On April 7th, the Center for Environmental Studies 1960 Scholars Program welcomed Mason Stahl, Assistant Professor in the Environmental Science, Policy and Engineering Program and the Geosciences Department at Union College. His research spans the fields of hydrogeology, geochemistry, and water resources and he studies how perturbations to the environment influence the flows of water, the cycling of elements, and the quality of our water resources. Much of his research falls into two key areas: (1) characterizing soil moisture and groundwater recharge processes; (2) elemental cycling in groundwater and surface water systems with a strong focus on the cycling of arsenic. A primary goal of his research is to help answer questions about how groundwater and surface water quality will respond to natural and anthropogenic changes to the environment and what this means for the health of people and the environment.
Stahl gave a lecture focusing on how seasonal variations in the water cycle are related to human health. To address this issue, Stahl concentrated on variations in groundwater recharge—our main source of water—across the United States. 2.5 billion people are reliant on groundwater and it supplies 40% of irrigation to agriculture. Our heavy reliance on groundwater means we are often depleting it, especially with irrigation use. The Western US, Middle East, and northern Africa are areas heavily depleted because of high reliance. We need to understand the gravity of this depletion and also how the recharging process works so we can be better equipped to prevent depletion. Stahl’s research has found that recharge is dominant in the summer in the middle of the United States due to get nocturnal rainstorms that efficiently recharge aquifers. Meanwhile, the western part of the country has winter dominant recharge and the eastern states aren’t dominated by a particular season, though nationwide, winter is generally more efficient at groundwater recharge than summer. With this finding in mind, Stahl encouraged his audience to think about the implications of climatic changes on the amount and efficiency of groundwater recharge in the coming decades; for example, if climate change leads to shorter winters and longer summers in the northern hemisphere, that would mean a shorter period of effective recharge in most of the country.
Another essential facet of the relationship between water cycles and human health that Stahl is focused on is the seasonal variation of soil moisture. While soil moisture is only 0.2% of liquid freshwater, it is 90% of water used by crops (known as greenwater). 65% of terrestrial water flows move through the soil, a crucial resource for primary production globally. Stahl studies the seasonal variation of soil moisture using satellite data that remotely measures soil moisture content every 3-4 days. This data has allowed him to see five distinct cycles in soil moisture variation that have been observed on Earth:
1. Dry summers, wet winters
2. Long summer peak of moisture
3. Muted spring and autumn peaks, not in the summer
4. Short-duration peak in soil moisture in the later summer
The most common pattern observed in this data was aseasonal, meaning that the soils are always wet or always dry. In general, aseasonal places are always dry.
The third aspect of the interplay between water and health that interests Stahl is the contamination of groundwater with arsenic, an issue that many communities are facing worldwide. 10 micrograms/L is the EPA maximum for arsenic content, yet 140 million people globally are consuming groundwater that exceeds these guidelines. 2 million of those people are in the US. Stahl has found in his own research in studying Cambodia wells that groundwater arsenic is strongly controlled by surface flooding seasonality. Studying the seasonality of flooding gives researchers like Stahl the tools to anticipate which areas will have high concentrations of arsenic without installing wells. Understanding the patterns of seasonal flooding, groundwater recharge rates, and the variation in soil moisture across seasons all work to help us understand how important and complex our relationship to water is, how much is dictates our ways of life, and how vulnerable it is to the consequences of our own decisions.
Log Lunch is a CES program hosted every Friday at noon. During Log Lunch, a vegetarian meal prepared by Williams students is served, followed by a talk on an environmental topic. Speakers are drawn from both the student body and faculty of Williams, as well as from local, national, and international organizations. Learn more here.
BY CAMPBELL LEONARD ’25