Influence of rolled erosion control systems on temporal rainsplash response—a laboratory rainfall simulation experiment

Reduction of erosion and sediment-related pollution from urban construction sites or other degraded hillslopes often relies on the initial application of suitable rolled erosion control systems (RECS) before natural vegetation cover can be established. However, research has not clearly explained why some RECS perform better than others, or under what particular conditions one system is more suitable than another. An important link between the application of the most suitable RECS and better product design is process-based studies relating the physical properties of products to the reduction of erosion subprocesses. This study investigates time-varying reduction of rainsplash detachment and transport by 13 commonly used RECS. The results indicate that product differences in the protection they provide against splash processes vary over the duration of a rain event, and that this variation is related to individual product properties, especially surface coverage and thickness. These results should aid in the design of more effective erosion control products and in the selection of the most suitable RECS for particular hillslope applications. © 1997 John Wiley & Sons, Ltd.     

Can organic farmers be ‘good farmers’? Adding the ‘taste of necessity’ to the conventionalization debate

Recent decades have seen a rapid increase in the rate of conversion from conventional to organic farming, as organic farming shifted from an alternative production approach practiced by a small number of idealists, to the de facto alternative to mainstream conventional production. Although there has been considerable academic debate as to the role of agri-business penetration into the production and marketing chains of organic farming (‘conventionalization’), less is known about how the economic drivers of conventionalization are negotiated into practices at the farm level. Drawing on Bourdieu’s conceptualization of economic and cultural capitals, the direct connection between symbols of ‘good farming’ and the economic requirements of maintaining a viable farming business (i.e., the ‘taste of necessity’) is demonstrated. Findings indicate that conventional and organic farmers in the study sites identified a similar range of cultural symbols, but organic farmers emphasized different symbols within this range. This diversity and selectivity demonstrates the fragmentation and contestation of ideals resulting from economic challenges at the time of the study. Economic capital is important to the decision to consider conversion to organic farming, but formal conversion reflects re-weighting of forms of cultural capital. The author argues that recognition of the impact of economic pressures on conventional farming, which in the study sites often led to reduced input use rather than intensification, is missing from the conventionalization debate. The mainstreaming of organic farming production has presented conventional farmers with a set of alternative or re-weighted symbols and a crucible for reflexive consideration of their own standards and practices of farming.     

Inflammatory cell and immune function in Merino sheep with chronic dermatophilosis

Components of inflammatory and immunological responses were compared in 17 Merino sheep with chronic dermatophilosis (Group 1) and 15 Merino sheep that had recovered from the disease (Group 2). The functions studied included: (i) total and differential white cell counts; (ii) phagocytic function and intracellular killing by neutrophils; (iii) humoral immune response to T-dependent and T-independent antigens and to Dermatophilus congolensis. (iv) lymphocyte blastogenic responses to phytohaemagglutinin; (v) bovine serum albumen and D. congolensis antigens; (vi) quantification of T-lymphocyte subsets in skin lesions resulting after re-infection with D. congolensis zoospores. After all lesions were treated and the sheep were shorn, both groups of sheep were re-infected with D. congolensis. Both groups had similar infection rate, severity of lesions and rate of resolution after re-infection. The Group 2 sheep had significantly higher primary and secondary antibody responses to killed Brucella abortus cells than Group 1 sheep, but Group 1 sheep had higher levels of specific D. congolensis antibody throughout the trial. Neutrophils from Group 1 sheep showed a higher phagocytic rate for D. congolensis zoospores than Group 2 sheep when the zoospores were opsonised by sera from the Group 1 sheep, but there was no difference in their ability to kill ingested zoospores. Although there were some differences between the groups in the proportion of lymphocytes in lesions that reacted with monoclonal antibodies to T4, T8 and T19-19 lymphocyte markers at various times after re-infection, the sheep in Group 2 consistently had higher levels of lymphocytes reacting to a monoclonal antibody for the T6 lymphocyte antigen in skin biopsies collected 9, 15 and 21 days post-inoculation (p.i.) than did sheep in Group 1. Group 2 sheep also had higher levels of epidermal cells with immunohistochemical properties of Langerhans cells at lesion sites 15 and 21 days p.i.     

Cytotoxic effect of serotypes of Pasteurella haemolytica on sheep bronchoalveolar macrophages

Ovine isolates of the 15 known serotypes found within the A and T biotypes of Pasteurella haemolytica were cytotoxic for sheep bronchoalveolar macrophages (BAM). Weaker toxicity for the same target cells was also expressed by non-serotypable ovine isolates of P. haemolytica. The results suggest that cytotoxicity for sheep BAM is a virulence factor common to both A and T biotypes of P. haemolytica.     

Quantification of accelerated soil erosion using the environmental tracer caesium-137

The principal objective of this investigation was to quantify erosion rates for five agricultural fields in three separate study areas in Saskatchewan. The radionuclide tracer caesium-137 (¹³⁷Cs) was used to quantify net erosion and net deposition within the landscape over a 30-year period. Uneroded (native) sites were used to establish the mean background level of ¹³⁷Cs in each of the study areas. The assumption being that agricultural sites with ¹³⁷Cs areal activities greater than the native site were subject to deposition, and sites with ¹³⁷Cs less than the native control site were subject to erosion. A linear proportionality model was used to convert the loss or gain of ¹³⁷Cs to net soil erosion or deposition. Results have indicated that accelerated (anthropogenic) erosion has been commonplace on arable land in Saskatchewan, even on near-level fields (< 1.3 degrees). The net integrated sediment output from the five agricultural fields ranged from — 0.6 t th⁻¹ y⁻¹ to — 6.8 t ha⁻¹ y⁻¹ (where negative values represent erosion). What is more alarming is that between 40 and 75 per cent of all sites sampled within individual fields had erosion rates in excess of the generally accepted rate of soil formation (1.0 t ha⁻¹ y⁻¹). Also, in one highly eroded field (Crystal Springs medium sloping site) 65 per cent of the sites sampled exceeded the upper tolerable erosion rate of 11.0 t ha⁻¹ y⁻¹. These results indicate significant degradation of the non-renewable soil resource has occurred over the past 30 years and is still presently active. Land degradation by accelerated erosion would result in reductions in effective rooting depth, soil moisture holding capacity, essential nutrient stores, and would adversely effect the physical structure of the topsoil. The major reason for accelerated erosion on arable land in Saskatchewan is the practice of summer fallowing, where the field is left in a ‘bare’ state and repeatedly tilled every second or third year. During a fallow period, or prior to crop emergence during a cropping year, fields are subject to wind and water erosion. On near-level fields wind would be the dominant transport agent, while on sloping fields inter-rill and rill erosion would be the primary forces of erosion. It is suggested that the appropriate conservation farming response would be to increase application of surface mulches and possibly to decrease the frequency of summer fallowing. Without such efforts long-term sustainable agricultural production in the Prairies of Canada is considered to be a tenuous land use practice.     

Hydrophysical degradation associated with hiking‐trail use: a case study of Hawai'iloa Ridge Trail,O'ahu,Hawai'i

Recreational activities can have significant impacts on geomorphic and hydrologic processes in drainage basins, often out of proportion to their areal extent. With increased stress on hiking trails nationwide, there is a need to characterize the impacts of human trampling on soil properties. We examine an 810 m segment of Hawai'iloa Ridge Trail (O'ahu, Hawai'i, USA). Soil compaction and surface erosion on moderate to steeply sloping sites have degraded the trail environment. Bulk density, penetration resistance, and vane shear strength were significantly higher on the trail than in adjacent undisturbed areas, with median differences ranging from 29 to 120 per cent. With compaction and exposure of subsoil on the trail, void ratio, air‐filled porosity, saturated hydraulic conductivity, effective and preferential porosity were significantly lower, with relative change values ranging from 23–93 per cent. No significant changes were noted in meso‐ or micro‐porosity, but macropores with a radius of >110 μm decreased significantly by 58 per cent for on‐trail locations. This comprehensive dataset indicates that hiking stress is deleterious to the soil–hydrologic system. Data point to a trail system that would be dominated by Hortonian overland flow and this was supported by field evidence during a storm event. Increased runoff has incised rills on some trail segments and there is evidence that run‐on to adjacent side slopes has lead to accelerated erosion. Management on most trails in Hawai'i, including the one studied, is limited, but from our data it is apparent that on‐trail sites directly influenced by an overhanging canopy of rapidly growing (aggressive) exotics were least impacted due to increased organic contributions to the surface and root network development. These data will allow land managers to more effectively address the potential geomorphic and hydrologic impacts of recreational land use. Copyright © 2001 John Wiley & Sons, Ltd.