Insect diversity at Shotton, urban
brownfield site
Background
Urban brownfield sites are potentially important
refuges for a variety of insects and a key concern of the TWIRLS project
is to establish whether the addition of organic wastes to brownfield sites
has a positive or negative effect on insect biodiversity. Within the UK,
brownfield sites (i.e. Canvey Island, Essex) are known to support many
rare (Red Data Book; RDB) species. This is because the intensification
of agriculture and increasing use of pesticides since the 1960s have resulted
in loss of species from farmland; many of these species survive on brownfield
sites that have escaped agricultural intensification. Brownfield sites
that have received dredged sand and gravel (such as Shotton and Canvey
Island) provide a mosaic of different habitats for invertebrates, including
all important patches of bare ground favoured by several species of predatory
ground-dwelling (Carabid) beetles.
In addition to calculating the abundance and
diversity of ground dwelling beetles at Shotton, we have compiled a database
consisting of high quality digital photographs of each species found.
Many of the beetles collected have been identified to species level, but
confirmation of each determination is being sought from expert entomologists
due to the difficulty in distinguishing truly different species from different
morphs of individual species.
Insect sampling at Shotton
Following a visit to Shotton, our urban brownfield site,
the opinion of John Bratton (invertebrate ecologist formerly with the
Countryside Council for Wales) is that carabid (ground) beetles are likely
to be the most prevalent insects at the bare site and are also likely
to respond strongly to the application of compost. As predators, the diversity
and abundance of carabid beetles will be affected by prey numbers, dictated
ultimately by the nutritional value of the compost and by the input of
fresh organic matter from vegetation. Accordingly we designed a sampling
programme that uses the randomised complete block vegetation establishment
experiment to test the effect of seeding and of two rates of application
(zero, high) of four of the composts produced in-vessel at Shotton in
2005. The composts are; greenwaste only, greenwaste + sewage, greenwaste
+ paper and paper + sewage. These comparisons were chosen to represent
a broad range of chemical and physical characteristics of the composts.
The insect sampling methodology compared plots sown with the mesotrophic
grassland seed mixture with plots that were not sown.
![](http://ies.bangor.ac.uk/TWIRLS/images/bug4.jpg)
Two pitfall traps were placed in each sub-plot (192 traps
in total) in July 2006 and emptied after 12 days. Each pitfall consisted
of a 1 l plastic container covered with 12 mm nylon mesh to exclude invertebrates
and mammals. 50 ml of NaCl solution was placed in the bottom of each trap
to act as preservative. On retrieval, insects were sorted into broad groups
(carabid beetles, ants, flies, spiders, springtails) and stored in 60
% ethanol prior to identification and further sorting of coleopteran to
species level. The plots will be sampled again in July 2007, when it is
expected that mesotrophic grassland vegetation will be well established
within the sown plots.
Effect of compost addition on insect abundance and
diversity
A minimum of 20 and a maximum of 34 species of ground
dwelling beetles have so far been observed at Site 2. The range represents
the difficulty in distinguishing separate species from different morphs
of individual species and until confirmation of species identity has been
received these results should be considered provisional. In total, 357
ground dwelling beetles have been retrieved from pitfall traps in plots
that received compost and 291 from plots that did not receive compost.
This represents an approximate 20 % increase in the number of insects
following compost application. The number of different species present
in sub-plots decreased slightly from 32 to 28 following application of
compost but this difference is not statistically significant.
Addition of seed mixture significantly increased the
number of ground-dwelling beetles collected. Across all compost types,
298 were collected from plots that did not receive seed mixture and 350
were collected from sown plots. Seeding did not affect the number of species
collected with 29 different species collected from sown plots and 30 from
plots that were not sown.
The most noticeable effect of the addition of compost
was an approximate 70 % increase in numbers of ground-dwelling beetles
in plots that received compost made from green-waste and tertiary treated
sewage sludge.
![](http://ies.bangor.ac.uk/TWIRLS/images/bug3.jpg)