About

Professor M. Todd Walter is a faculty member in the Department of Biological and Environmental Engineering. His research emphasizes the interactions between hydrology, ecology, and biogeochemistry, applying physical hydrology and water resources engineering to multidisciplinary research interests. He pursues questions that cross traditional academic boundaries of hydrology and terrestrial ecology. His recent research focuses on linkages between hydrology and biogeochemical hotspots, as well as applications of nano-biotechnology to ecohydrological systems. Professor Walter teaches courses in hydrology, ecohydrology, and water resources engineering, emphasizing data analysis, laboratory experiments, and field investigations using actual data collected by students.

Research topics

• Ecology
• Environmental science
• Biology
• Environmental engineering
• Business
• Geography
• Waste management
• Water resource management
• Environmental resource management
• Environmental planning
• Geology
• Engineering
• Meteorology
• Environmental protection

Selected publications

• Tracing Environmental DNA Transport in a Large Lake with Synthetic DNA Microparticles and Hydrodynamic Modeling

  Environmental Science & Technology · 2026-01-20 · 1 citations

  articleOpen access

  Natural environmental DNA (eDNA) offers a powerful tool for aquatic ecosystem monitoring. However, its transport in large lakes remains poorly understood due to its instability, scarcity, and heterogeneity, as well as the complex hydrodynamics of lakes. We developed biodegradable synthetic DNA particles (sDNAp) that encapsulate DNA fragments with unique sequences to serve as quantitative tracers for investigating eDNA transport. This sDNAp tracer was deployed in Cayuga Lake (NY, USA; 172 km2 surface area) and its dispersion was monitored for 33 h over ∼11 km2 through depth-integrated water sampling followed by quantitative PCR analysis. Despite gram-scale release quantities, sDNAp were detected over 7 km from the source after more than a day, at concentrations as low as ∼3–5 particles mL–1, demonstrating high sensitivity and durability. A 3D hydrodynamic model incorporating wind-driven circulation and stratification reproduced key dispersion patterns observed in the field. Forward particle-tracking simulations captured both horizontal advection and vertical displacement, while backward simulations revealed that vertical position sensitivity limited the accuracy of source attribution. This approach provides one of the first lake-scale demonstrations that time-resolved, probabilistic attribution of natural eDNA sources is feasible under favorable conditions. Using sDNAp tracers, it also establishes a robust benchmark for future studies on eDNA transport in large waterbodies.

  PublisherDOI

• Groundwater phosphorus contributions comparable to tributaries in a large, mesotrophic, polymictic lake

  The Science of The Total Environment · 2025-11-21

  articleOpen accessSenior author

  Groundwater is increasingly recognized as a significant yet underappreciated source of nutrients and pollutants to lakes. This study examines the role of groundwater seepage in nutrient dynamics during the summer season in Oneida Lake, a 207 km 2 polymictic lake in central New York, USA. Over nine weeks in 2020, we measured groundwater seepage and collected pore water samples at 10 representative shoreline sites. Concurrently, we collected grab and automated samples from the five main tributaries and obtained streamflow data from U.S. Geological Survey gauging stations. Data was summarized to compare the relative importance of the two sources of phosphorus (P) during the summer months, both at baseflow only and including high flow events as well. Tributaries dominated both external water input and the Soluble Reactive P (SRP) loading to the lake in summer of 2020. However, total P (TP) loads from groundwater was similar to the TP loads from tributaries and up to twice as high in weeks with baseflow conditions in streams. Nearshore groundwater and tributary P loading together represented ∼50 % of the late summer increase of P in the water column, with the remainder assumed to be from internal loading or deep groundwater seepage. Our results show that groundwater seepage can be a large component of the P budget even in large lakes and adds to the handful number of studies that have quantitatively measured and compared nutrient loading from both streams and groundwater into large lakes. • Groundwater seepage plays a key role for P transport into lakes • TP loadings from groundwater and all tributaries combined were comparable • This study is one of the few comparing surface and groundwater inputs in large lakes

  PublisherDOI

• The Curve Number’s Initial Abstraction and Physical Hydrology: ASCE-EWRI CN Hydrology Committee Synthesis

  Journal of Irrigation and Drainage Engineering · 2025-05-14 · 4 citations

  article

  The curve number method for estimating rainfall runoff has continually evolved since its creation in the mid-20th century. Because it is inherently an empirical model that is broadly applied to many hydrological applications, the rationales for its parameters have become removed from physical interpretation over its evolution. The ASCE EWRI CN-Hydrology Committee, i.e., some of the foremost experts on this methodology, often finds itself internally at odds regarding many aspects of CN-hydrology. Here, the committee has synthesized its member’s perspectives on the physical interpretations of one CN-method parameter, the initial abstraction (Ia). This note provides insights into how the Ia concept has evolved and offers some context into reasons behind its evolution. This note also synthesized different interpretations of Ia within the framework of different hydrological settings, applications, and spatial scales. Broadly speaking, the committee suggests that Ia might need to be interpreted on a case-by-case basis although this note places reasonable boundaries on Ia for most applications.

  PublisherDOI

• Microbial diversity and gene abundance in denitrifying bioreactors: A comparison of the woodchip surface biofilm versus the interior wood matrix

  Journal of Environmental Quality · 2024-07-16 · 4 citations

  articleOpen access

  Excessive amounts of nitrogen (N) and phosphorus (P) can lead to eutrophication in water sources. Woodchip bioreactors have shown success in removing N from agricultural runoff, but less is known regarding P removal. Woodchip bioreactors are subsurface basins filled with woodchips installed downgradient of agricultural land to collect and treat drainage runoff. Microorganisms use the woodchips as a carbon (C) source to transform N in the runoff, with unresolved biological impacts on P. This study aims to explore microbial communities present in the bioreactor and determine whether milling woodchips to probe the microbial communities within them reveals hidden microbial diversities or potential activities. Metagenomic sequencing and bioinformatic analyses were performed on six woodchip samples (i.e., three unmilled and three milled) collected from a 10-year-old woodchip bioreactor treating agricultural tile drainage. All samples had similar DNA purity, yield, quality, and microbial diversity regardless of milling. However, when sequences were aligned against various protein libraries, our results indicated greater relative abundance of denitrification and P transformation proteins on the outside of the woodchips (unmilled), while the interior of woodchips (milled) exhibited more functional gene abundance for carbohydrate breakdown. Thus, it may be important to characterize microbial communities both within woodchips, and on woodchip surfaces, to gain a more holistic understanding of coupled biogeochemical cycles on N, P, and C in woodchip bioreactors. Based on these findings, we advise that future microbial research on woodchips (and potentially other permeable organic materials) examine both the surface biofilm and the interior organic material during initial studies. Once researchers determine where specific proteins or enzymes of interest are most prevalent, subsequent studies may then focus on either one or both aspects, as needed.

  PublisherOA PDFDOI

• Groundwater inputs could be a significant but often overlooked source of phosphorus in lake ecosystems

  Scientific Reports · 2024-07-15 · 9 citations

  articleOpen accessSenior author

  Freshwater lakes are severely threatened, due largely to excess inputs of nutrients and other contaminants. Phosphorus (P) is receiving renewed attention due to recent increases in toxic cyanobacteria blooms in lakes worldwide. We investigated groundwater seepage for its role in P loading dynamics at Oneida Lake, New York, USA-one of the most well-studied lakes globally. P loading was measured at representative sites along the 88 km shoreline over three summers by directly measuring groundwater flow using seepage meters and porewater samplers. Groundwater seepage was a continuous and significant source of dissolved P over the summer months, comparable to tributary sources to the lake during that time. This constant input has enriched the concentrations of P in the nearshore surface waters, significantly above levels in the pelagic zone. Pore Total Phosphorus (TP) concentrations and loads reached extremely high values (up to 100 mg/L), with inorganic P representing only ~ 10% of TP per site. Groundwater seepage flows and P loadings were highly variable across space and time, partially explained by adjacent land uses and precipitation. Our research concludes that groundwater seepage is a significant, but overlooked, source of dissolved P and a crucial factor driving summer primary production at Oneida Lake, and likely other temperate lakes.

  PublisherOA PDFDOI

• Improved Regionalization of the CN Method for Extreme Events at Ungauged Sites across the US

  Journal of Hydrologic Engineering · 2024-09-25 · 4 citations

  articleSenior author

  The curve number (CN) equation is a semiempirical, event-based model commonly used to estimate rainfall runoff. This model was originally developed in the 1950s to estimate storm runoff from 24-h rainfall events from small catchments. The model consists of two parameters: (1) the curve number (CN), which represents soil type, land use, and land cover; and (2) the initial abstraction (Ia), i.e., the amount of rain that needs to accumulate before storm runoff begins. Despite its narrow-intended use, the CN model is widely used for many applications from engineering design to hydrologic modeling and uses parameter tables and guidelines developed in the mid-20th century. Changes in land management and hydrological science pose questions about the continued relevancy of the model in general and the tabulated parameters specifically. We used Catchment Attributes and Meteorology for Large-Sample Studies (CAMELS), a recently collated data set of watershed characteristics and performed regression analyses on the watershed attributes to determine whether the CN and Ia parameters can better fit a wider range of attributes than can the currently used tables. Our analyses focused on 5–35 year peak runoff events. We considered 333 small to medium watersheds distributed across the contiguous US and more than 40 watershed characteristics. We found that the CN model generally worked best if Ia was much smaller than traditionally assumed. Indeed, Ia=0 generally worked well. We also found that CN-values generally correlated well with climate (elevation, average precipitation) and soil permeability (sand fraction, saturated hydraulic conductivity). Our results suggest that the CN model can work relatively well for engineering purposes in ungauged watersheds and that the expanding stream of remotely sensed geographic data may allow for better CN-values than those from the current tables. We suggest that this study be expanded to include a wider range of watershed and storm characteristics.

  PublisherDOI

• Methods for monitoring urban street litter: a comparison of municipal audits and an app-based citizen science approach

  Environmental Science Advances · 2024-01-01 · 3 citations

  articleOpen accessSenior author

  Non-traditional methods, including citizen (or participatory) science and professional litter audits can provide high quality data for understanding street litter and associated plastic pollution.

  PublisherOA PDFDOI

• Towards a Crowdsourced Digital Coffee Atlas for Sustainable Coffee Farming

  2024-09-05 · 3 citations

  articleOpen access

  The present work summarizes the results of a 15-week student project addressing the field of sustainable coffee farming. Coffee farmers often lack scientific knowledge concerning the coffee varieties they cultivate, and having grown coffee for generations, they often have limited knowledge concerning the names of their coffee varieties used on the global market. This leads to significant disadvantages in market positioning. Consequently, farmers often receive lower prices for their coffee as they cannot accurately determine its true market value. In addition, the effects of climate change force farmers to reconsider the varieties they cultivate, as they cannot exhibit stable yield performance due to the changed climate. If farmers are unaware of the potential quality advantages of different coffee types, this prevents them from optimizing growing conditions specific to their climate. As part of a design thinking-based project course, a team of four design and computer science students at Hochschule Mannheim searched for a solution on how to overcome the aforementioned disadvantages for local coffee farmers with the support of digital technology. Coffee Consulate helped the team by connecting them to farmers around the world and sharing their domain knowledge. The student team’s main idea is to bridge the aforementioned knowledge gap by collecting globally distributed data about coffee species in one worldwide accessible, digital system, allowing farmers to be globally connected. Their concept proposes a digital Coffee Atlas for mobile phones, showing where on the planet and under which climate conditions coffee varieties are grown and how these species are named on the global market. The app allows one to identify coffee plants based on pictures uploaded from farmers’ phones. The team developed an implementation roadmap that considered how to subsequently extend the database behind the Coffee Atlas and how to accelerate the crowdsourcing process. AI-based image recognition trained with pictures taken from a living collection of coffee cultivars, like in the botanical garden of Wilhelma (Stuttgart, Germany), and DNA sequences could serve as an initial step for creating the database. Farmers should be motivated to upload pictures of their plants by additional services provided by the app. Therefore, information about coffee species can be crowdsourced with the help of farmers around the world. Such services could include the recognition of plant health conditions, as well as the estimation of the actual market price of a species based on the identification of coffee varieties or the recommendation of species that are better adapted to the actual or expected climate. In its final implementation, the Coffee Atlas will enhance agricultural practices and economic outcomes for farmers and provide a valuable source of data for researchers around the world.

  PublisherOA PDFDOI

• The effect of weathering in runoff-to-groundwater partitioning in the Island of Hawai'i: Perspectives for landscape evolution

  Earth and Planetary Science Letters · 2024-04-06 · 9 citations

  articleSenior author
  PublisherDOI

• Abundance of microbial community genes encoding terminal proteins of the aerobic and denitrification respiratory chains as indicators of ecohydrologic gradients in a coastal temperate rainforest

  Ecological Indicators · 2023-07-28

  articleOpen accessSenior author

  • Soil hydrology is linked to aerobic respiration marker gene relative abundance. • Limited denitrification gene relative abundance suggests N is tightly cycled. • Tree species are indicators or functional agents of respiratory marker genes. The persistence of soil organic carbon (SOC) is closely linked to the capacity of the soil microbial community to catalyze oxidative degradation of organic matter. This study uses a landscape-scale metagenomics approach to examine the relative abundances of genes encoding different terminal electron acceptors used for aerobic respiration and denitrification between soil microbial communities across an ecohydrologic gradient. The perhumid zone of the North Pacific coastal temperate rainforest serves as a template to test the associations between these differing respiratory pathways, soil conditions, and tree species biomass. We used the occurrence of reads in soil metagenomes as a proxy for the relative abundance of genes across the ecohydrologic gradient and identified distinct microbial fingerprints differentiating the driest (upland forest) and wettest (palustrine scrub-shrub and palustrine emergent wetland) ecosystem types. There was little gene-based differentiation between the ecosystem types at the wettest end of the ecohydrologic gradient - scrub-shrub wetland and emergent wetlands – while forested wetlands, which occur as gradient sites between upland forests and emergent wetlands on the landscape, were characterized by substantial metagenomic variability and, consequently, overlapped in their soil metagenome with the other ecosystem classes. Hydrology, as measured by groundwater depth was a predictor of O 2 and N-oxide reductase abundances. High affinity O 2 reductase genes were associated with wetter topographic positions, which has not been shown at the ecosystem scale, or in soils in-situ previously. N-oxide reductase genes were more associated with plant communities found at wetland sites but were not related to soil inorganic nitrogen, suggesting that nitrate supply may be limiting to denitrifiers ubiquitously across this gradient. Two plant species, Tsuga heterophylla (TSHE) and Pinus contorta spp. contorta (PICO), were more strongly correlated with O 2 -reductase and N-oxide reductase genes than site hydrology, respectively. This research represents a step toward fingerprinting the ecosystem microbiome using genes coding for specific terminal electron acceptors that control the fate of SOC and their ecohydrologic controls.

  PublisherDOI

Recent grants

• Eliminating 'Nonpoint:' Using nanotechnology to identify pollution sources in the landscape

  NSF · $495k · 2009–2012

Frequent coauthors

• Tammo S. Steenhuis

  70 shared

• Erin Brooks

  University of Idaho

  41 shared

• J.‐Y. Parlange

  Cornell University

  36 shared

• Zachary M. Easton

  35 shared

• Rebecca L. Schneider

  Louisiana Department of Natural Resources

  31 shared

• Michael F. Walter

  30 shared

• Olivier Dangles

  Institut de Recherche pour le Développement

  26 shared

• Stephen B. Shaw

  26 shared

Education

• PhD, Biosystems Engineering

  Washington State University

  1995

Awards & honors

• SUNY Chancellor's Award for Excellence in Teaching (2015)
• State University of NY 2013 Outstanding Teaching Award (2013…
• USDA-CSREES Mission Integration award (2008)
• 2007 Outstanding Teaching Award (2007)