Jaromir Dusek

A review of CO2 and associated carbon dynamics in headwater streams: A global perspective

Terrestrial carbon export via inland aquatic systems is a key process in the global carbon cycle. It includes loss of carbon to the atmosphere via outgassing from rivers, lakes or reservoirs and carbon fixation in the water column as well as in sediments. This review focuses on headwater streams that are important because their stream biogeochemistry directly reflects carbon input from soils and groundwaters that becomes superimposed by additional inputs further downstream. Major drivers of carbon dioxide partial pressures (pCO2) in streams and mechanisms of terrestrial dissolved inorganic, organic and particulate organic carbon (DIC, DOC, and POC) influxes are summarized in this work. Our analysis indicates that the global river average pCO2 of 3,100 ppmV is more often exceeded by contributions from small streams when compared to rivers with larger catchments (>500 km2). Because of their large proportion in global river networks (>96 % of the total number of streams), headwaters contribute large – but still poorly quantified – amounts of CO2 to the atmosphere. Conservative estimates imply that globally 36 % (i.e. 0.93 Pg C yr-1) of total CO2 outgassing from rivers and streams originate from headwaters. We also discuss challenges in determination of CO2 sources, concentrations and fluxes. To overcome uncertainties of CO2 sources and its outgassing from headwater streams on the global scale, new investigations are needed that should include groundwater data. Such studies would also benefit from applications of integral CO2 outgassing isotope approaches and multi-scale geophysical imaging techniques.

Simulated cadmium transport in macroporous soil during heavy rainstorm using dual-permeability approach

Numerical modelling is used to analyze the transport of cadmium in response to an extreme rainfall event. The cadmium transport through the soil profile was simulated by the one-dimensional dual-permeability model, which assumes the existence of two mutually communicating domains: the soil matrix domain and the preferential flow domain. The model is based on Richards’ equation for water flow and advection-dispersion equation for solute transport. A modified batch technique allowed us to consider domain specific sorption, i.e. each of the domains has its own distribution coefficient. The dual-permeability model predicts that the cadmium can be transported substantially below the root zone after the storm. On the other hand, classical single permeability approach predicted that almost all applied cadmium stays retained near the soil surface.

Field leaching of pesticides at five test sites in Hawaii: study description and results

BACKGROUND Following the discovery of pesticides in wells, the Hawaii Department of Agriculture (HDOA) supported research to evaluate the likelihood of pesticide leaching to the groundwater in Hawaii. The aim of this study was to evaluate the relative leaching pattern of five pesticides at five different sites on three islands and to compare their leaching behavior with bromide and a reference chemical (atrazine) that is known to leach in Hawaiian conditions. Laboratory measurements of sorption and degradation of the pesticides were made. RESULTS Most of the applied mass of pesticides was still present in the top 80 cm after the 16 week study period. The aggregated oxisol at Kunia showed the most intensive leaching among the five sites. The revised attenuation factor screening approach used by the HDOA indicated that all chemicals, with the exception of trifloxystrobin, had the potential to leach. Similarly, the groundwater ubiquity score ranked trifloxystrobin as a non-leacher. The field leaching data, however, suggested that trifloxystrobin was the most mobile compound among the pesticides tested. CONCLUSION Although the results were variable among the sites, the field and laboratory experiments provided useful information for regulating use of these pesticides in Hawaii.

Ponded infiltration into soil with biopores — field experiment and modeling

Preferential movement of water in macropores plays an important role when the process of ponded infiltration in natural porous systems is studied. For example, the detailed knowledge of water flow through macropores is of a major importance when predicting runoff responses to rainfall events. The main objectives of this study are to detect preferential movement of water in Chernozem soil and to employ numerical modeling to describe the variably saturated flow during a field ponded infiltration experiment. The infiltration experiment was performed at the Macov experimental station (Calcari-Haplic Chernozem in Danubian Lowland, Slovakia). The experiment involved single ring ponded infiltration. At the quasi steady state phase of the experiment dye tracer was added to the infiltrating water. Then the soil profile was excavated and the penetration pattern of the applied tracer was recorded. The abundance of biopores as a product of fauna and flora was found. To quantify the preferential flow effects during the infiltration experiment, three-dimensional axisymmetric simulations were carried out by a two-dimensional dual-continuum numerical model. The water flow simulations based on measured hydraulic characteristics without consideration of preferential flow effects failed to describe the infiltration experiment adequately. The 3D axisymmetric simulation based on dual-permeability approach provided relatively realistic space-time distribution of soil water pressure below the infiltration ring.

Field leaching of pesticides at five test sites in Hawaii: modeling flow and transport

BACKGROUND Physically based tier-II models may serve as possible alternatives to expensive field and laboratory leaching experiments required for pesticide approval and registration. The objective of this study was to predict pesticide fate and transport at five different sites in Hawaii using data from an earlier field leaching experiment and a one-dimensional tier-II model. As the predicted concentration profiles of pesticides did not provide close agreement with data, inverse modeling was used to obtain adequate reactive transport parameters. The estimated transport parameters of pesticides were also utilized in a tier-I model, which is currently used by the state authorities to evaluate the relative leaching potential. RESULTS Water flow in soil profiles was simulated by the tier-II model with acceptable accuracy at all experimental sites. The observed concentration profiles and center of mass depths predicted by the tier-II simulations based on optimized transport parameters provided better agreements than did the non-optimized parameters. With optimized parameters, the tier-I model also delivered results consistent with observed pesticide center of mass depths. CONCLUSION Tier-II numerical modeling helped to identify relevant transport processes in field leaching of pesticides. The process-based modeling of water flow and pesticide transport, coupled with the inverse procedure, can contribute significantly to the evaluation of chemical leaching in Hawaii soils.

Acid rain footprint three decades after peak deposition: Long-term recovery from pollutant sulphate in the Uhlirska catchment (Czech Republic)

The granitic Uhlirska headwater catchment with a size of 1.78km2 is located in the Jizera Mountains in the northern Czech Republic and received among the highest inputs of anthropogenic acid depositions in Europe. An analysis of sulphate (SO42-) distribution in deposition, soil water, stream water and groundwater compartments allowed to establish a SO42- mass-balance (deposition input minus surface water export) and helped to evaluate which changes occurred since the last evaluation of the catchment in 1997. The determined SO42- concentrations decreased in the following order: wetland groundwater>groundwater from 20m below ground level (bgl)>groundwater from 30m bgl>stream water>groundwater from10m bgl>hillslope soil water>wetland soil water>bulk deposition with median values of 0.24, 0.21, 0.17, 0.15, 0.11, 0.07, 0.03 and 0.01mmolL-1, respectively. Our results show that average deposition reductions of 62% did not result in equal changes of the sulphate mass-balance, which changed by only 47%. This difference occurs because sulphate originates from internal sources such as the groundwater and soil water. The Uhlirska catchment is subject to delayed recovery from anthropogenic acid depositions and remains a net source of stored sulphur even after three decades of declining inputs. The wetland groundwater and soil water provide environmental memories of legacy pollutant sulphate. Elevated stream water sulphate concentrations after the unusually dry summer 2015 imply importance of weather and climate patterns for future recovery from acidification.

Interpretation of ponded infiltration data using numerical experiments

Abstract Ponded infiltration experiment is a simple test used for in-situ determination of soil hydraulic properties, particularly saturated hydraulic conductivity and sorptivity. It is known that infiltration process in natural soils is strongly affected by presence of macropores, soil layering, initial and experimental conditions etc. As a result, infiltration record encompasses a complex of mutually compensating effects that are difficult to separate from each other. Determination of sorptivity and saturated hydraulic conductivity from such infiltration data is complicated. In the present study we use numerical simulation to examine the impact of selected experimental conditions and soil profile properties on the ponded infiltration experiment results, specifically in terms of the hydraulic conductivity and sorptivity evaluation. The effect of following factors was considered: depth of ponding, ring insertion depth, initial soil water content, presence of preferential pathways, hydraulic conductivity anisotropy, soil layering, surface layer retention capacity and hydraulic conductivity, and presence of soil pipes or stones under the infiltration ring. Results were compared with a large database of infiltration curves measured at the experimental site Liz (Bohemian Forest, Czech Republic). Reasonably good agreement between simulated and observed infiltration curves was achieved by combining several of factors tested. Moreover, the ring insertion effect was recognized as one of the major causes of uncertainty in the determination of soil hydraulic parameters.

Comparison of two methods to assess heterogeneity of water flow in soils

Abstract The heterogeneity of water flow and solute transport was assessed during radioactive tracer infiltration experiment in a black clay loam soil using modified methods to estimate the effective cross section (ECS) and the degree of preferential flow (DPF). The results of field and numerical experiments showed that these parameters characterized the heterogeneity of water flow in the soils unequivocally. The ECS decreases non-linearly and the DPF increases linearly with an increase of the bypassing ratio (ratio of macropore flow rate to total flow rate). The ECS decreased and the DPF increased with depth, which suggests an increase in the heterogeneity of water flow with depth. The plot of the DPF against ECS values calculated from the tracer experiment data was consistent with the relationship obtained by the numerical simulation assuming preferential flow in the neighbourhood of three probes.

Transport of iodide in structured soil under spring barley during irrigation experiment analyzed using dual-continuum model

Transport of radioactive iodide 131I− in a black clay loam soil under spring barley in an early ontogenesis phase was monitored during controlled field irrigation experiment. It was found that iodide bound in the soil matrix could be mobilized by the surface leaching enhanced by mechanical impact of water drops and transported below the root zone of crops via soil cracks. The iodide transport through structured soil profile was simulated by the one-dimensional dual-continuum model, which assumes the existence of two inter-connected flow domains: the soil matrix domain and the preferential flow domain. The model predicted relatively deep percolation of iodide within a short time, in a good agreement with the observed vertical iodide distribution in soil. The dual-continuum approach proved to be an adequate tool for evaluation of field irrigation experiments conducted in structured soils.

Heterogeneity of water flow in grassland soil during irrigation experiment

The heterogeneity of water flow was evaluated in sandy loam soil covered by grass. The radioactive tracer infiltration experiment was performed at two parallel plots with different irrigation intensities. Effective cross section and degree of preferential flow parameters were used to evaluate flow regime during the experiment. For both plots, the heterogeneity of water flow increased with depth. The differences in irrigation intensity did not result in different values of the effective cross section and degree of preferential flow, indicating similar flow regime within the two experimental plots. The heterogeneity of water flow in shallower depths (0–50 cm) did not change with cumulative infiltration except for early times/small cumulative infiltrations, when the flow paths of preferential flow were formed. In deeper depths (60–70 cm) the flow paths of preferential flow were formed later, and therefore, the heterogeneity of water changed with cumulative infiltration.