Assessment of the recovery of littoral zone food-webs in Lake Charr Lakes in Killarney Provincial Park affected by acidification and contemporary stressors

Abstract

Killarney Provincial Park is a site of significant environmental damage from acidic deposition resulting in the extreme loss of biodiversity. As many lakes in Killarney Park acidified to pH< 6, many populations of fish and sensitive species were lost from Killarney’s lakes and streams. In recent decades, effective legislation, and massive emission reductions programs have resulted in substantial chemical recovery, however biological recovery has lagged

considerably behind. The objective of my study was to assess the recovery of littoral zone food- webs in Killarney’s acid damaged lake charr (Salvelinus namaycush) lakes by resampling 20 lakes

previously studied 25-years earlier, with a focus on assessing change in water quality, and key prey and indicator species (crayfish, mayflies, amphipods, littoral fish). Dramatic water quality shifts have occurred in these lakes including increases in pH and DOC and decreases in SO4 2-, Ca2+ and metals and increase in surface water temperatures. The substantial rise in DOC may represent a significant increase in nutrient conditions, but more importantly appears to have affected the thermal structure and cold-water habitat for charr in some ultra-clear lakes. In contrast to the physicochemical changes in the lakes, particularly the substantial pH rise to above toxic levels, the biotic changes were not all as positive. There is evidence that emerging contemporary stressors, including declining Ca levels and shifts in littoral fish communities to centrarchid-dominated may be inhibiting recovery potential in the littoral zones. My results demonstrate the importance of the interactions between historical and contemporary stressors, and that contemporary stressors may now be controlling variables in determining littoral food web recovery. Overall, my study provides evidence that many of Killarney Park’s historically acid-damaged lakes are no longer limited by acidic conditions but contemporary stressors, such as the arrival of warm water centrarchids (e.g. smallmouth bass) have emerged as key factors shaping littoral zone recovery. In particular, the increase in concentration of dissolved organic carbon may be a potential driver of littoral zone recovery, providing food source additions to the nearshore environment and increasing the productivity capacity of food webs.