Soil analysis in Arizona catchments

Background/Question/Methods

Urbanization can have negative effects on natural systems. Streams in particular face problems caused by urbanization such as pollution, over abundance of runoff, and lack of sustainable hydrology. These systems are also affected by the soils in the catchments, which are also being heavily affected by urbanization. Erosion, nutrient overload, and lack of infiltration in some of these soils can have negative effects on the streams. Studying these urban catchments is crucial to understanding the material and water inputs to streams.

This research project is focused on catchments within the Phoenix Metropolitan area. Analyses of soils have been done before, but not much work has been done in dry urban ecosystems. We were especially interested in exploring the role of soil properties and how they affect infiltration rates and nutrient composition of soils in residential areas. We quantified soil texture, soil moisture and organic matter within yards of residential areas in three different catchments in order to better understand how soil properties affect whether storm water runs off or is absorbed.

We did this research by collecting soil samples from 60 sites within 3 different catchments. We divided the sites between two different yard types, mesic (grassy) and xeric (dry desert landscape), and collected samples at depths of 0-5 and 0-10 cm. This small-scale study on soil properties and chemistry can help us make inferences or predictions about what patterns we might see at the catchment scale.

Results/Conclusions

This initial study indicates: Higher infiltration rates in xeric sites vs. mesic lawns, slightly higher clay and silt % in mesic lawns, slightly higher sand % in xeric lawns and higher soil moisture and soil organic matter in mesic sites. Nutrients like phosphorous and nitrogen, which are capable of having adverse affects on the stream, are found more abundantly in mesic sites.

Understanding more about water infiltration and runoff could benefit hydrologists, engineers, and landscapers in that the data would provide more information on how soil type influences water movement which could be taken into account when designing cities. This can also influence homeowners in their decisions dealing with lawn type and care, which could therein impact the amount of runoff and overall health of the stream.