Consequences of roads and traffic-related stressors on freshwater biodiversity

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.