Trace metal residues in soil as markers of ancient site occupance in Greece

Wetensch. publicatieFaculty of Archeolog

Disturbance and investment: developmental responses of tropical lotic midges to repeated tube destruction in the juvenile stages

1. Investment in silken tubes may give tubicolous chironomid larvae more to lose than non-tube building taxa when physical disturbances or the actions of other organisms induce dispersal. In this study, two chironomid species from flood-prone Australian tropical streams were subjected to repeated experimental destruction of their larval and pupal tubes in laboratory experiments, with life-history parameter responses recorded.\ud \ud 2. When subjected to the tube destruction treatments, Echinocladius martini (Orthocladiinae), whose larvae construct branched loose silken tubes in fast flow, showed no reduction in survivorship to adult, whereas Polypedilum australotropicus (Chironominae), which builds compact tightly woven tubes incorporating detrital material within pool leaf packs, showed reduced survivorship of about 25%.\ud \ud 3. For both species, tube destruction reduced pupal duration, regardless of whether destruction occurred in the larval stage only, or in both the larval and pupal stages. This may be a response to the risks of exposure outside tubes in nature, particularly for pupae, which are incapable of spinning silk.\ud \ud 4. Tube destruction caused little or no reduction in adult size, longevity, or female fecundity (oocyte number) for either species, but oocyte development and size was retarded in E. martini females, reflecting the energetic and nutritive costs of the tube destruction treatments.\ud \ud 5. Contrasts in the responses of the two species reflect differences in tube-building behaviour and in situ habitat use. These results demonstrate that tube loss can affect the fitness of individual chironomids, though both species proved generally resilient, which may reflect their long-term exposure to variable tropical lotic conditions

The recent sedimentation history of Aqualate Mere (Central England): assessing the potential for lake restoration.

As part of English Nature's Lakes Flagship Project to address adverse environmental impacts on selected, important lakes, a proposal has been made to dredge Aqualate Mere. The site has experienced rapid, 'recent' sedimentation thought to be derived from a nearby canal. The aim of this study has been to determine the recent sedimentation history of the site in order to assess the possibility of the disposal to land of its sediments and the efficacy of this form of lake restoration. A predominantly clayey silt layer was found across the lake beneath which darker, organic-rich sediments were noted. This transition may represent the input of canal-derived sediments, although it may reflect other environmental changes at this time. The radiometric dating technique employed was unable to date this sediment boundary. A further change in the characteristics of the upper part of the clayey silt layer may represent an additional influence of the canal. Heavy metal levels were modest, whereas nutrient levels were relatively high and some pesticides were detected. Topsoil erosion supplying nutrients and other compounds associated with agriculture have been an important source of the lower layers of the clayey silt sediments in particular. The highest levels of most pollutants were found in the finer sediments in the uppermost (post-1950s) part of the sediment profile. These sediments appear to reflect a change in the characteristics of the sediments of the canal, which was associated with a change in the nature of its water supply. The key geochemical properties of the sediments should not preclude the land-based disposal of dredged materials under current UK regulations for waste management. Accurate estimation of sediment quantities was limited, as the interface between the 'recent' and underlying sediments was not positively identified at all sample points