Abstract
Soil organic carbon (SOC) is a crucial indicator of soil health and soil productivity. The long-term implications of rapid urbanization on sustainability have, in recent years, raised concern. This study aimed to characterize the SOC stocks in the Johannesburg Granite Dome, a highly urbanized and contaminated area. Six soil hydropedological groups; (recharge (deep), recharge (shallow), responsive (shallow), responsive (saturated), interflow (A/B), and interflow (soil/bedrock)) were identified to determine the vertical distribution of the SOC stocks and assess the variation among the soil groups. The carbon (C) content, bulk density, and soil depth were determined for all soil groups, and thereafter the SOC stocks were calculated. Organic C stocks in the A horizon ranged, on average, from 33.55 ± 21.73 t C ha−1 for recharge (deep) soils to 17.11 ± 7.62 t C ha−1 for responsive (shallow) soils. Higher C contents in some soils did not necessarily indicate higher SOC stocks due to the combined influence of soil depth and bulk density. Additionally, the total SOC stocks ranged from 92.82 ± 39.2 t C ha−1 for recharge (deep) soils to 22.81 ± 16.84 t C ha−1 for responsive (shallow) soils. Future studies should determine the SOC stocks in urban areas, taking diverse land-uses and the presence of iron (Fe) oxides into consideration. This is crucial for understanding urban ecosystem functions.
Highlights
An increasing urban population has stimulated interest in the status and sustainable use of soil resources in urban areas
This study aims to determine the vertical distribution of Soil organic carbon (SOC) stocks in six hydropedological groups identified in the Johannesburg Granite Dome area and assesses the variation among the groups
There was a statistical correlation between the interaction of the soil groups and diagnostic soil horizons and SOC stocks (F = (10, 247) = 2.58, p = 0.005)
Summary
An increasing urban population has stimulated interest in the status and sustainable use of soil resources in urban areas. Urban soils are generally characterized by increased bulk density, pH levels, and carbon (C) content due to organic pollutants at industrial sites, increased residential waste, traffic, and infrastructure [2,3,4,5]. A study by [6] found that soil pH and bulk density were not significantly different in urban areas. Soils in the city of Johannesburg, the economic hub of Africa, are diverse in both physical and biochemical aspects. Gold mine tailings across the city are often laden with lead and arsenic [7,8], reducing agricultural productivity and overall soil quality
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