project III
project I

project II

project III

project IV

project V

project VI

project VII

project VIII

project IX

project X

current vacancies

project III: climate as a mediating factor in the recovery of aquatic systems

The effects of any anthropogenic stress on an aquatic environment are mediated by a number of internal factors including the physical characteristics of each lake or stream, its initial chemical and biological conditions, and the ecosystem’s hydrologic regime, and external factors, particularly climate (Schindler et al. 1990). The physical factors and the initial state of the system are, of course, fixed, while the hydrologic regime and the climate are, in essence,complicating (although inter-related) variables. When evaluating the effects of a change in the magnitude of a stress such as acid deposition levels on aquatic ecosystems, it is important to understand the confounding effects of a variable climate. These effects take 3 forms: (a) that due to the natural year-to-year or shorter term variability in climate parameters, e.g. the inter-annual variability in precipitation; (b) that due to the repetitive pattern of certain kinds of events, e.g. the El Nino pattern which repeats, on average, every 5-7 years; and (c) that due to long-term trends, e.g. the systematic change in temperature caused by increases in greenhouse gases.

Each of these 3 levels of effects can be addressed. Meteorological data, both historical records and current, are readily available for many sites in Ontario and can be used to define the role of"normal" climate variability in the assessment of environmental response. These data will be collected and used in the analysis of existing long-term lake and stream data sets (project I), and in the analysis of new data collected as part of project II of this proposal. In effect, the climate data can be used as a "filter". The effects of short-term variability (factor (a) above) can be addressed reasonably well, but are probably the least important because lakes’ response time to change is governed by their hydrologic regimes - water replacement rates typically of 2 to 5 years means that short-term effects caused by variability in climate are damped. Evaluation of the effects of long-term climate change (factor (c) above) is governed by the availability (or lack of availability) of records of long enough duration. Some environmental data relevant to the effects of repetitive patterns (factor (b) above), particularly El Nino events, are available (Dillon et al. 1997), but are insufficient to sort out the relative roles of these event phenomena compared to the effects of changing emissions and deposition of acids and acid precursors.

Project III will include a detailed analysis and field measurement programme on 2 sites (lakes and their watersheds, including their wetland portion) that have been identified as impacted by acid deposition. It is hypothesized that these sites will demonstrate very substantial increases in acidification rates in the period 1998 to 2001 as a consequence of the El Nino; the purpose of the study will be to determine the relative roles of the increased acid deposition rates in this time period and the changes in chemical processes in the watersheds and lakes caused by the El Nino of 1997-98. The hypothesis that will be tested is that the El Nino will cause increased drought with lower stream flows in 1998, 1999 and 2000, lowered water tables in the wetland portion of these watersheds, remineralization of reduced sulphur and nitrogen compounds in the portions of the wetlands that become oxic, and the subsequent efflux of large quantities of mineral acid. It is also hypothesized that this source of acid will greatly outweigh the effects of the increase in sulphur and nitrogen deposition. Finally, the data collected as part of project III will be a valuable addition to existing environmental data defining the effects of long-term systematic climate change on aquatic systems if the appropriate data defining lake response are collected. It is already known that these changes are affecting aquatic ecosystems in Ontario - shorter periods of ice cover, slower flushing rates because of reduced flow, warmer water temperatures (Schindler et al. 1990). All of these have some influence on the sulphur and nitrogen cycles in lakes and their watersheds. Again, the information related to long-term climate trends can be used as a pre-filter when analyzing environmental response to any anthropogenic stress.