Mangrove ecosystems are important coastal carbon sinks, with soil carbon storage strongly influenced by site-specific hydrological, sedimentary, and climatic conditions. This study quantified soil carbon stocks in two mangrove systems in Puerto Rico-La Parguera and Laguna Grande-and evaluated the relative influence of hydrology, sediment deposition, and climate on carbon accumulation. Depth-standardized soil carbon stocks (0-50 cm) were higher at Laguna Grande (166 +/- 66 Mg C ha(-)(1)) than at La Parguera (115 +/- 68 Mg C ha(-)(1)), with a marginal difference (p < 0.10). Differences between sites are consistent with contrasting hydrological regimes: La Parguera experiences greater tidal flushing, which may enhance organic matter export and decomposition, whereas Laguna Grande is a semi-enclosed lagoon with restricted tidal exchange and higher standing biomass, conditions that may promote organic matter retention and carbon accumulation. Although regional climatic differences-higher temperatures and precipitation near Laguna Grande relative to La Parguera-may influence productivity and decomposition dynamics, hydrological setting and sediment retention appear to be primary controls on soil carbon storage. These findings emphasize the importance of incorporating hydrological processes and geomorphic context into blue carbon assessments and mangrove conservation strategies. Understanding how tidal exchange, sediment dynamics, and precipitation patterns interact is critical for predicting mangrove carbon responses to future climate change.

Salt marsh restoration can deliver multiple socio-economic and ecological benefits; however, there is a strong need for standardized monitoring and assessment methodologies to assess the effectiveness of these restorations. This study aimed to (1) gather baseline data and evaluate the ecosystem services related to nitrogen removal by denitrification provided by restored salt marshes in New York City, and (2) evaluate the ability of a statewide assessment protocol to encompass this biogeochemical function. We made measurements of denitrification potential in sediment samples from three restored and one reference salt marsh sites. The restored sites supported denitrification potential equivalent to the reference wetland, and the oldest restored sites had the highest and the youngest sites had the lowest potential. However, none of the variables included in the statewide assessment protocol (elevation, substrate, algae, and plant cover) encompassed or predicted this potential. Denitrification potential was significantly positively correlated with carbon cycle variables (soil organic matter [SOM] content, microbial respiration) and significantly negatively correlated with nitrogen cycle variables (potential net nitrogen mineralization and potential net nitrification). The negative correlations with nitrogen cycle processes suggest that denitrification is an important "sink" for reactive nitrogen in these wetlands, and the positive correlations with carbon cycle variables suggest that restoration should focus on facilitating plant growth and organic matter accumulation. If assessments are to include biogeochemical processes such as denitrification, they may need to incorporate indicators of belowground variables such as SOM content.

Constructed soils (CSs) are important for rehabilitation of degraded lands, carbon (C) sequestration, and urban agriculture, but little is known about the development and dynamics of organic matter pools in these soils. In this study, we tracked these pools over 21 months in CSs (1/3 compost and 2/3 fine glacio-fluvial sediments) planted with eight different vegetation treatments with densimetric and enzymatic approaches. Time was the main driver influencing soil parameters, followed by vegetation. A high diversity "All" treatment had a significant impact on soil development, notably enriching mineral/sand-associated organic carbon (MSOC) and nitrogen (MSON) by 15% and 12%, respectively, compared to a non-vegetated "Bare" treatment. The presence of sunflower (Helianthus annuus L.) in the vegetation treatment was associated with low values of nitrate-N, particulate organic N (PON), hot-water extractable carbon (HWEC), and beta-glucosidase. These CSs appear to be undergoing rapid soil development driven by organic matter accumulation processes that facilitate nutrient cycling and accumulation of stable MSOC.

Reducing nitrogen delivery to coastal waters is a 'wicked problem' that involves trade-offs among environmental, economic and social need domains. Because these trade-offs arise from spatial and temporal complexities in sources and sinks of this element, we hypothesized that a transdisciplinary focus on disproportionality could enable the identification of 'sweet spots' where multiple factors converge to create opportunities to control nitrogen flux. We applied this approach to the region of Baltimore, MD, USA, by mapping stream reaches with high nitrogen concentrations, hydrologic conditions that facilitate high rates of nitrogen removal following stream restoration, a high household willingness to pay for restoration projects and a high social need for restoration, and subsequently identifying locations where these factors converge to create sweet spots. Our analysis indicates that sweet spots that optimize environmental, economic and social need components of sustainability may be rare in cities across the USA. The desire to bundle multiple benefits in the budgeting for environmental interventions such as stream restoration may create a suboptimal distribution of these interventions.

Identifying which aspects of global environmental change are driving observed ecosystem process responses is a great challenge. Here, we address how long-term (10–25 years) alterations in soil moisture, and nitrogen (N) oligotrophication (i.e., decreases in soil N availability relative to plant demand), alter the production of plant-available N via net mineralization and nitrification in a northern hardwood forest. Our objectives were to determine whether soil moisture has changed over the past decade and whether N cycle processes have become less sensitive to soil moisture over time due to N oligotrophication. We used long-term datasets from several related studies to show (i) increasing winter soil temperatures and declining summer soil moisture from late 2010 into 2024, (ii) reductions in sensitivity of N cycling rates to soil moisture, and (iii) declining moisture-adjusted N cycle processes (the ratio of rate of N process:soil moisture) over time in both summer and winter. These changes suggest continued reductions in N availability to plants in these forests, with potential effects on forest productivity and response to disturbance.

Home lawns are one of the most common urban land surfaces in the United States and provision many cultural and ecological benefits. Many of these benefits arise from turfgrass soils and their belowground ecosystems. As homeowner interest in managing lawns for diverse ecosystem services grows, it is important to understand how varying management practices affect these goals and how efforts to manage belowground ecology may alter lawn quality and aesthetic. In this study we utilized an experimental lawn system to contrast the effects of management intensity on soil fauna communities, microbial biomass, and decomposition. Further, we simultaneously investigate how the prioritization of these belowground organisms and processes may inadvertently alter lawn quality. Our results show that decreasing management intensity leads to increases in the abundance, richness, and diversity of soil fauna communities, with these changes being most apparent in certain taxa like predatory mites (e.g. Mesostigmata). Despite significant increases in soil fauna, we did not observe downstream changes to soil microbial biomass carbon or nitrogen or decomposition, all aspects of soil ecosystem functioning which are mediated by soil fauna. Further, turf aesthetic assessments revealed substantial decreases in lawn quality in the presence of low-intensity management. Collectively, these results highlight the nuanced ecology of turfgrass systems, and the need to temper societal expectations for turfgrass aesthetics if we are to promote a shift towards valuing ecological integrity in turfgrass appraisals.

Biological nitrogen fixation is a key driver of global primary production and climate. Decades of effort have repeatedly updated nitrogen fixation estimates for terrestrial and open ocean systems, yet other aquatic systems in between have largely been ignored. Here we present an evaluation of nitrogen fixation for inland and coastal waters. We demonstrate that water column and sediment nitrogen fixation is ubiquitous across these diverse aquatic habitats, with rates ranging six orders of magnitude. We conservatively estimate that, despite accounting for less than 10% of the global surface area, inland and coastal aquatic systems fix 40 (30 to 54) teragrams of nitrogen per year, equivalent to 15% of the nitrogen fixed on land and in the open ocean. Inland systems contribute more than half of this biological nitrogen fixation.

AbstractBiological nitrogen fixation is the conversion of dinitrogen (N2) gas into bioavailable nitrogen by microorganisms with consequences for primary production, ecosystem function, and global climate. Here we present a compiled dataset of 4793 nitrogen fixation (N2‐fixation) rates measured in the water column and benthos of inland and coastal systems via the acetylene reduction assay, 15N2 labeling, or N2/Ar technique. While the data are distributed across seven continents, most observations (88%) are from the northern hemisphere. 15N2 labeling accounted for 67% of water column measurements, while the acetylene reduction assay accounted for 81% of benthic N2‐fixation observations. Dataset median area‐, volume‐, and mass‐normalized N2‐fixation rates are 7.1 μmol N2‐N m−2 h−1, 2.3 × 10−4 μmol N2‐N L−1 h−1, and 4.8 × 10−4 μmol N2‐N g−1 h−1, respectively. This dataset will facilitate future efforts to study and scale N2‐fixation contributions across inland and coastal aquatic environments.

Aquatic ecosystems are subjected to many chemical stressors, including nutrients and emerging contaminants like pharmaceuticals. While pharmaceutical concentrations in streams and rivers are often below the thresholds for acute toxicity, they nonetheless disrupt ecology through changes to organisms' physiology, metabolism, and behavior. However, analyzing samples for the wide range of manufactured pharmaceuticals is often prohibitively expensive for many monitoring efforts. As such, the ability to predict pharmaceutical concentrations over space and time using easier-to-monitor water quality parameters would expand our understanding of the scope and consequences of pharmaceutical contamination in aquatic ecosystems. We applied random forest models to data from the Baltimore Ecosystem Study to investigate how well routinely monitored water quality parameters could be used to predict concentrations of nutrients and pharmaceuticals. We found that concentrations of nutrients were accurately predicted by these models, but models for predicting concentrations of pharmaceuticals had high error rates and low predictive ability. Differences in our ability to predict concentrations of nutrients as opposed to pharmaceuticals could be due to differences in their sources, chemistries, or behavior in the environment. More concerted efforts to monitor pharmaceutical concentrations over time in aquatic ecosystems may help to resolve environmental drivers of their concentration and improve our ability to predict them.

Soil carbon dioxide (CO2) flux, or soil respiration, is a critical control on net ecosystem carbon (C) balance. Using long-term (2002-2020) measurements at the Hubbard Brook Experimental Forest (New Hampshire, U.S.), we show that soil respiration rates have notably increased since similar to 2015. In 2020, cumulative summer respiration flux was approximately 90% higher than the average summer flux over the 2002-2015 period. The increase in soil respiration cannot be explained directly by temperature or pH change alone. We also found that heterotrophic microbial C mineralization and microbial biomass C have also increased rapidly since similar to 2015, pointing towards an increase in the bioavailability of organic C substrates. We suggest that these observations are consistent with a hypothetical increase in plant allocation of C belowground in response to changing climatic and soil conditions. Quantification of interactions among co-occurring global change factors (e.g., warming temperatures, increasing atmospheric CO2, and nutrient limitation) is needed to predict how the soil C reservoir will continue to respond to global environmental changes.

Declining nitrogen (N) availability relative to plant demand, known as N oligotrophication, is a widespread phenomenon that has been particularly well documented in northern hardwood forests of the northeast U.S. It is hypothesized that later fall senescence contributes to this trend by increasing tree resorption of N, resulting in higher carbon:nitrogen ratios (C:N) in litterfall and reduced N availability in soil. To examine the effects of litterfall C:N on soil N cycling, we conducted a litter quality manipulation experiment comparing low C:N and high C:N litter with native litter along an elevation and aspect gradient at Hubbard Brook Experimental Forest, NH, USA. We found that potential net ammonification and mineralization rates were positively correlated with litter N and negatively correlated with litter C:N under high C:N litter, but these relationships were not present under native or low C:N litter. Differences in nitrate pools and net mineralization rates between high- and low-quality litter treatments were greater at colder sites where native litterfall tends to have lower C:N than at low elevation sites. Together, these results demonstrate that higher C:N litter and a warming climate may contribute to N oligotrophication through effects on microbially driven N cycling rates in organic soils.

ABSTRACTWe appear to be at a shining moment for interactions between soils and society. Popular interest in soils has increased along with interests in urban gardening, carbon sequestration, recognition of the vast biodiversity in soils, and the realisation that soils are a finite resource whose degradation has serious consequences. This increase in interest creates both opportunities and challenges for soil science. While there is great potential for increasing the diversity of people involved with soil science, key scientific and communication challenges need to be addressed for interactions between soils and society to be useful and productive. Here, I present case study issues on the mechanisms and limitations of carbon sequestration in soils and the need to restore and/or create new soils for specific uses, including urban agriculture and green infrastructure, to illustrate the opportunities and challenges associated with new societal interest in soil science. Addressing these issues requires advances in both basic and applied science, new participatory approaches to the design, execution, and interpretation of research, collaboration with multiple disciplines, including the social sciences, and improvements in the two‐way flow of information between science and society. Careful attention to these issues will attract new people to soil science, advance awareness of the importance of and threats to soils across the globe, and produce improvements in the quality of life for diverse human populations.

Green Infrastructure (GI) plays a crucial role in reducing stormwater runoff and providing ecological benefits in urban areas. Aggregation is a key process in many soil functions as it influences carbon storage, greenhouse gas emissions, nutrient cycling, hydraulic properties, and biotic activity. In this study, we investigated soil aggregation processes and stability in GI. Soil samples were collected from six bioswale sites in New York City that had two different designs - streetside infiltration swales and enhanced tree pits. The soil samples were taken from the inlet, center, and outlet positions (relative to stormwater input) of each site. These samples were then tested for 1) macro and micro aggregate sizes; 2) distribution of soil organic carbon (SOC) and nitrogen; 3) aggregate stability; and 4) microbial biomass and activity relevant to carbon and nitrogen cycles in macroaggregates. Our results showed that 60% g/g of the soil aggregates at these GI sites were smaller than 2 mm and had high structural stability. Microaggregates between 1-2 mm had the highest SOC and accounted for 60% g/g of all microaggregate size classes. GI aggregates are formed from the breakdown of macroaggregates into intermediate microaggregates. The newly formed microaggregates contained more stable SOC than macroaggregates and bonds within microaggregates were stronger than bonds grouping microaggregates, which is not consistent with a classical model of aggregate formation in natural soils. Microbial biomass and activity were correlated with the carbon and nitrogen content of aggregates and with GI type, allowing for the identification of microbial hot spots. These results suggest that aggregation processes in human-engineered soils included in GI play an important role in sustaining carbon and nitrogen cycles.

Late Cretaceous clays exposed at sites located on the north shore of Long Island, New York, USA, were sampled to explore questions about how contemporary factors and processes interact with ancient geological materials that are often assumed to not be biologically active. Chemically and biologically catalyzed weathering processes have produced multi-colored clays belonging to the kaolin group with inclusions of hematite, limonite, and pyrite nodules. We sampled exposed clays at three sites to address three questions: (1) do these exposed clays support significant amounts of microbial biomass and activity, i.e., are they alive? (2) Do these clays support significant nitrogen (N) cycle activity? (3) Are these clays a potential non-anthropogenic source of reactive N in the contemporary landscape? Samples were analyzed for total carbon (C) and N content, microbial biomass C and N content, microbial respiration, organic matter (OM) content, potential net N mineralization and nitrification, soil nitrate (NO3-) and ammonium (NH4+) content, and denitrification potential. Results strongly support the idea that ancient geologic materials play a role in contemporary N and C cycling in the Critical Zone. Respiration (average 4.098 µg C g−1d−1) was detectable in all samples and was strongly correlated to OM, indicating a living microbial community on the clays. There was evidence of an active N cycle. Higher levels of denitrification potential (average 1.376 µg N g−1 d−1) compared to both potential net nitrification (average 0.061 µg N g−1 d−1) and potential net N mineralization (average 0.144 µg N g−1 d−1) indicate that these clays act more as a sink rather than as a source of reactive N in the landscape.

Urban sustainability initiatives rely on healthy soils, and increasingly turn to constructed soils or constructed Technosols (CTs) to create green spaces, green infrastructure, and urban agriculture. However, CTs must be better understood, particularly in terms of their nutrient dynamics, to optimize their ecological functions. In the Carbon Sponge pilot study, located at the New York Hall of Science in Queens, NY, USA, our objective, through an artist-led collaboration, was to evaluate the effects of different plant communities on CT formation and carbon (C) and nitrogen (N) cycling. The artistic processes were rooted in social practice, focused more on practical outcomes than aesthetics. We constructed soils from excavated glacially-deposited sediments from the NYC Clean Soil Bank and urban municipal composts at a 2:1 vol:volume (v:v) ratio, and created 24 beds under 8 different planting regimes: control (bare, no plants); sunflowers; edibles (ground cherries and okra); cover crop mixture; and each of their combinations. We found that soils changed significantly over the study duration of 21 months (p = 0.001), particularly in terms of microbial biomass N content, an index of internal soil N cycling processes; the presence of sunflowers increased soil C and ammonium; and the presence of cover crop mixtures increased nitrate and ammonium. Over time, we observed an increase in microbial biomass C and N content and a decline in microbial respiration, suggesting the development of a soil microbial community that actively cycles C and N. Diverse planting combinations enhanced microbial development, yet all plants thrived in CTs, demonstrating their suitability for urban agriculture and horticulture, while enhancing ecosystem services and facilitating art-and-community-based initiatives.

In seasonally snow-covered ecosystems such as northern hardwood forests of the northeastern U.S., spring snowmelt is a critical transition period for plant and microbial communities, as well as for the biogeochemical cycling of nitrogen (N). However, it remains unknown how shifting snowmelt dynamics influence soil and plant processing and uptake of N in these forests, which are experiencing reductions in N availability relative to demand, a process known as oligotrophication. We characterized the role of changing spring snowmelt timing on root production and N pools and fluxes by manipulating snowmelt timing along a climate elevation gradient at the Hubbard Brook Experimental Forest in New Hampshire. We manually halved or doubled snow water equivalent (SWE) in experimental plots in March of 2022 and 2023 to accelerate or delay by an average of one week, respectively, the onset of spring snowmelt. Earlier snowmelt led to reduced snowpack depth and duration, as well as deeper, more sustained soil frost during the snowmelt period in 2022, but soil freezing did not occur in 2023. Soil nitrate and net nitrification rates were significantly lower with shallower snowpack and earlier snowmelt compared to plots with deeper snow and later snowmelt. Shallower snowpack and early snowmelt were also associated with decreased foliar N concentrations and δ15N values, indications that earlier snowmelt contributes to lower N availability relative to plant N uptake and demand. Our study provides evidence that early snowmelt resulting from shallower snowpack contributes to N oligotrophication, primarily through impacts on soil nitrate supply and uptake of N by trees.

Foliar resorption is a principal nutrient conservation mechanism in terrestrial vegetation that could be sensitive to ongoing changes in climate and atmospheric nitrogen (N) deposition. We quantified N resorption in northern hardwood forests along an elevation gradient of decreasing temperature and increasing soil N availability to evaluate how this critical nutrient cycling process can be expected to respond to global and regional environmental changes. Foliar N resorption proficiency (NRP) increased significantly at lower elevations for both sugar maple and American beech, the dominant species in these forests. Foliar N resorption efficiency (NRE) also decreased with increasing elevation, but only in one year. Both species exhibited strong negative relationships between NRP and soil N availability. Thus, we anticipate that with climate warming and decreasing N inputs, northern hardwood forests can be expected to exhibit stronger N conservation via foliar resorption. Both species also exhibited strong correlations between resorption efficiency of N and C, but resorption of both elements was much greater for beech than sugar maple, suggesting contrasting mechanisms of nutrient conservation between these two widespread species.

Mangroves are critically important ecosystems that are highly vulnerable to hurricanes. This study assessed the impact of Hurricane Maria on mangrove canopy heights and vegetation at two sites in Puerto Rico-La Parguera (southwest) and the Northeast Ecological Corridor (northeast)-and examined factors influencing recovery. Using remote sensing techniques, including light detection and ranging (LiDAR) and normalized difference vegetation index (NDVI) analysis, we quantified canopy height loss and vegetation health changes over time. Results show a significant reduction in canopy height immediately after the hurricane, with greater damage in the Northeast Corridor site than in the La Parguera site. NDVI analysis revealed site-specific variation in post-hurricane recovery, with some areas exceeding pre-hurricane vegetation health despite initial losses. Recovery patterns appeared to be linked to pre-storm canopy height and potential human disturbances, such as land-use change and hydrologic alteration. The integration of LiDAR and NDVI provided complementary insights, with LiDAR capturing structural damage and NDVI reflecting vegetation health dynamics. This study highlights the value of remote sensing in evaluating mangrove resilience and identifying factors influencing recovery after extreme weather events.

The timescales over which soil carbon responds to global change are a major uncertainty in the terrestrial carbon cycle. Radiocarbon measurements on archived soil samples are an important tool for addressing this uncertainty. We present time series (1969-2023) of radiocarbon measurements for litter (Oi/Oe and Oa/A) and mineral (0-10 cm) soils from the Hubbard Brook Experimental Forest, a predominantly hardwood forest in the northeastern USA. To estimate soil carbon cycling rates, we built different autonomous linear compartmental models. We found that soil litter carbon cycles on decadal timescales (Oi/Oe: ~7 years), whereas carbon at the organic-mineral interface (Oa/A), and mineral soil (0-10 cm) carbon cycles on centennial timescales (~104 and 302 years, respectively). At the watershed-level, the soil system appears to be at steady-state, with no observed changes in carbon stocks or cycling rates over the study period, despite increases in precipitation, temperature, and soil pH. However, at the site-level, the Oi/Oe is losing carbon (-15 g C m-2 year-1 since 1998). The observed decline in carbon stocks can be detected when the Oi and Oe layers are modeled separately. This pattern suggests that the rapidly cycling litter layer at the smaller scale is responding to recent environmental changes. Our results highlight the importance of litter carbon as an "early-warning system" for soil responses to environmental change, as well as the challenges of detecting gradual environmental change across spatial scales in natural forest ecosystems.