Climate Change: Defining Reference Conditions and Restoring Freshwater Ecosystems - Climate Change Impacts on Freshwater Ecosystems - page 220

Although increased pH should allow for the colonization of acid-sensitive species,
the simultaneous increases in nutrient and DOC concentrations could also result
in shifts in species composition, such as an increase of mixotrophic algae (Wetzel
1995) that is not solely related to declines in acidity.
It is important to understand how climate change may affect recovery pathways
and the underlying mechanisms. The North Atlantic Oscillation (NAO) is an
important regional-level driver of climate in southern Sweden (Weyhenmeyer
2004), with positive NAO values signifying higher precipitation and thus more
variable hydraulic and chemical conditions. Stendera and Johnson (2008) found
that interannual shifts in phytoplankton assemblages were positively correlated
with regional patterns that increased water colour, thereby lending further
support to the importance of large-scale, climatic drivers for changes in
biodiversity. Several studies have shown how interannual variability in NAO
affects lake plankton assemblages by affecting temperature, ice cover and timing
of spring algal blooms (Straile 2000; Weyhenmeyer et al . 1999). In the boreal
lakes studied by Stendera and Johnson (2008), the effect of NAO winter on
phytoplankton assemblages may be manifested through increased DOC (water
colour) and nutrients, resulting in shifts to more mixotrophic taxa, although the
increase in DOC may also be related to a reduction in acid deposition (Monteith
et al . 2007; see also Chapter 7).
In combination, these studies show that long-term data sets are needed to
better understand not only the drivers of regional changes in chemistry and
biology of aquatic systems, but also that knowledge of the direction and magnitude
of changing baseline conditions is needed to make informed decisions regarding
the efficacy of restoration efforts. In addition, these and other studies (e.g.
Johnson et al . 2007) support the contention that the scale of perturbation (e.g.
local- vs region-scale drivers of change) and the scale of restoration (e.g. individual
habitats within a stream or streams within a catchment or landscape) need to be
considered to design robust and cost-effective restoration programmes.
Global change and restoration
The presence or absence of organisms may depend on rare or large-scale dispersal
and colonization, while local abundance is more a function of continual, local
biotic interactions and habitat heterogeneity (e.g. Ricklefs 1987). Understanding
the processes and mechanisms that integrate patterns and scale is a growing
theme in restoration ecology (e.g. Bruinderink et al . 2003; Hanski 2005). For
aquatic ecosystems, position in the landscape along with catchment geology and
land use have been known for nearly a century to be good predictors of the
chemistry and biology of lakes and streams (e.g. Thienemann 1925; Naumann
1932; Vannote et al . 1980). Many studies have shown the importance of local
factors such as riparian vegetation, water chemistry and substratum as predictors
of lake and stream invertebrate assemblages (e.g. Ormerod et al . 1993; Johnson
& Goedkoop 2002; Stendera & Johnson 2005), while other studies have stressed
the importance of regional or landscape factors to be more important predictors
of communities (e.g. Allan et al . 1997; Heino 2002; Townsend et al . 2003).