Consequences of roads and traffic-related stressors on freshwater biodiversity

Algera, Dirk 1 ; Piczak, Morgan1; Currie, Warren2; Fahrig, Lenore1; Ricciardi, Anthony3; Rytwinski, Trina1; Taylor, Jessica1; Cooke, Steven1

Published Apr 21, 2026 on Dryad. https://doi.org/10.5061/dryad.tdz08kqd9

Data files

Apr 21, 2026 version files 214.78 KB

Evidence_base_r1.1.xlsx

209.92 KB
README.md

4.86 KB

Abstract

Road development has expanded globally, with growing recognition of the impacts on freshwater systems. We synthesized findings from 426 publications to assess: 1) where and for which taxa road effects on freshwater biodiversity have been studied; 2) the types of roads and putative stressors examined; 3) the study designs and biological responses measured; and 4) the reported road effects on freshwater biodiversity. Most studies were from North America (62.1%), focusing on amphibians (36.1%), fish (14.8%), and reptiles (10.9%) in ponds/wetlands, laboratory settings, and streams. Research primarily assessed the impacts of paved roads and stressors such as road density/proximity (20%), traffic (18.4%), and salt/de-icers (17.9%). mostly using Impact-only (51.0%) and Control-Impact (46.5%) study designs. Abundance/diversity and mortality responses were the most frequently measured outcomes. Reported road effects were predominantly negative, underscoring widespread road impacts on freshwater biodiversity. Major research gaps remain, including understudied taxa, life-stages, and putative stressors. Further, limited use of rigorous study designs restricted causal inference. Future research should focus on these gaps and apply standardized, comparative approaches to improve understanding and management.

Dataset DOI: 10.5061/dryad.tdz08kqd9

Description of the data and file structure

A systematic search of the publication database ISI Web of Science Core Collections was performed on August 31, 2021 using the following search string:

((road* OR highway$ OR traffic OR motorway$ OR freeway$) AND (wildlife OR fauna OR flora OR animal$ OR fish* OR mammal$ OR bird$ OR avian OR amphibian$ OR reptile$ OR plant$ OR vegetation OR macrophyte$ OR invertebrate$ OR insect$ OR arachnid* OR arthropod* hexapod$ OR rotifer$ OR mollus* OR crustacea* OR dragonfl* OR mayfl* OR springtail$ OR stonefl* OR caddisfl* OR beetle$ OR diptera$ or flatworm$ OR nematod* OR polychaet* OR annelid$) AND (aquatic* OR “Fresh water” OR Freshwater OR Stream$ OR Water$ OR River$ OR Fluvial OR Lake$ OR Pond$ OR Wetland$ OR Estuar* OR Reservoir$ OR Canal$) AND (effect$ OR impact$ OR affect))

The data contained in the evidence base spreadsheet was the final evidence base (i.e., studies that were included after full text screening was conducted) used to generate the results for the manuscript. A description of the evidence base spreadsheet used in generating the results, structured consistent with the Results section of the manuscript:

Publication Data

-Columns A, B, and C provides the number of unique publications (A) and the "cases" within each publication (B and C).

-Columns D and E provide additional data on the publications (this was not reported in the manuscript).

-Column F provides the year the study was published.

Geography, Freshwater Ecosystem Types, and Taxa

-Column G provides and the country the study took place.

-Column H provides region-level data (this was not reported in the manuscript).

-Column Q provides the freshwater ecosystem type that were investigated.

-Column R provides the freshwater organisms for which road effects were investigated. Freshwater organisms included flora (plants) and fauna (animals), which were further categorized into taxanomic groups (i.e., taxa).

-Columns S, T, and U provide additional species-level data on the freshwater taxa (this was not reported in the manuscript).

-Column V provides the life stage of the freshwater taxa.

-Column Z indicates whether the freshwater taxa investigated was considered an invasive species (yes or no; according to publication author's statements).

Road Phases and Types, and Study Designs and Settings

-Columns K and L provide the road phases (K) and types (L) for which road effects were investigated.

-Column J provides the study design employed, which could include Impact-only (i.e., no reference comparator), Before-After, Control-Impact, and Before-After-Control-Impact.

-Column P indicates the reference comparator (i.e., "before" or "control") used for Before-After, Control-Impact, and B-A-C-I study designs (this was not reported in the manuscript).

-Column I provides the setting for which road effects were investigated.

Putative Stressors and Biological Response Variables

-Column N provides the putative road stressors (i.e., presumed stressors) for which road effects were investigated on freshwater taxa.

-Column M provides a more detailed description of the stressor (this was not reported in the manuscript).

-Column O indicates a means (i.e., mechanism) for which the putative stressors could result in road effects on freshwater taxa (this was not reported in the manuscript).

-Columns W and AA provide the categorical biological response variables (W) and the specific response metrics (AA) of freshwater taxa that were investigated by researchers.

-Column X provides a more detailed description of the biological response (this was not reported in the manuscript).

Trends in Road Effects

-Column Y provides the outcome of the freshwater taxa's biological response (positive, negative, or neutral/inconclusive; based on publication author's statements). A positive outcome meant that the putative stressor had an advantageous biological outcome on the freshwater organism; a negative outcome meant that the putative road stressor had a disadvantageous biological outcome on the freshwater organism; a neutral/inconclusive outcome meant that the putative road stressor resulted in no detectable effect.

Files and variables

File: Evidence_base_r1.1.xlsx

Description: Evidence base for the manuscript resulting from the literature search.

Code/software

The records resulting from the literature search were exported into EPPI-Reviewer Web https://eppi.ioe.ac.uk/EPPIReviewer-Web/home

Data extraction, analysis, and visualization were performed using Microsoft Excel and R-Studio.

Access information

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