Impact of forest harvesting on water quality and fluorescence characteristics of dissolved organic matter in eastern Canadian Boreal Shield lakes in summer

P Glaz,J.-P Gagné,C Nozais,P Sirois,P Archambault

doi:10.5194/bg-12-6999-2015

Abstract

Abstract. Forestry activities in the Canadian Boreal region have increased in the last decades, raising concerns about their potential impact on aquatic ecosystems. Water quality and fluorescence characteristics of dissolved organic matter (DOM) were measured over a 3-year period in eight eastern Boreal Shield lakes: four lakes were studied before, 1 and 2 years after forest harvesting (perturbed lakes) and compared with four undisturbed reference lakes (unperturbed lakes) sampled at the same time. ANOVAs showed a significant increase in total phosphorus (TP) in perturbed lakes when the three sampling dates were considered and in DOC concentrations when considering 1 year before and 1 year after the perturbation only. At 1 year post-clear cutting DOC concentrations were about 15 % greater in the perturbed lakes at ~ 15 mgC L−1 compared to 12.5 mgC L−1 in the unperturbed lakes. In contrast, absorbance and fluorescence measurements showed that all metrics remained within narrow ranges compared to the range observed in natural waters, indicating that forest harvesting did not affect the nature of DOM characterized with spectroscopic techniques. These results confirm an impact of forestry activities 1 year after the perturbation. However, this effect seems to be mitigated 2 years after, indicating that the system shows high resilience and may be able to return to its original condition in terms of water quality parameters assessed in this study.

Highlights

Boreal forests, which contain large areas of wetlands and over 1.5 million lakes, are an ecological, economic and cultural source of wealth in Canada (NRCan, 2005; Kreutzweiser et al, 2008)
A statistically significant interaction between treatment and year was observed for total phosphorus (TP) concentrations (Table 3)
TP concentrations increased in the perturbed lakes in 2009 while it slightly decreased in unperturbed lakes

Summary

Introduction

Boreal forests, which contain large areas of wetlands and over 1.5 million lakes, are an ecological, economic and cultural source of wealth in Canada (NRCan, 2005; Kreutzweiser et al, 2008) These lakes receive allochthonous inputs of dissolved and particulate matter from natural sources and anthropic activities (Schindler et al, 1992). The export of dissolved nutrients to aquatic ecosystems increases, which is primarily related to a higher microbial activity in upper soil layers and the forest floor (Bormann and Likens, 1994; Kreutzweiser et al, 2008) This microbial activity converts nutrients from non-mobile to mobile forms, which are exported to receiving waters (Buttle et al, 2005), affecting loads of nutrients and organic compounds in lakes and rivers. There is a need to understand the long-term effects of forest harvesting on water quality, as well as its short transient repercussions

Methods

Results

Conclusion