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Abstract

Understanding how tropical montane catchments store and release water, and the resulting water ecosystem services they provide is crucial for improving water resource management. But while research in high–elevation tropical environments has made progress in defining streamflow generation processes, we still lack fundamental knowledge regarding water storage characteristics of catchments. Here we explore catchment storage and the factors controlling its spatial variability in seven Páramo catchments (0.20–7.53 km2) in southern Ecuador. We applied a field-based approach using hydrometeorological, water stable isotopic, and soils hydrophysical data from a 3 year collection period to estimate the passive (PasS) and dynamic (DynS) storage of the catchments. We also investigated relations between these storages and landscape and hydrometric variables using linear regression analysis. PasS estimates from hydrophysical soil properties and soil water mean transit times were consistent with estimates using streamflow mean transit times. Computed catchment PasS and DynS for the seven watersheds were 313–617 mm and 29–35 mm, respectively. PasS increased directly with the areal proportion of Histosol soils and cushion plant vegetation (wetlands). DynS increased linearly with precipitation intensity. Importantly, only 6–10% of the mixing storage of the catchments (DynS/PasS) was hydrologically active in their water balance. Wetlands internal to the catchments were important for PasS, where constant input of low intensity precipitation sustained wetlands recharge, and thus, the water regulation capacity (i.e., year–round water supply) of Páramo catchments. Our findings provide new insights into the factors controlling the water regulation capacity of Páramo catchments and other peaty soils dominated environments.

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... Understanding how catchments store and release water and the resulting ecosystem services they provide is a crucial element in improving the management of these resources [1]. It has long been recognised that the role of soils is critical to these processes. ...
... In mountainous regions, changes within the landscape occur over short distances, and this creates a marked internal (i.e., subsurface) heterogeneity within soils, as well as heterogeneity in the catchment conditions. This makes it difficult to determine the direct measure of how much water is stored within particular areas of the catchment as well as the internal flow dynamics [1]. This is particularly so given the added interrelated influence of climate, geology, topography, and vegetation characteristics on the flow dynamics of these watersheds [3]. ...
... This is particularly so given the added interrelated influence of climate, geology, topography, and vegetation characteristics on the flow dynamics of these watersheds [3]. The understanding of these processes is important as mountainous headwater catchments provide key water-related services for downstream ecosystems, and the regulation of streamflow by these catchments is highly influenced by their capacity to store and release water [1]. Recent studies have shown that the way in which water is stored and transferred within catchment areas is furthermore a crucial link in generating both base flows and storm flows during precipitation events as well as influences the sediment yield [3,13]. ...
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It has long been recognised that the role of soils is critical to the understanding of the way catchments store and release water. This study aimed to gain an understanding of the hydropedological characteristics and flow dynamics of the soils of three mountain catchment areas. Digital soil maps of the hydropedological characteristics of the catchments were interpreted and a conceptual response of these watersheds to precipitation was formed. This conceptual response was then tested with the use of site-specific precipitation and streamflow data. Furthermore, piezometers were installed in soils classified as the interflow hydropedological soil group as well as the saturated responsive hydropedological soil group and water table depth data for the three catchments were analysed. Climatic data indicated that there is a lag time effect in the quantity of precipitation that falls in the catchment and the corresponding rise in streamflow value. This lag time effect coupled with data obtained from the piezometers show that the various hydropedological soil groups play a pivotal role in the flow dynamics. Of importance is the unique influence of different wetland systems on the streamflow dynamics of the catchments. The drying and wetting cycles of individual wetland systems influenced both the baseflow connectivity and the overland flow during wetter periods. They are the key focus in understanding the connectivity between the hydropedological flow paths and the contribution of soil water to the stream networks of the three catchments.
... The LMWL slope and intercept can show if evaporation plays a major role in the hydrology of surface water bodies (Brooks et al., 2012;Landwehr and Coplen, 2004). In tropical regions, the isotopic composition of precipitation, surface, and subsurface waters has been used to delineate water flow paths in headwater catchments (Crespo et al., 2011;Minaya et al., 2016;Mosquera et al., 2016a;Muñoz-Villers et al., 2016), to quantify water storage (Lazo et al., 2019), and develop conceptual models of catchment hydrological behavior (Mosquera et al., 2020a). Notably, Mosquera et al (2016a) highlighted the value of water stable isotopes to understand hydrological processes of tropical Andean catchments in relatively short time periods (1-2 years), making these tracers a particularly powerful tool to fill key hydrological knowledge gaps in remote regions where monitoring is scarce. ...
... In contrast, the strongly attenuated isotopic signal in CU presenting almost negligible variation throughout the whole study period (Fig. 6a.) probably results from its location: the CU wetland site is located at the center of a topographic depression (Fig. 1c), and the stagnation of water in the wetland leads to dampening of the isotopic signal. Similar findings have been reported for Andean wetlands in southern Ecuador (Lazo et al., 2019). ...
... Future research is needed in headwater basins underlain by Holocene volcanic deposits to determine water sources, estimate the age of water in different hydrological compartments, and quantify water storage capacity. Our data indicate that streamflow generation in tropical Andean catchments with thick volcanic ash soils and permeable bedrock differs from that in other Andean catchments with thin soils developed on hard bedrock with very low permeability (e.g., Lazo et al., 2019, Molina et al., 2019. ...
Article
Traditional hydrometric data combined with environmental tracers such as water stable isotopes contributes to improve the understanding of catchment hydrology. Nevertheless, the application of isotopic tracers in headwater catchments of the tropical Andes with deep soils and permeable parent material influenced by recent volcanism remains limited. In this study, the stable isotopic composition of precipitation, soil water, wetlands, and streamflow was studied to provide insights into the hydrology of a small tropical Andean catchment with deep and permeable volcanic soils, ash layers, and fractured bedrock resulting from Holocene volcanic activity. Although local precipitation forms under isotopic equilibrium conditions, the stable isotopic composition of precipitation is influenced by atmospheric moisture recycling processes. The spatial and temporal variability of isotopic signals and the analysis of inverse transit time proxies (ITTPs) of surface (streamflow) and subsurface (soil and wetlands) waters indicate that vertical flow paths through the deep volcanic ash soils are dominant across the catchment. The strongly damped isotopic composition of these waters points to high soil and wetlands water storage, increasing the transit time or age of stream water in the hydrological system. These findings indicate that water mobilizing through subsurface flow paths – i.e., volcanic soils, ash layers, and cracks in the fractured bedrock resulting from Holocene volcanism – is the main contributor to streamflow generation. Comparison with previously published work from Andean catchments and other volcanic areas shows the diversity of hydrological conditions that can be found as a result of pedological and lithological differences shaped by volcanic activity. Therefore, site‐specific strategies may be needed to improve water resources management. This article is protected by copyright. All rights reserved.
... (Padrón et al., 2015). Precipitation is homogeneously distributed in space and time over the study area, with no bias and low mean daily precipitation errors, as evaluated via a dense network of rain gauges (Lazo et al., 2019;Seminario, 2016). Mosquera et al. (2015) determined an average annual discharge of 786 mm, with a runoff coefficient of 0.63. ...
... This is corroborated by a study in the ZEO, where Correa et al. (2019) found the same sources and concentration-discharge relations for these solutes as for the base cations (Fig. 4). Large DOC export (16.13 kg ha −1 yr −1 ) may be due to the high amounts of organic carbon in the soils and that runoff in this ecosystem is mainly generated from the wetlands/ Histosols (Lazo et al., 2019;Pesántez et al., 2018). For a tropical rainforest catchment in Costa Rica, Sánchez-Murillo et al. (2019) found significantly lower DOC values, with an average annual rate of 6.70E-07 kg ha −1 . ...
... These findings may be related to specific ecosystem hydrometeorological and biogeochemical processes. In the ZEO, Correa et al. (2017), Lazo et al. (2019), and Mosquera et al. (2015) have highlighted the importance of wetland contributions to runoff generation. Hence, a possible explanation might be that rainfall in the ZEO is predominant during the afternoon hours (Carrillo-Rojas et al., 2019;Padrón et al., 2015), which would produce soil water recharge at night and consequently an export from shallow horizons. ...
Article
Monitoring solute fluxes in water quality studies is essential to reveal potential ecosystem disturbances, and is particularly important in Andean headwater catchments as they are the main sources of water for downstream populations. However, such studies have mainly focused on organic matter and nutrients, disregarding other solutes that can threaten water quality (e.g. arsenic, lead, calcium or magnesium). Additionally, routine low-resolution (weekly or monthly) sampling schemes may overlook important solute dynamics. Therefore, we collected water samples every four hours for the analysis of twenty-four solutes in a pristine tropical Andean páramo catchment. Solute fluxes were calculated using five different methods. The 4-hourly data set was filtered to test for an optimum sampling frequency without compromising export rates. Based on the available 4-hourly data, the results showed that the interpolation export method was best suited, due to a weak correlation with discharges. Of the twenty-four solutes analyzed, Dissolved Organic Carbon (DOC), Total Nitrogen bound (TNb), Si, Ca, Mg, K, and Na presented the highest input rates (with DOC = 4.167E+08 mEq km⁻² yr⁻¹ and Si = 1.729E+07 mEq km⁻² yr⁻¹) and export rates (with DOC = 2.686E+08 mEq km⁻² yr⁻¹ and Si = 2.953E+08 mEq km⁻² yr⁻¹). Moreover, DOC, TNb, NH4-N, NO2-N, NO3-N, PO4, Al, B, Cu, Fe, Zn, As, Cd, Cr, Pb, and V presented more input than export, while Ca, K, Mg, Na, Rb, Si, Sr, and Ba presented more export than input (geogenic sources). Filtered sampling frequencies demonstrated that a minimum of daily grab samples would be required to obtain reliable export rates with differences consistently below 10%, when compared to the 4-hourly solute export. These findings can be particularly useful for the implementation of long-term monitoring programs at low cost, and they provide high-quality information, for the first time, on biogeochemical budgets in a pristine páramo catchment.
... All these human activities lead to land use and land cover change of natural grasslands which impacts the provision of hydrological services (Célleri and Feyen, 2009;Lazo et al., 2019). However, little is known about the qualitative and quantitative nature of those impacts, nor the impacts of restoration measures to recover the hydrological functioning of high-elevation grasslands. ...
... Using a nested system of páramo catchments in southern Ecuador, Mosquera et al. (2015) applied the closure of the water balance approach to investigate how the spatial extent of undisturbed tussock grasslands influences ET flux across catchments. ET was estimated as the difference between annual P and Q assuming little to no contributions of GW and small changes in internal water storage, which are valid assumptions for the study area according to Correa et al. (2017) and Lazo et al. (2019). The results showed that ET losses were positively correlated with the area of grasslands across catchments. ...
... Quantitative evaluations of the role of biophysical landscape features in the hydrology of a nested system of eight páramo catchments in southern Ecuador (Zhurucay Ecohydrological Observatory) showed that catchments having the strongest slope gradients and fractured bedrock presented higher baseflow values (Mosquera et al., 2015), shorter water ages (Mosquera et al., 2016b), and higher water storage capacity (Lazo et al., 2019) than their counterparts, highlighting the importance of topography and geology on streamflow regulation in catchments dominated by high Andean grasslands. ...
Article
High-elevation grasslands worldwide provide essential hydrological services including water provision, flow regulation, and erosion control. Despite their importance, hydrological research of grasslands in montane regions is usually scarce and disperse, limiting the capacity to improve water resource management. We present a systematic literature review of the hydrological function of high Andean grasslands under conserved, degraded, and restored conditions in ecosystems situated above the tree line in the tropical Andes (páramos, punas, and jalcas). Most hydrological research on these grasslands has been developed in páramos (92%), especially in Ecuador, while research in punas is scarce (6%) despite being the largest grassland extent in the region. For páramos, published literature highlights the importance of conserving grasslands to facilitate water infiltration to soils, which in turn reduces erosive processes. Water-vegetation relations for conserved páramos are well understood, indicating that about 50% of water inputs return to the atmosphere via evapotranspiration, but knowledge about hydrological functions of conserved punas and jalcas is virtually non-existent. Under changing land use, afforestation of grassland ecosystems with exotic tree species, especially pines, reduces soil water storage as well as water yield and flow regulation capacity. Impacts of grazing and agriculture on the hydrological function of páramo grasslands strongly depend on historical land management and current land use practices and are not generalizable. Short-term restoration studies indicate that more than two years are necessary to recover the hydrological function of degraded grasslands, therefore medium and long-term studies are required to determine efficient restoration periods. These knowledge gaps limit the ability to extrapolate and regionalize findings. Future directions aimed to fill them are proposed, and methods successfully used to investigate the hydrology of high Andean grasslands are highlighted. This research not only enlightens what is known about the hydrology of high Andean grasslands, but also seeks to guide future hydrological evaluations to fill identified geographical and topical knowledge gaps precluding improved management of water resources in the tropical Andes.
... In this scenario, macroporosity is greatly reduced by compaction, and hydraulic conductivity in the upper soil layers can decrease by an order of magnitude (Germer et al., 2010;Hassler et al, 2011;Litt et al., 2019;Bush et al., 2020). Accompanying these impacts to soil properties can be a two-fold increase in median peak runoff rates, and a reduction in dry season baseflow when forests are converted to pasture (Bruijnzeel, 1988;Ogden et al., 2013;Guzha et al., 2015;Laxo et al., 2019;Cheng et al., 2020). The observation of this phenomenon has produced the 'forest sponge effect' hypothesis, which proposes that in comparison to pasture lands, tropical forests behave like sponges; absorbing more wet season rainfall and releasing it more slowly during the dry season than deforested land covers (Ogden et al., 2013;Cheng et al., 2020). ...
... These distinct geochemical signatures can be used to quantitatively separate the hydrograph by its contributing sources (end-members) within the catchment. However, the corresponding flowpaths inferred from EMMA and hydrograph-separation techniques often depend on antecedent moisture conditions and the rainfall characteristics of the storm event (Klaus & McDonnell, 2013;Laxo et al., 2019;Birch et al., 2021). For example, numerous studies have documented increased event (new) water contributions to stormflow in cases of decreased antecedent wetness (Marc et al., 2001;Blume et al., 2008;Pellerin et al., 2008). ...
... For example, numerous studies have documented increased event (new) water contributions to stormflow in cases of decreased antecedent wetness (Marc et al., 2001;Blume et al., 2008;Pellerin et al., 2008). The effects of rainfall intensity and volume are both spatially and temporally variable (Moore, 1989;Brown et al., 1999;Pellerin et al., 2008;Renshaw et al., 2003;Litt et al., 2015;Laxo et al., 2019;Birch et al., 2021). Studies that sample storms across a sufficient range of hydrologic conditions to account for this variability are limited, particularly in remote tropical regions (Buttle & McDonnell, 2004;Klaus & McDonnell, 2013). ...
Article
Despite abundant research documenting that land use/ land cover (LULC) have substantial impacts on the hydrology of humid tropical systems, field-based evidence for the physical mechanisms behind these impacts are still lacking. In particular, our understanding of the hydrologic flowpaths that generate runoff in these systems, and how they vary with respect to LULC is insufficient to inform both physically based hydrologic modeling and land-use decision making. In this study we use end-member mixing analysis (EMMA) of stream chemistry, and hydrometric characterizations of hillslope soil moisture to identify hydrologic flowpaths in humid tropical steep-land catchments of varying LULC-mature tropical forest, young secondary tropical forest, cattle pasture. EMMA was applied to data from 14 storm events (six at the mature forest, five at the young secondary forest, and three at the cattle pasture) that were intensively sampled during the 2017 wet season representing a wide range of rainfall magnitudes and intensities. Additionally, volumetric-soil-moisture responses at multiple depths were characterized during and after 74 storm events occurring from 2015 to 2017. EMMA results indicated that lateral preferential flow within the top 30 cm of the soil profile was a dominant source of runoff generation at two forested catchments, with the contribution of this flow path increasing with rainfall magnitude and intensity. This was corroborated by volumetric-soil-moisture data, that showed that a perched zone of saturation developed at 30 cm at the time of peak storm runoff during the largest events and lasted for the remaining duration of the event. EMMA indicated that runoff was combination of infiltration-excess overland flow and lateral subsurface flow dominated in an actively grazed pastoral catchment. There, overland flow contributed 62 % of runoff during the highest runoff rate sampled (35.3 mm/hr) and this contribution increased dramatically with storm magnitude. This flowpath identification was also supported by volumetric-soil-moisture data at the pasture, with peak saturation at all depths during the largest storm events occurring up to 30 minutes after peak runoff. These results provide a mechanistic explanation for previously observed hydrological differences among tropical LULCs. Additionally, the wide range of hydrologic conditions during these storm events provide a basis for understanding how future changes to this, and similar humid tropical regions will impact hydrological processes and water availability.
... They regulate the transport and mixing of water and solutes in the subsurface (Fan et al., 2019;Lin, 2010). Most of these soils are able to store large amounts of water in their matrix (e.g., organic rich soils; van Huijgevoort, Tetzlaff, Sutanudjaja, & Soulsby, 2016;Lazo, Mosquera, McDonnell, & Crespo, 2019) or to deliver it rapidly to streams via preferential and/or shallow subsurface flow (e.g., steep and forested catchments; Anderson, Weiler, Alila, & Hudson, 2009;McDonnell, Owens, & Stewart, 1991;Uchida, Kosugi, & Mizuyama, 1999). The hydrological behavior of mountain soils depends on their specific physical, and chemical properties (e.g., hydraulic conductivity, bulk density [BD], porosity, organic matter content, texture). ...
... In the last two decades, insights into subsurface mixing processes and water ages improved thanks to the monitoring of the stable isotopes of hydrogen and oxygen ( 2 H and 18 O) in soil waters (Sprenger, Leistert, Gimbel, & Weiler, 2016). Tracer data do not only allow to investigate how incoming precipitation mixes with water previously stored in the soils, but also for the estimation of the "age" or mean transit time (MTT; i.e., the time it takes for a water molecule to travel to the outlet of a hydrological system; McGuire & McDonnell, 2006) of water mobilizing within different soil layers/horizons (Asano, Uchida, & Ohte, 2002;Lazo et al., 2019;McGuire & McDonnell, 2010;Muñoz-Villers & McDonnell, 2012;Stumpp, Maloszewski, Stichler, & Fank, 2009;Tetzlaff, Birkel, Dick, Geris, & Soulsby, 2014). ...
... The former indicates that vertical flow paths are dominant, and the latter that there is also a significant influence of lateral subsurface flow paths. Although soil water isotopes (SWIs) in Andosols have been used to investigate runoff generation Muñoz-Villers & McDonnell, 2012) and water storage (Lazo et al., 2019) in catchments, their application in combination with hydrometric observations and detailed characterization of soil properties is still inexistent. This situation hinders our ability to disentangle flow paths and mixing processes in hillslopes dominated by volcanic ash soils. ...
Article
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Andosol soils formed in volcanic ash provide key hydrological services in montane environments. To unravel the subsurface water transport and tracer mixing in these soils we conducted a detailed characterization of soil properties and analyzed a 3-year data set of sub-hourly hydrometric and weekly stable isotope data collected at three locations along a steep hillslope. A weakly developed (52-61 cm depth), highly organic andic (Ah) horizon overlaying a mineral (C) horizon was identified, both showing relatively similar properties and sub-surface flow dynamics along the hillslope. Soil moisture observations in the Ah horizon showed a fast responding (few hours) "rooted" layer to a depth of 15 cm, overlying a "perched" layer that remained near saturated year-round. The formation of the latter results from the high organic matter (33-42%) and clay (29-31%) content of the Ah horizon and an abrupt hydraulic conductivity reduction in this layer with respect to the rooted layer above. Isotopic signatures revealed that water resides within this soil horizon for short periods, both at the rooted (2 weeks) and perched (4 weeks) layer. A fast soil moisture reaction during rainfall events was also observed in the C horizon, with response times similar to those in the rooted layer. These results indicate that despite the perched layer, which helps sustain the water storage of the soil, a fast vertical mobilization of water through the entire soil profile occurs during rainfall events. The latter being the result of the fast transmissivity of hydraulic potentials through the porous matrix of the Andosols, as evidenced by the exponential shape of the water retention curves of the subsequent horizons. These findings demonstrate that the hydrological behavior of volcanic ash soils resembles that of a "layered sponge," in which vertical flow paths dominate. K E Y W O R D S Andosol/andisol, hillslope hydrology, soil moisture, stable isotopes, subsurface flow path, transit time, tropical alpine (Páramo), vadose/unsaturated zone
... Km 2 ), which later was used as the comparative framework to evaluate our understanding of runoff generation processes and water production controllers of P aramo catchments. Recent research in the Zhurucay observatory revealed that runoff generation is controlled by water originated from the catchment dominant soils, with small contributions from shallow groundwater (i.e., spring water) and rainfall (Correa et al., 2017, ;Lazo et al., 2019;Mosquera et al., 2015;Mosquera, Célleri, et al., 2016;Mosquera, Segura, et al., 2016). The same potential sources (or "end members") were monitored with the addition of lake water. ...
... The importance of wetlands in water storage and streamflow regulation has been widely recognized in mountainous ecosystem studies (Katsuyama et al., 2005;Lazo et al., 2019;Roa-García et al., 2011;Weiler et al., 2003). In the P aramo, for instance, Mosquera et al. (2015) found that the specific discharge of a nested system of catchments was strongly correlated with the area of Histosols or permanently saturated zones (wetlands) within the catchments. ...
Article
Hydrogeochemical based mixing models have been successfully used to investigate the composition and source identification of streamflow. The applicability of these models is limited due to the high costs associated with data collection and the hydrogeochemical analysis of water samples. Fortunately, a variety of mixing models exist, requiting different amount of data as input, and in data scarce regions it is likely that preference will be given to models with the lowest requirement of input data. An unanswered question is if models with high or low input requirement are equally accurate. To this end, the performance of two mixing models with different input requirement, the mixing model analysis (MMA) and the end‐member mixing analysis (EMMA), were verified on a tropical montane headwater catchment (21.7 km²) in the Ecuadorian Andes. Nineteen hydrogeochemical tracers were measured on water samples collected weekly during three years in streamflow and eight potential water sources or end‐members (precipitation, lake water, soil water from different horizons and springs). Results based on 6 conservative tracers, revealed that EMMA (using all tracers) and MMA (using pair‐combinations out of the 6 conservative ones), identified the same end‐members: rainfall, soil water and spring water., as well as, similar contribution fractions to streamflow from rainfall 21.9% and 21.4%, soil water 52.7% and 52.3%, and spring water 26.1% and 28.7%, respectively. Our findings show that a hydrogeochemical mixing model requiring a few tracers can provide similar outcomes than models demanding more tracers as input data. This underlines the value of a preliminary detailed hydrogeochemical characterization as basis to derive the most cost‐efficient monitoring strategy. This article is protected by copyright. All rights reserved.
... Several hydrological studies have been carried out in recent years in Andean páramo catchments, ranging from understanding hydrological processes and runoff generation (Mosquera et al., 2015;Correa et al., 2017Correa et al., , 2019Mosquera et al., 2018;Lazo et al., 2019) to the impacts of agriculture (Buytaert et al., 2005(Buytaert et al., , 2006Crespo et al., 2010;Ochoa-Tocachi et al., 2016a) and afforestation with exotic species (Buytaert et al., 2007;Crespo et al., 2012;Bonnesoeur et al., 2019Bonnesoeur et al., , 2018Marín et al., 2018). Similar studies have been conducted in Andean forests (Tobón, 2008;Roa-García et al., 2011;Crespo et al., 2012). ...
Article
Full-text available
Andean ecosystems provide important hydrological services for downstream communities. Due to this importance, several hydrological studies have been carried out in recent years, with emphasis on hydrological processes identification and land use change impacts. In several studies, but also for the operation of small-scale irrigation and drinking water projects, small streams have been equipped with compound, sharp-crested weirs for discharge estimation. To transform the water level (stage) into a discharge (water rate), weir equations use theoretical discharge coefficients, which do not necessarily apply under the actual field conditions, mainly site fluviomorphology and weir construction aspects, introducing uncertainty in their measurements. Therefore, this study analyzes the effect of using theoretical coefficients instead of adjusted coefficients in field. The study was conducted on 9 micro-catchments (0.2 – 7.53 km2) located in the Zhurucay Ecohydrological Observatory in the páramo of southern Ecuador. To calibrate the coefficients, discharge curves were generated by mechanical and salt-dilution gauging methods. Results revealed that the discharge coefficients differed from their theoretical value by up to 15% for triangular (V-notch) weir section (DCvn) and by up to 41% for rectangular weir section (DCr). The DCvn affects 4 times more in low and medium discharges estimation than DCvn in high discharges. On the other hand, salt-dilution method is more precise for medium and high discharges, but at very low discharges, it overestimates discharge up to 10%. Overall, results suggest that it is essential to calibrate the discharge coefficients in the field to avoid errors in hydrological studies.
... Páramo ecosystems have been recognized for the high carbon content of their soils and their role in water regulation and supply (Tonneijck et al. 2010;Benavides et al. 2018;Lazo et al. 2019). Although ample variation in soils characteristics occurs across the region, in general, it is accepted that these large accumulations of soil carbon are a consequence of the reduced decomposition of organic matter that results from cold weather and, in some areas, stabilization effects brought about by the presence of volcanic ash deposits (Poulenard et al. 2003(Poulenard et al. , 2004Tonneijck et al. 2010). ...
Article
Full-text available
Páramo peatlands are a regional reservoir of biodiversity and ecosystem services, accumulating large amounts of carbon and buffering water flows. Despite their importance, they have a long history of use and impacts including drainage for agriculture and grazing, and water withdrawal for human uses. Here we present a preliminary assessment of the conservation status of páramo peatlands in Ecuador and, using a case study, discuss peatland restoration as a tool for mitigation and adaptation to the impacts of current climate change. Through a simple index assessing the cumulative presence of signs of human activities on 163 peatland sites, we found that the level of impact was higher for peatlands located in the Western branch of the cordillera, whereas current human population density, precipitation, and elevation were not significant predictors of the levels of impact. Also, starting in 2017, we implemented a pilot restoration initiative on a 21-ha peatland which had been drained and converted into pasture for at least 150 years. The restoration consisted of two ditch blocking techniques implemented to stop fast-moving water and promote the rewetting of the peatland. During the next 3 years, water table increased from 27 ± 3 cm below the soil surface to 7 ± 1 cm by 2021, while wetland plant communities are colonizing and closing the pools in the blocked ditches. Re-wetting of the peatland has led to an increase in the abundance of native species. This case study suggests that restoration initiatives are an efficient and cost-effective approach to a better management of páramo peatlands, with high potential as a tool for mitigation and adaptation to climate change.
... First, a very high synchronicity can be observed between precipitation and runoff series at both the high mountain environment (La Laja) and at the outlet of the paramo sector (Playitas). It is somewhat surprising that given the high water storage capacity of the paramos (Célleri & Feyen, 2009;Flores-López et al., 2016;Lazo et al., 2019), the response to previously accumulated precipitation is almost direct, with a maximum lag time of one month (Fig. 7). This response suggests that the soils of the paramos store large amounts of water, and are able to provide a consistent baseflow, This article is protected by copyright. ...
Article
This study extends knowledge of the evolution of glacier shrinkage in the Cocuy‐Güican Mountains since the maximum glacier extent of the Little Ice Age (LIA). Mass balance data for the Ritacuba Glacier since 2009 was acquired and compared with available data for the Conejeras Glacier (Los Nevados National Park). This study also investigated the hydrological significance of Colombian glaciers, which is still largely unknown because the available information is very limited. Glaciers in the Cocuy‐Güican Mountains covered 13.2 km2 in 2019 compared with 127.8 km2 during the maximum LIA, representing a shrinkage of 89.7%. Analysis of glacier cover observations made in 1955, 1994, 2010, and 2019 revealed that the rate of ice loss was greatest from 1994 to 2010 (0.59 km2 yr‐1), and was then almost halved from 2010 to 2019 (0.34 km2 yr‐1). This slowing of glacier retreat is consistent with the moderate negative mass balance measured for 2009‐2019, and an accumulated loss of 1766 mm w.e. (mm water equivalent). The progressive confinement of glaciers to higher elevations, ice accumulation in topographic locations providing shelter from solar radiation, and an absence of recent marked climatic anomalies could explain why the Cocuy‐Güican glaciers have temporally reached a near equilibrium state conditions. This contrasts with the Conejeras Glacier, where 47,000 mm w.e. has been lost in the same period. The available data on runoff and isotope tracers of streamflow and precipitation suggest that precipitation rather than glacier melt water exerts primary control over the hydrological variability at high elevation sites. This article is protected by copyright. All rights reserved.
... Like all wet páramo ecosystems, the Zhurucay is a strategic source of water (SENPLADES, 2017) and a prime carbon storage zone . These attributes make the Zhurucay an ideal place for investigating the hydrological, meteorological, and ecological processes of páramo ecosystems (e.g., Carrillo-Rojas et al., 2020;Lazo et al., 2019;Ochoa-Sánchez et al., 2020). ...
Article
In high-altitude Andean grasslands (páramo), overgrazing leads to alterations in both vegetation and microclimate. These alterations need to be identified to devise land management strategies that will preserve and enhance ecosystem processes. To elucidate this issue, we designed an overgrazing experiment: we selected two plots covered with native grass (pajonal), in one of which we mowed to the ground surface. We left the second plot undisturbed to serve as a control. For both plots, we continuously monitored albedo and ancillary energetic components to generate quarterly and yearly comparisons for the following parameters: (a) impacts on albedo and resilience of grass; (b) radiative forcing of albedo; and (c) land surface temperature feedback during the recovery period. In the first quarter following removal, when the soil was covered with light litter, median albedo increased 38.81% (0.16 ± 0.02), then began a gradual decrease, which continued until its full recovery 1.75 years later (0.10 ± 0.01). During the first year of the experiment, a strong mean negative instantaneous radiative forcing was observed (−7.08 ± 6.03 Wm⁻²), signifying a reduction in net shortwave energy. This forcing returned to normal, pre-intervention conditions (−0.55 ± 0.97 Wm⁻²) after 1.75 years, equal to the energetic recovery period of the grass. Both the amount (from 133.0 ± 44.72 to 119.67 ± 39.30 Wm⁻²) and the partitioning (net shortwave decreased 5%; net longwave increased 9.7%) of net energy were altered after removal, evidence of cooling feedback during the recovery period. This feedback indicated that the decrease in albedo (1.25%) or instantaneous radiative forcing (4.67 Wm⁻²) resulted in a decrease in land surface temperature of 1 °C. Thus, our overgrazing experiment without soil destruction followed by a natural recovery time has identified the energetic recovery period for grass in the páramos; suggesting the albedo as a good indicator of grass resilience.
... Satellite viewVegetation affects pollutant concentrations by altering airflows(Stevens et al. 2020) and also assists in storing water in the soil(Lazo et al. 2019;Mobasheri et al. 2019). Moreover, planting trees and not covering the site with pavements allow water absorption and pollutant dispersal. ...
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This research aimed to explain the conceptual persistence of spatial transformations in the Joglo house nDalem Puspodiningratan based on Hamemayu Hayuning Bawana philosophy. This philosophy is the public wisdom directed towards maintaining a harmonious relationship between humans and each other, nature, and God. This philosophy is applied in several dimensions of the Javanese life such as the architecture which is meaningfully designed. Moreover, the Hamemayu Hayuning Bawana is observed to be playing an important role in the spatial configuration of the traditional Joglo house. It is important to note that nDalem Puspodiningratan is a traditional Joglo house with a well-maintained condition and which undergoes a spatial transformation due to the inhabitation of alternating families. This research was, therefore, conducted using visual observation and documentation, literature review, interviews, graphic method, and comparison to explore the Joglo transformation data and background. The results showed the Joglo nDalem Puspodiningratan persisted in preserving the Hamemayu Hayuning Bawana's philosophical principles despite the spatial transformations. Meanwhile, the transformations discovered to be violating the traditional house rules are believed to be reducing the Hamemayu Hayuning Bawana practice while those observed to be following the rules maintain the practice. There is a need for further research on the transformations of traditional buildings in other cases of the traditional Javanese architecture to show the existence of spatial transformations and conceptual persistence related to Hamemayu Hayuning Bawana.
... Although it is not possible for each site to use the tritium profile for SW dating, other alternative methods can be used for this purpose, such as chloride mass balance (Phillips et al., 1988). All the regressed equations include precipitation, indicating the overwhelming importance of precipitation in predicting SW (Dekker et al., 2007;Lazo et al., 2019;Wang et al., 2020;Yuan et al., 2021;Zhang et al., 2020a). This implies that it may be more accurate to develop models for each climate type. ...
Article
Identifying the variability and predominant factors affecting soil water (SW) is essential in regions with thick vadose zones and deep-rooted plants. This information is needed to clarify the balance between water availability and plant water demand. We collected 9263 soil samples from 128 profiles of 7–25 m deep soil under different climates (arid, semiarid and subhumid), soil textures and plant types (shallow or deep roots) in China's Loess Plateau. The factors dominating the horizontal and vertical variability of SW were identified using a multimodel inference approach and stepwise regression analysis. Horizontally, the mean water content and storage increased while the water deficits decreased from the northwest to the southeast. Vertically, mean water content and storage are highest in the relatively stable layer, followed by rapidly changing layers and active layers. Plant age and soil clay content dominate the horizontally varied SW, while plant age and normalized difference vegetation index (NDVI) dominate the vertical variability of SW. However, the dominant factors appeared to differ with climate and plant type. It was determined that for climate, soil clay content and plant age in arid regions, precipitation and plant age in semiarid regions, NDVI and plant age in subhumid regions were important factors. For plants, the dominant factors are NDVI and precipitation under shallow-rooted plants; however, NDVI and plant age were dominant under deep-rooted plants. The dominance of plant age highlighted the impact of vegetation patterns on SW, especially for deep-rooted plants, which should be taken into account when managing water resources and ecosystem rehabilitation in degraded regions.
... A SOC case study in Cameroon, on 3 horizons (0-15 cm, 15-30 cm and 30-100 cm) of soil used a hybrid machine learning modelling and legacy soil data, provided R 2 values between 0.52 and 0.67 for SOC ranges between 11 and 210 Mg/ha at the 0-30 cm horizon. In the case of study areas with large elevation ranges, the elevation and the weather variables precipitable water vapor and rain are typically linked with SOC [109]. In a Chinese case study with great variety of vegetation and soil types and distribution patterns, 67% of variation was explained by DEM and NDVI parameters through an artificial neural network combined with kriging (ANN-kriging), and regression tree (RT) models [28]. ...
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Background Soil organic carbon (SOC) affects essential biological, biochemical, and physical soil functions such as nutrient cycling, water retention, water distribution, and soil structure stability. The Andean páramo known as such a high carbon and water storage capacity ecosystem is a complex, heterogeneous and remote ecosystem complicating field studies to collect SOC data. Here, we propose a multi-predictor remote quantification of SOC using Random Forest Regression to map SOC stock in the herbaceous páramo of the Chimborazo province, Ecuador. Results Spectral indices derived from the Landsat-8 (L8) sensors, OLI and TIRS, topographic, geological, soil taxonomy and climate variables were used in combination with 500 in situ SOC sampling data for training and calibrating a suitable predictive SOC model. The final predictive model selected uses nine predictors with a RMSE of 1.72% and a R² of 0.82 for SOC expressed in weight %, a RMSE of 25.8 Mg/ha and a R² of 0.77 for the model in units of Mg/ha. Satellite-derived indices such as VARIG, SLP, NDVI, NDWI, SAVI, EVI2, WDRVI, NDSI, NDMI, NBR and NBR2 were not found to be strong SOC predictors. Relevant predictors instead were in order of importance: geological unit, soil taxonomy, precipitation, elevation, orientation, slope length and steepness (LS Factor), Bare Soil Index (BI), average annual temperature and TOA Brightness Temperature. Conclusions Variables such as the BI index derived from satellite images and the LS factor from the DEM increase the SOC mapping accuracy. The mapping results show that over 57% of the study area contains high concentrations of SOC, between 150 and 205 Mg/ha, positioning the herbaceous páramo as an ecosystem of global importance. The results obtained with this study can be used to extent the SOC mapping in the whole herbaceous ecosystem of Ecuador offering an efficient and accurate methodology without the need for intensive in situ sampling.
... p < 0.01), while the relationship between NDVI and C TWSC was positively correlated (r = 0.37, p < 0.01). The opposite effect of vegetation on R and TWSC has been confirmed by previous studies (Lazo et al., 2019;Sun et al., 2018;Ukkola et al., 2015;Yang et al., 2019a;Zhao et al., 2012). On the one hand, vegetation reduces R by rainfall intercept and transpiration (Iida et al., 2020;Yan et al., 2021), on the other hand, vegetation increases the soil infiltration rate, which promotes P to recharge TWS (Liu et al., 2014;Sun et al., 2018). ...
Article
Streamflow from forested mountain watersheds is critical to aquatic ecosystems and social development in watersheds. However, understanding the intra-annual variability of streamflow is limited by the lack of observation of terrestrial water storage (TWS) in large-scale watersheds. This study developed a monthly Budyko framework incorporating TWS from the Gravity Recovery and Climate Experiment (GRACE). The extended Budyko framework was applied using four classic Budyko equations in the Qinba Mountains. The results showed that the extended Budyko framework could competently represent the relationship between monthly water supply and demand, with better performance than the original Budyko framework. Based on the extended Budyko framework, this study further quantified the contributors of streamflow variability using the variance decomposition method. The dominant contributor to intra-annual streamflow variability was precipitation (50%), followed by TWS (11%) and their covariance (-21%) in this region. Specifically, precipitation played a dominant role on streamflow variability in summer and autumn, while evapotranspiration and TWS significantly impacted streamflow in spring and winter, respectively. Furthermore, the hydrologic effects of rainfall intensity and vegetation were investigated to explain streamflow variability. As the rainfall intensity decreases, more precipitation is partitioned into evapotranspiration and TWS, while the increase of rainfall intensity leads to the partitioning of precipitation into streamflow. Similarly, monthly vegetation promotes the partitioning of precipitation into TWS, while inhibiting the partitioning of precipitation into streamflow. The opposite effect of vegetation on streamflow and TWS is weakened due to the neglect of TWS at an annual timescale, which may lead to an overestimation of the effect of annual vegetation on streamflow. The results have implications for improving the performance of the Budyko framework to reveal the relationship between monthly water supply and demand and understanding streamflow variability at an intra-annual timescale.
... For example, Staudinger et al. (2017) found dynamic storage is increasingly derived from snow and groundwater in mountain watersheds as elevation increases. Lazo et al. (2019) documented that passive storage positively correlates with the proportion of soils with high water-holding capacity. Xiao et al. (2019) showed that catchments with steeper hillslopes tended to have smaller dynamic storage because of their smaller riparian-to-hillslope ratios. ...
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Large‐scale models often use a single grid to represent an entire catchment assuming homogeneity; the impacts of such an assumption on simulating evapotranspiration (ET) and streamflow remain poorly understood. Here, we compare hydrological dynamics at Shale Hills (PA, USA) using a complex model (spatially explicit, >500 grids) and a simple model (spatially implicit, two grids using “effective” parameters). We asked two questions: What hydrological dynamics can a simple model reproduce at the catchment scale? What processes does it miss by ignoring spatial details? Results show the simple model can reproduce annual runoff ratios and ET, daily discharge peaks (e.g., storms, floods) but not discharge minima (e.g., droughts) under dry conditions. Neither can it reproduce different streamflow from the two sides of the catchment with distinct land surface characteristics. The similar annual runoff ratios between the two models indicate spatial details are not as important as climate in reproducing annual scale ET and discharge partitioning. Most of the calibrated parameters in the simple model are within the ranges in the complex model, except that effective porosity has to be reduced to 40% of the average porosity from the complex model. The form of the storage‐discharge relationship is similar. The effective porosity in the simple model however represents the dynamic and mobile water storage in the effective drainage area of the complex model that connects to the stream and contributes to high streamflow; it does not represent the passive, immobile water storage in the often disconnected uphill areas. This indicates that an additional uphill functioning unit is needed in the simple model to simulate the full spectrum of high‐low streamflow dynamics in natural catchments.
... Activities such as ploughing break soil structure, increase its macro-porosity, and facilitate water infiltration. However, water is not retained efficiently in a ploughed soil structure and, therefore, river discharge will increase following rainfall events (Buytaert et al., 2005b;Lazo et al., 2019). ...
Article
The páramos biome of the northern Andes is a collection of high-mountain tropical grassland wetland ecosystems that provides important ecosystem services including hydrological buffering and water supply. Human activities in these ecosystems transform vegetation cover and soil hydro-physical properties, affecting their hydrological performance and water quality and quantity. Here, we conducted a systematic review on the influence of land use (agriculture, livestock grazing, and afforestation) on the hydro-physical properties of páramo soils and analyzed its implications for streamflow buffering. Our review protocol identified 32 relevant papers, from which key hydro-physical properties linked to streamflow variability were available: soil organic matter (SOM), soil organic carbon (SOC), porosity, bulk density, saturated hydraulic conductivity, and water retention capacity (WRC). The analysis shows that soils with native cover are characterized by a porous structure that allows a high WRC and SOM content. Agriculture increases macroporosity but it leads to bare fallow plots that promote loss of nutrients and SOM. Burning generates hydrophobic aggregates that affect WRC. Livestock grazing produces soil compaction and increases bulk density, reducing infiltration and WRC. Lastly, afforestation with exotic species (e.g. pines, eucalyptus) decreases SOM and WRC by changing soil structure. In general, the analyzed land-use activities generate hydrophobic aggregates, increase bulk density, promote erosion and runoff, and impair hydrological buffering capacity. This integrated evidence from multiple empirical studies can be used to effectively communicate the effects of different land use practices on páramo soils, provide information for modelling in data-scarce situations, and contribute to decision making processes for land use planning and conservation.
... Páramo ecosystems, a diverse set of high elevation vegetation types from the Northern Andes, offer a striking example of the disproportionate role that mountain ecosystems have in the provision of ecosystem services (Lazo et al. 2019). Páramo ecosystems account for less than 1 percent of the total land in Venezuela, Colombia, Peru, and Ecuador, yet millions of people from these countries depend on páramo ecosystems for the provision of water for human consumption and sanitation, and large portions of their economy rely on that same water supply for irrigation and generation of energy (International Union for Conservation of Nature 2002). ...
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The Andean páramo is notable for high soil carbon storage and its contribution to ecosystem services. However, the páramo’s ability to maintain high soil carbon levels is threatened by land use change from tussock grassland and shrublands to agricultural uses. A chronosequence study was conducted in the páramo around Quito, Ecuador, to determine the rate of soil carbon loss from traditional fallow agriculture. In parallel, a land use and land cover classification of Landsat images was used to measure the change in agricultural areas between 1991 and 2017. There was a significant negative relationship between the time since initial cultivation of a field and soil C: Older agricultural sites had significantly less C compared to natural ecosystems due to an average loss of 0.045 percent soil C per year. Undisturbed sites had significantly more soil C than cultivated sites but not pastures or fallow fields, indicating that cultivation is the most detrimental stage of the fallow agricultural cycle for soil C storage. There was an 838 percent increase in cultivated land between 1991 and 2017 but a 10 percent decrease in pastures, indicating a trend away from traditional regenerative agriculture toward land use types that lead to substantial losses in soil carbon.
... Our findings are in line with observations by Preti et al. [55,56] in that increasing accumulations of water behind a wall (high values of flow accumulation) lead to increasing levels of damage severity. However, while flow accumulation only provides information about where water tends to concentrate, to understand the real water concentration, other factors need to be considered as well, including (i) precipitation at the event scale, (ii) infiltration, and (iii) vegetation cover [58]. All these factors play an important role with regard to the amount of water that reaches a dry-stone wall. ...
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Agricultural terraces are an important element of the Italian landscape. However, abandonment of agricultural areas and increase in the frequency of destructive rainfall events has made it mandatory to increase conservation efforts of terraces to reduce hydrological risks. This requires the development of new approaches capable of identifying and mapping failed or prone-to-fail terraces over large areas. The present work focuses on the development of a more cost-effective alternative, to help public administrators and private land owners to identify fragile areas that may be subject to failure due to the abandonment of terracing systems. We developed a simple field protocol to acquire quantitative measurements of the degree of damage—dry stone wall deformation—and establish a damage classification system. This new methodology is tested at two different sites in Tuscany, central Italy. The processing is based on existing DTMs derived from Airborne Laser Scanner (ALS) data and open source software. The main GIS modules adopted are flow accumulation and water discharge, processed with GRASS GIS. Results show that the damage degree and terrace wall deformation are correlated with flow accumulation even if other factors other than those analyzed can contribute to influence the instability of dry stone walls. These tools are useful for local land management and conservation efforts.
... La capacidad de regulación de la cuenca se analiza año tras año a través de la construcción de curva de regulación hídrica y su respectivo valor del Índice de Regulación Hídrica (IRH) (ENA, 2018). La regulación hídrica en cuencas hidrográficas se da por las características de suelo y de las coberturas vegetales (Lazo Et Al., 2019). Suponiendo las condiciones del suelo invariables, en el estudio se maneja la hipótesis de que el cambio de regulación hídrica en la cuenca está asociado al cambio en las características de coberturas vegetales. ...
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La ocupación humana y sus actividades productivas dan lugar a los cambios de las coberturas, que afectan los servicios ecosistémicos y específicamente los servicios de regulación hídrica. La cuenca alta del río Chinchiná, es una cuenca que ha presentado cambios en sus coberturas vegetales y este cambio afecto su sistema de regulación hídrica, a esta conclusión se llegó realizando el análisis multitemporal de las coberturas y el análisis hidrológico a través de la construcción de las curvas de duración de caudales para los años con información geoespacial. Entre los resultados se encontró que, por sus condiciones iniciales en las características del suelo y las coberturas vegetales, la cuenca alta del río Chinchiná no tiene una buena capacidad de regulación de la escorrentía superficial, echo que se agrava por las dinámicas de expansión de las coberturas herbáceas y de pastos durante los años del estudio. El conocimiento de la relación entre los cambios de coberturas y la regulación de la escorrentía superficial, permite proyectar el uso adecuado de la tierra con el propósito de no afectar aún más la capacidad de regulación de la escorrentía superficial que sirve como fundamento de la biodiversidad, abastecimiento de la ciudad de Manizales.
... Habitat guilds have been proposed as a broad and useful approach to understand the effects of habitat modification on birds in tropical grasslands (Mckinney and Lockwood 1999;Tews et al. 2004) as well as in páramo grassland (Lazo et al. 2019). Avian trophic guilds, defined by habitat affinity and food preferences, are sensitive indicators of land-use change when these modifications impact the structure and composition of natural habitats (Hooper et al. 2012;Grass et al. 2013). ...
Article
El ecosistema de páramo alberga una alta concentración de especies de aves de rango restringido y amenazadas. Sin embargo, las modificaciones humanas al paisaje altoandino han generado pérdida y fragmentación de hábitat en todo este ecosistema. Por lo tanto, las áreas protegidas en esta región son prioritarias para la conservación de la biodiversidad. Las zonas de amortiguamiento en los alrededores de las áreas protegidas tienen por objeto reducir las perturbaciones en éstas; sin embargo, no están exentas de fuentes de estrés. La abundancia y la diversidad de aves, registradas en transectas, se usó para comparar la composición de la comunidad entre áreas protegidas y zonas de amortiguamiento en un hotspot de diversidad y endemismo: la Reserva de la Biósfera del Macizo del Cajas, en los altos Andes del sur del Ecuador. La comunidad de aves no varió en su composición entre las áreas protegidas y las zonas de amortiguamiento. No obstante, las características del hábitat sí explicaron diferencias en la presencia y abundancia de grupos tróficos. En particular, el incremento en la heterogeneidad del páramo, con mayor cobertura de plantas leñosas y menos intervención, explicó una mayor presencia y abundancia de gremios tróficos especializados, tales como nectarívoros en arbustos e insectívoros aéreos en árboles y arbustos. En conclusión, hay hábitats heterogéneos de páramo, en zonas de amortiguamiento, que deben considerarse en una planificación de conservación más formal para mantener la diversidad de aves especialistas y, por lo tanto, la funcionalidad del ecosistema de páramo herbáceo.
... Those samples were collected at approximately 14 sampling locations roughly separated 150 m from each other along three transects across the Zhurucay Observatory (41 sampling locations in total). The sampling strategy was designed such that the soil samples were collected at different positions along the hillslopes(Lazo, Mosquera, McDonnell, & Crespo, 2019). Samples were collected accordingly at the toe, the lower, the middle, and the upper sections of the hillslopes, as well as at the hilltops (i.e., the positions A-E inFigure 2b). ...
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Accurate determination of the water retention curve (WRC) of a soil is essential for the understanding and modelling of the subsurface hydrological, ecological, and biogeochemical processes. Volcanic ash soils with andic properties (Andosols) are recognized as important providers of ecological and hydrological services in mountainous regions worldwide due to their large fraction of small size particles (clay, silt, and organic matter) that gives them an outstanding water holding capacity. Previous comparative analyses of in situ (field) and standard laboratory methods for the determination of the WRC of Andosols showed contrasting results. Based on an extensive analysis of laboratory, experimental, and field measured WRCs of Andosols in combination with data extracted from the published literature we show that standard laboratory methods using small soil sample volumes (≤300 cm³) mimic the WRC of these soils only partially. The results obtained by the latter resemble only a small portion of the wet range of the Andosols’ WRC (from saturation up to ‐5 kPa, or pF 1.7), but overestimate substantially their water content for higher matric potentials. This discrepancy occurs irrespective of site‐specific land use and cover, soil properties, and applied method. The disagreement limits our capacity to infer correctly subsurface hydrological behavior, as illustrated through the analysis of long‐term soil moisture and matric potential data from an experimental site in the tropical Andes. These findings imply that results reported in past research should be used with caution and that future research should focus on determining laboratory methods that allow obtaining a correct characterization of the WRC of Andosols. For the latter, a set of recommendations and future directions to solve the identified methodological issues is proposed. This article is protected by copyright. All rights reserved.
... Such waterways have a function in storing and draining water from rainfall and other water sources. Water storage and drainage areas are arranged according to the natural conditions around them (Lazo et al. 2019). ...
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Sastranegara MH, Kusbiyanto, Pulungsari AE. 2020. Species richness and longitudinal distribution of crustaceans in the Logawa River, Banyumas, Indonesia. Biodiversitas 21: 5322-5330. The Logawa River originates in a forest on Slamet Mountain and empties into the Serayu River. In this river, crustaceans play an important role as river macrobenthos. This research aimed to evaluate the species richness and longitudinal distribution of crustaceans. The research method was a stratified random sampling technique at eight stations with five replicates. Crustacean samples were collected using a Surber net, and water samples were taken with a water sampler. The results showed that there were six species of Decapoda in the river. Of these six species, three were shrimps and three were crabs. In longitudinal distribution, the shrimp Macrobrachium idae could be categorized as a cosmopolitan species that inhabited all stations, although there were several river branches before Stations IV (Cangkring Stream), V (Mengaji Stream), and VI (Banjaran Stream), bedrock substrate at Station I, high ammonia at all stations and high chemical oxygen demand (COD) between Stations IV and VIII. The crab Varuna litterata was found only at Station VI. In general, the species richness decreased after Station IV due to COD from the riverside. This was caused by human activities such as stone and sand excavation and overfishing in the habitat. The upstream habitat with its bedrock substrate was not suitable for decapods, except for cosmopolitan species.
... Habitat guilds have been proposed as a broad and useful approach to understand the effects of habitat modification on birds in tropical grasslands (Mckinney and Lockwood 1999;Tews et al. 2004) as well as in páramo grassland (Lazo et al. 2019). Avian trophic guilds, defined by habitat affinity and food preferences, are sensitive indicators of land-use change when these modifications impact the structure and composition of natural habitats (Hooper et al. 2012;Grass et al. 2013). ...
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A�������. The páramo ecosystem harbors a high concentration of restricted range and threatened bird species. However, human modifications to the high Andean landscape have generated habitat loss and fragmentation throughout this ecosystem. Therefore, protected areas in this region are a priority for biodiversity conservation. Buffer zones around protected areas aim to reduce perturbation within them. However, these areas are still not exempt from sources of stress. We used abundance and diversity of birds, recorded by walking transects, in order to compare the community composition occurring in protected areas and adjacent buffer zones in a hotspot of diversity and endemism: the Macizo del Cajas Biosphere Reserve, in the southern high-Andes of Ecuador. The bird community did not vary in its composition between protected areas and buffer zones. However, the habitat characteristics explained differences in the presence and abundance of trophic guilds. Particularly, increasingly heterogeneous páramo grassland with greater woody plant cover and less intervention explained a greater presence and abundance of more specialized trophic guilds such as nectarivores in shrubs and aerial insectivores in trees and shrubs. We conclude that there are heterogeneous páramo habitats in buffer zones that should be considered in more formal conservation planning to maintain the diversity of specialized birds and therefore functionality of the páramo grassland ecosystem. [Keywords: páramo grassland, Macizo del Cajas Biosphere Reserve, elevation, trophic guilds, specialist birds] R������. La heterogeneidad del hábitat, en lugar de los límites de las áreas protegidas, influye en las comunidades de aves de una reserva de biosfera Andina. El ecosistema de páramo alberga una alta concentración de especies de aves de rango restringido y amenazadas. Sin embargo, las modificaciones humanas al paisaje altoandino han generado pérdida y fragmentación de hábitat en todo este ecosistema. Por lo tanto, las áreas protegidas en esta región son prioritarias para la conservación de la biodiversidad. Las zonas de amortiguamiento en los alrededores de las áreas protegidas tienen por objeto reducir las perturbaciones en éstas; sin embargo, no están exentas de fuentes de estrés. La abundancia y la diversidad de aves, registradas en transectas, se usó para comparar la composición de la comunidad entre áreas protegidas y zonas de amortiguamiento en un hotspot de diversidad y endemismo: la Reserva de la Biósfera del Macizo del Cajas, en los altos Andes del sur del Ecuador. La comunidad de aves no varió en su composición entre las áreas protegidas y las zonas de amortiguamiento. No obstante, las características del hábitat sí explicaron diferencias en la presencia y abundancia de grupos tróficos. En particular, el incremento en la heterogeneidad del páramo, con mayor cobertura de plantas leñosas y menos intervención, explicó una mayor presencia y abundancia de gremios tróficos especializados, tales como nectarívoros en arbustos e insectívoros aéreos en árboles y arbustos. En conclusión, hay hábitats heterogéneos de páramo, en zonas de amortiguamiento, que deben considerarse en una planificación de conservación más formal para mantener la diversidad de aves especialistas y, por lo tanto, la funcionalidad del ecosistema de páramo herbáceo. [Palabras clave: páramo herbáceo, Reserva de la Biósfera Macizo del Cajas, elevación, gremios tróficos, aves especialistas]
... The dynamic storage of the catchment increases with rainfall intensity, while the passive storage with larger wetlands extent. Less than 10% of passive storage is hydrologically active in the water balance(Lazo, Mosquera, McDonnell, & Crespo, 2019). The carbon source behaviour of páramos was evidenced by a net positive exchange of CO 2 (Carrillo-Rojas et al., 2019). ...
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Páramos, a neotropical alpine grassland‐peatland biome of the northern Andes and Central America, play an essential role in regional and global cycles of water, carbon, and nutrients. They act as water towers, delivering water and ecosystem services from the high mountains down to the Pacific, Caribbean, and Amazon regions. Páramos are also widely recognized as a biodiversity and climate change hot spots, yet they are threatened by anthropogenic activities and environmental changes. Despite their importance for water security and carbon storage, and their vulnerability to human activities, only three decades ago, páramos were severely understudied. Increasing awareness of the need for hydrological evidence to guide sustainable management of páramos prompted action for generating data and for filling long‐standing knowledge gaps. This has led to a remarkably successful increase in scientific knowledge, induced by a strong interaction between the scientific, policy, and (local) management communities. A combination of well‐established and innovative approaches has been applied to data collection, processing, and analysis. In this review, we provide a short overview of the historical development of research and state of knowledge of the hydrometeorology, flux dynamics, anthropogenic impacts, and the influence of extreme events in páramos. We then present emerging technologies for hydrology and water resources research and management applied to páramos. We discuss how converging science and policy efforts have leveraged traditional and new observational techniques to generate an evidence base that can support the sustainable management of páramos. We conclude that this co‐evolution of science and policy was able to successfully cover different spatial and temporal scales. Lastly, we outline future research directions to showcase how sustainable long‐term data collection can foster the responsible conservation of páramos water towers.
... Tracer methods require that source waters have substantial differences in chemical composition, and the time-varying chemistry of source waters is well quantified (Andermann et al., 2012;Brauer et al., 2013). Stream-derived storage values usually differ from those derived from soil moisture and groundwater measurements because not all subsurface water storage is dynamically connected to the stream (Dralle et al., 2018;Lazo et al., 2019). Consequently, methods for quantifying storage can differ by up to an order of magnitude (McNamara et al., 2011;Staudinger et al., 2017). ...
Article
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The discipline of hydrology has long focused on quantifying the water balance, which is frequently used to estimate unknown water fluxes or stores. While technologies for measuring water balance components continue to improve, all components of the balance have substantial uncertainty at the watershed scale. Watershed-scale evapotranspiration, storage, and groundwater import or export are particularly difficult to measure. Given these uncertainties, analyses based on assumed water balance closure are highly sensitive to uncertainty propagation and errors of omission, where unknown components are assumed negligible. This commentary examines how greater insight may be gained in some cases by keeping the water balance open rather than applying methods that impose water balance closure. An open water balance can facilitate identifying where unknowns such as groundwater import/export are affecting watershed-scale streamflow. Strategic improvements in monitoring networks can help reduce uncertainties in observable variables and improve our ability to quantify unknown parts of the water balance. Improvements may include greater spatial overlap between measurements of water balance components through coordination between entities responsible for monitoring precipitation, snow, evapotranspiration, groundwater, and streamflow. Measuring quasi-replicate watersheds can help characterize the range of variability in the water balance, and nested measurements within watersheds can reveal areas of net groundwater import or export. Well-planned monitoring networks can facilitate progress on critical hydrologic questions about how much water becomes evapotranspiration, how groundwater interacts with surface watersheds at varying spatial and temporal scales, how much humans have altered the water cycle, and how streamflow will respond to future climate change.
... The MTT of the organic horizon of the wetland soils (Histosols) varies between 212 and 292 days, and the MTT of the mineral horizon of these soils is 338 days. The water storage of the catchment available for mixing with precipitation is 457 mm, with only 6% of this storage being in the catchment water balance (Lazo, Mosquera, McDonnell, & Crespo, 2019). ...
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The problem of discharge forecasting using precipitation as input is still very active in Hydrology, and has plethora of approaches to its solution. But, when the objective is to simulate discharge values without considering the phenomenology behind the processes involved, Artificial Neural Networks, ANN give good results. However, the question of how the black box internally solve this problem remains open. In this research the classical rainfall‐runoff problem is approached considering that the total discharge is a sum of components of the hydrological system, which from the ANN perspective is translated to the sum of three signals related to the fast, middle and slow flow. Thus, the present study has two aims, i) to study the time‐frequency representation of discharge by an ANN hydrologic model, and ii) to study the capabilities of ANN to additively decompose total river discharge. This study adds knowledge to the open problem of the physical interpretability of black‐box models, which remains very limited. The results show that total discharge is adequately simulated in the time frequency domain, although less power spectrum is evident during the rainy seasons in the ANN model, due to fast flow underestimation. The wavelet spectrum of discharge represents well the slow, middle and fast flow components of the system with transit times of 256 days, 12 to 64 days and 2 to 12 days, respectively. Interestingly, these transit times are remarkably similar to those of the soil water reservoirs of the studied system, a small headwater catchment in the tropical Andes. This result needs further research because it opens the possibility of determining MMT on a fraction of the cost of isotopic based methods. The cross‐power spectrum indicates that the error in the simulated discharge is more related to the misrepresentation of the fast and the middle flow components, despite limitations in the recharge period of the slow flow component as observed. With respect to the representation of individual signals of the slow, middle and fast flows components, the three neurons were uncapable to individually represent such flows. However, the combination of pairs of these signals resemble the dynamics and the spectral content of the aforementioned flows signals. These results show some evidence that signal processing techniques may be used to infer information about the hydrological functioning of a basin. This article is protected by copyright. All rights reserved.
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Vegetation changes that are driven by soil conservation measures significantly affect subsurface water flow patterns and soil water status. Much research on water consumption and sustainability of newly introduced vegetation types at the plot scale has been done in the Loess Plateau of China (LPC), typically using local scale measurements of soil water content (SWC). However, information collected at the plot scale cannot readily be up‐scaled. Geophysical methods such as electromagnetic induction (EMI) offer large spatial coverage and, therefore, could bridge between the scales. A noninvasive, multicoil, frequency domain, EMI instrument was used to measure the apparent soil electrical conductivity (σa) from six effective depths under four typical land‐covers (shrub, pasture, natural fallow, and crop) in the north of the LPC. Concurrently, SWC was monitored to a depth of 4 m using an array of 44 neutron probes distributed along the plots. The measurements of σa for six effective depths and the integrated SWC over these depths, show consistent behavior. High variability of σa under shrub cover, in particular, is consistent with long term variability of SWC, highlighting the potential unsustainability of this land cover. Linear relationships between SWC and σa were established using cumulative sensitivity forward models. The conductivity–SWC model parameters show clear variation with depth despite lack of appreciable textural variation. This is likely related to the combined effect of elevated pore water conductivity as was illustrated by the simulations obtained with water flow and solute transport models. The results of the study highlight the potential for the implementation of the EMI method for investigations of water distribution in the vadose zone of the LPC, and in particular for qualitative mapping of the vulnerability to excessive vegetation demands and hence, unsustainable land cover. An increasing trend in apparent electrical conductivity (ECa) corresponds with the increase in soil water content (SWC) under four typical land‐covers. Linear relationships between SWC and ECa were established using the cumulative sensitivity model. Elevated pore water conductivity effects the relationship between conductivity and SWC.
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Los páramos colombianos son ecosistemas estratégicos en cuanto al suministro de diferentes servicios ambientales, incluyendo servicios asociados al recurso hídrico. A pesar de las acciones encaminadas hacia la conservación de páramos, muchos de estos se encuentran intervenidos por diferentes actividades antrópicas. La cuenca del río Gachaneca I del páramo Rabanal no es la excepción a estas dinámicas y, aunque una parte de la cuenca está en buen estado de conservación, otra se caracteriza por la ocupación de cultivos transitorios que vulnera la prestación de servicios de provisión y de regulación hídrica. En este estudio se diseñó una metodología en donde se evaluó el efecto que genera el desarrollo de actividades agrícolas sobre los servicios hídricos. Entre los principales hallazgos se encontró que la oferta hídrica media disminuyó en un 8,8% bajo el escenario de presión por agricultura, llegando a ser equivalente a la oferta hídrica en los meses de estiaje de años hidrológicos secos. La variabilidad interanual del recurso hídrico incrementa en un 9,9% indicando una mayor irregularidad en la oferta temporal de escorrentía superficial y, como consecuencia, mayor irregularidad del servicio de provisión del agua. El desarrollo de actividades de riego disminuye en un 27,8% la capacidad de regulación de la cuenca que, por sus condiciones de suelo y coberturas vegetales, no dispone de una condición natural apropiada para regular la escorrentía superficial. De esta manera, es necesario profundizar en la investigación de este panorama para mitigar los efectos negativos sobre este tipo de ecosistemas.
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This is an investigation carried out through a systematic literature review prepared in order to study the current situation of the páramos in Colombia through the Parsifal program (Stefany Urquijo, nd) in which inclusion and exclusion criteria were implemented for the Selection of articles to which data extraction was carried out by means of questions based on the effects of climate change and human actions on the ecosystems of the páramos, so that they would serve to propose solutions to the current problems of the country by means of alternatives for the care and protection of critical points in high mountain areas in charge of the water regulation process. These ecosystems vulnerable to climate change and other factors have been deteriorating due to the actions of man, agriculture, livestock, mining and the use of the land that is being given to these areas, and which in turn destroys no only the ecosystems of Colombian paramos but the quality of human life.
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Hydrological extremes such as floods and droughts are the most common and threatening natural disasters worldwide. Particularly, tropical Andean headwaters systems are prone to hazards due to their complex climate conditions. However, little is known about the underlying mechanisms triggering such extremes events. In this study, the Generalized Additive Models for Location, Scale and Shape (GAMLSS) were used for investigating the relations between the Annual-Peak-Flows (APF) and Annual-Low-Flows (ALF), respecting to climate and land use/land cover (LULC) changes. Thirty years of daily streamflow data-sets taken from two Andean catchments of southern Ecuador are used for the experimental research. Global climate indices (CI), describing the large-scale climate variability were used as hypothetical drivers explaining the extreme's variations on streamflow measures. Additionally, the Antecedent-Cumulative-Precipitation (AP) and the Standardized-Precipitation-Index (SPI), and LULC percentages were also included as possible direct drivers – synthetizing local climate conditions and localized hydrological changes. The results indicate that AP and SPI clearly explain the extreme streamflow variability. Nonetheless, global variables play a significant role underneath the local climate. For instance, ENSO and CAR exert influence over the APF, while ENSO, TSA, PDO and AMO control ALF. Furthermore, it was found that LULC changes strongly influence both extremes; although this is particularly important for relative more disturbed catchments. These results provide valuable insights for future forecasting of floods and droughts based on precipitation and climate indices, and for the development of mitigation strategies for mountain catchments.
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In places with high spatiotemporal rainfall variability, such as mountain regions, input data could be a large source of uncertainty in hydrological modeling. Here we evaluate the impact of rainfall estimation on runoff modeling in a small páramo catchment located in the Zhurucay Ecohydrological Observatory (7.53 km2) in the Ecuadorian Andes, using a network of 12 rain gauges. First, the HBV-light semidistributed model was analyzed in order to select the best model structure to represent the observed runoff and its subflow components. Then, we developed six rainfall monitoring scenarios to evaluate the impact of spatial rainfall estimation in model performance and parameters. Finally, we explored how a model calibrated with far-from-perfect rainfall estimation would perform using new improved rainfall data. Results show that while all model structures were able to represent the overall runoff, the standard model structure outperformed the others for simulating subflow components. Model performance (NSeff) was improved by increasing the quality of spatial rainfall estimation from 0.31 to 0.80 and from 0.14 to 0.73 for calibration and validation period, respectively. Finally, improved rainfall data enhanced the runoff simulation from a model calibrated with scarce rainfall data (NSeff 0.14) from 0.49 to 0.60. These results confirm that in mountain regions model uncertainty is highly related to spatial rainfall and, therefore, to the number and location of rain gauges.
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In response to increasing pressures on water resources, watershed-services management programs are implemented throughout the tropics. These programs aim to promote land management activities that enhance the quantity and quality of water available to local communities. The success of these programs hinges on our ability to i) understand the impacts of watershed interventions on ecohydrology; ii) model these impacts and design efficient management programs; and iii) develop strategies to overcome barriers to practical policy development, including resource limitations or the absence of baseline data. In this paper, we review opportunities in ecohydrological science that will help address these three challenges. The opportunities are grouped into measurement techniques, modeling approaches, and access to resources in our hyperconnected world. We then assess management implications of both the knowledge gaps and the new research developments related to the effect of land management. Overall, we stress the importance of policy-relevant knowledge for implementing efficient and equitable watershed-services programs in the tropics.
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The framework for ecosystem services has been increasingly used in integrated watershed ecosystem management practices that involve scientists, engineers, managers, and policy makers. The objective of this review is to explore the intimate connections between ecohydrological processes and water-related ecosystem services in human-dominated ecosystems in the Anthropocene. We synthesize current literature to illustrate the importance of understanding the ecohydrological processes for accurately quantifying ecosystem services under different environmental and socioeconomic settings and scales. Our synthesis focuses on managed ecosystems that are dominated by humans and explores how ecological processes affect the tradeoffs and synergies of multiple ecosystem services. We identify research gaps in studying ecological processes mainly including energy, carbon, water, and nutrient balances to better assess and quantify ecosystem services that are critical for sustaining natural resources for future generations. To better assess ecosystem services, future ecohydrological studies need to better account for the scaling effects of natural and anthropogenic stressors exerted on evapotranspiration and other water supply and demand processes. Future studies should focus on the bidirectional interactions between hydrological functions and services and human actions to solve real world problems such as water shortages, ecological degradation, and climate change adaptation.
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Tropical ecosystems offer a unique setting for understanding ecohydrological processes, but to date such investigations have been limited. The purpose of this paper is to highlight the importance of studying these processes—specifically, how they are being affected by the transformative changes taking place in the tropics—and to offer an agenda for future research. At present, the ongoing loss of native ecosystems is largely due to agricultural expansion, but parallel processes of afforestation are also taking place, leading to shifts in ecohydrological fluxes. Similarly, shifts in water availability due to climate change will affect both water and carbon fluxes in tropical ecosystems. A number of methods exist that can help us better understand how changes in land use and climate affect ecohydrological processes; these include stable isotopes, remote sensing, and process-based models. Still, our knowledge of the underlying physical mechanisms, especially those that determine the effects of scale on ecosystem processes, remains incomplete. We assert that development of a knowledge base concerning the effects of transformative change on ecological, hydrological, and biogeochemical processes at different spatio-temporal scales is an urgent need for tropical regions, and should serve as a compass for emerging ecohydrologists. To reach this goal, we advocate a research agenda that expands the number and diversity of ecosystems targeted for ecohydrological investigations and connects researchers across the tropics. We believe that the use of big data and open source software—already an important integrative tool/skill for the young ecohydrologist—will be key in expanding research capabilities.
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Payments for Hydrologic Services (PHS) programs are increasingly used as a policy tool to provide incentives for upstream landowners to adopt land use activities that favor sustainable provision of high-quality water to downstream areas. However, the effectiveness of PHS programs in achieving their objectives and the potential for unintended (often undesirable) consequences remain poorly understood. We integrate results from ecohydrological and socioeconomic research to explore the impact of Mexico's PHS program on the target hydrologic services and people's decisions, behavior, and knowledge regarding forest conservation and water. Using central Veracruz as our case study, we identify areas of both synchrony and disconnection between PHS goals and outcomes. Mature and regenerating cloud forests (targeted by PHS) were found to produce enhanced hydrologic services relative to areas converted to pasture, including reduced peak flows during large rain events and maintenance of dry-season base flows. However, unexpectedly, these hydrologic benefits from cloud forests were not necessarily greater than those from other vegetation types. Consequently, the location of forests in strategic watershed positions (e.g., where deforestation risk or hydrologic recharge are high) may be more critical than forest type in promoting hydrologic functions within watersheds and should be considered when targeting PHS payments. While our results suggest that participation in PHS improved the level of knowledge among watershed inhabitants about forest-water relationships, a mismatch existed between payment amounts and landowner opportunity costs, which may contribute to the modest success in targeting priority areas within watersheds. Combined, these findings underscore the complexity of factors that influence motivations for PHS participation and land use decisions and behavior, and the importance of integrating understanding of both ecohydrological and socioeconomic dynamics into PHS design and implementation. We conclude by identifying opportunities for improving the design of PHS programs and recommending priority areas for future research and monitoring, both in Mexico and globally.
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The bedrock controls on catchment mixing, storage, and release have been actively studied in recent years. However, it has been difficult to find neighboring catchments with sufficiently different and clean expressions of geology to do comparative analysis. Here, we present new data for 16 nested catchments (0.45 to 410 km2) in the Alzette River basin (Luxembourg) that span a range of clean and mixed expressions of schists, phyllites, sandstones and quartzites to quantify the relationships between bedrock permeability and metrics of water storage and release. We examined 9 years’ worth of precipitation and discharge data, and 6 years of fortnightly stable isotope data in streamflow, to explore how bedrock permeability controls (1) streamflow regime metrics, (2) catchment storage and (3) isotope response and catchment mean transit time (MTT). We used annual and winter precipitation-runoff ratios, as well as average summer and winter precipitation-runoff ratios to characterize the streamflow regime in our 16 study catchments. Catchment storage was then used as a metric for catchment comparison. Water mixing potential of 12 catchments was quantified via the standard deviation in streamflow δD (σδD) and the amplitude ratio (AS/AP) of annual cycles of δ18O in streamflow and precipitation. Catchment MTT values were estimated via both stable isotope signature damping and hydraulic turnover calculations. In our 16 nested catchments, the variance in ratios of summer vs. winter average runoff was best explained by bedrock permeability. While active storage (defined here as a measure of the observed maximum inter-annual variability in catchment storage) ranged from 107 to 373 mm, total catchment storage (defined as the maximum catchment storage connected to the stream network) extended up to ~1700 mm [+/- 200 mm]. Catchment bedrock permeability was strongly correlated with mixing proxies of σδD in streamflow and δ18O AS/AP ratios. Catchment mean transit time (MTT) values ranged from 0.5 to 2 years, based on stable isotope signature damping, and from 0.5 to 10 years, based on hydraulic turnover.
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Near-surface air temperature variation with altitude (Tlr) is important for several applications including hydrology, ecology, climate, and biodiversity. To calculate Tlr accurately, a dense monitoring network over an altitudinal gradient is needed. Typically, meteorological monitoring in mountain regions is scarce and not adequate to calculate Tlr correctly. To overcome this problem in our region, we monitored temperature over a gradient ranging 2600–4200 m a.s.l. during an 18 month period. Using these data, we calculated Tlr for the first time at this altitude in the Andes and tested the impact of using the standard Tlr values instead of the observed ones to map temperature by means of the MTCLIM model. We found that annual lapse rate values (6.9 °C km−1 for Tmean, 5.5 °C km−1 for Tmin, and 8.8 °C km−1 for Tmax) differ significantly from the MTCLIM default values and that temperature maps improved vastly when measured Tlr was entered, especially for Tmax and Tmin. Our results may be representative of the broader area, as Tlr in our study period is not affected by microclimatic conditions generated by differences in topography and land cover between our monitoring sites; moreover, observed temperature during our study period was found to be representative of the longer-term annual climatology of the region.
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This study focuses on the investigation of the mean transit time (MTT) of water and its spatial variability in a tropical high-elevation ecosystem (wet Andean páramo). The study site is the Zhurucay River Ecohydrological Observatory (7.53 km2) located in southern Ecuador. A lumped parameter model considering five transit time distribution (TTD) functions was used to estimate MTTs under steady-state conditions (i.e., baseflow MTT). We used a unique data set of the δ18O isotopic composition of rainfall and streamflow water samples collected for 3 years (May 2011 to May 2014) in a nested monitoring system of streams. Linear regression between MTT and landscape (soil and vegetation cover, geology, and topography) and hydrometric (runoff coefficient and specific discharge rates) variables was used to explore controls on MTT variability, as well as mean electrical conductivity (MEC) as a possible proxy for MTT. Results revealed that the exponential TTD function best describes the hydrology of the site, indicating a relatively simple transition from rainfall water to the streams through the organic horizon of the wet páramo soils. MTT of the streams is relatively short (0.15–0.73 years, 53–264 days). Regression analysis revealed a negative correlation between the catchment's average slope and MTT (R2 = 0.78, p < 0.05). MTT showed no significant correlation with hydrometric variables, whereas MEC increases with MTT (R2 = 0.89, p < 0.001). Overall, we conclude that (1) baseflow MTT confirms that the hydrology of the ecosystem is dominated by shallow subsurface flow; (2) the interplay between the high storage capacity of the wet páramo soils and the slope of the catchments provides the ecosystem with high regulation capacity; and (3) MEC is an efficient predictor of MTT variability in this system of catchments with relatively homogeneous geology.
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In Part 1 of this 2-part series, Hale and McDonnell [2015] showed that bedrock permeability controlled baseflow mean transit times (MTT) and MTT scaling relations across two different catchment geologies in western Oregon. This paper presents a process-based investigation of storage and release in the more permeable catchments to explain the longer MTTs and (catchment) area-dependent scaling. Our field-based study includes hydrometric, MTT, and groundwater dating to better understand the role of subsurface catchment storage in setting baseflow MTTs. We show that baseflow MTTs were controlled by a mixture of water from discrete storage zones: 1) soil; 2) shallow hillslope bedrock; 3) deep hillslope bedrock; 4) surficial alluvial plain; and 5) sub-alluvial bedrock. We hypothesize that the relative contributions from each component changes with catchment area. Our results indicate that the positive MTT-area scaling relationship observed in Part 1 is a result of older, longer flowpath water from the suballuvial zone becoming a larger proportion of streamflow in a downstream direction (i.e., with increasing catchment area). Our work suggests that the subsurface permeability structure represents the most basic control on how subsurface water is stored and therefore is perhaps the best direct predictor of baseflow MTT (i.e. better than previously-derived morphometric-based predictors). Our discrete storage zone concept is a process explanation for the observed scaling behavior of Hale and McDonnell [2015], thereby linking patterns and processes at scales from 0.1 to 100 km2. This article is protected by copyright. All rights reserved.
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This study focuses on the investigation of the yet unknown mean transit time (MTT) of stream waters and its spatial variability in tropical alpine ecosystems (wet Andean páramo). The study site is the Zhurucay River Ecohydrological Observatory (7.53 km2) located in south Ecuador. A lumped parameter model considering five transit time distribution (TTD) functions was used to estimate MTTs. We used a unique data set of δ18O and δ2H isotopic composition of rainfall and streamflow water samples collected for three years (May 2011-May 2014) in a nested monitoring system of streams. Linear regression between MTT and landscape (soil and vegetation cover, geology, and topography) and hydrometric (runoff coefficient and specific discharge rates) variables was used to determine controls on MTT variability, as well as mean electrical conductivity (MEC) as a possible proxy for MTT. Results revealed that the exponential TTD function best describes the hydrology of the site, indicating a relatively simple transition from rainfall water to the streams through the organic horizon of the wet páramo soils. MTT of the streams is relatively short (0.15-0.73 yr, 53-264 days). Regression analysis revealed negative correlation between the catchment’s average slope and MTT (R2 = 0.78, p < 0.05). MTT showed no significant correlation with hydrometric variables whereas MEC increases with MTT (R2 = 0.89 p < 0.001). Overall, we conclude that: 1) MTT of streams confirms that the hydrology of the ecosystem is dominated by shallow subsurface flow; 2) the interplay between the high storage capacity of the wet páramo soils and the slope of the catchments provides the ecosystem with high regulation capacity; and 3) MEC is an efficient predictor of MTT variability in this system of catchments with relatively homogeneous geology.
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Cosmic ray neutron sensors (CRS) are a promising technique to measure soil moisture at intermediate scales. To convert neutron counts to average volumetric soil water content a simple calibration function can be used (the N0-calibration of Desilets et al., 2010). This calibration function is based on soil water content derived directly from soil samples taken within the footprint of the sensor. We installed a CRS in a mixed forest in the lowlands of north-eastern Germany and calibrated it 10 times throughout one calendar year. Each calibration with the N0-calibration function resulted in a different CRS soil moisture time series, with deviations of up to 0.12 m3 m-3 for individual values of soil water content. Also, many of the calibration efforts resulted in time series that could not be matched with independent in situ measurements of soil water content. We therefore suggest a new calibration function with a different shape that can vary from one location to another. A two-point calibration proved to be adequate to correctly define the shape of the new calibration function if the calibration points were taken during both dry and wet conditions covering at least 50 % of the total range of soil moisture. The best results were obtained when the soil samples used for calibration were linearly weighted as a function of depth in the soil profile and non-linearly weighted as a function of distance from the CRS, and when the depth-specific amount of soil organic matter and lattice water content was explicitly considered. The annual cycle of tree foliation was found to be a negligible factor for calibration because the variable hydrogen mass in the leaves was small compared to the hydrogen mass changes by soil moisture variations. Finally, we provide a best practice calibration guide for CRS in forested environments.
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We characterize how regional watersheds function as simple, dynamic systems through a series of hysteresis loops using measurements from NASA's Gravity Recovery and Climate Experiment (GRACE) satellites. These loops illustrate the temporal relationship between runoff and terrestrial water storage in three regional-scale watersheds (> 150 000 km2) of the Columbia River Basin, USA and Canada. The shape and size of the hysteresis loops are controlled by the climate, topography, and geology of the watershed. The direction of the hystereses for the GRACE signals moves in opposite directions from the isolated groundwater hystereses. The subsurface water (soil moisture and groundwater) hystereses more closely resemble the storage-runoff relationship of a soil matrix. While the physical processes underlying these hystereses are inherently complex, the vertical integration of terrestrial water in the GRACE signal encapsulates the processes that govern the non-linear function of regional-scale watersheds. We use this process-based understanding to test how GRACE data can be applied prognostically to predict seasonal runoff (mean Nash-Sutcliffe Efficiency of 0.91) and monthly runoff during the low flow/high demand month of August (mean Nash-Sutcliffe Efficiency of 0.77) in all three watersheds. The global nature of GRACE data allows this same methodology to be applied in other regional-scale studies, and could be particularly useful in regions with minimal data and in trans-boundary watersheds.
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Reference evapotranspiration (ETo) is often calculated using the Penman-Monteith (FAO 56 PM; Allen et al 1998) method, which requires data on temperature, relative humidity, wind speed, and solar radiation. But in high-mountain environments, such as the Andean páramo, meteorological monitoring is limited and high-quality data are scarce. Therefore, the FAO 56 PM equation can be applied only through the use of an alternative method suggested by the same authors that substitutes estimates for missing data. This study evaluated whether the FAO 56 PM method for estimating missing data can be effectively used for páramo landscapes in the high Andes of southern Ecuador. Our investigation was based on data from 2 automatic weather stations at elevations of 3780 m and 3979 m. We found that using estimated wind speed data has no major effect on calculated ETo but that if solar radiation data are estimated, ETo calculations may be erroneous by as much as 24%; if relative humidity data are estimated, the error may be as high as 14%; and if all data except temperature are estimated, errors higher than 30% may result. Our study demonstrates the importance of using high-quality meteorological data for calculating ETo in the wet páramo landscapes of southern Ecuador.
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To assess the influence of storage dynamics and non-linearities in hydrological connectivity on time-variant stream water ages, we used a new long-term record of daily isotope measurements in precipitation and stream flow to calibrate and test a parsimonious tracer-aided runoff model. This can track tracers and the ages of water fluxes through and between conceptual stores in steeper hillslopes, dynamically saturated riparian peatlands and deeper groundwater; these represent the main landscape units involved in runoff generation. Storage volumes are largest in groundwater and on the hillslopes, though most dynamic mixing occurs in the smaller stores in riparian peat. Both stream flow and isotope variations are generally well-captured by the model, and the simulated storage and tracer dynamics in the main landscape units are consistent with independent measurements. The model predicts that the average age of stream water is ∼1.8 years. On a daily basis, this varies between ∼1 month in storm events, when younger waters draining the hillslope and riparian peatland dominates, to around 4 years in dry periods when groundwater sustains flow. This variability reflects the integration of differently aged water fluxes from the main landscape units and their mixing in riparian wetlands. The connectivity between these spatial units varies in a non-linear way with storage that depends upon precipitation characteristics and antecedent conditions. This, in turn, determines the spatial distribution of flow paths and the integration of their contrasting non-stationary ages. This approach is well-suited for constraining process-based modelling in a range of northern temperate and boreal environments. This article is protected by copyright. All rights reserved.
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Predicting runoff source areas and how they change through time is a challenge in hydrology. Topographically induced lateral water redistribution and water removal through evapotranspiration lead to spatially and temporally variable patterns of watershed water storage. These dynamic storage patterns combined with threshold mediation of saturated subsurface throughflow lead to runoff source areas that are dynamic through time. To investigate these processes and their manifestation in watershed runoff, we developed and applied a parsimonious but spatially distributed model (WECOH—Watershed ECOHydrology). Evapotranspiration was measured via an eddy-covariance tower located within the catchment and disaggregated as a function of vegetation structure. This modeling approach reproduced the stream hydrograph well and was internally consistent with observed watershed runoff patterns and behavior. We further examined the spatial patterns of water storage and their evolution through time by building on past research focused on landscape hydrologic connectivity. The percentage of landscape area connected to the stream network ranged from less than 1% during the fall and winter base flow period to 71% during snowmelt. Over the course of the 2 year study period, 90% of the watershed areas were connected to the stream network for at least 1 day, leaving 10% of area that never became connected. Runoff source areas during the event shifted from riparian dominated runoff to areas at greater distances from the stream network when hillslopes became connected. Our modeling approach elucidates and enables quantification and prediction of watershed active areas and those active areas connected to the stream network through time.
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We combined a conceptual rainfall-runoff model and input-output relationships of stable isotopes to understand ecohydrological influences on hydrological partitioning in snow-influenced northern catchments. Six sites in Sweden (Krycklan), Canada (Wolf Creek; Baker Creek; Dorset), Scotland (Girnock) and the USA (Dry Creek) span moisture and energy gradients found at high-latitudes. A meta-analysis was carried out using the HBV-model to estimate the main storage changes characterising annual water balances. Annual snowpack storage importance was ranked as Wolf Creek > Krycklan > Dorset > Baker Creek > Dry Creek > Girnock. The subsequent rate and longevity of melt was reflected in calibrated parameters that determine partitioning of waters between more rapid and slower flowpaths and associated variations in soil and groundwater storage. Variability of stream water isotopic composition depends on: (i) rate and duration of spring snowmelt; (ii) significance of summer/autumn rainfall; (iii) relative importance of near-surface and deeper flowpaths in routing water to the stream. Flowpath partitioning also regulates influences of summer evaporation on drainage waters. Deviations of isotope data from the Global Meteoric Water Line showed subtle effects of internal catchment processes on isotopic fractionation most likely through evaporation. Such effects are highly variable among sites and with seasonal differences at some sites. After accounting for climate, evaporative fractionation is strongest at sites where lakes and near-surface runoff processes in wet riparian soils can mobilize isotopically-enriched water during summer and autumn. Given close soil-vegetation coupling, this may result in spatial variability in soil water isotope pools available for plant uptake. We argue that stable isotope studies are crucial in addressing the many open questions on hydrological functioning of northern environments. This article is protected by copyright. All rights reserved.
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In mountainous regions, rainfall plays a key role in water supply for millions of people. However, rainfall data for these sites are limited and generally of low quality, making it difficult to evaluate the nature, amount, and timing of rainfall. This is particularly true for the Páramo, a high-elevation grassland in the northern Andes that is a primary source of water for large populations in Ecuador, Colombia, and Venezuela. In this study, high-resolution laser disdrometer data and standard tipping-bucket rain gauge data were used to improve our knowledge of rainfall in the Páramo. For 36 months, rainfall was monitored in a high-elevation (3780 m a.s.l.) headwater catchment in southern Ecuador. Average annual rainfall during this period was 1345 mm. Results indicate that (i) when input from very low intensity events (drizzle) is taken into account, rainfall is 15% higher than previously thought; (ii) rainfall occurs throughout the year (only approximately 12% of the days are dry); (iii) rainfall occurs primarily as drizzle (80% of rainfall duration), which accounts for 29% of total rainfall amount; and (iv) the timing and average intensity of rainfall varies throughout the year (shorter afternoon events are common from October to May, whereas longer night events—with lower intensities—are more frequent from June to September). Although some of these numbers may vary regionally, the results contribute to a better understanding of rainfall in the wet Andean Páramo.
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While most hydrological models reproduce the general flow dynamics, they frequently fail to adequately mimic system-internal processes. In particular, the relation-ship between storage and discharge, which often follows annual hysteretic patterns in shallow hard-rock aquifers, is rarely considered in modelling studies. One main reason is that catchment storage is difficult to measure, and another one is that objective functions are usually based on individ-ual variables time series (e.g. the discharge). This reduces the ability of classical procedures to assess the relevance of the conceptual hypotheses associated with models. We analysed the annual hysteric patterns observed be-tween stream flow and water storage both in the saturated and unsaturated zones of the hillslope and the riparian zone of a headwater catchment in French Brittany (Environmen-tal Research Observatory ERO AgrHys (ORE AgrHys)). The saturated-zone storage was estimated using distributed shal-low groundwater levels and the unsaturated-zone storage us-ing several moisture profiles. All hysteretic loops were char-acterized by a hysteresis index. Four conceptual models, pre-viously calibrated and evaluated for the same catchment, were assessed with respect to their ability to reproduce the hysteretic patterns. The observed relationship between stream flow and satu-rated, and unsaturated storages led us to identify four hydro-logical periods and emphasized a clearly distinct behaviour between riparian and hillslope groundwaters. Although all the tested models were able to produce an annual hystere-sis loop between discharge and both saturated and unsatu-rated storage, the integration of a riparian component led to overall improved hysteretic signatures, even if some misrep-resentation remained. Such a system-like approach is likely to improve model selection.
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We examined the storage dynamics and isotopic composition of soil water over 12 months in three hydropedological units in order to understand runoff generation in a montane catchment. The units form classic catena sequences from freely draining podzols on steep upper hillslopes through peaty gleys in shallower lower slopes to deeper peats in the riparian zone. The peaty gleys and peats remained saturated throughout the year, while the podzols showed distinct wetting and drying cycles. In this region, most precipitation events are <10 mm in magnitude, and storm runoff is mainly generated from the peats and peaty gleys, with runoff coefficients (RCs) typically <10%. In larger events the podzolic soils become strongly connected to the saturated areas, and RCs can exceed 40%. Isotopic variations in precipitation are significantly damped in the organic-rich soil surface horizons due to mixing with larger volumes of stored water. This damping is accentuated in the deeper soil profile and groundwater. Consequently, the isotopic composition of stream water is also damped, but the dynamics strongly reflect those of the near-surface waters in the riparian peats. "pre-event" water typically accounts for >80% of flow, even in large events, reflecting the displacement of water from the riparian soils that has been stored in the catchment for >2 years. These riparian areas are the key zone where different source waters mix. Our study is novel in showing that they act as "isostats," not only regulating the isotopic composition of stream water, but also integrating the transit time distribution for the catchment. Hillslope connectivity is controlled by small storage changes in soil unitsDifferent catchment source waters mix in large riparian wetland storageIsotopes show riparian wetlands set the catchment transit time distribution.
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Soil water storage and stable isotopes dynamics were investigated in dominant soil-vegetation assemblages of a wet northern headwater catchment (3.2 km2) with limited seasonality in precipitation. We determined the relative influence of soil- and/or vegetation cover on storage and transmission processes. Forested and non-forested sites were compared; on poorly drained histosols in riparian zones and freely draining podzols on steeper hillslopes. Results showed that soil properties exert a much stronger influence than vegetation on water storage dynamics and fluxes, both at the plot and catchment scale. This is mainly linked to the overall energy-limited climate, restricting evaporation, in conjunction with high soil water storage capacities. Threshold behaviour in runoff responses at the catchment scale was associated with differences in soil water storage and transmission dynamics of different hydropedological units. Linear input–output relationships occurred when runoff was generated predominantly from the permanently wet riparian histosols which show only small dynamic storage changes. In contrast, non-linear runoff generation was related to transient periods of high soil wetness on the hillslopes. During drier conditions, more marked differences in soil water dynamics related to vegetation properties emerged, in terms of evaporation and impacts on temporarily increasing dynamic storage potential. Overall, our results suggest that soil type and their influence on runoff generation are dominant over vegetation effects in wet, northern headwater catchments with low-seasonality in precipitation. Potential increase of subsurface storage by tree cover (e.g. for flood management) will therefore be spatially distributed throughout the landscape and limited to rare and extreme dry conditions. This article is protected by copyright. All rights reserved.
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Páramo is one of the most vulnerable ecosystems to global environmental change due primarily to the human activities. Furthermore, the problem is aggravated for the lack of understanding of many of the processes that occur within that ecosystem. In this context, this study aimed to quantify the effects of the change in vegetal soil coverage and land use with respect to the physical and chemical properties of soils. The study was conducted in a watershed located in the Andean mountains of Southern Ecuador, Páramo of Quimsacocha , where eight types of vegetal coverage and land use were studied: cushion plants, upper montane forest, pine forest, polylepis forest, potatoes crops, tussock grasses, extensive-grazed grass and burned-tussock grass. They were defined in thirty six observation sites by transect sampling. In these sites physical and chemical properties of soils were characterized according to surface and subsurface horizons, based on field data sampling, with disturbed and undisturbed samples. The results showed that changes in coverage have occurred basically on Andisols, especially on its physical properties at the level of surface horizons due to cultivation and forest plantations. Modification of the chemical properties was most visible at the level of subsurface horizons, where illuviation processes are dominating.
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Soils of Páramo ecosystems regulate the water supply to many Andean populations. In spite of being a necessary input to distributed hydrological models, regionalized soil water retention data from these areas are currently not available. The investigated catchment of the Quinuas River has a size of about 90 km2 and comprises parts of the Cajas National Park in southern Ecuador. It is dominated by soils with high organic carbon contents, which display characteristics of volcanic influence. Besides providing spatial predictions of soil water retention at the catchment scale, the study presents a detailed methodological insight to model setup and validation of the underlying machine learning approach with random forest. The developed models performed well predicting volumetric water contents between 0.55 and 0.9 cm3 cm− 3. Among the predictors derived from a digital elevation model and a Landsat image, altitude and several vegetation indices provided the most information content. The regionalized maps show particularly low water retention values in the lower Quinuas valley, which go along with high prediction uncertainties. Due to the small size of the dataset, mineral soils could not be separated from organic soils, leading to a high prediction uncertainty in the lower part of the valley, where the soils are influenced by anthropogenic land use.
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Montane ecosystems are known for their high numbers of endemic species, unique climate conditions, and wide variety of ecosystem services such as water supply and carbon storage. Although many ecohydrological and climatic studies of montane environments have been carried out in temperate and boreal regions, few have been done in Neotropical regions. Hence, the objective of this review is to synthesize the existing literature on the main factors (biotic and abiotic) that influence vegetation distribution, functional traits, and ecohydrological processes and feedbacks in tropical montane ecosystems (TME) and to identify key knowledge gaps. Most of the literature used includes work conducted in Neotropical montane rainforests, cloud forests, and grass/scrublands (e.g., páramos, punas, and campos de altitude/rupestres). Fog is a major climatic attribute in tropical montane habitats. We found that fog regimes (frequency and intensity of fog events) influence both water inputs (i.e., canopy interception, foliar water uptake) and outputs (evapotranspiration), and represent an important driver of local species composition, dominance of plant functional types, and ecological functioning. The stability and conservation of TME depends on such ecohydrological fluxes, which are sensitive to increases in air temperature and changing precipitation and fog regimes. Furthermore, to better inform effective conservation and restoration strategies, more work is needed to elucidate how key ecohydrological processes are affected by land use conversion to agriculture and pasture lands, as human activities influence the water budgets in Neotropical montane watersheds not only at regional-scales, but also globally.
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The relative importance of catchment's water provenance and flow paths varies in space and time, complicating the conceptualization of the rainfall-runoff response. We assessed the temporal dynamics in source areas, flow paths and age by End Member Mixing Analysis (EMMA), Hydrograph Separation (HS) and Inverse Transit Time Proxies (ITTPs) estimation within a headwater catchment in the Ecuadorian Andes. Twenty-two solutes, stable isotopes, the pH and electrical conductivity from a stream and twelve potential sources were analyzed. Four end members were required to satisfactorily represent the hydrological system, i.e., rainfall, spring water and water from the bottom layers of Histosols and Andosols. Water from Histosols in and near the riparian zone was the highest source contributor to runoff throughout the year (39% for the drier season, 45% for the wetter season), highlighting the importance of the water that is stored in the riparian zone. Spring water contributions to streamflow tripled during the drier season, as evidenced by geochemical signatures that are consistent with deeper flow paths rather than shallow interflow through Andosols. Rainfall exhibits low seasonal variation in this contribution. HS reveals that 94% and 84% is pre-event water in the drier and wetter seasons, respectively. From low to high flow conditions, all the sources increase their contribution except spring water. The relative age of streamwater decreased during wetter periods, when the contributing area of the riparian zone expands. The multi-method and multi-tracer approach enabled to closely study the interchanging importance of flow processes and water-source dynamics from an inter-annual perspective.
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Using stable isotope data from soil and vegetation xylem samples across a range of landscape positions, this study provides preliminary insights into spatial patterns and temporal dynamics of soil-plant water interactions in a humid, low-energy northern environment. Our analysis showed that evaporative fractionation affected the isotopic signatures in soil water at shallow depths but was less marked than previously observed in other environments. By comparing the temporal dynamics of stable isotopes in soil water mainly held at suctions around and below field capacity, we found that these waters are not clearly separated. The study inferred that vegetation water sources at all sites were relatively constant, and most likely to be in the upper profile close to the soil/atmosphere interface. The data analyses also suggested that both vegetation type and landscape position, including soil type, may have a strong influence on local water uptake patterns, although more work is needed to explicitly identify water sources and understand the effect of plant physiological processes on xylem isotopic water signatures.
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We used End-Member Mixing Analysis (EMMA) to investigate the spatiotemporal variability of source water contributions to streamflow generation from three headwater catchments that span a precipitation and ecosystem type gradient across ∼1500 m elevation in the Colorado Front Range, USA. We additionally characterized the magnitude and type (rain versus snow) of precipitation and the resulting hydrologic response of surface and subsurface waters to this precipitation variability. The three catchments were representative of the montane rain-snow transition zone (snow was 39% of total precipitation; σ (standard deviation) = 10%), the subalpine zone (69% snow; σ = 5%), and the alpine zone (84% snow; σ = 10%). All three catchments were identified as three end-member systems with their respective source waters being groundwater, snow precipitation or melt, rain (montane and subalpine only), and subsurface water from talus slopes (alpine only). Mean annual groundwater contributions were greater in forested catchments (28%; σ = 6% in the montane, 31%; σ = 8% in the subalpine) than in the alpine (19%; σ = 5%) catchment. Snow-derived water contributions to streamflow were inversely related to groundwater and increased but became less variable with elevation from 46% (σ = 15%) in the montane zone to 58% (σ = 12%) in the subalpine and 61% (σ = 7%) in the alpine. Rain was 27% (σ = 8%) of discharge in the montane and 11% (σ = 4%) in the subalpine, while talus waters made up the final 21% (σ = 12%) of streamflow in the alpine. Our results suggest that subsurface source waters (groundwater and talus water) that are influenced by the timing, magnitude, and type of recharge and by the storage capabilities of the subsurface may be the most sensitive to climate variability at higher elevations. In contrast, the proportion of rain versus snow was the primary control on source water variability at lower elevations.
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One of the most important functions of catchments is the storage of water. Catchment storage buffers meteorological extremes and inter-annual streamflow variability, controls the partitioning between evaporation and runoff and influences transit times of water. Hydrogeological data to estimate storage are usually scarce and seldom available for a larger set of catchments. This study focused on storage in pre-alpine and alpine catchments, using a set of 21 Swiss catchments comprising different elevation ranges. Catchment storage comparisons depend on storage definitions. This study defines different types of storage including definitions of dynamic and mobile catchment storage. We then estimated dynamic storage using four different methods, water balance analysis, streamflow recession analysis, calibration of a bucket-type hydrological model (HBV), and calibration of a transfer function model (TRANSEP) using stable isotope observations. The HBV model allowed quantifying the contributions of snow, soil and groundwater storages compared to the dynamic catchment storage. With the TRANSEP model both dynamic and mobile storage was estimated. Dynamic storage of one catchment estimated by the four methods differed up to one order of magnitude. Nevertheless, the storage estimates ranked similarly among the 21 catchments. The largest dynamic and mobile storage estimates were found in high elevation catchments. Besides snow, groundwater contributed considerably to this larger storage. Generally, we found that with increasing elevation the relative contribution to the dynamic catchment storage increased for snow, decreased for soil, but remained similar for groundwater storage.
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Isotope hydrograph separation (IHS) is a valuable tool to study runoff generation processes. To perform an IHS, samples of baseflow (pre-event water) and streamflow are taken at the catchment outlet. For rainfall (event water) either a bulk sample is collected or it is sampled sequentially during the event. For small headwater catchment studies, event water samples are usually taken at only one sampling location in or near the catchment because the spatial variability in the isotopic composition of rainfall is assumed to be small. However, few studies have tested this assumption. In this study, we investigated the spatiotemporal variability in the isotopic composition of rainfall and its effects on IHS results using detailed measurements from a small pre-alpine headwater catchment in Switzerland. Rainfall was sampled sequentially at eight locations across the 4.3 km² Zwäckentobel catchment and stream water was collected in three subcatchments (0.15, 0.23, and 0.70 km²) during ten events. The spatial variability in rainfall amount, average and maximum rainfall intensity and the isotopic composition of rainfall was different for each event. There was no significant relation between the isotopic composition of rainfall and total rainfall amount, rainfall intensity or elevation. For eight of the ten studied events the temporal variability in the isotopic composition of rainfall was larger than the spatial variability in the rainfall isotopic composition. The isotope hydrograph separation results, using only one rain sampler, varied considerably depending on which rain sampler was used to represent the isotopic composition of event water. The calculated minimum pre-event water contributions differed up to 60%. The differences were particularly large for events with a large spatial variability in the isotopic composition of rainfall and a small difference between the event and pre-event water isotopic composition. Our results demonstrate that even in small catchments the spatial variability in the rainfall isotopic composition can be significant and has to be considered for IHS studies. Using data from only one rain sampler can result in significant errors in the estimated pre-event water contributions to streamflow.
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Receding mountain glaciers affect the hydrology of downslope ecosystems with consequences for drinking water, agriculture, and hydropower production. Here we combined land cover derived from satellite imagery and other environmental data from the northern Peruvian Andes into a first differencing regression model to assess wetland hydrologic connectivity. Wetland area was considered the response variable and a variety of land cover, climatic, and stream discharge explanatory variables were tested to evaluate effects of possible hydrologic connectivity. The results indicate that there were two primary spatial driving forces of wetland change in Peru's Cordillera Blanca from 1987 to 1995: 1) loss in glacier area was associated with increased wetland area, controlling for other factors; while 2) an increase in mean annual stream discharge in the previous 12 months increased wetland area. The general approach we used expands the ways that connectivity between landscape changes and hydrologic and ecosystem processes can be assessed.
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In a Mediterranean climate where much of the precipitation falls during winter, snowpacks serve as the primary source of dry season runoff. Increased warming has led to significant changes in hydrology of the western United States. An important question in this context is how to best manage forested catchments for water and other ecosystem services? Answering this basic question requires detailed understanding of hydrologic functioning of these catchments. Here, we depict the differences in hydrologic response of 10 catchments. Size of the study catchments ranges from 50 to 475 ha, and they span between 1,782 and 2,373 m elevation in the rain-snow transitional zone. Mean annual streamflow ranged from 281 to 408 mm in the low elevation Providence and 436 to 656 mm in the high elevation Bull catchments, resulting in a 49 mm streamflow increase per 100 m (R² = 0.79) elevation gain, despite similar precipitation across the 10 catchments. Although high elevation Bull catchments received significantly more precipitation as snow and thus experienced a delayed melt, this increase in streamflow with elevation was mainly due to a reduction in evapotranspiration (ET) with elevation (45 mm/100 m, R² = 0.65). The reduction in ET was attributed to decline in vegetation density, growing season, and atmospheric demand with increasing elevation. These findings suggest changes in streamflow in response to climate warming may likely depend on how vegetation responds to those changes in climate.
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Studies on hydrology, biogeochemistry or mineral weathering often rely on assumptions about flow paths, water storage dynamics and transit times. Testing these assumptions requires detailed hydrometric data which are usually unavailable at the catchment scale. Hillslope studies provide an alternative for obtaining a better understanding, but even on such well-defined and delimited scales it is rare to have a comprehensive set of hydrometric observations from the water divide down to the stream which can constrain efforts to quantify water storage, movement and turnover time. Here we quantified water storage with daily resolution in a hillslope during the course of almost an entire year using hydrological measurements at the study site, and an extended version of the Vertical Equilibrium Model (VEM). We used an exponential function to simulate the relationship between hillslope discharge and water table; this was used to derive transmissivity profiles along the hillslope and map mean pore water velocities in the saturated zone. Based on the transmissivity profiles, the soil layer transmitting 99 % of lateral flow to the stream had a depth that ranged from 8.9 m at the water divide to under 1 m closer to the stream. During the study period the total storage of this layer varied from 1189 – 1485 mm, resulting in a turnover time of 2172 days. From the pore water velocities we mapped the time it would take a water particle situated at any point of the saturated zone anywhere along the hillslope to exit as runoff. Our calculations point to the strengths as well as limitations of simple hydrometric data for inferring hydrological properties and water travel times in the subsurface. This article is protected by copyright. All rights reserved.
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As a consequence of the remote location of the Andean páramo is knowledge on their hydrologic functioning limited, notwithstanding this alpine tundra ecosystem act as water towers for a large fraction of the society. Given the harsh environmental conditions in this region is year-round monitoring cumbersome, and it would be beneficially if the monitoring needed for the understanding of the rainfall-runoff response could be limited in time. To identify the hydrological response and the effect of temporal monitoring a nested (n = 7) hydrological monitoring network was set up in the Zhurucay catchment (7.53 km2), south Ecuador. The research questions were: (1) can event sampling provide similar information in comparison to continuous monitoring, and (2) if so, how many events are needed to achieve a similar degree of information? A subset of 34 rainfall runoff events was compared to monthly values derived from a continuous monitoring scheme from December 2010 to November 2013. Land cover and physiographic characteristics were correlated with eleven hydrological indices. Results show that despite some distinct differences between event and continuous sampling, both datasets reveal similar information; more in particular the monitoring of a single event in the rainy season provides the same information as continuous monitoring, while during the dry season 10 events ought to be monitored. This article is protected by copyright. All rights reserved.
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Assessing catchment runoff response remains a key research frontier due to limitations in current observational techniques to fully characterize water source areas and transit times in diverse geographical environments. Here, we report a study that combines empirical data with modelling to identify dominant runoff processes in a sparsely monitored humid tropical catchment. The analysis integrated isotope tracers into conceptual rainfall-runoff models of varying complexity (from five to eleven calibrated parameters) that are able to simulate discharge and tracer concentrations and track the evolving age of stream water exiting the catchment. The model structures can be seen as competing hypotheses of catchment functioning and were simultaneously calibrated against uncertain streamflow gaugings and a two-year daily isotope rainfall-runoff record. Comparison of the models was facilitated using global parameter sensitivity analysis and the resulting effect on calibration. We show that a variety of tested model structures reproduced water and tracer dynamics in stream, but the simpler models failed to adequately reproduce both. The resulting water age distributions of the tested models varied significantly with little similarity between the stream water age and stored water age distributions. The sensitivity analysis revealed that only some of the more complex models (from eight parameters) could be better constrained to infer more plausible water age distributions and catchment storage estimates. These models indicated that the age This article is protected by copyright. All rights reserved. of water stored in the catchment is generally older compared to the age of water fluxes, with evapotranspiration age being younger compared to streamflow. However, the water age distributions followed a similar temporal behaviour dominated by climatic seasonality. Stream water ages increased during the dry season (greater than 1year) and decreased with
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The potential for dynamic storage to serve as a metric of basin behaviour was assessed using data from five drainage basins with headwaters on the thick sand and gravel deposits of the Oak Ridges Moraine in southern Ontario, Canada. Dynamic storage was directly correlated with the ratio of variability of δ²H in streamflow relative to that in precipitation. This ratio has previously been shown to be inversely related to basin mean transit time (MTT), suggesting an inverse relationship between dynamic storage and MTT for the study basins. Dynamic storage was also directly correlated with interannual variability in stream runoff, baseflow and baseflow:runoff ratio, implying that basins with smaller dynamic storage have less interannual variability in their streamflow regimes. These preliminary results suggest that dynamic storage may serve as a readily derived and useful metric of basin behaviour for inter-basin comparisons.
Article
Few high-elevation tropical catchments worldwide are gauged and even fewer are studied using combined hydrometric and isotopic data. Consequently, we lack information needed to understand processes governing rainfall-runoff dynamics and to predict their influence on downstream ecosystem functioning. To address this need, we present a combination of hydrometric and water stable isotopic observations in the wet Andean páramo ecosystem of the Zhurucay Ecohydrological Observatory (7.53 km2). The catchment is located in the Andes of south Ecuador between 3400 and 3900 m a.s.l. Water samples for stable isotopic analysis were collected during 2 years (May 2011 – May 2013), while rainfall and runoff measurements were continuously recorded since late 2010. The isotopic data reveal that Andosol soils predominantly situated on hillslopes drain laterally to Histosols (Andean páramo wetlands) mainly located at the valley bottom. Histosols, in turn, feed water to creeks and small rivers throughout the year, establishing hydrologic connectivity between wetlands and the drainage network. Runoff is primarily comprised of pre-event water stored in the Histosols, which is replenished by rainfall that infiltrates through the Andosols. Contributions from the mineral horizon and the top of the fractured bedrock are small and only seem to influence discharge in small catchments during low flow generation (non-exceedance flows < Q35). Variations in source contributions are controlled by antecedent soil moisture, rainfall intensity, and duration of rainy periods. Saturated hydraulic conductivity of the soils, higher than the year-round low precipitation intensity, indicates that Hortonian overland flow rarely occurs during high intensity precipitation events. Deep groundwater contributions to discharge seem to be minimal. These results suggest that, in this high-elevation tropical ecosystem: 1) subsurface flow is a dominant hydrological process and 2) (Histosols) wetlands are the major source of stream runoff. Our study highlights that detailed isotopic characterization during short time periods provides valuable information about ecohydrological processes in regions where very few basins are gauged.
Article
Models simulating stream flow and conservative tracers can provide a representation of flow paths, storage distributions and mixing processes that is advantageous for many predictive purposes. Compared with models that only simulate stream flow, tracer data can be used to investigate the internal consistency of model behaviour and to gain insight into model performance. Here, we examine the strengths and weaknesses of a data-driven, spatially distributed tracer-aided rainfall-runoff model. The model structure allowed us to assess the influence of landscape characteristics on the routing and mixing of water and tracers. The model was applied to a site in the Scottish Highlands with a unique tracer data set; ~4years of daily isotope ratios in stream water and precipitation were available, as well as 2years of weekly soil and ground water isotopes. The model structure was based on an empirically based, lumped tracer-aided model previously developed for the catchment. The best model runs were selected from Monte Carlo simulations based on dual calibration criteria using objective functions for both stream isotopes and discharge at the outlet. Model performance for these criteria was reasonable (Nash-Sutcliffe efficiencies for discharge and isotope ratios were ~0.4-0.6). The model could generally reproduce the variable isotope signals in the soils of the steeper hill slopes where storage was low, and damped isotope responses in valley bottom cells with high storage. The model also allowed us to estimate the age distributions of internal stores, water fluxes and stream flow. Average stream water age was ~1.6years, integrating older groundwater in the valley bottom and dynamic younger soil waters. By tracking water ages and simulating isotopes, the model captured the changes in connectivity driven by distributed storage dynamics. This has substantially improved the representation of spatio-temporal process dynamics and gives a more robust framework for projecting environmental change impacts. © 2016 The Authors Hydrological Processes Published by John Wiley & Sons Ltd. © 2016 The Authors Hydrological Processes Published by John Wiley & Sons Ltd.
Article
Evaluation of a recession-based “top-down” model for distributed hourly runoff simulation in macroscale mountainous catchments is rare in the literature. We evaluated such a model for a 3090 km² boreal catchment and its internal sub-catchments. The main research question is how the model performs when parameters are either estimated from streamflow recession or obtained by calibration. The model reproduced observed streamflow hydrographs (Nash-Sutcliffe efficiency up to 0.83) and flow duration curves. Transferability of parameters to the sub-catchments validates the performance of the model, and indicates an opportunity for prediction in ungauged sites. However, the cases of parameter estimation and calibration excluding the effects of runoff routing underestimate peak flows. The lower end of the recession and the minimum length of recession segments included are the main sources of uncertainty for parameter estimation. Despite the small number of calibrated parameters, the model is susceptible to parameter uncertainty and identifiability problems. EDITOR D. Koutsoyiannis; ASSOCIATE EDITOR A. Carsteanu
Article
The importance of conceptualising the dynamics of storage-driven saturation area connectivity in runoff generation has been central to the development of TOPMODEL and similar low parameterised rainfall-runoff models. In this contribution, we show how we developed a 40 year hydrometric data base to simulate storage-discharge relationships in the Girnock catchment in the Scottish Highlands using a simple conceptual model. The catchment is a unique fisheries reference site where Atlantic salmon populations have been monitored since 1966. The modelling allowed us to track storage dynamics in hillslopes, the riparian zone and groundwater, and explicitly link non-linear changes of streamflows to landscape storage and connectivity dynamics. This provides a fundamental basis for understanding how the landscape and riverscape are hydrologically connected and how this regulates in-stream hydraulic conditions that directly influence salmonids. We use the model to simulate storage and discharge dynamics over the 40 year period of fisheries records. The modelled storage-driven connectivity provides an ecohydological context for understanding the dynamics in stream flow generation which determine habitat hydraulics for different life stages of salmon population. This new, long-term modelling now sets this variability in the riverscape in a more fundamental context of the inter-relationships between storage in the landscape and stream flow generation. This provides a simple, robust framework for future ecohydrological modelling at this site, which is an alternative to more increasingly popular but highly parameterised and uncertain commercial ecohydrological models. It also provides a wider, novel context that is a prerequisite for any model-based scenario assessment of likely impacts resulting from climate or land use change. This article is protected by copyright. All rights reserved.