Wetlands cover at least 6 % of the Earth’s surface. They play a key role in hydrological and biogeochemical cycles, harbour a large part of the world’s biodiversity, and provide multiple services to humankind. However, pressure in the form of land reclamation, intense resource exploitation, changes in hydrology, and pollution threaten wetlands on all continents. Depending on the region, 30–90 % of the world’s wetlands have already been destroyed or strongly modified in many countries with no sign of abatement. Climate change scenarios predict additional stresses on wetlands, mainly because of changes in hydrology, temperature increases, and a rise in sea level. Yet, intact wetlands play a key role as buffers in the hydrological cycle and as sinks for organic carbon, counteracting the effects of the increase in atmospheric CO2. Eight chapters comprising this volume of Aquatic Sciences analyze the current ecological situation and the use of the wetlands in major regions of the world in the context of global climate change. This final chapter provides a synthesis of the findings and recommendations for the sustainable use and protection of these important ecosystems

The literature was reviewed to determine the direct temperature effects on photosynthetic capacity (P max ), specific respiration rate (R est ), and growth rate of bloom-forming cyanobacteria (Anabaena, Aphanizomenon, Microcystis, Oscillatoria) and to assess the importance of direct t ernperature effects on cyanobacterial dominance in lakes. This analysis is supported by field studies of Microcystis aeruginosa in a hypertrophic lake. The literature and field data show that P max, R est , and growth rate are temperature-dependent with optima usually at 25 °C or greater. The four genera varied in their response to low temperatures with Microcystis being most severely limited belw about 15 °C. Oscillatoria tended to tolerate the widest range of temperatures. However, an examination of field data from representative lakes around the world indicated that direct temperature effects were secondary to indirect temperature effects (mixing) and nutrients in determining the dominance of bloom-forming cyanobacteria in lakes, direct t ernperature effects probably act synergistically with other factors in this process.

We evaluated the potential of prairie wetlands in North America as carbon sinks. Agricultural conversion has resulted in the average loss of 10.1 Mg ha À 1 of soil organic carbon on over 16 million ha of wetlands in this region. Wetland restoration has potential to sequester 378 Tg of organic carbon over a 10-year period. Wetlands can sequester over twice the organic carbon as no-till cropland on only about 17% of the total land area in the region. We estimate that wetland restoration has potential to offset 2.4% of the annual fossil CO 2 emission reported for North America in 1990. D

In this study we experimentally tested the hypothesis that phosphorus was the primary nutrient limiting phytoplankton and bacterial growth in the eastern Mediterranean Sea, and examined the spatial variability in P limitation during winter. Complementary measurements were employed using water sampled during January 1995 from nine pelagic stations east of the Straits of Sicily. Ambient concentrations of inorganic P (P,) in the upper 50 m of the water column in seven of the stations were 20-40 nM. The upper limit of bioavailable P ranged from 6 to 18 nM, suggesting severe P shortage. Orthophosphate turnover time ranged from 2 to 7 h in those P,-depleted waters. In nutrient-enrichment bioassays using subsurface water from the Ionian and Levantine basins, P addition caused significant increases in bacterial activity, bacterial numbers, and chlorophyll a relative to unenriched controls. The addition of NH,' + Fe + EDTA did not have these effects. In a similar bioassay using Cretan water, microbial growth was obtained even in the unemriched controls, suggesting that other factors (e.g. grazing, light) were influential. Higher ambient P, concentrations were encountered in the Cretan Sea (90 nM) and in the core of the Rhodes gyre (210 nM), where our sampling coincided with a convective mixing event. In those stations, P sufticiency was indicated. We concluded that in the pelagic waters of the eastern Mediterranean in winter, P was the primary limiting nutrient when other factors (such as light or grazing) did not control microbial biomass or activity. In ultra-oligotrophic waters, a delicate and dynamic balance differentiates between times when the microbial populations are nutrient limited and times when growth becomes limited by other factors. We caution that the interpretation of data obtained using conventional methods that were developed and tested in more enriched systems may not be valid in ultra-oligotrophic systems.

Diclofop methyl, a commercial herbicide, was used as the sole carbon source to cultivate diclofop-degrading biofilms in continuous-flow slide culture. The biofilms were analyzed by using scanning confocal laser microscopy and image analysis. Spatial relationships among members of the community were distinctive to diclofop-grown biofilms. These relationships did not develop when the biofilms were grown on more labile substrates but were conserved when the biofilms were cultivated with other chlorinated ring compounds. The structures included conical bacterial consortia rising to 30 ,um above the surrounding biofilm, grape-like clusters of cocci embedded in a matrix of perpendicularly oriented bacilli, and other highly specific patterns of intraand intergeneric cellular coaggregation and growth. These unique consortial relationships indicated that syntrophic interactions may be necessary for optimal degradation of diclofop methyl and other chlorinated ring compounds.

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We used a scanning spectroradiometer to conduct underwater optical surveys of 44 waterbodies during the ice-free seasons of three consecutive years in wetlands and lakes in central Saskatchewan, Canada. The waterbodies ranged widely in dissolved organic carbon (DOC) concentration (4.1-156.2 mg L Ϫ1) and conductivity (270-74,300 ohms cm Ϫ1). Although penetration of UV radiation (UV-R; 280-400 nm) in these systems was largely a function of DOC concentration, as has been reported previously, UV-R penetrated more deeply in saline waterbodies than in freshwater systems with similar DOC concentrations. Power models representing our K dUV-B or K dUV-A versus DOC relationships were described by K dUV-B ϭ 0. . UV-B radiation (280-320 nm) is not expected to penetrate deeply (typically Ͻ50 cm) in prairie lakes and wetlands because of high intrinsic DOC concentrations. However, the central plains are characteristically windy and this, coupled with the shallowness of many of these systems, suggests that biota may still be at risk from present-day and future-enhanced levels of UV-B (which may result from ozone depletion). Moreover, this risk may be exacerbated in saline systems. This could be significant, especially because saline waterbodies are often highly productive and represent important North American staging areas for shorebirds and waterfowl.Ultraviolet radiation (UV) has influenced the evolution of life on earth since it first appeared. Even in recent times, in 1 Corresponding author. AcknowledgmentsWe thank J. C. Mollison of the Instrument Technology Services for designing and constructing the parallelogram swing arm used to deploy the Optronics minicosine and submersible sphere sensors. We are grateful to H. I. Browman, Institute of Marine Research, Storebø, Norway, for supplying us with the underwater immersion correction factors used with the submersible sphere and for his sound advice on several technical aspects of the Optronics OL-754 meter. We thank R. Young and C. Rapp/C. Johnson, Optronics Laboratories Inc., Orlando, Florida, for providing us with the immersion correction factors for the minicosine sensor and for answering our technical questions, respectively. We are indebted to R. A. Bourbonniere and K. Edmondson (NWRI-Burlington) for performing DOC analyses on the 1998 samples. This research was made possible by funding through Environment Canada's National Water Research Institute to M.T.A. and R.D.R.

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