Comparative impacts of fire and forest harvesting on water quality in Boreal Shield lakes

Abstract

Water quality was monitored in Boreal Shield lakes for 3 years following their simultaneous impact by clearcut logging or wildfire. Seventeen similar undisturbed lakes served as references. Dissolved organic carbon (DOC) and the light attenuation coefficient (εPAR) were up to threefold higher in cut lakes than in reference and burnt lakes. Compared with median values for reference lakes, cut and burnt lakes had higher concentrations of total phosphorus (TP) (two- to three-fold), total organic nitrogen (TON) (twofold), and K+, Cl-, and Ca2+ (up to sixfold). NO3- and SO42- concentrations were up to 60- and 6-fold higher, respectively, in burnt lakes than in reference and cut lakes. In most cases, impacts were directly proportional to the area harvested or burnt divided by the lake's volume or area. These simple models correctly predicted the changes observed in three lakes harvested during the study. Some of the ob served effects occur on different time scales. Mobile ions released by fire (K+, Cl-, SO42-, NO3-) or harvesting (K+, Cl-, some DOC) are rapidly flushed out of the watershed (50% decrease in 3 years). Other constituents or properties (TP, TON, DOC, εPAR, Ca2+, Mg2+) show little change or are still increasing after 3 years and will take a longer time to reach normal levels.

Translocation of soil organic matter following reservoir impoundment in boreal systems: Implications for in situ productivity

“…Moreover, it has been shown that in reservoirs the recycling of allochthonous organic matter enhances aquatic productivity and that the main pathway of carbon flow to secondary producers shifted from an autochthonous to an allochthonous base originating from flooded vegetation (Paterson et al 1997). In some natural lakes, the substantial increase in runoff of soil nutrients resulting from large-scale perturbations to their watershed (deforestation, Carignan et al 2000;wetland drainage, Hambright et al 2004) has also been invoked to explain enhanced levels of primary productivity and concomitant transfer of algal carbon to sediments (Meyers 2003). The study at the Experimental Lake Area in northwestern Ontario (Paterson et al 1997) revealed that the response of in situ productivity and food web structure to reservoir flooding is rapid and results from pulse inputs of phosphorus, nitrogen, and dissolved carbon to the water column (c.f.…”

Advances in Canadian Forest Hydrology, 2003-2007

“…There has been considerable debate in Canada as to whether management techniques must emulate these natural disturbances to sustain forest dynamics and biodiversity (Hunter, 1993). Hydrochemical responses to natural disturbances such as fire have (Schindler et al, 1980;Bayley et al, 1992;Carignan et al, 2000) and continue to be a major research focus. For example, Prepas et al (2003) found greater water yield during stormflow periods and increased particulate P export from a burned relative to a forested reference basin in central Alberta.…”

Impact of harvesting and logging slash on nitrogen and carbon dynamics in soils from upland spruce forests in northeastern Ontario

“…Whether there will be an increased export of N after harvesting to aquatic systems depends on the coincident occurrence of increased production and/or decreased uptake by plants and microorganisms within the terrestrial ecosystem and the ability to transfer these nutrients to adjacent receiving waters. The minimal surface water impacts of harvesting reported for the Canadian boreal forest region (Nicolson et al, 1982;Carignan et al, 2000;Lamontagne et al, 2000;Steedman 2000;Prepas et al, 2001), even in studies where no shoreline buffer zones had been established, may be partly explained by the limited potential of upland boreal forest soils to mineralize organic-N to inorganic forms. In general, unharvested boreal forest organic and mineral soils have been shown to have low net inorganic-N production, particularly NO À 3 -N. This has been shown in Quebec (Brais et al, 1995;Smith et al, 2000) and Michigan (Stottlemyer and Toczydlowski, 1999) on the boreal shield and in Saskatchewan on the boreal plain (Walley et al, 1996).…”