Theme 1: Grassland Ecology
Description
Globally, road networks are expanding in the countryside. Though beneficial to society, the roads potentially have detrimental effects on grazing quality. The effects are seldom quantified. In this study Eragrostis lehmanniana, a common native grazing grass in parts of the world, was examined for indicative data on the impacts of roads on grasses. Aboveground tissue samples were collected monthly on three occasions during the growing season, at the same respective locations near three high traffic highways. Non-senescent specimens were sampled along transects of up to 400 m perpendicular to the highways, starting from the road edge and then at intervals of at least 10 m. Concurrent control samples were collected at a site more than 3 km from a road. In the laboratory, a whole stem of each specimen was washed in 40 ml of distilled water, whose pH and electrical conductivity were then measured. Heavy metal concentrations (HMC) in dry grass tissue were determined using ICP-MS analysis. Consistently, tissue surface pH was lower, and electrical conductivity higher, close to the road edge than farther away. Heavy metal concentrations were high close to the road edge, some (Fe, Ni) beyond the tolerable limits of cattle and gazelle-like grazers. Using the respective control site means as thresholds, linear regression of pH and conductivity against distance showed that the effects were pronounced for 70 m – 600 m from the road edge. The low pH was due to acidity caused by motor vehicle- emmited nitrogen and sulpher oxides (NOx, SOx) reacting with atmospheric water vapour. High conductivity and HMC were judged to be due to motor vehicle-sourced metal elements and particulate matter. Spacing roads at least 1.2 km apart in grazing areas is recommended to reduce the detrimental effects.
Included in
Agricultural Science Commons, Agronomy and Crop Sciences Commons, Plant Biology Commons, Plant Pathology Commons, Soil Science Commons, Weed Science Commons
Effects of Proximity to Roads on Tissue Surface PH, Conductivity and Heavy Metal Contents of a Grazing Grass Species
Globally, road networks are expanding in the countryside. Though beneficial to society, the roads potentially have detrimental effects on grazing quality. The effects are seldom quantified. In this study Eragrostis lehmanniana, a common native grazing grass in parts of the world, was examined for indicative data on the impacts of roads on grasses. Aboveground tissue samples were collected monthly on three occasions during the growing season, at the same respective locations near three high traffic highways. Non-senescent specimens were sampled along transects of up to 400 m perpendicular to the highways, starting from the road edge and then at intervals of at least 10 m. Concurrent control samples were collected at a site more than 3 km from a road. In the laboratory, a whole stem of each specimen was washed in 40 ml of distilled water, whose pH and electrical conductivity were then measured. Heavy metal concentrations (HMC) in dry grass tissue were determined using ICP-MS analysis. Consistently, tissue surface pH was lower, and electrical conductivity higher, close to the road edge than farther away. Heavy metal concentrations were high close to the road edge, some (Fe, Ni) beyond the tolerable limits of cattle and gazelle-like grazers. Using the respective control site means as thresholds, linear regression of pH and conductivity against distance showed that the effects were pronounced for 70 m – 600 m from the road edge. The low pH was due to acidity caused by motor vehicle- emmited nitrogen and sulpher oxides (NOx, SOx) reacting with atmospheric water vapour. High conductivity and HMC were judged to be due to motor vehicle-sourced metal elements and particulate matter. Spacing roads at least 1.2 km apart in grazing areas is recommended to reduce the detrimental effects.
