A mass‐balance approach to estimate in‐stream processes in a large river

A mass‐balance approach was used to estimate in‐stream processes related to inorganic nitrogen species (NH₄⁺, NO₂^? and NO₃^?) in a large river characterized by highly variable hydrological conditions, the Garonne River (south‐west France). Studies were conducted in two consecutive reaches of 30 km located downstream of the Toulouse agglomeration (population 760 000, seventh order), impacted by modification of discharge regime and high nitrogen concentrations. The mass‐balance was calculated by two methods: the first is based on a variable residence time (VRT) simulated by a one‐dimensional (1‐D) hydraulic model; the second is a based on a calculation using constant residence time (CRT) evaluated according to hydrographic peaks. In the context of the study, removal of dissolved inorganic nitrogen (DIN) for a reach of 30 km is underestimated by 11% with the CRT method. In sub‐reaches, the discrepancy between the two methods led to a 50% overestimation of DIN removal in the upper reach (13 km) and a 43% underestimation in the lower reach (17 km) using the CRT method. The study highlights the importance of residence time determination when using modelling approaches in the assessment of whole stream processes in short‐duration mass‐balance for a large river under variable hydrological conditions. Copyright © 2007 John Wiley & Sons, Ltd.     

The influence of negative emission technologies and technology policies on the optimal climate mitigation portfolio

Combining policies to remove carbon dioxide (CO₂) from the atmosphere with policies to reduce emissions could decrease CO₂ concentrations faster than possible via natural processes. We model the optimal selection of a dynamic portfolio of abatement, research and development (R&D), and negative emission policies under an exogenous CO₂ constraint and with stochastic technological change. We find that near-term abatement is not sensitive to the availability of R&D policies, but the anticipated availability of negative emission strategies can reduce the near-term abatement optimally undertaken to meet 2°C temperature limits. Further, planning to deploy negative emission technologies shifts optimal R&D funding from ??carbon-free?? technologies into ??emission intensity?? technologies. Making negative emission strategies available enables an 80% reduction in the cost of keeping year 2100 CO₂ concentrations near their current level. However, negative emission strategies are less important if the possibility of tipping points rules out using late-century net negative emissions to temporarily overshoot the CO₂ constraint earlier in the century.     

Rural household demographics, livelihoods and the environment

This paper reviews and synthesizes findings from scholarly work on linkages among rural household demographics, livelihoods and the environment. Using the livelihood approach as an organizing framework, we examine evidence on the multiple pathways linking environmental variables and the following demographic variables: fertility, migration, morbidity and mortality, and lifecycles. Although the review draws on studies from the entire developing world, we find the majority of microlevel studies have been conducted in either marginal (mountainous or arid) or frontier environments, especially Amazonia. Though the linkages are mediated by many complex and often context-specific factors, there is strong evidence that dependence on natural resources intensifies when households lose human and social capital through adult morbidity and mortality, and qualified evidence for the influence of environmental factors on household decision-making regarding fertility and migration. Two decades of research on lifecycles and land cover change at the farm level have yielded a number of insights about how households make use of different land-use and natural resource management strategies at different stages. A thread running throughout the review is the importance of managing risk through livelihood diversification, ensuring future income security, and culture-specific norms regarding appropriate and desirable activities and demographic responses. Recommendations for future research are provided.     

Flexible–inflexible: socio-demographic,spatial and temporal dimensions of flat sharing in Leipzig (Germany)

Flat sharers are one of the most distinct representatives of the ‘new’ household types, but have received only very limited attention from researchers. Back in the 1960s shared flats were usually founded with a strong ideological impetus, whereas flat sharing nowadays is just one household type among many others. Typically, this housing arrangement consists of at least two young adult individuals without children. Sharing the flat and the housing costs is the basis of their relationship but living with others is an additional motive. As a rule, flat sharing bridges two distinct events in the course of one’s life: the leaving of the parental home and the foundation of the first independent household. Thus for a restricted period in time, it is a flexible household type adapted to the situational needs of its members. Germany has one of the strongest and longest traditions of flat sharing in Europe, especially among university students. An explorative study was conducted in Leipzig to come to a deeper understanding of what flat sharing means in its ambivalence of being both an economic unit and a social arrangement. Based on qualitative and quantitative evidence from group discussions and Internet adverts, we shed light on the highly under-researched social practice of flat sharing. We will show that despite the structural flexibility of this household type, there is also evidence for its socio-demographic selectivity, spatial concentration and temporal limitation over the individual life courses.     

Options to overcome the barriers to pricing European agricultural emissions

Although agriculture could contribute substantially to European emission reductions, its mitigation potential lies untapped and dormant. Market-based instruments could be pivotal in incentivizing cost-effective abatement. However, sector specificities in transaction costs, leakage risks and distributional impacts impede its implementation. The significance of such barriers critically hinges on the dimensions of policy design. This article synthesizes the work on emissions pricing in agriculture together with the literature on the design of market-based instruments. To structure the discussion, an options space is suggested to map policy options, focusing on three key dimensions of policy design. More specifically, it examines the role of policy coverage, instruments and transfers to farmers in overcoming the barriers. First, the results show that a significant proportion of agricultural emissions and mitigation potential could be covered by a policy targeting large farms and few emission sources, thereby reducing transaction costs. Second, whether an instrument is voluntary or mandatory influences distributional outcomes and leakage. Voluntary instruments can mitigate distributional concerns and leakage risks but can lead to subsidy lock-in and carbon price distortion. Third, the impact on transfers resulting from the interaction of the Common Agricultural Policy (CAP) with emissions pricing will play a key role in shaping political feasibility and has so far been underappreciated.

POLICY RELEVANCE

Following the 2015 Paris Agreement, European climate policy is at a crossroads. Achieving cost-effectively the 2030 and 2050 European targets requires all sectors to reduce their emissions. Yet, the cornerstone of European climate policy, the European Union Emissions Trading System (EU ETS), covers only about half of European emissions. Major sectors have been so far largely exempted from carbon pricing, in particular transport and agriculture. While transport has been increasingly under the spotlight as a possible candidate for an EU ETS sectoral expansion, policy discussions on pricing agricultural emissions have been virtually absent. This article attempts to fill this gap by investigating options for market-based instruments to reduce agricultural emissions while taking barriers to implementation into account.     

Escaping the climate policy uncertainty trap: options contracts for REDD+

Climate policy uncertainty significantly hinders investments in low-carbon technologies, and the global community is behind schedule to curb carbon emissions. Strong actions will be necessary to limit the increase in global temperatures, and continued delays create risks of escalating climate change damages and future policy costs. These risks are system-wide, long-term and large-scale and thus hard to diversify across firms. Because of its unique scale, cost structure and near-term availability, Reducing Emissions from Deforestation and forest Degradation in developing countries (REDD+) has significant potential to help manage climate policy risks and facilitate the transition to lower greenhouse gas emissions. ‘Call’ options contracts in the form of the right but not the obligation to buy high-quality emissions reduction credits from jurisdictional REDD+ programmes at a predetermined price per ton of CO₂ could help unlock this potential despite the current lack of carbon markets that accept REDD+ for compliance. This approach could provide a globally important cost-containment mechanism and insurance for firms against higher future carbon prices, while channelling finance to avoid deforestation until policy uncertainties decline and carbon markets scale up.

Key policy insights

• Climate policy uncertainty discourages abatement investments, exposing firms to an escalating systemic risk of future rapid increases in emission control expenditures.

• This situation poses a risk of an abatement ‘short squeeze,’ paralleling the case in financial markets when prices jump sharply as investors rush to square accounts on an investment they have sold ‘short’, one they have bet against and promised to repay later in anticipation of falling prices.

• There is likely to be a willingness to pay for mechanisms that hedge the risks of abruptly rising carbon prices, in particular for ‘call’ options, the right but not the obligation to buy high-quality emissions reduction credits at a predetermined price, due to the significantly lower upfront capital expenditure compared to other hedging alternatives.

• Establishing rules as soon as possible for compliance market acceptance of high-quality emissions reductions credits from REDD+ would facilitate REDD+ transactions, including via options-based contracts, which could help fill the gap of uncertain climate policies in the short and medium term.

     

Behavior of arsenic and antimony in the surface freshwater reaches of a highly turbid estuary, the Gironde Estuary, France

This study reports on the behavior of two redox-sensitive elements, As and Sb, along the turbidity gradient in the freshwater reaches of the turbid Gironde Estuary. During a 17-month survey, surface water and suspended particulate matter (SPM) were sampled monthly at six sites representing both fluvial branches of the Gironde Estuary. Additionally, two longitudinal high resolution profiles were sampled along the fluvial estuary of the Garonne Branch during two contrasted seasons, i.e. with and without the presence of the maximum turbidity zone (MTZ). Seasonal variability and spatial distribution of dissolved (<0.2 μm; <0.02 μm) and particulate As, Sb and Fe were measured and combined with SPM data to understand metalloid behavior in the estuarine freshwater turbidity gradient.At the two main fluvial entries of the Gironde Estuary, dissolved As and Sb concentrations showed strong (by a factor of 2–4) seasonal variations, that were only partly controlled by discharge-related dilution. Seasonal addition of dissolved As and Sb was attributed to the degradation of particulate As and Sb carrier phases in bottom sediment and/or in the adjacent aquifers, rather than release from SPM. In the surface freshwater reaches of the Gironde Estuary, Sb behaved conservatively under all hydrological conditions. In contrast, As was strongly reactive in the presence of the MTZ, with opposite behaviors in the two fluvial branches of the estuary: in the Garonne Branch As was removed from the dissolved phase, whereas in the Dordogne Branch As was added. Redistribution of As between the dissolved and the particulate phases along the turbidity gradient in estuarine freshwater only affected the <0.02 μm fraction, as the 0.02–0.2 μm fraction remained constant (300 ng L⁻¹ in September 2005). Accordingly, As removal seemed to be decoupled from concomitant “colloidal” (0.02–0.2 μm) Fe flocculation in the turbidity gradient. The contrasting behavior of dissolved As in the fluvial estuaries of the Garonne and Dordogne Branches was attributed to sorption processes during equilibration of river-borne dissolved As with estuarine SPM forming the MTZ. This equilibrium, described by a distinct distribution coefficient K_d(As)  11,000 L kg⁻¹ in the MTZ, resulted in either As release (desorption; Dordogne Branch) or removal (adsorption; Garonne Branch) in the respective fluvial estuaries. A mixing experiment under controlled laboratory conditions tended to support that equilibration between the dissolved phase and MTZ particles may induce both As release and removal in the estuarine freshwater reaches, with As distribution evolving towards a distinct K_d value for increasing SPM concentrations. The long-term survey allowed estimating annual (2004) dissolved fluxes of As and, for the first time Sb, at the main fluvial entries of the Gironde Estuary at 30.7 t a⁻¹ and 3.2 t a⁻¹ (Garonne River) and at 8.0 t a⁻¹ and 2.3 t a⁻¹ (Dordogne River), respectively.     

Slow, but steady: dispersal of freshwater molluscs

Molluscs are the proverbial examples of slow movement. In this review, dispersal distances and speed were assessed from literature data. Active upstream movement can occur both individually and in groups; and depends on traits such as size, sex and reproductive status, and on external factors such as flow velocity, temperature, sediment structure, and food availability. The potential for active dispersal follows the sequence Pulmonata ≥ Prosobranchia > Bivalvia, although data for Pulmonata originated from short-term experiments that likely overestimated dispersal capabilities. Active upstream movement may be 0.3 to 1.0 km per year for most snails and is probably well below 0.1 km per year for bivalves. Natural passive upstream dispersal increases the range 10-fold (snails) to 100-fold (bivalves), and anthropogenic vectors can increase upstream dispersal more than 100-fold (snails) to 1000-fold (bivalves). Three km seems to be the maximal within-stream distance at which many species display regular population mixing, and at which re-colonisation or successful restoration can be expected within 3–10 years. Lateral dispersal between unconnected water bodies is passive and mostly known from observational reports, but potential distances depend on vectors, climate and geomorphology. In general, active dispersal seems insufficient to furnish a compensatory mechanism, e.g., for the rate of projected climate change. We provide an overview on dispersal strategies in the light of applied issues. More rigorous field surveys and an integration of different approaches (such as mark-recapture, genetic) to quantify distances and probabilities of lateral dispersal are needed to predict species distributions across space and time.