Arsenic removal from water/wastewater using adsorbents—A critical review

Human production of food and energy is the dominant continental process that breaks the triple bond in molecular nitrogen (N2) and creates reactive nitrogen (Nr) species. Circulation of anthropogenic Nr in Earth’s atmosphere, hydrosphere, and biosphere has a wide variety of consequences, which are magnified with time as Nr moves along its biogeochemical pathway. The same atom of Nr can cause multiple effects in the atmosphere, in terrestrial ecosystems, in freshwater and marine systems, and on human health. We call this sequence of effects the nitrogen cascade. As the cascade progresses, the origin of Nr becomes unimportant. Reactive nitrogen does not cascade at the same rate through all environmental systems; some systems have the ability to accumulate Nr, which leads to lag times in the continuation of the cascade. These lags slow the cascade and result in Nr accumulation in certain reservoirs, which in turn can enhance the effects of Nr on that environment. The only way to eliminate Nr accumul...

http://bioeeos660-f12-bowen.wikispaces.umb.edu/file/view/Galloway+et+al.+2003.pdf

The Nitrogen Cascade

https://www.ipcc-nggip.iges.or.jp/public/gpglulucf/gpglulucf_files/0_Task1_Cover/Cover_TOC.pdf

Good Practice Guidance for Land Use, Land-Use Change and Forestry

Nature And Properties Of Soils

Summary
Soil is a complex and dynamic biological system, and still in 2003 it is difficult to determine the composition of microbial communities in soil. We are also limited in the determination of microbially mediated reactions because present assays for determining the overall rate of entire metabolic processes (such as respiration) or specific enzyme activities (such as urease, protease and phosphomonoesterase activity) do not allow any identification of the microbial species directly involved in the measured processes. The central problem posed by the link between microbial diversity and soil function is to understand the relations between genetic diversity and community structure and between community structure and function. A better understanding of the relations between microbial diversity and soil functions requires not only the use of more accurate assays for taxonomically and functionally characterizing DNA and RNA extracted from soil, but also high-resolution techniques with which to detect inactive and active microbial cells in the soil matrix.

Soil seems to be characterized by a redundancy of functions; for example, no relationship has been shown to exist between microbial diversity and decomposition of organic matter. Generally, a reduction in any group of species has little effect on overall processes in soil because other microorganisms can take on its function.

The determination of the composition of microbial communities in soil is not necessary for a better quantification of nutrient transformations. The holistic approach, based on the division of the systems in pools and the measurement of fluxes linking these pools, is the most efficient. The determination of microbial C, N, P and S contents by fumigation techniques has allowed a better quantification of nutrient dynamics in soil. However, further advances require determining new pools, such as active microbial biomass, also with molecular techniques. Recently investigators have separated 13C- and 12C-DNA, both extracted from soil treated with a 13C source, by density-gradient centrifugation. This technique should allow us to calculate the active microbial C pool by multiplying the ratio between labelled and total DNA by the microbial biomass C content of soil. In addition, the taxonomic and functional characterization of 13C-DNA allows us to understand more precisely the changes in the composition of microbial communities affected by the C-substrate added to soil.

/pdf/microbial-diversity-and-soil-functions-3p2xvso2y0.pdf

Microbial diversity and soil functions

Denitrifying bioreactors - an approach for reducing nitrate loads to receiving waters.

An understanding of the main factors influencing microbial diversity in soils is necessary to predict the eAects of current landuse trends on terrestrial diversity. We used microbial catabolic evenness as a measure of one component of soil microbial diversity. Catabolic evenness was assessed by measuring the short-term respiration responses of soil to a range of simple organic compounds. DiAerences in catabolic evenness between pasture and other land-uses on matched soils were related to diAerences in organic C pools (total organic C, microbial biomass C, and potentially mineralizable C). This approach enabled comparison of land-use eAects on organic C pools in relation to catabolic evenness without the eAects of soil type. In general, microbial catabolic evenness was greatest in soils under pasture and indigenous vegetation (range: 19.7‐23.3), and least in soils under cereal/maize/horticultural cropping (range: 16.4‐19.6). Soils under mixed cropping land-uses had catabolic evenness that ranged between these extremes (range: 17.7‐20.5), but under pine forestry there was no characteristic level of evenness (range: 15.1‐ 22.3). Catabolic evenness correlated poorly with the absolute values of soil organic C pools (r 2 < 0.36). However, across a range of paired comparisons between pasture and other land-uses, greater diAerences in microbial catabolic evenness corresponded with greater diAerences in organic C (r 2 =0.76) and, to a lesser degree, with diAerences in microbial biomass C (r 2 < 0.45) or potentially mineralizable C (r 2 < 0.13). Therefore, land-uses that deplete organic C stocks in soils may cause declines in the catabolic diversity of soil microbial communities. Although the implications of this for microbial processes are unknown, maintenance of soil organic C may be important for preservation of microbial diversity. # 2000 Elsevier Science Ltd. All rights reserved.

/pdf/decreases-in-organic-c-reserves-in-soils-can-reduce-the-bpvtc8w83x.pdf

Decreases in organic C reserves in soils can reduce the catabolic diversity of soil microbial communities

Hot-water-soluble C as a simple measure of labile soil organic matter: the relationship with microbial biomass C

Microbial catabolic diversity can be reduced by intensive land-uses, which may have implications for the resistance of the soils to stress or disturbance. We tested the hypothesis that the microbial community in a soil where catabolic diversity has been reduced by cropping is less resistant to increasing stress or disturbance compared with a matched soil under pasture, where catabolic diversity was high. Increasing stress was imposed by reducing pH, increasing salinity (imposed by increasing soil electrical conductivity; EC) or increasing heavy metal contamination in the soils. Disturbance was simulated by a series of wet‐dry or freeze‐thaw cycles. After incubation of the soils under these regimes, catabolic evenness (a component of microbial functional diversity defined as the uniformity of substrate use) was calculated from catabolic response profiles. These profiles were determined by adding a range of simple C substrates to the soils and measuring shortterm respiration responses. Stress or disturbance caused much greater changes in catabolic evenness in the crop soil (low catabolic evenness) than the pasture soil (high catabolic evenness). Increasing Cu or salt stress caused increases in catabolic evenness at low intensities in both soils, but, in the crop soil, greater stress caused greater declines in catabolic evenness. Declines in pH also caused much greater decreases in catabolic evenness in the crop than the pasture soil. Catabolic evenness initially increased with increasing numbers of wet‐dry or freeze‐thaw cycles, but after four cycles, evenness declined in both soils. These changes in evenness could be attributed to significant changes (P , 0.05) in most catabolic responses. In contrast, there were generally few changes in microbial biomass C as a result of stress or disturbance treatments. Except for EC stress, all treatments caused slight increases in biomass C at low levels (only significant in the pH and Cu treatments) that subsequently diminished at the highest stress or disturbance levels. Microbial catabolic diversity generally followed the classical ‘hump-back’ responses of diversity to increasing stress or disturbance. We concluded that reduction in catabolic diversity and changes in soil properties due to land use could reduce the resistance of microbial communities to stress or disturbance. q 2001 Elsevier Science Ltd. All rights reserved.

Louis A. Schipper

Papers

Denitrifying bioreactors - an approach for reducing nitrate loads to receiving waters.

Decreases in organic C reserves in soils can reduce the catabolic diversity of soil microbial communities

Hot-water-soluble C as a simple measure of labile soil organic matter: the relationship with microbial biomass C

Is the microbial community in a soil with reduced catabolic diversity less resistant to stress or disturbance

Nitrate removal, communities of denitrifiers and adverse effects in different carbon substrates for use in denitrification beds.