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Wastewater from agricultural runoff and human waste contains nutrients such as nitrogen and phosphorus, which can pollute natural waters and cause harmful algal blooms. These nutrients may persist at low levels even after wastewater has been biologically and chemically treated.

In southern Florida, many wastewater treatment facilities inject the treated water into wells 60–120 feet deep. As the water percolates underground, it is diluted by rainwater and groundwater. Chemical interactions with Key Largo Limestone—the rock that makes up the subsurface in the upper and middle Keys—and with microbes living in the groundwater filter out residual nutrients, such as the nitrogen-bearing compounds nitrate and nitrite.

“The idea is that the microbial nitrogen cycle will transform nitrate and nitrite to ammonium and nitrogen gas, which is then released to the atmosphere, before the effluent reaches coastal waters,” explained Miquela Ingalls, a sedimentary geochemist at Pennsylvania State University (Penn State). Similarly, phosphorus is removed from wastewater via a chemical reaction that attaches it onto the limestone bedrock.

But a new study, coauthored by Ingalls, shows that shallow injection doesn’t entirely eliminate nitrogen, raising the possibility that the nutrient may be contaminating coastal ecosystems.

The study’s authors analyzed water from monitoring wells near a wastewater injection site in the Florida Keys. They found that nitrogen and phosphorus levels decreased as water moved away from the site, but were still detectable at a depth of 6 meters (20 feet) and a distance of 350 meters (~1,150 feet) from the injection site, close to the Florida Bay shoreline.

In an earlier study targeting phosphorus, also in the Florida Keys, Ingalls and other researchers at Penn State concluded that up to 10% of initially present soluble reactive phosphorus (the form of phosphorus that can be directly taken up by plants) remained in injected water and was ultimately discharged into the ocean.

The new study aimed to determine how effectively shallow injection eliminates nitrogen.

Some Nitrogen Persists

The study focused on a wastewater injection site in Marathon, located on Vaca Key. The city of Marathon currently pumps treated wastewater between 18 and 27 meters (59–89 feet) into the underlying Key Largo Limestone. In 2021 and 2022, Penn State scientists installed nine monitoring wells 3–27 meters (10–89 feet) deep near the injection site. The researchers then measured levels of nitrate, dissolved nitrogen, and other chemicals at the monitoring wells from 2021 to 2023 and compared them with the levels found in the injected wastewater.

Nitrate levels were elevated at a monitoring well 350 meters (~1,150 feet) from the injection site and close to the Florida Bay.

At most wells, nitrate was completely eliminated from wastewater 2 weeks after injection. However, nitrate levels remained elevated 3–6 meters (10–20 feet) deep in a monitoring well 350 meters (~1,150 feet) north of the injection site and close to the Florida Bay.

This monitoring well is farthest from the injection site and is probably in the path of injected wastewater, according to the previous study, which found that wastewater injected in Marathon mostly travels north and east. As it travels, the water rises toward the surface. This may explain why nitrate is elevated at the most distant well: Close to the injection site, wastewater remains at its initial depth, but after traveling hundreds of meters, it has risen far enough to contaminate shallow groundwater. The contaminated well’s location on the Florida Bay shoreline suggests that along with phosphorus, some wastewater-derived nitrogen may be washing out to sea.

The authors attributed the imperfect filtering of nutrients to the unique setting of the Florida Keys. For wastewater injection, timing is important: The longer wastewater remains underground, the more time there is for microbial and chemical processes to filter out contaminants. But the Keys are mostly composed of small, narrow islands, so the injected wastewater doesn’t travel very far before reaching the ocean.

Groundwater in the Keys also mixes with seawater, making an especially salty and dense mixture. The injected wastewater has a lower density, causing it to buoy up toward the surface and limit the time spent underground.

Nitrogen Pollution Harms Coastal Ecosystems

The discharge of nitrogen into the Florida Bay may have consequences for marine life. The researchers found total nitrogen concentrations of 18 micromoles per kilogram just offshore of the contaminated monitoring well, surpassing the local threshold of 16.1 micromoles per kilogram defined by the Florida Department of Environmental Protection.

Such pollution from wastewater and other human activities is harmful to wildlife, said Brian Lapointe, a marine scientist at Florida Atlantic University who was not involved in the research, because “increased nutrient concentrations support not only algal blooms and microbial pathogens, including coral diseases, but also myriad water quality problems.”

“Nutrient pollution from shallow injection wells has been a major local pollution source driving eutrophication in coastal waters of the Florida Keys for decades.”

“Nutrient pollution from shallow injection wells has been a major local pollution source driving eutrophication in coastal waters of the Florida Keys for decades,” Lapointe said. But both Lapointe and Ingalls highlighted that nutrient pollution in certain parts of the Florida Keys has decreased in recent years, largely due to advances in wastewater treatment. “The effluent being injected into the subsurface starts with a lower concentration of nutrients, so there is less to remediate by biological and chemical processes within the Key Largo Limestone,” Ingalls said.

Nonetheless, Lapointe recommended eliminating shallow injection of wastewater as a way to reduce nutrient pollution. The city of Marathon is set to phase out shallow injection following a 2022 lawsuit filed by the environmental group Friends of the Lower Keys (FOLKs). Instead, the city will transition to deep well injection, which is used in other parts of the Florida Keys. Deep wells inject wastewater more than 2,000 feet underground, lowering the chances that wastewater will rise to the surface before microbes and chemical reactions can filter out contaminants.

—Caroline Hasler (@carbonbasedcary), Science Writer

Citation: Hasler, C. (2025), Shallow injection imperfectly filters Florida wastewater, Eos, 106, https://doi.org/10.1029/2025EO250357. Published on 26 September 2025. Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

Powerful pulses of groundwater flow up from beneath Lakes Michigan and Huron, which together form one of the largest freshwater systems in the world. This groundwater flux may dramatically alter how and where ice forms, with important implications for ice-climate models. As climate change pressures the system, new research suggests that conventional models may underestimate how groundwater can destabilize lake ice along its shorelines (coasts).

Author(s): Ph. Korneev, N. D. Bukharskii, I. V. Kochetkov, M. Ehret, Y. Abe, K. F. F. Law, S. Fujioka, G. Schaumann, and B. Zielbauer

Experimental and numerical investigations into the generation of strong magnetic fields in plasma, using a picosecond petawatt laser interacting with specially designed “snail” targets, open paths to the creation of all-optical ultrabright sources of directed high-energy charged particle beams.

#ElegantVisuals #TheoryExperiment

[Phys. Rev. E 112, 035211] Published Fri Sep 26, 2025

SummaryWe present a high-order tetrahedral spectral element (SE) method for the computation of three-dimensional (3D) magnetotelluric (MT) forward responses, designed to overcome the limitations of conventional SE methods that rely on hexahedral grids. Our approach utilizes tetrahedral grids, enabling the accurate simulations of large-scale, geophysically complex models, including intricate subsurface anomalies and irregular topography. Starting from Maxwell’s equations, we derive the governing SE equations using a magnetic vector potential A and an electric scalar potential Φ, incorporating the Coulomb gauge to suppress spurious solutions. The computational domain is discretized using the weighted residual Galerkin method, with Proriol-Koornwinder-Dubiner (PKD) polynomials serving as the weighting and shape functions within each tetrahedral element. Two coordinate transformations-affine and collapse transformations are applied during the solution process. To better leverage the properties of the basis functions, both the interpolation and integration nodes are chosen from the same Warp & Blend point set, rather than using two separate sets, which simplifies the computation of the coefficient matrix terms. The resulting global sparse linear system is solved efficiently using the PARDISO direct solver. We assess the accuracy and computational performance of our method through validation against well-established MT community models. Our evaluation, based on misfit (relative error), degrees of freedom (DOFs), computational time, and memory usage for various polynomial orders, demonstrates that the proposed SE method on tetrahedral grids offers a robust and efficient solution for high-precision forward modeling in MT applications.

SummaryWe conduct a seismological monitoring study for groundwater fluctuations within the 12-years period of 2012-2023 in Beijing using relative seismic velocity changes (dv/v) from continuous ambient noise data. Our measured dv/v time series agree with groundwater level changes observed from groundwater wells and reveal significant characteristics on hydrological and other environmental changes. The most intriguing feature is a dv/v increase of ∼0.02% in winter, which is interpreted as the imprint of frozen ground perhaps associated with decoupling between air pressure and groundwater. In addition, a rapid reduction of dv/v during the second half of 2021 indicates the development of a groundwater recharging event resulting from heavy rainfall. The long-term trends of dv/v suggest a groundwater rebound from 2018 to 2023 over the study area, which we attribute to increased precipitation, recharging due to the South-to-North Water Transfer Project, and reduced irrigation.

SummaryWe present a novel method for generating kinematic rupture models for near-source broadband ground motion simulations. Our approach constructs realistic rupture-parameter distributions for slip, rupture velocity and rise time using Von Karman (VK) fields. To more realistically model the slip pattern, we propose rescaling the VK field to follow a truncated exponential distribution rather than a Gaussian, following previous findings on inversion results. For rupture propagation, we initiate the rupture from slip-constrained hypocenter locations, which is crucial for accurately capturing directivity effects. Finally, to characterize the local slip-rate evolution at each computational point on the fault, we propose to employ the regularized Yoffe functions to which small-scale variations are added using 1D VK-fields whose properties are constrained from a database of dynamic rupture simulations. The statistical properties of these fields are calibrated using a database of dynamic rupture simulations, ensuring appropriate high frequency radiation from the generated rupture.Our rupture generator produces kinematic source descriptions to simulate ground motions that successfully reproduce the mean and standard deviation from ground motion models (GMM) for Mw 6.0-7.0 earthquakes. Additionally, our generator allows for the integration of low-frequency source inversions and complements the high frequency radiation of a seismic rupture with physics-constrained stochastic variations. Our broadband pseudo-dynamic kinematic rupture generator facilitates and possibly improves the simulation of realistic high-frequency ground motions to advance seismic hazard analysis.

Salt intrusion is a growing concern worldwide. Eleonora Saccon, who completed a master's degree in climate change ecology in her native Italy, studied the effects of salty surface water at the NIOZ branch in Zeeland.

UC Riverside researchers have discovered a piece that was missing in previous descriptions of the way Earth recycles its carbon. As a result, they believe that global warming can overcorrect into an ice age.

A vital waterway connecting the Atlantic and Pacific oceans, the Panama Canal relies on fresh water supplied by a reservoir to raise and lower the locks that allow the transit of thousands of ships a year.

Typhoons and their Atlantic counterparts—hurricanes—can develop into massively destructive storms that can take a severe toll on both infrastructure and human life. Climate change is additionally spurring even more intense storms with higher wind speeds and rainfall.

Earth scientists often face huge challenges when researching Earth's history: many significant events occurred such a long time ago that there is little direct evidence available. Consequently, researchers often have to rely on indirect clues or on computer models.

Editors’ Highlights are summaries of recent papers by AGU’s journal editors. Source: Journal of Geophysical Research: Solid Earth

Seismologists have long detected unusual structures deep beneath continents at mid-lithospheric depths (80–120 kilometers), but their cause has remained uncertain.

In a new study, Zhang et al. [2025] use state-of-the-art computer simulations that combine first-principles (or fundamental assumption) calculations with machine learning to discover a new form of calcium carbonate, an important carbon-bearing mineral in Earth’s deep interior. This newly identified phase undergoes remarkable elastic softening under mid-lithospheric conditions, greatly reducing seismic wave speeds. Even trace amounts of such carbonate could explain the puzzling seismic signals and anomalous electrical properties observed beneath ancient continental regions.

These findings suggest that carbonates play a far more important role in shaping continental structure than previously recognized. Moreover, the results demonstrate that advanced computational methods can uncover unexpected aspects of the deep carbon cycle and the long-term stability of continental roots.

Citation: Zhang, P., Man, L., Yuan, L., Wu, X., & Zhang, J. (2025). Ultra-low-velocity disordered CaCO3 may explain mid-lithospheric discontinuities. Journal of Geophysical Research: Solid Earth, 130, e2025JB031906. https://doi.org/10.1029/2025JB031906

—Jun Tsuchiya, Editor, JGR: Solid Earth

Text © 2025. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

SummarySeismic scattering waves in random media are usually regarded as noise in conventional seismic imaging, inversion and interpretation. However, the spatial and temporal variation of the scattering energy depends on the stochastic properties of the random media. The extraction of heterogeneity information such as the correlation scale and fluctuation strength from seismic scattering waves remains a challenge. These parameters are inverted from real scattering data by fitting the synthetic envelopes to the observed seismic envelopes. The synthetic envelopes are usually computed using the Monte-Carlo radiative transfer (MCRT) method. However, physical verification of the stochastic parameter inversion based on MCRT theory has not been realized although it is believed to be correct. To this end, we conducted a physical modelling experiment using an ultrasonic acquisition system and recorded the transmitted wavefields through an artificial heterogeneous medium. In this paper, the elastic MCRT method was used to simulate the energy transport, and the correlation length and fluctuation strength of the artificial heterogeneous medium were inverted with a revised objective function, which can better balance the energy level of direct waves and scattering waves in the inversion process. The inversion results of the correlation scale and fluctuation strength match well with true values, suggesting that this method is accurate and reliable. A combination of our physical experiments and the MCRT theory gives strong proof that this inversion method is correct. Therefore, it can be used with confidence to estimate the properties of the heterogeneities from the ‘undesired’ scattering waves, both in the oil/gas exploration and earth structure investigation.

SummaryThe attenuation operator t* represents the total path attenuation and characterizes the amplitude decay of a propagating seismic wave. Calculating t* is typically required in seismic attenuation tomography. Traditional methods for calculating t* require determining the ray path explicitly. However, ray tracing can be computationally intensive when processing large datasets, and conventional ray tracing techniques may fail even in mildly heterogeneous media. In this study, we propose a modified fast sweeping method (MFSM) to solve the governing equation for t* without explicitly calculating the ray path. The approach consists of two main steps. First, the traveltime field is calculated by numerically solving the eikonal equation using the fast sweeping method. Second, t* is computed by solving its governing equation with the MFSM, based on the discretization of the gradient of t* using an upwinding scheme derived from the traveltime gradient. The MFSM is rigorously validated through comparisons with analytical solutions and by examining t* errors under grid refinement in both simple and complex models. Key performance metrics, including convergence, number of iterations, and computation time, are evaluated. Two versions of the MFSM are developed for both Cartesian and spherical coordinate systems. We demonstrate the practical applicability of the developed MFSM in calculating t* in North Island, and discuss the method’s efficiency in estimating earthquake response spectra.

SummaryVarious methods for determining the magnetic field at the core-mantle boundary (CMB) from the observed geomagnetic core field have been explored over recent decades. These include the harmonic downward continuation of surface data and the stabilised iterative upward continuation. The instability of the inverted poloidal magnetic field at the CMB for a radial conductivity structure is complemented by the non-uniqueness of determining the toroidal magnetic field at the CMB for a laterally inhomogeneous conductivity model. We reformulate this unstable and non-unique inverse problem as an iterative upward continuation approach, in which the magnetic field at the CMB is successively updated. The uniqueness of the inverse solution is ensured by the initial choice of the toroidal magnetic field at the CMB, while the stability is achieved by stopping the iterations once the desired tolerance is reached between the spectral index of the updated solution and that obtained from numerical geodynamo simulations. We consider two significantly different radial electrical conductivity models of the lower mantle, each with conductance near 108 S: conductivity model A, based on external electromagnetic sounding, which includes a significant conductivity increase in a 10 km thick layer above the CMB, and conductivity model B, characterized by a gradual conductivity increase determined from the Voigt-Reuss-Hill average of the bridgmanite-ferropericlase aggregate, with an additional conductivity increase in the 300 km thick D” layer associated with post-perovskite. Models A and B bracket the lower and upper bounds of conductivity structures derived from thermal and compositional constraints below 1600 km depth. We find that the differences between the magnetic field components at the CMB inverted for models A and B are approximately 1-2 per cent of the total field. To explore lateral variations, we construct a synthetic model of the Pacific and African superplumes by simplifying their geometric shapes, estimating the temperature increase within the plumes and allowing mantle mineral activation energies to vary only with temperature. Our results show that, in the regions of the superplumes, the poloidal and toroidal magnetic fields at the CMB change by approximately 12,000 nT and 2,500 nT, respectively. The changes in the horizontal poloidal field at the CMB are comparable in magnitude to those resulting from substituting model A with model B. However, the changes in the radial field inverted for the three-dimensional plume conductivity model are significantly larger than those arising from replacing model A with model B.

The highest rock wall in the Alps—the Monte Rosa East Face on the border between Italy and Switzerland—has for the first time been surveyed three-dimensionally with high precision. An international research team from the universities of Milan, Prague and Heidelberg has taken more than 3,000 high-resolution photos from a helicopter. Using a special method, a detailed 3D model is now emerging.

Tornadoes on the outer edges of a typhoon's spiral rain bands are a severe convective weather phenomenon that occurs on the periphery of tropical cyclone systems. Compared to the core region near the typhoon's center, the atmospheric instability and vertical wind shear conditions in these outer areas often combine in more subtle and easily overlooked ways, making their occurrence and development more sudden and localized. This poses greater challenges for forecasting and early warning.

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Unchecked greenhouse gas emissions could cause the world’s income to fall by nearly a quarter within the century, projects a new study published in PLOS Climate.

“Climate change reduces income in all countries, hot and cold, rich and poor alike.”

“Climate change reduces income in all countries, hot and cold, rich and poor alike,” the study’s authors wrote in a press release.

Gross domestic product, or GDP, is the total value of goods and services produced in a given year. A country’s per-capita GDP is a measure of the average income of a person living there. 

In the new study, researchers turned to information about the previously studied link between rising temperatures and GDP, along with possible scenarios of future warming, called Shared Socioeconomic Pathways. They used this data to simulate more precisely how rising temperatures might impact global GDP over time.

Their projections show warming could cause widespread economic losses as higher temperatures and climate variability impact the activities of industries including agriculture and manufacturing. But reducing greenhouse gas emissions could soften the effect, the authors write. 

In a moderate emissions scenario (SSP2-4.5), global GDP decreased by about 2.5% by 2100. In a high-emissions scenario with minimal adaptation (SSP3-7.0), the projections showed global per-capita GDP dropping by up to 11%. And in a more extreme emissions scenario (SSP5-8.5) without any climate mitigation or adaptation, the researchers projected per-capita income losses of up to 24%.

Under this extreme scenario, the United States would lose nearly a third of its per-capita GDP by 2100. 

The estimated changes in global income compared to the 1960-2014 warming trend, as well as a world without climate change, varied depending on the warming scenario that the researchers used. Credit: Mohaddes and Raissi, 2025, https://doi.org/10.1371/journal.pclm. 0000621

The results are in line with previous research from 2024, which indicated a likely decrease in global income by 11% to 29%, depending on future emissions scenarios. However, the new study finds that if the world’s governments abide by Paris Agreement goals—that is, limiting temperature increases to 0.01°C (0.02°F) per year—global GDP could slightly increase by 0.25% by 2100.

 
Related

•  Read the paper: “Rising temperatures, melting incomes: Country-specific macroeconomic effects of climate scenarios”
•  Climate Change Is Likely to Slash Global Income
• Get Involved: AGU Science Policy Action Center
 

In both the new study and previous research, low-income and hotter countries fared the worst: In the new study’s projections, countries located in hot climates and classified as low-income faced income losses between 30% and 60% of the global average. 

The publication comes on the heels of a speech at the United Nations General Assembly in which President Trump called climate change the “greatest con job ever perpetrated on the world.” That denialism won’t preserve global income, according to the authors: “Urgent action is needed to address climate change and protect economies from further income losses,” they wrote.

—Grace van Deelen (@gvd.bsky.social), Staff Writer

These updates are made possible through information from the scientific community. Do you have a story about science or scientists? Send us a tip at eos@agu.org. Text © 2025. AGU. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.

A joint research group has identified that the spatial scale of "heterogeneity" in the upper mantle, caused by a large-scale flow called a mantle plume rising from deep Earth, is less than 10 kilometers.

Most Californians are familiar with earthquakes. But researchers say the state faces an overlooked threat: "supershear" earthquakes that move so fast they outrun their own seismic waves.