Policy Spillovers to Biodiversity: The Impacts of Interventions for Water Quality on Bird Abundance

• In Event: Biodiversity, Water Resources, and Global Environmental Change

Abstract

Human activities have drastically impacted biodiversity, leading to significant declines in bird populations across many habitats. While water pollution control policies like the Clean Water Act (CWA) Title II grants have heavily invested in human health and recreation by improving water quality, their spillover benefits to biodiversity remain largely unquantified. While the policy emphasized the cleanup and preservation of federal jurisdictional waters of the United States, studies of the policy's externalities and cost-benefit analyses have largely focused on the monetized returns from the CWA. This has typically fallen in hedonics or effects on human morbidity. However, aside from select ecological regions, quantification of the broader ecological benefits beyond immediate downstream improvements in water quality has remained largely understudied. Such quantifications merit further research in light of frontier literature and long-standing cost-benefit analysis practices: mismeasurement of quantifiable benefits, even if not initially monetized, leads to a downward bias in the overall policy analysis. For ecological indicators like birds and biodiversity signals in particular, these forms of analysis have been particularly relevant for the recreational value they provide, with surveys conducted by the US Fish and Wildlife Services in 2024 estimating that individuals spend over $100 billion on birding-related activities. This project thus investigates the causal impacts of CWA Title II wastewater sanitation grants on relative bird abundance and species richness - the first important step in any form of cost-benefit analysis for outcomes that have remained largely understudied. By linking citizen-science data from the Christmas Bird Count - a very novel dataset that has seldom been used but contains a rich archive of historical count data, preceeding even the Breeding Bird Survey - with the EPA's Grants Information and Controls System (GICS) and the National Hydrography Dataset Plus (NHDPlus), the study creates a comprehensive spatial panel of downstream catchments. This analysis follows well-established literature from both applied economics and ecology to first develop indices of abundance and richness, conditional on effort characteristics. It then uses those indices in a staggered difference-in-differences framework to estimate the average treatment effect of grant-funded plant upgrades on downstream bird populations. Preliminary results indicate positive ecological spillovers. Specifically, results demonstrate a statistically significant increase of 0.130 standard deviations in the log relative abundance of resident bird species (i.e., birds that remain through breeding and wintering periods) up to 25 miles downstream of plant upgrades. This is equivalent to roughly 3,000 more birds in the catchment area. Examining all birds across any season (migratory or not) also showed positive trends (0.107 standard deviation), though not statistically significant. These findings highlight that historical water-quality interventions yielded vital, previously unaccounted-for ecological benefits. Quantifying these spillovers offers critical insights for targeting future environmental infrastructure investments to maximize both human and ecosystem health.

Author

• Anthony Ponce, Cornell University
  Presenting Author