The effects of urbanization on aquatic insect communities in low order streams in Binghamton, NY
Impacts on streams by urbanization are well known in large cities. The effects of urbanization on streams in small to medium sized cities are less understood. However, humans and nature often interact more closely in small cities than in large metropolitan areas. The City of Binghamton, NY and its neighboring towns are situated on the Upper Susquehanna River Watershed in the headwaters of the Chesapeake Bay. There are a number of small streams running through its urbanized areas. We postulated that these small streams would be degraded even though the magnitude of urbanization in Binghamton is lower than that of a larger city. To test this hypothesis, insect and stream data were collected monthly from April to September in 2014. Insects were collected by kick-net sampling three riffle habitats from five streams that each had paired 50 m downstream urban and upstream rural reaches. We also sampled two rural reference streams at both upstream and downstream reaches. Conductivity, pH, water temperature, NO3-N, NH4-N, flow, and water depth were measured at each reach. Insect samples were sorted and identified to the family or genus level.
From the five streams with paired sample sites, fewer than half of the insects were collected from urban reaches (n=321) than from rural reaches (n=739). Taxonomic richness was lower in urban reaches (F=15.63, p<0.0201) though evenness was similar (F=2.61, p=0.11). EPT richness, a popular metric for stream health, also did not differ (F=2.61 p=0.11). Conductivity increased from 177 ±22 µS/cm in the spring (April - May) to 301 ±30 µS/cm in the summer (June-September), potentially due to a seasonal decrease in flow (0.40 ±0.05 m/s and 0.25 ±0.02 m/s) and water depth (184 ±2 mm and 110 ±1 mm). Water temperature (10.9 ±1.6 oC and 19.7 ±0.5 oC) and pH (6.8 ±0.2 and 7.4 ±1.2) also increased from spring to summer. Concentrations of NO3-N (0.22 ±0.02 mg/l) and NH4-N (0.04 ±0.01 mg/l) did not change through time. Only conductivity was significantly higher in urban reaches (F=8.18, p=0.005). However, conductivity alone did not adequately account for the spatial variation of taxonomic richness in these urban streams (R2=0.04, p=0.06). Our results suggest that while stream communities are clearly disturbed in Binghamton, mechanisms beyond water pollution must be considered, and traditional measures of EPT degradation may not hold in these small urban streams.