Summer Water Research Articles

Fishery Resource Evaluation with Hydroacoustic and Remote Sensing in Yangjiang Coastal Waters in Summer

Yangjiang coastal waters provide vital spawning grounds, feeding grounds, and nursery areas for many commercial fish species. It is important to understand the spatial distribution of fish for the management, development, and protection of fishery resources. In this study, an acoustic survey was conducted from 29 July to 5 June 2021. Meanwhile, remote sensing data were collected, including sea surface temperature (SST), chlorophyll concentration (Chla), sea surface salinity (SSS), and sea surface temperature anomaly (SSTA). The spatial distribution of density and biomass of fish was analyzed based on acoustic survey data using the geostatistical method. Combining with remote sensing data, we explored the relation between fish density and the environment based on the GAMs model. The results showed that fish are mainly small individuals. The horizontal distri-bution of fish density had a characteristic of high nearshore and low offshore. In the vertical direc-tion, fish are mainly distributed in surface-middle layers in shallow waters (<10 m) and in middle-bottom layers in deeper waters (>10 m), respectively. The deviance explained in the optimal GAM model was 59.2%. SST, Chla, SSS, and longitude were significant factors influencing fish density distribu-tion with a contribution of 35.3%, 11.8%, 6.5%, and 5.6%, respectively. This study can pro-vide a scientific foundation and data support for rational developing and protecting fishery re-sources in Yangjiang coastal waters.

Using a non-invasive multiple-method approach to characterize rock glaciers in the periglacial critical zone: An example from the San Juan Mountains, Colorado

Anthropogenic climate change threatens water storage and supply in the periglacial critical zone. Rock glaciers are widely distributed alpine aquifers with slower response to temperature increases, that provide the summer water flow of many alpine streams. Knowing the extent and makeup of rock glaciers is necessary to evaluate their potential for water supply. We used non-invasive methods, integrating geological, geomorphological, meteorological, and geophysical information to characterize the internal structure and hydrology of the Upper Camp Bird rock glacier (UCBRG) located on level 3 of Camp Bird Mine in Ouray, Colorado, and assessed the applicability of two electromagnetic induction systems in this highly heterogeneous landform with a history of anthropogenic activity. The time-domain (G-TEM™) system achieved deep subsurface penetration (~100 m) and realistic modeling of the internal structure of the UCBRG: a shell of volcanic rock fragments (<3 m thick; 1–100 Ohm-m), a meltwater component (102–103 Ohm-m), located between 50 and 100 m near the toe (subpermafrost flow), and 1–30 m in the soundings farthest from the toe (suprapermafrost flow within the active layer), and a frozen component (permafrost 50–80 m thick; 103–106 Ohm-m). The frequency-domain system, however, was highly susceptible to local environmental conditions, including anthropogenic objects (i.e., mine carts, lamp posts, tunnel tracks, etc.) and was unable to resolve UCBRG's internal makeup. The non-invasive methodology and general conceptual framework presented here can be used to characterize other alpine aquifers, contributing to the quantification of global water resources, and highlighting the importance of preserving rock glaciers as storage for critical water supply in the future.

Multi-year trends and interannual variation in ecosystem resource use efficiencies in a young mixedwood plantation in northern China

Understanding the long-term trends and interannual variability in ecosystem resource use efficiencies (RUEs) and their controlling factors is central to the prediction of ecosystem response to climate change. However, knowledge in this area, particularly as it pertains to young urban plantations, remains largely absent. In this study, we used continuous eddy covariance and site-specific climatic data collected from a 12-year-old mixedwood plantation in Beijing, China, to assess (i) long-term trends, (ii) interannual variability, and (iii) key controlling factors of RUEs with respect to plantation use of carbon (i.e., CUE), water (WUE) and light (LUE). On average, annual CUE and WUE over the 2012–2020 growing seasons increased by about 5.2 and 7.6%. Trends in RUEs corresponded with increases in normalized difference vegetation index (NDVI) when the plantation transitioned from a carbon source to a sink. Analysis of controlling factors indicated that RUEs were regulated by NDVI and other environmental factors at varying degrees dependent on season. Interannual variability in (i) CUE was largely controlled by spring soil temperature, (ii) WUE by summer water vapor pressure deficit and spring soil water content (SWC), and (iii) LUE by photosynthetically active radiation, summer SWC and spring air temperature. Relative seasonal changes in paired RUEs were positively correlated, with soil water availability being the most limiting. Long-term summer drought was shown to evoke severe and persistent decline in same-year RUEs. Ample mid-summer rainfall lessened the impact of early spring drought on plantation performance. Our results emphasized the need to account for the combined effects of climatic controls and canopy-physiological characteristics in the management of young plantations.

Physiological strategies for handling summer water stress differ among co-existing species and between juvenile and mature trees

Determining tree response to climate stress is critical for predicting changes in forest carbon dynamics as well as tree mortality. In temperate deciduous forests, describing this response is complicated by the complex diversity of leaf and wood characteristics among co-existing species. Furthermore, because of the inherent logistical limitations of measuring mature forest trees, many carbon models and stress-response studies are informed by physiological data collected from juvenile trees (seedlings or saplings). However, the extent to which juvenile and mature trees differ in their physiological responses to water stress is not well documented under natural conditions. The majority of carbon sequestered in a forest is in mature trees; therefore, direct canopy measurements comparing responses to climate in juvenile and mature trees would allow us to more accurately predict changes in ecosystem carbon uptake. Here, we present data describing the physiological responses to summer water stress in juvenile trees of six temperate deciduous species. Our results indicate that species exhibited variation and plasticity in stress hydraulic parameters yet maintained similar rates of carbon uptake. We demonstrate how integrative photosynthetic parameters, such as photosynthetic capacity and quantum efficiency of photosystem II, are beneficial for wholistically displaying physiological responses at the leaf level. We further compared seasonal patterns of leaf water potential during decreasing soil water availability between the juvenile trees and co-existing mature trees of the same species. Our data reveal that while some species remain static in their hydraulic behavior from the juvenile to adult stage, other species are dynamic between life stages. Models, as well as experimental studies examining tree response to stressors, should plan for plasticity in physiological parameters among co-existing species, and should further allow variability between life stages for particular species. The capacity to effectively inform models from data collected in mature trees will inevitably lead to improved predictions of tree mortality and forest carbon trajectories.

КЛИМАТИЧЕСКИЕ ИЗМЕНЕНИЯ ГИДРОЛОГИЧЕСКИХ ХАРАКТЕРИСТИК НА РЕКАХ РЕСПУБЛИКИ САХА (ЯКУТИЯ)

The paper deals with long-term series of different hydrological characteristics (average annual water discharges, maximum discharges throughout the year, maximum discharges during spring floods and rain floods, spring flood runoff layers, minimum summer and winter water discharges) on the rivers of the Republic of Sakha (Yakutia) and their approximation by models of the non-stationary average (the linear trend and the stepwise change model). It has been found that there are practically no effective non-stationary models for the maximum water discharges, but there are such models for flood layers and for average annual and minimum water discharges, which increased mainly in the late 20th and early 21st centuries due to the possible additional inflow of water from the thawed permafrost. The number of effective non-stationary average models increases from 30% of all cases for flood layers to 50–60% for average annual and minimum summer water discharges, and almost to 100% for minimum winter water discharges. Estimation of the stationarity of the mean values and variances by statistical criteria when dividing the series of stepwise changes by year confirmed the nonstationarity of the mean values for all a priori established nonstationary models and, in some cases, the nonstationarity of the variances. The largest increase in average values up to 100% takes place in the minimum winter water discharges, up to 70–80% – in the minimum summer water discharges, and up to 40–50% – in the average annual water discharges; a change in average values up to 20% cannot be considered statistically significant and reliably determined. Relative to natural variability, the excess is up to 1.5–1.6 standard deviation, but no more. Spatial distributions of the increase in river runoff characteristics in % relative to the previous stationary period and to natural variability are constructed. The greatest increase in the minimum winter water discharge takes place in the northern part of Yakutia. In recent years, water discharges have been observed even on freezing rivers. For the minimum summer and average annual water discharges, the largest increase occurs in the northeast and east.

Spatiotemporal changes of biogenic elements in the Changjiang River Estuary and adjacent waters in summer over the last decade

Spatiotemporal changes of biogenic elements in the Changjiang River Estuary and adjacent waters in summer over the last decade

Районы зимовок орлана-белохвоста на юге Казахстана

Районы зимовок орлана-белохвоста на юге Казахстана

ПОКАЗАТЕЛИ ФЛУКТУИРУЮЩЕЙ АСИММЕТРИИ СЕЙСМОСЕНСОРНЫХ КАНАЛОВ ГОЛОВЫ У ПЛОТВЫ RUTILUS RUTILUS (L.) ИЗ СРЕДНИХ РЕК УДМУРТИИ С РАЗНЫМ УРОВНЕМ ХИМИЧЕСКОГО ЗАГРЯЗНЕНИЯ

In the middle rivers of the Udmurt Republic, fish were caught near the sampling stations for the state environmental monitoring. The fluctuating asymmetry (FA) of the pore number of the seismosensory canals in the dermal head bones of the roach, Rutilus rutilus (L.), which prevailed in the catches, was estimated using osteological analysis. Its indicators in the roach individuals caught in the different river sections have been collated with the values of specific combinatorial water pollution index (SCWPI) of the examined sections and with the average concentrations of some pollutants in water in late spring and early summer for the several years preceding the years of catching. A statistically significant trend for the increase in the FA variance (Sas2), calculated on the basis of the total number of pores in the head seismosensory system of the roach, with the increase in the SCWPI and the content of some anions (chlorides, nitrites, nitrates) in the river water of its habitats has been identified. The highest (Sas2) was observed in the roach individuals caught in the Izh River dowstream from Izhevsk in the environment, severely polluted by municipal wastewater, while the lowest one was recorded in the Kilmez River, the least polluted by wastewaters. No significant relationships between the FA indicators in this fish species and the content of heavy metals or other pollutants in the middle rivers of Udmurtia have been revealed. These results are considered to be attributable to a decrease in stability of morphogenesis in the fish organisms that developed under non-optimal (stressful) hydrochemical conditions.

Positive effects of warming do not compensate growth reduction due to increased aridity in Mediterranean mixed forests

AbstractIncreased winter and early spring temperatures due to climate change can enhance forest productivity due to earlier growth onset in temperate regions. However, drought‐prone forests can be highly vulnerable to the combined effect of high summer temperatures and water stress. Understanding how water stress and rising temperatures along the growing season control tree growth in co‐occurring species with contrasting drought tolerances is key to project climate change effects on forest dynamics. Here, we evaluated the interactive effect of seasonal temperature and water availability on annual radial growth and climate–growth instability over six decades (1951–2015) in three pine species with contrasting drought tolerances (Pinus pinaster, Pinus nigra, and Pinus sylvestris). For this, we retrospectively observed radial tree growth using dendroecological methods and evaluated seasonal temperature and water availability effects by using linear mixed models. Early growing season temperature and water availability had a positive effect on tree growth, but the positive effect of late season temperature was modulated by water availability. Moving time‐window analyses revealed temporal instability in climate–growth relationships. Since the 1980s, pine species showed a higher growth sensitivity to both seasonal temperatures and annual water availability. Furthermore, growth reductions were more pronounced due to increased summer temperatures and reduced precipitation. Our results were similar for the three studied pine species despite their contrasting tolerance to drought. Overall, climate warming effects on pine growth are contingent upon water availability in Mediterranean continental forests. Synchronization among species, climate–growth instability, and negative growth trends suggests an increased vulnerability to drought of Mediterranean pine species in response to ongoing climate change.

Body size dictates physiological and behavioural responses to hypoxia and elevated water temperatures in Murray cod (Maccullochella peelii).

Increasing drought frequency and duration pose a significant threat to fish species in dryland river systems. As ectotherms, fish thermal and hypoxia tolerances directly determine the capacity of species to persist in these environments during low flow periods when water temperatures are high and waterbodies become highly stratified. Chronic thermal stress can compound the impacts of acute hypoxic events on fish resulting in significant fish mortality; however, it is not known if all size classes are equally susceptible, or if the allometric scaling of physiological processes means some size classes are disproportionately affected. We investigated the physiological responses of Murray cod (Maccullochella peelii) over a four-fold body size range (0.2-3000g) to acute changes in water temperature and oxygen concentration following 4 weeks of acclimation to representative spring (20°C) and summer (28°C) water temperatures. We recorded maximum thermal tolerance (CT max), oxygen limited thermal tolerance (PCTmax ), lowest tolerable oxygen level (as the oxygen level at which lose equilibrium; O2,LOE), gill ventilation rates and aerial surface respiration threshold, blood oxygen transport capacity and lactate accumulation. Acclimation to elevated water temperatures improved thermal and hypoxia tolerance metrics across all size classes. However, body size significantly affected thermal and hypoxia responses. Small M. peelii were significantly less hypoxia tolerant than larger individuals, while larger fish were significantly less thermal tolerant than smaller fish. Hypoxia constrained thermal tolerance in M. peelii, with both small and large fish disproportionally compromised relative to mid-sized fish. Our findings indicate that both very small/young (larvae, fry, fingerlings) and very large/older M. peelii in dryland rivers are at significant risk from the combined impacts of a warming and drying climate and water extraction. These data will inform policy decisions that serve to balance competing demands on precious freshwater resources.

Spring heat waves drive record western United States snow melt in 2021

Throughout the western US snow melted at an alarming rate in April 2021 and by May 1, hydrologic conditions were severely degraded with declining summer water supply forecasts compared to earlier in the winter. The objectives of this study are to (a) quantify the magnitude and climatological context of observed melt rates of snow water equivalent (SWE) and (b) underpin the hydrometeorological drivers during April 2021 based on atmospheric reanalysis and gridded meteorological data. Peak SWE indicated snow drought conditions were widespread (41% of stations between 5th and 20th percentile) but not necessarily extreme (only 9% of stations less than 5th percentile). Here, using observations from the Snow Telemetry (SNOTEL) network we found record 7 day snow melt rates (median of −99 mm; ±one standard deviation of 61 mm) occurred at 24% of SNOTEL sites and in all 11 Western states. Strong upper atmospheric ridging that began initially in the north Pacific with eastward propagation by mid-April to the Pacific Northwest Coast led to near-surface conditions across the western US conducive to rapid snow loss. One heat wave occurred inland across the Rockies the first week of April and then later in April, a second heat wave impacted the Cascades and northern California. We find that ripening of the snowpack by both record high surface solar radiation and air temperatures were factors in driving the rapid snow melt. Equatorial Pacific sea surface temperatures and the La Niña pattern that peaked in winter along with an eastward propagating and intensifying Madden–Julian Oscillation were likely responsible for driving the placement, strength, and progression of the north Pacific Ridge. This study documents the role of two extreme spring ‘sunny heat wave’ events on snowpack, and the cascading drought impacts which are anticipated to become more frequent in a warming world.

Effects of two categorically differing emergent wetland plants on evapotranspiration

AbstractAlthough wetlands are an important component of many landscapes, emergent plants have had variable impacts on wetland hydrology. In the present study, similar to what others have done with emergent plants, we investigated the impacts of black willow (Salix nigra Marshall) and Pennsylvania smartweed (Persicaria pensylvanica L.) on water loss from standing water relative to water loss with no emergent plants from 2018 to 2020. Pans were established with soil and standing water for three replications of five treatments: open water control, low population density black willow, high density black willow, low density smartweed, and high density smartweed. Each week during the growing season water levels, water temperature, leaf area index, and height were recorded. Pans were then refilled to the standard level. The assumption was that open water was just evaporation and the increase in water loss in the presence of plants was due to transpiration. Thus, we could partition water loss between evaporation and transpiration by calculating the difference between pans without plants and pans with plants. This difference is the transpiration by the plants. Water temperature was measured to check on any possible shading effect. Open water evaporation was lower than black willow and smartweed evapotranspiration. Mean increases in water use relative to the control were 37% for smartweed and 66% for black willow. These differences were even more dramatic when calculated for only the last 2 years. Smartweed increased water use by 40% and black willow by 92%. Because pans with plants had lower maximum daily water temperatures than those of the control in the summer, the increased water loss with plants was largely due to transpiration. Smartweed transpired more than willows. The willow root system and leaf area greatly increased after the first year, resulting in more water loss and lower summer water temperature. Low and high density treatments did not differ significantly for any metrics gathered, with few exceptions. This evapotranspiration information addresses wetland water balance questions and is useful for process‐based models.

Thermal stress gradient causes increasingly negative effects towards the range limit of an invasive mussel

Environmental filtering (EF), the abiotic exclusion of species, can have first order, direct effects with cascading consequences for population dynamics, especially at range edges where abiotic conditions are suboptimal. Abiotic stress gradients associated with EF may also drive indirect second order effects, including exacerbating the effects of competitors, disease, and parasites on marginal populations because of suboptimal physiological performance. We predicted a cascade of first and second order EF-associated effects on marginal populations of the invasive mussel Mytilus galloprovincialis, plus a third order effect of EF of increased epibiont load due to second order shell degradation by endoliths. Mussel populations on rocky shores were surveyed across 850 km of the south–southeast coast of South Africa, from the species' warm-edge range limit to sites in the centre of their distribution, to quantify second order (endolithic shell degradation) and third order (number of barnacle epibionts) EF-associated effects as a function of along-shore distance from the range edge. Inshore temperature data were interpolated from the literature. Using in situ temperature logger data, we calculated the effective shore level for several sites by determining the duration of immersion and emersion. Summer and winter inshore water temperatures were linked to distance from the mussel's warm range edge (our proxy for an EF-associated stress gradient), suggesting that seasonality in temperature contributes to first order effects. The gradient in thermal stress clearly affected densities, but its influence on mussel size, shell degradation, and epibiosis was weaker. Relationships among mussel size, shell degradation, and epibiosis were more robust. Larger, older mussels had more degraded shells and more epibionts, with endolithic damage facilitating epibiosis. EF associated with a gradient in thermal stress directly limits the distribution, abundance, and size structure of mussel populations, with important indirect second and third order effects of parasitic disease and epibiont load, respectively.

Degradation pathways for organic matter of terrestrial origin are widespread and expressed in Arctic Ocean microbiomes

BackgroundThe Arctic Ocean receives massive freshwater input and a correspondingly large amount of humic-rich organic matter of terrestrial origin. Global warming, permafrost melt, and a changing hydrological cycle will contribute to an intensification of terrestrial organic matter release to the Arctic Ocean. Although considered recalcitrant to degradation due to complex aromatic structures, humic substances can serve as substrate for microbial growth in terrestrial environments. However, the capacity of marine microbiomes to process aromatic-rich humic substances, and how this processing may contribute to carbon and nutrient cycling in a changing Arctic Ocean, is relatively unexplored. Here, we used a combination of metagenomics and metatranscriptomics to assess the prevalence and diversity of metabolic pathways and bacterial taxa involved in aromatic compound degradation in the salinity-stratified summer waters of the Canada Basin in the western Arctic Ocean.ResultsCommunity-scale meta-omics profiling revealed that 22 complete pathways for processing aromatic compounds were present and expressed in the Canada Basin, including those for aromatic ring fission and upstream funneling pathways to access diverse aromatic compounds of terrestrial origin. A phylogenetically diverse set of functional marker genes and transcripts were associated with fluorescent dissolved organic matter, a component of which is of terrestrial origin. Pathways were common throughout global ocean microbiomes but were more abundant in the Canada Basin. Genome-resolved analyses identified 12 clades of Alphaproteobacteria, including Rhodospirillales, as central contributors to aromatic compound processing. These genomes were mostly restricted in their biogeographical distribution to the Arctic Ocean and were enriched in aromatic compound processing genes compared to their closest relatives from other oceans.ConclusionOverall, the detection of a phylogenetically diverse set of genes and transcripts implicated in aromatic compound processing supports the view that Arctic Ocean microbiomes have the capacity to metabolize humic substances of terrestrial origin. In addition, the demonstration that bacterial genomes replete with aromatic compound degradation genes exhibit a limited distribution outside of the Arctic Ocean suggests that processing humic substances is an adaptive trait of the Arctic Ocean microbiome. Future increases in terrestrial organic matter input to the Arctic Ocean may increase the prominence of aromatic compound processing bacteria and their contribution to Arctic carbon and nutrient cycles.6hGoymMH-pRJKwnwbycG8JVideo

Distributions of Cisco (Coregonus artedi) in the upper Great Lakes in the mid-twentieth century, when populations were in decline.

The restoration of the once abundant Cisco (Coregonus artedi) is a management interest across the Laurentian Great Lakes. To inform the restoration, we (1) described historical distributions of Cisco and (2) explored whether non-indigenous Rainbow Smelt (Osmerus mordax) and Alewife (Alosa pseudoharengus) played a role in the decline of Cisco populations across the upper Great Lakes (i.e., Lakes Superior, Michigan, and Huron). Our source data were collected from fishery-independent surveys conducted by the U.S. Fish and Wildlife Service's research vessel R/V Cisco in 1952-1962. By analyzing data collected by gill-net surveys, we confirmed the importance of embayment and shallow-water habitats to Cisco. We found that Cisco was abundant in Whitefish Bay and Keweenaw Bay, Lake Superior, and in Green Bay, Lake Michigan, but we also found a sign of Cisco extirpation in Saginaw Bay, Lake Huron. Our results also showed that Ciscoes generally stayed in waters <80 m in bottom depth throughout the year. However, a substantial number of Ciscoes stayed in very deep waters (>150 m in bottom depth) in summer and fall in Lake Michigan, although we cannot exclude the possibility that these Ciscoes had hybridized with the other Coregonus species. By comparing complementary data collected from bottom-trawl surveys, we concluded that the spatiotemporal overlap between Rainbow Smelt and Cisco likely occurred across the upper Great Lakes throughout 1952-1962. These data were consistent with the hypothesis that Rainbow Smelt played a role in the decline of Cisco populations across the upper Great Lakes in the period. We also found that the spatiotemporal overlap between Alewife and Cisco likely occurred only in Saginaw Bay in fall 1956 and in Lake Michigan after 1960. Thus, any potential recovery of Cisco after the 1950s could have been inhibited by Alewife in Lakes Michigan and Huron.

Simultaneous invasion decouples zebra mussels and water clarity

Species invasions are a leading threat to ecosystems globally, but our understanding of interactions among multiple invasive species and their outcomes on ecosystem properties is undeveloped despite their significance to conservation and management. Here we studied a large lake in Minnesota, USA, that experienced a simultaneous surge in invasive zebra mussel and spiny water flea populations. A long-term (2000–2018) dataset offered a rare opportunity to assess whole-ecosystem shifts following the co-invasion. Within two years, the native crustacean zooplankton community declined abruptly in density and productivity (−93% and −91%, respectively). Summer phytoplankton abundance and water clarity remained stable across the time series, an unexpected outcome given the high density of zebra mussels in the lake. Observational data and modeling indicate that removal of native herbivorous zooplankton by the predatory spiny water flea reduced zooplankton grazing pressure enough to compensate new grazing losses due to zebra mussels, resulting in a zero net effect on phytoplankton abundance and water clarity despite a wholesale shift in secondary production from the pelagic to the benthic food web. This study reveals the extent of direct and indirect effects of two aquatic invaders on food-web processes that cancel shifts in water clarity, a highly valued ecosystem service.

Riverine CO2 variations in permafrost catchments of the Yangtze River source region: Hot spots and hot moments

Rivers and streams are pivotal modulators in regional and global carbon cycles, but riverine CO2 flux is still uncertain for permafrost watersheds. Here we present the seasonal CO2 partial pressure (pCO2) and CO2 emission flux (FCO2) of 8 rivers and streams in the Yangtze River source region (YRSR), which have high permafrost coverage and seasonally thawed active layer. The YRSR rivers and streams are generally supersaturated with CO2, although there are a few sites with CO2 undersaturation during spring. The small headwater streams are CO2 hot spots that show significantly higher pCO2 (52 % higher) and FCO2 (792 % higher) than larger rivers. Both pCO2 and FCO2 show distinct seasonality across the study sites. pCO2 and FCO2 peak in summer and exhibit much lower levels in autumn and spring, indicating that hot moments of riverine CO2 occur in summer. Seasonal pCO2 and FCO2 variations are jointly controlled by hydrology, active layer dynamics and associated processes. The warm summer causes active layer thaw and highly active soil respiration, which release a large quantity of soil carbon and increase the CO2 sources via strengthened hydrologic connectivity. The high rainfall and more thaw-released water in summer bring high discharge, which can increase the water velocity and gas exchange rate and thus CO2 emission flux. Most of the variances of seasonal FCO2 (95 %) can be explained by hydrology and active layer thaw depth. Nevertheless, the hydrological process and seasonally thawed active layer over Qinghai-Tibet Plateau (QTP) play crucial roles in riverine carbon export due to the summer monsoon-dominated climate in QTP. Our results suggest that full seasonal coverage of CO2 dynamics is essential to quantify the annual CO2 flux accurately. Changing climate and warming permafrost may alter the annual CO2 emission due to deeper flow paths, hydrology changes, and longer emission windows throughout the year.

A hybrid statistical-dynamical prediction model for summer precipitation in northwestern China based on NCEP CFSv2

As a typical arid/semi-arid area, summer rainfall in northwestern China (NWC) is critical for the ecological environment there. The NWC summer rainfall prediction using statistical and dynamical models shows very poor performance. The dynamical model NCEP CFSv2 shows very low prediction skill in NWC summer precipitation. NWC precipitation index (NWC PI) is defined as the regional mean summer precipitation over NWC. This study first investigates the soil moisture and SST (sea surface temperature) signals in the preceding months, and CFSv2 April predicted summer large-scale circulation anomalies significantly related with NWC PI during 1982–2016 (2011 missing). The April soil moisture in the upstream central Asia, and SST in the preceding winter over tropical Pacific, Atlantic and Indian Ocean are identified as predictor candidates in the observation. Besides, six April predicted large-scale circulation factors in CFSv2 are also hired. The potential model predictors are selected generally based on three criteria: where CFSv2 has significant prediction skill, and NWC PI is significantly correlated with the variable in both the observation and its counterpart in CFSv2 prediction. Hybrid models are then constructed based on different predictor combinations. The leave-one-out cross validation illustrates that the hybrid model using three predictors (April soil moisture in the upstream central Asia, April predicted zonal wind over the Maritime Continent, April predicted SLP over the Mediterranean Sea) presents best performance, with anomalies correlation coefficient–ACC of 0.65, percentage of the same sign–PERC 76.5%, relative error–RE 6.97%, and root mean square error–RMSE 0.344 mm/day for NWC PI. The April soil moisture in the upstream central Asia is linked with the summer water vapor flux over NWC, and April predicted zonal wind over the Maritime Continent is related with the large-scale circulation over NWC, while caution must be taken when April predicted SLP over the Mediterranean Sea is used as predictor of NWC PI.

A kinetic study of the photolysis of sulfamethoxazole with special emphasis on the photoisomer

The previously not studied photochemical degradation of sulfamethoxazole (SMX) to the isomer of SMX (ISO) was measured via a polychromatic (Xe) and a monochromatic (Hg) light source and accompanied by quantum chemical DFT calculations. In addition to the mathrm{p}K_mathrm{a} = ;7.0 pm 0.1 of ISO, tautomer-dependent properties such as the K_mathrm{OW} were measured and theoretically confirmed by DFT. The kinetics in solutions below and above the mathrm{p}K_mathrm{a} = 5.6 of SMX were studied for the available and quantifiable products SMX, ISO, 3-amino-5-methylisoxazole (AMI), 2-amino-5-methyloxazole (AMO), and sulfanilic acid (SUA). The quantum yields of the neutral (Phi _mathrm{N}) and anionic Phi _mathrm{A}) forms of SMX (Phi _mathrm{A} = 0.03 pm 0.001, Phi _mathrm{N} = 0.15 pm 0.01) and ISO (Phi _mathrm{A} = 0.05 pm 0.01 and Phi _mathrm{N} = 0.06 pm 0.02) were found to be wavelength-independent. In a competitive reaction to the formation of ISO from SMX, the degradation product TP271 is formed. Various proposed structures for TP271 described in the literature have been studied quantum mechanically and can be excluded for thermodynamic reasons. In real samples in a northern German surface water in summer 2021 mean concentrations of SMX were found in the range of 120 ng/L. In agreement with the pH-dependent yields, concentrations of ISO were low in the range of 8 ng/L.Graphical abstract

The strong activity of noctilucent clouds at middle latitudes in 2020

The 2020 summer season had more frequent than usual occurrences of noctilucent clouds (NLCs) in the Northern Hemisphere at middle latitudes (45–50°N), with the lowest latitude at which NLCs were seen being 34.1°N. In order to investigate a reason for this extraordinary NLC season, we have analyzed long-term Aura/MLS satellite data for all available summer periods from 2005 to 2021. Both Aura/MLS summer temperature and water vapor in the mesopause region, between about 79 and 89 km altitude, have been considered. There has been a decrease in the summer mesopause temperature between 2016 and 2020. At the same time, water vapor mixing ratio has significantly increased (by about 12–17%) in the zonal mean H2O value in the 2020 summer compared to 2017. There exists a positive linear trend in the H2O amount by about 5% between 2005 and 2021 at middle latitudes 45–50°N at 0.0046 hPa. A combination of lower mesopause temperature and water vapor mixing ratio maximum at middle latitudes is the main reason for frequent and widespread occurrences of NLCs seen around the globe at middle latitudes in the summer of 2020. The 24th solar cycle minimum can explain neither the H2O maximum nor NLC maximum in 2020.