Groundwater,Acid and Carbon Dioxide Dynamics Along a Coastal Wetland,Lake and Estuary Continuum

Coastal wetlands are hotspots for biodiversity and biological productivity, yet the hydrology and carbon cycling within these systems remains poorly understood due to their complex nature. By using a novel spatiotemporal approach, this study quantified groundwater discharge and the related inputs of acidity and CO₂ along a continuum of a modified coastal acid sulphate soil (CASS) wetland, a coastal lake and an estuary under highly contrasting hydrological conditions. To increase the resolution of spatiotemporal data and advance upon previous methodologies, we relied on automated observations from four simultaneous time-series stations to develop multiple radon mass balance models to estimate groundwater discharge and related groundwater inputs of acidity and dissolved inorganic carbon (DIC), along with surface water to atmosphere CO₂ fluxes. Spatial surveys indicated distinct acid hotspots with minimum surface water pH of 2.91 (dry conditions) and 2.67 (flood conditions) near a non-remediated (drained) CASS area. Under flood conditions, groundwater discharge accounted for ～14.5 % of surface water entering the lake. During the same period, acid discharge from the acid sulphate soil section of the continuum produced ～4.8 kg H₂SO₄?ha^?1 day^?1, a rate much higher than previous studies in similar systems. During baseflow conditions, the low pH water was rapidly buffered within the estuarine lake, with the pH increasing from 4.22 to 6.07 over a distance of ～250 m. The CO₂ evasion rates within the CASS were extremely high, averaging 2163?±?125 mmol m^?2 day^?1 in the dry period and 4061?±?259 mmol m^?2 day^?1 under flood conditions. Groundwater input of DIC could only account for 0.4 % of this evasion in the dry conditions and ～5 % during the flood conditions. We demonstrated that by utilising a spatiotemporal (multiple time-series stations) approach, the study was able to isolate distinct zones of differing hydrology and biogeochemistry, whilst providing more reasonable groundwater acid input estimates and air–water CO₂ flux estimates than some traditional sampling designs. This study highlights the notion that modified CASS wetlands can release large amounts of CO₂ to the atmosphere because of high groundwater acid inputs and extremely low surface water pH.     

Enhanced Dissolved Organic Matter Recovery from Saltwater Samples with Electrodialysis

Complexities associated with dissolved organic matter (DOM) isolation from seawater have hampered compositional characterization of this key component of global carbon and nutrient cycles. DOM isolation efficiency by electrodialysis (ED) from salt-containing waters was optimized and evaluated on samples including coastal ocean seawater, open ocean seawater, artificial seawater from axenic cultures of marine phytoplankton, and artificial seawater samples containing standard compounds of different molecular sizes and charge. ED was performed with a system optimized for processing 2–10 L sample volumes. Additionally, the combination of ED and solid-phase extraction, using Bond Elut PPL exchange resin, was evaluated. Using only ED, the following DOC recoveries were achieved: coastal seawater, 71.3 ± 6.5 %; open ocean, 50.5 ± 3.1 %; phytoplankton cultures, 70.3 ± 12.5 %; glucose, 90.2 ± 2.1 %; EDTA, 67.5 ± 9.9 %; and vitamin B₁₂, 98.3 ± 1.6 %. With the combination of PPL and ED techniques, an average DOC recovery of 76.7 ± 2.6 % was obtained for coastal seawater, but this recovery was not statistically different from seawater recoveries using only ED. Comparison of C/N ratios and fluorescence excitation emission matrices taken at the beginning and end of the recovery process for coastal samples processed using only ED indicated that the final recovered material was representative of the DOM present in the original samples. Typical recoveries using combined PPL and ED exceed those of previous isolation methods.     

Bypassing the ‘ratification straitjacket’: reviewing US legal participation in a climate agreement

The issue of US ratification of international environmental treaties is a recurring obstacle for environmental multilateralism, including the climate regime. Despite the perceived importance of the role of the US to the success of any future international climate agreement, there has been little direct coverage in terms of how an effective agreement can specifically address US legal participation. This article explores potential ways of allowing for US legal participation in an effective climate treaty. Possible routes forward include the use of domestic legislation such as section 115 (S115) of the Clean Air Act (CAA) and the use of sole–executive agreements, instead of Senate ratification. Legal participation from the US through sole–executive agreements is possible if the international architecture is designed to allow for their use. Architectural elements such as varying legality and participation across an agreement (variable geometry) could allow for the use of sole–executive agreements. Two broader models for a 2015 agreement with legal participation through sole–executive agreements are constructed based upon these options: a modified pledge and review system and a form of variable geometry composed of number of opt-out, voting-based protocols on specific issues accompanied by bilateral agreements on mitigation commitments with other major emitters through the use of S115 and sole–executive agreements under the Montreal Protocol and Chicago Convention (‘Critical Mass Governance'). While there is no single solution, Critical Mass Governance appears to provide the optimum combination of tools to effectively allow for US legal participation whilst ensuring an effective treaty.

Policy relevance

This article provides some recommendations on how to create an effective, legally binding treaty that allow for US legal participation without Senate approval. Given the recent election of a Republican majority in the US Senate and Congress, increasing willingness of the President to utilize his executive powers, as well as a strong shift in negotiations to appease US interests, the insights of this research are timely and relevant to delegations and other United Nations Framework Convention on Climate Change (UNFCCC) actors. It will also be of use to domestic US actors involved with climate policy by illustrating how to allow for effective and sustainable US multilateral engagement that bypasses domestic political gridlock.     

Extreme heat in New Zealand: a synthesis

Climatic Change - The usefulness of global integrated assessment model (IAM) results for policy recommendation in specific regions has not been fully assessed to date. This study presents the...     

Conceptualising the Migration–Food Security Nexus: Lessons from Nepal and Vanuatu

In the past decade, international development practitioners have increasingly argued that migration improves the food security of households at origin, by providing the capital necessary for agricultural intensification or food purchase. These debates have occurred largely in isolation from a discussion of the values that underpin food production and consumption in the communities that migrants call home. We question the assumption that a shift from an agricultural-based economy to an economy based on remittances increases the ability of communities to secure access to food in the face of rapid economic and cultural change. In this paper, we present two independently conducted studies from Nepal and Vanuatu that investigate the impact of out-migration on local perceptions of agricultural and residential land and the meaning given to food security. Our data reveal that the value changes associated with large-scale out-migration have the potential to make the agricultural sector at origin more vulnerable, unproductive, unsustainable or unattractive, leaving a longer-term impact on food security. We offer some reflections on the implications of these findings for the structure of the migration–food security nexus.     

Constructing an idealized model of the North Atlantic Ocean using slippery sacks

This paper documents the continued development and testing of a new Lagrangian oceanic general circulation model. The slippery sacks ocean model (SSOM), which represents a body of water as a pile of conforming parcels, is improved and is used to simulate circulations in homogeneous oceans and in an idealized model of the North Atlantic Ocean.A method for including horizontal mixing in the SSOM is presented. A given sack’s nearest neighbors are identified in the positive and negative x- and y-directions, and the sack exchanges momentum and/or tracers with these neighbors. This formulation of mixing is straightforward to implement, computationally efficient, and it produces results similar to a standard Eulerian finite-difference representation of diffusion.The model’s ability to reproduce the Stommel and Munk solutions to the classical western boundary current problem is tested. When steps are taken to reduce the potential energy barrier to sacks crossing one another, the model generates circulations that are consistent with linear theory. In moderately non-linear regimes the model produces appropriate departures from linear solutions including a boundary current that continues along the northern boundary for a time.Taking advantage of the new mixing scheme and lessons learned from simulations of homogeneous oceans, the authors construct an idealized model of the North Atlantic Ocean. They compare simulations conducted with the SSOM to similar simulations conducted with the Massachusetts Institute of Technology general circulation model (MITgcm). The SSOM and the MITgcm produce similar wind-forced gyres, thermocline structure, and meridional overturning. The SSOM is also used to explore how circulations change in the limit when tracer diffusion goes to zero.     

Ecological assessment to detect imminent change in coral reefs of Admiral Cockburn Land and Sea National Park,Turks and Caicos Islands

Coral reefs of the Turks and Caicos Islands (TCIs) (Caribbean Sea) constitute some of the few pristine coral reef systems in the world and play a crucial role in the islands’ economy because they support rich fisheries catches and tourism development. Ambitious development plans involving increase in fishing and tourism pressures are about to bring changes in coastal zone resources of the TCIs associated with increased sediments and nutrients and reduced predation by herbivorous fish on coral reefs. Understanding change is critical when attempting to protect the resources that these coral reefs support and to adopt proper management strategies. Yet, an environmental assessment program to detect imminent human‐induced changes on the surrounding reefs of the TCIs is lacking. Thus, (i) we obtained baseline data on benthic composition and coral community structure at seven reef sites of representative reefs of the TCIs within the Admiral Cockburn Land and Sea National Park (ACLSNP) of South Caicos Island and (ii) performed a priori statistical power analysis to calculate replication requirements for safely and confidently detecting small (δ = 0.1), medium (δ = 0.3), and large (δ = 0.5) effect sizes for a number of relevant to anticipated changes, univariate, benthic indices and for power β = 0.95. The platforms of the margin reefs studied (9–12 m depth) appeared rather variable regarding benthic composition but quite homogeneous regarding hard coral community structure. Mean percent cover of algal functional groups was 0.1 ± 0.3 (mean ± sd) percent for coralline algae and Halimeda, 0.1 ± 0.6 (mean ± sd) percent for macroalgae, 21.7 ± 33 (mean ± sd) percent for turf algae and 4.8 ± 4.0 (mean ± sd) percent for hard coral cover. The dominant benthic component, however, was carbonate substrate (mean ± sd = 30.4 ± 34.3), thus indicating an accreting reef framework. Mean hard coral density, colony size and recruit density were 5.5 ± 1.8 (mean ± sd) corals per 20‐m line transect, 13.0 ± 2.3 (mean ± sd) cm maximum colony diameter, and 1.3 ± 1.4 (mean ± sd) recruits per square foot, respectively. Due to high natural variance, hard coral colony size and density were practically the most sensitive indices in detecting even small size changes on benthos. Also, the geometric mean of log‐transformed colony size‐frequency distributions of the most abundant hard coral taxa, i.e. Montastrea annularis, Agaricia spp., Siderastrea spp. and Porites asteroides were practically sensitive for the same purpose. We hope that the study will optimize the spatial component of a necessary environmental impact assessment program on coral reefs of the TCIs once the natural spatial variability of the system has been assessed and sensitive, benthic, univariate indices have been identified for representative reference coral reef sites of the TCIs.     

Impacts of successive wildfire on soil hydraulic properties: Implications for debris flow hazards and system resilience

Climate and land use changes have led to recent increases in fire size, severity, and/or frequency in many different geographic regions and ecozones. Most post-wildfire geomorphology studies focus on the impact of a single wildfire but changing wildfire regimes underscore the need to quantify the effects of repeated disturbance by wildfire and the subsequent impacts on system resilience. Here, we examine the impact of two successive wildfires on soil hydraulic properties and debris flow hazards. The 2004 Nuttall-Gibson Complex and the 2017 Frye Fire affected large portions of the Pinaleño Mountains in southern Arizona, creating a mosaic of burn severity patterns that allowed us to quantify differences in wildfire-induced hydrologic changes as a function of burn severity and recent fire history (i.e. burned in only the Frye Fire or burned in both fires). Field observations after the 2017 Frye Fire indicated debris flow activity in areas burned predominantly at low severity. Many of these areas, however, were also affected by the 2004 Nuttall-Gibson Complex, suggesting that the relatively short recovery time between the two wildfires may have played a role in the geomorphic response to the most recent wildfire. Field measurements of soil hydraulic properties suggest that soils burned at moderate severity in 2004 and low severity in 2017 have a lower infiltration capacity relative to those that remained unburned in 2004 and burned at low severity in 2017. Simulations of runoff demonstrate that measured differences in infiltration capacity between once- and twice-burned soils are sufficient in some cases to influence the rainfall intensities needed to initiate runoff generated debris flows. Results quantify the impact of wildfire history and burn severity on runoff and debris flow activity in a landscape affected by successive wildfires and provide insight into how the resilience of geomorphic systems may be affected by successive wildfires. © 2019 John Wiley & Sons, Ltd.     

Debris-covered Glaciers and Rock Glaciers in the Nanga Parbat Himalaya, Pakistan

The origin and mobilization of the extensive debris cover associated with the glaciers of the Nanga Parbat Himalaya is complex. In this paper we propose a mechanism by which glaciers can form rock glaciers through inefficiency of sediment transfer from glacier ice to meltwater. Inefficient transfer is caused by various processes that promote plentiful sediment supply and decrease sediment transfer potential. Most debris‐covered glaciers on Nanga Parbat with higher velocities of movement and/ or efficient debris transfer mechanisms do not form rock glaciers, perhaps because debris is mobilized quickly and removed from such glacier systems. Those whose ice movement activity is lower and those where inefficient sediment transfer mechanisms allow plentiful debris to accumulate, can form classic rock glaciers. We document here with maps, satellite images, and field observations the probable evolution of part of a slow and inefficient ice glacier into a rock glacier at the margins of Sachen Glacier in c. 50 years, as well as several other examples that formed in a longer period of time. Sachen Glacier receives all of its nourishment from ice and snow avalanches from surrounding areas of high relief, but has low ice velocities and no efficient system of debris removal. Consequently it has a pronounced digitate terminus with four lobes that have moved outward from the lateral moraines as rock glaciers with prounced transverse ridges and furrows and steep fronts at the angle of repose. Raikot Glacier has a velocity five times higher than Sachen Glacier and a thick cover of rock debris at its terminus that is efficienctly removed. During the advance stage of the glacier since 1994, ice cliffs were exposed at the terminus, and an outbreak flood swept away much debris from its margins and terminus. Like the Sachen Glacier that it resembles, Shaigiri Glacier receives all its nourishment from ice and snow avalanches and has an extensive debris cover with steep margins close to the angle of repose. It has a high velocity similar to Raikot Glacier and catastrophic breakout floods have removed debris from its terminus twice in the recent past. In addition, the Shaigiri terminus blocked the Rupal River during the Little Ice Age and is presently being undercut and steepened by the river. With higher velocities and more efficient sediment transfer systems, neither the Raikot nor the Shaigiri form classic rock‐glacier morphologies.     

Winchcombe: An example of rapid terrestrial alteration of a CM chondrite

Winchcombe is a CM chondrite that fell in England on February 28, 2021. Its rapid retrieval was well characterized. Within two polished sections of Winchcombe, terrestrial phases were observed. Calcite and calcium sulfates were found in a sample recovered from a field on March 6, 2021, and halite was observed on a sample months after its recovery from a driveway on March 2, 2021. These terrestrial phases were characterized by scanning electron microscopy, Raman spectroscopy, and transmission electron microscopy. Calcite veins crosscut the fusion crust and therefore postdate it. The calcite likely precipitated in the damp environment (sheep field) where the meteorite lay for six days prior to its retrieval. The sulfates occur on the edges of the sample and were identified as three minerals: gypsum, bassanite, and anhydrite. Given that the sulfates occur only on the sample's edges, including on top of the fusion crust, they formed after Winchcombe fell. Sulfate precipitation is attributed to the damp fall environment, likely resulted from sulfide-derived H₂S reacting with calcite within the meteorite. Halite occurs as euhedral crystals only on the surface of a polished section and exclusively in areas relatively enriched in sodium. It was likely produced by the interaction of the polished rock slice with the humid laboratory air over a period of months. The sulfates, fusion crust calcite, and halite all post-date Winchcombe's entry into the Earth's atmosphere and showcase how rapidly meteorite falls can be terrestrially altered.