Observations Of Natural Systems Research Articles

Element mobility during basalt-water-CO2 interaction: observations in natural systems vs. laboratory experiments and implication for carbon storage

Today, carbon dioxide removal from the atmosphere is the most ambitious challenge to mitigate climate changes. Basalt rocks are abundant on the Earth’s surface (≈ 10%) and very abundant in the ocean floors and subaerial environments. Glassy matrix and minerals constituting these rocks contain metals (Ca2+, Mg2+, Fe2+) that can react with carbonic acid to form metal carbonates (CaCO3, MgO3 and FeCO3). Here, we present a data compilation of the chemical composition of waters circulating in basalt aquifers worldwide and the results of simple basalt-water-CO2 experiments. Induced or naturally occurring weathering of basalts rocks release elements in waters and elemental concentration is closely dependent on water CO2 concentration (and hence on water pH). We also performed two series of experiments where basaltic rock powder interacts with CO2-charged waters for one month at room temperature. Laboratory experiments evidenced that in the first stages of water-rock interaction, the high content of CO2 dissolved in water accelerates the basalt weathering process, releasing in the water not only elements that can form carbonate minerals but also other elements, which depending on their concentration can be essential or toxic for life. Relative mobility of elements such as Fe and Al, together with rare earth elements, increases at low pH conditions, while it decreases notably at neutral pH conditions. The comparison between experimental findings and natural evidence allowed to better understand the geochemical processes in basaltic aquifers hosted in active and inactive volcanic systems and to discuss these findings in light of the potential environmental impact of CO2 storage in mafic and ultramafic rocks.

Indigenous Community Fishing Practices in Nagaland, Eastern Indian Himalayas

The significance of indigenous knowledge under the current scenario of biodiversity imperilment is well-known since such knowledge is gained through continuous intergenerational observations of natural systems. In this study, we present a description of indigenous community fishing practices in Nagaland and investigate their relationship with the cultural and traditional aspects of the associated communities through oral interactions, questionnaires and as a participatory observer. We observed inter- and intra-community fishing in which the piscicidal plants Millettia pachycarpa and Derris elliptica (both Fabaceae) were used as fish poison. M. pachycarpa was commonly used in inter-community ‘fishing festivals’ since it is easily available, less laborious to collect and there are no reports of harm to the body in comparison to D. elliptica which causes allergy and/or dermatological effects. Indigenous community fishing is conducted to develop a sense of peaceful co-existence and prosperity within and among the neighboring communities. However, the increasing use of synthetic fish poisons has overlapped with the traditional practices of fishing, exerting pressure on the livelihoods and food security of the tribal populations while contributing to riverine ecosystem degradation. Formulation of policies banning synthetic fish poison, and judicious use of traditional piscicidal plant fishing is therefore recommended.

Toward catchment hydro‐biogeochemical theories

AbstractHeadwater catchments are the fundamental units that connect the land to the ocean. Hydrological flow and biogeochemical processes are intricately coupled, yet their respective sciences have progressed without much integration. Reaction kinetic theories that prescribe rate dependence on environmental variables (e.g., temperature and water content) have advanced substantially, mostly in well‐mixed reactors, columns, and warming experiments without considering the characteristics of hydrological flow at the catchment scale. These theories have shown significant divergence from observations in natural systems. On the other hand, hydrological theories, including transit time theory, have progressed substantially yet have not been incorporated into understanding reactions at the catchment scale. Here we advocate for the development of integrated hydro‐biogeochemical theories across gradients of climate, vegetation, and geology conditions. The lack of such theories presents barriers for understanding mechanisms and forecasting the future of the Critical Zone under human‐ and climate‐induced perturbations. Although integration has started and co‐located measurements are well under way, tremendous challenges remain. In particular, even in this era of “big data,” we are still limited by data and will need to (1) intensify measurements beyond river channels and characterize the vertical connectivity and broadly the shallow and deep subsurface; (2) expand to older water dating beyond the time scales reflected in stable water isotopes; (3) combine the use of reactive solutes, nonreactive tracers, and isotopes; and (4) augment measurements in environments that are undergoing rapid changes. To develop integrated theories, it is essential to (1) engage models at all stages to develop model‐informed data collection strategies and to maximize data usage; (2) adopt a “simple but not simplistic,” or fit‐for‐purpose approach to include essential processes in process‐based models; (3) blend the use of process‐based and data‐driven models in the framework of “theory‐guided data science.” Within the framework of hypothesis testing, model‐data fusion can advance integrated theories that mechanistically link catchments' internal structures and external drivers to their functioning. It can not only advance the field of hydro‐biogeochemistry, but also enable hind‐ and fore‐casting and serve the society at large. Broadly, future education will need to cultivate thinkers at the intersections of traditional disciplines with hollistic approaches for understanding interacting processes in complex earth systems.This article is categorized under: Engineering Water > Methods

Kinetics and mechanism of the abiotic decomposition of dimethyl polysulfides with three, four and five sulfur atoms under dark, oxic conditions

Environmental contextDimethyl polysulfides are malodorous compounds formed from decomposing algal matter. The decomposition of dimethylpolysulfides with 3–5 sulfur atoms was studied in aqueous solution under dark, oxygenated conditions and compared with observations of natural systems. The half-lives of dimethyl tri- and tetrasulfides are very long (176–100000 years), while the half-life of dimethyl pentasulfide (<2 years) is similar to the observed time of its removal from natural aquatic systems. AbstractThe presence of malodorous dimethyl polysulfides (DMPSs) has been documented in various aquatic systems. In this work, we studied the kinetics and mechanisms of the chemical decomposition of DMPSs with 3–5 sulfur atoms in aqueous solutions in the presence of oxygen and absence of light. DMPSs are shown to undergo reaction with hydroxyl ions, which results in their decomposition. The orders of the decomposition reactions with respect to dimethyl trisulfide (DMTS), dimethyl tetrasulfide (DM4S) and dimethyl pentasulfide (DM5S) are 2.0±0.3, 1.7±0.3 and 2.0±0.2, respectively. The reaction orders with respect to OH− are 0.59±0.06, 0.56±0.08 and 0.58±0.11, respectively. The activation energies of these reactions are 170kJmol−1K−1, 114kJmol−1K−1 and 75kJmol−1K−1, respectively. The initial products of the decomposition are Me2Sn−1 and Me2Sn+1 and the apparent final products are elemental sulfur and dimethyl disulfide (DMDS). DMDS, which is formed during the decomposition of DMTS, is depleted in 34S (ϵ=−13.2 ‰), while the DM4S is enriched 34S (ϵ=4.7 ‰). A mechanism for the decomposition of DMPSs is proposed based on the results. Under these conditions, half-lives for the decomposition of DMPSs in Lake Kinneret vary from 2 months for DM5S to 100000 years for DMTS. The relatively short time scale of the reported odour episodes indicates that other chemical, photochemical or biological processes are responsible for the decomposition of DMTS and DM4S.

The Ability of Soil Pore Network Metrics to Predict Redox Dynamics is Scale Dependent

Variations in microbial community structure and metabolic efficiency are governed in part by oxygen availability, which is a function of water content, diffusion distance, and oxygen demand; for this reason, the volume, connectivity, and geometry of soil pores may exert primary controls on spatial metabolic diversity in soil. Here, we combine quantitative pore network metrics derived from X-ray computed tomography (XCT) with measurements of electromotive potentials to assess how the metabolic status of soil depends on variations of the overall pore network architecture. Contrasting pore network architectures were generated using a Mollisol—A horizon, and compared to intact control samples from the same soil. Mesocosms from each structural treatment were instrumented with Pt-electrodes to record available energy dynamics during a regimen of varying moisture conditions. We found that volume-based XCT-metrics were more frequently correlated with metrics describing changes in available energy than medial-axis XCT-metrics. An abundance of significant correlations between pore network metrics and available energy parameters was not only a function of pore architecture, but also of the dimensions of the sub-sample chosen for XCT analysis. Pore network metrics had the greatest power to statistically explain changes in available energy in the smallest volumes analyzed. Our work underscores the importance of scale in observations of natural systems.

Jump rope vortex in liquid metal convection

Understanding large-scale circulations (LSCs) in turbulent convective systems is important for the study of stars, planets, and in many industrial applications. The canonical model of the LSC is quasi-planar with additional horizontal sloshing and torsional modes [Brown E, Ahlers G (2009) J Fluid Mech 638:383-400; Funfschilling D, Ahlers G (2004) Phys Rev Lett 92:194502; Xi HD et al. (2009) Phys Rev Lett 102:044503; Zhou Q et al. (2009) J Fluid Mech 630:367-390]. Using liquid gallium as the working fluid, we show, via coupled laboratory-numerical experiments in tanks with aspect ratios greater than unity ([Formula: see text]), that the LSC takes instead the form of a "jump rope vortex," a strongly 3D mode that periodically orbits around the tank following a motion much like a jump rope on a playground. Further experiments show that this jump rope flow also exists in more viscous fluids such as water, albeit with a far smaller signal. Thus, this jump rope mode is an essential component of the turbulent convection that underlies our observations of natural systems.

Growing Forced Bars Determine Nonideal Estuary Planform

The planform of estuaries is often described with an ideal shape, which exponentially converges in landward direction. We show how growing topographically forced nonmigratory (i.e., anchored) bars determine the large‐scale estuary planform, which explains the deviations observed in the planform of natural estuaries filled with bars compared to the ideal planform. Experiments were conducted in a 20‐m long, 3‐m‐wide tilting flume, the Metronome. From a narrow, converging channel a self‐formed estuary developed characterized by multiple channels, braided bars, a meandering ebb channel, and an ebb delta. Bars hardly migrated due to the alternating current, but the bar width increased with increasing estuary width. At locations where the estuary width was narrow, major channel confluences were present, while the zones between the confluences were characterized by a higher braiding index, periodically migrating channels, and a relatively large estuary width. At the seaward boundary, confluences were forced in place by the presence of the ebb tidal delta. Between confluences, bars were topographically forced to be nonmigratory. Diversion of flow around forced midchannel bars caused bank erosion. This resulted in a planform shape with a quasiperiodic widening and narrowing at the scale of forced bars. Observations in natural systems show that major confluence locations can also be caused by inherited geology and human engineering, but otherwise the estuary outline is similarly affected by tidal bars. These observations provide a framework for understanding the evolution of tidal bar patterns and the planform shape of the estuary, which has wide implications for navigation, dredging, and ecology.

Gap Filling of Precipitation Data by SSA - Singular Spectrum Analysis

From the macroscopic standpoint, the precipitation time series is obtained from observation of natural systems rather than in the laboratory. These time series are often full of gaps (missing values) due to the conditions under which the measurements are made. Missing values give rise to various problems in spectral estimation, inhibit statistical analysis and in specifying boundary conditions for numerical models. Hence, gap filling is necessary in environmental science. The aim of this study is to highlight the application of the SSA forecasting algorithm to fill in missing values to real-life time series. It was applied to several monthly precipitation time series recorded over a large savannah area in Brazil. The results are promising and the accuracy and reliability depend on the pattern and relative length of the gaps with respect to the total length of the time series and presence of noise.

Emergence of Leadership within a Homogeneous Group.

Large scale coordination without dominant, consistent leadership is frequent in nature. How individuals emerge from within the group as leaders, however transitory this position may be, has become an increasingly common question asked. This question is further complicated by the fact that in many of these aggregations, differences between individuals are minor and the group is largely considered to be homogeneous. In the simulations presented here, we investigate the emergence of leadership in the extreme situation in which all individuals are initially identical. Using a mathematical model developed using observations of natural systems, we show that the addition of a simple concept of leadership tendencies which is inspired by observations of natural systems and is affected by experience can produce distinct leaders and followers using a nonlinear feedback loop. Most importantly, our results show that small differences in experience can promote the rapid emergence of stable roles for leaders and followers. Our findings have implications for our understanding of adaptive behaviors in initially homogeneous groups, the role experience can play in shaping leadership tendencies, and the use of self-assessment in adapting behavior and, ultimately, self-role-assignment.

Analysis of the drainage density of experimental and modelled tidal networks

Abstract. Based on controlled laboratory experiments, we numerically simulate the initiation and long-term evolution of back-barrier tidal networks in micro-tidal and meso-tidal conditions. The simulated pattern formation is comparable to the morphological growth observed in the laboratory, which is characterised by relatively rapid initiation and slower adjustment towards an equilibrium state. The simulated velocity field is in agreement with natural reference systems such as the micro-tidal Venice Lagoon and the meso-tidal Wadden Sea. Special attention is given to the concept of drainage density, which is measured on the basis of the exceedance probability distribution of the unchannelled flow lengths. Model results indicate that the exceedance probability distribution is characterised by an approximately exponential trend, similar to the results of laboratory experiments and observations in natural systems. The drainage density increases greatly during the initial phase of tidal network development, while it slows down when the system approaches equilibrium. Due to the larger tidal prism, the tidal basin has a larger drainage density for the meso-tidal condition (after the same amount of time) than the micro-tidal case. In both micro-tidal and meso-tidal simulations, it is found that there is an initial rapid increase of the tidal prism which soon reaches a relatively steady value (after approximately 40 yr), while the drainage density adjusts more slowly. In agreement with the laboratory experiments, the initial bottom perturbations play an important role in determining the morphological development and hence the exceedance probability distribution of the unchannelled flow lengths. Overall, our study indicates an agreement of the geometric characteristics between the numerical and experimental tidal networks.

Conformational study of poly‐ΔAbu peptides and construction of amphipathic nanostructure

Generally, it is believed that alpha,beta-dehydroamino acid residues are most stable in the Z- form rather than in the E- form. In this study, it has been shown that poly-DeltaAbu exists in alternate Delta(E)Abu and Delta(Z)Abu form, with phi, psi values of approximately 0 degrees , 80 degrees and 35 degrees , 27 degrees for the E- and Z- forms, respectively, rather than the all Z- form. The conformational results for the peptides Ac-DeltaAbu(2)-NHMe and Ac-L/D-Ile-Delta(Z)Abu/Delta(E)Abu-NHMe suggest the incorporation of DeltaAbu in both the Z- and E- forms, which is consistent with the available observations in natural systems. Because of adoption of phi, psi values corresponding to the collagen type structure ( approximately -30 degrees , 120 degrees ) by Ile residue and with phi, psi values in the left-handed helical region for Delta(Z)Abu residue, the peptide Ac-(L-Ile-Delta(Z)Abu)(3)-NHMe adopts an amphipathic left-handed helical beta-sheet type structure. This structure is stabilized by network of hydrogen bonding, carbonyl-carbonyl, and CH-O interactions and can be exploited for the construction of antimicrobial peptides and nanomaterials.

Surface enthalpy of goethite

AbstractHigh-temperature oxide-melt solution calorimetry and acid-solution calorimetry were used to determine the heat of dissolution of synthetic goethite with particle sizes in the range 2–75 nm and measured surface areas of 30–273 m2/g (27–240 × 103 m2/mol). Sample characterization was performed using X-ray diffraction, Fourier transform infrared spectroscopy, the Brunauer, Emmett and Teller method and thermogravimetric analysis. Water content (structural plus excess water) was determined from weight loss after firing at 1100°C. Calorimetric data were corrected for excess water assuming this loosely adsorbed water has the same energetics as bulk liquid water. The enthalpy of formation was calculated from calorimetric data using enthalpies of formation of hematite and liquid water as reference phases for high-temperature oxide-melt calorimetry and using enthalpy of formation of lepidocrocite for acid-solution calorimetry. The enthalpy of formation of goethite can vary by 15–20 kJ/mol as a function of surface area. The plot of calorimetric data vs. surface area gives a surface enthalpy of 0.60±0.10 J/m2 and enthalpy of formation of goethite (with nominal composition FeOOH and surface area = 0) of −561.5±1.5 kJ/mol. This surface enthalpy of goethite, which is lower than values reported previously, clarifies previous inconsistencies between goethite-hematite equilibrium thermodynamics and observations in natural systems.

Kinetics of pyrite formation by the H 2S oxidation of iron (II) monosulfide in aqueous solutions between 25 and 125°C: The mechanism

H 2S acts as an oxidizing agent in natural systems and compares with molecular oxygen as an electron acceptor. The experimentally determined lowest unoccupied molecular orbital (LUMO) for H 2S is −1.1 eV, which means that H 2S can be an excellent electron acceptor. In the oxidation of Fe(II) monosulfide by H 2S in aqueous solutions between 25 and 125°C, FeS + H 2 S ( aq ) = FeS 2 + H 2 ( g ) (where FeS is any Fe(II) monosulfide, H 2S (aq) is aqueous H 2S, FeS 2 is pyrite and H 2(g) is hydrogen gas), FeS is the electron donor (reductant) and aqueous H 2S is the electron acceptor (oxidant) and the product of the oxidation is H 2 gas. Because of the relative destabilization of H 2S caused by the presence of an antibonding LUMO orbital in a significantly bent molecule, electrons added to this LUMO orbital cause a weakening of both S H bonds as an S S bond forms. This allows the hydrogen atoms to combine to form H 2 because of their proximity and favorable interaction based on the original LUMO of H 2S. The reaction is transport-controlled. The mean Arrhenius energy for the reaction is 33.7 kJ mol −1. The Arrhenius energy is temperature dependent, which is consistent with electroactive, colloidal FeS being the FeS reactant. MO calculations suggest that the reaction proceeds through a FeS → SH 2 intermediate. The intermediate allows for the formation of an S S bond, the breaking of H S bonds with the formation of H 2 and the conversion of Fe(II) from high to low spin. The H 2 and FeS 2 formed interact with adsorption of H 2 onto the FeS 2 surface. The reaction mechanism can be summarised 1. FeS ( s ) → FeS ( aq ) ( fast < ca. 100 ° C > slow ) 2. FeS ( aq ) + H 2 S ( aq ) → { FeS → SH 2 } ( fast ) 3. { FeS → SH 2 } → [ FeS 2 ⋅ H 2 ( occluded ) ] ( fast ) 4. [ FeS 2 ⋅ H 2 ( occluded ) ] → FeS 2 ( s ) + H 2 ( g ) ( slow < ca. 100 ° C > fast ) The product pyrite forms as mixtures of individual cubes (up to 800 nm in size) and sub-spherical aggregates up to 1400 nm in diameter (“protoframboids”) on the surface of aggregates of particulate FeS. The lack of crystal growth observed in the pyrite products through 20 days of reaction at 125°C suggests that growth is nutrient limited. Observations show that initially, pyrite nucleates on the FeS but subsequently nucleation occurs on pre-formed pyrite crystals. Nucleation is rapid and kinetically favored over crystal growth leading to no significant increase in crystal size as the reaction progresses. There is some evidence that the crystal growth mechanism is through screw dislocation growth. HS − cannot be an electron acceptor because of the high positive calculated energy for the LUMO orbital (+8.015 eV). It is not possible to write an electronically balanced redox reaction involving HS − with FeS without the presence of an additional electron acceptor. In contrast, it is possible at high pH values that the complex FeSH + could react with HS − to form pyrite: however, the reaction is very slow and has not been observed experimentally. The net effect of these observations in natural systems is that reduced systems may change from oxidized to reduced merely by changing pH, from H 2S-dominant (oxidizing) at pH < 7 to HS − dominant (reducing) at pH > 7.

SUSTAINABLE EXPLOITATION OF RENEWABLE RESOURCES

Sustainable exploitation of renewable resources depends on the existence of a reproductive surplus, which is determined by the balance between births, deaths, and somatic growth. The reproductive surplus differs spatially and temporally as environmental conditions vary, and even in the absence of exploitation, change is the rule and constancy is the exception. Sustainable yields may be estimated by direct experimentation, observation of natural systems, or deduction from biological understanding. Each of these approaches has limitations, and for large-scale unique resources, the only way to determine the response of the population to harvesting is by direct exploitation. To find the maximum potential yield, the resource must be overexploited at some time, or very similar resources must have been overexploited. Temporal changes in environmental conditions mean that information on sustainability collected in the past may have limited applicability in the future. The unregulated dynamic of exploiters is to push the resources to overexploitation, and even when regulated, exploiters have been very successful at modifying their behavior so that regulations are less effective than anticipated. The most successful institutions at maintaining sustainability have been small-scale community or pri