Zero-tension Lysimeters Research Articles

The role of nitrogen and iron biogeochemical cycles in the production and export of dissolved organic matter in agricultural headwater catchments

Abstract. To better understand the seasonal variations in environmental conditions regulating dissolved organic matter (DOM) export in agricultural headwater catchments, we combined the monitoring of nitrate, iron, soluble phosphorus, and DOM concentration (as dissolved organic carbon; DOC) and composition (3D fluorescence) in soil and stream waters at regular intervals during 1 hydrological year. We installed 17 zero-tension lysimeters in organic-rich top soil horizons (15 cm below the surface) in the riparian area of a well-monitored agricultural catchment in French Brittany and collected them at a fortnightly frequency from October 2022 to June 2023. We observed a large increase in DOC concentrations in soil waters during the high-flow period linked to the establishment of Fe-reducing conditions and the subsequent release of DOM. We also noted that the timing and the spatial variability in Fe(II) biodissolution in soils was regulated by nitrate from agricultural origin and the heterogeneity of water flow paths at the hillslope scale. Contrary to our current understanding of DOM export in headwater catchments, these results lead us to consider the winter high-flow period as an active phase of both DOM production and export.

Subsurface mixing of different soil water pools in a permafrost-underlain headwater catchment, Qilian Mountains, Northeastern Tibetan Plateau

Recently studies postulate that there are two distinct soil water pools, i.e., mobile and immobile soil water (MSW and IMSW), and different soil waters have different mobility to generate runoff. Evaluating the influences of soil thawing on the subsurface mixing between different soil waters is important for understanding subsurface hydrological processes. In this study, the isotopic differences between different soil waters were evaluated in a permafrost-underlain headwater catchment by comparing the variations of stable isotopes and seasonal origin of MSW and bulk soil water (BSW), including both IMSW and MSW. BSW was sampled using soil augering and cryogenic vacuum distillation in thawed and frozen soil layers, and MSW was collected using a zero-tension lysimeter in thawed soil layers. The results show the following: (1) The average δ2H values of MSW, thawed BSW, and frozen BSW were similar during the spring snowmelt period (SSP), this can be attributed to weak evaporation and their similar origin, which is supported by the high line-conditioned excess values and their similar seasonal origin index values. (2) The enriched MSW collected during the SRP compared to the spring MSW and was associated with enriched summer precipitation, and the IMSW experienced strong evaporation during the period from the SSP to the SRP, both leading to enriched summer BSW compared to the spring BSW. (3) The frozen and thawed BSW had very similar isotopic compositions and seasonal origin, indicating the close hydrological connection between them and the important recharge of the melting frozen soil to soil water or runoff. The different freeze–thaw stages and soil moisture conditions controlled the stable isotope variations and mixing of different soil waters, this results in the different mobility of the mobile/immobile soil waters involved in the runoff generation processes during the SRP and the SSP, and therefore these features are useful to verify the isotopes-aided precipitation–runoff models applied in such catchments.

Long-term analysis of soil water regime and nitrate dynamics at agricultural experimental site: Field-scale monitoring and numerical modeling using HYDRUS-1D

Intensive agricultural practices increase agrochemical pollution, particularly nitrogen (N) based fertilizers, which present an environmental risk. This study aims to evaluate long-term (2009–2020) data on soil water regime and nitrate dynamics at an agricultural experimental site on fine-textured soils and to better understand the implications of N management in relation to groundwater pollution. The field site is located in the Biđ field (eastern Croatia), in the proximity of the Sava river. Zero-tension lysimeters were installed at six selected locations. Lysimeters were used to monitor the water regime, i.e., outflows in which nitrate concentration was measured, while additional soil-water samples were collected via 4 and 15-meter-deep monitoring wells. Soil hydraulic parameters were estimated by combining the laboratory measurements, and estimation in RETC software. Water regime and nitrate leaching in lysimeters were simulated using HYDRUS-1D for each year to allow crop rotation and to evaluate their effects individually. The HYDRUS-1D model successfully reproduced lysimeter outflows and nitrate dynamics, which was confirmed with high R2 values (water: 93% above 0.7, and nitrate: 73% above 0.7) indicating the good performance of the model simulating nitrification chain reactions. Principal component analysis (PCA) was performed to identify the relationships among all soil properties and environmental characteristics. The results showed the complex interaction of soil hydraulic properties, precipitation patterns, plant uptake, and N application. All locations have a decreasing trend of nitrate leaching over the investigation period. Most of the lysimeter outflows and elevated nitrate concentrations were connected to the wet period of the year when the soil was saturated, and evapotranspiration was low. The results of this study show that it is important to optimize N fertilizer applications for each particular environmental condition to reduce nitrate loss. The study indicates the importance of long-term field studies, key for agro-hydrological modeling and the improvement of agricultural practices.

Two types of installation of 3D‐printed zero tension lysimeter for soil leaching and water bucket model validation

AbstractQuantifying and analysing leaching water is essential to understand water and nutrient cycles and the vertical transport of elements through soils. Zero tension lysimeters (ZTLs) have been widely used to capture the soil solution leaching by gravity. This study designed and evaluated a 3D‐printed ZTL (ZTL3D) with specific characteristics and materials to quantitatively capture dissolved element fluxes. By 3D‐printing the ZTLs, we were able to include specific 3D structures and precise details in the design allowing installation of samplers from the surface rather than trenches, and thus avoiding the need for installation trenches to remain open. The ZTLs3D connect directly with the surface, do not depend on secondary collectors, can be installed at any depth, and samplers are easily retractable when dismantling the field set up. The material used, Nylon 12, was tested for dissolved organic carbon (DOC) release. The ZTL3D design was printed in two different external shapes while characteristics and internal design were identical. The difference in external shape was to study the effects of two contrasting types of installation: a cylindrical sampler for vertical installation (by soil coring from the surface) and a rectangular samplers for horizontal installation (from a pit or a trench wall). We installed them at different depths (2, 30 and 75 cm) in a forest soil and conducted rainfall simulation experiments. A water bucket model (WBM), created to calculate the water drainage fluxes that the ZTLs3D should collect, reproduced very well the variation in soil water content measured by soil moisture sensors installed adjacent to the ZTLs3D at 16, 30, 50 and 75 cm depth. Drainage fluxes simulated by the WBM showed that the vertical installation performed better at collecting water at all depths than the horizontal installation, but overall the ZTLs3D failed to collect the simulated amounts of drainage water. Nonetheless, the ZTLs3D did collect leachate water, enabling their chemical analysis. Combining the concentrations in the water collected by the ZTLs3D with the modelled drainage fluxes does allow estimation of DOC‐ and elemental leaching rates. This article presents the novel design of these two types of ZTLs3D because future improvements may result in better performance, and discusses their (dis)agreement with the modelled WBM fluxes.Highlights New 3D‐printed zero tension lysimeters (ZTLs) to capture element fluxes when installed vertically (cylindrical design) or horizontally (cubic design) were tested. Two external sampler shapes were created to optimise the installation process and both collected drainage water successfully. Vertical installation ZTLs worked better than horizontal types, but neither well‐reflected drainage fluxes simulated by water bucket model (WBM). Combined with WBM, both ZTL types provided a reliable method for quantifying nutrient and organic carbon leaching at different soil depths.

Modeling seasonal soil moisture dynamics in gley soils in relation to groundwater table oscillations in eastern Croatia

This study aims to explain complex vadose zone hydrology of fine-textured (gley) agricultural soils influenced by a shallow and dynamic groundwater (GW) levels. The field site was located in the Biđ field (Eastern Croatia), where a detailed soil survey was performed. The simulations included a three-year period (2016–2018) at four locations. Soil hydraulic parameters (SHP) were estimated based on variables determined in the laboratory, while soil water flow was monitored using in-field zero-tension lysimeters. Piezometers were installed and used to monitor daily oscillations of groundwater levels (average depth to GW 2.2 m), while data from nearby Sava River was monitored. Unsaturated flow and water regime assessment was performed using HYDRUS-1D numerical modeling. Additional SHP optimization of van Genuchten-Mualem parameters (α and n) was performed using Shuffled Complex Evolution algorithm (SCE). The autocorrelation analysis was used to detect patterns in the precipitation, GW, and river level time series, while the Mutual Information (MI) was used to estimate the codependence of the processes in unsaturated zone and the main hydrological events. The model successfully (R2 0.72 – 0.94) reproduced measured lysimeters outflows. The outflows from lysimeters were connected to precipitation patterns, transpiration intensity, and soil moisture content influenced by the shallow water table. Comparable MI values obtained for precipitation, GW, and river level suggest a concurrent role of these parameters in the unsaturated flow dynamics. The relationship between upward flux/water storage change into the domain, and transpiration/growth stages, suggests a strong connection between the water fluxes and the root water uptake. Results confirm the importance of GW for the agricultural production due to the major influence on upper soil layer moisture.

Evaluation of contribution rate of the infiltrated water collected using zero-tension lysimeter to the downward migration of 137Cs derived from the FDNPP accident in a cedar forest soil

The vertical distribution of 137Cs in forest soil is important for predicting air dose rates and future cycling in forest ecosystems. However, there are many unexplained questions about the mechanisms of its downward migration. In this study, the 137Cs flux by rainfall infiltration was observed for three years from August 2017 using zero-tension lysimeters in a mature cedar forest where monitoring of the vertical distribution of 137Cs has been conducted since 2011. As a result, the 137Cs concentration in infiltrated water through the litter layer, 5 cm and 10 cm showed a tendency to be high in summer, but no such seasonal variation was found at 20 cm. Although the 137Cs inventory in the litter layer has been exponentially decreasing, the annual 137Cs fluxes in infiltrated water through the litter layer were almost the same in three years, and about 0.14–0.17% of the deposition density of 137Cs. Comparing these 137Cs fluxes with the apparent amounts of downward migration of 137Cs estimated from the change in the vertical distribution of 137Cs, the contribution rate of the infiltrated water to downward migration of 137Cs from litter to soil was calculated to be 8.5–17.7%. Similarly, the contribution rate in mineral soil layers was calculated to be 0.6–0.8% on a measured basis and estimated to be 3.0 ± 0.2% after correcting the amount of collected water, which is a problem with zero-tension lysimeter. It indicates that rainfall infiltration can explain a small part of the downward migration of 137Cs, thus further studies are required to clarify the contribution rate of remaining mechanisms such as advection-diffusion, colloidal transport, physical mixing, bioturbation, and growth and death of plant roots.

Leaching of Phosphomonoesterase Activities in Beech Forest Soils: Consequences for Phosphorus Forms and Mobility

Phosphomonoesterases play an important role in the soil phosphorus (P) cycle since they hydrolyze P monoester to phosphate. Their activity is generally measured in soil extracts, and thus, it remains uncertain how mobile these enzymes are and to which extent they can be translocated within the soil profile. The presence of phosphomonoesterases in soil solutions potentially affects the share of labile dissolved organic P (DOP), which in turn would affect P leaching. Our study aimed at assessing the production and leaching of phosphomonoesterases from organic layers and topsoil horizons in forest soils and its potential effect on dissolved P forms in leachates obtained from zero-tension lysimeters. We measured phosphomonoesterase activities in leached soil solutions and compared it with those in water extracts from litter, Oe/Oa, and A horizons of two beech forests with a contrasting nitrogen (N) and P availability, subjected to experimental N × P fertilization. In addition, we determined phosphate and DOP. In soil solutions leached from litter, Oe/Oa, and A horizons, phosphomonoesterase activities ranged from 2 to 8 μmol L–1 h–1 during summer, but remained below detection limits in winter. The summer values represent 0.1–1% of the phosphomonoesterase activity in soil extracts, indicating that enzymes can be translocated from organic layers and topsoils to greater soil depths. Activities of phosphomonoesterases obtained by water extracts were greater in the organic layer of the P-poor site, while activities of those in soil solutions were similar at the two sites. Nitrogen addition increased phosphomonoesterase activities in leached soil solutions of the organic layer of the N- and P-poor soil. Using a modeling approach, we estimated that approx. 76% of the initial labile DOP was hydrolyzed to dissolved inorganic P within the first 24 h. Back calculations from measured labile DOP revealed an underestimation of approx. 15% of total dissolved P, or 0.03 mg L–1. The observed leaching of phosphomonoesterases implies that labile organic P could be hydrolyzed in deeper soil horizons and that extended sample storage leads to an underestimation of the contribution of DOP to total dissolved P leaching. This has been neglected in the few field studies measuring DOP leaching.

Soil Phosphorus Translocation via Preferential Flow Pathways: A Comparison of Two Sites With Different Phosphorus Stocks

Weather events where a dry period is followed by a heavy rainfall event appear to affect phosphorus (P) exports through preferential flow pathways from forest soils. Furthermore, the P stock of a site seems to influence the amount of exported P. To explore this, we installed zero-tension lysimeters in three trenches at two sites with contrasting soil P stocks. Lysimeters were installed in three different depths (topsoil, upper subsoil and deep subsoil) to explore P depth transport. We covered the forest floor above the lysimeters with tarpaulins to simulate a dry period and afterwards artificially irrigated the area. This experiment was repeated three times at each site. Lysimeter samples were analyzed for concentrations of total P, organic and inorganic dissolved P and particle bound P (> 0.45 µm). Loads of P and water flow rates were calculated. Results reveal differences between sites, events and depths. At both sites, concentrations and loads of P in the topsoil lysimeters were higher than in the subsoil lysimeters. This difference was particularly evident at the low P site and emphasized its nutrient recycling efficiency. Dissolved inorganic P showed clear peaks in the topsoil lysimeters, whereby in the subsoil, particle-bound P peaks were partly noticeable at both sites. Depth transport of P into the subsoil depended on initial soil moisture, soil texture and the spatial distribution of flow pathways. Further, we observed large heterogeneity within a single site, dependent on profile-specific characteristics. We conclude that under certain conditions, there is a depth transport of P into the subsoil and therefore a potential of P loss, especially for particle-bound P. Heterogeneity of the sites hampered the clear identification of effects and illustrated the need for further research with a specific focus on the role of soil heterogeneity.

Low-intensity surface fire effects on carbon and nitrogen cycling in soil and soil solution of a Scots pine forest in central Germany

Dissolved and particulate organic carbon (DOC, POC) and nitrogen (DN, PN) are important constituents and indicators of the C and N dynamics in forested ecosystems, but little is known about fire effects on the fluxes of these elements. Biweekly fluxes at three different soil depths (organic layer O, mineral soil A, mineral soil B) were measured with zero-tension lysimeters before and after (prescribed) low-intensity surface fires in a Scots pine forest in central Germany. Measurements of soil organic C and total N concentrations, cold (soluble) and hot (labile) water-extractable DOC and DN, and soil respiration also were conducted for both pre- and post-burn bulk soils. Linear mixed-effect modelling (LMM) revealed that repeated low-intensity fire reduced DOC (−64%) and DN (−11%) fluxes in the organic layer, but increased soil CO2 fluxes (+7%). A nutrient flush from the charred material into the A horizon, as indicated by an enhanced solution pH (+11%) and electrical conductivity (+68%), may have stimulated microbial activity, leading to enhanced DOC (+47%) and DN (+202%) production and fluxes, respectively. The B horizon was unaffected by the fire treatment and retained DOC and DN. In contrast to DOC and DN fluxes, POC and PN fluxes were less affected by the fire treatment and decoupled from those of dissolved organic matter (DOM). Our findings indicate that low-intensity surface fires can significantly affect generally nutrient-poor soil systems by causing a short-term flush (“hot moment”) of DOM in the mineral A horizon (vertical “hot spot”) and by sorption in the mineral B horizon.

Post-fire interactions between soil water repellency, soil fertility and plant growth in soil collected from a burned piñon-juniper woodland

Woody plant encroachment can increase nutrient resources in the plant-mound zone. After a fire, this zone is often found to be water repellent. This study aimed to understand the effects of post-fire water repellency on soil water and inorganic nitrogen and their effects on plant growth of the introduced annual Bromus tectorum and native bunchgrass Pseudoroegneria spicata. Plots centered on burned Juniperus osteosperma trees were either left untreated or treated with surfactant to ameliorate water repellency. After two years, we excavated soil from the untreated and treated plots and placed it in zero-tension lysimeter pots. In the greenhouse, half of the pots received an additional surfactant treatment. Pots were seeded separately with B. tectorum or P. spicata. Untreated soils had high runoff, decreased soil-water content, and elevated NO3–N in comparison to surfactant treated soils. The two plant species typically responded similar to the treatments. Above-ground biomass and microbial activity (estimated through soil CO2 gas emissions) was 16.8-fold and 9.5-fold higher in the surfactant-treated soils than repellent soils, respectably. This study demonstrates that water repellency can influence site recovery by decreasing soil water content, promoting inorganic N retention, and impairing plant growth and microbial activity.

Nitrogen leaching from grassland ecosystems managed with organic fertilizers at different stocking rates

ABSTRACTThis study shows the effect of organic fertilizers at different stocking rates, on nitrogen (N) leaching, measured using zero-tension lysimeters under undisturbed grassland soil. The experiment included two organic fertilizer types – cow dung with dung water (D) and slurry (S), both at a range of stocking rates: 0.9 LU (livestock unit) ha−1, 1.4 LU ha−1, 2.0 LU ha−1 (corresponding to 54, 84 and 120 kg N ha−1, respectively) and a control (C) treatment. In percolated water, the contents of ammonia nitrogen (NH4+–N) and nitrate nitrogen (NO3−–N) were studied. The average concentration of NH4+–N ranged from 0.91 to 1.44 mg l−1 on fertilized plots compared to 0.55 mg l−1 on the control plot. The average concentration of NO3−–N ranged from 5.2 to 9.5 mg l−1 on fertilized plots compared to 3.2 mg l−1 on the control plot. The results of this study showed that the use of organic fertilizers at chosen stocking rates influenced N leaching, but the concentration of N did not exceed the limits for drinking water permitted by Czech legislation. Stocking rates at 2.0 LU ha−1 and below do not result in elevated N concentrations in percolated water that pose environmental threat.

Lysimetry methods for monitoring soil solution electrical conductivity and nutrient concentration in greenhouse tomato crops

In intensive agricultural systems, such as Mediterranean greenhouses, monitoring soil nutrient and salt status is essential for optimising vegetable production and minimising soil and water pollution. This work analyses the dynamics of electrical conductivity (ECSS) and nutrient concentration in soil solution collected simultaneously with various zero-tension lysimeters and a suction cup (a tension lysimeter) throughout two greenhouse tomato crops. The ECSS obtained with zero-tension lysimeters (funnel and plate lysimeter) was generally lower than that with the suction cup, irrespective of soil depth. Moreover, the soil solution concentration of potassium, calcium, magnesium, sodium, chloride and sulphate obtained with funnel lysimeter (FullStop™) was generally lower than that with suction cup throughout both cycles, while no clear differences were found for the nitrate concentration at 0.25m depth in the 2013/14 cycle or at 0.38m depth in the 2015 one. Overall, it appears that the soil solutions collected with the suction cup and the funnel lysimeter represent different soil solution status and processes. The funnel lysimeter collects freely draining soil solution, and it may therefore provide better information about the movement of elements between soil horizons, whereas the suction cup can sample soil solution from soil pores with longer residence times, especially under unsaturated flow conditions, and might represent better the available element concentrations for plant nutrition studies. The differential response found for nitrate could be due to the fact that it is a very mobile element within the soil. The soil water matric potential was slightly higher in the soil with zero-tension lysimeters throughout most of the 2013/14 cycle, and so these devices might alter soil solution movement and water and nutrient availability. On the other hand, in general, a good fit was found between the soil solution concentration of nitrate, potassium, calcium and sodium measured with a rapid analysis system (Laqua™) and that measured using the reference laboratory method. This rapid system, in combination with the suction cup, can facilitate the farmers’ control of soil nutrient and salt status.

Temporal variation in the strength of podzolization as indicated by lysimeter data

This study examines trends in podzolization – both temporally and with depth – as indicated by translocation of dissolved organic carbon (DOC), iron (Fe) and aluminum (Al) in soil water. Water as saturated flow was captured by zero-tension lysimeters installed below the O, E and B horizons of six Spodosol pedons in Michigan, USA. Over a 2-year timespan, we sampled soil water on 36 different dates, resulting in 505 samples. All samples were analyzed for DOC, whereas Fe and Al contents were determined for a subset of 227 samples.Cumulative water fluxes are high during both spring snowmelt and the fall (autumn) season, when much water is moving as saturated flow. Water flux rates are much greater during snowmelt, and when averaged over all horizons, 1.15 times more water is translocated through the soil during snowmelt than in fall, even though the latter is routinely twice as long. Translocation of DOC out of the O horizon is a dominant process in these soils during snowmelt, peaking in mid-snowmelt. It peaks again – even higher – in fall, as rains strip C from fresh litter. Overall, little DOC leaves the soil system; B horizons are effective traps for C being transported in soil water. Surprisingly, E horizons retain DOC in almost all seasons, but particularly in fall and early snowmelt, as water percolates through C-rich, fresh litter. The thick, bright, C-poor E horizons in these soils suggest that, over long timescales, in situ mineralization of C exceeds the net retention of DOC from the O horizons above. Translocation of Fe and Al in soil water also has a distinct annual bimodality, largely following that of DOC. This component of podzolization peaks in mid-snowmelt and again late in fall. On an annual basis, considerably more Al moves in soil water than Fe; 1.9 times more Al than Fe is translocated out of E horizons, and 1.8 times more Al is lost from B horizons.Our study supports existing pedogenic theory for the snowy midlatitudes, in which snowmelt is seen as a key period for podzolization. Daily rates of translocation of metals and DOC moving in saturated flow during snowmelt are considerably higher than for any other time of year. Our study also sheds new light on the importance of fall rains to podzolization. Although the daily rates of translocation for fall are much less than during snowmelt, the greater length of the season, the relatively high frequency of rain events, and the abundance of fresh C combine to make fall an important period for translocation of metals and DOC. Thus, our study highlights that podzolization here has a short but intense “pulse” during snowmelt, and a second, less intense but longer period during fall. Little podzolization occurs during winter, and during summer, translocation occurs only during infrequent, large storms.

Effect of Inorganic and Organic Fertilizer Application on Nitrate Leaching in Wetland Soil Under Field Tomato (Lycopersicon esculentum) and Leaf Rape (Brassica napus)

The implications of increased application of N inputs to agricultural systems in Africa for nitrate leaching are still only partially understood in Africa. A lysimeter experiment was carried out on a loamy sandy soil in central Zimbabwe in order to determine the effect of cattle manure and mineral N application on nitrate leaching. A cluster of zero-tension (free flowing) lysimeters was established, and leachates and soil samples were analyzed for nitrate N concentration and mineral N content, respectively. Increasing the application rates from 100 kg N fertilizer + 15 Mg manure to 200 kg N fertilizer + 30 Mg manure ha−1 increased NO3–N leaching by 60 %. Applied N lost in leachate increased by 6 and 19 % for the tomato and rape crops, respectively, when N fertilizer and manure application rate was doubled. Higher mineral N fertilizer and cattle manure applications increase total N lost in leachate. The pollution of groundwater with nitrate in leaf rape cropping in Zimbabwe is potentially higher than that found in the production of tomato for the crop rotation in the current study.

Pulses of Podzolization: The Relative Importance of Spring Snowmelt, Summer Storms, and Fall Rains on Spodosol Development

This study was performed in the eastern Upper Peninsula of Michigan, where Spodosols are extremely well developed. We instrumented a Typic Durorthod with zero-tension lysimeters to capture water leaving the O, E, and B horizons and with sensors to determine volumetric water contents with depth. We also occasionally measured snowpack depths and determined snow water equivalents. These field data were used to validate a hydrologic model that was run for the site using nearby National Weather Service (NWS) data. Good agreement between the modeled output and field data from the site enabled us to apply 1961 to 2013 NWS data from three additional stations along a transect that spans the range of podzolization strength in Michigan as inputs to the model. Soils remain dry throughout the summer and slowly wet up in fall. The more strongly developed soils in the north are slightly wetter in fall, facilitating breakdown of fresh litter and enhancing production of soluble organic materials. Their translocation into the mineral soil is presumably deepest and most pronounced during snowmelt, facilitated by a strong “pulse” of cold snowmelt water. This pulse comprises well over half of the annual flux of water at 100-cm depth, even though its timespan is short. Snowmelt fluxes are larger and of shorter duration in the north, where podzolization is strongest. By storing precipitation in a thick snowpack, the pedogenic system compresses inputs of water, creating deeper, more concentrated pulses of percolation when soluble organic materials are readily available; this is the essence of podzolization in this region.

Variability of drainage and solute leaching in heterogeneous urban vegetation environs

Abstract. Deep percolation enhancement from recycled wastewater irrigation may contribute to salt accumulation and water table elevation that can ultimately cause soil and ground water degradation. Variation of drainage rate and solute leaching were investigated in an urban park containing heterogeneous landscape plants that were irrigated with recycled wastewater. Field monitoring was undertaken at Veale Gardens in the Adelaide Parklands, Australia. Based on landscape variation in Veale Gardens, two landscape zones were defined: one being largely covered with turf grasses with few trees and shrubs (MG) with the second zone being mostly trees and shrubs with intermittent turf grasses (MT). Experiments were performed on two zero-tension lysimeters placed horizontally 100 cm below ground to monitor the variation of volume and quality indicators of drained water for four seasons. The outcomes showed a significant variation of drainage quantity and quality in the MT and MG zones. The low vegetation cover in the MG zone resulted in more drained water than in the high vegetation cover (MT zone). In both zones, more drainage water was collected in winter than in other seasons. This is in spite of the input water showing a maximum rate in summer. The seasonal salinities measured in the two lysimeters showed very similar trends with the lowest salinity rate in autumn with the levels increasing through winter and spring. Chemical analyses of leachate solute and salt loading indicated no impact from using recycled wastewater.

Dynamic modelling of the long term behaviour of cadmium, lead and mercury in Swiss forest soils using CHUM-AM

The applicability of the dynamic soil model CHUM-AM was tested to simulate concentrations of Cd, Pb and Hg in five Swiss forest soils. Soil cores of up to 50cm depth were sampled and separated into two defined soil layers. Soil leachates were collected below the litter by zero-tension lysimeters and at 15 and 50cm soil depths by tension lysimeters over two years. The concentrations of Cd, Pb and Hg in the solid phase and soil solution were measured by ICP-MS (Cd, Pb) or CV-AFS (Hg). Measured metal concentrations were compared with modelled concentrations using CHUM-AM. Additionally we ran the model with three different deposition scenarios (current deposition; maximum acceptable deposition according to the Swiss ordinance on Air Pollution Control; critical loads according to CLRTAP) to predict metal concentrations in the soils for the next 1000years. Assuming current loads concentrations of Cd and Pb showed varying trends (increasing/decreasing) between the soils. Soils rich in organic carbon or with a high pH value showed increasing trends in Cd and Pb concentrations whereas the concentrations in the other soils decreased. In contrast Hg concentrations are predicted to further increase in all soils. Critical limits for Pb and Hg will partly be exceeded by current loads or by the critical loads proposed by the CLRTAP but the critical limits for Cd will rarely be reached within the next 1000years. In contrast, maximal acceptable deposition will partly lead to concentrations above the critical limits for Pb in soils within the next 400years, whereas the acceptable deposition of Cd will not lead to concentrations above the proposed critical limits. In conclusion the CHUM-AM model is able to accurately simulate heavy metal (Cd, Pb and Hg) concentrations in Swiss forest soils of various soil properties.

A Comparison of Tension and Zero-Tension Lysimeter and PRS™ Probes for Measuring Soil Water Chemistry in Sandy Boreal Soils in the Athabasca Oil Sands Region, Canada

Because soil acidification models use soil solution chemistry as a critical endpoint for predicting adverse biological effects, it is essential that various options for measuring soil water chemistry are assessed. This is particularly true for the Athabasca oil sands region of Alberta, Canada, as widespread acidification impacts are predicted based on modelled soil solution chemistry, but no soil solution data are currently available to validate these estimates. In this study, tension and zero-tension lysimeters were compared over a 3-year period at a jack pine stand (Pinus banksiana Lamb.) established in an acidic, sandy brunisol adjacent (<2 km) to one of the largest mines in the region. During the final year, plant root simulator (PRS™) probes were also installed for comparative purposes as they are currently being used in the region to assess changes in soil chemistry. Despite the close proximity to the mine and high sulphur (S) and nitrogen (N) deposition, the annual average pH of the soil water collected by both lysimeter types was around 6.5 and NO3–N concentrations were negligible. Annual SO4 concentrations in tension lysimeters averaged 12–14 mg L−1 and were typically two to four times higher than in zero-tension lysimeters; similar differences between lysimeters were observed for divalent base cations (Ca and Mg). Values (ion supply rates) obtained by PRS™ were affected by both the position of the probes (horizontal vs. vertical) and the duration of probe insertion (1, 2 and 5 months), such that higher values for most nutrients were obtained using probes that were installed vertically and for shorter periods of time. The Ca/Mg ratio in lysimeters and PRS™ probes were comparable, but other elemental ratios such as Ca/S or Ca/Al were much higher in PRS™ probes than in lysimeter water. Similar to lysimeter data, NO3–N values obtained by PRS™ probes were very low. PRS™ probes may be useful for assessing differences in nutrient availability among sites, but they do not reflect soil water chemistry that is used in geochemical acidification models.

Forest floor leachate fluxes under six different tree species on a metal contaminated site

Trees play an important role in the biogeochemical cycling of metals, although the influence of different tree species on the mobilization of metals is not yet clear. This study examined effects of six tree species on fluxes of Cd, Zn, DOC, H+ and base cations in forest floor leachates on a metal polluted site in Belgium. Forest floor leachates were sampled with zero-tension lysimeters in a 12-year-old post-agricultural forest on a sandy soil. The tree species included were silver birch (Betula pendula), oak (Quercus robur and Q. petraea), black locust (Robinia pseudoacacia), aspen (Populus tremula), Scots pine (Pinus sylvestris) and Douglas fir (Pseudotsuga menziesii). We show that total Cd fluxes in forest floor leachate under aspen were slightly higher than those in the other species' leachates, yet the relative differences between the species were considerably smaller when looking at dissolved Cd fluxes. The latter was probably caused by extremely low H+ amounts leaching from aspen's forest floor. No tree species effect was found for Zn leachate fluxes. We expected higher metal leachate fluxes under aspen as its leaf litter was significantly contaminated with Cd and Zn. We propose that the low amounts of Cd and Zn leaching under aspen's forest floor were possibly caused by high activity of soil biota, for example burrowing earthworms. Furthermore, our results reveal that Scots pine and oak were characterized by high H+ and DOC fluxes as well as low base cation fluxes in their forest floor leachates, implying that those species might enhance metal mobilization in the soil profile and thus bear a potential risk for belowground metal dispersion.

Nutrient Leaching and Soil Retention in Mined Land Reclaimed with Stabilized Manure

Two environmental problems in Pennsylvania are degraded mined lands and excess manure nutrients from intensive animal production. Manure could be used in mine reclamation, but the large application rates required for sustained biomass production could result in significant nutrient discharge. An abandoned mine site in Schuylkill County, Pennsylvania, was used to test manure nutrient stabilization by composting and by mixing with primary paper mill sludge (PMS). Reclamation treatments were lime and fertilizer, composted poultry manure (78 and 156 Mg ha), and poultry manure (50 Mg ha) mixed with PMS (103 and 184 Mg ha) to achieve C-to-N ratios of 20 and 29. Leachates were collected with zero-tension lysimeters, and during 3 yr following amendment application, <1% of added N leached from the compost treatments. The manure+PMS C:N 29 treatment leached more N than any other treatment (393 kg N ha during 3 yr, 12.4 times more N than compost treatments), mostly as pulses of NO in the first two fall seasons following reclamation. The manure+PMS C:N 20 treatment leached 107 kg N ha during 3 yr. Three years after amendment application, most of the N and P added with the manure-based amendments was retained in the mine soil even though net immobilization of N by PMS appeared to be limited to 3 mo following application. Composting or mixing PMS with manure to achieve a C-to-N ratio of 20 can effectively minimize N leaching, retain added N in mine soil, and provide greater improvement in soil quality than lime and fertilizer amendment.