Nitrogen pollution has been shown to have strong potential threaten to the human drinking water and agriculture. However, identifying the nitrogen and spatial-temporal variation and nitrogen ...pollution sources among surface water, sediments and groundwater at the watershed scale is still of insufficient understanding. In this study, multi-methods (dual isotopes, hydraulic, hydrogeochemical methods) have been used and 400 samplings (40 sediments, 20 shallow groundwater and 40 surface waters in four periods in dry and wet seasons) were collected from 2018 to 2020. The results showed that the concentration of NO3−-N, NH4+-N, NO2−-N and total nitrogen (TN) had variable spatial and temporal changes in whole watershed. The concentration of TN, NO3−-N, NH4+-N and NO2−-N in downstream was higher than midstream and upstream both in dry and wet seasons. The concentration of TN, NO3−-N, NH4+-N and NO2−-N of the whole watershed in wet season was higher than dry season. The dual isotope values indicate that nitrogen sources were mainly derived from manure and sewage waste input (MSI), agriculture chemical fertilizers (ACFI) and sediments nitrogen input (SNI). Those nitrogen sources have different proportion in downstream, midstream and upstream in dry and wet seasons (the largest proportion: MSI 95.24% in downstream and ACFI 86.26% in upstream both in dry season, SNI 31.75% in midstream in wet season). Water exchange has positive correlation with the nitrogen concentration. High level of nitrogen in river also can be a diver in different location and seasons. Those results can be useful for developing regional management strategies and plans for water pollution control and treatment at watershed-scale.
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•Spatiotemporal nitrogen transport and source tracing at watershed-scale•Nitrogen transport and source tracing at surface water-sediments-groundwater system using dual isotopes method•Nitrogen transport and source tracing displayed seasonal and spatial variations•Manure, sewage waste, agriculture chemical fertilizers were the main nitrogen input with different spatiotemporal proportion
ABSTRACT
WRKY‐type transcription factors are involved in multiple aspects of plant growth, development and stress response. WRKY genes have been found to be responsive to abiotic stresses; however, ...their roles in abiotic stress tolerance are largely unknown especially in crops. Here, we identified stress‐responsive WRKY genes from wheat (Triticum aestivum L.) and studied their functions in stress tolerance. Forty‐three putative TaWRKY genes were identified and two multiple stress‐induced genes, TaWRKY2 and TaWRKY19, were further characterized. TaWRKY2 and TaWRKY19 are nuclear proteins, and displayed specific binding to typical cis‐element W box. Transgenic Arabidopsis plants overexpressing TaWRKY2 exhibited salt and drought tolerance compared with controls. Overexpression of TaWRKY19 conferred tolerance to salt, drought and freezing stresses in transgenic plants. TaWRKY2 enhanced expressions of STZ and RD29B, and bound to their promoters. TaWRKY19 activated expressions of DREB2A, RD29A, RD29B and Cor6.6, and bound to DREB2A and Cor6.6 promoters. The two TaWRKY proteins may regulate the downstream genes through direct binding to the gene promoter or via indirect mechanism. Manipulation of TaWRKY2 and TaWRKY19 in wheat or other crops should improve their performance under various abiotic stress conditions.
WRKY‐type transcription factors are involved in multiple aspects of plant growth and development. Their roles in abiotic stress tolerance are largely unknown especially in crops. Here, we find that TaWRKY2 and TaWRKY19 from wheat play differential roles in abiotic stress tolerance through activation of different downstream genes.
Rapid urbanization has considerably altered carbon biogeochemical cycle and river hydrology. However, the influences of urban land use and urban-induced nutrient increase on dissolved organic matter ...(DOM) characteristics are poorly understood. Here we hypothesize that the alterations significantly change sources and levels of DOM in river systems that drain the urban areas. To test the hypothesis, we investigated DOM in headwater rivers with varied urban intensities in the Three Gorges Reservoir Area (TGRA), China, through field sampling conducted in the dry and wet seasons. We found positive relationships of urban land (%Urban) with DOC concentration and chromophoric DOM (CDOM) absorption coefficients a254, a280 and a350, as well as fluorescence index (FI370), indicating the significantly increased levels of DOM and autochthonous sources along an urbanization gradient. A stepwise regression analysis demonstrated that occurrences of DOC and CDOM can be predicted by %Urban, while increasing autochthonous source is predictable by the increase in riverine nitrogen. Moreover, a254, a280 and FI370 values showed distinct seasonal variations, with significantly higher CDOM concentration in the wet season and with much higher autochthonous signal in the dry season with high nitrogen loading. Based on the findings, we conclude that urbanization influences occurrences and sources of DOM, with increasing urbanization making an important and direct contribution to DOM, and an indirect effect of urban induced nutrient enrichment, i.e., enhanced nutrient loadings increase autochthonous DOM production in rivers.
•Urbanization largely enhances levels of DOC, CDOM, nutrients and biological sources.•DOC, CDOM and FI370 are positively related to of nutrient concentrations.•DOC and CDOM are predicted well by urban land, FI370 is explained by nutrient level.•CDOM abundance is higher in wet season, autochthonous DOM is higher in dry season.
Sources and quality of dissolved organic matter (DOM) in streams may be largely controlled by the landscape and season. In this study, we attempted to answer three critical questions: 1) Do land ...use/land cover (LULC) types affect DOM characteristics? 2) Is there a seasonal fluctuation in DOM components? 3) How do DOM quality and LULC types influence aqueous carbon dioxide partial pressure (pCO2). To achieve this, we investigated the fluorescence characteristics of DOM and its implication for pCO2 in three streams draining land with different urban intensities under distinctive dry and wet seasons. Four fluorescence components were identified, including two terrestrial humic-like components, one protein-like component and one microbial humic-like component. We found a significant positive relationship of the maximum fluorescence intensity (Fmax) of the four components and fluorescence index (FI370) with urbanization intensity in both the dry and wet seasons. The mean Fmax, biological index (BIX) and FI370 all exhibited an increasing trend from upstream to downstream in the stream with highest proportions of urban and cropland. The fluorescence characteristics were negatively related to proportion of forested land in the both seasons. The terrestrial humic-like DOM was dominating in the studied streams. Moreover, the seasonality altered the DOM composition, with protein-like component emerging only in stream waters during the dry season, while microbial humic-like component exclusively occurred during the wet season. pCO2 values were positively related to terrestrial humic-like and biological protein-like components, and urban land. The dry season had much higher pCO2 than the wet season. Results from the Partial Least Squares Path (PLS-PM) models further indicated that LULC types were important in mediating fluorescence DOM whilst pCO2 was more sensitive to the direct effect from FDOM dynamics. We conclude that DOM source and quality in streams are reflective to LULC and climate seasonality, and are good indicators of pCO2 via source tracer and quality of fluorescence components.
•Urban land significantly increases levels of endogenous and exogenous DOM, and pCO2.•Elevated forest land decreases the terrestrial and autochthonous DOM, and pCO2.•Protein-like DOM occurs in the dry season while microbial DOM emerges in wet season.•Higher protein-like DOM and FI370 in dry season indicates increasing stream DOM process.•DOM is a good indicator of pCO2 via source tracer and fluorescence component quality.
Dissolved organic matter (DOM) is a diverse and highly complex mixture of organic macromolecules, and thus plays a central role in aquatic ecosystems. However, responses of components and sources of ...DOM to hydrological processes and trophic levels (nutrient stoichiometric ratios) are poorly understood, particularly in monsoonal headwater streams of Asia that are vulnerable to catchment physical characteristics. In this study, the excitation - emission matrix florescence spectroscopy coupled with parallel factor analysis (EEM-PARAFAC) was used to explore the DOM characters in a headwater stream, where seasonal rainfalls and nutrient levels vary largely. The EEM-PARAFAC modelling identified one autochthonous protein-like fluorescence substance (C1) and two allochthonous fulvic- and humic-like fluorescence compounds (C2 and C3). The allochthonous compounds dominated the overall DOM signal in the headwaters. The hydrological seasonality coupled with nutrients was key in modulating headwater DOM sources and components. Seasonal rainfall events contributed more allochthonous terrestrial-derived DOM flushing into river waters, resulting in higher fulvic- and humic-like organic matter (C2 + C3) in the wet season. In the dry season, longer water residence time accompanying with higher C:P stoichiometric ratio was responsible for higher autochthonous microbial- and plant-derived DOM (tryptophan and tyrosine fractions), also reflected by higher C1, biological index (BIX) and freshness index (β:α). In-stream microbial metabolism of labile DOM fractions largely contributed to autochthonous DOM and partial pressure CO2 increase in the headwater stream. Our findings indicate that quality and quantity of DOM in headwater streams play a crucial role in downstream carbon cycle. Furthermore, the evidence combined from PARAFAC components, pCO2 and spectral slope clearly highlights the importance of microbial metabolism of carbon in lotic systems, especially during a dry season with increased residence time.
One autochthonous protein-like fluorescence substance (C1) and two allochthonous fulvic- and humic-like fluorescence compounds (C2 and C3). The evidence combined from PARAFAC components, pCO2 values, and spectral slope highlights the importance of microbial metabolism in stream carbon dynamics. Display omitted
•Hydrological seasonality and nutrients control DOM characterization in headwaters•One protein- and two fluvic and humic-like fluorescence components are identified.•Allochthonous fulvic/humic-like components are dominant DOM in headwater streams of a monsoonal region.•BIX and β:α are much higher during dry seasons, while HIX is higher during wet seasons.•Wet season contributes more terrestrial-derived DOM flushing into headwater streams.
Urban lakes are hotspots of methane (CH4) emissions. Yet, actual field measurements of CH4 in these lakes are rather limited and our understanding of CH4 response to urban lake eutrophication is ...still incomplete. In this study, we measured dissolved CH4 concentrations and quantified CH4 diffusion from four urban lakes in subtropical China during wet and dry seasons. We found that these lakes were constantly CH4-saturated, contributing the greenhouse gas (GHG) to the atmosphere. Nutrient enrichment significantly increased CH4 concentrations and diffusive fluxes. Average CH4 flux rate in the highly-eutrophic lake zones (4.18 ± 7.68 mmol m−2 d−1) was significantly higher than those in the mesotrophic (0.19 ± 0.18 mmol m−2 d−1) and lightly/moderately-eutrophic zones (0.72 ± 2.22 mmol m−2 d−1). Seasonally, CH4 concentrations and fluxes were significantly higher in the wet season than in the dry season in the mesotrophic and the lightly/moderately-eutrophic lake zones, but an inverse pattern existed in the highly-eutrophic lake zones. CH4 concentrations and fluxes increased with elevated levels of nitrogen, phosphorus and dissolved organic carbon (DOC). The accumulation of nutrients provided autochthonous substrate for methanogenesis, indicated by a negative correlation between CH4 and the C:N ratio. Ammonium-nitrogen (NH4+-N) was the best predictor for spatial fluctuation of CH4 concentrations and diffusive fluxes in the mesotrophic and the lightly/moderately-eutrophic lake zones, while total nitrogen (TN) and total phosphorus (TP) levels showed the highest predictability in the highly-eutrophic lake zones. Based on the findings, we conclude that nutrient enrichment in urban lakes can largely increase CH4 diffusion, and that urban sewage inflow is a key concern for eutrophication boosting CH4 production and diffusive emission. Furthermore, our study reveals that small urban lakes may be an important missing source of GHG emissions in the global C accounting, and that the ratio of littoral-to-pelagic zones can be important for predicting lake-scale estimation of CH4 emission.
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•CH4 diffusion in highly-eutrophic zones is 22 times higher than in mesotrophic zones.•Wet season has an overall higher CH4 concentration and diffusive flux than dry season.•Predictors of water quality parameters for CH4 are linked to trophic state.•Ratio of littoral-to-pelagic zones is useful for predicting lake-scale CH4 emissions.
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•Distributed hydrological modeling platform integrating wetland modules projected future hydrological processes.•Increasing precipitation extremes will lead to a higher flood risk ...with the increase of warming levels.•Wetlands overall suppress future flood duration, mean flow, volume and peak under future climate change.•Wetland mitigation function is limited to small floods and will be less efficient with the increase of flood magnitude.
It is common to conceptualize wetlands as a nature-based flood defense for improving basin resilience to climate change. Yet, such a solution is often ignored when projecting or assessing river flood risk under future climate change. To fill this gap, we apply a hydrological modeling platform integrating wetland modules to a 297,000-km2 large river basin in Northeast China under different climate change scenarios. The overarching goal of this study is to predict future precipitation extremes and flood events, and to explore whether and to what extent wetlands can effectively mitigate the risk of future flood at the basin scale. We first assessed the trend in future precipitation extremes extracted from multi-global climate models (GCMs) and found that the future precipitation extremes will increase both under RCP4.5 and RCP 8.5 scenarios. The increasing precipitation extremes, therefore, are projected to bring about higher flood risks with the increase in warming levels. Wetlands can suppress flood duration, mean flow, volume, and peak by 1.9–10.2%, 4.6–7.1%, 8.7–15.7% and 12.5–14.1% under future climate change in this large river basin, respectively. Our study found that wetlands can attenuate the risk of floods with a 2- and 5-year return period to a great extent. However, the wetland mitigation function is limited to floods with a 10-, 20-, and 50- return, and even failed to extreme floods with a 100- and 200-year return. These findings imply that future precipitation extremes will cause flood risks in this large river basin that cannot be mitigated by its wetlands, and substantial wetland restoration is needed to enhance the capacity of their service in order to improve the basin’s resilience to future flood risks.
•A 3.5 °C warming of lake has marginal effect on dissolved CO2 and CH4 concentrations.•Monthly temperature and nutrient changes drive seasonal lake water carbon.•The dependence of CO2 and CH4 on ...temperature and nutrients is different.•The temperature threshold affecting aqueous CO2 is likely to be around 9 °C.
Shallow lake ecosystems are highly sensitive to temperature fluctuation because of their high water surface-to-volume ratios. Shallow lakes have been increasingly identified as a hotspot of CO2 and CH4 emissions, but their response to temperature variation remains unclear. Here, we report from a 5-month outdoor mesocosm experiment where we investigated the impacts of a projected 3.5 °C future warming and monthly temperature changes on lake CO2 and CH4, as well as the key drivers affecting the lake carbon cycling. Our results show that CO2 and CH4 concentrations had a significantly positive correlation with monthly temperatures. CH4 concentration was primarily regulated by monthly temperature, while nutrients effects on CO2 concentration overrode climate warming and temporal temperature changes. These findings imply the varied roles that temperature and nutrient levels can play on CO2 and CH4 dynamics in shallow lake systems. The relationship between temperature and CO2 concentration was nonlinear, showing a threshold of approximately 9 °C, at which CO2 concentration could be strongly modified by nutrient level in the lake systems. Understanding this complex relationship between temperature with CO2 and CH4 concentrations in shallow lakes is crucial for effective lake management and efficient control of greenhouse gases (GHGs) emissions.
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