Freshwater Reviews, Vol 7, No 2 (2014)

Landscape disturbance and lake response: temporal and spatial perspectives

John Anderson
DOI: 10.1608/FRJ-7.2.811 | Pages: 77-120

Abstract

Lake sediments are natural archives that record the response of a lake to both in-lake processes and catchment disturbance (over a range of timescales).  The response (or lack of) of a lake to external forcing is a function of the severity of the disturbance (and its areal extent) but is also strongly mediated by catchment characteristics, such as slope and hydrological connectivity.  Many studies of recent lake disturbance have focussed on anthropogenic disruption of geochemical cycles, e.g. acidification and eutrophication, which because of their “ecological” power appear to over-ride catchment filters.  Lake sediments also record the variability of natural disturbance regimes themselves (fire, volcanic ash falls, species invasions, and climate) and the consequent lake response but this aspect has received much less attention.  The possibility of using lake sediments to address long-term (102 – 103 yr) interactions between e.g., climate, catchment ontogeny and disturbance events (and their synergies) has not been fully explored, largely because of an over-riding emphasis on climate as a direct driver of ecological change.

Traditionally, limnology has also focussed on a few key sites (sentinels) but in response to the development of landscape ecology has progressively embraced a regional approach to understanding how lakes respond to external forcing (climate) and disturbance (“lakes in the landscape”).  Although the interaction of a lake with its catchment is implicit, i.e. via hydrological and nutrient loading, palaeolimnologists rarely take an explicitly spatial view of this interaction nor have they considered spatial location (i.e. response of a number of lakes within a lake district).  Arguably, the inherent spatial variability of terrestrial disturbance has been ignored by palaeolimnologists, largely as a result of focussing on one core from a single lake.

This paper reviews the impact of terrestrial disturbance on lakes but also argues for explicit consideration of space and location in determining the resultant temporal variability of the ecological response.  The importance of within-lake spatial heterogeneity is also high-lighted (i.e. the major contribution of the littoral zone to both diversity and production).  However, any attempt to determine spatially replicated (i.e. at a regional scale), holistic (i.e. whole lake) responses to disturbance will encounter considerable problems associated with dating, loss of temporal resolution and among site comparison.  Despite this, it is clear that recent methodological developments in the area of biomarkers, compound specific stable isotopes coupled with progress in dating (age-models), ecological modelling and statistical analysis offer the possibility of undertaking regionally-replicated studies of lake response to natural disturbance, thereby contributing and expanding our understanding of ecosystem dynamics at a range of spatial and temporal scales.

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