Fire Severity,Water Repellency Characteristics and Hydrogeomorphological Changes Following the Christmas 2001 Sydney Forest Fires

Soil water repellency can enhance overland flow and erosion and may be altered by fire. The Christmas 2001 bushfires near Sydney allowed investigation of the relationship between fire severity, water repellency and hydrogeomorphological changes. For two sub-catchments with differences in fire severities in Nattai National Park, south-west of Sydney, this paper considers: (1) the links between fire severity based on SPOT image analysis and ground observation of fire severity and repellency; (2) the textural and organic/minerogenic characteristics of eroded sediment; and (3) erodibility, erosion and deposition of soils in both catchments. Ground surveys show that image analysis reflects well the degree of vegetation consumption by fire, but cannot adequately predict the degree of ground litter consumption, associated soil heating and repellency effects. Fire had varying effects on repellency, leaving it unchanged, destroying it or enhancing it, depending on the soil temperature reached. The main post-fire hydrogeomorphological changes have been widespread erosion and colluvial and alluvial deposition of topsoil in foot-slope locations and river systems, but only localised redistribution of the highly erodible, repellent sandy subsurface layer. The fire did not trigger major geomorphological change in the study area, but fires probably cause important topsoil and nutrient depletion and may also affect water quality.     

Soil hydrophobic effects on infiltration and catchment runoff

After dry summers or drought, eucalypt forest soils at two sites in southeastern Australia developed hydrophobic or non-wetting surface characteristics that reduced infiltration, measured using a sprinkling infiltrometer. At one site the development of hydrophobic conditions caused the rainfall to runoff conversion efficiency of a forested catchment to increase from 5 per cent to 15 per cent. Under non-hydrophobic conditions at this site, grassland always generated more runoff than forest. However, one major rainfall-runoff was recorded at a time of highly hydrophobic forest soil conditions and this storm generated greater runoff on the forested catchment than the grassland catchment. At the second site forest soils have naturally highly conductive surface layers because of a dense network of macropores and pathways for preferential flow. Hydrophobic conditions produced by drought caused soil water movement to be confined to only a few of the larger macropores exposed to surface ponded water. Even so, infiltration rates remained relatively high so that the impacts of hydrophobic soils were not translated into increased catchment runoff as at the first site.     

The role of organic matter in the sorption capacity of marine sediments

Past studies have suggested that desiccation enhances hydrophobicity of salt marsh sediment, and that drying and rewetting sediment can be used to investigate sorption mechanisms of amino acids and other organic compounds [Liu, Z., Lee, C., 2006. Drying effects on sorption capacity of coastal sediment: The importance of architecture and polarity of organic matter. Geochim. Cosmochim. Acta 70, 3313–3324]. Here we further develop this technique to study sorption of hydrophobic and hydrophilic organic compounds in a wide range of marine sediments. Our results show that hydrophilic compounds sorb strongly to wet coastal sediments; in dried sediments, sorption of hydrophilic compounds decreases, while sorption of hydrophobic compounds is greatly enhanced. Small compounds with aromatic rings sorb more in dried than wet coastal sediments, suggesting that aromatic groups have a stronger effect on sorption than polar groups like amino and carboxyl moieties. Sorption of lysine, glutamic acid and putrescine decreases greatly when sediment is pretreated with KCl, indicating the importance of cation ion exchange. However, α-amino acids sorb much more than corresponding β- or γ-amino acids, and l-alanine sorbs more than d-alanine, suggesting that amino group location and chiral selectivity play an important role in sorption. Comparison of lysine and tyrosine sorption in different sediments indicates that source and diagenetic state of organic matter are important factors determining sorption capacity. Lysine sorbs much more to organic detritus from salt marsh sediment than to fresh Spartina root materials, marine particles, lignin or humic acids, indicating the importance of structural integrity in sorption. Desorption hysteresis of glutamic acid, putrescine and lysine (in dried sediment) suggests the presence of enzyme-type sorption sites of high sorption energy or multiple binding mechanisms. Taken together, these findings suggest that organic matter plays the major role in amino acid sorption in organic-rich sediments.     

Spatial variability of soil hydrophobicity after wildfires in Montana and Colorado

Increases in runoff and erosion after wildfires are often attributed to the development of hydrophobic soils. The potential for increased overland flow depends on the spatial contiguity of the hydrophobicity as well as its overall strength, but there is limited information on the spatial variability of soil hydrophobicity. We conducted spatially intensive hydrophobicity measurements in 225 m² and 1 m² plots in forested areas of Montana and Colorado burned at moderate to high severity, and in unburned control plots. Both the burned and unburned 225 m² plots contained 10–23 hydrophobic soil patches in which hydrophobicity was strongest at the surface and declined rapidly with depth. The hydrophobic patches were closer together and up to 3 times larger in the burned plots. Consequently, 19% to 76% of the burned plots were hydrophobic compared to just 11% of the unburned plots. In five of the six burned plots, the patches were not laterally connected, suggesting that in most cases Hortonian overland flow generated from hydrophobic patches will infiltrate near its point of origin. The 1 m² plots were smaller than most of the hydrophobic patches, so they did not capture the spatial characteristics of soil hydrophobicity. Characterization of the spatial variability of soil hydrophobicity should be based on measurements conducted at  1 m intervals across areas of > 100 m². Due to the patchiness of soil hydrophobicity at the 10⁰ to 10¹ meter scale, overland flow measurements in small ( 1 m²) plots may overestimate the magnitude and variability of runoff from burned catchments.     

Water repellency in a dry sclerophyll eucalypt forest — measurements and processes

The magnitude of soil water repellency in a dry sclerophyll eucalypt forest was measured periodically over four years. The varying responses from a range of sites within the forest are discussed and the effect of amount and frequency of rainfall is shown. It was found that some weeks of consistently wet weather were required for water repellency breakdown, and a frequency of rainfall much greater than normal in the study area for it to remain broken down. Even after an extended period of breakdown, it was found that repellency can be reestablished after one week of hot dry weather. Laboratory tests were used to examine the major repellency processes; three were identified and the relative importance of each considered in the context of the field study. The relative influence of each depended on the physical and chemical characteristics of the sites. The repellent soil samples were more repellent to water of throughfall origin, and even more repellent to stemflow than to distilled water. The repellency response also varied with the type of vegetative cover present. The influence of these phenomena on the preservation of water repellency and the relevance of repellency in macropore infiltration processes are discussed.     

Scum in Activated Sludge Plants: Impact of Non‐filamentous and Filamentous Bacteria

Excessive scum production is a widespread phenomenon in present activated sludge wastewater treatment. The question how foaming is initiated and stabilized is still unanswered. Hydrophobic wastewater ingredients and surface active material such as synthetic surfactants are discussed among others as major causative agents for scum production. Focusing on biological impacts non‐filamentous bacteria isolated from scum turned out to contribute to flotation by both cell surface hydrophobicity and emulsification activity, depending on the prevailing substrate and milieu conditions. The biological characterization of scum based on microscopic sludge investigation of conspicuous microorganisms resulted in a significant shift of filamentous and non‐filamentous organism populations with Gram‐positive bacteria prevailing in present nutrient removal plants as compared to the situation ten years ago. Their hydrophobic cell surface is supposed to support adherence and stabilization of interfaces and thus promote sludge flotation. In scum six types of filamentous bacteria turned out to be numerous: Microthrix parvicella and nocardioform actinomycetes, both of them being enriched in the scum fraction, moreover Nostocoida limicola and Eikelboom types 0041/0675, 1851, and 0092. Possible interactive mechanisms between non‐filamentous and filamentous scum bacteria and their selection factors are discussed in order to contribute to a better understanding of scum formation and to provide efficient troubleshooting measures.     

Biochar application reduces protein sorption in soil

The application of biochar (BC) as a soil amendment is of growing interest. BC has recently been shown to decelerate the cycling of soil organic N, and adsorption of proteins to BC surfaces has been put forward as an explanation. However, the effect of BC on the sorption of proteins in soil is largely unknown. The main objective of this study was therefore to test the sorption of a model protein (bovine serum albumin, BSA) on a soil amended with different types of BC. Contrary to our assumption, BC application reduced the sorption of BSA. The BC feedstock type and pyrolysis temperature affected BSA sorption; however, the underlying mechanisms require further investigation. BC-induced liming had no effect on BSA sorption, while BC’s hydrophobicity and surface area seemed to be important factors.     

The effect of particle shape and hydrophobicity in flotation

The effect of particle shape on the flotation process has been investigated in laboratory experiments with monosized spherical ballotini and ground ballotini. The particles were treated by partial methylation with trimethylchlorosilane to achieve varying degrees of hydrophobicity. In flotation, the process of film thinning and liquid drainage is critical in the formation of stable bubble–particle attachments and this is affected by the particle shape and surface hydrophobicity. Flotation tests with different particle sizes were conducted in a modified batch Denver cell. Predictions from a computational fluid dynamic model of the flotation cell that incorporates fundamental aspects of bubble–particle attachment were compared with data from flotation tests. Contact angles of the particles were measured using a capillary rise technique to indicate surface hydrophobicity. Ground ballotini generally has higher flotation rates than spherical ballotini; the results are consistent with effects from faster film thinning and rupture at rough surfaces and are well correlated by the sphericity index.     

磁性微球吸附法研究盐藻细胞的疏水性

采用正相悬浮聚合法制备了聚苯乙烯－二乙烯苯磁性微球。由于微球表面的聚苯乙烯是疏水性材料，可用于制定微生物细胞表面的疏水性。用聚苯乙烯磁性微球吸附法测定了不同生长期盐藻细胞的表面疏水性，以及pH值、NaCl浓度、Fe^3 浓度、（NH4）2SO4浓度对盐藻细胞疏水性的影响。结果表明，盐藻细胞表面具有疏水性质， 其疏水性与细胞生长阶段及环境条件有关。