Warming may offset impact of precipitation changes on riverine nitrogen loading

Chain assembly of Rhodococcus bacteria with O-doped g-C3N4 for photocatalysis mediated high-performance partial nitrification: From nitrite resource evolution to device application

Nitrogen conversion via partial nitrification-anammox (PN/A), utilizing nitrite as a key intermediate, is an ideal low-carbon approach for wastewater nitrogen removal. However, the partial nitrification process, which is rate-limited and relies on less common bacteria with slow reaction kinetics, poses challenges for high-throughput PN/A implementation. Herein, we developed a microbial/photocatalysis coupling system using Rhodococcus bacterial and O-doped g-C3N4 (OCN) photocatalysts. This approach leverages photogenerated electrons and free radicals from photocatalysts to directly activate microorganisms, enhancing the redox gradient. This intensification selectively inhibits the enzymatic conversion of nitrite to nitrate and its reduction to nitrogen in Rhodococcus bacteria. Consequently, it promotes a highly selective partial nitrification process, generating ample nitrite to facilitate anammox reactions. Transmission electron microscopy and electrochemical characterization showed bacteria forming chain-like assemblies on OCN particles, with the composite exhibiting a favorable redox profile, low impedance, and high stability. Ammonia conversion to nitrite reached 96 % in 3 days, with an enriched NO2- concentration of 36.3 mg/L, 10 times higher than the raw bacterial control. Hence, this strategy of constructing bacterial-photocatalysis system achieved high selectivity and efficiency in partial nitrification. Transcriptome and qPCR analyses showed upregulation of genes linked to the short-cut denitrification metabolic pathway. Photocatalyst band structure and redox potential analysis suggest a new bio-photoelectrochemical partial nitrification pathway. Finally, the feasibility and applicability in future industrial and ecological water treatment were validated through demo H-type reactors and aquarium experiments. These findings offer innovative perspectives for controlled modulation of ammonia nitrogen conversion focus on nitrite intermediate, advancing an energy-efficient, low-carbon nitrogen cycle.

Hydrological connectivity and dissolved organic matter impacts nitrogen and antibiotics fate in river-lake system before and after extreme wet season

The impact and mechanism of hydrological connectivity and dissolved organic matter on the fate of nitrogen and antibiotics are still lack off in a river-lake connected system under climate extreme events. This study examined the fate of NO3--N, 38 antibiotics, and dissolved organic matter (DOM) in Baiyangdian Basin, through dry and wet seasonal (after extreme rainfall) samplings at 2023. In the system, NO3--N and ∑antibiotics average concentrations were higher in the dry season, while the relative abundance of humic-like components was higher in the wet season. Spatial autocorrelation analysis showed that the high-high clusters of pollutants and DOM components were mainly distributed in rivers, and the temporal difference was significant. MixSIAR and PMF model were respectively applied to nitrogen and antibiotics sources apportionment. The results showed that non-point sources (NPS) of nitrogen and antibiotics exhibited an upward trend, while the point sources decreased from dry to wet seasons. Hydrological connectivity was characterized by using δ18O-H2O, which was higher in the wet season. Partial least squares path model revealed that hydrological connectivity directly impacted humic-like components, which were the direct influencing factor of the concentration and NPS for antibiotics and nitrogen in the connected system. Extreme rainfall weaken the impact of hydrological connectivity on the concentration and NPS of pollutants, while enhanced the impact of humic-like components on pollutants NPS. These findings clarified the impact mechanism of hydrological connectivity and DOM on nitrogen and antibiotics fate in the connected system, which plays an important role in future water quality management under extreme events.

Uncovering the spatial characteristics of global net anthropogenic nitrogen input at high resolution and across 1.42 million lake basins

Global Net Anthropogenic Nitrogen Input (NANI) at high resolution is crucial for assessing the impact of human activities on aquatic environments. Insufficient global high-resolution data sources and methods have hindered the effective examination of the global characteristics and driving forces of NANI. This study presents a general framework for calculating global NANI, providing estimates at a 5-arc-minute resolution and over 1.42 million lake basins in 2015. The results highlight the region near the Tropic of Cancer as a concentration area for high NANI and an inflection point for latitude-based accumulation variation. It also emphasizes the uneven distribution of NANI among continents, with Asia and Africa having the highest proportions, yet their high and low values are notably lower than those of Europe and South America. A similar pattern is observed in global lakes, where Asia has the smallest quantity and volume, but the highest NANI intensity. In contrast, North America and Europe have larger quantities and volumes but the lowest NANI intensity. The global distribution characteristics reveal a clustering pattern in high and low values, with 1.25 % of the area having a sum of NANI exceeding 20 %. The uncertainty analysis regarding model parameters indicates that continents with the highest NANI do not always exhibit the highest uncertainty. These results bridge the gap between global nitrogen sustainable management and anthropogenic nitrogen input. They support research on spatiotemporal changes and controlling factors of global river nutrient loads, as well as the impact of climatic factors on basin nitrogen loss and its variability.

Water quality-fisheries tradeoffs in a changing climate underscore the need for adaptive ecosystem-based management

Changes driven by both unanticipated human activities and management actions are creating wicked management landscapes in freshwater and marine ecosystems that require new approaches to support decision-making. By linking a predictive model of nutrient- and temperature-driven bottom hypoxia with observed commercial fishery harvest data from Lake Erie (United States-Canada) over the past century (1928-2022) and climate projections (2030-2099), we show how simple, yet robust models and routine monitoring data can be used to identify tradeoffs associated with nutrient management and guide decision-making in even the largest of aquatic ecosystems now and in the future. Our approach enabled us to assess planned nutrient load reduction targets designed to mitigate nutrient-driven hypoxia and show why they appear overly restrictive based on current fishery needs, indicating tradeoffs between water quality and fisheries management goals. At the same time, our temperature results show that projected climate change impacts on hypoxic extent will require more stringent nutrient regulations in the future. Beyond providing a rare example of bottom hypoxia driving changes in fishery harvests at an ecosystem scale, our study illustrates the need for adaptive ecosystem-based management, which can be informed by simple predictive models that can be readily applied over long time periods, account for tradeoffs across multiple management sectors (e.g., water quality, fisheries), and address ecosystem nonstationarity (e.g., climate change impacts on management targets). Such approaches will be critical for maintaining valued ecosystem services in the many aquatic systems worldwide that are vulnerable to multiple drivers of environmental change.

Multifaceted Dinoflagellates and the Marine Model Prorocentrum cordatum

BACKGROUND

Dinoflagellates are a monophyletic group within the taxon Alveolata, which comprises unicellular eukaryotes. Dinoflagellates have long been studied for their organismic and morphologic diversity as well as striking cellular features. They have a main size range of 10-100 µm, a complex "cell covering", exceptionally large genomes (∼1-250 Gbp with a mean of 50,000 protein-encoding genes) spread over a variable number of highly condensed chromosomes, and perform a closed mitosis with extranuclear spindles (dinomitosis). Photosynthetic, marine, and free-living Prorocentrum cordatum is a ubiquitously occurring, bloom-forming dinoflagellate, and an emerging model system, particularly with respect to systems biology.

SUMMARY

Focused ion beam/scanning electron microscopy (FIB/SEM) analysis of P. cordatum recently revealed (i) a flattened nucleus with unusual structural features and a total of 62 tightly packed chromosomes, (ii) a single, barrel-shaped chloroplast devoid of grana and harboring multiple starch granules, (iii) a single, highly reticular mitochondrion, and (iv) multiple phosphate and lipid storage bodies. Comprehensive proteomics of subcellular fractions suggested (i) major basic nuclear proteins to participate in chromosome condensation, (ii) composition of nuclear pores to differ from standard knowledge, (iii) photosystems I and II, chloroplast complex I, and chlorophyll a-b binding light-harvesting complex to form a large megacomplex (>1.5 MDa), and (iv) an extraordinary richness in pigment-binding proteins. Systems biology-level investigation of heat stress response demonstrated a concerted down-regulation of CO2-concentrating mechanisms, CO2-fixation, central metabolism, and monomer biosynthesis, which agrees with reduced growth yields.

KEY MESSAGES

FIB/SEM analysis revealed new insights into the remarkable subcellular architecture of P. cordatum, complemented by proteogenomic unraveling of novel nuclear structures and a photosynthetic megacomplex. These recent findings are put in the wider context of current understanding of dinoflagellates.

Decreasing denitrification rates poses a challenge to further decline of nitrogen concentration in Lake Taihu, China

Nitrogen (N) concentrations in many lakes have decreased substantially in recent years due to external load reduction to mitigate harmful algal blooms. However, little attention has been paid to the linkage between the lakes' nitrogen removal efficiency and improved water quality in lakes, especially the variation of denitrification rate (DNR) under decreasing N concentrations. To understand the efficiency of N removal under improving water quality and its influence on the N control targets in Lake Taihu, a denitrification model based on in situ experimental results was developed and long-term (from 2007 to 2022) water quality and meteorological observations were used to estimate DNR and relate it to the amount of N removal (ANR) from the lake. The concentration of total nitrogen (TN) in Lake Taihu decreased from 3.28 mg L-1 to 1.41 mg L-1 from 2007 to 2022 but the reduction showed spatial heterogeneity. The annual mean DNR decreased from 45.6 μmol m-2 h-1 to 4.2 μmol m-2 h-1, and ANR decreased from 11.85×103 t yr-1 to 1.17×103 t yr-1 during the study years. N budget analysis suggested that the amount of N removed by denitrification accounted for 23.3 % of the external load in 2007, but decreased to only 4.0 % in 2022. Thus, the contribution of N removal by internal N cycling decreased significantly as water quality improved. Notably, the proportion of ANR in winter to total ANR increased from 14 % in 2007 to 23 % in 2022 due to warming. This could potentially lead to N deficiencies in spring and summer, thus limiting the availability of N to phytoplankton. A TN concentration of less than 1.0 mg L-1 in the lake and 1.5 mg L-1 in the inflowing lake zones in spring contribute to local N-limitation in Lake Taihu for cyanobacteria control. Our study revealed a general pattern that N removal efficiency decreases with improved water quality, which is instructive for eutrophic lakes in nitrogen management.

China's anthropogenic N2O emissions with analysis of economic costs and social benefits from reductions in 2022

We assess China's overall anthropogenic N2O emissions via the official guidebook published by Chinese government. Results show that China's overall anthropogenic N2O emissions in 2022 were around 1593.1 (1508.7-1680.7) GgN, about 47.0 %, 27.0 %, 13.4 %, 4.9 %, and 7.7 % of which were caused by agriculture, industry, energy utilization, wastewater, and indirect sources, respectively. Maximum reduction rate for N2O emissions from agriculture, industry, energy utilization, wastewater, and indirect sources can achieve 69 %, 99 %, 79 %, 86 %, and 48 %, respectively, in 2022. However, given current global scenarios with a rapidly changing population and geopolitical and energy tension, the emission reduction may not be fully fulfilled. Without compromising yields, China's theoretical minimum anthropogenic N2O emissions would be 600.6 (568.8-633.6) GgN. In terms of the economic costs for reducing one kg of N2O-N emissions, the price ranged from €12.9 to €81.1 for agriculture, from €0.08 to €0.16 for industry, and from €104.8 to €1571.5 for energy utilization. We acknowledge the emission reduction rates may not be completely realistic for large-scale application in China. The social benefits gained from reducing one kg of N2O-N emissions in China was about €5.2, indicating anthropogenic N2O emissions caused a loss 0.03 % of China's GDP, but only justifying reduction in industrial N2O emissions from the economic perspective. We perceive that the present monetized values will be trustworthy for at least three to five years, but later the numerical monetized values need to be considered in inflation and other currency-dependent conditions.

Hypoxia and salinity constrain the sediment microbiota-mediated N removal potential in an estuary: A multi-trophic interrelationship perspective

Reactive nitrogen (N) enrichment is a common environmental problem in estuarine ecosystems, while the microbial-mediated N removal process is complicated for other multi-environmental factors. Therefore, A systematic investigation is necessary to understand the multi-trophic microbiota-mediated N removal characteristics under various environmental factors in estuaries. Here, we studied how multiple factors affect the multi-trophic microbiota-mediated N removal potential (denitrification and anammox) and N2O emission along a river-estuary-bay continuum in southeastern China using the environmental DNA (eDNA) approach. Results suggested that hypoxia and salinity were the dominant environmental factors affecting multi-trophic microbiota-mediated N removal in the estuary. The synergistic effect of hypoxia and salinity contributed to the loss of taxonomic (MultiTaxa) and phylogenetic (MultiPhyl) diversity across multi-trophic microbiota and enhanced the interdependence among multi-trophic microbiota in the estuary. The N removal potential calculated as the activities of key N removal enzymes was also significantly constrained in the estuary (0.011), compared with the river (0.257) and bay (0.461). Structural equation modeling illustrated that metazoans were central to all sediment N removal potential regulatory pathways. The top-down forces (predation by metazoans) restrained the growth of heterotrophic bacteria, which may affect microbial N removal processes in the sediment. Furthermore, we found that the hypoxia and salinity exacerbated the N2O emission in the estuary. This study clarifies that hypoxia and salinity constrain estuarine multi-trophic microbiota-mediated N removal potential and highlights the important role of multi-trophic interactions in estuarine N removal, providing a new perspective on mitigating estuarine N accumulation.