Green infrastructure influences soil health: Biological divergence one year after installation

Global threats to soils remain one of the greatest concerns and challenges of the 21st century. Built landscapes have profound local and global effects because they create urban heat islands, increase habitat fragmentation, and reduce biological diversity. Additionally, impervious surfaces alter natural watersheds and reduce infiltration increasing runoff that leads to erosion and soil degradation. To combat these effects, green infrastructure (GI) practices, like water harvesting rain gardens, are implemented in the Southwest United States to restore natural ecological function, yet little is known about how GI impacts soil health. Soil health can be measured using indicators that include physical, chemical, and biological characteristics that support ecosystem processes. This study aimed to evaluate changes in water holding capacity, bulk density, pH, electrical conductivity, Gibbs free energy, species richness and Shannon diversity in response to rain gardens that received different inputs (frequency and amount) and sources of harvested water (rain, municipal, greywater) one year after installation. We hypothesized that soil health indicators in GI diverge from the unaltered control treatment one year following installation. Although physical and chemical indicators were comparatively less sensitive to GI treatments than biological indicators, they varied within treatments after one year of GI management (pH increased: H = 36.37; p-value = 0.00; electrical conductivity decreased: H = 33.94; p-value = 0.00). Overall, we observed significantly higher soil microbial diversity (F = 4.29; p-value = 0.015) and richness (F = 4.02; p-value = 0.019) in surface soils in GI treatments after one year of management. Our findings suggest GI practices enhanced soil biological health which may lead to positive feedbacks that assist gradual changes in the abiotic environment thus enhancing soil health over time. These findings have broad implications for effectively assessing the success of GI management practices over short time periods using soil biological health indicators.