Brief Summary of Minutes of Annual Meeting

The NADP is governed by an Executive Committee (EC), which oversees two standing Technical Subcommittees — the Network Operations Subcommittee (NOS) and the Education and Outreach Subcommittee (EOS) — as well as two Advisory Groups focused on quality assurance (QAAG) and data management (DMAG) and four Science Committees. Each committee and subcommittee operate independently, elects its own officers, and brings recommendations forward to the EC for final approval. The EC also has authority to establish ad hoc working groups as needed. Approved committee minutes are posted to the NADP website within 60 days of each meeting. Full details on committee structure, charges, and membership are available in the NADP Governance Handbook at https://nadp.slh.wisc.edu/pubs/nadp-governance-handbook/.

During the 2026 Spring Science Symposium, the EC and EOS met on Tuesday, June 9. The NOS met on May 27, 2026. Meeting minutes are available on each committee’s website.

The National Research Support Project – No. 3 (NRSP-3) provides a framework for cooperation among State Agricultural Experiment Stations (SAES), the U.S. Department of Agriculture–National Institute of Food and Agriculture (USDA-NIFA), and other cooperating governmental and non-governmental organizations that support the National Atmospheric Deposition Program (NADP). The NADP provides quality-assured data and information on the exposure of managed and natural ecosystems and cultural resources to acidic compounds, nutrients, base cations, mercury, and emerging contaminants in precipitation (e.g., per- and polyfluoroalkyl substances, PFAS) and through dry deposition. NADP data support informed decisions on air quality and ecosystem issues related to precipitation chemistry and directly support NIFA priority areas including soil health, water quality, and agricultural productivity and nutrient management.

Researchers use NADP data to investigate the impacts of atmospheric deposition on the productivity of managed and natural ecosystems; the chemistry of estuarine, surface, and groundwaters; and biodiversity across forests, shrublands, grasslands, deserts, and alpine vegetation. NADP mercury network data are used to examine the effects of atmospheric deposition on mercury in fish and to better understand links between environmental mercury exposure and human health — directly supporting USDA food safety priorities. NADP data also underpin assessments of nitrogen and sulfur loading relevant to agricultural productivity and ecosystem sustainability.

Within this NRSP, there are three stated goals: (1) management and coordination of NADP monitoring networks; (2) site support, chemical analysis, and data validation for network sites directly supported by this agreement; and (3) quality assurance and quality control activities to ensure consistent operation and standard operating procedures. During this reporting period (10/1/24-6/12/26), all three goals were met. Since the NADP Symposium was moved from the fall to the spring, this reporting period covers the time between the 2024 Fall Science Symposium and the 2026 Spring Science Symposium.

Plans for the Coming Year

During FY2027 (July 1, 2026-June 30, 2027), the NADP will continue operation of all five networks and the PFAS-NTN subnetwork (PFN), with a focus on growing PFN site coverage and building out its data and mapping products. The Program Office will also support planning for the 2027 NADP Annual Meeting, coordinate committee activities across all subcommittees and science committees, and continue engagement with USDA-NIFA and federal agency partners on network funding and scientific priorities.

Outreach and communication efforts will focus on increasing awareness of NADP's expanded monitoring portfolio, particularly PFAS atmospheric deposition, among new stakeholder audiences including public health agencies, agricultural land managers and land-grant extension programs, environmental decisionmakers, and drinking water utilities. The Program Office will support development of new educational and outreach materials through the Education and Outreach Subcommittee (EOS) to accompany the PFN launch and other emerging network activities.

A. Outputs

1. Network Operations

The major accomplishment of the NADP is the continued operation of its monitoring networks. During this reporting period, the NADP operated five active networks: the National Trends Network (NTN), the Mercury Deposition Network (MDN), the Ammonia Monitoring Network (AMoN), the Atmospheric Mercury Network (AMNet), and the Mercury Litterfall Network (MLN). In addition, the PFAS-NTN subnetwork (PFN), a subnetwork of the NTN focused on per- and polyfluoroalkyl substances (PFAS) in wet deposition, continued to expand, and is discussed more below. At the close of this reporting period, 233 NTN sites, 78 MDN sites, 100 AMoN sites, 7 AMNet sites, and 25 MLN sites were active. The PFN included 19 operational sites.

The NADP Program Office, located at the Wisconsin State Laboratory of Hygiene (WSLH) at the University of Wisconsin–Madison, provided network coordination, site operator support, data management, and quality assurance services throughout the reporting period. The NADP Analytical Laboratory (NAL), also housed at WSLH, performed chemical analysis and data validation for NTN and MDN precipitation samples.

2. Samples Collected

NADP's principal output is the collection, analysis, and quality assurance of precipitation chemistry and atmospheric chemistry samples. During this reporting period, the following samples were collected:

NTN: 16,385 precipitation samples collected and analyzed across all network sites, yielding concentration and deposition flux data for 10 analytes plus precipitation volume

MDN: 5,024 total mercury precipitation samples collected

AMoN: 4,206 two-week passive ammonia samples collected

AMNet: approximately 47,756 hourly gaseous mercury concentration observations collected

MLN: 63 litterfall samples collected during the 2024 Season

3. NADP Database

Across all networks, the NADP databases now contain over 1,621,428 records. This includes an NTN database of more than 516,262 observations, a MDN database of over 129,558 observations, an AMoN database of over 54,706 observations, and AMNet records of over 920,870 observations. Data through calendar year 2025 are finalized and publicly available on the NADP website (http://nadp.slh.wisc.edu). Data for the first half of 2026 are posted with final quality assurance to be completed following the close of the full calendar year. All data are available at no charge.

During the reporting period, there have been 98 unique data records requests to the NADP PO. Of these requests, 53 requested network data, 19 requested precipitation data, and 26 requested both network and precipitation data.  

4. Spring Science Symposium

The NADP Spring Business Meeting and Scientific Symposium was held in Madison, Wisconsin, from June 9-12, 2026. The business meeting portion convened all standing technical and advisory subcommittees, science committees, and the Executive Committee, and featured scientific presentations from NADP data users spanning federal agencies, universities, and state programs to a state government panel discussing atmospheric deposition data uses and needs. This provided a forum for stakeholder engagement, network updates, and discussion of emerging science priorities including PFAS deposition monitoring and aeroallergen science.

During the 2026 Spring Science Symposium portion, 29 talks, 11 posters, and 1 panel discussion were presented. The panel discussion focused on state agency air quality data needs to support agricultural, ecosystem, and human health. These presentations represented the full diversity of NADP’s research and outreach efforts and included international presenters from Canada, Mexico, and India. For the first time, we had 2 high school students present about their NADP site at Oldsfield School (MD91). A select set of presentations are highlighted below (may have been edited for content and brevity), including information about outcomes and beneficiaries related to agricultural and environmental systems:

a)      FarmFlux: Connecting Agriculture, Atmospheric Composition, and Ecosystems, presented by Glenn Wolfe (NASA), Emily Fischer (Colorado State), and Jeff Geddes (Boston University)

Gaseous emissions from agricultural activities affect atmospheric composition, with significant consequences for air quality, climate, stratospheric ozone, and ecosystem health. FarmFlux is a NASA airborne mission to quantify U.S. agricultural emissions and trace their Earth system impacts. In late 2026 and 2027, FarmFlux will equip two aircraft with in situ gas and particle instrumentation and acquire observations over croplands and animal feeding operations throughout the Midwest and Western U.S. Analysis with advanced techniques (mass balance, eddy covariance) will provide near-direct quantification of actual emission and deposition fluxes that can be used to understand environmental drivers, improve model parameterizations, and enhance the utility of satellite retrievals. This presentation will detail the motivation, objectives, techniques, and expected outcomes of FarmFlux.

This mission is expected to inform NADP’s understanding of agricultural emission sources contributing to nitrogen and mercury deposition, benefiting model developers and agricultural land managers.

b)      Understanding Land-Atmosphere Exchange of Reactive Nitrogen through Tiered and Machine Learning Assisted Monitoring, presented by Da Pan (Georgia Institute of Technology)

Atmospheric reactive nitrogen (Nr), including its reduced form ammonia (NH₃) and oxidized forms (NO_y), is a critical component of the Earth system that significantly impacts air quality, ecosystem health, and climate. While essential for agriculture, excess Nr is lost to the environment, initiating a cascade of detrimental effects, including the formation of ground-level ozone and fine particulate matter (PM_2.5), ecosystem acidification, and biodiversity loss. As emissions of oxidized nitrogen decline, the role of agricultural ammonia in driving these impacts has grown, yet it remains the largest source of uncertainty in the U.S. nitrogen budget due to a lack of direct flux observation.  To address these significant knowledge gaps, we propose a novel Tiered and Machine Learning Assisted Monitoring (TMLAM) framework designed to provide comprehensive and cost-effective NH₃ flux data. The framework synergistically combines:   Tier 1) direct, high-fidelity eddy covariance flux measurements at a few "supersites" to develop and evaluate process models;   Tier 2) inferential modeling driven by low-cost sensors to expand spatial coverage into critical regions; and   Tier 3) upscaling using existing air quality monitoring networks and reanalysis data.  A key innovation of the TMLAM framework is a data-driven site selection strategy that moves beyond traditional ecoregions. We hypothesize that coherent regions for NH₃ land atmosphere exchange are defined by multivariate environmental drivers, including soil, vegetation, and atmospheric composition. Using unsupervised machine learning (K-means clustering) on principal components of high-resolution environmental data, we identify these "Nitrogen Exchange Similar Areas" (NESAs). This approach allows for strategic placement of Tier 1 sites in highly representative areas and Tier 2 sites at the boundaries between NESAs to characterize model uncertainty. This presentation will detail the TMLAM framework and the ML-based methodology for NESA determination. In addition, we will discuss sensors suitable for each tier and recent advances in inferential modeling for Tier 2 sites. Finally, we will also evaluate and rank potential sites for the future implementation of TMLAM for NH₃ or Nr fluxes.

c)      From Canopy to Rain Chemistry: Vegetation Phenology as a Driver of Organic Matter Wet Deposition, presented by Paola Miramontes Gonzalez (University of New Hampshire), Desneiges S. Murray (Boston University), Michael D. Bell (National Parks Service), Michael Palace (University of New Hampshire), and Adam Wymore (University of New Hampshire)

Atmospheric wet deposition of nutrients plays a critical role in the biogeochemical exchange between the atmosphere and terrestrial ecosystems. One component of atmospheric wet deposition is dissolved organic matter (DOM), comprised of both dissolved organic carbon (DOC) and dissolved organic nitrogen (DON), which originate from emission sources such as industrial and agricultural activity, biomass burning, and plant organic compounds. Current monitoring networks primarily analyze inorganic compounds in wet deposition, which leaves a key fraction of wet deposition compounds unreported. In the northern hemisphere, seasonality of DOM wet deposition has been shown to correlate with the growing season, however the role of vegetation phenology and potential plant emissions as a major driver of DOM wet deposition variability remains to be examined. Here we used archived samples (n = 836) from the National Atmospheric Deposition Program (NADP) collected in 2018 to develop a spatially distributed dataset of DOM wet deposition across eastern temperate forests. Monthly average deposition concentrations were combined with NASA Moderate Resolution Imaging Spectroradiometer (MODIS) vegetation indices and Daymet Daily Surface Weather data to examine the relationship between vegetation growth and potential precursor plant emissions to DOM wet deposition at 27 NADP sites. Results suggest that seasonal peaks in DOM wet deposition concentrations are linked to higher temperatures and active vegetation growth (i.e. increased vegetation cover and vegetation index metrics) during summer months. This result highlights the role of biogenic emission deposition processes to drive the seasonal exchange of organic matter between the biosphere and atmosphere. Investigating the links between terrestrial phenology and DOM wet deposition clarifies the influence of vegetation-based emission sources on the timing and magnitude of DOM wet deposition. This study offers new insight into under-represented organic forms of nitrogen and carbon in deposition and improving our ability to predict bioavailable forms of nutrient inputs to ecosystems.

This work demonstrates that NADP’s long-term sample archive can be repurposed to answer emerging science questions beyond the program’s routine inorganic analyte list, extending the existing infrastructure without additional field costs. This work will be of use to ecosystem modelers and land managers working on nutrient cycling and biogeochemical budgets in forested landscapes.

d)      Dragonfly Biosentinels Link Hydrologic Extremes and Mercury Bioaccumulation in the Merrimack River Watershed, presented by Sarah Nelson (Appalachian Mountain Club), Celia Chen (Dartmouth College), Collin Eagles-Smith (US Geological Survey), Braedon Lineman (University of Maine), Ralph Perron (US Forest Service, retired), Colleen Flanagan Pritz (National Parks Service), Vivien Taylor (Dartmouth College), and James Willacker (US Geological Survey)

Biosentinels have been used to indicate relative risk of mercury (Hg), a contaminant that has led to fish consumption advisories in all 50 states, tribes, and territories, to food webs across the US. Dragonfly larvae have been employed as biosentinels for Hg at the national scale, with good correspondence to fish, amphibian, and biogeochemical drivers. Although intra-annual variability in Hg concentrations in dragonflies is typically low relative to spatial variation, few studies have investigated the effects of extreme hydrologic events on Hg bioaccumulation. Regionally, the Northeastern US has experienced long-term atmospheric deposition of Hg from long-range transport, and has also seen the greatest increases in frequency of extreme precipitation events in the US. Such events can influence Hg via increases in dissolved organic carbon (DOC) mobilization, or potentially redistribution of legacy Hg from historic deposition or industrial pollution. The Merrimack River Watershed in New England was the earliest industrialized area in the US, with known in-watershed Hg releases including use of kyanized (Hg-treated) lumber in the 1800s to construct a canal and lock system, and the Nyanza Superfund site that used Hg in dye manufacturing through the 1970s. The Merrimack Watershed also includes remote, forested landscapes in its headwaters in the White Mountain National Forest (WMNF), NH. This project used dragonfly larvae, biosentinels for Hg in food webs, to investigate spatial patterns in Hg within the Merrimack River Watershed, with focus on both the industrialized areas within the watershed (Lowell and Lawrence, MA) and headwater areas in WMNF. Over five years of dragonfly collections, the watershed experienced extreme drought and wet years (e.g., July 2023 was the fourth wettest July since recordkeeping began for the Northeast; in 2025, New Hampshire had its highest coverage of extreme drought in the history of the U.S. Drought Monitor), providing hydrologic extremes that reveal how these climate related events influence potential Hg changes in food webs. Although previous research has shown limited inter-annual variability in dragonfly Hg, such extreme hydrologic events did not occur in that study period. Thus, the current study offers the opportunity to refine our understanding of how these types of events could inform interpretation of long-term trends and underscores the need for long-term monitoring.

These findings refine the interpretation of long-term mercury trends and underscore the continued need for sustained deposition monitoring. This work is of use to state and tribal public health agencies issuing fish consumption advisories and federal land managers overseeing watershed and wildlife health.

e)      Evaluating Methods for NADP Phosphate Wet Deposition Measurement, presented by Jeffrey L. Collett Jr. (Colorado State University), Amy P. Sullivan (Colorado State University), Lillian E. Naimie (Colorado State University), Jihee Ban (Colorado State University), and Bret A. Schichtel (National Parks Service and Colorado State University)

Phosphorus (P) is an essential nutrient for terrestrial and aquatic ecosystems. Important sources of P to the atmosphere include marine aerosols, wildfires, soil dust, and industrial activity. Atmospheric deposition of phosphate has received little attention in the United States despite its potential impacts on ecosystem health. Consequently, the NADP community is considering ways to pilot measurement of P wet deposition in weekly precipitation samples. Given potential microbial transformation of P in precipitation samples, use of SNiPiT (Sampler for Nitrogen and Phosphorus in Total) samplers charged with sulfuric acid has been a focus of method testing. Very low concentrations of P in measured samples stimulated testing of high sensitivity analytical methods. Following initial work by the NADP Central Analytical Lab, we pursued further tests to: (1) quantify blanks in prototype SNiPiT samplers, (2) select an analytical method with sufficient sensitivity to measure trace-level phosphate concentrations in precipitation samples, and (3) test for effects of sample acidification on P measurement. Flow injection analysis was selected as an optimal method for quantifying phosphate ion. A Skalar SAN++ classic series automated wet chemistry analyzer was chosen for P measurement.  The system adds reagents to the sample to form a light absorbing complex that is measured at high sensitivity (MDL ~ 0.1 µg P L-1) using a long-path (50 cm) flow cell.  Measurements of precipitation and snowpack samples collected in Colorado and Kentucky revealed P levels ranging from <1 to approximately 20 µg P L-1.  Initial SNiPiT sampler prototypes, constructed from PVC, were found to yield unacceptably high P blanks. New Delrin SNiPiT prototypes provided by the NADP Program Office yield consistent, low blank values below 0.1 µg P L-1. Preliminary SNiPiT sampling protocols call for pre-charging the sampler with sulfuric acid to yield a final collected sample pH < 2 to limit microbial growth. Over-acidification (pH<1.5), however, interferes with color development and P quantification. This limits the optimal range of sample:acid volume, creating a challenge for a network with diverse and variable weekly precipitation amounts.

This work directly advances the TNTP (Total Nitrogen Total Phosphorus) initiative described in this report’s Milestones section, moving phosphorus deposition measurement from a research question to a field-deployable protocol. This capability supports more accurate agricultural nutrient budgets, refined nutrient management planning, and better tracking of atmospheric contributions to nutrient loads in agricultural watersheds. Agricultural nutrient management researchers, and state water quality programs will benefit from this dataset.

B. Activities

1. Annual Map Summary

The 2024 Annual Map Summary — comprising of national maps of wet deposition concentration and flux for all analytes, plus summary figures for gaseous networks — was produced and distributed during this reporting period. Maps are available for download in multiple formats at nadp.slh.wisc.edu.

The 2025 Annual Map Summary will be available to download beginning in Fall 2026, outside of this reporting period.

2. Publications

The NADP tracks the number of journal and report publications for each calendar year that use NADP data in research. As a National Research Support Project #3 (NRSP-3), our principal goal is to produce data that the research community uses.

During calendar year 2024, we found 161 publications that used NADP data in some way in their research, including a number of dissertations and theses. During calendar year 2025, 146 peer-reviewed journal articles and reports were published using NADP data, including 22 dissertations and theses. Counting publications for 2026 will begin in January 2027, when annual publications are complete. The continued volume of publications and reports using NADP data reflects the sustained demand for and relevance of NADP data to the scientific and policy communities, as well as its role in supporting graduate education and research. More information about publications can be found in the Publications section within this report.

C. Milestones

1. PFAS Monitoring Expansion

A significant milestone during this reporting period was the official launch of the PFAS-NTN Subnetwork (PFN) and continued expansion. The PFN represents a major new direction for the NADP, extending the program's monitoring mission to include PFAS. Outreach to prospective site sponsors and collaborative partners was ongoing throughout the year, with the Program Office actively engaging federal agencies, universities, and state organizations to grow the subnetwork and secure long-term site support.

2. AMoN Sampler Change

A nine-month AMoN passive sampler intercomparison project began in November 2024, across 10 sites in the United States and Canada. The study aimed to assess the performance of a Radiello and ALPHA (Adaptive Low-cost Passive High Absorption) passive samplers. Based on results of this project, NADP switched to the lower-cost ALPHA samplers in January 2026.

3. Passive Mercury Pilot

A new pilot network measuring quarterly gaseous elemental mercury concentrations at 10 sites began on December 31, 2024. The first three quarters of data showed decreasing gaseous elemental mercury concentrations, consistent with increased stomatal uptake by vegetation during the growing season. Based on these preliminary results, the NADP Executive Committee voted to extend the passive mercury pilot through 2026 to capture a full annual cycle and approved minor changes to the sampling protocol. Evaluation of the protocol change and overall data will continue throughout 2026.

4. MDN Updates

Work continues on redesigning the MDN sample train, which currently relies on glass components requiring expensive and time-consuming weekly cleaning. After encountering difficulty sourcing an affordably priced bag option, we continue to test Teflon bottles as an alternative. Preliminary results testing different cleaning protocols on Teflon bottles are promising, as all blanks tested below detection. Future testing will include repeated exposure of the same sample bottles under different cleaning protocols, as well as evaluation of a plastic funnel replacement. In parallel, we are field testing 1-week versus 2-week MDN sampling intervals to help reduce sample cost.

5. Total Nitrogen and Phosphorus Sampler (TNTP)

The effort continues to add total nitrogen (N) and total phosphorus (P) capability (and by subtraction, organic nitrogen (ON) and inorganic phosphorus) to the regular NTN analyses. This required the development of a supplemental sampler that works with the standard NTN sampler. Total nitrogen and total phosphorus (TNTP) data generated through this expanded wet deposition measurement effort will be of particular interest to agricultural scientists, as N and P are two of the most agronomically significant compounds tracked by NADP. Atmospheric deposition of N and P represents an external, often unaccounted-for input to agricultural nutrient budgets, alongside fertilizer application, manure management, and soil mineralization. Quantifying these atmospheric contributions can help refine nutrient management planning, improve estimates of total nutrient loading to agricultural watersheds, and support efforts to meet state and regional water quality goals tied to nutrient runoff. TNTP data may also support research on crop nutrient use efficiency, help distinguish atmospheric versus agronomic sources of nutrient enrichment in downstream waterways, and inform models used to evaluate the effectiveness of best management practices (BMPs) aimed at reducing nutrient loss from agricultural land.

As a National Research Support Project (NRSP-3), our main mission is to support research, and in particular, to provide data for research journal articles and reports.

Each calendar year, the NADP compiles a list of research articles, reports and theses/dissertations that used NADP data in some fashion, or compared their results to NADP data. For this project year, we can report over 161 articles and reports published in 2024 and over 146 published in 2025. The journal articles that follow are examples from the project period that have a strong connection to agriculture. The annual bibliography of articles and reports can be found here: https://nadp.slh.wisc.edu/pubs/nadp-bibliography/.

These example publications, which are more agricultural-related publications, were published during this project period (October 2024-June 2026).

1.      Schmadel, N. M., Miller, O. L., Ator, S. W., Miller, M. P., Schwarz, G. E., Robertson, D. M., ... & Saad, D. A., 2024. Seasonally varying contributions of contemporaneous and lagged sources of instream total nitrogen and phosphorus load across the Illinois River basin. Science of The Total Environment 955: 176816. https://doi.org/10.1016/j.scitotenv.2024.176816.

The authors determine the nutrient sources of streams across the Illinois River valley (~10 rivers) in an effort to improve water resource management. The authors used a dynamic SPARROW (Spatially Referenced Regressions on Watershed attributes) model to simulate seasonal and source-specific total nitrogen (TN) and total phosphorus (TP) loads. Results showed that a third of the TN and a quarter of the TP instream load originated from non-point sources of land-application, lagging by more than a season. This lagged mass was the largest overall TN source, originating from fertilizer, manure, atmospheric deposition and fixation, and urban land uses. Treated wastewater effluent was the largest TP source exported from the basin (39% of TP, 15% of TN load), and dominated the urban Chicago River load in the upper Illinois River near Chicago. Lower river loading was attributed primarily to a mix of agricultural sources and their lagged fractions. With appropriate datasets, the models could be extended to other basins or time periods.

The authors use long-term and weekly NADP deposition measurements at about 5 sites across IL, from 2000 to 2020.

2.      Diaz, M. A., Fortner, S. K., & Lyons, W. B., 2024. High resolution concentration-discharge relationships in managed watersheds: A 30+ year analysis. Applied Geochemistry 175: 106192. https://doi.org/10.1016/j.apgeochem.2024.106192.

The authors discuss measurements and relationships of chemical discharge from agricultural operations in western Ohio. They focused on the chemical concentration and discharge relationship over a 30-year period, using both agricultural, suburban and forested landscapes. They also compared baseflow to precipitation events. One main conclusion was that highly managed agricultural watersheds with no stream baseflow had static chemical behavior, while mixed use areas had changed much more over time. They also documented that chemical outflow was influenced by many factors, including soil and baseflow geochemistry, pore fluid concentration, and land type/land use legacy effects. These observations may transfer to other agricultural lands.

The authors used weekly NADP values from the OH49 site in Ohio for precipitation and all analytes in the study from 2000-2011 to define the wet deposition of site compounds. Deposition input was used to compare to discharge outflow.

3.      Gibson, J., Franz, T. E., Gilmore, T., Heeren, D., Gates, J., Thomas, S., & Neale, C. M., 2024. Groundwater recharge response to reduced irrigation pumping: Checkbook irrigation and the water savings payment plan. Water 16(20): 2910. DOI: 10.3390/w16202910.

The authors discuss the need for accurate irrigation estimates within agricultural operations, with a goal of ensuring long-term groundwater availability and avoiding needless loss of water to the watershed. They investigated water savings at three 65-acre Nebraska sites with varying soil, management practices and groundwater depths. The authors conclude that groundwater response times to pumping (using chloride as a tracer) are short and water savings are small (50-900 mm depth over 10 years with 120 mm/year reduction), and that sandy soil with shallow groundwater have minimal savings. The model developed with this work agrees with measurements to about 80 percentage.

NADP chloride data was used in the water mass balance from a number of sites over multiple years in the Nebraska area.

4.      Kumanan, V., 2024. Variability and drivers of system-level nitrogen use efficiency and surplus across conterminous united states. Master’s Thesis, Agricultural and Biological Engineering, Pennsylvania State University. https://etda.libraries.psu.edu/catalog/29327vkk5154.

Kumanan (Masters Thesis) used a large amount data to investigate nitrogen (N) use efficiency (NUE) over the coterminous U.S. and over multiple major crops. First, Kumanan found that the diversity of different N source input types had a large impact to county level NUE, since the type of N source effected the rates of N biological fixation. This result was clear given the decrease in manure usage. Second, Kumanan found that irrigation rates further control NUE and N surplus rates, and offer the best predictor for NUE and N surplus, and is more important than growing degree days, vapor pressure deficit, soil texture, soil structure, and depth to groundwater. The author used artificial intelligence models for his predictive ability.

Kumanan use NADP data from all U.S. sites, for many years in the nitrogen balance information in his observations and modeling.

5.      Shukla, S., & Shukla, A., 2024. Retrofitting agricultural detention systems can economically enhance nitrogen treatment with payment for services approach. Science of The Total Environment 954: 176145. https://doi.org/10.1016/j.scitotenv.2024.176145.

The authors investigate the water quality of agricultural stormwater detention areas (SDA), beginning with evaluation of an SDA in the Florida Everglades and focusing on baseline N. With simplification of the flow design and compartmentalization, increase in flow elevation, and channel plugs, the total N retentions doubled (7500 kg from 3700 kg), and a similar trend was observed with water volume. The authors concluded that water retention drives N retention. Actual costs for the retrofit and increase detention were much less than traditional N retention methods. A modeling effort calculated that a scaled-up facility could reduce N discharge from one basin in the Everglades by 50%.

The authors used the wet deposition values from the NADP Everglade’s site, and also estimated dry deposition (for total N deposition) from the NADP wet deposition for their box model estimates.

6.      Timilsina, A. P., Steinbeck, G., Shah, A., & Khanal, S., 2024. Assessing the Multifaceted Tradeoffs of Agricultural Conservation Practices on Ecosystem Services in the Midwest US. Sustainability 16(13): 5622. https://doi.org/10.3390/su16135622.

The authors studied the potential effects of conservation practices on soil health, crop productivity, and greenhouse gas emissions at an ARS agricultural site in northern Ohio (Maumee River basin) using the DeNitrification–DeComposition (DNDC) model for the period 1998–2020. Several crops were considered including corn, soybean, rye, silage corn, winter wheat, and alfalfa. Several improvements were noted, including by applying half the total N to corn through synthetic fertilizer during spring increased yield and soil organic carbon and sequestration of carbon, over fall applications. No-till practices lowered warming gases and higher carbon sequestration, but with lower yields. Substituting synthetic fertilizer with manure for corn production improved corn yield.

The authors used weekly nitrogen deposition data from the nearby NADP site for over 20 years of observations (1987-2020).

7.      Vo, T., & Christiansen, A. E., 2024. Impact of Recent Agricultural Ammonia Increases on Fine Particulate Matter Burden over the Midwestern United States. ACS Earth and Space Chemistry 8(11): 2209-2217. https://doi.org/10.1021/acsearthspacechem.4c00180.

The authors studied the impact of increasing ammonia (NH₃) emissions on Midwest air quality. Ammonia levels form atmospheric particulates easily, and some of the major sources are agricultural activities. The study included the years 2007 to 2019 with NH₃ observations and modeling. Increasing atmospheric concentrations and wet deposition (+20%) of NH₃/ammonium (NH₄) were clear in all seasons. Agricultural NH₃ is estimated to contribute 40% of the particulate matter measured, and is particularly high in the Midwest, relative to the US in general. Finally, agricultural NH₃ emissions have a disproportionate role in degrading air quality.

The authors used NADP data for both NH₃ concentrations (53 AMoN sites covering 34 states from 2008 to 2019, and 10 Midwest sites) and wet deposition of NH₄ (162 US NTN sites from 2007 to 2019, and 31 Midwest sites).

8.      Bruulsema, T., & Olson, R., 2024. The Role of Sulfur in Meeting 4R Nutrient Stewardship Goals. Crops & Soils 57(3): 34-39. DOI: 10.1002/crso.20360. AG Connection (American Society of Agronomy).

The authors reassert the importance that sulfur plays in 4R plant nutrition (“right fertilizer source, at the right rate, the right time, and in the right place). Sulfur is (1) an essential plant nutrient applied to optimize yields, (2) there may be a need to replenish the sulfur removed from the soil by crop harvests, and (3) some sulfur may have additional benefits through effects on soil pH and nitrogen processes. Needed sulfur additions have been evident for several years now, and the authors focus on these necessities in an article meant for outreach to working agricultural professionals concerning sustainable addition of sulfur fertilizers.

The authors published NADP maps from the years 2000 and 2022 as evidence of atmospheric sulfur reductions over the years, and the needs to appropriate sulfur addition to specific crops.

9.      Kumanan, V., Cibin, R., Irmak, S., Van Meter, K., Schott, L., Ladha, J.K., Kukal, M.S., 2025. How is Nitrogen Use Efficiency Impacted by Varying Contributions from Fertilizer, Manure, and Biological Fixation in U.S. and Global Croplands? Journal of the American Society of Agricultural and Biological Engineers. https://doi.org/10.13031/ja.16114

The authors used large-scale nitrogen (N) budgets and random forest modeling to evaluate how the source of N inputs — fertilizer, manure, and biological fixation — drives nitrogen use efficiency (NUE) across both CONUS and global croplands. The models explained 71% of NUE variance for CONUS croplands and 47% globally. Biological N fixation was the single most important driver of NUE variability, followed by manure and then synthetic fertilizer contributions, indicating that the mix of N sources — not just total N applied — strongly shapes how efficiently cropping systems use nitrogen.

The authors incorporated NADP atmospheric nitrogen deposition data as one of the N input terms within their multi-source county-level N budget framework.

10.  Sharma, A., Prasad, R., Nguyen, A. T., Ortiz, B. V., Gamble, A. V., Worosz, M. R., Duzy, L., Francisco, E., Hoogenboom, G., & Shelar, V. B., 2025. Exploring the bottlenecks of low nitrogen efficiency among yield zones in a commercial row crop farm using a nitrogen budget approach. Agronomy Journal. https://doi.org/10.1002/agj2.70242

Using a four-year (2021–2024) N budget on a commercial northern Alabama farm, the scientists compared N inputs, outputs, and unaccounted-for N losses across yield-based management zones for maize, wheat, and soybean. Maize in low-yielding zones showed the largest unaccounted-for N losses (115 ± 19 kg/ha), and winter wheat exhibited substantial N losses across all zones despite high N inputs, pointing to fertilizer-timing and rate inefficiencies. The authors conclude that site-specific, zone-level N management — rather than uniform farm-wide rates — is needed to improve both profitability and crop sustainability.
The nitrogen budget framework incorporated NADP wet deposition data as a background atmospheric N input term alongside fertilizer, manure, and biological fixation.

11.  Crespo, C., Kovar, J. L., Hart, C. E., Roth, R. T., O'Brien, P. L., & Ruis, S. J., 2025. Long-term field study on corn response to sulfur fertilization in Iowa, USA. Field Crops Research 330: 109990. https://doi.org/10.1016/j.fcr.2025.109990

Drawing on 12 field trials conducted in Iowa from 2006–2017, the authors evaluated corn grain yield and plant sulfur (S) response to three S fertilizer sources (ammonium sulfate, ammonium thiosulfate, and gypsum). Yield increased significantly in only 2 of the 12 trials, and none of the soil, organic matter, or plant-tissue S measurements tested proved to be a reliable diagnostic tool for predicting yield response. S fertilization was economically profitable in half of the trials tested. The study frames declining atmospheric S deposition and continued S removal through harvest as the underlying drivers of increased crop S deficiency risk.
The authors cite long-term NADP records of declining atmospheric sulfur deposition as the motivating context for the increased frequency of S fertilization response in Midwest row crops.

12.  Preza Fontes, G., Jones, J., Greer, K. D., Schaefer, D., Kaiser, D., & Fernández, F. G., 2025. Corn response to sulfur fertilizer rate and source in Illinois. Agronomy Journal 117: e70169. https://doi.org/10.1002/agj2.70169

The scientists ran 40 field trials across Illinois (2009–2011) testing corn grain yield response to varying S fertilizer rates (0–52 kg S/ha) and sources (ammonium sulfate, elemental S, gypsum, monoammonium phosphate). Only 2 of the 40 trials showed a significant yield increase from S application, and one S source actually decreased yield in one trial; leaf and soil S concentrations at the growth stage V6 were not reliable predictors of yield response. The authors conclude that, despite well-documented declines in atmospheric S inputs, the soil S supply (including through atmospheric deposition) was adequate to meet S demand under their study and that S fertilization is unlikely to increase corn yields in Illinois.
As with the companion Iowa study, this paper situates its S fertilizer trials against the backdrop of long-term NADP-documented reductions in atmospheric sulfur deposition.

13.  Acharya, B., Sharma, V., Barrett, C., Dukes, M.D., Zotarelli, L., Bayabil, H., Sharma, L., Hochmuth, R.C.., Sidhu, S. S., Crain, A., & Love, J., 2025. Comparative Analysis of Conventional and Sod-based Rotational Production Systems: Impacts on Yield and Nitrogen Dynamics. Journal of Natural Resources and Agricultural Ecosystems 3(3): 165-186. https://doi.org/10.13031/jnrae.16256

In a four-year field study (2019–2022) at the North Florida Research and Education Center-Suwannee Valley, the authors compared conventional maize-peanut and maize-carrot-peanut rotations against sod-based rotations incorporating two years of bahiagrass. Sod-based rotations reduced nitrate-nitrogen leaching by 39% in maize and 46% in peanut compared to conventional rotations, and improved maize nitrogen use efficiency by 13%, while maintaining comparable crop productivity. The authors conclude sod-based rotation is an effective best management practice (BMP) for balancing environmental protection with sustained yields in Florida's sandy, karst-influenced soils.
The nitrogen budget and leaching analysis in this study incorporated NADP wet deposition.