Research

1. Managed Aquifer Recharge: Weighing the Promise Against the Practical Hurdles

HSGG faculty: Helen E. Dahlke
Citation: Owen, D., Dahlke, H.E., Fisher, A.T., Bruno, E., Kiparsky, M. (2025). “Navigating the Growing Prospects and Growing Pains of Managed Aquifer Recharge.” Groundwater. Read the paper

As groundwater levels decline and water demand climbs across the western United States, managed aquifer recharge (MAR) has drawn growing interest as a tool that can ease water-supply pressure and deliver environmental co-benefits, often at lower cost than alternative water-management strategies. This 2025 synthesis, co-authored by UC Davis’s Helen Dahlke along with researchers from UC Law San Francisco, UC Santa Cruz, and UC Berkeley, takes stock of where MAR stands today. Alongside the prospects, the authors lay out the practical “growing pains” that have slowed wider adoption: locating physically suitable sites, the economics of recharge infrastructure, gaps in public policy and water law, and equity considerations in how recharge benefits and costs are distributed across communities.

2. Extreme Weather Is Speeding Up Nitrate Contamination of Groundwater

HSGG faculty: Isaya Kisekka, Thomas Harter, Helen E. Dahlke (co-authors)
Citation: Raij-Hoffman, I., Dahan, O., Dahlke, H.E., Harter, T., & Kisekka, I. (2024). Assessing nitrate leaching during drought and extreme precipitation: Exploring deep vadose-zone monitoring, groundwater observations, and field mass balance. Water Resources Research, 60, e2024WR037973. Covered in UC Davis CAES News, Nov. 13, 2024.  Read the paper

Conventional wisdom held that nitrate from fertilizer could take weeks to years to migrate from a crop’s root zone down to groundwater. This study, conducted on a tomato and cucumber field near Esparto, California between 2021 and 2023 — a period that swung from drought into atmospheric-river flooding — found otherwise: a heavy rain event following drought pushed nitrate 33 feet down to the water table in as little as 10 days. About 40% of nitrogen fertilizer applied to vegetable crops is never taken up by the plant and instead remains in the soil; during drought, that surplus builds up, and the researchers found that a subsequent burst of rain flushes it toward groundwater far faster than previously assumed. Nitrate concentrations in the shallow groundwater exceeded the EPA’s maximum contaminant level for drinking water. The findings point to a need for affordable, real-time soil nitrate monitoring so Central Valley farmers can manage fertilizer application more precisely as extreme wet-dry swings become more common under climate change.

Read the CAES News coverage 

3. Helping California Agriculture Adapt to a More Volatile Water Future

HSGG faculty: Alvar Escriva-Bou
Citation: Medellín-Azuara, J., Escriva-Bou, A., Gaudin, A.C., Schwabe, K.A., Sumner, D.A. (2024). “Cultivating climate resilience in California agriculture: Adaptations to an increasingly volatile water future.” Proceedings of the National Academy of Sciences, 121(32), e2310079121.  Read the paper

California agriculture depends on a water supply that is becoming less predictable as droughts and floods intensify under climate change. This PNAS paper, co-authored by HSGG’s Alvar Escriva-Bou along with researchers from UC Merced, UC Santa Cruz, and UC Davis, examines how the state’s farming sector can adapt to that volatility — from shifting cropping patterns and water-use efficiency investments to the institutional and policy changes needed to support those adaptations. The paper draws on Escriva-Bou’s broader research linking engineering and economic models to evaluate how drought and policy decisions ripple through agricultural and urban water systems, work he has also pursued through the Public Policy Institute of California on groundwater sustainability in the San Joaquin Valley.

4. Wildfire Smoke Is Cooling Down Lakes — and Slowing Their Metabolism

HSGG faculty: Steven Sadro
Citation: Farruggia, M.J., Smits, A.P., Sadro, S. (2026). “Wildfire smoke reduces water temperature and metabolic rates in lakes and ponds across a small headwater watershed.” Limnology and Oceanography Letters, 11(3), e70125.  Read the paper

As wildfire smoke has become a near-annual feature of California summers, this 2026 study examines what that smoke does to the lakes and ponds it settles over. Working across a small headwater watershed, the authors found that smoke cover measurably lowers water temperature and slows down ecosystem metabolic rates — the pace at which a lake’s organisms produce and consume energy. It builds on Sadro’s earlier work (Smits et al., 2024, Communications Earth & Environment) showing that wildfire smoke reduces lake metabolic rates unevenly depending on a lake’s position in the food web. Sadro, recently named chair of UC Davis’s Department of Environmental Science and Policy, studies how lakes and streams — particularly in the Sierra Nevada — respond to environmental change, often in collaboration with the Tahoe Environmental Research Center.

5. Tracing How Mercury Becomes Dangerous in Wetlands

HSGG faculty: Brett A. Poulin
Citation: Poulin, B.A., Tate, M.T., Janssen, S.E., Aiken, G.R., Krabbenhoft, D.P. (2025). “A Comprehensive Sulfate and DOM Framework to Assess Methylmercury Formation and Risk in Subtropical Wetlands.” Nature Communications, 16, 4253. Read the paper (open access — figure reuse permitted under CC BY 4.0)

Mercury itself isn’t the main threat to wetland ecosystems — its organic form, methylmercury, is what accumulates in fish and wildlife and poses risks to human health. This 2025 Nature Communications paper, led by Poulin with USGS collaborators, develops a framework linking sulfate and dissolved organic matter (DOM) chemistry to where and when methylmercury forms in subtropical wetlands, using the Florida Everglades as a testing ground. The framework helps predict methylmercury risk from measurable water-chemistry conditions, giving land and water managers a more direct way to anticipate contamination hotspots. Poulin’s broader research program in UC Davis’s Department of Environmental Toxicology focuses on how metal contaminants, especially mercury, move through natural and human-altered environments.