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This work examines the potential of spaceborne microwave remote sensing for the discrimination and analysis of morphological and surface cover-features in semi-arid Tunisia. The study area in central Tunisia comprises a region of overlap between two satellite radar passes: namely Seasat and SIR-A. This allows the influence of two different radar depression angles, look directions and resolutions upon image appearance to be determined. Botn these systems operated at a wavelength of 23cm and hence the characteristic responses of semi-arid surfaces at this wavelength are assessed. This is achieved through visual and digital image interpretation and discriminant analysis of image data. As SIR-A data is available only in optical format, the image had to be digitised before digital image processing could be undertaken. Several radiometric and geometric pre-processing procedures have to be accomplished. Despite the time-lag and calibration difficulties involved, the dominant ground controls on radar backscatter are identified through statistical analysis of information collected in the field. Surface relief, feature geometry and surface roughness are the most important parameters for both systems. The difference in depression angle causes relief information to dominate the Seasat image, while roughness information dominates the SIR-A image. The availability of Landsat Thematic Mapper data for part of the SIR-A swath west of the coastal study area provides a valuable opportunity to assess the complementary nature of data from the visible, infra-red and microwave parts of the electromagnetic spectrum. This is examined through digital and statistical analysis of image data. In the mountain environments, slope angle and aspect are found to be the dominant parameters influencing SIR-A backscatter through their effect on local radar incidence angle. The special quality of radar is its sensitivity to relief and roughness information. This is exploited in a number of applied studies that assess the contributions of radar to environmental management in semi-arid areas. Finally, recommendations are made for future research in the light of the multi-parameter radar systems due to be launched in the 1990s.

Increased use of fertilisers and pesticides has raised levels of agricultural pollution in surface and ground waters. Organism using these water sources are at risk of exposure to ammonium nitrate fertiliser. The effects of ammonium nitrate on spawn, larva and adult common frogs was investigated using ammonium nitrate fertiliser in solution and granular form at various stages of frog development. The concentrations used, up to 100mgIL NO-3-N used reflect nitrate concentrations on agricultural land in the United Kingdom in water bodies located within and adjacent to agricultural land at times when common frogs are actively breeding or developing. Nitrate concentrations in frog breeding ponds were high (> 1OOmgIL NO-3-N) during the frog breeding season, especially when water entered from field drains, but significantly lower (<25 mglL) for the remainder of the year. Frogs did not show a selective preference for ponds with low nitrate concentrations. Frog spawn swelled when exposed to ammonium nitrate and its viability was reduced (87% survival in controls; 63% at 80 mgIL NH\NO-3). The 96 hour LCso for frog larvae was 781 mglL (95% confidence intervals of 587 to 942) and the 48 hour ECso was 399 mgIL (95% Cl = 234 to 546). Long term exposure to 100 mgIL NW4NO-3 in a flow through system reduced larval survival from 85% (controls) to 53% after 96 days, with most mortality occurring during the three weeks prior to metamorphosis. Larval growth was affected marginally but with some evidence of enhanced mass in the treated larvae, especially at the lowest nitrate concentration of 25 mWL NH\NO-3. Metamorphosis in this group was earlier than in the other groups; by day 80, 48% of the metamorphs had emerged, by comparison with 38, 34 and 24% for the controls and those exposed to 50 and 100 mgIL NW4NO'3 respectively. Furthermore, the mass of emergent metamorphs in the 25 mgIL treatment group was significantly higher than that of the controls.

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