Urbanization has been occurring rapidly in the 21st Century. While large cities have attracted a lot of research effort, small and medium-size cities are spatially distributed all over the world, have much closer interactions with nature and often have their unique challenges of sustainable development. We studied Binghamton, a medium-size city in central New York, addressing biogeochemistry of nitrogen (N), an essential nutrient that has been profoundly altered by human activities, and chloride (Cl), a non-essential element elevated in concentration due to winter deicing salt input. At the metropolitan scale, we followed river fluxes and input from the point-source wastewater treatment plant (WWTP). We also selected eight headwater streams that flow from rural upstream to urban downstream before discharging into the Susquehanna River, to quantify non-point source urban pollution. The stream benthic invertebrate community was investigated to quantify the biological response to urbanization. There was a wall collapse at WWTP in 2011 followed by a major flooding after the Tropical Storm Lee. We hypothesize in this medium-size city, human impacts would negatively affect water chemistry and stream benthic communities; yet non-point source pollution would be at moderate level to allow substantial elements of nature to co-exist with human society.
Results/Conclusions
Sampling (2011-13) showed impaired stream water chemistry; seasonally flow-weighted NO3- concentrations were 0.03-0.58 mg/L at urban sites and 0.0-0.43 mg/L at rural sites, with minimal NH4+ contribution. WWTP effluent was dominated by NH4+ at 6.0-19.1 mg/L, and NO3- 0.03-0.9 mg/L. Point source WWTP discharged x10 more inorganic N (480-1100 kg/d) than all stream export combined, despite the latter constituting x6 more drainage area than urbanized land. Concentrations of Cl- were significantly higher at urban sites and positively correlated with the conductivity (r2=0.744, p<0.0001). WWTP was also a significant source of Cl- and phosphorus to the Susquehanna River. In 2014-15 benthic insects were collected from five streams, plus two reference streams draining rural watersheds. Our results showed unsurprisingly lower taxonomic richness at urban sites, yet percentage EPT richness was similar between land-uses (69.2-73.4%). Furthermore, the loss of taxa in urban sites were spatially heterogeneous, led to higher dissimilarity among urban sites (β-diversity); at metropolitan scale, urban and rural sites harbor similar taxonomic richness (γ-diversity) and support unique rare taxa. Our study showed in this medium-size city, significant biodiversity exists even in impaired streams, while infrastructure failure due to engineering design and/or natural disturbance can severely damage the function of the ecosystem.