Paul van Gardingen

Carbon dioxide emissions at an Italian mineral spring: measurements of average CO2 concentration and air temperature

Abstract Emissions of carbon dioxide from vents at the Bossoleto mineral spring in Central Italy have been calculated to exceed 12 t day −1 . This emission leads to enhanced atmospheric concentrations of CO 2 over an area of more than 3000 m 2 . The vent gas is over 99% pure CO 2 , with a characteristic isotopic signature that is totally depleted in 14 C. At night, concentrations at the bottom of the bowl-like depression can increase to levels approaching 75%. In the morning, this high concentration of CO 2 is associated with a rapid temperature increase of over 10°C before the CO 2 disperses. This site is being used in a number of studie of the response of plant communities to long-term enhanced CO 2 concentrations. The problem of defining CO 2 concentrations in these studies was approached by comparing estimates determined by gas analysis measurements and isotopic analysis of leaf material. The isotopic method used 14 C as a tracer, integrating effective concentration over the life of a leaf by calculating from the ratio of 14 C measurements of plant material growing near the spring and at a control site. The estimates obtained using isotopic analysis of leaf material were similar to gas analysis measurements obtained during the day. This suggests that plants at this site are responding to the concentrations during the day, rather than the much higher night-time concentrations, making the system useful for biological research.

Drivers and impacts of land-use change in the Maasai Steppe of northern Tanzania: an ecological, social and political analysis

In this article, we discuss the drivers, causes, and impacts of land-use change in the Maasai Steppe of northern Tanzania. Remote sensing data were used to analyze land-use change, and Geographical Information Systems (GIS) was used to link-up with wildlife population dynamics and livestock distribution data derived from aerial censuses. Agriculture increased fivefold between 1984 and 2000, while human population increased exponentially from 3.3% p.a. in 1988 to 3.4% p.a. in the same period. Wildlife migratory routes declined from nine in 1964 to five in 2000, out of which three were seriously threatened with blockage by the extensive cultivation. Recurrent droughts and diseases have contributed to the declining livestock economy over the years due to livestock loss and the unpredictable and erratic rainfall has limited their recovery. To reverse the on-going trends in land use, proper land-use plans should be instituted in parallel with community-based wildlife ventures to maintain long-term ecosystem viability.

Evaporation of intercepted precipitation based on an energy balance in unlogged and logged forest areas of central Kalimantan, Indonesia

The effect of logging practices on rainfall interception loss has been investigated in a humid tropical rainforest of central Kalimantan. The traditional volume balance method was used to measure throughfall, stemflow and interception loss. The evaporation rate during and after rainfall has ceased in canopy-saturated conditions was calculated by an energy balance method, which relied on the modified Penman equation using directly determined microclimatic and canopy structure variables as inputs. The results obtained showed that the evaporation from wet canopies in this research area is driven more by advected energy than by radiative energy. In the unlogged plot, advective energy accounted for 0.38 mm h ˇ1 of the 0.51 mm h ˇ1 of evaporation, whereas radiative energy accounted for only 0.13 mm h ˇ1 . A similar relationship between the major driving variables and the rate of evaporation was also found in the logged plot and this implies that logging activities did not change the proportion of energy used for interception loss. The Priestley‐Taylor equation was found to be a poor model for evaporation of intercepted water in tropical forests because advected energy is very important at the canopy scale. # 1998 Elsevier Science B.V. All rights reserved.

The importance of multimodel projections to assess uncertainty in projections from simulation models

Simulation models are increasingly used to gain insights regarding the long-term effect of both direct and indirect anthropogenic impacts on natural resources and to devise and evaluate policies that aim to minimize these effects. If the uncertainty from simulation model projections is not adequately quantified and reported, modeling results might be misleading, with potentially serious implications. A method is described, based on a nested simulation design associated with multimodel projections, that allows the partitioning of the overall uncertainty in model projections into a number of different sources of uncertainty: model stochasticity, starting conditions, parameter uncertainty, and uncertainty that originates from the use of key model assumptions. These sources of uncertainty are likely to be present in most simulation models. Using the forest dynamics model SYMFOR as a case study, it is shown that the uncertainty originated from the use of alternate modeling assumptions, a source of uncertainty seldom reported, can be the greatest source of uncertainty, accounting for 66-97% of the overall variance of the mean after 100 years of stand dynamics simulation. This implicitly reveals the great importance of these multimodel projections even when multiple models from independent research groups are not available. Finally, it is suggested that a weighted multimodel average (in which the weights are estimated from the data) might be substantially more precise than a simple multimodel average (equivalent to equal weights for all models) as models that strongly conflict with the data are given greatly reduced or even zero weights. The method of partitioning modeling uncertainty is likely to be useful for other simulation models, allowing for a better estimate of the uncertainty of model projections and allowing researchers to identify which data need to be collected to reduce this uncertainty.

A portable cryo-storage system for low-temperature scanning electron microscopy, suitable for international transport of cryo-specimens

A cryo‐specimen storage system for low‐temperature scanning electron microscopy (LTSEM) specimens is described, which: liberates multi‐specimen experiments from sampling restrictions imposed by the rate at which LTSEM specimens can be examined in the SEM; provides security against experiment loss resulting from breakdown of the SEM or cryo‐system; enables collection of specimens in the field or in laboratories remote from the SEM laboratory; and facilitates international air transport of LTSEM specimens. The components of the system, which has a capacity of 98 stub‐mounted specimens, are readily made in a laboratory workshop. The details of the design may be altered to suit particular specimen types or experimental approaches.