Invertebrate Diversity and Abundance: Indicators of Urban Stream Condition in Central Iowa

Small scale urbanization is known to have more influence on aquatic ecosystems than agriculture.  Although the state of Iowa is dominated by row crops, urban sprawl is also increasing.  In order to better understand the impact of urbanization on headwater streams, I measured  landscape features physical variables associated with degraded systems in relation to biological variables; in this case, the abundance and diversity of benthic invertebrates.  In June 2011 I quantified these relationships by taking measurements of physical stream variables, mapping landscape variables, and harvesting benthic invertebrates from 10 streams in central Iowa.  Impervious surface in the surrounding watershed was found to have a positive relationship with conductivity, which is an indicator of pollutants.  Additionally, higher turbidity, a feature associated with sediment and nutrient loading, was related to several indicators of degraded conditions, including reduced total invertebrate taxa richness and reduced coarse substrate availability.  In turn, coarse substrate was negatively related to with net-spinning caddisfly (Hydropsychidae) abundance.  Overall, my findings demonstrated that in Iowa, even small scale urban development (0-33% impervious surface) can adversely affect headwater streams within the watershed.