Increasing fish diversity of Chicago's waterways

Abstract

Descriptions of shifts in biodiversity across time are desired for urban freshwater systems to better study ecosystem change and causal mechanisms. I document changes in fish diversity within the Chicago Area Waterways across 35 years using a battery of diversity metrics calculated on both abundance and biomass data. Has diversity of Chicago's waterways changed over 35 years and if so, do different diversity metrics exhibit different trends or breakpoints in trends? Diversity of the fish assemblage increased across the three decades of study. Breakpoint analysis suggested that trends across the timeseries were nonlinear. Changes in dominant species influenced behavior of less traditional metrics, whereas Margalef's Richness, Shannon-Weiner, and Gini-Simpson appeared more robust. Increases in richness and taxonomic diversity combined with decreases in species dominance suggest an ecosystem of increasing quality. The fish community of the Chicago Area Waterway System is more diverse both in abundance as well as biomass (i.e., energy flows) in the late 2010's than it was in the late 1980's. Although external factors related to wastewater treatment increased water quality and likely led to these assemblage-level changes breakpoint analysis did not allow verification of causal mechanisms.

Increased fishing quality of Chicago's waterways following the Clean Water Act

“…We found that Bluntnose Minnow populations increased in abundance, biomass, and individual size. Similarly, abundance and biomass of several other minnow species also increased in the CAWS (Happel, 2022).…”

“…Water quality of the system increased following these improvements and led to lower concentrations of wastewater related contaminants now compared to the 1980s (Happel & Gallagher, 2022; Pluth et al, 2021). Within the CAWS, fish species richness, diversity, abundance, and biomass have increased steadily since 1985 (Happel, 2022; Happel & Gallagher, 2021). Reductions in wastewater contaminants and increases in wastewater storage capacities were better predictors of increases in species richness over various weather and water quality (i.e., temperature, pH, dissolved oxygen) parameters (Happel & Gallagher, 2022).…”

“…Within the CAWS, fish species richness, diversity, abundance, and biomass have increased steadily since 1985 (Happel, 2022;Happel & Gallagher, 2021). Reductions in wastewater contaminants and increases in wastewater storage capacities were better predictors of increases in species richness over various weather and water quality (i.e., temperature, pH, dissolved oxygen) parameters (Happel & Gallagher, 2022).…”

Natural shorelines support greater diversity and abundances of fishes than armoured shores along Chicago's waterways

“…Shoreline armouring amounts differ across the system (Table 1 and Figure 1 The CAWS fish community is numerically dominated by gizzard shad (Dorosoma cepedianum) and common carp (Cyprinus carpio), who alone account for nearly half of the fish in the system (Happel, 2022;Happel & Gallagher, 2021). The next four most abundant species help account for a further 20%-25% of the individuals, and the nine most abundant species account for 80%, leaving 20% of the total fish in the system spread across some 63 species' abundances.…”