Soil nitrogen (N) leaching is recognized to have negative effects on the environment. There is a lack of studies on different simultaneously occurring drivers of environmental change, including changing rainfall and N deposition, on soil N leaching. In this study, a two factorial field experiment was conducted in a Korean pine forest with the following four treatments: 30% of throughfall reduction (TR), 50 kg N ha⁻¹ yr⁻¹ of N addition (N+), throughfall reduction plus N addition (TRN+) and natural forest (CK). The zero-tension pan lysimeter method was used to assess the response of soil N leaching loss to manipulated N addition and throughfall reduction. The results showed that the soil N leaching loss in natural forest was 5.0 ± 0.4 kg N ha⁻¹yr⁻¹, of which dissolved organic nitrogen (DON) accounted for 48%. Compared to natural forest, six years of N addition (NH₄NO₃, 50 kg N ha⁻¹ year⁻¹) significantly (P < 0.05) increased soil N leaching losses by 122%, especially in the form of NO₃⁻; a 30% reduction in throughfall slightly decreased N leaching losses by 23%; in combination, N addition and throughfall reduction increased N leaching losses by 48%. There was a strong interaction between N addition and throughfall reduction, which decreased N leaching loss by approximately 2.5 kg N ha⁻¹ yr⁻¹. Our results indicated that drought would diminish the enhancing effect of N deposition on soil N leaching. These findings highlight the importance of incorporating both N deposition and precipitation and their impacts on soil N leaching into future N budget assessments of forest ecosystems under global environmental change.

Surface water is a vital and sometimes stressed resource in the U.S. The quantity of this resource is threatened by population shifts and growth concurrently with climate change intensification. Additionally, growing population centers can impact water quality by discharging treated wastewater effluent, which is typically of lower quality than its receiving surface waters. Depending on baseflow and environmental factors, this could decrease water quality. From a previous model prepared in our lab, this study can improve the understanding of water resource quality and quantity, surface water availability for the contiguous U.S. was estimated for each USGS Hydrologic Unit Code (HUC) during 2015. The Mississippi River generally served as a dividing line for surface water availability, with five of the six regions with very low water availability (<24,000 LD⁻¹Km⁻²) residing in the west. These same areas also experience more drought as well as more severe droughts than regions in the east. In regions with lower surface water flows, their water quality is more susceptible to the influence of wastewater effluent discharges, especially near large and growing population centers like San Antonio, Texas. A prediction model was established for this city, which found that from 2009 to 2017 wastewater effluent increased by 1.8%. As cities grow, especially in the Southwest and Western U.S. together with intensified climate change, surface water quantity and quality become more crucial to sustainability. This study shows where surface water availability is already an issue and provides a model to estimate, as well as project, wastewater effluent flows into surface water bodies.

Atmospheric pollution could significantly alter tree growth independently and synergistically with meteorological conditions. North China offers a natural experiment for studying how plant growth responds to air pollution under different meteorological conditions, where rapid economic growth has led to severe air pollution and climate changes increase drought stress. Using a single aspen clone (Populus euramericana Neva.) as a ‘phytometer’, we conducted three experiments to monitor aspen leaf photosynthesis and stem growth during in situ exposure to atmospheric pollutants along the urban-rural gradient around Beijing. We used stepwise model selection to select the best multiple linear model, and we used binned regression to estimate the effects of air pollutants, atmospheric moisture stress and their interactions on aspen leaf photosynthesis and growth. Our results indicated that ozone (O₃) and vapor pressure deficit (VPD) inhibited leaf photosynthesis and stem growth. The interactive effect of O₃ and VPD resulted in a synergistic response: as the concentration of O₃ increased, the negative impact of VPD on leaf photosynthesis and stem growth became more severe. We also found that nitrogen (N) deposition had a positive effect on stem growth, which may have been caused by an increase in canopy N uptake, although this hypothesis needs to be confirmed by further studies. The positive impact of aerosol loading may be due to diffuse radiation fertilization effects. Given the decline in aerosols and N deposition amidst increases in O₃ concentration and drought risk, the negative effects of atmospheric pollution on tree growth may be aggravated in North China. In addition, the interaction between O₃ and VPD may lead to a further reduction in ecosystem productivity.

Ten surface sediments collected from Joanes River, Bahia, Brazil in rainy and drought periods in 2019 were evaluated according to the enrichment factor (EF), potential ecological risk index (RI), potential contamination index (PCI), pollution load index (PLI), and index of geoaccumulation (Igₑₒ). Initially the dry sediment was subjected to granulometric analysis and determination of the concentration of organic matter. Then, the samples were digested in HNO₃ and analyzed by Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) to determine the metals cadmium (Cd), copper (Cu), chromium (Cr), nickel (Ni), lead (Pb) and zinc (Zn). Zn and Cu were classified in that order as the most contaminated elements in most sediment. Comparison of the total metal concentrations with the threshold (TELs) and probable (PELs) effect levels in sediment quality guidelines suggested a more worrisome situation for Zn (648.83–1415.90 μg g⁻¹; PELZₙ = 315 μg g⁻¹), of which concentrations were occasionally associated with adverse biological effects in four sediments, followed by Cu in five sediments during dry and rainy periods; while adverse effects were rarely associated with Cd, Cr, Ni, and Pb. In another evaluation, Cd, Cu, Cr, and Zn could be considered the most dangerous in the entire river, as they were classified in the high levels of contamination by the PCI, associated with serious adverse effects in most samples. In an assessment regarding the ecological risks in the study environment, the sediment samples remained below the limit established by the risk index (IR). The Zn presented moderately severe enrichment (6.78–11.83) in all the collection stations in the dry and rainy periods, followed by the Cd that presented moderate enrichment (2.23–4.17), whose values exceeded almost 1000 times the background at one site. Through the PCA it was possible to evidence the existing correlation between metals, organic matter, and silt and clay fraction. The results obtained in the PCA represented more than 80% of the variance between the data. The environmental risk assessment revealed a significant increase in the risk associated with metals during the rainy season. This is probably due to the greater supply of organic matter from the leaching of the margins.

During drier periods estuarine salinization can stimulate the colonization of marine organisms and further bioinvasion, therefore, may cause future ecological change. In this sense, we applied the Rapid Assessment Surveys (RAS) on natural and artificial hard substrates during the most intense drought period (between 2014 and 2016) since 1950, in a tropical estuary in Eastern Brazil. Through the estuary salinization the ascidian Didemnum psammatodes overgrow the dominant native taxa; this dominance taxa shift provided suitable habitat favorable for invasion of Ophiothela mirabilis across the estuary. Even the invasion starts on artificial substrates, the higher resilience of natural substrates were not enough to enable the establishment of invasive species. This baseline is the first evidence of bioinvasion influenced by climate change drought periods in tropical estuaries in South America, which is a great advance for the development of management strategies to mitigate this and future climate change scenarios.

In this study, the performance of Datura stramonium, an invasive weed of soybean and solanaceous crops, was examined under different elements of climate change. Experiments conducted in CO₂ chambers at ambient CO₂ (400 ppm) and elevated CO₂ (700 ppm) levels under both well-watered and drought conditions exhibited the fertilization effect of elevated CO₂. This was, however, limited by drought. Clearly, growth of D. stramonium will be significantly enhanced by enriched atmospheric CO₂ concentration under well-watered conditions, producing taller plants with greater biomass and higher seed output. Glasshouse experiments were conducted to evaluate the effect of different soil moisture regimes (100%, 75%, 50% and 25% water-holding capacity (WHC)) on the growth and fecundity of D. stramonium. Plants grown in 75% WHC had the highest plant height (15.24 cm) and shoot diameter (4.25 mm). The lowest leaf area (305.91 mm²), fresh weight (14.48 g) and dry weight (4.45 g) were observed in 25% WHC conditions. The ability of D. stramonium plants to grow and complete their life cycle with high seed output, even under limited water availability, shows the weedy nature of this species which is well adapted to survive future inhospitable climatic conditions. Radiant heat treatment on the plants indicated that temperatures of 120 °C and above for more than 180 s were enough to kill the plants, suggesting that thermal weeding or wildfires will be adequate to act as a circuit breaker on the D. stramonium invasion cycle, thus allowing other control measures to be engaged for greater control.

Microbiological, physical, chemical, cytotoxic, and genotoxic analyses of waters from ten tubular wells intended for irrigation of a community garden complex in the state of Piaui, northeastern Brazil, were carried out in two periods of 2018 (rainy and drought). All wells in both periods were contaminated with total coliforms, and wells P1, P3, P5, and P10 also had fecal coliforms. The waters, in the two collections performed, presented low concentration of dissolved oxygen, and nitrate and chlorine concentrations higher than allowed by law. Water from P1, P3, P5, and P10 were cytotoxic to root meristem cells of A. cepa in the two periods studied. However, no water sample was genotoxic to root meristems. The results show that the analyzed waters are contaminated with untreated effluents as well as with pesticides. Such conditions are pointed out because the rivers near these wells are degraded by human activities, and the gardens where the wells are found have ditches, sinks, and black cesspools for the disposal of sewage. In view of this, the intervention of the State Government in these places is necessary, since the evaluated wells irrigate community gardens in overcrowded poor neighborhoods, and from there comes part of the food of their residents. Another activity for the government is to put in place management plans for the restoration of rivers and the implementation of public sanitation in the neighborhoods where the wells are located.

Climate warming greatly affects the frequency and intensity of flash droughts, which can cause huge damage to agriculture. It is important to understand the changing rules of future flash droughts and take precautionary measures in advance. Thus, we focused on the flash drought characteristic of the Jinghe River basin using variable infiltration capacity (VIC) model and four-model ensemble in the two representative concentration pathway scenarios. Four-model ensemble mean can well capture hydrological changes in the reference period. The heat wave flash drought (HWFD) and the precipitation deficit flash drought (PDFD) mainly occur in the northern during reference period. The HWFD and PDFD have shown a linear growth trend in the future and both shown higher growth rates in the RCP8.5 scenario. The frequency of occurrence (FOC) increments of flash droughts were relatively high in the southern Jinghe River basin. And the HWFD and the PDFD mainly occurred in May–September. Further results indicate that the contribution of the maximum temperature to HWFD was the biggest (greater than 0.7), followed by evapotranspiration (ET) and soil moisture (SM). The contribution of maximum temperature to PDFD was the biggest (greater than 0.5), followed by precipitation and ET. Global warming in the twenty-first century is likely to lead to intensification of flash droughts. Therefore, measures and suggestions were proposed to effectively respond to flash droughts in our study.

Several studies were carried out and drought coexistence technologies were developed to deal with the problem of drought in semiarid regions, such as the construction of underground dams, which became a tool for rural development, mainly for family agriculture. However, there are still scarce informations regarding technical studies on the water security level of underground dams, especially about trace metal contamination due to the use and agricultural occupation of the soils downstream of the dams. In this work, the level of contamination of trace metals in waters of underground dams, during two hydrological years, was evaluated around of the sub-basin of the Cobras river, in the Rio Grande do Norte state, Brazil. The analysis of the results indicated that the water samples stored in the Alexandre and Ginaldo underground dams are within the permitted drinking patterns and did not suffer, on the other hand, any alteration in their quality that requires treatment for human consumption, fitting into Class 1. Most of the samples from the waters of the Boa Vista and Ademar dams are above the maximum allowable value for iron (Fe), lead (Pb), chromium (Cr), and nickel (Ni), requiring a differentiated treatment for human consumption, and can be classified as Class 2. The probable contamination of the waters stored in the underground dams may be of geological origin, since the largest accumulation of trace metals occurred in the lower area of the river course greater drained area, leading to believe that the metals come from the rock weathering that make up the geological framework of the region.

Rivers play an irreplaceable role in nature and human society but are the most vulnerable ecosystem in the world to multiple environmental stressors. However, the global-scale research status and the distribution patterns of major stressors in large rivers remain unclear. This study analysed research publications (12,807 documents from 1900 to 2019) related to six large rivers with continental representativeness to tackle these knowledge gaps. The results showed that the total outputs have grown rapidly over the study period, particularly since the 1990s. Consistent with the varied environmental characteristics and problems among the rivers, the research outputs and focuses demonstrated clear differences, which could further be attributed to geographical location, journal preferences and the economic strength of the country in which the river is located. Overall, climate change was the most frequently and widely considered environmental stressor in large rivers. Regardless of climate change, species diversity and hydropower development were widely addressed in the Amazon, Congo and Mekong river basins. Water pollution was the main stressor studied in the Rhine River and Mississippi River, while agricultural irrigation and drought were the most frequently addressed research subjects in the Murray-Darling River. This study provides a comprehensive understanding of the research status and stressor distribution in large global rivers, highlighting the relationship between river research and geographical regions, pointing out future research directions and providing management guidance for large rivers.