Pulling apart the urbanization axis: patterns of physiochemical degradation and biological response across stream ecosystems

Abstract

Watershed urbanization introduces a variety of physical, chemical, and thermal stressors to receiving streams and leads to well-documented declines in the diversity of fish and macroinvertebrates. Far less knowledge is available about how these urban stressors affect microbial communities and microbially mediated ecosystem properties. We examined 67 chemical, physical, and biological attributes of streams draining 47 watersheds in the metropolitan area surrounding Raleigh, North Carolina. Watersheds ranged from undeveloped to 99.7% developed watershed area. In contrast to prior investigators, we found no consistent changes in habitat structure, channel dimensions, or bed sediment size distributions along the urbanization gradient. Watershed urbanization led to large and consistent changes in receiving stream chemistry (increases in NO 3 2 , bioavailable and algal-derived dissolved organic C, and the trace metals Pb, Cd, and Zn) and thermal regimes. These chemical and thermal changes were not associated with any consistent shifts in microbial community structure or taxonomic richness, based on terminalrestriction fragment length polymorphism and pyrosequencing methods, despite the fact that these urban stressors were associated with commonly reported declines in macroinvertebrate taxonomic richness and altered macroinvertebrate community composition. Chemical and thermal changes as a function of % developed watershed area also were unrelated to shifts in microbially mediated biogeochemical processes (C mineralization, denitrification potential, and substrate-induced respiration). A broad urbanization gradient sampled in this region suggests that stream ecosystem responses to watershed urbanization can follow diverse trajectories.

In search of microbial indicator taxa: shifts in stream bacterial communities along an urbanization gradient

“…() and Hassett et al . (). All sites were sampled in late May through late July 2009; at each site, macroinvertebrates were collected before sediment collection using two distinct methodologies.…”

“…This study focused on the microbial community of the sediments as a potential informative proxy to assess the impact of urbanization on streams and biofilms were not studied because many sites had sandy substrates with limited number of rocks for biofilm collection. The site selection process and an extensive physical, chemical and biological characterization (67 parameters measured) of the sites are detailed in Somers et al (2013) and Hassett et al (2018). All sites were sampled in late May through late July 2009; at each site, macroinvertebrates were collected before sediment collection using two distinct methodologies.…”

“…As urbanization is a multifaceted disturbance, we used different environmental variables to characterize the urban gradient and the response of the sediment microbiome. We selected five environmental variables that best described this urban gradient, based on the extensive physical, chemical and biological characterization (67 variables measured) previously presented in Hassett et al (2018). The five complementary variables used to describe the urban gradient were: % developed, % unforested, % field land cover derived from land cover GIS data at each site; sediment zinc concentrations (a common urban pollutant) and a biotic index score based on the tolerance of the aquatic macroinvertebrate community living in each stream used to assess biological impairment as a water quality criterion.…”

Coupled fish-hydrogeomorphic responses to urbanization in streams of Columbus, Ohio, USA

“…Canopy cover over both banks of the stream, as well as over the stream, was measured using a densiometer following methods outlined in Lemmon ([66]; utilized in streams in [67][68][69]). Percentage canopy coverage was calculated every 25 m over the entire reach, or up to 200 m centered in the middle of longer reaches.…”

Disrupting the biodiversity – ecosystem function relationship: response of shredders and leaf breakdown to urbanization in Andean streams

“…Urbanized streams often show a reduction in channel width and substrate size of streambed due to sediment inputs, as well as an increase in nutrient concentrations and other pollutants from sewage inputs and runoff (Allan, 2004). When these stream characteristics are altered by urbanization there will be a consequence on the macroinvertebrate communities (Roy et al, 2003;de Jesús-Crespo, Rebeca Ramírez, 2011;Hassett et al, 2018), resulting in species loss (Chadwick et al, 2006;Urban et al, 2006) that can lead to a disruption of the biodiversity-ecosystem functioning relationship (Meyer et al, 2005;Tilman et al, 2014). Therefore, the interruption of this interaction can turn into a serious issue at the ecosystem level when keystone species are removed or replaced from streams (Iñiguez-Armijos et al, 2016).…”