Thomas Meixner - Academia.edu (original) (raw)

Papers by Thomas Meixner

Research paper thumbnail of Dryland Riparian Ecosystems in the American Southwest: Sensitivity and Resilience to Climatic Extremes

Research paper thumbnail of Quantifying mountain block recharge by means of catchment-scale storage-discharge relationships

Water Resources Research, 2011

1] Despite the importance of mountainous catchments for providing freshwater resources, especiall... more 1] Despite the importance of mountainous catchments for providing freshwater resources, especially in semi-arid regions, little is known about key hydrological processes such as mountain block recharge (MBR). Here we implement a data-based method informed by isotopic data to quantify MBR rates using recession flow analysis. We applied our hybrid method in a semi-arid sky island catchment in southern Arizona, United States. Sabino Creek is a 91 km 2 catchment with its sources near the summit of the Santa Catalina Mountains northeast of Tucson. Southern Arizona's climate has two distinct wet seasons separated by prolonged dry periods. Winter frontal storms (November -March) provide about 50% of annual precipitation, and summers are dominated by monsoon convective storms from July to September. Isotope analyses of springs and surface water in the Sabino Creek catchment indicate that streamflow during dry periods is derived from groundwater storage in fractured bedrock. Storage-discharge relationships are derived from recession flow analysis to estimate changes in storage during wet periods. To provide reliable estimates, several corrections and improvements to classic base flow recession analysis are considered. These corrections and improvements include adaptive time stepping, data binning, and the choice of storage-discharge functions. Our analysis shows that (1) incorporating adaptive time steps to correct for streamflow measurement errors improves the coefficient of determination, (2) the quantile method is best for streamflow data binning, (3) the choice of the regression model is critical when the stage-discharge function is used to predict changes in bedrock storage beyond the maximum observed flow in the catchment, and (4) the use of daily or night-time hourly streamflow does not affect the form of the storage-discharge relationship but will impact MBR estimates because of differences in the observed range of streamflow in each series. Citation: Ajami, H., P. A. Troch, T. Maddock III, T. Meixner, and C. Eastoe (2011), Quantifying mountain block recharge by means of catchment-scale storage-discharge relationships, Water Resour. Res., 47, W04504,

Research paper thumbnail of Determining the importance of model calibration for forecasting absolute/relative changes in streamflow from LULC and climate changes

Journal of Hydrology, 2015

Land use/land cover (LULC) and climate changes are important drivers of change in streamflow. Ass... more Land use/land cover (LULC) and climate changes are important drivers of change in streamflow. Assessing the impact of LULC and climate changes on streamflow is typically done with a calibrated and validated watershed model. However, there is a debate on the degree of calibration required. The objective of this study was to quantify the variation in estimated relative and absolute changes in streamflow associated with LULC and climate changes with different calibration approaches. The Soil and Water Assessment Tool (SWAT) was applied in an uncalibrated (UC), single outlet calibrated (OC), and spatially-calibrated (SC) mode to compare the relative and absolute changes in streamflow at 14 gaging stations within the Santa Cruz River Watershed in southern Arizona, USA. For this purpose, the effect of 3 LULC, 3 precipitation (P), and 3 temperature (T) scenarios were tested individually. For the validation period, Percent Bias (PBIAS) values were >100% with the UC model for all gages, the values were between 0% and 100% with the OC model and within 20% with the SC model. Changes in streamflow predicted with the UC and OC models were compared with those of the SC model. This approach implicitly assumes that the SC model is ''ideal''. Results indicated that the magnitude of both absolute and relative changes in streamflow due to LULC predicted with the UC and OC results were different than those of the SC model. The magnitude of absolute changes predicted with the UC and SC models due to climate change (both P and T) were also significantly different, but were not different for OC and SC models. Results clearly indicated that relative changes due to climate change predicted with the UC and OC were not significantly different than that predicted with the SC models. This result suggests that it is important to calibrate the model spatially to analyze the effect of LULC change but not as important for analyzing the relative change in streamflow due to climate change. This study also indicated that model calibration in not necessary to determine the direction of change in streamflow due to LULC and climate change.

Research paper thumbnail of Nitrate in polluted mountainous catchments with Mediterranean climates

TheScientificWorldJournal, Jan 7, 2001

The mountains of southern California receive some of the highest rates of nitrogen (N) deposition... more The mountains of southern California receive some of the highest rates of nitrogen (N) deposition in the world (approximately 40 kg ha(-1) year(-1)). These high rates of deposition have translated into consistently high levels of nitrate (NO3-) in some streams of the San Bernardino Mountains. However, not all streams are exhibiting these high levels of NO3-. Perennial streams have high NO3- concentrations (approximately 200 micromoles l(-1)) while ephemeral streams do not (approximately 20 micromoles l(-1)). This difference points to groundwater as the source of the NO3- observed in streams. Furthermore, the evidence indicates a differential impact of N deposition on terrestrial and aquatic systems in Mediterranean climates, with aquatic systems being impacted more quickly. The primary reason for this difference involves the asynchrony between the time that atmospheric deposition occurs (summer), the time period of maximum soil NO3- availability and leaching (winter), and the time o...

Research paper thumbnail of Determination of baseflow inputs in riparian areas along a North American Monsoon gradient

Research paper thumbnail of Carbon and nutrient cycling in ephemeral streams in the American Southwest

Research paper thumbnail of Nitrogen dynamics in chaparral ecosystems: Limitations to the use of traditional N saturation indicators

Research paper thumbnail of Quantifying Variation in Solute Sources and Nutrient Cycling in Montane Headwater Catchments

Research paper thumbnail of Hydrologic response to modeled snowmelt input in alpine catchments in the Southwestern United States

Research paper thumbnail of Modeling the Sensitivity of a Semi-arid Groundwater System to the Seasonality and Quantity of Recharge and Evapotranspiration

Research paper thumbnail of Determining the Importance of Calibration for Predicting Relative Changes in Streamflow from Land Use/Cover Changes

Research paper thumbnail of Production, gaseous loss and export of N in urban desert stream ecosystems

Research paper thumbnail of Water Presence in an Arid and Semi-arid River: Pattern, causes, mechanisms and change

Research paper thumbnail of Determining solute inputs to soil and stream waters in a seasonally snow-covered mountain catchment in northern New Mexico using Ge/Si, 87Sr/86Sr and ion chemistry

Research paper thumbnail of Inorganic nitrogen cycling in ephemeral urban waterways of the semi-arid Southwest

Research paper thumbnail of SEASONALITY OF RECHARGE MECHANISMS IN THE BASIN AND RANGE OF NORTH AMERICA

Research paper thumbnail of Assessing the Sensitivity of a Semi-arid Aquifer to the Quantity of Recharge and Evapotranspiration using a Seasonalized Model

Research paper thumbnail of Insights on Biogeochemistry from the Triple Isotope System of Nitrate

Research paper thumbnail of Forecasting Relative/Absolute Changes in Streamflow from Land Use/Cover and Climate Changes: Effect of Model Calibration

Research paper thumbnail of Tradeoffs of modifications of storm water managements systems for nitrogen loss pathways in semi-arid ecosystems

Research paper thumbnail of Dryland Riparian Ecosystems in the American Southwest: Sensitivity and Resilience to Climatic Extremes

Research paper thumbnail of Quantifying mountain block recharge by means of catchment-scale storage-discharge relationships

Water Resources Research, 2011

1] Despite the importance of mountainous catchments for providing freshwater resources, especiall... more 1] Despite the importance of mountainous catchments for providing freshwater resources, especially in semi-arid regions, little is known about key hydrological processes such as mountain block recharge (MBR). Here we implement a data-based method informed by isotopic data to quantify MBR rates using recession flow analysis. We applied our hybrid method in a semi-arid sky island catchment in southern Arizona, United States. Sabino Creek is a 91 km 2 catchment with its sources near the summit of the Santa Catalina Mountains northeast of Tucson. Southern Arizona's climate has two distinct wet seasons separated by prolonged dry periods. Winter frontal storms (November -March) provide about 50% of annual precipitation, and summers are dominated by monsoon convective storms from July to September. Isotope analyses of springs and surface water in the Sabino Creek catchment indicate that streamflow during dry periods is derived from groundwater storage in fractured bedrock. Storage-discharge relationships are derived from recession flow analysis to estimate changes in storage during wet periods. To provide reliable estimates, several corrections and improvements to classic base flow recession analysis are considered. These corrections and improvements include adaptive time stepping, data binning, and the choice of storage-discharge functions. Our analysis shows that (1) incorporating adaptive time steps to correct for streamflow measurement errors improves the coefficient of determination, (2) the quantile method is best for streamflow data binning, (3) the choice of the regression model is critical when the stage-discharge function is used to predict changes in bedrock storage beyond the maximum observed flow in the catchment, and (4) the use of daily or night-time hourly streamflow does not affect the form of the storage-discharge relationship but will impact MBR estimates because of differences in the observed range of streamflow in each series. Citation: Ajami, H., P. A. Troch, T. Maddock III, T. Meixner, and C. Eastoe (2011), Quantifying mountain block recharge by means of catchment-scale storage-discharge relationships, Water Resour. Res., 47, W04504,

Research paper thumbnail of Determining the importance of model calibration for forecasting absolute/relative changes in streamflow from LULC and climate changes

Journal of Hydrology, 2015

Land use/land cover (LULC) and climate changes are important drivers of change in streamflow. Ass... more Land use/land cover (LULC) and climate changes are important drivers of change in streamflow. Assessing the impact of LULC and climate changes on streamflow is typically done with a calibrated and validated watershed model. However, there is a debate on the degree of calibration required. The objective of this study was to quantify the variation in estimated relative and absolute changes in streamflow associated with LULC and climate changes with different calibration approaches. The Soil and Water Assessment Tool (SWAT) was applied in an uncalibrated (UC), single outlet calibrated (OC), and spatially-calibrated (SC) mode to compare the relative and absolute changes in streamflow at 14 gaging stations within the Santa Cruz River Watershed in southern Arizona, USA. For this purpose, the effect of 3 LULC, 3 precipitation (P), and 3 temperature (T) scenarios were tested individually. For the validation period, Percent Bias (PBIAS) values were >100% with the UC model for all gages, the values were between 0% and 100% with the OC model and within 20% with the SC model. Changes in streamflow predicted with the UC and OC models were compared with those of the SC model. This approach implicitly assumes that the SC model is ''ideal''. Results indicated that the magnitude of both absolute and relative changes in streamflow due to LULC predicted with the UC and OC results were different than those of the SC model. The magnitude of absolute changes predicted with the UC and SC models due to climate change (both P and T) were also significantly different, but were not different for OC and SC models. Results clearly indicated that relative changes due to climate change predicted with the UC and OC were not significantly different than that predicted with the SC models. This result suggests that it is important to calibrate the model spatially to analyze the effect of LULC change but not as important for analyzing the relative change in streamflow due to climate change. This study also indicated that model calibration in not necessary to determine the direction of change in streamflow due to LULC and climate change.

Research paper thumbnail of Nitrate in polluted mountainous catchments with Mediterranean climates

TheScientificWorldJournal, Jan 7, 2001

The mountains of southern California receive some of the highest rates of nitrogen (N) deposition... more The mountains of southern California receive some of the highest rates of nitrogen (N) deposition in the world (approximately 40 kg ha(-1) year(-1)). These high rates of deposition have translated into consistently high levels of nitrate (NO3-) in some streams of the San Bernardino Mountains. However, not all streams are exhibiting these high levels of NO3-. Perennial streams have high NO3- concentrations (approximately 200 micromoles l(-1)) while ephemeral streams do not (approximately 20 micromoles l(-1)). This difference points to groundwater as the source of the NO3- observed in streams. Furthermore, the evidence indicates a differential impact of N deposition on terrestrial and aquatic systems in Mediterranean climates, with aquatic systems being impacted more quickly. The primary reason for this difference involves the asynchrony between the time that atmospheric deposition occurs (summer), the time period of maximum soil NO3- availability and leaching (winter), and the time o...

Research paper thumbnail of Determination of baseflow inputs in riparian areas along a North American Monsoon gradient

Research paper thumbnail of Carbon and nutrient cycling in ephemeral streams in the American Southwest

Research paper thumbnail of Nitrogen dynamics in chaparral ecosystems: Limitations to the use of traditional N saturation indicators

Research paper thumbnail of Quantifying Variation in Solute Sources and Nutrient Cycling in Montane Headwater Catchments

Research paper thumbnail of Hydrologic response to modeled snowmelt input in alpine catchments in the Southwestern United States

Research paper thumbnail of Modeling the Sensitivity of a Semi-arid Groundwater System to the Seasonality and Quantity of Recharge and Evapotranspiration

Research paper thumbnail of Determining the Importance of Calibration for Predicting Relative Changes in Streamflow from Land Use/Cover Changes

Research paper thumbnail of Production, gaseous loss and export of N in urban desert stream ecosystems

Research paper thumbnail of Water Presence in an Arid and Semi-arid River: Pattern, causes, mechanisms and change

Research paper thumbnail of Determining solute inputs to soil and stream waters in a seasonally snow-covered mountain catchment in northern New Mexico using Ge/Si, 87Sr/86Sr and ion chemistry

Research paper thumbnail of Inorganic nitrogen cycling in ephemeral urban waterways of the semi-arid Southwest

Research paper thumbnail of SEASONALITY OF RECHARGE MECHANISMS IN THE BASIN AND RANGE OF NORTH AMERICA

Research paper thumbnail of Assessing the Sensitivity of a Semi-arid Aquifer to the Quantity of Recharge and Evapotranspiration using a Seasonalized Model

Research paper thumbnail of Insights on Biogeochemistry from the Triple Isotope System of Nitrate

Research paper thumbnail of Forecasting Relative/Absolute Changes in Streamflow from Land Use/Cover and Climate Changes: Effect of Model Calibration

Research paper thumbnail of Tradeoffs of modifications of storm water managements systems for nitrogen loss pathways in semi-arid ecosystems