Carbon standing stock distribution in the cuphotic zone of Lake Kinneret and the immediate fate of primary-produced carbon arc very different during late winter-early spring (with the occurrence of the annual dinollagellate bloom) than they are in late summer (when nanophytoplankton are the dominant primary producers). We used a linear programming model to construct balanced carbon flow charts for these two seasons based on measured primary productivity; on carbon standing stocks of algae, bacteria, flagellates, ciliates, cladocerans, rotifers, and fish; and on data on turnover times, respiration, and grazing rates obtained in 1989. The charts were compiled to fit as closely as possible all obscrvcd and inferred estimates of carbon fluxes while simultaneously ensuring that mass balance and key biological constraints were maintained for each of the 10 compartments representing the principal biota of the Kinneret food web. We used the model to examine the extent to which individual intercompartmental flux rates were free to vary while the mass-balance and biological constraints were enforced. The model was also capable of generating different yet feasible flow-chart scenarios; it thus proved useful in suggesting alternative hypotheses concerning the role of the microbial food web in the euphotic waters of Lake Kinneret.A major aim of both theoretical and applied aquatic research has long been to understand the patterns of flow of carbon and other elcments through the pelagic biota in lakes and seas. Within the last decade it has become increasingly evident that the complex communities of microbial organisms in the pelagic zone in both marine and freshwater environments play a key role in processing and transferring carbon, nitrogen, and phosphorus from primary producers to metazoan plankton and fish (Pomeroy 1974;Azam et al. 1983; Berman 1990). Much debate has been generated concerning the function of microbial food webs as Acknowledgments WC are indebted to B. Azoulai, K. D. Hambright, M. Gophen, G. Nahum, 0. Hadas, U. Pollinghcr, Y. 2. Yacobi, and T. Zohary for data, discussion, and dissent. We are grateful for the comments of two rcvicwcrs that enabled us to improve and revise the original version of the paper.

SUMMARY The lead and zinc contents of shoot material of Agrostis tennis, Festuca ovina and Minuartia verna and of the soil in which they were growing at an abandoned lead‐mining area on Grassington Moor, Yorkshire, England were determined. The relationship between the zinc contents of shoot material and soil was broadly linear. There was little increase, however, in the lead content of the shoot material over the range 500‐20000 μg g−1 lead in the soil. Above this value the lead content of the shoot material increased markedly. There were large differences between samples in the metal contents of the shoot material collected from soils having the same metal contents. Possible reasons for this variation are discussed and specific suggestions for future comparative work are made.

Wetlands are one of the major contributors of methane (CH4) emissions to the atmosphere and the intensity of emissions is driven by local environmental variables and spatial heterogeneity. Peatlands are a major wetland class and there are numerous studies that provide estimates of methane emissions at chamber or eddy covariance scales, but these are not often aggregated to the site/ecosystem scale. This study provides a robust approach to map dominant vegetation communities and to use these areas to upscale methane fluxes from chamber to site scale using a simple weighted-area approach. The proposed methodology was tested at three peatlands in Ireland over a duration of 2 years. The annual vegetation maps showed an accuracy ranging from 83 to 99% for near-natural to degraded sites respectively. The upscaled fluxes were highest (2.25 and 3.80 gC m−2 y−1) at the near-natural site and the rehabilitation (0.17 and 0.31 gC m−2 y−1), degraded (0.15 and 0.27 gC m−2 y−1) site emissions were close to net-zero throughout the study duration. Overall, the easy to implement methodology proposed in this study can be applied across various landuse types to assess the impact of peatland rehabilitation on methane emissions by mapping ecological change.

CO2 sequestered by peatlands is accounted for and offset against national emissions. Observational and modelling studies are used to estimate emission factors that dictate the rate of CO2 emissions or removals from peatlands accounted for within the Landuse and landuse change including forestry (LULUCF) sector and often use simple Tier 1 emission factors found in the IPCC (1996) guidebook. However, the current estimates are predominately based off peatland surface fluxes measured using either chamber methods or eddy covariance techniques. These methods do not focus on sub-surface conditions while this information may prove useful in understanding efflux rates and conditions that influence them. To help assess the potential significance of subsurface dynamics in overall CO2 efflux rates from peatlands this study proposes to review the literature dealing with subsurface conditions. The review found that the production of CO2 in the sub-surface layers was often uncoupled from emissions and that on short time-scales the storage of CO2 in soil pores and dissolved in soil water may account for this. The rate of production was found to be influenced by decomposition rate, vegetation type, nutrient availability and peat depth. The review also found that the mechanism of transport of CO2 within the sub-surface was important in accounting for efflux rates. While diffusion is often assumed the most significant form of transport, the quantification and dynamics of other non-diffusive transport methods were found to also be important and further research is required to ascertain the drivers of both diffusive and non-diffusive transport.

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