequent cycle of turning, drying and cultivation leads to an overexploitation of the soils, ending in decline and abandonment. Although burning, a practice commonly associated with agriculture and grazing, increase the available SOM, without protection, the organic matter is rapidly oxidized and released to the atmosphere in the form of CO2, resulting in a progressive loss of SOM (Peña-Quemba et al., 2016). In the short-term, agricultural practices might seem to produce positive changes on soil properties that are useful to increase crop yields; however, in the long-term, these practices deteriorate soil hydrophysical properties (Strudley et al., 2008) and thus their hydrological regulation capacity (Patiño et al., 2021).
Agricultural activities, such as ploughing, reduce soil roughness and create artificial drainages that accelerate runoff and disrupt water storage, leading to an increase in peak flows (Buytaert, Célleri, et al., 2006). This could result in a high impact on water management in the Andean region due to the loss of dry-season base flow in surface sources originating in the páramo highlands (Buytaert et al., 2002). As result of agricultural activities, a variety of impacts have been identified: i) an increase in the ratio between peak flow and base flow (6.9) (Buytaert et al., 2004; Ochoa-Tocachi et al., 2016); ii) a reduction of the hydrological regulation capacity of up to 40%, using the linear reservoir concept (Buytaert et al., 2005); (iii) and an increase on surface runoff of up to 300% (Poulenard et al., 2001). However, other studies have found a modest increase on surface runoff (e.g., 2%, (L. Sarmiento, 2000), or a lack of statistically significant differences in soil infiltration capacity caused by the transformation of natural vegetation to crops (Hofstede, 1995). This shows the complexity of the phenomenon of land use change in páramos and the need to undertake further research in this topic (Ochoa-Tocachi et al., 2018).
New conservation practices, such as waste reuse or zero tillage in agricultural areas aiming at decreasing soil depletion (Giller et al., 2015) have been proposed to improve soil structure and reduce erosion. This is expected to maintain the soil water retention capacity (Kirkegaard et al., 2014) compared to traditional agricultural practices. These alternative practices could have a potential in páramo ecosystems, where the conflict between conservation and people’s livelihoods who have traditionally inhabited these areas is present.