Pronounced Temporal Variability Research Articles

A hybrid deep learning approach for streamflow prediction utilizing watershed memory and process-based modeling

Abstract Accurate streamflow prediction is essential for optimal water management and disaster preparedness. While data-driven methods’ performance often surpasses process-based models, concerns regarding their ‘black-box’ nature persist. Hybrid models, integrating domain knowledge and process modeling into a data-driven framework, offer enhanced streamflow prediction capabilities. This study investigated watershed memory and process modeling-based hybridizing approaches across diverse hydrological regimes – Korean and Ethiopian watersheds. Following watershed memory analysis, the Soil and Water Assessment Tool (SWAT) was calibrated using the recession constant and other relevant parameters. Three hybrid models, incorporating watershed memory and residual error, were developed and evaluated against standalone long short-term memory (LSTM) models. Hybrids outperformed the standalone LSTM across all watersheds. The memory-based approach exhibited superior and consistent performance across training, evaluation periods, and regions, achieving 17–66% Nash–Sutcliffe efficiency coefficient improvement. The residual error-based technique showed varying performance across regions. While hybrids improved extreme event predictions, particularly peak flows, all models struggled at low flow. Korean watersheds’ significant prediction improvements highlight the hybrid models’ effectiveness in regions with pronounced temporal hydrological variability. This study underscores the importance of selecting a specific hybrid approach based on the desired objectives rather than solely relying on statistical metrics that often reflect average performance.

Horizontal profiles of size-segregated particle number concentration and black carbon beside a major roadway

The distribution pattern of near-road air pollutants is important for addressing air pollution issues. In this study, size-segregated particle number concentration (PNC) and black carbon (BC) concentration were measured at different locations perpendicular to a major roadway in Shanghai, aiming to improve the understanding of distribution patterns of traffic-related air pollutants. Results suggest that, despite the high emission level of on-road traffic, PNC 0.3-1 (particle diameter in 0.3–1 μm) exhibited negligible concentration gradients (no variation trend) with increasing distance from the road. BC and PNC >1 (>1 μm, coarse particles) exhibited significant spatial gradients, showing a pronounced increase in concentration near the road. This is closely associated with the high spatial homogeneity of fine particles and the high spatial variability of BC and coarse particles. The influence zone of traffic on pollutants was increased in rush hours due to increased emission intensity and pollutants dispersed a longer distance downwind. Additionally, the horizontal profiles of pollutants can all be well characterized by exponential curves, despite the small spatial gradient of PNC 0.3-1 . The concentration gradient and fall-off range of pollutants increased with the particle size (in 0.3–25 μm). This study provides implications that fine particles (e.g., PNC 0.1-1 , PM 1 ) are poor tracers of traffic emissions, which could perform poorly in characterizing the behavior of traffic emissions in the road environment but are more related to regional and background components. Moreover, the evaluation of pollutant traceability before the field study could contribute to improved experimental efficiency and more satisfactory results. • Near-road PNC 0.3-1 showed negligible spatial gradients (poor tracer of traffic emissions). • PNC 0.3-1 suggested pronounced temporal variability. • Black carbon and PNC >1 showed high spatial variability. • Pollutant decay distance increased in rush hours. • Near-road pollutant profiles can be well described by exponential curves.

Temporal changes of the food web structure and function driven by changes in hydrological regimes and water quality in a large shallow lake

Assessing food web structural properties and energy fluxes under changing hydrological regimes and water quality reveals the temporal patterns of ecosystem dynamics in shallow lakes. Here, we studied northern China’s largest shallow lake (Lake Baiyangdian) using quantitative food web models for five representative years (1958, 1980, 1993, 2009, and 2019). We analyzed the temporal patterns of food web structure and function by combining a Bayesian isotope mixing model with a food web energetics model. We further examined the temporal changes of unweighted and weighted food web topological attributes. Lake Baiyangdian changed from a detritus-based into a phytoplankton-based food web based on the relative contributions of basal food sources and energy flux distributions. The trophic position of fingerlings, large omnivorous fish, and carnivorous fish decreased with increasing eutrophication. The highest energy fluxes were from detritus to zooplankton and mollusks in 1958, from detritus and phytoplankton to zooplankton in 1980, 1993, and 2009, and from phytoplankton to zooplankton and detritus to mollusks in 2019. The highest total energy flux was in 1993, followed by 2019, with the lowest value in 1958. Unweighted food web metrics showed similar patterns. We observed more pronounced temporal variability in the node- and link-weighted food web metrics than in the unweighted metrics. In addition, hydrological factors (threshold, duration, reversals between high, and low water levels), eutrophication, and some water quality factors (chemical oxygen demand, dissolved oxygen, and pH) played important roles in the temporal changes of food web dynamics in Lake Baiyangdian. Our findings demonstrate the importance of integrating unweighted and weighted indicators to holistically comprehend how highly aggregated food webs respond to changing hydrological regimes and water quality, thereby improving management and restoration of shallow lake ecosystems.

A new approach to processing and imaging multibeam water column echosounder data: Application to a complex methane seep on the southern Cascadia margin

Acoustic echosounding systems are increasingly used to image water-column backscatter in addition to mapping the seafloor. We have imaged an acoustic flare generated by methane bubbles emanating from a vent sourced at 1840 m water depth offshore northern California using a shipboard Kongsberg EM122. Data include five transits over the flare and approximately 11 h of continuous observation when the ship held station. Shipboard observations showed a strong flare splitting into multiple smaller, intermittent flares at a water depth of 800–1200 m and pronounced temporal variability. We introduce a new approach to processing the data in which we correct the backscatter data for ship motion and bin the data into voxels with dimensions of 20 m in X and Y and 40 m in Z for a transit over the flare and into vertical slices with dimensions of 15 m in X and Z and 4 min in time when the ship was stationary. The processed data indicate that the signal is dominated by bubbles emanating from a source region with a diameter of approximately 40 m located on the southern edge of what is likely a ring of sources with a diameter of approximately 600 m. When the ship was stationary, we were able to track an individual pulse rising at a rate of 8–10 m/min. Our results illustrate the limitations of monitoring temporal variation in gas flux using multibeam echosounders because of the trade-off between imaging the entire flare by averaging over tens of minutes to hours and observing a slice through the flare to capture short-lived pulses of gas expulsion. Nevertheless, because echosounders are widely available, they can continue to provide valuable data on the spatial and temporal distribution of gas emissions on continental margins that can be used to frame hypotheses and plan more comprehensive follow-up experiments.

Seasonality of gross ammonification and nitrification altered by precipitation in a semi-arid grassland of Northern China

Gross ammonification (GA) and gross nitrification (GN) are key regulators of the bioavailability of nitrogen (N) in terrestrial ecosystems. In arid and semi-arid grassland ecosystems, the impacts of precipitation change on in situ GA and GN and their seasonal variations are understudied. A manipulative experiment with five precipitation levels (−60%, −30%, unchanged ambient precipitation as control, +30%, +60% of ambient precipitation) was set up in May 2012. After a 2-year equilibration period, the 15N pool dilution technique was applied to determine GA and GN rates in surface soil (0–5 cm) within 8 sampling dates ranging from the onset to the end of the growing season. Pronounced temporal variability of GA and GN rates were observed with the highest GA and GN rates in the mid-growing season (August) and the lowest in the post-growing season (October). GA rates during the growing season were primarily controlled by precipitation and soil water availability, while this effect diminished at the onset and end of the growing season when the temperature dropped. In contrast, GN was predominately controlled by ammonium (NH4+) production through GA. In the peak-growing season, the +60% precipitation treatment enhanced GA and GN rates by up to 4-fold, while the −30% precipitation treatment marginally suppressed GA and GN rates. The −60% precipitation treatment suppressed GA and GN rates to below detection limits across the entire study period, suggesting that extreme and persistent droughts greatly inhibited N turnover in the surface soil, thereby forcing plants to mobilize and access nutrients from deeper soil layers. Our findings provide a season-specific mechanistic insight into precipitation impacts on topsoil gross N turnover and suggest that the N cycling represented in ecosystem models needs to consider a mechanism that allows a strong suppression of microbial functions under extreme droughts.

Influence of Local Sources and Meteorological Parameters on the Spatial and Temporal Distribution of Ultrafine Particles in Augsburg, Germany

Ultrafine particles (UFP; diameter less than 100 nm) are ubiquitous in urban air, and an acknowledged risk to human health. At the same time, little is known about the immission situation at typical urban sites such as high-traffic roads, residential areas with a high amount of solid fuels for home heating or commercial and industrial areas due to missing legal requirements for measurements of UFP. Therefore, UFP were measured and evaluated in the (sub-)urban background as well as on spots influenced by these various anthropogenic local sources in the city of Augsburg, Germany, for the year 2017. In particular, the spatial and temporal correlations of the UFP concentrations between the seven measurement sites, the quantification and valuation of the contribution of local emitters with regard to their diurnal, weekly and seasonal variations and the influence of meteorological conditions on the formation and dispersion of UFP were investigated. Our analysis results demonstrate that urban UFP concentrations show a pronounced temporal and spatial variability. The mean concentration level of UFP varies between below 8,000 ultrafine particles/cm3at the suburban background site and above 16,700 ultrafine particles/cm3at the measurement station located next to a busy street canyon. At this particularly traffic-exposed measurement station, maximum concentrations of over 50,000 ultrafine particles/cm3were measured. The additional UFP load caused by intensive traffic volume during evening rush hour in connection with the unfavourable exchange processes in the street canyon can be quantified to concentrations of 14,000 ultrafine particles/cm3on average (compared to the immission situation of the urban background). An aggravating effect is brought about by inversion weather conditions in connection with air-polluted easterly winds, low wind speeds, lack of precipitation and very low mixing layer heights, such as over Augsburg at the end of January 2017, and cause peak concentrations of UFP.

Nitrous oxide in the northern Gulf of Aqaba and the central Red Sea

Nitrous oxide (N2O) is a climate-relevant atmospheric trace gas. It is produced as an intermediate of the nitrogen cycle. The open and coastal oceans are major sources of atmospheric N2O. However, its oceanic distribution is still largely unknown. Here we present the first measurements of the water column distribution of N2O in the Gulf of Aqaba and the Red Sea. Samples for N2O depth profiles were collected at the time-series site Station A in the northern Gulf of Aqaba (June and September 2003, and February 2004) and at several stations in the central Red Sea (October 2014, January and August 2016). Additionally, we measured N2O concentrations in brine pool samples collected in the northern and central Red Sea (January 2005 and August 2016). In the Gulf of Aqaba, N2O surface concentrations ranged from 6 to 8 nmol L−1 (97–111% saturation) and were close to the equilibrium with the overlying atmosphere. A pronounced temporal variability of the N2O water column distribution was observed. We suggest that this variability is a reflection of the interplay between N2O production by nitrification and its consumption by N2 fixation in the layers below 150 m during summer. N2O surface concentrations and saturations in the central Red Sea basin ranged from 2 to 9 nmol L−1 (43–155% saturation). A pronounced temporal variability with significant supersaturation in October 2014 and undersaturation in January and August 2016 was observed in the surface layer. In October 2014, N2O in the water column seemed to result from production via nitrification. Low N2O water column concentrations in January and August 2016 indicated a significant removal of N2O. We speculate that either in-situ consumption or remote loss processes of N2O such as denitrification in coastal regions were responsible for this difference. Strong meso- and submesoscale processes might have transported the coastal signals across the Red Sea. In addition, enhanced N2O concentrations of up to 39 nmol L−1 were found at the seawater-brine pool interfaces which point to an N2O production via nitrification and/or denitrification at low O2 concentrations. Our results indicate that the Red Sea and the Gulf of Aqaba are unique natural laboratories for the study of N2O production and consumption pathways under extreme conditions in one of the warmest and most saline region of the global oceans.

The Spatial and Temporal Variability of Air-Sea CO2 Fluxes and the Effect of Net Coral Reef Calcification in the Indonesian Seas: A Numerical Sensitivity Study

A numerical model system was developed and applied to simulate air-sea fluxes of CO2 and coral reef calcification in the Indonesian Seas and adjacent ocean basin for the period 1960 to 2014 on a fine resolution grid (ca. 11 km) in order to study their response to rising sea water temperatures and CO2 concentrations in the atmosphere. Results were analyzed for different sub-regions on the Sunda Shelf (Gulf of Thailand, Malacca Strait, Java Sea) and show realistic and different levels, signs and pronounced temporal variability in air-sea CO2 flux. The Gulf of Thailand changes from an atmospheric CO2 sink during the boreal winter to a CO2 source in summer due to higher water temperatures, while other sub-regions as well as the entire averaged Sunda Shelf act as a continuous source of CO2 for the atmosphere. However, increasing atmospheric CO2 concentrations weakened this source function during the simulation period. In 2007, the model simulations showed even a first flux inversion, in course of which the Java Sea took up CO2 . The simulated trends suggest that the entire Sunda Shelf will turn into a permanent sink for atmospheric CO2 within the next 30 to 35 years if current trends remain constant. Considering the period between 2010 and 2014, coral reef calcification enhanced the average CO2 emission of the Sunda Shelf by more than 10 % from 15 to 17 Tg C yr−1 due to lowering the pH and increasing the partial pressure of CO2 in surface water. During the entire period of simulation, net reef calcification decreased although increasing seawater temperature mitigated effects of reduced CO2 emission and the resulting decrease of the pH values on reef calcification. Our realistic simulation results already without consideration of any biological processes suggest that biological processes taking up and releasing CO 2 are currently well balanced in these tropical regions. However, the counteracting effects of climate change on the reef calcification, on other biological processes and the carbonate system need to be investigated in more detail. SST ◦increased by about 0.6 C during the last 55 years, while SSS decreased by about 0.7 psu.

The lunar semidiurnal tide at the polar summer mesopause observed by SOFIE

The polar summer mesopause, particularly the presence of noctilucent clouds (NLCs), exhibits pronounced temporal variability. Parts of this variability are thought to be caused by lunar tidal influences. We extract the semidiurnal lunar tide in various NLC related parameters by applying the superposed epoch analysis method to the dataset of the SOFIE satellite instrument. Analyzing the NLC seasons from 2007 to 2015 in the northern and southern hemisphere we, first, confirm the influence of the lunar tide on ice water content (IWC) and temperature. For both parameters the lunar influence had already recently been demonstrated in satellite measurements. Second, we apply the analysis to the variety of parameters observed by SOFIE including trace gases (H2O, O3, CH4, and NO), NLC properties (e.g., NLC altitudes and ice mass density), microphysical properties (e.g., particle concentration and mean radius), and mesopause properties. In all of these parameters we find signatures of the semidiurnal lunar tide, which is the first demonstration of this effect for all of these parameters. We quantify the lunar influence in terms of amplitudes and phases. Whereas the focus of the present study is providing observational evidence for the existence of lunar tidal signatures in various parameters, we do not aim at investigating the underlying mechanisms in detail, which is only possible with the utilization of comprehensive modeling approaches. Nevertheless, we briefly discuss the relations to known processes of the NLC evolution where appropriate, e.g., the relevance of the freeze-drying effect for the signature in H2O and the relation of IWC and NLC altitudes.

On the Spatial and Temporal Variability of Atmospheric Heat Transport in a Hierarchy of Models

Abstract The present study analyzes the spatial and temporal variability of zonally integrated meridional atmospheric heat transport due to transient eddies in a hierarchy of datasets. These include a highly idealized two-layer model seeded with point geostrophic vortices, an intermediate complexity GCM, and the European Centre for Medium-Range Weather Forecasts interim reanalysis (ERA-Interim) data. The domain of interest is the extratropics. Both the two-layer model and the GCM display a pronounced temporal variability in the zonally integrated meridional transport, with the largest values (or pulses) of zonally integrated transport being associated with extended regions of anomalously strong local heat transport. In the two-layer model these large-scale coherent transport regions, termed “heat transport bands,” are linked to densely packed baroclinic vortex pairs and can be diagnosed as low-wavenumber streamfunction anomalies. In the GCM they are associated with both the warm and cold sectors of midlatitude weather systems. Both these features are also found in ERA-Interim: the heat transport bands match weather systems and occur primarily in the storm-track regions, which in turn correspond to planetary-scale climatological streamfunction anomalies. The authors hypothesize that the temporal variability of the zonally integrated heat transport is partly linked to oscillatory variations in the storm-track activity but also contains a background red noise component. The existence of a pronounced variability in the zonally integrated meridional heat transport can have important consequences for the interplay between midlatitude dynamics and the energy balance of the high latitudes.

Reliable and Elastic Propagation of Cortical Seizures In Vivo

Mapping the fine-scale neural activity that underlies epilepsy is key to identifying potential control targets of this frequently intractable disease. Yet, the detailed invivo dynamics of seizure progression in cortical microcircuits remain poorly understood. We combine fast (30-Hz) two-photon calcium imaging with local field potential (LFP) recordings to map, cell by cell, the spread of locally induced (4-AP orpicrotoxin) seizures in anesthetized and awake mice. Using single-layer and microprism-assisted multilayer imaging in different cortical areas, we uncover reliable recruitment of local neural populations within and across cortical layers, and we find layer-specific temporal delays, suggesting an initial supra-granular invasion followed by deep-layer recruitment during lateral seizure spread. Intriguingly, despite consistent progression pathways, successive seizures show pronounced temporal variability that critically depends on GABAergic inhibition. We propose an epilepsy circuit model resembling an elastic meshwork, wherein ictal progression faithfully follows preexistent pathways but varies flexibly in time, depending on the local inhibitory restraint.

Evolution of climate, glaciation and subglacial environments of Antarctica from the deep ice core and Lake Vostok water sample studies (Key results of implementation of the Russian Science Foundation project, 2014–2016)

Work on the project focused on the following five areas: 1) field works in Antarctica at Vostok and Concordia stations; 2) experimental and theoretical studies in the field of ice core and paleoclimate research; 3) experimental and theoretical works related to the exploration of subglacial Lake Vostok; 4) development of technology and drilling equipment for deep ice coring and exploration of subglacial lakes; 5) upgrading the analytical instrumentation in the Climate and Environmental Research Laboratory (CERL) of the Arctic and Antarctic Research Institute. The main achievements in the field of ice core and paleoclimate research include 1) further elaboration of a new method of ice core dating, which is based on the link between air content of ice and local insolation, 2) investigation of the possible applications of the 17O-excess measurements in ice core to the paleoclimate research, 3) a better understanding of the mechanisms of the formation of relief-related variations in the isotopic content of an ice core drilled in the area of Antarctic megadunes, and 4) obtaining the first reliable data set on the variations of the 17O-excess in the Vostok core corresponding to marine isotope stage 11. As part of our studies of subglacial Lake Vostok, we have obtained a large body of new experimental data from the new ice core recovered from the 5G-3 borehole to the surface of the subglacial lake. Stacked profiles of isotopic composition, gas content and the size and orientation of the ice crystals in the lake ice have been composed from the data of three replicate cores from boreholes 5G-1, 5G-2 and 5G-3. The study reveals that the concentration of gases in the lake water beneath Vostok is unexpectedly low. A clear signature of the melt water in the surface layer of the lake, which is subject to refreezing on the icy ceiling of Lake Vostok, has been discerned in the three different properties of the accreted ice (the ice texture, the isotopic and gas content of the ice). These sets of data indicate in concert that poor mixing of the melt (and hydrothermal) water with the resident lake water and pronounced spatial and/or temporal variability of local hydrological conditions are likely to be the characteristics of the southern end of the lake. A considerable part of the funding allocated by the RSF to this project was used for upgrading the analytical instrumentation for ice core studies in the CERL of AARI. Using this grant, we purchased and started working with the Picarro L-2140i, a new-generation laser mass analyzer, and set the upgraded mass spectrometer Delta V Plus into operation. The new equipment was used to carry out research planned as part of the project, including the setting up and carrying out of new measurements of 17О in ice cores.

Atmospheric outflow of PM2.5 saccharides from megacity Shanghai to East China Sea: Impact of biological and biomass burning sources

In an effort to more fully understand atmospheric outflow of PM2.5-associated saccharide species, we investigated primary saccharides (fructose, glucose, sucrose, and trehalose), saccharide alcohols (arabitol and mannitol), and anhydrosaccharides (levoglucosan and mannosan) in atmospheric aerosols at both a megacity site, Shanghai, and a sea background site, Huaniao Island. The results showed that the saccharide species presented pronounced temporal and spatial variability in the outflow from the megacity to the East China Sea, and varied widely with a total concentration range of 8.6–2400 ng m−3 (283 ng m−3 mean) in Shanghai and 0–1050 ng m−3 (51 ng m−3 mean) in Huaniao Island. Both saccharide species (e.g., levoglucosan and sucrose) showed higher concentrations and a noticeable seasonal gradient during the study period ― there was a high level of levoglucosan in the cold season (161 ng m−3 in winter and 229 ng m−3 in autumn) due to elevated biomass burning activities, and a high level of sucrose in the warm seasons (146 ng m−3 in summer and 145 ng m−3 in spring) due to elevated levels of intense biological aerosols including fungal spores and pollen. The calculated levoglucosan/mannosan (L/M) ratio, which may represent the signature of aerosol particles at the two sites, ranged from 5.2 to 10.9 during the cold season. Back-trajectory analysis results indicated that the saccharides originated from regional sources in East and North China before being transported to the sampling site. Emissions due to biomass burning were estimated to correspond to 46% (mass) of the saccharides quantified in the haze particle samples, whereas biogenic emissions corresponded to 18%, indicating that biomass burning was a considerable aerosol source to the regional atmosphere throughout the year. The results presented here support the theory that levoglucosan could be utilized as a molecular marker for East Asian biomass burning outflow, and sucrose as a molecular marker for airborne pollen grains. The results of this study may help future researchers clarify the aerosol sources, as well as their atmospheric transport pathways over East Asia to the western Pacific Ocean.

Atmospheric 210 Pb and anthropogenic trace metals in the continental outflow to the Bay of Bengal

Abstract Atmospheric 210 Pb and trace metals (Pb, Cd, Cu, Mn, Cr, Co, Ni and Zn) have been studied in fine mode aerosols (PM 2.5 ) from a sampling site (Kharagpur: 22.3°N, 87.3°E) in the Indo-Gangetic Plain (IGP) during the continental outflow (November–March) to the Bay of Bengal (BoB). The aerosol 210 Pb activity (1.3–6.6 mBq m −3 ) is significantly high in the wintertime (December–January) compared to model based data in the literature. The cause for higher 210 Pb activity is attributed to enhanced 222 Rn emanation from Alluvium in the IGP as well as lower boundary layer height. The trace metal concentrations (in ng m −3 ) also exhibit pronounced temporal variability (Pb: 8–296, Mn: 8–568, Cr: 4.5–33, Cu: 2.1–29.3, Ni: 2.3–14.3, Co: 0.5–1.6 and Cd: 1–29.5) and are of comparable magnitude with those documented over the BoB ( Srinivas and Sarin, 2013b ), suggesting dominant impact of IGP-outflow on marine atmospheric boundary layer. The enrichment factors (EF crust ) of Pb, Cd, Cu, Mn, Cr, Co and Ni in PM 2.5 , relative to upper continental crust, varied as 105–1561, 1265–24006, 13–87, 3–99, 7–27, 3–19 and 9–27, respectively. Significant linear relationship among trace metals and chemical species (non-sea-salt-K + , nss-SO 4 2− and EC) emphasizes their anthropogenic source. The high concentrations and EF crust of Pb, Cd and Cu, together with residence time of PM 2.5 (2–13 days, assessed from 210 Pb) in the IGP-outflow has implications to increase in the aerosol toxicity and their impact on biogeochemistry of ocean surface waters via air-sea deposition.

Temporal variability of primary and secondary aerosols over northern India: Impact of biomass burning emissions

Abstract The ambient particulate matter injected from biomass burning emissions (BBEs) over northern India has been a subject of major debate in the context of regional air quality and atmospheric chemistry of several organic and inorganic constituents. This necessitates an observational approach over a large spatial and temporal scale. We present an extensive data set on PM 2.5 samples (n = 147) collected for one full year from a sampling site (Patiala: 30.2°N, 76.3°E) in the source region of BBEs in northern India. During the sampling period from October 2011 to September 2012, PM 2.5 mass concentration varied from ∼20 to 400 μg m −3 . Among the major constituents, contribution of total carbonaceous aerosols (OC + EC) ranged from 8 to 60%. The average OC/EC and K + /EC ratio, varying from 3.2 to 12 and 0.26 to 0.80, respectively, emphasizes the dominance of BBEs over the annual seasonal cycle. The average secondary organic matter (SOM) accounts for ∼10–40% of PM 2.5 mass in different seasons; whereas contribution of secondary inorganics was maximum (∼40%) during the winter. The pronounced temporal variability in SOM suggests its contribution from varying sources, their emission strength and process of secondary organic formation. Diurnal differences in the chemical constituents are attributable to regional meteorological factors and boundary layer dynamics. The emerging data set from this study is important to understand feedback mechanism from anthropogenic activities to the regional climate change scenario.

Atmospheric outflow of nutrients to the Bay of Bengal: Impact of anthropogenic sources

The air–sea deposition of nutrients (N, P and Fe) to the oceanic regions located downwind of pollution sources in south and south-east Asia is gaining considerable attention in the present-day scenario of climate change. We report here a case study on the atmospheric outflow of nutrients from the Indo-Gangetic Plain (IGP) to the Bay of Bengal (BoB). Air mass back trajectories suggest conspicuous downwind transport of chemical constituents from the IGP to the BoB during the late NE-monsoon (January–April); thus, representing BoB as one of the unique oceanic regions influenced by anthropogenic sources over a short span of 3–4months. During the course of this study (November'09–March'10), nutrient (NO3−, NH4+, NOrg, PO43− and Fews) concentrations in the atmospheric outflow show pronounced temporal variability. The inorganic nitrogen (NH4+-N: ~90% of NInorg) dominates the total soluble nitrogen (NTot). Although the contribution of organic nitrogen is not significant, the mass ratio of NOrg/NTot in the outflow varied from 0.07 to 0.40. The abundances of PInorg and Fews varied from 0.4 to 4.8nmolm−3 and 0.2 to 0.6nmolm−3, respectively. The high abundance of K+ and significant (P-value<0.05) correlation with PInorg and Fews suggest their significant contribution from biomass burning emissions (BBEs). The characteristic mass ratios of nutrients (NInorg/NTot: 0.92±0.13, NOrg/NTot: 0.21±0.11, and PInorg/nss-Ca2+: 0.35±0.23) in the IGP-outflow show striking similarity with those reported over the BoB. These results have implications to further increase in the atmospheric deposition of nutrients and their impact on biogeochemistry of surface Bay of Bengal.

Validation of SMOS L1C and L2 Products and Important Parameters of the Retrieval Algorithm in the Skjern River Catchment, Western Denmark

The Soil Moisture and Ocean Salinity (SMOS) satellite with a passive L-band radiometer monitors surface soil moisture. In addition to soil moisture, vegetation optical thickness $\tau_{\rm NAD}$ is retrieved (L2 product) from brightness temperatures ( $T_{B}$ , L1C product) using an algorithm based on the L-band Microwave Emission of the Biosphere (L-MEB) model with initial guesses on the two parameters (derived from ECMWF products and ECOCLIMAP Leaf Area Index, respectively) and other auxiliary input. This paper presents the validation work carried out in the Skjern River Catchment, Denmark. L1C/L2 data and the most sensitive algorithm parameters were analyzed by network and airborne campaign data collected within one SMOS pixel (44 km diameter). The SMOS retrieval is based on the prevailing low vegetation class. For the L1C comparison, $T_{B}$ 's were calculated from in situ soil moisture using L-MEB. Consistent with worldwide findings, the initial/retrieved SMOS soil moisture captures the in situ dynamics well but with significant wet/dry biases and too large amplitudes in case of the latter. While the initial $\tau_{\rm NAD}$ is in range with an in situ estimate for low agricultural vegetation, the retrieved $\tau_{\rm NAD}$ is too high with too pronounced temporal variability. A filter based on L2 criteria removed radio frequency interference (RFI) and improved the $R^{2}$ between retrieved and network soil moisture from 0.49 to 0.61, while the bias remained $(-0.092/-\!0.087 \hbox{m}^{3}/\hbox{m}^{3})$ . Likely error sources include the following: 1) still present RFI; 2) potential link between high retrieved $\tau_{\rm NAD}$ and other L-MEB parameters, e.g., low roughness parameter $(H_{R})$ ; 3) $\sim$ 18% lower sand and $\sim$ 8% higher clay fractions while $\sim\!\!0.35 \hbox{g/cm}^{3}$ lower bulk density in SMOS algorithm than in situ; and 4) caveats in the Dobson dielectric mixing model implemented in the L-MEB model. A previous study at the Danish validation site had revealed superior performance of the Mironov dielectric mixing model at the 2 $\times$ 2 km scale. Studies are ongoing to address the aforementioned issues, and the role of organic surface layers will be investigated.

Temporal variability in the diversity and composition of stream bacterioplankton communities

Bacterioplankton in freshwater streams play a critical role in stream nutrient cycling. Despite their ecological importance, the temporal variability in the structure of stream bacterioplankton communities remains understudied. We investigated the composition and temporal variability of stream bacterial communities and the influence of physicochemical parameters on these communities. We used barcoded pyrosequencing to survey bacterial communities in 107 streamwater samples collected from four locations in the Colorado Rocky Mountains from September 2008 to November 2009. The four sampled locations harboured distinct communities yet, at each sampling location, there was pronounced temporal variability in both community composition and alpha diversity levels. These temporal shifts in bacterioplankton community structure were not seasonal; rather, their diversity and composition appeared to be driven by intermittent changes in various streamwater biogeochemical conditions. Bacterial communities varied independently of time, as indicated by the observation that communities in samples collected close together in time were no more similar than those collected months apart. The temporal turnover in community composition was higher than observed in most previously studied microbial, plant or animal communities, highlighting the importance of stochastic processes and disturbance events in structuring these communities over time. Detailed temporal sampling is important if the objective is to monitor microbial community dynamics in pulsed ecosystems like streams.

The Goldilocks effect: intermittent streams sustain more plant species than those with perennial or ephemeral flow

Summary1. Drylands worldwide are typified by extreme variability in hydrologic processes, which structures riparian communities at various temporal and spatial scales. One key question is how underlying differences in hydrology over the length of interrupted perennial rivers influence spatial and temporal patterns in species richness and species composition.2. We examined effects of differences in dry season hydrology on species richness, composition and cover of herbaceous plant communities in the streamside zone (the zone influenced directly by low flows in the channel). Data were collected at ephemeral, intermittent and perennial flow reaches on three rivers of the desert Southwest (Arizona, U.S.A.): Lower Cienega Creek, Hassayampa River and Lower San Pedro River.3. Patterns of species richness varied with temporal scale of analysis, that is between single‐year and multi‐year time frames. At the annual timescale, quadrat species richness (m−2) and herbaceous cover were higher at sites with perennial flow than at either intermittent or ephemeral sites. In contrast to this single‐year pattern, the highest long‐term richness occurred at intermittent sites.4. Quadrat species richness, total species richness at a site (per 18 1‐m2 plots) and cover were more variable year to year at non‐perennial sites than at perennial flow sites. On two of the three rivers, ephemeral sites had the highest inter‐annual compositional variance, while the perennial sites had the lowest.5. Compositional differences between the hydrologic site types were dominated by species turnover, not nestedness. The perennial sites had more wetland and perennial species than the other two site types. The intermittent sites had more annual species than did the other two types.6. High long‐term species richness and distinct species composition of intermittent sites are probably sustained by pronounced temporal variability in environmental conditions (i.e. frequent and persistent flow events, and dry periods). Plants at these sites take advantage of greater moisture than those at ephemeral sites and also experience less competition from resident species than those at perennial sites.7. Conservation of desert riparian diversity depends upon the protection of consistently wet conditions at perennial flow sites, as well as the maintenance of the processes that cause fluctuations in environmental conditions at non‐perennial sites.

Extremely large anthropogenic-aerosol contribution to total aerosol load over the Bay of Bengal during winter season

Abstract. Ship-borne observations of spectral aerosol optical depth (AOD) have been carried out over the entire Bay of Bengal (BoB) as part of the W-ICARB cruise campaign during the period 27 December 2008–30 January 2009. The results reveal a pronounced temporal and spatial variability in the optical characteristics of aerosols mainly due to anthropogenic emissions and their dispersion controlled by local meteorology. The highest aerosol amount, with mean AOD500&gt;0.4, being even above 1.0 on specific days, is found close to the coastal regions in the western and northern parts of BoB. In these regions the Ångström exponent is also found to be high (~1.2–1.25) indicating transport of strong anthropogenic emissions from continental regions, while very high AOD500 (0.39±0.07) and α380–870 values (1.27±0.09) are found over the eastern BoB. Except from the large α380–870 values, an indication of strong fine-mode dominance is also observed from the AOD curvature, which is negative in the vast majority of the cases, suggesting dominance of an anthropogenic-pollution aerosol type. On the other hand, clean maritime conditions are rather rare over the region, while the aerosol types are further examined through a classification scheme based on the relationship between α and dα. It was found that even for the same α values the fine-mode dominance is larger for higher AODs showing the strong continental influence over the marine environment of BoB. Furthermore, there is also an evidence of aerosol-size growth under more turbid conditions indicative of coagulation and/or humidification over specific BoB regions. The results obtained using OPAC model show significant fraction of soot aerosols (~6 %–8 %) over the eastern and northwestern BoB, while coarse-mode sea salt particles are found to dominate in the southern parts of BoB.