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Four PhD students at 51����’s Nicholas School of the Environment have developed an innovative new multilevel hierarchical modeling methodology to quantify the effects of urbanization on aquatic biota communities.

The methodology, devised by Roxolana Kashuba, Yoon Kyung Cha, Ibrahim Alameddine and Boknam Lee, allows water managers to better assess how stream macroinvertebrate communities are affected by factors associated with residential and industrial development, including loss of riparian buffers and decreased tree canopies; increased surface runoff; and increased levels of human waste, pesticides and industrial chemicals in stream water and sediments.

The students describe their pioneering work in a United State Geological Survey Scientific Investigations Report, available online at/.

They developed the methodology and wrote the report with Thomas F. Cuffney of the United States Geological Survey Water Science Center in Raleigh, N.C.

The team used their new methodology to assess the effects of urbanization in nine metropolitan areas: Boston, Raleigh, Atlanta, Birmingham, Milwaukee-Green Bay, Denver, Salt Lake City, Dallas-Fort Worth, and Portland, Ore. These locations were chosen to represent the effects of urbanization in different regions and climate zones.

Using multilevel hierarchical modeling allowed the researchers to predict stream invertebrate response to urbanization at both the individual basin level and at the regional scale. They used mean precipitation, air temperatures, and antecedent agriculture as regional-level predictors.

Their multilevel methodology yielded models that “are both statistically more rigorous and ecologically more interpretable than simple linear regression models,” they write in the report.

For instance, “whereas non-hierarchical regressions were only able to show differing relations between invertebrate responses and urban intensity separately for each region, the multilevel hierarchical approach directly establishes the importance of antecedent agricultural conditions in masking the response of invertebrates to urbanization in metropolitan regions such as Milwaukee-Green Bay, Denver and Dallas-Forth Worth,” they write. “Also, these models show that regions with high precipitation such as Atlanta, Birmingham and Portland start out with better regional background conditions of invertebrates prior to urbanization, but experience faster negative rates of change with urbanization.”

Kashuba, Cha, Alameddine and Lee are PhD students in the lab of Kenneth Reckhow, professor water resources.