Implications of urbanization related land use change on the Carbon and Nitrogen cycle from subtropical soils

This research established the first non-CO2 Global Warming Potential for subtropical peri-urban environments from the N2O and CH4 soil-atmosphere gas exchange dynamics after land use change due to urbanization. Two years of high temporal gas flux measurements identified immediate, seasonal and inter-annual C and N flux changes after turf grass establishment compared to forest and pasture land use to highlight the impact of our growing cities on the environment. Despite turf grass establishment increases soil greenhouse gas emissions, which increases the Global Warming Potential, the subtropical climate of SEQ may increase the potential to reduce these emissions in the long-term

Urbanisation-related land use change from forest and pasture into turf grass modifies soil nitrogen cycling and increases N2O emissions

Urbanisation is becoming increasingly important in terms of climate change and ecosystem functionality worldwide. We are only beginning to understand how the processes of urbanisation influence ecosystem dynamics, making peri-urban environments more vulnerable to nutrient losses. Brisbane in South East Queensland has the most extensive urban sprawl of all Australian cities. This research estimated the environmental impact of land use change associated with urbanisation by examining soil nitrogen (N) turnover and subsequent nitrous oxide (N2O) emissions using a fully automated system that measured emissions on a sub-daily basis. There was no significant difference in soil N2O emissions between the native dry sclerophyll eucalypt forest and an extensively grazed pasture, wherefrom only low annual emissions were observed amounting to 0.1 and 0.2 kg N2O ha−1 yr−1, respectively. The establishment of a fertilised turf grass lawn increased soil N2O emissions 18-fold (1.8 kg N2O ha−1 yr−1), with highest emissions occurring in the first 2 months after establishment. Once established, the turf grass lawn presented relatively low N2O emissions for the rest of the year, even after fertilisation and rain events. Soil moisture was significantly higher, and mineralised N accumulated in the fallow plots, resulting in the highest N2O emissions (2.8 kg N2O ha−1 yr−1) and significant nitrate (NO3−) losses, with up to 63 kg N ha−1 lost from a single rain event due to reduced plant cover removal. The study concludes that urbanisation processes creating peri-urban ecosystems can greatly modify N cycling and increase the potential for losses in the form of N2O and NO3−

Establishing turf grass increases soil greenhouse gas emissions in peri-urban environments

Urbanization is becoming increasingly important in terms of climate change and ecosystem functionality worldwide. We are only beginning to understand how the processes of urbanization influence ecosystem dynamics and how peri-urban environments contribute to climate change. Brisbane in South East Queensland (SEQ) currently has the most extensive urban sprawl of all Australian cities. This leads to substantial land use changes in urban and peri-urban environments and the subsequent gaseous emissions from soils are to date neglected for IPCC climate change estimations. This research examines how land use change effects methane (CH4) and nitrous oxide (N2O) fluxes from peri-urban soils and consequently influences the Global Warming Potential (GWP) of rural ecosystems in agricultural use undergoing urbanization. Therefore, manual and fully automated static chamber measurements determined soil gas fluxes over a full year and an intensive sampling campaign of 80 days after land use change. Turf grass, as the major peri-urban land cover, increased the GWP by 415 kg CO2-e ha−1 over the first 80 days after conversion from a well-established pasture. This results principally from increased daily average N2O emissions of 0.5 g N2O ha−1 d−1 from the pasture to 18.3 g N2O ha−1 d−1 from the turf grass due to fertilizer application during conversion. Compared to the native dry sclerophyll eucalypt forest, turf grass establishment increases the GWP by another 30 kg CO2-e ha−1. The results presented in this study clearly indicate the substantial impact of urbanization on soil-atmosphere gas exchange in form of non-CO2 greenhouse gas emissions particularly after turf grass establishment

Effect of urbanization on soil methane and nitrous oxide fluxes in subtropical Australia

Increasing population densities and urban sprawl are causing rapid land use change from natural and agricultural ecosystems into smaller, urban residential properties. However, there is still great uncertainty about the effect that urbanization will have on biogeochemical C and N cycles and associated greenhouse gas (GHG) budgets. We aimed to evaluate how typical urbanization related land use change in subtropical Australia affects soil GHG exchange (N2O and CH4) and the associated global warming potential (GWP). Fluxes were measured from three land uses: native forest, a long‐term pasture, and a turf grass lawn continuously over two years using a high‐resolution automated chamber system. The fertilized turf grass had the highest N2O emissions, dominated by high fluxes >100 g N2O‐N day-1 immediately following establishment though decreased to just 0.6 kg N2O‐N ha-1 in the second year. Only minor fluxes occurred in the forest and pasture, with the high aeration of the sandy topsoil limiting N2O emissions while promoting substantial CH4 uptake. Native forest was consistently the strongest CH4 sink (−2.9 kg CH4‐C ha-1 year-1), while the pasture became a short‐term CH4 source after heavy rainfall when the soil reached saturation. On a two‐year average, land use change from native forest to turf grass increased the non‐CO2 GWP from a net annual GHG sink of −83 CO2‐e ha–1 year−1 to a source of 245 kg CO2‐e ha-1 year-1. This study highlights that urbanization can substantially alter soil GHG exchange by altering plant soil water use and by increasing bulk density and inorganic N availability. However, on well‐drained subtropical soils, the impact of urbanization on inter‐annual non‐CO2 GWP of turf grass was low compared to urbanized ecosystems in temperate climates

Rangeland management effects on soil properties in the savanna biome, South Africa: A case study along grazing gradients in communal and commercial farms

Although the savanna biome of South Africa is a major resource for rangeland management, little is known about how differences in rangeland management systems affect soil properties in such biomes. Near to Kuruman, commercial farms have practiced rotational grazing for decades. In communal areas of former homeland Bophuthatswana, similar strategies were used prior to 1994. Nowadays, a continuous grazing system is common. We hypothesized that these changes in management affected soil properties. To test this, we sampled soils at communal and commercial land along a gradient with increasing distance to water points. The results revealed that communal systems with continuous grazing showed enlarged spatial gradients. The soils were depleted in most nutrients close to the water relative to those of commercial systems. In contrast, as the distance to the water increased, the nutrient stocks of these communal systems were higher. Changes in soil nutrient stocks were related to a zone of increased bush encroachment (up to 25%). Specific analyses (phosphorus fractions, particulate organic carbon, δ13C) confirmed that the soils of the communal grazing systems benefited from the shift of grass-dominated to bush-dominated system with woody Acacia vegetation, while the rangeland degraded in the sense that it lost palatable grass species