Five Sacramento National Wildlife Refuges show pesticides
By the USGS
A new paper in Science of the Total Environment, co‑authored by researchers from several USGS Mission Areas and Centers, including the California Water Science Center, finds fungicides, herbicides, and insecticides at every sampling site across five Sacramento Valley wildlife refuges. Because levels stayed high even far from crops, scientists are probing what this means for pollinators.
Nestled within the interior wetlands, grasslands, and riparian habitats of California’s northern Sacramento Valley, the Sacramento National Wildlife Refuge (NWR) embodies the core mission of the National Wildlife Refuge System: protecting wildlife, native vegetation, and the habitats they depend on for the benefit of present and future generations. Established in 1937, the refuge spans approximately 10,819 acres, providing essential habitat for migratory birds along the Pacific Flyway, the western migration path for millions of birds each year.
Unlike national parks, which balance public enjoyment with natural and cultural preservation, national wildlife refuges are managed with a primary focus on protecting wildlife, habitat, and ecological function. While recreational activities such as wildlife viewing, photography, hiking, and hunting are encouraged at Sacramento NWR, each is carefully managed to ensure they do not impede the refuge’s conservation objectives. Management practices include regulating water levels, planting native vegetation, controlling invasive species, and collaborating with local farmers to maintain optimal habitat conditions for wildlife.
Sacramento NWR serves as the headquarters for the Sacramento National Wildlife Refuge Complex, which encompasses five national wildlife refuges: Sacramento, Delevan, Colusa, Sutter, and Sacramento River, as well as three wildlife management areas: Willow Creek-Lurline, Butte Sink, and Steve Thompson North Central Valley. Collectively, the complex protects a diverse array of habitats across multiple counties, offering migratory birds and other wildlife the necessary resources to thrive.
The refuge complex supports a rich diversity of species, including migratory waterfowl like snow geese, which travel thousands of miles from breeding grounds in Canada, Alaska, and Russia to winter in the Sacramento Valley. Other notable species include tule elk, vernal pool fairy shrimp, giant garter snakes, and various native plant communities.
Recognizing that ecological boundaries extend beyond refuge borders, Sacramento NWR engages in ongoing monitoring and research to address external environmental challenges, such as agricultural runoff and pesticide drift. These efforts inform adaptive management strategies aimed at mitigating impacts and enhancing habitat quality within the refuge.
Each winter, visitors can witness the spectacular sight of thousands of snow geese taking flight at sunrise, a testament to the refuge’s vital role in wildlife conservation. In spring, fields of goldfields wildflowers brighten the landscape, offering a different kind of spectacle. The auto tour route, observation decks, and educational programs provide opportunities for people of all ages and abilities to connect with nature and learn about the importance of preserving these critical habitats.
Because many refuges in California are located near active farmland, the wildlife and plants they protect can be exposed to pesticide drift. This proximity raises important questions about how chemicals used on nearby crops may be affecting pollinators, wetland wildlife, and other species that rely on these protected lands. So, how far does that exposure really reach? To find out, scientists looked at whether pesticide levels dropped off the farther you got from the nearest farmland.
You might expect pesticide levels to be highest along the edges of protected lands, where they border agricultural fields, and to taper off toward the interior. However, pesticides were found at every site, and surprisingly, being farther from the edge didn’t always mean lower exposure. This tells us that interior areas of these refuges may not actually offer more protection from pesticide drift than their outer edges, though in general, larger refuges might still help buffer some of that impact.
To measure this, researchers used passive samplers, which are small silicone bands that absorb chemicals from the air. The results showed that it wasn’t just the distance to the farmland that mattered, but the type of crop nearby. For example, when rice fields were the nearest crop, pesticide levels in the interior, the area furthest distance from the crop, were also high. This is likely because rice is often sprayed from above, which increases the chance of chemicals drifting into the farther reaches of a protected refuge.
Why Does This Matter?
National Wildlife Refuges are supposed to be safe places for wildlife, but if pesticides are drifting into these areas, they could harm insects, birds, and other animals that rely on these lands. Pesticides can affect animals in different ways:
- Insecticides can kill or weaken pollinators like bees and butterflies.
- Herbicides may reduce the plants that insects and other animals depend on for food.
- Fungicides can have unknown long-term effects on both plants and animals.
Many species, including pollinators, rely on refuges for survival. Pollinators, in turn, help support ecosystems by fertilizing plants. If their populations decline due to pesticide exposure, this could disrupt entire food chains.
How the Study Was Conducted
To measure pesticide contamination, the research team placed silicone bands at 49 locations across five National Wildlife Refuges:
1) Sacramento NWR
2) Colusa NWR
3) Sutter NWR
4) Rio Vista (a sub-unit of the Sacramento River NWR)
5) Llano Seco (part of the North Central Valley Wildlife Management Area)
These silicone bands used for measurement were left outside for four weeks to absorb chemicals from the air. After collecting the bands, scientists analyzed them in a laboratory to identify the types and amounts of pesticides present.
Some key findings from the study include:
- Every single site had pesticides detected, showing that chemicals can spread far beyond where they are applied.
- Distance from farmland did not make a big difference –pesticides were found even deep inside the refuges.
- Certain pesticides were found almost everywhere, including insecticides like bifenthrin and permethrin, herbicides like metolachlor and trifluralin, and fungicides like chlorothalonil.
- Rice farming contributed significantly to pesticide exposure. Several herbicides used exclusively in rice fields (including benzobicyclon, thiobencarb, and clomazone) were detected at most sites, even more than 15 kilometers away from the nearest rice field.
What’s Next?
This study provides occurrence data for a range of pesticides that occur in wildlife refuges. We know the pesticides mainly come from applications to nearby crops. We used to think that meant only the periphery of the protected might be impacted. However, the data demonstrates that even the refuge’s interiors are affected by the surrounding land use, says Michelle Hladik, a research chemist.
The findings raise important questions about how pesticides affect wildlife in conserved lands. Scientists say more research is needed to understand how these chemicals impact animals, especially pollinators like bees and butterflies. The next step in the research will focus on whether pesticides are accumulating in plants that these insects depend on, such as milkweed.
Since expanding the size of refuges alone may not be enough to protect wildlife from pesticide exposure, conservationists may need to explore new strategies for reducing pesticide drift. This could include better farming practices, buffer zones, or alternative pest control methods.
Even though National Wildlife Refuges are designed to protect biodiversity, this study shows they are not immune to pollution. The findings highlight the need for stronger efforts to manage pesticide use, both inside and outside protected areas, to ensure the health of these important ecosystems.
