Chemical status of soils in four urban riparian plant communities

Soil characteristics of four distinct urban riparian plant communities were studied along a drainage ditch in Tempe, AZ. Our objective was to test if plant communities occured in similar soil chemical conditions in an urban riparian area. We quantified reduction oxidation (redox) potential, pH, electrical conductivity, phosphorus, reduced iron and soil texture. Our results indicate that the four communities sampled occur in differing chemical conditions. Redox potentials in cattail and bulrush dominated communities ranged from -240 to -303 mV while levels of ferrous iron ranged from 17.0 to 38.5 mg kg^-1. This indicates that soils of a highly anaerobic nature occur in these two communities. Redox potentials in knotgrass and Johnson grass communities were significantly (P≤0.05) higher, ranging from +194 to +244 mV. Reduced iron was not found in these communities, indicating the more aerobic nature of these stands. Both cattail and bulrush communities were found in significantly finer soil textures than the knotgrass and Johnson grass communities. In addition to occupying the stream margins, the more aerobic conditions in knotgrass and Johnson grass communities may result from increased water interflow through the soils of these communities. Data of this type are important so that managers can set realistic goals for re-establishement of vegetation in riparian areas that have been impacted by urban and suburban development.