Browsing by Author "Birkel, Christian"

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Bridging the gap between hydrological and biogeochemical processes in a high Andean catchment: a comprehensive tracer-aided model framework
(Universidad de Cuenca, 2023-09-29) Pesántez Vallejo, Juan Patricio; Crespo Sánchez, Patricio Javier; Birkel, Christian; Célleri Alvear, Rolando Enrique
The Andean mountains satisfy the vital needs of the Andean population and its lowlands. However, they are projected to experience significant impacts attributed to land-use change and climate change. Despite our understanding of the hydrology in these areas, to date, there has been no modeling framework that incorporates direct data acquisition, simple models, and extends to a distributed modeling framework. Such a framework should be able to elucidate hydrological and biogeochemical processes in a manner comprehensible to decision-makers. Therefore, the primary objective of this thesis is to spatially and temporally assess the production and distribution of water and dissolved organic carbon (DOC) in a páramo catchment using tracer-aided models. To achieve this, we have monitored hydrometeorological and biogeochemical parameters, as well as water stable isotopes. In combination with field observations and perceptual knowledge of these catchments, we evaluated them within a comprehensive hydrological modeling framework. We found that DOC and other solutes can be estimated through in-situ spectrometry. Using these solutes as tracers made it possible to compare different hydrological pathways and was the only way to identify that streamflow response consisted of near-surface rapid flow, more mixed flow through the two main soil types, as well as flow from shallow fractured rock, especially under base flow conditions. Based on the hydrological processes found, a new module was developed to simulate DOC production and incorporate it into a spatially distributed hydrological model at a high spatial (10 x 10 meters) and temporal (1 hour) resolution. This model allowed us to identify DOC hots pots and hot moments. The results showed increased hydrological connectivity between hillslopes and valleys with increasing precipitation. Wetter conditions also favored DOC production, especially in valleys (Histosols), and DOC transport to the river. Our findings suggest that minor changes in meteorological conditions directly affect water dynamics in páramo soils and its biogeochemistry. These conclusions will enable informed decisions to be made regarding water security, taking into account the effect of carbon loss from the soils to the rivers in the páramo.
Characterizing solute budgets of a tropical Andean páramo ecosystem
(2022) Peña Fernández, Pablo Andrés; Mora Abril, Enmita Lucía; Crespo Sánchez, Patricio Javier; Pesántez Vallejo, Juan Patricio; Arízaga Idrovo, Viviana Cristina; Birkel, Christian
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.
Characterizing solute budgets of a tropical andean páramo ecosystem
(2022) Arízaga Idrovo, Viviana Cristina; Pesántez Vallejo, Juan Patricio; Birkel, Christian; Peña Fernández, Pablo Andrés; Mora Abril, Enmita Lucía; Crespo Sánchez, Patricio Javier
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.
Corrigendum to “Characterizing solute budgets of a tropical andean páramo ecosystem”
(2022) Birkel, Christian; Arízaga Idrovo, Viviana Cristina; Crespo Sánchez, Patricio Javier; Mora Abril, Enmita Lucía; Pesántez Vallejo, Juan Patricio; Peña Fernández, Pablo Andrés
The authors regret that the printed version of the above article contained a number of errors. The correct and final version follows. The authors would like to apologise for any inconvenience caused. The authors wish to advice of a systemic error in our reported export rates, which were unintentionally miscalculated. The error occurred when calculating the total discharge load with the 5-min discharge values. Instead of multiplying the total discharge by 300 (300 s in 5 min) to obtain the total load, it was multiplied by 100. To correct for this error, all export rates should be multiplied by a correction factor of 3. The reported export errors from the methods to sampling frequencies are not affected since they are expressed as a percentage rate. However, wrongly reported solute budgets are therefore the result of the mistaken export rates. This document presents the sections with the aforementioned error and should be correctly reported as follows: 3.3.2. Solute export rates estimate 3.4. Total solute budgets and retention ratios Unlike the previous results, most solutes presented negative than positive budgets (Fig. 6) because of the greater export rates. The highest negative budget was for Si with −8.69E+08 mEq km−2 yr−1, followed by Sr with −7.82E+05 mEq km−2 yr−1, and Na with −6.70E+07 mEq km−2 yr−1. The cations predominantly presented this behavior, indicating a release from these solutes from the catchment. Zn was the only cation that presented a positive budget (9.54E+05 mEq km−2 yr−1). The nutrients budgets remained positive even with the greater export rates, suggesting an accumulation of these solutes in the catchment. In contrast, DOC budget turned negative with a value of −3.90E+08 mEq km−2 yr−1 (193 % retention ratio). As for the heavy metals, Cd and Pb budgets also turned from positive to negative. (See Table 2.) These trends were the same for all solutes at all sampling frequencies, except for B that randomly presented positive budgets at twice-weekly, weekly, and biweekly sampling frequencies. 4. Discussion 4.2. Export calculation methods, sampling frequency and hour Throughout all the solutes, Si presented the greatest export with a rate of 62.20 kg ha−1 yr−1, suggesting chemical weathering as the watershed acts as a sink of atmospheric CO2 (Carrillo-Rojas et al., 2019; Turner et al., 2010). The base cations presented similar export rates than what was found in the tropical montane forest at southern Ecuador. For instance, they showed export rates of 10.27 kg ha−1 yr−1 for Ca, 5.12 kg ha−1 yr−1 for K, 2.77 kg ha−1 yr−1 for Mg, and 16.41 kg ha−1 yr−1 for Na; while in the montane forest the rates were 6–8 kg ha−1 yr−1 for Ca, 7–8 kg ha−1 yr−1 for K, 4–5 kg ha−1 yr−1 for Mg, and 11–14 kg ha−1 yr−1 for Na. Bhatt and McDowell (2007) concluded that high concentrations of Ca and Na in surface waters is due to the plagioclase being the main mineral weathered from the catchment. 4.3. Negative and positive total budgets in a páramo ecosystem Considering DOC presented a negative budget, it can thus be suggested that the páramo acts a source of carbon from its surface waters.
High-frequency multi-solute calibration using an in situ UV–visible sensor
(2021) Crespo Sánchez, Patricio Javier; Peña Saltos, Pablo Gabriel; Mora Abril, Enmita Lucía; McDowell, William H.; Pesántez Vallejo, Juan Patricio; Birkel, Christian; Mosquera Rojas, Giovanny Mauricio; Arízaga Idrovo, Viviana Cristina
Monitoring the temporal variation of solute concentrations in streams at high temporal frequency can play an important role in understanding the hydrological and biogeochemical behaviour of catchments. UV–visible spectrometry is a relatively inexpensive and easily used tool to infer those concentrations in streams at high temporal resolution. However, it is not yet clear which solutes can be modelled with such an in-situ sensor. Here, we installed a UV–visible spectrometer probe (200–750 nm) in a high-altitude tropical Páramo stream to record the wavelength absorbance at a 5-min temporal resolution. For calibration, we simultaneously sampled stream water at a 4-h frequency from February 2018 to March 2019 for subsequent laboratory analysis. Absorbance spectra and laboratory-determined solute concentrations were used to identify the best calibration method and to determine which solute concentrations can be effectively inferred using in situ spectrometry through the evaluation of six calibration methods of different mathematical complexity. Based on the Nash–Sutcliffe efficiency (NSE) and Akaike information criterion metrics, our results suggest that multivariate methods always outperformed simpler strategies to infer solute concentrations. Eleven out of 21 studied solutes (Al, DOC, Ca, Cu, K, Mg, N, Na, Rb, Si and Sr) were successfully calibrated (NSE >0.50) and could be inferred using UV–visible spectrometry even with a reduced daily sampling frequency. It is worth noting that most calibrated solutes were correlated with wavelengths (WLs) in the low range of the spectra (i.e., UV range) and showed relatively good correlation with DOC. The latter suggests that estimation of metal concentrations could be possible in other streams with a high organic load (e.g., peat dominated catchments). In situ operation of spectrometers to monitor water quality parameters at high temporal frequency (sub-hourly) can enhance the protection of human water supplies and aquatic ecosystems as well as providing information for assessing catchment hydrological functioning.
Insight into the stable isotopic composition of glacial lakes in a tropical alpine ecosystem: Chirripó, Costa Rica
(2018) Esquivel Hernández, Germain; Sánchez Murillo, Ricardo; Quesada Román, Adolfo; Mosquera Rojas, Giovanny Mauricio; Birkel, Christian; Boll, Jan
Tropical high-elevation lakes are considered sentinels of global climate change. This work characterizes the hydrological conditions of tropical alpine glacial lakes located in the highlands of Chirripó, Costa Rica, using a unique data set of water stable isotopes (δ2H and δ18O) in precipitation, stream water, and lake water between September 2015 and July 2017. A combined dataset of bathymetric, hydrometric, and isotope data collected between July 2016 and July 2017 on Lake Ditkevi was used to calculate the annual water balance of the lake. Evaporation to inflow ratios from three lake systems was estimated using a linear resistance model, the experimentally estimated local evaporation line of Chirripó, and the first glacial lake water evaporation lines in the region. The temporal isotopic variations (δ18O, d-excess, and lc-excess) confirm variations in the dry and wet season evaporative conditions for the glacial lakes and consistently average annual low evaporation to inflow (E/I) ratios in the range of 2.0 ± 0.8% and 18.1 ± 12.2%. Lake Ditkevi's water balance indicates annual steady-state conditions, with an estimated evaporation loss of 650 mm/year (10.0 ± 5.0% of inflow), a high-water contribution to the catchment (90% of inflow), a residence time of 0.53 ± 0.27 years, and a catchment scale (0.289 km2) water yield or depth equivalent run-off of 278 mm/yr. These results provide novel information about water balance and evaporation losses in tropical alpine glacial lakes, which can serve as baseline information for future isotope-based hydro-climate research in high-elevation regions in the tropics and elsewhere.
Moisture transport and seasonal variations in the stable isotopic composition of rainfall in Central American and Andean Páramo during El Niño conditions (2015-2016)
(2019) Esquivel Hernández, Germain; Mosquera Rojas, Giovanny Mauricio; Sánchez Murillo, Ricardo; Quesada Román, Adolfo; Birkel, Christian; Crespo Sánchez, Patricio Javier; Célleri Alvear, Rolando Enrique; Windhorst, David; Breuer, Lutz; Boll, Jan
High‐elevation tropical grassland systems, called Páramo, provide essential ecosystem services such as water storage and supply for surrounding and lowland areas. Páramo systems are threatened by climate and land use changes. Rainfall generation processes and moisture transport pathways influencing precipitation in the Páramo are poorly understood but needed to estimate the impact of these changes, particularly during El Niño conditions which largely affect hydrometeorological conditions in tropical regions. To fill this knowledge gap, we present a stable isotope analysis of rainfall samples collected on a daily to weekly basis between January 2015 and May 2016 during the strongest El Niño event recorded in history (2014‐2016) in two Páramo regions of Central America (Chirripó, Costa Rica) and the northern Andes (Cajas, south Ecuador). Isotopic compositions were used to identify how rainfall …
Spatially distributed hydro-chemical data with temporally high-resolution is needed to adequately assess the hydrological functioning of headwater catchments
(2019) Correa Barahona, Alicia Beatriz; Breuer, Lutz; Crespo Sánchez, Patricio Javier; Célleri Alvear, Rolando Enrique; Feyen, Jan; Birkel, Christian; Silva Alemán, Camila Fernanda; Windhorst, David
Abstract We demonstrated the great value of spatially distributed and temporally high-resolution hydro-chemical data to enhance knowledge about the intra-catchment variability of flow processes and the runoff composition of individual storms in a tropical alpine (Paramo) ecosystem. In this study, water sources (rainfall, spring water, and water from soil layers of Histosols and Andosols) and nested streams were sampled bi-weekly (2013–2014), including three storm high-resolution events (5–240 min). Water samples were analyzed for 14 tracers including electrical conductivity (EC) and rare earth trace elements and used as input to perform End-Member Mixing Analysis (EMMA). End-members identified for the outlet could explain the hydrological behavior of four out of the five tributaries, indicating similar hydro-geochemical processes and geomorphic features within the catchments. The runoff source contributions of the individual sub-catchments varied among (e.g. Andosols ~40% in tributaries and ~25% at the outlet) and within storm events (e.g. Histosols 15% higher in small peak discharge event), indicating a time-variable composition of streamflows. The latter was also reflected by the interaction of different sources and the chronology of flow paths in EMMA-space, evidencing a faster connectivity with hillslopes in the upper sub-catchments compared to the lower sub-catchments. We found counter-clockwise hysteresis patterns of storms in the lower catchments and clockwise hysteresis loops in the upper catchments. The latter bi-directionality can be related to lower slopes, wider riparian areas and the higher proportion of Histosols in the lower catchments compared to the upper sites.
Spatially distributed tracer-aided modelling to explore DOC dynamics, hot spots and hot moments in a tropical mountain catchment
(2023) Crespo Sánchez, Patricio Javier; Pesántez Jiménez, Juan Fernando; Birkel, Christian; Mosquera, Giovanny M.; Célleri Alvear, Rolando Enrique; Jiménez Zamora, Enma Lucrecia; Murray, Desneiges S.; Arciniega Esparza, Saul; Gaona, Gabriel V.
Tracer-aided rainfall-runoff modelling is a promising tool for understanding catchment hydrology, particularly when tracers provide information about coupled hydrological-biogeochemical processes. Such models allow for predicting the quality and quantity of water under changing climatic and anthropogenic conditions. Here, we present the Spatially-distributed Tracer-Aided Rainfall-Runoff model with a coupled biogeochemi- cal reactive tracer module (STARR-DOC) to simulate dissolved organic carbon (DOC) dynamics and sources. The STARR-DOC model was developed and tested for a humid high Andean ecosystem (páramo) using high-resolution hourly DOC and hydrometeo- rological data to simulate hourly discharge and DOC at a fine spatial (10 10 m) resolution. Overall, the model was able to acceptably reproduce discharge (KGE 0.45) and stream DOC (KGE 0.69) dynamics. Spatially distributed DOC simulations were independently compared using point DOC measurements for different soil types across the catchment, which allowed for identifying DOC production hot spots and hot moments. Results showed higher hydrological connectivity between slopes and valleys with increasing precipitation. Wetter conditions also favoured DOC production (wet month = 82 mg L 1, dry month = 5 mg L 1) and transport to the stream network (DOC concentrations: during events 15 mg L 1 , during baseflows 4 mg L 1 ). Our results also suggest that minor changes in meteorological conditions directly affect páramo soil water dynamics and biogeochemistry. Knowledge of when and where DOC production in mountain catchments is greatest is important for water managers to understand when they make decisions about water security, especially considering climate change predictions for the Andean region