Linking field experiments to long-term simulation of impacts of nitrogen deposition on heathlands and moorlands

The results from three long-term field manipulation studies of the impacts of increased nitrogen deposition (0–120 kg N ha^?1 yr^?1) on lowland and upland heathlands in the UK were compared, to test if common responses are observed. Consistent increases in Calluna foliar N content and decreases in litter C:N ratios were found across all sites, while increases in N leaching were not observed at any site over the range 0–80 kg ha^?1 yr^?1. However, the response of Calluna biomass did vary between sites, possibly reflecting site differences in nutrient status and management histories. Five versions of a simulation model of heathland responses to N were developed, each reflecting different assumptions about the fate and turnover of soil N. Model outputs supported the deduction from mass balance calculations at two of the field sites that N additions have resulted in an increase in immobilisation; the latter was needed to prevent the model overestimating measured N leaching. However, this version of the model significantly underestimated Calluna biomass. Model versions, which included uptake of organic N by Callunaand re-mobilisation of N from the soil organic store provided some improvement in the fit between modelled and field biomass data, but re-mobilisation also led to an overestimation of N leaching. Quantification of these processes and their response to increased N deposition are therefore critical to interpreting experimental data and predicting the long-term impacts of atmospheric deposition on heathlands and moorlands.     

Analyzing interdependent impacts of resource sustainability

Quantifying the impact of the shortage of a scarce resource requires a systemic account of the interdependent nature of several industry and infrastructure sectors that rely either directly or indirectly on that resource. An ability to quickly and easily quantify such an impact provides policymakers with a useful measure of the efficacy of discovering, designing, or developing a sustainable alternative. Discussed in this paper is a methodological approach for measuring the broader interdependent impacts of a resource shortage. The dynamic inoperability input–output model (DIIM) is used to illustrate both the economic effects of resource shortages over a period of time and the time-dependent recovery of industry sectors. Extensions to the DIIM are introduced to produce an accessible tool for policymakers and industry decision makers. Case studies using publicly available data illustrate the usefulness of the model for describing local oil production shortages and global rare earth metals supply shortages, highlighting the industries that will need to adapt to changes in resource availability, as well as those industries that will remain relatively unaffected. Above all, the model presented in this paper is an effective means of communicating the impact and importance of resource shortages to assist in the design and development of a sustainable future.     

Feeding and cleaning mechanisms in the suspension feeding bivalve Mytilus edulis

Feeding and pseudofeces formation were studied in intact Mytilus edulis clearing suspensions of graphite particles, and the processes were compared with activities observed in mussels with a severed adductor muscle. Most particulate material in the stomach was present in the suspended state. Ingestion of particles in suspension could take place concurrently with the production of pseudofeces. Severing of the adductor muscle resulted in profuse secretion of mucus that gradually subsided to a constant low level. Addition of graphite particles at concentrations that did not cause mucus secretion in the intact mussels strongly stimulated secretion in the operated mussels, resulting in the accumulation of highly viscid, mucusparticle aggregates. These aggregates were mechanically stable, in contrast to the fragile pseudofeces. It is indicated that normal feeding depends upon hydromechanical mechanisms that produce highly concentrated suspensions of particles for ingestion, and that mucociliary mechanisms serve to clean the gills and other organs of the mantle cavity for excess particulate material. It is further indicated that intact mussels secrete mucus only in the amounts needed to consolidate excess particulate material, and that lesions affect the normal balance between particles in suspension and mucus secretion by enhancing the sensitivity of the mechanisms that control mucus secretion.     

Conservation mycology in Australia and the potential role of citizen science

Fungi are undoubtedly important for ecosystem functioning; however, they have been omitted or given scant attention in most biodiversity policy documents, management plans, and formal conservation schedules throughout the world. This oversight may be due to a general lack of awareness in the scientific community and compounded by a scarcity of mycology‐associated curricula at the tertiary level and a lack of mycologists in research institutions. Although molecular techniques advance the systematic cataloging of fungi and facilitate insights into fungal communities, the scarcity of professional mycologists in the environmental sciences hampers conservation efforts. Conversely, citizen science initiatives are making significant contributions to the mycology discipline by increasing awareness and extending the scope of fungal surveys. Future research by professional and amateur mycologists into the distribution of fungi and their function in ecosystems will help identify wider and more effective conservation goals.     

A hydromechanical principle for particle retention in Mytilus edulis and other ciliary suspension feeders

It is generally thought that the laterofrontal cirri of the bivalve gill act as filters that retain suspended particles in the through current and transfer the particles onto the frontal surface of the gill filaments. In Mytilus edulis calculations indicated that if water passed between the branching cilia of the cirri that are assumed to constitute the filter the pressure drop needed would amount to about 10 times the actual pressure drop across the whole gill. Thus, instead of acting as filters the laterofrontal cirri seem to move water. Presumably, the cirri together with the frontal cilia produce the water currents along the frontal surface of the gill filaments. Particle retention in the bivalve gill implies the transfer of suspended particles from the current of water about to enter an interfilamentar space into a neighbouring frontal surface current. The complex three-dimensional pattern of flow that arises where the 2 systems of current meet is characterized by steep velocity gradients. Particles that enter such steep, steady velocity gradients become exposed to transverse forces that cause the particles to migrate perpendicularly to the direction of flow. Whether particles enter the surface current, i.e. are retained, or they stay within the through current andescape, depends primarily upon particle size, and upon the steepness and height of the gradients within the boundary zone between the surface current and through current. Further studies are needed to evaluate the capacities and relative importance of this hydromechanical particle-trapping mechanism in suspension feeding bivalves. It is suggested that in downstream particle-retaining systems, e.g. on the tentacles of polychaetes and entoprocts, velocity gradients between through currents and surface currents also act as the particle-collecting mechanism.     

Fluid mechanics of the mussel gill: The lateral cilia

Quantitative data on the water currents produced by the ciliary tracts of the gill filaments are needed to understand the fluid mechanics of suspension feeding in bivalves, as well as in other ciliary suspension feeders. This paper investigates the water currents produced by the bands of lateral cilia, as studied on isolated gill filaments, gill fragments, and intact gills of the mussel Mytilus edulis L with severed adductor muscles. The metachronally beating cilia produce oscillatory currents near the oscillating enveloping surface of the ciliary bands and rectilinear currents, the interfilamentary through-currents, farther from the surface. It is suggested that the oscillatory currents play an important role in the fluid mechanical capture of suspended particles. In the intact gill the interfilamentary currents pass the bands of lateral cilia at velocities that are two or more times higher than those generated by the bands of isolated filaments. The mussel gill is compared with an optimized peristaltic pump.