Climate Change: Defining Reference Conditions and Restoring Freshwater Ecosystems - Climate Change Impacts on Freshwater Ecosystems - page 204

from putatively comparable contemporary landscapes or by using historical or
palaeoecological methods to reconstruct a past undisturbed condition.
In this chapter, we focus on the use of different methods to establish reference
conditions, as well as on how climate change might affect contemporary baselines or
restoration targets. In particular, we are interested in comparing different methods
for establishing reference states. Our first main objective is to understand the inherent
variability that might be associated with the use of different methods to establish
reference conditions. Secondly, with the growing awareness that climate change is
currently affecting ecosystems, we are interested in determining how climate change
might affect how we view contemporary reference conditions or baselines, and
hence influence interpretation of restoration. Finally, we consider how freshwater
ecosystems can best be restored in a world of ongoing climate change.
Detecting the effects that human activities are having on freshwater ecosystems
is complex, as ecosystems themselves are complex and often diffuse entities. A
challenge therefore for ecologists is to understand the importance of linkages
between the structure and function of ecosystems as well as to understand
ecosystem properties such as resistance and resilience to natural and human-
induced stress. Often restoration endeavours have focused on a single system of
interest (i.e. a single lake or stream), usually ignoring that freshwater systems are
intricately linked with their surroundings (e.g. lakes may be perceived as islands
nested in a terrestrial environment). However, there is now an increasing
recognition that ecosystems are strongly interconnected, and this understanding
needs to reach land-use managers.
Establishing reference conditions
Effective management of aquatic resources requires knowledge of when a water
body differs from the natural condition (i.e. absence of human disturbance) and
what has caused the deviation from the expected unimpaired condition. Reference
conditions ( sensu Bailey et al . 2004) are being increasingly used to gauge the
effects and magnitude of human intervention. A number of problems
emerge, however, in the use of reference conditions. Although seemingly trivial,
the definition of what constitutes a reference condition often results in
misunderstanding and contention. Definitions can be based on narrative or
empirical data and range from the natural condition where human influence is
lacking or minimal, to the best attainable condition which recognizes that humans
are an inherent part of the ecosystem (e.g. Nowicki 2003).
According to the European Water Framework Directive (European Commission
2000; Annex 5, section 1.2), high ecological status (i.e. reference conditions) for
biological attributes is defined as having 'no, or only very minor' evidence of
distortion. Consequently, the Directive does not sanction the use of the best
available sites within a region, unless these sites can be shown to reflect a natural
state with no or only minor human influence. In an attempt to add clarity to the
use of reference condition terminology, Stoddard et al . (2006) proposed that
the term reference should be reserved solely for 'naturalness' or 'biological
integrity', and when referring to reference conditions that deviate from
naturalness or integrity, the authors propose the use of four terms: (i) minimally
disturbed condition, to describe the condition in the absence of significant human