Recent Warming, Rather than Industrial Emissions of Bioavailable Nutrients, Is the Dominant Driver of Lake Primary Production Shifts across the Athabasca Oil Sands Region

Abstract

Freshwaters in the Athabasca Oil Sands Region (AOSR) are vulnerable to the atmospheric emissions and land disturbances caused by the local oil sands industry; however, they are also affected by climate change. Recent observations of increases in aquatic primary production near the main development area have prompted questions about the principal drivers of these limnological changes. Is the enhanced primary production due to deposition of nutrients (nitrogen and phosphorus) from local industry or from recent climatic changes? Here, we use downcore, spectrally-inferred chlorophyll-a (VRS-chla) profiles (including diagenetic products) from 23 limnologically-diverse lakes with undisturbed catchments to characterize the pattern of primary production increases in the AOSR. Our aim is to better understand the relative roles of the local oil sands industry versus climate change in driving aquatic primary production trends. Nutrient deposition maps, generated using geostatistical interpolations of spring-time snowpack measurements from a grid pattern across the AOSR, demonstrate patterns of elevated total phosphorus, total nitrogen, and bioavailable nitrogen deposition around the main area of industrial activity. However, this pattern is not observed for bioavailable phosphorus. Our paleolimnological findings demonstrate consistently greater VRS-chla concentrations compared to pre-oil sands development levels, regardless of morphological and limnological characteristics, landscape position, bioavailable nutrient deposition, and dibenzothiophene (DBT)-inferred industrial impacts. Furthermore, breakpoint analyses on VRS-chla concentrations across a gradient of DBT-inferred industrial impact show limited evidence of a contemporaneous change among lakes. Despite the contribution of bioavailable nitrogen to the landscape from industrial activities, we find no consistency in the spatial pattern and timing of VRS-chla shifts with an industrial fertilizing signal. Instead, significant positive correlations were observed between VRS-chla and annual and seasonal temperatures. Our findings suggest warmer air temperatures and likely decreased ice covers are important drivers of enhanced aquatic primary production across the AOSR.

Assessment of seven Canadian rivers in relation to stages in oil sands industrial development, 1972–2010

“…Studies have also reported an association between natural gradients, such as flooding or regional warming, and bitumen-associated contaminants in lakes (e.g., Hall et al 2012;Summers et al 2016). In the present study, 51% of the variation in 17 heavy metals or priority pollutants could be attributed to differences between reference and post-development phases of mining activity.…”

Increased size and relative abundance of migratory fishes observed near the Athabasca oil sands

“…Total N deposition in the oil sands region estimated for current development is 165 eq/ha per year (Cho et al 2017) and may be associated with increased productivity in local waterbodies (Hazewinkel et al 2008). Summers et al (2016) suggested, however, that warming, rather than nutrient enrichment, is driving increased productivity in local lakes, which may have a role in explaining some of our results. Inconsistencies in the deposition of nitrogenous compounds on the landscape and transportation to watercourses over time may also explain some noise in TN among stations compared with TP.…”

Internal phosphorus loading in Canadian fresh waters: a critical review and data analysis

“…Further, as climate change proceeds, anticipated changes in permafrost thaw, length of seasonal ice cover, and water temperatures will likely increase the productivity of northern ecosystems (Antoniades et al 2011). In fact, increases in internal P loading in boreal lakes in northern Alberta due to climate change have resulted in long-term increases in lake productivity (Hazewinkel et al 2008;Kurek et al 2013;Summers et al 2016).…”