Organic carbon content controls the severity of water repellency and the critical moisture level across New Zealand pasture soils

After an initial evaluation of several solvents, the efficiency of Soxhlet extractions with isopropanol/ammonia (s.g. 0.88) (70 : 30 v : v; 24 h) in extracting compounds associated with water repellency in sandy soils was examined using a range of repellent and wettable control soils (n = 15 and 4) from Australia, Greece, Portugal, The Netherlands, and the UK. Extraction efficiency and the role of the extracts in causing soil water repellency was examined by determining extract mass, sample organic carbon content and water repellency (after drying at 20°C and 105°C) pre- and post-extraction, and amounts of aliphatic C–H removed using DRIFT, and by assessing the ability of extracts to cause repellency in acid-washed sand (AWS). Key findings are: (i) none of organic carbon content, amount of aliphatic C–H, or amount of material extracted give any significant correlation with repellency for this diverse range of soils; (ii) sample drying at 105°C is not necessarily useful before extraction, but may provide additional information on extraction effectiveness when used after extraction; (iii) the extraction removed repellency completely from 13 of the 15 repellent samples; (iv) extracts from all repellent and wettable control soils were capable of inducing repellency in AWS. The findings suggest that compounds responsible for repellency represent only a fraction of the extract composition and that their presence does not necessarily always cause repellency.

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The Impacts of Vineyard Afforestation on Soil Properties, Water Repellency and Near-Saturated Infiltration in the Little Carpathians Mountains

Water ◽

10.3390/w12092550 ◽

2020 ◽

Vol 12 (9) ◽

pp. 2550

Author(s):

Andrej Hrabovský ◽

Pavel Dlapa ◽

Artemi Cerdà ◽

Jozef Kollár

Keyword(s):

Land Use ◽

Organic Carbon ◽

Soil Properties ◽

Carbon Content ◽

Water Repellency ◽

Infiltration Rate ◽

Organic Carbon Content ◽

Soil Water Repellency ◽

Infiltration Process ◽

Vineyard Soils

Vineyards are a 7000-year-old land-use tradition and both management and abandonment have result in altered soil properties. These have a great effect on water resources and soil services, and this inspired our investigation into the effects of land-use and land-use change on soils in the Modra wine-growing region in South-western Slovakia. Ten topsoil samples were taken at each of the seven research sites (n = 70) on granite parent material in cultivated and afforested vineyards and original forest soils. Laboratory analyses included determination of soil texture, organic carbon content, soil pH, and water repellency. This was supplemented by infiltration measurements under near-saturated conditions at the vineyard and afforested study sites. Studied soils have a low clay content and a high proportion of sand. The vineyard soils have significantly higher pH than the forest and afforested soils because the naturally acidic soils have been limed. The forest and afforested soils have similar properties, with higher organic carbon content. This makes them strongly to extremely water repellent and contrasts sharply with the wettability of cultivated vineyard soils. One afforested site, however, was less acidic and therefore was considered transitional between forest and vineyard soils. Our infiltration measurements established the influence of soil water repellency on the infiltration process, and our results highlighted that the infiltration rate in the vineyard soils was significantly higher than in afforested soils. The infiltration rate also gradually increased over time in afforested soils due to decreasing water repellency. Physically impossible negative sorptivity values in afforested soils were noted because of changes in water repellency during the infiltration process. Finally, we conclude that soil afforestation results in increased soil water repellency and a subsequent reduction in the infiltration rate at the matrix scale.

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Drivers of soil water repellency after wildfires: case study in the south-central Appalachian Mountains, US

10.5194/egusphere-egu21-3738 ◽

2021 ◽

Author(s):

Jingjing Chen ◽

Brian Strahm ◽

Ryan Stewart

Keyword(s):

Organic Carbon ◽

Carbon Content ◽

Soil Water ◽

Functional Groups ◽

Appalachian Mountains ◽

Water Repellency ◽

Organic Carbon Content ◽

Soil Water Repellency ◽

South Central ◽

Mount Pleasant

Increasing frequency of wildfire in humid hardwood forests make it necessary to understand the occurrence and origin of soil water repellency in these systems, as wildfire-induced soil water repellency has been observed to severely impact many biophysical processes in other forest types. In this project, we studied two sites in the Appalachian Mountains, United States, (at Mount Pleasant Wildlife Refuge, Virginia, and Chimney Rock State Park, North Carolina) where wildfires occurred in late 2016. In each site, burned and unburned soils were evaluated for actual (in the field) and potential (in the laboratory) water repellency using the water drop penetration time method. In addition, samples were analyzed for organic carbon content (measured using C/N analyzer), hydrophobic functional groups (using Fourier transform infrared, FTIR), and their rank correlations (rs) based on multiple samples collected one year after the fires. We found that soil water repellency was substantial greater in burned soils in the first months after the fire, and persisted for the entire year in the more severely burned soils. We also determined that potential water repellency was much greater than actual water repellency, and that organic carbon content and hydrophobic functional groups were significantly correlated to potential water repellency (p < 0.0001). Correlations were stronger at Mount Pleasant (0.77 < rs <0.91) than at Chimney Rock (0.06 < rs < 0.70). For actual water repellency only had significant correlations with soil organic content at Mount Pleasant (p < 0.0001), and with hydrophobic functional groups (p < 0.0001) at both sites except the unburned soils at Chimney Rock. However, these correlations were weaker than with potential water repellency, likely due to the influence of soil water content. Altogether, this study provides new insight into the influence of soil organic matter and its composition on post-wildfire soil water repellency.

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Water repellency in a New Zealand development sequence of yellow brown sands

Soil Research ◽

10.1071/sr9930641 ◽

1993 ◽

Vol 31 (5) ◽

pp. 641 ◽

Cited By ~ 33

Author(s):

MG Wallis ◽

DJ Horne ◽

AS Palmer

Keyword(s):

New Zealand ◽

Carbon Content ◽

Water Content ◽

Fulvic Acid ◽

Soil Water ◽

Soil Water Content ◽

Water Repellency ◽

Organic Carbon Content ◽

Dune Sands ◽

Acid Ratio

A series of sands on the west coast of the lower North Island, New Zealand, were studied to investigate the effects of time, topography and vegetation cover upon the development of soil water repellency. Severe repellency was measured with the molarity of ethanol droplet (MED) index in the Waitarere and Motuiti dune phase sands, of age <130 years and c. 500 years respectively. In each dune phase, the dune sands were more repellent than the lower lying soils of the sand plains. Low or zero MED values were measured in the 1600-6000 year old Foxton dune phase sands and 10 000-25 000 year old Koputaroa dune phase sandy loams under either pasture or native bush. There was no consistent relationship between bush or pasture cover and repellency severity in the Foxton and Koputaroa soils, however, the species composition of the pasture and bush differed. The Waitarere sand was the most repellent soil, despite a low organic carbon content. The carbon content profiles of most of the soils did not appear to be related to the respective MED profiles of repellency severity. The MED values of the surface layer from five dune sands were generally related inversely to the fulvic acid (FA) content and proportionally to the humic acid to fulvic acid ratio (HA/FA), which were measured in a previous study. The pH of the five soils ranged from 5.61 to 6.89, with no apparent relationship between pH and MED. A study of soil water content indicated that repellency reduced rainfall infiltration into the Waitarere and Motuiti sands and the Himatangi sand, found on elevated sand plains. The most severely repellent sands had the greater variability in soil water content after rainfall.

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