Surface water chemistry of burned and undisturbed watersheds on the Boreal Plain: an ecoregion approach

Abstract

The water chemistry of the euphotic zone in 12 lakes within burned and reference watersheds on Alberta's Boreal Plain was surveyed two years post-fire. Five burned and four reference lakes were located in the Boreal Foothills (mean elevation = 1048 m) and three reference lakes were situated at lower elevations in the Boreal Mixedwood ecoregion (748 m). Mean dissolved organic carbon (DOC) concentration in lake water from burned watersheds was 1.4-fold higher than in lake water from reference Foothills watersheds, whereas lake colour increased with the area of catchment burned divided by lake volume (r = 0.98). Reference Mixedwood lakes had higher mean total phosphorus (TP, 1.8-fold) and chlorophyll a (chl a; 4.4-fold) concentrations than reference Foothills lakes. Ten additional lakes from a previous study in boreal Alberta were used to further compare water chemistry between ecoregions. Boreal Mixedwood lakes (n = 13) had higher TP (2.3-fold), chl a (3-fold), and Ca2+ + Mg2+ (3.3-fold) concentrations than Boreal Foothills lakes (n = 9). Our data suggest an influence of forest fire on lake chemistry in the Boreal Foothills, and demonstrate the need for an ecoregion approach to detect the impacts of watershed disturbance on the Boreal Plain. Key words: watershed disturbance, forest fire, lake nutrients, lake elevation, phosphorus, chlorophyll a, anions, cations, dissolved organic carbon.

Do lakes feel the burn? Ecological consequences of increasing exposure of lakes to fire in the continental United States

“…Scrimgeour et al (2001) and Kelly et al (2006) found that chl-a was 1.5-to 3.5-fold greater up to 2-3 years postfire. In contrast, McEachern et al (2000) and Allen et al (2003) found no significant increases in chl-a, likely because of light limitation (DOC) offset nutrient increases. Although these lakes were primarily P-limited preceding fire, the disproportionate increase in benthic algal biomass was attributed primarily to increased exports of NO 3 following fire.…”

“…Carignan et al (2000) found that median DOC increased up to 20% at 3 years postfire following moderate-to high-severity fire. Allen et al (2003) found that mean lake DOC and color were 1.4-and 2.3-fold greater up to 2 years postfire, respectively, for 20%-90% watersheds burned (mean = 62%). Similarly, Scrimgeour, Tonn, Paszkowski, and Goater (2001) found that mean color approximately doubled in lakes with watershed fires in the Caribou Mountains, Alberta up to 2 years postfire.…”

“…Results were also inconsistent across studies for pH. Although McEachern et al (2000) found mean pH significantly increased by 0.7 up to 2 years postfire, Allen et al (2003) reported mean pH declines of 0.3 in lakes with watershed fires, which were insignificant. Although McEachern et al (2000) found mean pH significantly increased by 0.7 up to 2 years postfire, Allen et al (2003) reported mean pH declines of 0.3 in lakes with watershed fires, which were insignificant.…”

“…Lathrop (1994) reported pH declines at two of four sample stations in Yellowstone Lake, Wyoming up to 3 years postfire. Allen et al (2003) noted, however, that lake pH was negatively correlated with the watershed burned area/lake area ratio, so larger fires may have increased pH, citing previous work in boreal watersheds showing increased SO 4 in lakes with watershed fires (e.g., Carignan et al, 2000, McEachern et al, 2000. Allen et al (2003) noted, however, that lake pH was negatively correlated with the watershed burned area/lake area ratio, so larger fires may have increased pH, citing previous work in boreal watersheds showing increased SO 4 in lakes with watershed fires (e.g., Carignan et al, 2000, McEachern et al, 2000.…”

“…Erosion and runoff from burned areas can increase sediment loads to lakes and tributaries, reducing light penetration (Figure 4d,f,g;Earl & Binn, 2003;Oliver, Reuter, et al, 2012;Rhoades et al, 2011). Soil erosion, soil exposure, and reduced plant uptake can increase N and P concentrations in runoff, particularly near lakes and tributaries if vegetation buffers have burned (Figure 4d,f;Allen et al, 2003;Carignan et al, 2000;Kelly et al, 2006;McEachern et al, 2000;Scrimgeour et al, 2001). Vegetation loss and altered soil properties after fire also influence runoff chemistry.…”