Soil aggregation is an important property, affecting issues such as soil structure and dust load. To investigate the potential to evaluate soil aggregation status via proximal sensing, we conducted a comprehensive study using the legacy soil spectral library (SSL) of Israel representing arid and semiarid environments. The SSL was segregated into six soil aggregate size fractions as follows: 2-1.4 mm, F1; 1.4-1.0 mm, F2; 1.0-0.5 mm, F3; 0.5-0.25 mm, F4; 0.25-0.1 mm, F5; < 0.1 mm, F6; and the average aggregate size (AVG, in mm) was calculated. In addition, another 74 soil attributes were measured along with their sample reflectance spectra across the 0.4-2.5-mu m spectral region. A comprehensive correlation matrix between all soil attributes enabled isolating four cementing agents (CAs) that bind the primary particles into aggregates: clay content, clay mineral (smectite), organic matter and free iron oxide content. Generating pedotransfer functions (PTFs) with these CAs revealed equations that fairly predicted the aggregate size fractions F1 (R-2 = 0.68), F2 (R-2 = 0.79), F3 (R-2 = 0.67), F5 (R-2 = 0.61) and AVG (R-2 = 0.78) with high accuracy. The six aggregate size fractions and AVG were divided into three groups based on their relation to the CAs: group A (F1, F2, F3, AVG) presenting positive correlations with the CAs, group B (F4, F6) presenting poor relationships with the CAs, and group C (F5) presenting negative correlations with the CAs. As the CAs were found to be chromophoric substances, it was possible to predict each CA from spectral-based models. A separate spectral-based analysis was also performed to evaluate the aggregate size fractions directly with no a priori information or PTF adoption. This analysis revealed high statistical agreement with spectral assignments for the four selected CAs. Whereas groups A and C were successfully predicted in the validation stage spectral-based models (F1 [R-2 = 0.68], F2 [R-2 = 0.79], F3 [R-2 = 0.7], F5 [R-2 = 0.57] and AVG [R-2 = 0.67]), the predictions of group B were poorer relationships against the selected CAs that present important spectral assignments. We concluded that soil aggregation stage can be assessed directly or indirectly (via PTF) using spectral analysis and a data-mining approach. Assuming that the reflectance information from hyperspectral remote-sensing means, such as EMIT (NASA initiative), will soon be available from orbit (2022), this approach may pave the way for monitoring soil aggregation status from afar, to determine the soil's potential as a dust source.

Soil Aquifer Treatment (SAT) of secondary effluents activates biogeochemical processes in the soil and aquifer environment to accomplish large-scale reclamation of municipal wastewater. We studied in detail the long-term geochemical processes of SAT soils in the Dan Region Reclamation Project, near Tel Aviv, Israel. Soil redox potential shifts between the anoxic/reduced state during the recharge stage and oxic/oxidized state following drainage. Extensive geochemical changes have occurred in the soils over the 23 yr period of operation during which 1650 m cumulative hydraulic load of effluents has been recharged. Organic matter accumulated in the top horizon of the soil profile while Ca carbonate and Mn oxide were dissolved and leached. Minor and trace elements typically enriched in municipal effluents, accumulated in the topsoil. A conceptual model was developed to describe the array of biogeochemical processes at the upper soil horizons of the SAT system.

We investigated changes in element content and distribution in soil profiles in a study designed to monitor the geochemical changes accruing in soil due to long-term secondary effluent recharge, and its impact on the sustainability of the Soil Aquifer Treatment (SAT) system. Since the initial elemental contents of the soils at the studied site were not available, we reconstructed them using scandium (Sc) as a conservative tracer. By using this approach, we were able to produce a mass-balance for 18 elements and evaluate the geochemical changes resulting from 19 years of effluent recharge. This approach also provides a better understanding of the role of soils as an adsorption filter for the heavy metals contained in the effluent. The soil mass balance suggests 19 years of effluent recharge cause for a significant enrichment in Cu, Cr, Ni, Zn, Mg, K, Na, S and P contents in the upper 4m of the soil profile. Combining the elements lode record during the 19 years suggest that Cr, Ni, and P inputs may not reach the groundwater (20 m deep), whereas the other elements may. Conversely, we found that 58, 60, and 30% of the initial content of Mn, Ca and Co respectively leached from the upper 2-m of the soil profile. These high percentages of Mn and Ca depletion from the basin soils may reduce the soil's ability to buffer decreases in redox potential pe and pH, respectively, which could initiate a reduction in the soil's holding capacity for heavy metals.

The fate of organic matter (OM) in large-scale infiltration basins used for wastewater treatment by the soil aquifer treatment (SAT) system was investigated. Measured changes in the organic matter concentrations in the soil profiles of the infiltration basins and detailed long-term records of OM concentrations in the recharged effluent and in the observation wells and recovery wells water, were used to calculate OM material balances in the SHAFDAN wastewater treatment plant. serving the City of Tel-Aviv, Israel, since 1977. The average annual total organic matter (TOM) load delivered by the effluents to the soil was similar to 5 kg m(-2) y(-1). Soil OM concentrations increased from 0.11% in the pristine soil to similar to 0.8% and similar to 0.6%, in the 0-0.15 m and 0.15-0.30 m soil layers, respectively, after similar to 20 y of effluent recharge, but did not change significantly in the 1.80-2.10 m deep layer. The OM accumulation rates in the top two soil layers were fast initially, then declined slowly and the OM concentrations approached a steady state following 10-15 y of effluent recharge, This suggests that stabilization of the 'active biofilm' layer in the infiltration basins' soils is a relatively slow process. Material-balance calculations showed, that accumulated OM in the top 0-2.1 m soil layer amounted to only similar to 4% of the TOM added by the effluents during similar to 20 y of recharge. Along the flow pathway of the effluent through the vertical 50-100 m thick soil-sediment column. DOC concentrations decreased by 70-90% (from similar to 18.9 mg L(-1) to similar to 3.7 mg L(-1)). Continued flow in the aquifer from the observation wells to the recovery wells further decreased DOC concentrations by about 50% (from similar to 3.7 to similar to 1.5 mg L(-1)). (C) 2008 Elsevier B.V. All rights reserved.

We studied the long-term in situ accumulation of Cu, Cr, Ni, and Zn in the soil profile of a large-scale effluent recharge basin after 24 yr of operation in a wastewater reclamation plant using the Soil Aquifer System approach in the Coastal Plain of Israel. The objective was to quantify metals accumulation in the basin's soil profile, clarify retention mechanisms, and calculate material balances and metal removal efficiency as the metal loads increase. Effluent recharge led to measurable accumulation, relative to the pristine soil, of Ni and Zn in the 0- to 4-m soil profile, with concentration increases of 0.3 to 1.3 mg kg(-1) and 2.9 to 6.4 mg kg(-1), respectively. Copper accumulated only in the 0- to 1-m top soil layer, with concentration increase of 0.28 to 0.76 mg kg(-1). Chromium concentration increased by 3.1 to 7.3 mg kg(-1) in the 0- to 1-m horizon and 0.9 to 2.3 mg kg(-1) at deeper horizons. Sequential selective extraction showed Cu tended to be preferentially retained by Fe oxides and organic matter (OM), Cr by OM, Ni by OM, and carbonate and Zn by carbonate. The average total retained amounts of Cu, Cr, Ni, and Zn were 0.7 +/- 1.0, 13.6 +/- 4.8, 4.3 +/- 3.6, and 28.7 +/- 5.4 g per a representative unit soil slab (1 m(2) x 4 m) of the basin, respectively. This amounts to 3.6 +/- 4.9%, 79.5 +/- 28.0%, 8.0 +/- 6.9%, and 9.3 +/- 1.8% of the Cu, Cr, Ni, and Zn loads, respectively, applied during 24 yr of effluent recharge (total of approximately 1880 m effluent load). The low long-term overall removal efficiency of the metals from the recharged effluent in the top horizon may be due to the metals' low concentrations in the recharged effluent and the low adsorption affinity and retention capacity of the sandy soil toward them. This leads to attainment of a quasi-equilibrium and a steady state in element distribution between the recharged effluent solution and the soil after few years of recharge and relatively small cumulative effluent loadings.

Retardation and breakthrough of phosphorous in the soil/sediment profiles of a SAT system at the Shafdan wastewater treatment plant, Israel, were investigated in situ. Area-weighted average effluent load to the whole site was 65 m yr−1. Annual average concentrations of P in the recharged effluent ranged between about 1.5 and 7.7 mg L−1 during 25 yr of operation, while P in groundwater remained ⩽0.05 mg L−1 in most wells. Recharge is done through an overlying layer of >40 m sandy soil/sediment formations. By combining results of isotherm tests, long-term monitoring of phosphorous (P) in solid and liquid phases of the recharge site, a simple multi-cell tracer-movement model and measured chloride breakthrough curves to the groundwater we calculated P distribution coefficients and estimated the retardation factor of P. Laboratory measured, isotherm-based distribution coefficient, KdI, was about 4–6 L kg−1 at equilibrium P concentration <6 mg L−1, while field-based KdF was considerably higher, reaching about 20–55 L kg−1 after a load of around 1800 m effluent was recharged. Measured P breakthrough times into two shallow observation wells were 19–21 yr. Calculated P breakthrough times using KdF data agreed with observations while those calculated using KdI grossly underestimated retardation and predicted much shorter breakthrough times. This validated the approach and model used. Estimated P breakthrough times to the deeper observation wells and the recovery wells are more than 100 yr and 400–1100 yr, respectively. These estimates show that P contamination of the reclaimed effluents in the Shafdan plant will not be a problem in the foreseeable future.

-Reduction of structural Fe in Na-exchanged dioctahedral smectites decreases swellability in water, but because clay interlayers also collapse in the process the concomitant effect on surface hydration energy is uncertain. This study examined the hydration behavior of oxidized and reduced dioctahedral smectite clays exchanged with polar (Na) and weakly-polar (organic) cations to determine the nature of the surface before and after Fe reduction, and to determine if clay surfaces are hydrophilic or hydrophobic. The H20 content in various dioctahedral smectites decreased if Na was replaced by tetramethylammonium (TMA), trimethylphenylammonium (TMPA), or hexadecyltrimethylammonium (HDTMA). Among the organo-clays, H20 adsorption decreased with increasing complexity of the cation. For oxidized smectites, those exchanged with TMPA retained less H20 than those exchanged with Na at all pressures. The extent of this difference depended on the clay and decreased with increasing applied pressure. Reduction of Fe(III) to Fe(II) in the octahedral sheets decreased the swelling of Na-saturated smectites, apparently causing some previously swelling interlayers to collapse. If the Na interlayer cation was exchanged to alkylammonium after reduction, but prior to swelling-pressure measurements, the swelling increased or remained near constant, suggesting that the organo-cation disrupted the collapse process of the interlayers associated with the reduced smectite layers. Reduced TMPA-saturated smectite surfaces are more strongly hydrated if the octahedral sheet is reduced than if oxidized. Thus, reduction of structural Fe increases the hydration energy of smectite basal surfaces, but swellability could decrease or increase depending on the extent of interlayer collapse occurring with different exchangeable cations. Key Words--Alkylammonium, Ferric Iron, Ferrous Iron, HDTMA, Hydrophilic Surface, Hydrophobic Surface, Interlayer Cation, Oxidation, Reduction, Surface Hydration, Swelling, TMA, TMPA. USA I N T R O D U C T I O N Clay minerals and humic substances substantially influence the sorption properties of soils. A m o n g clay minerals, smecti tes have the greatest effect on the sorption of cations, owing to the negat ive charge der ived f rom isomorphous substitution in the octahedral and/or tetrahedral sheets, and to water, because of surface hydration energy. The negat ive surface charge is balanced by exchangeable cations, which are most ly hydrated inorganic cations (e.g., Na § K +, Ca 2§ Mg 2+) in nature. Such clays may be ineffect ive as sorbents for poorly water-soluble (hydrophobic) organic contaminants (Sheng and Boyd, 1998), but replacement of the inorganic cation with an organic cation such as te t raa lkylammonium causes considerable change in the hydration and swell ing properties o f the clay. Replacement of the inorganic cation with an organic cat ion decreases the affinity o f the smecti te surface for H20 because the hydrat ion energy of the organic cations is much lower than that of inorganic cations. Moreover , the substantial amount of organic carbon associated with the organo-clay causes these modif ied clays to become effect ive sorbents for r emoving organic cont Present address: Brown and Williamson Tobacco Company, 2600 Weaver Road, Macon, Georgia 31217, USA. taminants f rom wate r (Boyd and Jaynes , 1994; Lawrence et al., 1998; Xu et al., 1997). Exchange of inorganic cations by a lky lammonium is also a we l l -known method for measur ing the layer charge of smectites, vermiculi tes , and other clay minerals (Lagaly and Weiss, 1976; Laird, 1994). Charge heterogenei ty is a c o m m o n property of swell ing 2:1 clay minerals which arises f rom charge density variations f rom layer to layer or within individual layers (Lagaly, 1994). Inhomogeneous charge-densi ty distributions were reported for H-exchanged smecti tes which had auto-transformed to (H, A1, Fe, Mg)-exchanged forms with aging (Janek et al., 1997). In that study, the fraction of highest -charge layers was decreased or complete ly r emoved during auto-transfor-

We studied the long-term accumulation processes and material balances of phosphorus (P) in the soil/sediment profiles of large-scale effluent recharge basins used for wastewater reclamation by the soil aquifer treatment (SAT) system. The objective was to quantify and clarify the long-term performance of soil/sediment in the SAT system as a sorbent to filter out P from the recharged effluent. Total P concentration in the soil/sediment profiles of the Shafdan wastewater treatment plant (WWTP) increased over 25 years of operation (1977-2001) by 20-220 mg kg(-1), as a result of adding loads of 0.17-6.2 kg m(-2) of P. Retained P in the 0-2.0 m soil layer increased from 0.06 to 0.31 kg m(-2) with increasing cumulative load of P while the retained percentage gradually decreased from 19 to 5% of the cumulative P load. Accumulation rate of P in the 0-0.15 m horizon in the basins was inversely proportional to recharge time, decreasing from similar to 28 mg P kg(-1) year(-1) during the first 3 years of operation, to < 2.3 mg P kg(-1) year(-1) between the 20th and 25th years of operation. Thus, P content in this horizon approached a steady state after about 10-15 years of effluent recharge under the operational conditions of the Shafdan WWTP. Phosphorus concentration in deeper horizons increased at constant rates of approximately 7.8, 5.9 and 2.9 mg P kg(-1) year(-1) in the 0.15-0.30, 0.30-0.60 and 1.80 to 2.10-m horizons, respectively, over the 25 years of effluent recharge. However, the accumulation front of P appears gradually to have moved deeper in the soil profile. In general, this phenomenon may be explained by kinetic limitations to the achievement of full adsorption equilibrium for P between the flowing solution and the solid phase components of the soil. In addition, both the increase of EPC0(the equilibrium P concentration in solution at which there is no sorption or desorption to or from the soil under the given conditions), caused by long-term effluent recharge, and gradual decrease of the annual average concentration of P in the effluent input after 1995, may result in the steady-state level of P in the topsoil of the basin.

The Soreq recharge basins, used for wastewater reclamation employing the Soil-Aquifer Treatment (SAT) system, have been recharged, on average, by about 1,800 m depth of secondary effluent during their operation period of ∼25 years. An estimated amount of ∼6 kg P m−2 was added to the soil/sediment column during this period. The objective of this study was to compare phosphorous sorption characteristics of representative pristine soils in the Soreq recharge site to those of the basin soils sampled after a long period of effluent recharge. Batch isotherm experiments were conducted: samples of one g of soil were equilibrated with 25 mL of 0.02 M NaCl solution containing 0–3.2 mM of phosphate for 7 days at 25± 1∘C and P sorption was measured. Long-term effluent recharge significantly decreased the maximum P sorption capacity of the top sandy soil (0.15–0.3 m) and only very slightly decreased maximum P isotherm capacity of the deep clayey-sand soil (10–10.5 m). The retention of P in the basin sandy soil primarily involved sorption and surface precipitation reactions on soil carbonates. In the basin clayey-sand soil, P was retained by its sorption on surfaces of Fe, Al, Mn oxide/hydroxides and clay minerals. Long-term effluent recharge increased EPC0, (the equilibrium P concentration in solution at which there is no sorption or desorption to or from the soil under the given conditions), of the basin soils compared to the pristine soils. Due to loading of the top horizons with P by prolonged recharge and reduced P concentration in the effluent, EPC0 of the basin sandy soil is now equal to the average P concentration of the recharged effluents. If effluent P concentration will decrease further, the top sandy soil will become a source of P to the reclaimed water, rather than a sink. The clayey-sand layers and lenses in the vadose zone of the SAT system of the Soreq site offer a large capacity for P adsorption. With gradual leaching of carbonate minerals and synthesis of secondary clay minerals, driven by long-term effluent recharge, P retention mechanisms in the basin soil may be changed, but this process would be extremely slow.

A rapid semi-micro digestion technique for the determination of organic carbon was described. Our approach was stressed on the dichromate digestion process of organic carbon in soil. We optimized digestion temperature and time, adapted potentiometric titration for organic C detection. Optimal digestion condition was heating at 140 degrees C (block set temperature) and holding for 30min. The method was compared with classical wet method and a good agreement was achieved.

The overall objectives of the project were: (a) To measure and study in situ the effect of irrigation with reclaimed sewage effluents on redox processes and related chemical dynamics in soil profiles of agricultural fields. (b) To study under controlled conditions the kinetics and equilibrium states of selected processes that affect redox conditions in field soils or that are effected by them. Specifically, these include the effects on heavy metals sorption and desorption, and the effect on pesticide degradation. On the basis of the initial results from the field study, increased effort was devoted to clarifying and quantifying the effects of plants and water regime on the soil's redox potential while the study of heavy metals sorption was limited. The use of reclaimed sewage effluents as agricultural irrigation water is increasing at a significant rate. The relatively high levels of suspended and, especially, dissolved organic matter and nitrogen in effluents may affect the redox regime in field soils irrigated with them. In turn, the changes in redox regime may affect, among other parameters, the organic matter and nitrogen dynamics of the root zone and trace organic decomposition processes. Detailed data of the redox potential regime in field plots is lacking, and the detailed mechanisms of its control are obscure and not quantified. The study established the feasibility of long-term, non-disturbing monitoring of redox potential regime in field soils. This may enable to manage soil redox under conditions of continued inputs of wastewater. The importance of controlling the degree of wastewater treatment, particularly of adding ultrafiltration steps and/or tertiary treatment, may be assessed based on these and similar results. Low redox potential was measured in a field site (Site A, KibutzGivat Brenner), that has been irrigated with effluents for 30 years and was used for 15 years for continuous commercial sod production. A permanently reduced horizon (Time weighted averaged pe= 0.33±3.0) was found in this site at the 15 cm depth throughout the measurement period of 10 months. A drastic cultivation intervention, involving prolonged drying and deep plowing operations may be required to reclaim such soils. Site B, characterized by a loamy texture, irrigated with tap water for about 20 years was oxidized (Time weighted average pe=8.1±1.0) throughout the measurement period. Iron in the solid phases of the Givat Brenner soils is chemically-reduced by irrigation. Reduced Fe in these soils causes a change in reactivity toward the pesticide oxamyl, which has been determined to be both cytotoxic and genotoxic to mammalian cells. Reaction of oxamyl with reduced-Fe clay minerals dramatically decreases its cytotoxicity and genotoxicity to mammalian cells. Some other pesticides are affected in the same manner, whereas others are affected in the opposite direction (become more cyto- and genotoxic). Iron-reducing bacteria (FeRB) are abundant in the Givat Brenner soils. FeRB are capable of coupling the oxidation of small molecular weight carbon compounds (fermentation products) to the respiration of iron under anoxic conditions, such as those that occur under flooded soil conditions. FeRB from these soils utilize a variety of Fe forms, including Fe-containing clay minerals, as the sole electron acceptor. Daily cycles of the soil redox potential were discovered and documented in controlled-conditions lysimeter experiments. In the oxic range (pe=12-8) soil redox potential cycling is attributed to the effect of the daily temperature cycle on the equilibrium constant of the oxygenation reaction of H⁺ to form H₂O, and is observed under both effluent and freshwater irrigation. The presence of plants affects considerably the redox potential regime of soils. Redox potential cycling coupled to the irrigation cycles is observed when the soil becomes anoxic and the redox potential is controlled by the Fe(III)/Fe(II) redox couple. This is particularly seen when plants are grown. Re-oxidation of the soil after soil drying at the end of an irrigation cycle is affected to some degree by the water quality. Surprisingly, the results suggest that under certain conditions recovery is less pronounced in the freshwater irrigated soils.

Soil aquifer treatment (SAT) of wastewater relies on extensive biogeochemical processes in the soil and aquifer to achieve large-scale and economic reclamation of municipal effluents. Removal of trace metals from the wastewater is a prime objective in the operation, but the long-term sustainability of the adsorptive filtration capacity of the soils is an open question. Solid/solution partitioning (measured by the distribution coefficient, K(d)) and solid/solid partitioning (measured by selective sequential dissolution, SSD) of heavy metals were measured in soils sampled from active recharge basins in a wastewater reclamation plant and were compared to the adjacent pristine dune. K(d) values for the adsorption of Cu, Ni and Zn, measured in short-term adsorption experiments positively and significantly correlated with solution pH. Quantitative estimation of Cu, Ni and Zn adsorption on multi-sorbents indicated that surface adsorption and precipitation on Fe oxides and/or carbonate may be the major mechanisms of metal retention in these soils. SSD analyses of metal partitioning in soils exposed to approximately 20yr of effluent recharge showed that all solid-phase components, including the most stable 'residual' component, competed for and retained added Cu and Zn. Copper preferentially partitioned into the oxide component (32.0% of the soil-accumulated metal) while Zn preferentially partitioned into the carbonate component (51.6% of the soil-accumulated metal).

Arsenic, a carcinogenic trace element, threatens not only the health of millions of humans and other living organisms, but also global sustainability. We present here, for the first time, the global industrial-age cumulative anthropogenic arsenic production and its potential accumulation and risks in the environment. In 2000, the world cumulative industrial-age anthropogenic arsenic production was 4.53 million tonnes. The world-wide coal and petroleum industries accounted for 46% of global annual gross arsenic production, and their overall contribution to industrial-age gross arsenic production was 27% in 2000. Global industrial-age anthropogenic As sources (as As cumulative production) follow the order: As mining production >As generated from coal >As generated from petroleum. The potential industrial-age anthropogenic arsenic input in world arable surface in 2000 was 2.18 mg arsenic kg −1 , which is 1.2 times that in the lithosphere. The development of substitute materials for arsenic applications in the agricultural and forestry industries and controls of arsenic emissions from the coal industry may be possible strategies to significantly decrease arsenic pollution sources and dissipation rates into the environment.

The bioavailability and mobility of heavy metals in soils is dependent upon redistribution processes between solution and solid phases and among solid-phase components. This paper reviews the definitions and applications of two newly developed parameters, the redistribution index and the reduced partitioning parameter, in quantifying redistribution processes of heavy metals in contaminated soils. The redistribution index depicts the removal/attainment of metal-contaminated soils from/to the fractional distribution pattern characteristic of non-amended soils, while the reduced partitioning parameter quantifies the relative binding intensity of heavy metals in soils. Over time, metal salt-spiked and sludge-amended soils approached the fractional distribution pattern of non-amended soils. The rates of redistribution of metals and their binding intensity in soils were affected by the metal species, loading levels and soil properties. Metals in contaminated soils at low loading levels approach the fractional distribution pattern of non-amended soil more rapidly than those at high loading levels. The sequence order of approach by metals to the fractional distribution pattern of non-amended soil was: Cd>Cu>Ni=Zn>Cr. In both non-amended and contaminated soils, Cr had the highest binding intensity, Cd the lowest, and Cu, Ni and Zn, intermediate values. In addition to our own data, primarily on metal salt-spiked soils, these two indices are also used to evaluate redistribution processes of heavy metals in sewage sludge-amended soils from other published reports.

Nitrogen is an essential element for life. Specifically, fixed nitrogen (i.e. NH3, NH4+, NOx or N that is chemically bound to either inorganic or organic molecules and can be released by hydrolysis to form NH3 or NH4+) is useful to living organisms. Nitrogen on present-day Mars has been analysed only in the atmosphere. The inventory is a small fraction of the amount of nitrogen presumed to have been received by the planet during its accretion. Where is the missing nitrogen? Answering this question is crucial for understanding the probability of the origin and evolution of life on Mars, and for its future astrobiological exploration. The two main processes that could have removed nitrogen from the atmosphere include: (1) non-thermal escape of N atoms to space and (2) burial within the regolith as nitrates and ammonium salts. Nitrate would probably be stable in the highly oxidized surface soil of Mars and could have served as an NO3− sink. Such accumulations are observed in certain desert environments on Earth. Some NH4+ nitrogen may also be fixed and stabilized in the soil by inclusion as a structural cation in the crystal lattices of certain phyllosilicates replacing K+. Analysis of the Martian soil for traces of NO3− and NH4+ during future missions will provide important information regarding the nitrogen abundance on Mars. We hypothesize that Mars soil, as typical of extremely dry desert soils on Earth, is likely to contain at least some of the missing nitrogen as nitrate salts and some fixed ammonium bound to aluminosilicate minerals.

We report the results of a systematic long-term study of infiltration rate (IR) in a large scale effluent recharge plant, showing a significant dependence of the infiltration rate on temperature (T). Water level and T were continuously monitored and recorded in several infiltration basins of an operating wastewater treatment plant (WWTP) during the course of a 4-yr study of basin geochemistry and performance. Infiltration rates were calculated from the slope of linear plots of water level vs. time during the drainage phase. Systematic interseasonal variations of IR were observed and were strongly correlated to water T Calculations showed that the variation of IR with T was generally 1.5 to 2.5 times larger than that predicted from effluent viscosity changes per se, suggesting the possible involvement of other T-dependent factors. This may have profound effects on the overall efficacy of wastewater reclamation and other water-recharge operations.