Overview
I am a biogeochemist studying nutrient cycling and ecosystem processes in both freshwater and estuarine ecosystems and how those processes are impacted by human activities. Much of my work focuses on nitrogen and how controls on nitrogen inputs and availability, cycling processes, and element interactions influence primary production and eutrophication. Cross-system comparisons can lend new insights in these areas and often motivate the questions I investigate. I particularly enjoy doing experiments at the lab, field, and mesocosm scale and working in collaborative ecosystem studies that combine observational data at different scales with modeling. In addition to research, I work to bring objective science to promote environmental protection and sustainable policy actions at the local level, as an elected official and on volunteer boards.
Research Focus
Our lab group works on a wide variety of both theoretical and practical questions in ecosystem science across interrelated topical areas (nutrient biogeochemistry, ecosystem metabolism, global change, fluxes of nutrients, water, and carbon) and spatial scales. My current primary research focus is a long-term, whole ecosystem study I have been co-leading since 2005, looking at the effects of nitrogen pollution from a contaminated groundwater plume on a shallow, coastal lagoon seagrass ecosystem on Cape Cod, MA. Research questions include: 1) How does a large nitrogen input, with no concomitant phosphorus input, affect primary production and ecosystem metabolism? 2) How do external nitrogen inputs affect sediment and seagrass epiphytic dinitrogen fixation rates, and how significant are these in the nitrogen budget for the system? 3) What is the relative importance of nitrogen biogeochemical transformation and loss processes? and 4) What is the trajectory and timeline of recovery for the ecosystem as the plume nitrogen input decreases, and as climatic conditions and nutrient exchange with the coastal ocean change? Additionally, I am working on a group of highly collaborative projects related to the expansion and toxicity of harmful algal blooms in deep, low nutrient lakes such as the NY Finger Lakes. We are investigating questions such as whether these harmful algal blooms reflect amplification of historically present cyanobacteria or functional community shifts towards more toxic assemblages in response to recent environmental change, and whether high nitrogen in the lakes (and from surrounding land uses) contributes to formation and persistence of the blooms. Tools used for these studies include paleolimnological analyses, simulation models, field measurements of atmospheric nitrogen deposition, and analysis of relevant monitoring and historical data.
Publications
- Swaney, D.P., T.J. Butler, R.W. Howarth, R. Marino, G. M. Beachley, and C. Baublitz. 2026. Atmospheric ammonia deposition: A significant source of nitrogen to an oligotrophic lake and its watershed. Journal of Geophysical Research Biogeosciences 131. https://doi.org/10.1029/2025JG009389
- Hayn, M., R. Marino, and R.W. Howarth. 2026. Long-term trends in nutrient exchange between a New England estuary and coastal waters. Ocean-Land-Atmosphere Research; in review.
- Hayn, M., R. Marino, N.K. Ganju, R.W. Howarth, and K.H. Foreman. 2025. Using multiple lines of evidence to evaluate spatio-temporal trends in nitrogen loading to a eutrophic estuary. Estuaries & Coasts 49,24. https://doi.org/10.1007/s12237-025-01630-0
- Haviland, K.A., R.W. Howarth, A.E. Giblin, and R. Marino. 2024. The potential role of sediment iron and sulfur speciation in seagrass meadow loss and recovery. Ocean-Land-Atmosphere Research; 2024(3): Article 0069. https://doi.org/10.34133/olar.0069
- Marino, R., M. Hayn, R.W. Howarth, A.E. Giblin, K.J. McGlathery, and P. Berg. 2023. Nitrogen fixation associated with epiphytes on the seagrass Zostera marina in a temperate lagoon with moderate to high nitrogen loads. Biogeochemistry 166:211-226. doi:10.1007/s10533-023-010083-2
- Haviland, K.A, R.W. Howarth, R. Marino, and M. Hayn. 2022. Variation in sediment and seagrass characteristics reflect multiple stressors along a eutrophication gradient in a New England. lagoon. Limnology & Oceanography 67:660-672.
- Marino, R. and R.W. Howarth. 2022. Nitrogen Fixation. Pages 163-170 in: Mehner, Thomas and Tockner, Klement (eds), Encyclopedia of Inland Waters, 2nd Edition. vol [1]. Oxford: Elsevier.
- Schneider, R., N. Baker, E. Chase, S. Dunn, R. Marino, D. Orr, W. Pluer, and S. Reynolds. 2022. Replumbing watersheds: a how-to guide for improving roadside ditch management to buffer the impacts of climate change. In: W.L. Filho (ed.), Climate Change Strategies: Handling the challenges of adapting to a changing climate, ICCIR, Springer Nature.
- Howarth, R.W., F. Chan, D.P. Swaney, R. Marino, and M. Hayn. 2021. Role of External inputs of nutrients to aquatic ecosystems in determining prevalence of nitrogen vs. phosphorus limitation of net primary productivity. Biogeochemistry. doi:10.1007/s10533-021-00765-z
- Wong, M., C. Neill, R. Marino, D. Silvério, and R.W. Howarth. 2020. Molybdenum, phosphorus, and pH do not constrain nitrogen fixation in a tropical forest in the southeastern Amazon. Ecology. doi:10.1002/ecy.3211
- Marino, R. and R.W. Howarth. 2016. Why is planktonic nitrogen fixation so rare in coastal marine ecosystems? Insights from a cross-systems approach. Pages 127-139 in: P.M. Glibert and T.M. Kana (eds.), Aquatic Microbial Ecology and Biogeochemistry: A Dual Perspective. Dordrecht:Springer. doi:10.1007/978-3-319-30259-1_11
