Abstract
IntroductionConstruction activities in and along urban streams increase the sediment input into surface waters, causing an overall decline in water quality and aquatic ecosystems. In this case study, we investigate the water quality impacts of local hydromodification in an urban stream (discharge 0.4 m3/s). At the site of interest, workers removed a stream crossing consisting of an embankment with culverts and replaced it with a small bridge (single span of 25 m) in an effort to improve flow capacity.MethodsWater samples were taken at four sites along the North Branch Park River in Connecticut, Northeastern United States. Turbidity and dissolved oxygen (DO) were measured in situ, and nitrate and total phosphorus (TP) were measured in the laboratory. Benthic macroinvertebrate samples were also collected and analyzed for taxon richness and Shannon-Weaver species diversity. Data were compared between upstream and downstream sites and before, during, and after hydromodification. We used one-way ANOVA combined with the post hoc Turkey test to derive statistical significance.ResultsDuring construction, turbidity increased temporarily by 60.9% [from 2.48 Nephelometric Turbidity Units (NTU) over ambient to 4.00 NTU]. Once construction was completed, DO increased locally from 11.0 to 13.0 mg/L. Benthic macroinvertebrate taxon richness and species diversity declined by 61.6 and 32.6% respectively, with no recovery observed in the year following construction. Water quality was only affected within 50 m downstream. Nitrate and TP concentrations were unaffected.ConclusionsSmall-scale hydromodification temporarily increased the turbidity as a result of increased sediment input, approaching the maximum level for clean water (5 NTU). Benthic macroinvertebrate communities declined in the immediate downstream vicinity of construction but are expected to recover soon given that turbidity recovered to pre-construction levels, and DO increased. These outcomes emphasize that environmental assessment is important not only for large-scale hydromodification but also for smaller scale stream modifications.
Highlights
Construction activities in and along urban streams increase the sediment input into surface waters, causing an overall decline in water quality and aquatic ecosystems
We evaluated the impacts of this flow improvement project on water quality by comparing turbidity [a common indicator of suspended solids], dissolved oxygen (DO), total phosphorus (TP), and benthic macroinvertebrate abundance, taxon richness and diversity (Weigel et al 2002; Chen et al 2009; Hassan et al 2015) measured before, during, and after construction
During the construction period, a significant difference started to develop, when turbidity increased immediately downstream of the construction site during construction period and returned to prior levels after construction. This is reflected by measurements for site C (Fig. 2), where values first increased from 2.48 ± 0.36 Nephelometric Turbidity Unit (NTU) to 4.00 ± 0.94 Nephelometric Turbidity Units (NTU) (+ 60.9%) and decreased to 2.4 ± 0.15 NTU
Summary
Construction activities in and along urban streams increase the sediment input into surface waters, causing an overall decline in water quality and aquatic ecosystems. Highway construction can lead to a rapid decline in stream water quality (e.g., suspended solids, iron, chloride, sulfate, nitrogen, and pH), during construction and in the period that follows (Chen et al 2009; Purcell et al 2012). The pollution from this type of large construction projects degrades aquatic ecosystems and has severe impacts on food webs (Bennett et al 2001). This explains why they are an important proxy for water quality and ecosystem health (e.g., Quinn et al 1997; Weigel et al 2002; Chen et al 2009; Mundahl and Hunt 2011)
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