Wildlife and conservation review 2003
Chris Mason and colleagues at the Universities of Essex and St Andrews reported their work looking
at the role of sublethal concentrations of herbicides in the erosion of salt marshes in eastern England,
which included field trials on the Stour Estuary. Concentrations of triazine herbicides (eg Simazine
and Atrazine, both widely used in agriculture) within the ranges present in the aquatic environment
were found to reduce the growth and photosynthctic efficiency of both diatoms and higher plants,
and the stability of sediments was found to be reduced as a result of the impacts upon the diatom
biofilm. Reduced sediment stability was found to result in greater deposition of sediment loads on
the leaves of Common Sea-lavender; this, together with the direct effects of the herbicides on this
species, were suggested as having large negative consequences for productivity and survival, lending
support to the hypothesis that sublethal herbicide concentrations could be playing a role in the
increased erosion rate of our salt marshes.
MASON, C.M., UNDERWOOD, G.J.C, BAKER, N.R., DAVEY PA., DAVIDSON, I., HANLON, A.,
LONG, S.P., OXBOROUGH, K., PATERSON, D.M. & WATSON, A. (2003) The role of herbicides in
the erosion of salt marshes in eastern England. Environmental Pollution 122: 41-49.
Also from Chris Mason comes a short report in Bird Study, relating the density of breeding Blackbirds
to various features of housing developments, based on a study around Harwich and Dovercourt. By
walking all roads and paths, and recording the presence of Blackbirds displaying breeding behaviour,
he was able to build up a picture of the best urban habitat for the species, relating nesting activity
to attributes such as housing density, and the proportion of gardens and open space. Perhaps
unsurprisingly, the breeding density of Blackbirds was significantly positively related to the
percentage of gardens and open space, and inversely related to housing density. But the fact that it
matches our expectation does not in any way denigrate the reasons for doing the research. Indeed,
there is remarkably little scientific information published about the factor controlling wildlife in
our built-up areas, so every contribution is worthwhile, especially with the Government's ideas of
plastering yet more houses on our overstuffed county.
MASON, C.F. (2003) Some correlates of density in an urban Blackbird Turdus merula population. Bird
Study 50: 185-188.
A final offering from Chris (what a remarkable range of interests and scientific expertise he has!) is
a study of long-term trends in water quality, and their implications for invertebrate diversity, in a
range of East Anglian Rivers, from the Chelmer to the Waveney. Over the past 40 years, dissolved
oxygen levels have fallen, whereas chloride levels increased, the latter as a result of industrial
discharges, road salt washings and water softening, for example. Nitrate and phosphate levels
increased in the first half of that period, then declined when new sewage treatment and water
quality legislation took effect. Invertebrate quality indices showed some correlation with
environmental variables, though largely remained stable or increased; surprisingly they were not
clearly associated with declining dissolved oxygen. But in dry years, the impacts of water quality
upon invertebrates were clear, and this emphasises the vulnerability of water 1 ife to drought which
exacerbates the impact of changes in water quality. Of course, as global climate change intensifies,
and droughts become more frequent, this may push the tolerances of aquatic invertebrates beyond
the limits of recovery.
PARR, L.B. & MASON, C.F. (2003) Long-term trends in water quality and their impact on
macroinvcrtebrate assemblages in eutrophic lowland rivers. Water Research 37: 2969-2979.
Essex Naturalist (New Series) 21 (2004)