Mobilisation of Al, Fe, and DOM from topsoil during simulated early Podzol development and subsequent DOM adsorption on model minerals

Podzols are characterised by mobilisation of metals, particularly Al and Fe, and dissolved organic matter (DOM) in topsoil horizons, and by immobilisation in subsoil horizons. We mimicked element mobilisation during early podzolisation by irrigating the AE horizon of a Dystric Arenosol with acetic acid at different flow velocities and applying flow interruptions to study rate-limited release in experiments with soil cylinders. We used eluates in batch experiments with goethite and Al-saturated montmorillonite to investigate DOM reactivity towards minerals. Both the flow velocity and flow interruptions affected element release, pointing to chemical non-equilibrium of release and to particles, containing Fe and OM mobilised at larger flow velocity, characteristic of heavy rain or snowmelt. Based on chemical extractions, the source of mobilised Al and Fe, the vast majority of which was complexed by DOM, was no oxide phase, but rather organic. Rate limitation also affected the composition of DOM released. Carboxyl and phenolic species were the most important species adsorbed by both minerals. However, DOM composition affected the extent of DOM adsorption on goethite more distinctly than that on montmorillonite. Our findings evidence that the intensity of soil percolation affects quantitative and qualitative element release during early podzolisation and adsorptive DOM retention in subsoil horizons.

The Life Cycle Environmental Performance of On-Site or Decentralised Wastewater Treatment Systems for Domestic Homes

There is little knowledge regarding the environmental sustainability of domestic on-site or decentralised wastewater treatment systems (DWWTS). This study evaluated six unique life cycle environmental impacts for different DWTTS configurations of five conventional septic tank systems, four packaged treatment units, and a willow evapotranspiration system. Similar freshwater eutrophication (FE), dissipated water (DW), and mineral and metal (MM), burdens were noted between the packaged and conventional system configurations, with the packaged systems demonstrating significantly higher impacts of between 18% and 56% for climate change (CC), marine eutrophication (ME), and fossils (F). At a system level, higher impacts were observed in systems requiring (i) three vs. two engineered treatment stages, (ii) a larger soil percolation trench area, and (iii) pumping of effluent. The evapotranspiration system presented the smallest total environmental impacts (3.0–10.8 lower), with net benefits for FE, ME, and MM identified due to the biomass (wood) production offsetting these burdens. Further analysis highlighted the sensitivity of results to biomass yield, operational demands (desludging or pumping energy demands), and embodied materials, with less significant impacts for replacing mechanical components, i.e., pumps. The findings highlighted the variation in environmental performance of different DWTTS configurations and indicated opportunities for design improvements to reduce their life cycle impacts.

Improvement of root morphological characteristics on water percolation rate in grassland soils of Yellow River riparian buffer strips

Soil water percolation is an important process required to meet plant water needs, determine soil water storage, and affect soil water quality in riparian buffer strips. However, the effects of plant roots on soil percolation in riparian buffer strips are not totally understood, and contradictory results have been carried out on the effects of the root system on soil percolation rates. This study aimed to investigate soil percolation in natural grasslands and evaluate the relationships between root morphological characteristics and percolation rates. Path analysis was used to provide information on the relative contribution of root characteristics on soil percolation rates. Three mixed grasslands (Imperata cylindrica + Phragmites australis, Imperata cylindrica + Cynodon dactylon, Imperata cylindrica + Juncellus serotinus) were selected in the Yellow River wetland natural reserves of Zhengzhou. Soil percolation rates (initial, average and steady infiltration rates) were measured by using double-ring methods, and plant root morphological characteristics were analyzed. Soil percolation rates and plant root characteristics parameters of Imperata cylindrica + Phragmites australis and Imperata cylindrica + Cynodon dactylon were higher than those of Imperata cylindrica + Juncellus serotinus. Initial percolation rate of Imperata cylindrica + Phragmites australis and Imperata cylindrica + Cynodon dactylon at 0-10cm depth was 58.06% and 95.55% higher than that of Imperata cylindrica + Juncellus serotinus, respectively. Percolation rates had a significant positive correlation with root characteristic parameters, and the main factor controlling soil percolation rates was root volume density. Mixed natural grasslands with more root volume density improved soil infiltration and percolation rates.

A Large-volume Rhizotron for Evaluating Root Growth Under Natural-like Soil Moisture Conditions

An experimental system that allows imposition of precise irrigation treatments with easy and quick observations of unrestricted root growth of woody plants was developed. The system mimics natural deep soil percolation and facilitates rapid assessment of large root populations. It was designed to be relatively inexpensive to build so that treatments could be efficiently replicated. Designs for this star-shaped rhizotron were developed and evaluated with the goals of: 1) optimizing volume and shape for minimal physical restriction and use with mature woody plants; 2) developing a drainage system comparable to natural deep soils; and 3) facilitating ease, accuracy, and duration of data acquisition. The final design allows efficient root observation, uses a wick-type drainage system to provide a near-uniform profile of soil moisture, and is easily manageable for precise long-term data acquisition. This rhizotron has eight independent viewing/sampling windows and holds 0.16 m3 of soil. An associated lightweight and compact camera positioning frame was developed that facilitates acquisition of digital photographs of soil profiles for time-series assessment of morphological and architectural parameters.

Amounts of throughfall and lysimetric water in a sub-mountain beech forest in the Kremnické vrchy Mts. (West Carpathian Mts., Slovakia)

The paper deals with throughfall and soil percolation in a sub-mountain beech forest situated at the Ecological Experimental Site (EES) Kremnické vrchy Mts. (the West Carpathian Mts., Slovakia). The research was conducted in 1988–2008. The throughfall was sampled at regular periods, both from the open plot (clear-cut) and from the plot with complete stocking, covered with a mature beech stand. The soil percolation was evaluated with soil lysimeters. In 1989 and 2004, the plots were treated with cutting – with the aim to reduce the current stocking. The average amount of throughfall was 772.2 mm in the open plot and 616.3 mm in the control. The amount of soil percolation decreased with increasing depth: from 398.9 mm to 103.8 mm in the control and from 488.8 mm (surface) through 169.9 mm (10 cm) to 188.8 mm (25 cm) in the open plot. The differences between the plots were statistically highly significant. No significant differences were found between the soil horizons.

Nutrient cycling in a poplar plantation (Populus trichocarpa × Populus deltoides 'Beaupré') on former agricultural land in northern Belgium

Hydrological fluxes, atmospheric deposition, litterfall, and soil percolation of the most important nutrients were measured in an 18-year-old poplar plantation on a well-drained silt loam soil during 2 consecutive years. Downward soil water flux and transpiration are the most important factors in the water balance. Around 80% of total nitrogen input (6.6 and 6.5 kmol·ha–1 in years 1 and 2, respectively) originates from litterfall. After nitrification only a negligible amount of nitrate leaches during the growing season. Yearly uptake of nitrogen by the poplar ecosystem (woody biomass, leaves, and ground vegetation) approximately equals the input, of which more than 50% is accounted for by the leaves. This indicates very efficient nitrogen cycling. Total deposition of base cations originates from two processes, dry deposition (Mg2+ and Ca2+) and canopy leaching (K+ and Ca2+). Litter input of Ca2+ represents about 83% of the total input (stand deposition + litterfall), Mg2+ about 61%, and K+ less then 50%. Percolation of base cations at 1 m depth is very limited. Rather high Ca2+ and K+ contents of the woody biomass can lead to high exports at harvest. Nutrient cycling in the poplar stand proved to be very efficient, with no significant nutrient losses.