Transport of Dissolved Si from Soil to River: A Conceptual Mechanistic Model

This paper reviews the processes which determine the concentrations of dissolved silicon (DSi) in soil water and proposes a conceptual mechanistic model for understanding the transport of Si through soils to rivers. The net DSi present in natural waters originates from the dissolution of mineral and amorphous Si sources in the soil, as well as precipitation processes. Important controlling factors are soil composition (mineralogy and saturated porosity) and soil water chemistry (pH, concentrations of organic acids, CO₂ and electrolytes). Together with production, polymerization and adsorption equations they constitute a mechanistic framework determining DSi concentrations. We discuss how key controls differ across soil horizons and how this can influence the DSi transport. A typical podzol soil profile in a temperate climate is used as an example, but the proposed model is transferrable to other soil types. Additionally, the impact of external forcing factors such as seasonal climatic variations and land use is evaluated. This blueprint for an integrated model is a first step to mechanistic modelling of Si transport processes in soils. Future implementation with numerical methods should validate the model with field measurements.     

Benefit and Implementation of Groundwater Protection Zoning in South Africa

Groundwater studies in several African countries show that the contamination of water-supply aquifers is mainly due to improper placement of land-based activities such as agriculture, industries, waste disposal. In South Africa, groundwater pollution is also of increasing concern due to fast population growth and accompanying development. Groundwater protection zoning is a supplemental methodology for groundwater management that incorporates land use planning. The land is managed to minimize the potential of groundwater contamination by human activities that occur on or below the land surface. The various benefits associated with implementation of protection zoning are discussed for stakeholders such as communities, water supply companies, ecosystems and policy makers. A South African case study is presented comparing the cost of protection with the cost incurred due to the treatment of sick and dying people due to contaminated drinking water. These benefits must be communicated to the stakeholders to start the implementation at all management levels. Implementation steps of groundwater protection zones are discussed and can be tested even with low budgets and little data available. Monitoring and reassessment of protection zones are important to test the effectiveness and prove to decision makers that the money was well spent. The legal framework for implementation of groundwater protection zoning in a South African context is described, where the water law makes provision for tools like differentiated protection, licensing and recovery of cost. Challenges regarding implementation of groundwater protection are discussed with some action steps on how to move forward.     

Assessing and predicting biodiversity in a floodplain ecosystem: Assimilation of net primary production derived from imaging spectrometer data into a dynamic vegetation model

New concepts for river management in northwestern Europe are being developed which aim at both flood protection and nature conservation. As a result, methods are required that assess the effect of management activities on the biodiversity of floodplain ecosystems. In this paper, we show that dynamic vegetation models (DVMs) in combination with regional scale derived remote sensing products can be adopted to assess both current and future ecosystem development and biodiversity status of a complex floodplain ecosystem in the Netherlands. The dynamic vegetation model SMART2-SUMO2 in combination with the nature valuation model NTM3 predicting potential floristic diversity was applied to simulate the biodiversity status of the Millingerwaard floodplain along the river Rhine in the Netherlands. Estimates of net primary production (NPP) derived from airborne HyMap imaging spectrometer data were used for validation of the simulated NPP by the DVM at the time of data acquisition in 2004. Imaging spectrometer derived NPP was in good agreement with the SMART2-SUMO2 modeled results. The NTM3 derived nature valuation in 2004 expressed as plant diversity for the floodplain was high and well in agreement with field observations. In a next step, the DVM was re-initialized using imaging spectrometer derived NPP in 2004 and a forecast of plant diversity and biomass development in 2050 was made. A comparison was performed for three pre-defined floodplain management scenarios using a data-assimilation based approach as well as one without. Significant differences in biomass development can be observed between the scenarios. Predicted plant diversity for individual ecosystems in 2050 shows increased variability for forest ecosystems compared to grass ecosystems. This shows that floodplain management should take advantage of spatiotemporal dynamics of the floodplain as a basis for fostering the development of increased biodiversity. The results of this study demonstrate that imaging spectrometer derived products can be used for validation and initialization of DVMs.     

Biofiltration for mitigation of methane emission from animal husbandry

Removal of methane from exhaust air of animal houses and manure storage has a large potential for the reduction of greenhouse gas emissions from animal husbandry. The aim of this study was to design a biofilter for methane removal at a full-scale livestock production facility. Air from the headspace of a covered 6 m3 liquid manure storage (air flow: 0.75-8.5 m3 m(-3) h(-1); CH4: 500-5500 mg m(-3)) was treated in an experimental biofilter (160 L). The filterbed, a mixture of compost and perlite in a 40:60 (v/v) ratio, was inoculated with activated sludge that had shown a good methane oxidation rate as compared to pure cultures in preceding laboratory tests. Methane removal up to 85% could be achieved in the experimental biofilter. The methane removal (g m(-3) h(-1)) appeared to be proportional to the concentration (g m(-3)) with k = 2.5 h(-1). Relatively low methane concentrations and high air flows, as reported for the exhaust air of animal houses, would require very large biofilter sizes. Extrapolation of the results showed that treatment of air from a 1000 m3 liquid manure storage with a methane concentration of 22 g m(-3) would require a 20 m3 biofilter for a desired emission reduction of 50%. The costs for such a biofilter are USD 26 per t of CO2 equiv reduction.     

Odour and ammonia removal from pig house exhaust air using a biotrickling filter.

Odour from agricultural activities, such as the spreading of manure and the housing of animals, is increasingly being considered a nuisance in densely populated countries like the Netherlands. The objective of this research was to study the odour removal from pig house exhaust air by a biotrickling filter that had been implemented for ammonia abatement. At a regular pig production farm, the performance of a running full-scale biotrickling filter was studied for 72 days. Ammonia and odour removal efficiency were on average 79% and 49% respectively. Ammonia removal appeared to be based on an unintended accumulation of ammonium and nitrite in the system, instead of on production and discharge of nitrate. The odour removal efficiency showed a large variation that, for a major part, about 80%, could be attributed to actual changes in the performance of the biotrickling filter. These changes were probably caused by variations in the composition of the air that were not completely reflected by the olfactometrically measured odour concentration, as the many different components that make up the odour each have different removal characteristics. It seemed that the biotrickling filter was operated below its maximum absolute odour removal capacity [OUE/(m3 filter)/s], which means that the absolute odour removal will probably rise at increasing load. It was, however, not possible to distinguish between the influence of either the odour load or the odour concentration on the odour removal, because of a positive correlation between the odour concentration and the air flow. To increase the odour removal efficiency (%), the design of the filter probably needs to be optimised for both well and poorly water-soluble odour components.     

Managing urban wastewater in China: a survey of build–operate–transfer contracts

This paper reports on a nationwide field survey of wastewater plants under build–operate–transfer (BOT) contracts in China. The survey yielded information on contracting parties, size, duration and location of 37 BOT contracts. The key findings are that municipal governments feature as first parties to BOTs, and that many second parties are domestic rather than international entities. Municipalities favour BOT contracts because of familiarity with infrastructure BOTs and the access they offer to the capital market. A subsample of five BOT contract documents was examined. Gaps in contract specifications included clauses allocating responsibility for defects in plant design and environmental incidents, and coverage of commercial risk. Many of the BOT contracts examined qualify as public–public partnerships rather than public–private partnerships (PPPs) in the classic sense of the word. This dampens the risk of contract failure.     

Comparative evaluation of oxidative enzyme activities during adventitious rooting in the cuttings of grapevine rootstocks

BACKGROUND: This study investigated changes in peroxidase (POX) and polyphenol oxidase (PPO) activities through adventitious rooting in hardwood cuttings of grapevine rootstocks. Three grapevine rootstocks with different propensity to produce adventitious roots were selected: recalcitrant (Ramsey), non‐recalcitrant (Rupestris du Lot) and intermediate (99R) cultivars. RESULTS: The averages of root number at 65 days were 96 in Lot, 76 in 99R and 30 in Ramsey. Both enzyme activities characteristically increased before adventitious rooting, regardless of rooting ability of the rootstocks, and then decreased. POX activity increased in Ramsey cuttings at 22 days, in Lot and 99R cuttings at 14 days after planting, and then decreased gradually until 51 days. The highest POX activity was determined in Ramsey rootstock with the highest rooting ability and the lowest activity was determined in the rootstocks with the lowest rooting ability. PPO activity gradually increased in Ramsey rootstock cuttings from 10 days to 22 days, in Lot and 99R cuttings at 14 days, and then decreased until 51 days. A significant correlation was identified between high POX activity and adventitious rooting capability in rootstocks, but the same result was not determined with PPO activity. CONCLUSION: A recalcitrant rooting variety cannot increase POX activity sufficiently before rooting. Therefore applications that could increase POX activity in stem cuttings during rooting may facilitate increased rooting in such rootstocks. Copyright © 2011 Society of Chemical Industry     

Structure-Guided Modulation of the Catalytic Properties of [2Fe−2S]-Dependent Dehydratases

The FeS cluster-dependent dihydroxyacid dehydratases (DHADs) and sugar acid-specific dehydratases (DHTs) from the ilvD/EDD superfamily are key enzymes in the bioproduction of a wide variety of chemicals. We analyzed [2Fe−2S]-dependent dehydratases in silico and in vitro, deduced functionally relevant sequence, structure, and activity relationships within the ilvD/EDD superfamily, and we propose a new classification based on their evolutionary relationships and substrate profiles. In silico simulations and analyses identified several key positions for specificity, which were experimentally investigated with site-directed and saturation mutagenesis. We thus increased the promiscuity of DHAD from Fontimonas thermophila (FtDHAD), showing >10-fold improved activity toward D-gluconate, and shifted the substrate preference of DHT from Paralcaligenes ureilyticus (PuDHT) toward shorter sugar acids (recording a six-fold improved activity toward the non-natural substrate D-glycerate). The successful elucidation of the role of important active site residues of the ilvD/EDD superfamily will further guide developments of this important biocatalyst for industrial applications.