Ks Reduction Research Articles

Minimizing sampling induced errors in Ks-measurements of stone bearing soils

Macropores have a great effect upon the overall saturated hydraulic conductivity (Ks) of soil samples. However, when using steel-cylinders for soil sampling, especially in stone-rich sites, soil core samples often bear sampling induced macropores due to improper sampling operation. The minimization of this macropore related bias of stone bearing soils‘ matrix Ks values is of high concern. To quantify the sampling induced error of Ks values of stony soils, Ks values were measured on a series of soil cores (n = 46) collected at 5 Bavarian sites under arable and grassland management. Based on texture-related tabulated Ks values, so-called Ks factors were extrapolated, which are related to the macropore fraction of the soil (RoGeR model). The overall Ks values of the soil cores were reduced by these Ks factors. The resulting matrix-related Ks values of the stone bearing soils were contrasted against the General Effective Medium (GEM) approach. Here, the shape of stones was parameterized as well as the critical stone fraction (fc). When applying sample specific fc values, the correlation between the RoGeR- and the GEM approach resulted in a good agreement (R² = 0.9) with an acceptable root mean square error (RMSE) of 4.6 cm/d. Ks reduction using the RoGeR approach seems to be a viable way to fit measured Ks values of stone bearing soil cores with sampling induced macropores to matrix conditions. Alternatively, GEM provides a way to calculate matrix Ks values of stone bearing soils based on tabulated Ks values and soil particle information.

Modulation of IKs channel-PIP2 interaction by PRMT1 plays a critical role in the control of cardiac repolarization.

Recent studies have shown that protein arginine methyltransferase 1 (PRMT1) is highly expressed in the human heart, and loss of PRMT1 contributes to cardiac remodeling in the heart failure. However, the functional importance of PRMT1 in cardiac ion channels remains uncertain. The slow activating delayed rectifier K+ (I Ks) channel is a cardiac K+ channel composed of KCNQ1 and KCNE1 subunits and is a new therapeutic target for treating lethal arrhythmias in many cardiac pathologies, especially heart failure. Here, we demonstrate that PRMT1 is a critical regulator of the I Ks channel and cardiac rhythm. In the guinea pig ventricular myocytes, treatment with furamidine, a PRMT1‐specific inhibitor, prolonged the action potential duration (APD). We further show that this APD prolongation was attributable to I Ks reduction. In HEK293T cells expressing human KCNQ1 and KCNE1, inhibiting PRMT1 via furamidine reduced I Ks and concurrently decreased the arginine methylation of KCNQ1, a pore‐forming α‐subunit. Evidence presented here indicates that furamidine decreased I Ks mainly by lowering the affinity of I Ks channels for the membrane phospholipid, phosphatidylinositol 4,5‐bisphosphate (PIP2), which is crucial for pore opening. Finally, applying exogenous PIP2 to cardiomyocytes prevented the furamidine‐induced I Ks reduction and APD prolongation. Taken together, these results indicate that PRMT1 positively regulated I Ks activity through channel–PIP2 interaction, thereby restricting excessive cardiac action potential.

Effects of sodium adsorption ratio and electrolyte concentration on soil saturated hydraulic conductivity

Sodium adsorption ratio (SAR) and electrolyte concentration (EC) can significantly affect water movement in soil. However, the theoretical mechanisms behind it are rarely studied. In the present study, an analytical function between electrostatic repulsive pressure (PEDL) and SAR/EC was derived in Na-Ca mixed electrolyte solutions or soil water. Soil water SAR and EC controls PEDL through surface potential and midpoint potential between two adjacent soil particles, which consequently influences the saturated soil hydraulic conductivity (Ks). Theoretical calculations show that the PEDL decreases with increasing EC and increases with increasing SAR, and the reduction in Ks is correlated with the repulsive PEDL. Five soils of different dominant clay minerals, specifically kaolinite (K), illite (I) and montmorillonite (M), were used to investigate the relationship between PEDL and change of Ks. The soils were packed in columns and leached with a serial of solutions (constant EC values of 0.5, 1, and 2 ds m−1, respectively) with increasing SAR from 0 to infinity. Our study showed that the Ks decreases with increasing PEDL. At the inflection point of the percent of Ks reduction (Kred) vs. PEDL curve, the critical PEDL values are 8.358 ∼ 8.569 atm and Kred > 92% for the Mungana soil (M), Yarrandoo soil (M, K) and Dunholm soil (M), while the average critical PEDL value is about 12.34 atm and Kred is only ∼51.75% for the Urrbrae soil (I) and Timberlea soil (K). For a given soil, the PEDL is the determinant factor, while other factors such as soil texture and clay type can also affect Ks.

Incorporating solution alkalinity into a hydraulic reduction model to account for disaggregation and dispersion

The use of alkaline and sodic water for irrigation has increased in recent years due to constrained freshwater sources and a rapid increase in industrial by-product wastewater from industries such as coal seam gas and effluent management from other industrial sources. The use of alkaline sodic water can significantly impact soil condition, in particular soil physical properties. The threshold electrolyte concentration (CTH) is generally used to assess soil structural stability when it is subjected to a solution of a given sodium adsorption ratio and electrolyte concentration. The current disaggregation model commonly used is mainly based on the sodium and calcium system, without considering the adverse effects of alkaline anions (e.g., HCO3–) reducing saturated hydraulic conductivity (Ks). This study aimed to assess the incorporation of HCO3– into the semi-empirical disaggregation model approach to determine CTH. The percentage reduction in Ks increased with increasing solution alkalinity and this reduction rate was dependent on soil type. The results indicated that there is a correlation between the reduction of Ks produced by non-alkaline and alkaline solutions represented as SAR and adjusted SAR (SARadj) for up to 30% Ks reduction. This association confirms that the effect of SAR and SARadj on CTH are similar. Therefore, HCO3– can be incorporated into the current disaggregation model to determine CTH (≤20% Ks reduction) for alkaline irrigation waters when disposed of on lands.

The interaction between Sedum root traits and engineered media in green roofs

Sedum sarmentosum and Sedum lineare, two common plants for green roof, were planted in two engineered media meeting FLL standards at three depths. Root characteristics of root length density, root surface area density, and root volume density were quantified. And a key hydraulic property, saturated hydraulic conductivity (Ks) values of the engineered media with and without plants were measured. The results showed that engineered media type, engineered media depth, and their interaction all have a significant impact on Sedum root traits. For the engineered media with Sedum, only engineered media type and depth had a significant effect on Ks. When the type of engineered media was the same, with the same plant used, Ks of the engineered media at a depth of 14 cm was significantly smaller than Ks of any other depth. This can be attributed to the maximum level of RSD and RVD at the 14-cm depth. The reduction in Ks of the perlite-based engineered media due to plant roots is an important finding, as plant roots clog the pore spaces and lead to poor drainage and unexpected ponding in roofs. This research provides better understanding of the interaction between plant roots and engineered media in green roofs.

Mechanisms and processes affecting aggregate stability and saturated hydraulic conductivity of top and sublayers in semi-arid soils

Soils are turned over during agronomic and environmental activities, such that the sublayer becomes the topsoil. Because subsoils have been subjected to high pressures over long periods in the field, their activities and functionality can be changed when they are shifted to the top layer. The present work objective was to investigated the mechanisms and processes affecting the structural stability, and consequently saturated hydraulic conductivity (Ks), of a semi-arid soils, which were taken from < 0.3 m depth (top soils) and > 0.3 m depth (sublayers soils). Disturbed soil samples, with similar aggregate-size distribution and bulk densities, were packed in columns, prewetted with saline solution (SS), and then their Ks values were determined during consecutive leaching with SS and deionized water (DI). The Ks values of the various soils under SS leaching differed due to slaking and swelling processes that changed the soil structure. The effect of the slaking process on Ks reduction was more significant in the top- than sublayer soils. Soil swelling under SS wetting and leaching caused mainly by penetration of water molecules into capillary pores in the soil that increases the pores volumes, and enlarges the aggregate swelling (matrix-type swelling). The average bulk density, and consequently the structural strength, of the aggregates in the sublayer soils were significantly higher than that of the top soils. This suggested that, under matrix-type swelling, less aggregates would be broken in the sublayer than in the top-layer soils. During leaching of the top and the sublayer soils with DI, the aggregates breakdown and Ks reduction were caused mainly by dispersion and osmotic swelling of the clay fractions in the soil. In this case, a negative relationship between the Ks and SAR values was obtained, regardless of the soil depths.

Evaluation of Different Methods to Assess the Hydraulic Behavior in Horizontal Treatment Wetlands

While there have been numerous studies on the rate and development of clogging in horizontal subsurface treatment wetlands (HSTWs) and, consequently, the effects on its hydraulic characteristics, research has not shown a clear understanding of the processes. The existing methods for measuring the impact of clogging provide limited information on the extension and degree of the phenomenon. This study aimed to evaluate the capacity of various measurement techniques to assess the degree and variation in space and time of clogging in HSTWs. Hydraulic conductivity at saturation (Ks) measurements were conducted using a newly implemented scheme, the drainage equation method, and traditional tracer tests, which were carried out in a full-scale HSTW system, located in Sicily, Italy, during 2019. After five years of operation, the results highlighted a severe decrease in Ks (&lt;1000 m day−1) in the inlet zone (despite the fact that the filter gravel was replaced in 2017), a very high reduction of Ks along the central path inside the bed, a nonuniform flow through the HSTW, the presence of stagnant zones, and a reduction of the porosity of the bed gravel. Nonetheless, the mean values of the physical–chemical and bacteriological parameters at the hybrid treatment wetland (hybrid TW) outlet indicated that the partial clogging had no significant effect on the quality of the discharged water. Moreover, the results obtained using the different measurement techniques (in terms of both the Ks values and the flow distribution inside the bed) were consistent with each other and with results obtained previously for the same system. Finally, the most efficient combination of methods to assess clogging in HSTWs was identified.

Effect of Irrigation Water pH on Saturated Hydraulic Conductivity and Electrokinetic Properties of Acidic, Neutral, and Alkaline Soils

The demand for the use of marginal‐quality water as an irrigation resource is increasing in arid and semiarid region lands due to the freshwater shortage. Marginal waters usually have high salinity and high alkalinity and may contain high proportions of ions such as sodium. This study investigated the impact of irrigation water pH on saturated hydraulic conductivity (Ks), cation exchange capacity, net particle charge, and dispersivity of soils. Nine soils with differing pH, alkalinity, clay content, and mineralogy were used in leaching column experiments, with solutions of varying sodium adsorption ratio (20 and 40), electrical conductivity (0.8, 1.5, 2.5, 5, 10, 25, and 50 dS m−1), and pH (6, 7, 8, and 9). The desired pH was achieved by adjusting the HCO3−/Cl− ratio and CO2 partial pressure using CO2 gas with 99.9% purity. Results showed that the increase of solution pH causes an increase in net negative charges on clay particles, resulting in higher exchangeable cations, negative ζ‐potential, and clay dispersion and movement of dislodged particles into pore spaces, resulting in Ks reduction. This effect was more evident for acidic and low‐clay‐content soils. The Ks reduction in relation to pH was less for smectitic and high clay content soil than for kaolinite dominant soils for all concentrations, suggesting resiliency of the smectitic soils under irrigation water with high pH. Results reinforce that it is essential to consider the original pH, clay content, and mineral of the soil and the pH, electrical conductivity, and sodium adsorption ratio of the irrigation water to accurately predict the Ks reduction of the soil.

A pH‐Based Pedotransfer Function for Scaling Saturated Hydraulic Conductivity Reduction: Improved Estimation of Hydraulic Dynamics in HYDRUS

Core Ideas Soil‐specific pedotransfer functions can be incorporated into the HYDRUS model. Electrolyte concentration reduces the adverse effect of pH and Na on soil structural stability. Clay content is important in governing soil hydraulic reduction dynamics due to pH. Hydraulic conductivity is a key soil property governing agricultural production and is thus an important parameter in hydrologic modeling. The pH scaling factor for saturated hydraulic conductivity (Ks) reduction in the HYDRUS model was reviewed and evaluated for its ability to simulate Ks reduction. A limitation of the model is the generalization of Ks reduction at various levels of electrolyte concentration for different soil types, i.e., it is not soil specific. In this study, a new generalized linear regression model was developed to estimate Ks reduction for a larger set of Australian soils compared with three American soils. A nonlinear pedotransfer function was also produced, using the Levenberg–Marquardt optimization algorithm, by considering the pH and electrolyte concentration of the applied solution as well as the soil clay content. This approach improved the estimation of the pH scaling factor relating to Ks reduction for individual soils. The functions were based on Ks reduction in nine contrasting Australian soils using two sets of treatment solutions with Na adsorption ratios of 20 and 40; total electrolyte concentrations of 8, 15, 25, 50, 100, 250, and 500 mmolc L−1; and pH values of 6, 7, 8, and 9. A comparison of the experimental data and model outputs indicates that the models performed objectively well and successfully described the Ks reduction due to the pH. Further, a nonlinear function provided greater accuracy than the generalized function for the individual soils of Australia and California. This indicates that the nonlinear model provides an improved estimation of the pH scaling factor for Ks reduction in specific soils in the HYDRUS model and should therefore be considered in future HYDRUS developments and applications.

Comparing Beerkan infiltration tests with rainfall simulation experiments for hydraulic characterization of a sandy‐loam soil

AbstractSaturated soil hydraulic conductivity, Ks, data collected by ponding infiltrometer methods and usual experimental procedures could be unusable for interpreting field hydrological processes and particularly rainfall infiltration. The Ks values determined by an infiltrometer experiment carried out by applying water at a relatively large distance from the soil surface could however be more appropriate to explain surface runoff generation phenomena during intense rainfall events. In this study, a link between rainfall simulation and ponding infiltrometer experiments was established for a sandy‐loam soil. The height of water pouring for the infiltrometer run was chosen, establishing a similarity between the gravitational potential energy of the applied water, Ep, and the rainfall kinetic energy, Ek. To test the soundness of this procedure, the soil was sampled with the Beerkan estimation of soil transfer parameters procedure of soil hydraulic characterization and two heights of water pouring (0.03 m, i.e., usual procedure, and 0.34 m, yielding Ep = Ek). Then, a comparison between experimental steady‐state infiltration rates, isR, measured with rainfall simulation experiments determining runoff production and Ks values for the two water pouring heights was carried out in order to discriminate between theoretically possible (isR ≥ Ks) and impossible (isR &lt; Ks) situations. Physically possible Ks values were only obtained by applying water at a relatively large distance from the soil surface, because isR was equal to 20.0 mm h−1 and Ks values were 146.2–163.9 and 15.2–18.7 mm h−1 for a height of water pouring of 0.03 and 0.34 m, respectively. This result suggested the consistency between Beerkan runs with a high height of water pouring and rainfall simulator experiments. Soil compaction and mechanical aggregate breakdown were the most plausible physical mechanisms determining reduction of Ks with height. This study demonstrated that the height from which water is poured onto the soil surface is a key parameter in infiltrometer experiments and can be adapted to mimic the effect of high intensity rain on soil hydraulic properties.

Influence of Anionic Surfactant on Saturated Hydraulic Conductivity of Loamy Sand and Sandy Loam Soils

Surfactants released into the terrestrial environment in large amounts can potentially alter the physical, chemical and biological properties of soils, particularly the saturated hydraulic conductivity (Ks). Unfortunately findings regarding this process are quite limited. In this study, column tests were used to analyze the effects of Aerosol 22, a widely used anionic surfactant, on Ks of loamy sand and sandy loam soils. Solutions were injected into columns from the bottom with controlled pressure heads. Both the overall Ks of columns and the Ks of 6 layers at distances of 0–1 cm, 1–3 cm, 3–5 cm, 5–7 cm, 7–9 cm, and 9–10 cm from the bottom, were continuously monitored before and after the surfactant injections. Results showed that the overall Ks of all columns decreased after 2–4 pore volumes of the surfactant injections. However, stabilization and even increase at the beginning of the surfactant injection was also observed due to the different Ks variations in different layers. Specifically, a surfactant injection of 2–4 pore volumes continuously decreased the Ks of the 0–1 cm layers which yielded a Ks reduction of two orders of magnitude and dominated the Ks variations of the column. In contrast, an increase in the Ks of the 1–3 cm and 3–5 cm layers was more likely, while Ks variation of the 5–10 cm layers was less likely. We hypothetically attributed the Ks variations to the swelling of clay, the collapse of soil aggregates and subsequent particle displacements from surfactant adsorption, which caused pore clogging in the bottom 0–1 cm layer and higher porosities in the layers above. The adsorption of the surfactant aggregates and crystallization were also possibly thought to cause a pore clogging in the bottom layer thus decrease the surfactant concentration from the inlet, the severity of which affects these layers less at greater distances from the inlet. In view of the uncertainty showed by the experimental results, we also suggest to include more replicate columns in future studies, so as to increase the repeatability of the measurements.

Evolution of saturated hydraulic conductivity with compression and degradation for municipal solid waste

Municipal solid waste (MSW) specimens were created from synthetic fresh MSW degraded in a laboratory scale enhanced degradation reactor. The degree of degradation and saturated hydraulic conductivity ks were measured to study the effects of compression and degradation on ks of MSW. The degree of degradation was characterized through the ratio of cellulose content to lignin content (i.e., C/L) and the loss ratio of volatile solid (i.e., DOD). ks of MSW specimens with different degrees of degradation was measured through triaxial permeameter tests under different confining pressures. It was found that, when the degradation time increased from 0month to 18months, ks decreased less than 1 order of magnitude for specimens with the same porosity (i.e., n=0.63 or 0.69). However, for specimens with the same degradation time, the decrease of ks could reach 2 orders of magnitude with n decreasing from 0.8 to 0.6. It indicates that compression has much greater influence on the reduction of ks than that of degradation. Based on the Kozeny-Carman model and first-order kinetics, a prediction model related to n and C/L (or DOD) of MSW was proposed to analyze the evolution of ks with compression and biodegradation. The methods to determine the values of model parameters were also proposed.

HYDRAULIC CONDUCTIVITY VARIABILITY IN HORIZONTAL SUBSURFACE FLOW CONSTRUCTED WETLANDS

ABSTRACT Many modifications in hydrodynamic conditions occur inside the bed of a horizontal subsurface flow constructed wetland (HSSF–CW) in operation. Studies on hydraulic conductivity measurement techniques in HSSF–CW are imperative since the monitoring of flow conditions is essential for understanding and controlling its clogging. This study aimed to assess the hydrodynamic behavior in HSSF–CW by means of saturated hydraulic conductivity (Ks) analysis. For this, six HSSF–CW were used: two non-cultivated (control), two cultivated with Tifton 85 (Cynodon spp.), and two cultivated with alligator weed (Alternanthera philoxeroides). Application of swine wastewater (SW) in HSSF–CW started on June 15, 2011, with Ks measurement period between September 9 and November 11, 2011, in which five measurements were performed in different positions along the system length and over experimental period in order to assess the effects of vegetation, position, and time factors on this variable. Ks values ranged from 1,392 to 2,834 m d−1. Plant presence led to Ks decreasing in the systems, but cultivated species had no influence on this variable. Monitoring time of HSSF–CW was no longer enough to provide a reduction in Ks, at 10% probability level.

Effects of petroleum hydrocarbon concentration and bulk density on the hydraulic properties of lean oil sand overburden

In the Alberta oil sands, sand containing less than 8% petroleum hydrocarbon (PHC) is referred to as lean oil sand (LOS) and is used as subsoil in reclamation. The objective of this study was to determine how bulk density and PHC concentration affect the hydraulic properties of LOS. The LOS was packed in soil cores at varying bulk densities and PHC concentrations, representing the range in these parameters that occur in the reclamation setting. The cores were placed on a tension table and pressure plates to measure water retention. The constant head method was used to measure the saturated hydraulic conductivity (Ks) of the LOS. Results show that increasing PHC concentration reduced the water retention of LOS due to the presence of PHCs in soil micropores. PHC concentration also had a significant effect on the van Genuchten curve fitting parameters for the water retention curve, although the shape of the curves remained similar regardless of PHC content. Furthermore, there is a significant reduction in Ks at the high bulk density and high PHC concentrations (3.25%–7.48%), compared with low PHC concentrations (0%–1.63%). Due to the reduced Ks with increased PHCs and bulk density, LOS used as the base material in reclamation will reduce percolation and increase water storage in the reclamation soil cover.

The Effect of Treated Municipal Wastewater and Fresh Water on Saturated Hydraulic Conductivity of a Clay-Loamy Soil

The effect of irrigating with treated municipal wastewater (TMW) and fresh water (FW) on saturated hydraulic conductivity (Ks) was investigated. Ks was determined in undisturbed soil samples, collected from the upper soil layer (0–15 cm) of an illitic clay-loamy soil, after two irrigation periods. Soil samples were analyzed for a number of factors potentially affecting Ks. Analysis of variance for each of these factors was performed between the two treatments in order to detect their differences. Statistically significant differences were found for pH, ECe, SAR, ESP and the concentrations of K+, Na+, Mg2+ which are elements related with TMW and FW quality-characteristics. Correlation between all factors and Ks showed that this was positive for soil ECe, CaCO3 and negative for SAR, ESP, and bulk density. Although the influence of each separate factor was investigated and the differences between the two treatments were verified, their quantitative characteristics could not explain based on existing criteria, (the Ks reduction observed between the TMW-Ks and FW-Ks). The 2:1 type clay minerals which are more susceptible to SAR increase and EC decrease affected Ks values between the two treatments. Our findings are in line with some recently reported results and in this sense, more specific research is needed to clarify all aspects relevant to Ks and the use of TMW for irrigation purposes.

Effects of bacterial cells and two types of extracellular polymers on bioclogging of sand columns

Summary Microbially induced reductions in the saturated hydraulic conductivity, Ks, of natural porous media, conventionally called bioclogging, occurs frequently in natural and engineered subsurface systems. Bioclogging can affect artificial groundwater recharge, in situ bioremediation of contaminated aquifers, or permeable reactive barriers. In this study, we designed a series of percolation experiments to simulate the growth and metabolism of bacteria in sand columns. The experimental results showed that the bacterial cell amount gradually increased to a maximum of 8.91 log10 CFU/g sand at 144 h during the bioclogging process, followed by a decrease to 7.89 log10 CFU/g sand until 336 h. The same variation pattern was found for the concentration of tightly bound extracellular polymeric substances (TB-EPS), which had a peak value of 220.76 μg/g sand at 144 h. In the same experiments, the concentration of loosely bound extracellular polymeric substances (LB-EPS) increased sharply from 54.45 to 575.57 μg/g sand in 192 h, followed by a slight decline to 505.04 μg/g sand. The increase of the bacterial cell amount along with the other two concentrations could reduce the Ks of porous media, but their relative contributions varied to a large degree during different percolation stages. At the beginning of the tests (e.g., 48 h before), bacterial cells were likely responsible for the Ks reduction of porous media because no increase was found for the other two concentrations. With the accumulation of cells and EPS production from 48 to 144 h, both were important for the reduction of Ks. However, in the late period of percolation tests from 144 to 192 h, LB-EPS was probably responsible for the further reduction of Ks, as the bacterial cell amount and TB-EPS concentration decreased. Quantitative contributions of bacterial cell amount and the two types of extracellular polymers to Ks reductions were also evaluated.

Reduction in Saturated and Unsaturated Hydraulic Conductivities of an Andisol by Vinasse Application

With the increase in the production of bioethanol, it has become urgent to establish a sustainable system for recycling vinasse that includes its application to land. The purpose of this study was to determine the impact of vinasse application on the hydraulic properties of the soil. An incubation experiment was conducted to investigate the biological effects. Temporal changes in both saturated and unsaturated hydraulic conductivities [Ks and K(ψ), respectively] after applying vinasse were measured by the falling‐head method and the steady‐state flux control method, respectively. After vinasse application, the number of bacteria increased by one order of magnitude, whereas the number of fungi increased by two orders of magnitude compared with a test with deionized water. A remarkable reduction in Ks was observed within the fourth day after vinasse was applied instead of deionized water. The reduction in Ks was due to both biological and physical clogging. We attempted to determine what factors contributed to these effects on the Ks reduction and found that 73 to 92% of the Ks reduction was caused by physical clogging due to suspended solids. The temporal reduction in K(ψ) was within one order of magnitude; however, the values of K(ψ) dropped by two orders of magnitude for the same matric potential (ψ) value at the end of each column experiment. Moreover, 91% of the increase in the total amount of organic matter came from vinasse. From the experimental results, we concluded that the reductions in both Ks and K(ψ) occurred during vinasse application and the main reason for the reductions was the physical clogging due to suspended solids.

Effects of Irrigation with Different Effluents on Saturated Hydraulic Conductivity of Arid and semiarid Soils

The use of recycled wastewater that has undergone various treatments (effluent) for irrigation is becoming one of the main means by which to mitigate the pressure on freshwater resources. The main objective of this study was to improve the basic understanding of the effects of irrigation with various effluents on the saturated hydraulic conductivity (Ks) of arid and semiarid soils. Clay, loamy, and sandy soils were sampled from experimental plots irrigated with freshwater or secondary effluent for &gt;3 yr, and were used in column experiments. Leaching the loamy and clay soils with reverse osmosis (RO) effluent, which contained low electrolyte concentrations, led to clay swelling and dispersion and thereby decreased the soil Ks In these soils, the high concentration of suspended solid particles and dissolved organic matter (DOM) in oxidation pond (OP) effluent caused significant pore clogging, which reduced the Ks Leaching the soils with ultrafiltered effluent maintained high Ks values due to the low concentration of suspended solid particles and DOM, their small sizes, and the relatively high electrical conductivity of this effluent. The relatively large average pore size in the sandy soil prevented pore clogging and Ks reduction when leached with RO and OP effluent. Secondary effluent irrigation increased the soil exchangeable Na percentage (ESP) compared with freshwater irrigation but did not change the organic matter content in the soil. In the loamy and clay soils, this higher ESP of the effluent‐irrigated soils resulted in greater reductions in Ks when leached with deionized water than occurred in freshwater‐irrigated soils.

Reuse of laundry greywater as affected by its interaction with saturated soil

Summary We conducted laboratory experiments on a well aggregated, non-swelling clay soil to measure water retention, saturated hydraulic conductivity (Ks) and salts present in the irrigation and drainage water to study the impacts of reusing untreated laundry greywater (GW) to irrigate soils in the residential garden beds. We used undisturbed (field) and disturbed (loose and compacted) soil cores to represent situations typical in old and recently established garden beds. Using tap water (TW), soil water retention within 0–10 kPa matric suction was found to be significantly lower and hysteresis significantly higher for the loose soil than the field or compacted soil. Measured values of Ks with TW were in the order loose >field>compacted soil, but these values were reduced to 5–16% when GW was used. Further measurements of Ks with application of TW to soil cores which had been previously saturated with GW, greater reduction in Ks occurred with Ks → 0 for the compacted soil. A comparison of the quality of GW with TW as irrigation water indicated an approx. increase in pH of GW by 3 pH units over TW, twofold increase in EC, fivefold increase in Na concentration and a 10-fold increase in Sodium Adsorption Ratio (SAR). Measurements of drainage water during the water flux measurements for Ks showed that the soil was able to reduce pH and EC of infiltrating water, store some salts (Na and K) and released Ca and Mg from soil so that the quality of drainage water improved substantially to become similar in quality to TW. Thus, long-term use of untreated laundry greywater may reduce salt contamination of groundwater, but predispose soils to future environmental hazards from excess sodium accumulation.

A New Role for Calmodulin in Ion Channel Biology

See related articles, pages 1048–1054 and 1055–1063 A time-dependent repolarizing current carried by outward movement of potassium ions was first identified by Hodgkin and Huxley, and has been recognized in heart since the 1960s.1,2 Experiments in the 1980s found that the amplitude of the current, then termed I K, increased when intracellular calcium was increased.3 The key advance to further understanding of the physiology of this important repolarizing current was the recognition in 1990 that it includes at least two distinct components, now termed I Kr and I Ks.4 These two currents have very different voltage-dependent gating behaviors and sensitivities to drugs and to activation of second messenger pathways. The amplitude and gating of I Ks is quite labile in experimental preparations and increases dramatically in response to activation of PKA.5–7 Such I Ks variability has been invoked as a mechanism underlying variability in the extent to which I Kr blockers prolong QT interval, a common problem in clinical medicine and drug development.7–10 At its simplest level, patients with robust I Ks display minimal QT prolongation with I Kr block, whereas those with I Ks reduction may display little QT prolongation at baseline but striking QT prolongation when I Kr, the major mechanism supporting normal repolarization in this setting, is blocked by drugs. Molecular genetic studies in the mid 1990s led to identification of the genes whose expression underlies these currents: I Kr is generated by expression of KCNH2 (initially termed HERG ), and I Ks is generated by the coexpression of a pore forming subunit, KCNQ1 (formerly termed KvLQT1 ), with important function modifying ancillary subunit KCNE1 (or minK).11 Mutations in KCNQ1 are the most common cause of type 1 long QT syndrome (LQT1). When mutations in KCNQ1 , KCNE1 , …