Bass confusion from land pollution

Traces of just about anything in our 64,000 square mile watershed can be found in our rivers and streams. Plants, animals, microscopic life and the chemical elements of water itself are part of the mix, but so are medicines, fertilizers, man-made chemicals, oil and other contaminants courtesy of humans.

The entire ecosystem can be affected by contaminants, including some of our favorite recreational fish. Among the contaminant troubles for aquatic life are endocrine disruptors: chemicals that cause reproductive changes and can result in intersex fish. Here in the watershed, male fish, including large and small mouth bass, are being found with female protein in the blood, immature eggs in the testes and reduced sperm motility. Incidences of intersex fish in multiple tributaries of the Chesapeake Bay have been documented for several years but taking action to stop these changes has been difficult without knowing the causes or risk factors.

To find the source of these hormonal disruptions for aquatic life, scientists and researchers are using one of the most powerful tools in their arsenal: data. Multiple studies on degraded fish health led the Chesapeake Bay Program in 2014 to include toxic contaminants outcomes in the Chesapeake Bay Watershed Agreement. In a new report, United States Geological Survey (USGS) scientists have analyzed more than fifteen years of data to identify how landscape changes (e.g. natural lands developed for homes and farms) contribute to endocrine disruption in fish.

Endocrine disruptors in the environment

The endocrine system is made up of glands that produce hormones, which affect most every system in the body. Like most living creatures, fish rely on hormones and other biological triggers to help guide growth and development. Some foreign chemicals can mimic these natural hormones, disrupting that natural process. Endocrine disruption can cause many changes for a fish, including intersex characteristics.

There’s a long list of contaminants that can act as endocrine disruptors, including steroid estrogens, pharmaceuticals, fuels, industrial chemicals, pesticides, human and animal waste matter and natural estrogens, like those found in soybeans. The major sources of these contaminants—wastewater treatment plants, development, manicured lawns, industrial areas, animal operations, agricultural fields and stormwater runoff—are therefore all potential causes for the rise in intersex fish in Chesapeake Bay tributaries.

In the USGS study, lead researcher Vicki Blazer and participating scientists used a statistical analysis method known as Classification and Regression Trees (CART) to gain a comprehensive understanding of how these potential sources are impacting aquatic life in the watershed.

Sampling the watershed

Knowing this was a complex issue, researchers designed their data collection to provide a wide view. Samples of water and fish were collected from tributaries in Pennsylvania, Maryland, Virginia and West Virginia. Researchers used 43 landscape variables, mapping out the possible sources of contamination in the watershed and looking at associations with instances of endocrine disruption on two scales: “immediate,” which included only the immediate catchment area surrounding the sampling site, and “upstream,” which included that particular region and all the catchment areas included in the watershed above it. Multiple sites were sampled at different points throughout the year, including spawning (January–May) and post-spawning (June–December).

Findings and Recommendations

Feminization of male fish was often thought to be caused by and concentrated near wastewater treatment plants, but the study shows the cause is not as direct as previously thought. Wastewater and high concentrations of animal operations (livestock, poultry) do play a role, but nonpoint sources (where pollutants come from several sources across a wide area, as with stormwater runoff) look to be the major influencer. On the immediate scale, cultivated land was a major factor. On the upstream scale, impervious surfaces (areas of hardened, nonporous material like buildings, parking lots and pavement) were the primary predictor of endocrine disruption in the bodies of fish downstream.

A positive finding in the report was that natural filters in the watershed are acting as protection for aquatic life. Wherever significant wetland areas or swaths of forests (known as riparian buffers when they’re along the banks of a river) were located, the study showed a lower incidence of intersex fish. Wetlands and buffer areas act as shields for waterways, reducing sediment and nutrient inputs and helping transform contaminants that do move through these natural filters.

The report also helped researchers see how bass might be particularly vulnerable to endocrine disruptors. Bass build nests—round depressions built on the bottom of stream beds— to raise their young. Sediment in waterways is often the soil from farms, as poor soil health in agriculture and a lack of buffers lead to erosion during storm events. The organic matter and estrogen-disrupting contaminants in the sediment then reach bass at their critical stages of development, leading to intersex adults. The study indicates that intersex effects developed in young may be exacerbated by other point sources of chemicals they encounter throughout rivers and streams during their adult lives.

Utilizing the findings in decision making

This study’s years of collaborative data can help policymakers on federal and local levels be strategic in creating management strategies, and can assist organizations, farmers and individuals in making the right decisions about which best management practices to implement when trying to reduce pollution. However, several unknowns still remain--though scientists tested a broad selection of sites, most were only sampled at a snapshot in time. There are hundreds of miles of rivers and streams in the Chesapeake watershed, where conditions vary seasonally and annually. Scientists will need to look at the full breadth of the watershed to continue honing the impacts of land development on fish, but we now have baseline data for how endocrine disruption in fish is connected to how humans choose to use the land.

Read the full study, Retrospective analysis of estrogenic endocrine disruption and land-use influences in the Chesapeake Bay watershed and check out other ways the USGS is studying the Chesapeake Bay watershed: https://www.usgs.gov/centers/cba.