Spring coherence in dissolved organic carbon export dominates total coherence in Boreal Shield forested catchments

The wide range of forested landscapes in boreal environments store and cycle substantial amounts of carbon, although the capacity of these systems to act as either a carbon sink or source is uncertain under a changing climate. While there are clear reports of regional-scale increases in dissolved organic carbon (DOC) concentrations in streams and lakes, there remains substantial watershed-scale variability in these patterns. Coherence is a framework for examining if variables of interest within adjacent spatial units change synchronously or asynchronously through time and has been widely applied in the context of lentic hydrochemistry, and which can shed light on the relative importance of regional- vs. local-scale controls. The objective of this research was to quantify coherence in discharge, DOC concentrations, and DOC loads in forested boreal watersheds, and to what extent coherence varied by season. Coherence was assessed using data from three long-term ecological research sites spanning boreal forest environments (IISD-Experimental Lakes Area, Turkey Lakes Watershed Study, and Dorset Environmental Science Centre) that included 29,829 DOC measurements across 739 stream-years, examining correlation between stream-pairs within each site, but not between sites. Seasonal coherence in DOC export was consistent across the three sites; coherence was significantly greater in spring than all other seasons, and was strongly related to discharge coherence. Currently, the season with the greatest loads (spring) is also the most coherent season, suggesting that annual between-stream coherence may be reduced if spring becomes proportionally less important in hydrologic budgets under a changing climate. This research aids in determining which factors contribute to synchronous watershed behaviour, and which factors may contribute to the timing and extent of individual watershed-scale deviations from landscape-level patterns.

The Freshwater Oil Spill Remediation Study (FOReSt): 2018 Pilot Study at the Experimental Lakes Area, Canada

ABSTRACT (#667537) Monitored natural recovery (MNR) was assessed as a non-invasive method for limiting residual oil exposure in the aquatic environment following contained spills of Cold Lake Blend diluted bitumen (CLB) and conventional heavy crude (CHV) at the IISD-Experimental Lakes Area in Canada. Oils were applied and left in place for 72h to simulate potential spill cleanup response times. After physical removal of free surface oil, biological response and recovery (microbes, zooplankton communities, emergent insects, and benthic invertebrate) was assessed over 80d and exposure of polycyclic aromatic compounds (PACs) and their alkylated forms (aPACS) in water and sediment were characterized. Embryonic development of fathead minnow eggs exposed to water from each of the enclosures was used to determine potential impacts on fish early life stage development. There were significantly different concentrations of PACs in the enclosures treated with diluted bitumen and CHV immediately after application and attenuation differed between the two products throughout the study period. Water contained primarily 3 ring PACs and aPACs. Microbial taxa with known oil degrading capacity increased in water relative to total community abundance. Emergent insect abundance was significantly lower in both oil treated enclosures relative to reference enclosures, but fish development was not significantly impacted by oil treatments. Monitored natural recovery could be successfully applied to oil spill affected freshwater shorelines, but additional data are required to determine long term recovery trajectories.

Anoxygenic phototrophic Chloroflexota member uses a Type I reaction center

Phototrophic bacteria within the Chloroflexota phylum are puzzling in their evolutionary origin. Previously known phototrophic Chloroflexota members use a Type II photosynthetic reaction center for light energy conversion but contain other photosynthesis machinery associated with Type I reaction center-utilizing phototrophs. We sampled an iron-rich boreal lake at the IISD-Experimental Lakes Area and enriched ‘Candidatus Chlorohelix allophototropha’, a phototrophic Chloroflexota member that uses a Type I reaction center. Phylogenomic evidence suggests that ancestors of ‘Ca. Chx. allophototropha’ served as a bridge for historic phototrophy gene exchange within the phylum. The Chloroflexota now represents the only bacterial phylum outside the Cyanobacteria where both major classes of photosynthetic reaction center occur and can serve as a model system to explore fundamental questions about the evolution of photosynthesis.

Fieldwork in the Experimental Lakes Area Adapts to COVID-19

Though anticipating long days and hard work as a few key crew members do the job of many, researchers heading to the lakes this summer are excited to leave the house.

Sedimentary phosphorus speciation dynamics following artificial eutrophication of Lake 227, Experimental Lakes Area, Ontario, Canada

<p>Stringent environmental policies in many countries have played an extensive role in reducing external phosphorus (P) loading to lakes from agriculture and urban sources. Nonetheless, such reductions in external P loading to many eutrophic lakes have not resulted in the expected concurrent restitution of water quality. Such a delayed recovery of many lakes is blamed both on internal loading of legacy P from lake sediments (i.e., benthic recycling) and the amplification of such internal P loading processes due to the reduction in external P concentrations. Hence, a detailed process understanding of P cycling at the sediment-water interface (SWI) is critical to understand nutrient loading, water quality and associated effects on lake water quality. Much of the work on sedimentary P cycling has traditionally focused on inorganic processes of soluble phosphate, particularly sorption to metals (Fe, Mn, Al) oxyhydroxides and clays. However, there is increasing recognition that organic forms of P, along with interactions between phosphate and humic substances, also play a decisive role in controlling P fluxes between sediments and the overlying water column.</p><p>This study focused on gaining further understanding of the such processes through the collection of sediment cores from the oxygenated epilimnion and the mostly anoxic hypolimnion of Lake 227 of the Experimental Lakes Area (ELA) in Ontario, Canada. Since 1969, this unique experimental lake has been fertilized with phosphorus (P), which triggered a relatively rapid trophic transition from oligotrophic to eutrophic conditions. The cores contain a chronological record of changes in sediment burial rates and sediment P speciation across this trophic transition.</p><p>Interpretation of such changes was undertaken by coupling results of chemical extractions with <sup>210</sup>Pb sediment dating, <sup>31</sup>P NMR, XANES and Mössbauer spectroscopy. The major sedimentary P fraction prior to lake enrichment starting in 1969 was organic P (P<sub>Org</sub>). Fertilization of the lake in 1969 coincided with significant increases in the accumulation rate of sediment, total organic carbon (TOC) and total P (TP), in addition to a marked relative contribution of NaHCO<sub>3</sub> extractable P. The combined proportion of P<sub>Hum</sub> and P<sub>Org</sub> desposited since artificial fertilization in 1969 account for ≥70% of total P burial in the sediments. The anticipated composition of such P<sub>Hum</sub> fractions was hypothesized to be ternary phosphate (PO<sub>4</sub>) complexes with humic substances. In support of this, the strong linear correlation between P and iron (Fe) extracted by NaHCO<sub>3</sub> implies a close association of the two elements in the humic fraction. Furthermore, XANES and Mössbauer spectra indicate that most Fe in the post-1969 sediments is conserved in the +3 oxidation state, which may be ascribed to the stabilization of reducible Fe by organic matter, partially due to the formation of ternary PO<sub>4</sub>-Fe(III)-humic complexes. Our findings suggest the artificial eutrophication of Lake 227 resulted in the accelerated accumulation of a large sedimentary reservoir of reactive sediment P that may drive continued internal P loading to the water column following the cessation of artificial fertilization. </p><p><strong> </strong></p>

Long-term influence of climate and experimental eutrophication regimes on phytoplankton blooms

Phytoplankton blooms respond to multiple drivers, including climate change and nutrient loading. Here we examine a long-term dataset from Lake 227, a site exposed to a fertilization experiment (1969–present). Changes in nitrogen:phosphorus loading ratios (high N:P, low N:P, P-only) did not impact mean annual biomass, but blooms exhibited substantial inter- and intra-annual variability. We used a process-oriented lake model, MyLake, to successfully reproduce lake physics over 48 years and test if a P-limited model structure predicted blooms. The timing and magnitude of blooms was reproduced during the P-only period but not for the high and low N:P periods, perhaps due to N acquisition pathways not currently included in the model. A model scenario with no experimental fertilization confirmed P loading is the major driver of blooms, while a scenario that removed climate-driven temperature trends showed that increased spring temperatures have exacerbated blooms beyond the effects of fertilization alone.Significance StatementHarmful algal blooms and eutrophication are key water quality issues worldwide. Managing algal blooms is often difficult because multiple drivers, such as climate change and nutrient loading, act concurrently and potentially synergistically. Long-term datasets and simulation models allow us to parse the effects of interacting drivers of blooms. The performance of our model depended on the ratio of nitrogen to phosphorus inputs, suggesting that complex biological dynamics control blooms under variable nutrient loads. We found that blooms were dampened under a “no climate change” scenario, suggesting that the interaction of nutrient loading and increased temperature intensifies blooms. Our results highlight successes and gaps in our ability to model blooms, helping to establish future management recommendations.Data Availability StatementData and metadata will be made available in a GitHub repository (https://github.com/biogeochemistry/Lake-227). Upon manuscript acceptance, the repository will be made publicly available and a DOI will be provided. We request that data users contact the Experimental Lakes Area directly, per their data use policy (http://www.iisd.org/ela/wp-content/uploads/2016/04/Data-Terms-And-Conditions.pdf).

Increased relative abundance of colonial scaled chrysophytes since pre-industrial times in minimally disturbed lakes from the Experimental Lakes Area, Ontario

A top–bottom paleolimnological analysis of 30 undisturbed lakes in the Experimental Lakes Area (ELA) in northwest Ontario showed marked increases in the relative abundance of colonial scaled chrysophyte taxa in most lakes since pre-industrial times. The increase in abundance of colonial taxa was primarily driven by Synura sphagnicola in small, high-nutrient, and warm lakes. The colonial taxa Synura petersenii and Synura echinulata also increased in the deeper study lakes. Detailed analysis of sediment cores from six lakes revealed that these changes occurred in the early to mid-1900s. Based on the modern distribution of scaled chrysophytes relative to lake physicochemical data, we propose multiple processes that may be contributing to these changes, such as changes in lake thermal properties and historical changes in the flux of important particles and solutes to lakes. Additional mechanisms that may contribute to the observed changes are discussed, including trophic interactions and changes in limnetic pCO2. Because the ELA is relatively undisturbed, our findings provide important information on the drivers responsible for increases in colonial chrysophyte abundance, which have been documented in studies of lakes in central Ontario and northeast United States.

Changing nitrogen deposition with low δ15N−NH4 + and δ15N−NO3 − values at the Experimental Lakes Area, northwestern Ontario, Canada

Ammonium deposition at the International Institute for Sustainable Development Experimental Lakes Area (IISD–ELA), in northwestern Ontario, Canada, has doubled in the last 45 years and thus is no longer among the low nitrogen (N) deposition sites in North America. This may be related to the concurrent intensification of Manitoba agriculture to the west and upwind of the ELA. Large increases in ammonium deposition at the ELA were important in driving the observed trend and increased the NH4 + to NO3 − ratio of input to aquatic and terrestrial systems. Stable isotope analyses of two years of bulk (wet and dry) atmospheric deposition revealed very large ranges in δ15N−NH4 + (22‰ range), δ15N−NO3 − (18‰), and δ18O–NO3 − (19‰). Few other δ15N−NH4 +, δ15N−NO3 −, and δ18O–NO3 − values have been published for Canadian precipitation. Increases in δ15N of NH4 + and NO3 − in July occurred with increases in total N deposition. The wide range and seasonal trends of δ15N and δ18O values in ELA precipitation mean that studies characterizing N inputs to watersheds and lakes require an ongoing and comprehensive annual sampling regime. Global trends of declining δ15N of N deposition evident in lake sediment records may be a result of increases in NH4 + deposition with lower δ15N−NH4 + values. Similarly, the relationship in Lake Superior between increasing NO3 − and lower δ15N−NO3 − values may be explained by increased atmospheric deposition of N with low δ15N values.