London scoping - ukcip

Final Report
79
For the purpose of this report, it is convenient to group climate-related changes in London’s
biodiversity by the following major environments: 1) freshwater (including wetlands), 2)
intertidal (including estuarine), and 3) terrestrial (including gardens). As previously indicated,
current threats to biodiversity include loss of wildlife habitat to redevelopment, lack of, or
inappropriate management (such as tree-planting) (Table 3.3). The following sections highlight
factors that are directly and indirectly climate sensitive, such as loss of ecological niche(s),
invasion by exotic species, incidence of disease and pests, air and water pollution, sea-level rise,
impacts of changing river flow regimes, and summer drought stress.
5.6.2 Freshwater Habitats
Freshwater habitats – renowned for their high biodiversity and endemism – include lakes,
permanent and temporary ponds, ephemeral streams, rivers, canals, and wetlands. The most
important potential climate change impacts on lakes and streams include warming of waters
(Webb, 1996); absence of shorter periods of ice cover (Magnuson et al, 2000); reduced summer
flows and dilution of nutrients (Wilby et al., 1998); changes in physical habitat availability
(Keleher and Rahel, 1996); changes in biogeochemical cycles including the mobilisation of
heavy metals and pesticides (Schindler, 1997); increased primary production, eutrophic
conditions, and oxygen depletion (Hassan et al., 1998). The importance of river corridors and
wetlands to nature conservation across London is evident from their association with Sites of
Special Scientific Interest (SSSIs) (EA, 2001b). For instance, the London Wetland Centre
gained national recognition for its value to wildlife, having been designated a SSSI just 6 years
after restoration work began on the site. Local Environment Agency Plans (LEAPs) provide a
further framework for the integrated management of river catchments by, for example,
enhancing marshland habitats created by new flood defence projects.
Changes in river flow regimes, water temperature and water quality can affect the survival,
spawning times, reproductive success and growth of invertebrates, freshwater fish and
amphibians (Beebee, 1995; Cowx, 2000). For example, the proportion of salmon migrating
upstream in summer may be very low if the summer is dry – noticeable declines were evident in
the droughts of 1989 and 1995 for instance. This pattern of behaviour may, however, be
reversed if the flows are dominated by groundwater contributions (George, 1999). Given the
slight decreases in summer flows from clay and urban catchments projected by Davis (2001),
coupled with possible water quality changes, the outlook for the Thames salmon population is
suggestive of further long-term decline. In some regulated rivers, however, there may be
opportunities to maintain physical habitats by controlled releases from reservoirs.
London’s wetlands are of ecological significance to a variety of plant communities, birds,
amphibians and invertebrates (Table 3.3). Nationally, these habitats are under threat from
altered flood regimes, drainage, groundwater abstraction, and development, in addition to global
climate change (Dawson et al., 2001). Their vulnerability arises from the delicate balance
between seasonal evapotranspiration, surface inflows and outflows of water, soil moisture, and
groundwater discharges – changes to any one of these components can seriously impact the
wetland. Following implementation of Water Level Management Plans (WLMPs), however,
the Agency has been able to alleviate the effects of abstraction on a number of rivers and
wetlands. For example, by redirecting a spring and installing water control devices at
Ingrebourne Marshes, background water levels have been increased along with periodic
flooding of the site. This has led to a dramatic improvement in the diversity of bird life and
growth of reed and sedge (EA, 2001a).