Recent research at Whiteface Mountain, one of the few remaining sites in the U.S. where long-term cloud water chemistry research has continued to the present day, has revealed a doubling in cloud water organic carbon concentrations since measurements began in 2009. This dramatic increasing trend was an unexpected result, which requires further investigation. The present study attempts to verify these results using additional independent datasets from within the region and explores potential driving factors behind the observed organic carbon trends. Through evaluation of measurements from four additional sites in the north eastern U.S., each with long-term measurements of organic carbon concentrations within bulk cloud water or wet deposition samples, we show that there is strong evidence for a regional increasing trend in organic concentrations within aqueous atmospheric samples. These results provide further context behind the growing inorganic ion imbalance observed in wet deposition samples collected across the eastern U.S. and Canada, as identified in a separate study published in 2021. We discuss hypotheses for the potential driving factors behind the increasing organic carbon trends observed, including increased biomass burning influence, increased biogenic emissions and a changing chemical regime characterized by relatively high concentrations of reactive nitrogen chemical species.

Machine-learning models have been surprisingly successful at predicting stream solute concentrations, even for solutes without dedicated sensors. It would be extremely valuable if these models could predict solute concentrations in streams beyond the one in which they were trained. We assessed the generalisability of random forest models by training them in one or more streams and testing them in another. Models were made using grab sample and sensor data from 10 New Hampshire streams and rivers. As observed in previous studies, models trained in one stream were capable of accurately predicting solute concentrations in that stream. However, models trained on one stream produced inaccurate predictions of solute concentrations in other streams, with the exception of solutes measured by dedicated sensors (i.e., nitrate and dissolved organic carbon). Using data from multiple watersheds improved model results, but model performance was still worse than using the mean of the training dataset (Nash-Sutcliffe Efficiency < 0). Our results demonstrate that machine-learning models thus far reliably predict solute concentrations only where trained, as differences in solute concentration patterns and sensor-solute relationships limit their broader applicability.

Riverine N2O and N-2 fluxes, key components of the global nitrogen budget, are known to be influenced by river size (often represented by average river width), yet the specific mechanisms behind these effects remain unclear. This study examined how environmental and microbial factors influenced sediment N2O and N-2 fluxes across rivers with varying widths (2.8 to 2,000 m) in China. Sediment acted as sources of both N2O and N-2 emissions, with both N-2 (0.2 to 20.8 mmol m(-2) d(-1)) and N2O fluxes (0.7-54.2 mu mol m(-2) d(-1)) decreasing significantly as river width increased. N-2 fluxes were positively correlated with denitrifying bacterial abundance, whereas N2O fluxes, when normalized by the abundance of denitrifying bacteria, were negatively correlated with the abundance of N2O-reducing microbes. Water physicochemical factors, particularly temperature and nitrate, were more important drivers of these fluxes than sediment factors. Nitrate significantly increased denitrifying bacterial abundance, whereas higher temperatures enhanced cell-specific activity. Lower N2O and N-2 emissions in wider rivers were attributed to decreased denitrifying microbial abundance and lower denitrification rates, in addition to the commonly assumed reduction in exogenous N2O and N-2 inputs. Rolling regression analysis showed that nitrate concentration had a stronger effect on sediment N2O and N-2 fluxes in narrower rivers, whereas temperature was more influential in wider rivers. This difference is attributed to more stable nitrate concentrations and decreased nitrogen removal efficiency in wider rivers, while temperature variation remained consistent across all river widths. Beyond sediments, temperature had a greater effect on excess N2O concentrations than nitrate in the overlying water of wider rivers (>165 m), highlighting its broader impact. This study provides new biogeochemical insights into how river width influences sediment N2O and N-2 fluxes and highlights the importance of incorporating temperature into flux predictions, particularly for wider rivers.

Intermittent rivers and ephemeral streams (IRES), which represent more than half of the global river network, remain largely understudied as potential sources of atmospheric nitrous oxide (N2O), particularly in the context of peri‑urban areas experiencing intensive anthropogenic pressures (e.g., hydrological alterations, elevated organic matter (OM) and nutrient inputs). To address this critical knowledge gap, we conducted a multi-month investigation across Beijing's peri‑urban IRES network in China. N2O flux dynamics were quantified across five distinct hydrological phases, including dry riverbeds, exposed riverbeds, isolated pools, standing open waters, and flowing waters, and underlying mechanisms were elucidated via integrated analysis of physicochemical variables and microbial gene profiles. Dry riverbeds exhibited the highest N2O emissions (215±1060 μmol·m-2·d-1), primarily driven by denitrification facilitated by substrate accumulation, a high abundance of nitrogen transformation genes, and favorable moisture conditions. Rainfall-induced rewetting further stimulated microbial activities and short-term N2O emissions in dry riverbeds. Fragmented hydrological phases (dry riverbeds, exposed riverbeds, and isolated pools) exhibited significantly higher N2O fluxes than connected phases (standing open waters and flowing waters). The temporal dynamics of N₂O fluxes revealed significant decreases during hydrological wetting transitions from fragmented to connected phases and dry to partially saturated phases. These reductions were primarily due to enhanced microbial OM decomposition and favored complete denitrification, driven by increased terrestrial OM inputs, reduced nirS and nirK gene abundances, and elevated ratios of dissolved organic carbon to nitrate. Peri-urban IRES emitted significantly more N2O during hydrological phase transitions than perennial rivers did during the study period. Our findings demonstrate that IRES can be significant N2O sources, particularly in peri‑urban areas due to high emissions during dry phases. This study advances the understanding of N2O emission patterns and mechanisms in IRES, emphasizing their previously overlooked role in global N2O budgets, with implications for N2O emission mitigation through environmental flow management.

Nitrous oxide (N2O) reductase, the sole natural microbial sink for N2O, exists in two microbial clades: nosZI and nosZII. Although previous studies have explored inter-clade ecological differentiation, the intra-clade variations and their implications for N2O dynamics remain understudied. This study investigated both inter- and intra-clade ecological differentiation among N2O reducers, the drivers influencing these patterns, and their effects on N2O emissions across continental-scale river systems. The results showed that both nosZI and nosZII community turnovers were associated with similar key environmental factors, particularly total phosphorus (TP), but these variables explained a larger proportion of variation in the nosZI community. The influence of mean annual temperature (MAT) on community composition increased for more widespread N2O-reducing taxa. We identified distinct ecological clusters within each clade of N2O reducers and observed identical ecological clustering patterns across both clades. These clusters were primarily characterized by distinct MAT regimes, coarse sediment texture as well as low TP levels, and high abundance of N2O producers, with MAT-related clusters constituting predominant proportions. Intra-clade ecological differentiation was a crucial predictor of N2O flux and reduction efficiency. Although different ecological clusters showed varying or even contrasting associations with N2O dynamics, the shared ecological clusters across clades exhibited similar trends. Low-MAT clusters in both the nosZI and nosZII communities were negatively correlated with denitrification-normalized N2O flux and the N2O:(N2O + N2) ratio, whereas high-MAT clusters showed positive correlations. This contrasting pattern likely stems from low-MAT clusters being better adapted to eutrophic conditions and their more frequent co-occurrence with N2O-producing genes. These findings advance our understanding of the distribution and ecological functions of N2O reducers in natural ecosystems, suggesting that warming rivers may have decreased N2O reduction efficiency and thereby amplify temperature-driven emissions.

Tropical watersheds are thought to exert a strong control on the global carbon cycle because elevated temperature and rainfall rates promote the chemical weathering of silicate rocks. However, the critical factors that control tropical weathering, such as the role of subsurface flowpaths in setting the sensitivity of weathering to climate change, remain obscure. Here, we relate solute dynamics to flowpath partitioning using new and existing data from the Luquillo Critical Zone Observatory (LCZO) in the tropical forests of eastern Puerto Rico. We used new measurements of deuterium excess in streamflow and rainfall to show that the fraction of young water (F yw , fraction of streamflow less than 1–3 months old) for each catchment increases with increasing discharge. We attribute F yw ‐Q behavior to the activation of shallow flowpaths that efficiently route incident rainfall to streamflow. Results from this 2‐year sampling period are comparable to results from end‐member mixing analysis of longer‐term solute records, suggesting that water routed via shallow flowpaths acquires little additional solutes from weathering reactions. Our findings of apparent mixing between flowpaths can be unified with time‐dependent weathering reactions and time‐variable transit time distributions. To estimate the response of the LCZO to climatic change, we compare F yw ‐Q behavior between sites that experience different mean annual precipitation amounts. Intriguingly, we find that climatically driven changes in flowpath partitioning reconcile watershed fluxes with regolith‐based studies. This suggests that shallow flowpath activation is the mechanism for maintaining constant weathering rates despite variable rainfall rates in the supply limited regions where weathering is already maximized.

Long‐term litterfall trends are unexplored in hurricane‐prone regions but are needed to understand the consequences of altered hurricane regimes. In a wet tropical forest in northeastern Puerto Rico, we monitored litterfall mass (leaf fall, <2.5 cm diameter wood fall and miscellaneous), litterfall carbon (C) and nitrogen (N) and stream nitrate every 2 weeks for 29 years (1989–2017). Litterfall from the nine observed hurricanes averaged 500 g m −2 hurricane −1 (CV = 90%), nearly half of the long‐term mean of 951 g m −2 year −1 . Hurricane‐generated leaf fall and wood fall increased with increasing disturbance intensity (peak wind speed) and time since a previous hurricane. Wood fall from the two most intense hurricanes exceeded corresponding leaf fall and mean annual wood fall. Litterfall increased over the 29 years due to increases in wood fall and miscellaneous materials but not leaf fall. Recovery of litterfall after individual hurricanes was distinctive and illustrated the varying effects of hurricane intensity and history on litterfall dynamics. Leaf fall N concentrations [N] surged immediately after hurricanes yet decreased by around 33% over the 29 years. Similar changes were observed at the watershed scale, with increasing nitrate in streams following major hurricanes but then a long‐term decline. Mean annual leaf fall [N] was negatively related to the previous year's fine wood fall but positively related to that wood fall's [N], suggesting a link between fine wood dynamics and plant N uptake. Stream nitrate‐[N] showed a strong positive correlation with leaf fall [N] after hurricanes and across years, demonstrating tight coupling between terrestrial and aquatic N cycling throughout periods of cyclonic disturbances and recovery. The decadal decreases in litterfall [N] and stream nitrate‐[N] and the increase in wood fall suggest a trend towards more conservative cycling of N. Microbial immobilization of N in wood fall from hurricanes and during recovery likely contributed to the lower N availability. Synthesis . More conservative cycling of N can be expected under the current hurricane disturbance regime. However, with increased hurricane frequencies and intensities, the lack of high wood fall typical of mature canopies may alter present N cycling trends.

Tropical rainforests in many regions are experiencing an increased frequency of severe hurricanes and droughts due to climate change, which can alter the quantity and quality of organic matter inputs entering tropical freshwater ecosystems through inputs of leaf litter. This study leached dried senesced and freshly abscised leaves in a controlled laboratory setting as proxies of drought‐ and hurricane‐induced changes to leaf litter inputs, respectively. The nine species that were leached are representative of the dominant riparian vegetation across most of the Luquillo Mountains of Puerto Rico. Leachate analytics, including forms of carbon, nitrogen, and major cations and anions, were analyzed across leaf condition and species to assess relationships between climatic events, species type, and leaf leachate composition. Total accumulation of solutes and concentrations of dissolved organic matter and major ions were about 2–4 times higher in leachate from dried senesced leaves (i.e., drought litter inputs) than freshly abscised leaves (i.e., hurricane litter inputs); however, the magnitudes of these differences were highly variable across species, potentially connected to leaf tissue chemistry. These data allow for scaling the impact of riparian leaf litter inputs to further our understanding of the biogeochemical and metabolic response of tropical streams to increasingly frequent climatic disturbances.

The pace and trajectory of ecosystem development are governed by the availability and cycling of limiting nutrients, and anthropogenic disturbances such as acid rain and deforestation alter these trajectories by removing substantial quantities of nutrients via titration or harvest. Here, we use six decades of continuous chemical and hydrologic data from three adjacent headwater catchments in the Hubbard Brook Experimental Forest, New Hampshire-one deforested (W5), one CaSiO3-enriched (W1), and one reference (W6)-to quantify long-term nutrient and mineral fluxes. Acid deposition since 1900 drove pronounced depletion and export of base cations, particularly calcium, across all watersheds. Experimental deforestation of W5 intensified loss of biomass and nutrient cations and triggered sustained increases in streamwater pH, Ca2+, and SiO2 exports over nearly four decades, greatly exceeding the effects of direct CaSiO3 enrichment in both duration and magnitude. We detect no long-term changes in water yield or water flow paths in the experimental watersheds, and we attribute this multidecadal increase in weathering rates following deforestation to biological responses to severe nutrient limitation. Our evidence suggests that in the regrowing forest, plants are investing photosynthate into belowground processes that amplify mineral weathering to access phosphorus and micronutrients, consequently elevating the export of less limiting elements present in silicate parent material. Throughout decades of forest regrowth, enhanced biotic weathering has continued to deplete the acid buffering capacity of the terrestrial ecosystem while the export of weathering products has elevated the pH of the receiving stream.

Streams and rivers export dissolved materials and eroded sediments from the watersheds they drain. Much can be learned about rivers and their watersheds by measuring the magnitude, timing and form of these exports. Such watershed load datasets are used to gain fundamental understanding of watershed ecosystems as well as to assess water quality and the efficacy of management approaches to sustain both terrestrial and aquatic ecosystem health. Despite the widespread use of watershed load estimates, comparisons at macroscales (i.e. across many sites) are currently complicated by differences in underlying data quality and estimation methods between sites, periods, and solutes. Using high-frequency sensor data from the Hubbard Brook Experimental Forest and the Plynlimon Research Catchments, we generated time series of increasingly coarse sampling frequencies, and tested the sensitivity of various load estimation methods. We further tested the accuracy of common methods using synthetic time series, spanning a range of flow regimes and concentration-discharge (C:Q) relationships. Lastly, we applied each estimation method to the MacroSheds dataset (macrosheds.org), generating a publicly available dataset of 16,489 site-years of data across 93 sites and 112 solutes. Results from both the simulated data coarsening and synthetic time series experiments indicate that load estimates with high sampling frequency (daily or better) and an informative concentration-discharge relationship are well suited for macroscale science efforts (errors within ~10%). Estimates based on coarse (biweekly or coarser) underlying data and incompletely described and/or complex C:Q relationships showed large enough error (>50%) to suggest they would be misleading if included in macroscale efforts. Our results suggest that scientists interested in comparing load estimates should first consider (1) sensitivity of their analysis to changes in load magnitudes, (2) the underlying data frequency used to generate estimates, (3) the C:Q relationship of their solute of interest, and (4) their confidence in the completeness of that C:Q relationship over the period of study.

River networks play a crucial role in the global carbon cycle, as relevant sources of carbon dioxide (CO2) to the atmosphere. Advancements in high-frequency monitoring in aquatic environments have enabled measurement of dissolved CO2 concentration at temporal resolutions essential for studying carbon variability and evasion from these dynamic ecosystems. Here, we describe the adaptation, deployment, and validation of an open-source and relatively low-cost in situ pCO(2) sensor system for lotic ecosystems, the lotic-SIPCO2. We tested the lotic-SIPCO2 in 10 streams that spanned a range of land cover and basin size. Key system adaptations for lotic environments included prevention of biofouling, configuration for variable stage height, and reduction of headspace equilibration time. We then examined which input parameters contribute the most to uncertainty in estimating CO2 emission rates and found scaling factors related to the gas exchange velocity were the most influential when CO2 concentration was significantly above saturation. Near saturation, sensor measurement of pCO(2) contributed most to uncertainty in estimating CO2 emissions. We also found high-frequency measurements of pCO(2) were not necessary to accurately estimate median emission rates given the CO2 regimes of our streams, but daily to weekly sampling was sufficient. High-frequency measurements of pCO(2)remain valuable for exploring in-stream metabolic variability, source partitioning, and storm event dynamics. Our adaptations to the SIPCO2 offer a relatively affordable and robust means of monitoring dissolved CO2 in lotic ecosystems. Our findings demonstrate priorities and related considerations in the design of monitoring projects of dissolved CO(2 )and CO2 evasion dynamics more broadly.

AbstractAfter 4.5 billion years as an evolving and dynamic planet, the Earth continues to evolve but with human‐altered dynamics. Earth scientists have special opportunities and responsibilities to accelerate our understanding of Earth's changes that are transforming our most remarkable home.

Fluvial silicon (Si) plays a critical role in controlling primary production, water quality, and carbon sequestration through supporting freshwater and marine diatom communities. Geological, biogeochemical, and hydrological processes, as well as climate and land use, dictate the amount of Si exported by streams. Understanding Si regimes-the seasonal patterns of Si concentrations-can help identify processes driving Si export. We analyzed Si concentrations from over 200 stream sites across the Northern Hemisphere to establish distinct Si regimes and evaluated how often sites moved among regimes over their period of record. We observed five distinct regimes across diverse stream sites, with nearly 60% of sites exhibiting multiple regime types over time. Our results indicate greater spatial and interannual variability in Si seasonality than previously recognized and highlight the need to characterize the watershed and climate variables that affect Si cycling across diverse ecosystems.

Climate and atmospheric deposition interact with watershed properties to drive dissolved organic carbon (DOC) concentrations in lakes. Because drivers of DOC concentration are inter-related and interact, it is challenging to assign a single dominant driver to changes in lake DOC concentration across spatiotemporal scales. Leveraging forty years of data across sixteen lakes, we used structural equation modeling to show that the impact of climate, as moderated by watershed characteristics, has become more dominant in recent decades, superseding the influence of sulfate deposition that was observed in the 1980s. An increased percentage of winter precipitation falling as rain was associated with elevated spring DOC concentrations, suggesting a mechanistic coupling between climate and DOC increases that will persist in coming decades as northern latitudes continue to warm. Drainage lakes situated in watersheds with fine-textured, deep soils and larger watershed areas exhibit greater variability in lake DOC concentrations compared to both seepage and drainage lakes with coarser, shallower soils, and smaller watershed areas. Capturing the spatial variability in interactions between climatic impacts and localized watershed characteristics is crucial for forecasting lentic carbon and nutrient dynamics, with implications for lake ecology and drinking water quality.

Soils are a principal global reservoir of mercury (Hg), a neurotoxic pollutant that is accumulating through anthropogenic emissions to the atmosphere and subsequent deposition to terrestrial ecosystems. The fate of Hg in global soils remains uncertain, however, particularly to what degree Hg is re-emitted back to the atmosphere as gaseous elemental mercury (GEM). Here we use fallout radionuclide (FRN) chronometry to directly measure Hg accumulation rates in soils. By comparing these rates with measured atmospheric fluxes in a mass balance approach, we show that representative Arctic, boreal, temperate, and tropical soils are quantitatively efficient at retaining anthropogenic Hg. Potential for significant GEM re-emission appears limited to a minority of coniferous soils, calling into question global models that assume strong re-emission of legacy Hg from soils. FRN chronometry poses a powerful tool to reconstruct terrestrial Hg accumulation across larger spatial scales than previously possible, while offering insights into the susceptibility of Hg mobilization from different soil environments. Fallout radionuclide (FRN) chronometry reveals that accumulation of Hg in soils is five times higher than reported in sediment or peat archives. This confirms that global forest soils are strong and stable sinks of gaseous elemental mercury (GEM).

Cities are at the heart of global anthropogenic greenhouse gas (GHG) emissions, with rivers embedded in urban landscapes as a potentially large yet uncharacterized GHG source. Urban rivers emit GHGs due to excess carbon and nitrogen inputs from urban environments and their watersheds. Here relying on a compiled urban river GHG dataset and robust modelling, we estimated that globally urban rivers emitted annually 1.1, 42.3 and 0.021 Tg CH4, CO2 and N2O, totalling 78.1 +/- 3.5 Tg CO2-equivalent (CO2-eq) emissions. Predicted GHG emissions were nearly twofold those from non-urban rivers (similar to 815 versus 414 mmol CO2-eq m(-2) d(-1)) and similar to scope-1 urban emissions in intensity (1,058 mmol CO2-eq m(-2) d(-1)), with particularly higher CH4 and N2O emissions linked to widespread eutrophication and altered carbon and nutrient cycling in urban rivers. Globally, the emissions varied with national income levels with the highest emissions happening in lower-middle-income countries where river pollution control is deficient. These findings highlight the importance of pollution controls in mitigating urban river GHG emissions and ensuring urban sustainability.

We measure the age of soil organic matter (SOM) in soil depth profiles using fallout radionuclide (FRN) chronometry. The FRN age model quantifies the well-known lag in ∆14C which is the time between biological carbon fixation and its incorpration into SOM 1–3. The FRN model also reveals sharp excursions in ∆14C at depth to extremely old ages, which we attribute to legacy petrogenic, pedogenic, or passive carbon pools because corresponding soil carbon fluxes based on legacy ∆14C do not reconcile with independent ecosystem measures. FRN ages may thus resolve a foundational uncertainty regarding ages of SOM, agreeing with mass balance of carbon pools and fluxes at both soil profile and global scales 4,5, 𝛿13C experiments at profile and global scales 6,7, compilation of global experimental soil carbon fluxes 8, and independent 35Cl bomb-pulse dating 9. We confirm that the pool of SOM relevant to climate transition is up to 10 times younger than deduced from global ∆14C turnover times. We thereby estimate that temperate and tropical forest soils store ca. 10% of Net Primary Productivity (NPP) over decadal timescales. These observations demonstrate that SOM cycling is more dynamic than deduced from 14C and may respond rapidly to both climate change as well as mitigation efforts aimed at sequestering atmospheric CO2 over annual to decadal timescales.

The seasonal behavior of fluvial dissolved silica (DSi) concentrations, termed DSi regime, mediates the timing of DSi delivery to downstream waters and thus governs river biogeochemical function and aquatic community condition. Previous work identified five distinct DSi regimes across rivers spanning the Northern Hemisphere, with many rivers exhibiting multiple DSi regimes over time. Several potential drivers of DSi regime behavior have been identified at small scales, including climate, land cover, and lithology, and yet the large-scale spatiotemporal controls on DSi regimes have not been identified. We evaluate the role of environmental variables on the behavior of DSi regimes in nearly 200 rivers across the Northern Hemisphere using random forest models. Our models aim to elucidate the controls that give rise to (a) average DSi regime behavior, (b) interannual variability in DSi regime behavior (i.e., Annual DSi regime), and (c) controls on DSi regime shape (i.e., minimum and maximum DSi concentrations). Average DSi regime behavior across the period of record was classified accurately 59% of the time, whereas Annual DSi regime behavior was classified accurately 80% of the time. Climate and primary productivity variables were important in predicting Average DSi regime behavior, whereas climate and hydrologic variables were important in predicting Annual DSi regime behavior. Median nitrogen and phosphorus concentrations were important drivers of minimum and maximum DSi concentrations, indicating that these macronutrients may be important for seasonal DSi drawdown and rebound. Our findings demonstrate that fluctuations in climate, hydrology, and nutrient availability of rivers shape the temporal availability of fluvial DSi. The amount of dissolved silicon (DSi) in rivers is an important control on numerous ecological and biogeochemical processes, such as types of algae that bloom and rates of carbon sequestration. Compared to our knowledge of other nutrients, such as nitrogen and phosphorus, we have limited understanding of what controls the timing and concentration of DSi in rivers. Previous work identified five distinct seasonal patterns of DSi concentrations in rivers across the Northern Hemisphere; here we look at the environmental variables that control these seasonal patterns. We found that rivers often have one to five seasonal patterns over time due to interannual shifts in temperature, evapotranspiration, and streamflow. In addition, we found that the average shape of the seasonal pattern for a given river, specifically minimum and maximum DSi concentrations, was related to nitrogen (N) and phosphorus (P) concentrations, highlighting linkages between N, P, and DSi cycling in rivers. This work identifies why river DSi concentrations exhibit both within and between year variability, highlighting that temperature, streamflow, and nutrient availability control the timing of river DSi availability for biological uptake. Seasonal variations in annual riverine dissolved silica concentrations (DSi regime) were correctly classified 80% of the time Climate and primary productivity emerge as the most important drivers in differentiating among average DSi regimes Median nitrogen and phosphorus concentrations strongly predicted minimum and maximum DSi concentration, regardless of regime type

Riverine exports of silicon (Si) influence global carbon cycling through the growth of marine diatoms, which account for ∼25% of global primary production. Climate change will likely alter river Si exports in biome‐specific ways due to interacting shifts in chemical weathering rates, hydrologic connectivity, and metabolic processes in aquatic and terrestrial systems. Nonetheless, factors driving long‐term changes in Si exports remain unexplored at local, regional, and global scales. We evaluated how concentrations and yields of dissolved Si (DSi) changed over the last several decades of rapid climate warming using long‐term data sets from 60 rivers and streams spanning the globe (e.g., Antarctic, tropical, temperate, boreal, alpine, Arctic systems). We show that widespread changes in river DSi concentration and yield have occurred, with the most substantial shifts occurring in alpine and polar regions. The magnitude and direction of trends varied within and among biomes, were most strongly associated with differences in land cover, and were often independent of changes in river discharge. These findings indicate that there are likely diverse mechanisms driving change in river Si biogeochemistry that span the land‐water interface, which may include glacial melt, changes in terrestrial vegetation, and river productivity. Finally, trends were often stronger in months outside of the growing season, particularly in temperate and boreal systems, demonstrating a potentially important role of shifting seasonality for the flux of Si from rivers. Our results have implications for the timing and magnitude of silica processing in rivers and its delivery to global oceans.