Microbial Drivers of Nutrient Cycling

Phosphorus Equilibrium as Influenced by Microbial Communities Within Sediments

Terrestrial environments provide important nutrients, such as phosphorus, to the freshwater tributaries that surround them. Despite current reduction efforts set out by agencies, there is still sufficient phosphorus loading discharged to freshwater systems inducing anthropogenically accelerated eutrophication. One method of phosphorus loading generates from nonpoint sources, which are diffuse and include agriculture. In Lake Erie, phosphorus loading from nonpoint sources account for 88 to 93 % of inputs to the lake. In small tributaries, phosphorus loading from agricultural fields are partially altered by a sediment buffering mechanism that governs phosphorus sorption. Where phosphorus buffering capacity had, historically, been strictly related to sediment sorption and desorption, current studies prove that microbial communities play an important role in this mechanism. Despite their undeniable importance, sediment microbial communities are severely under characterised and typical laboratory adsorption experiments do not favor biotic processes. During batch adsorption studies, sediments are disrupted via sampling, transportation, homogenization, and are subjected to light exclusion which may suppress biotic activity. Additionally, the mechanism of shaking utilized in these experiments disrupts biofilms, modifies redox structure, and increases surface area of mineral phases in a way that is no longer representative of the consolidated interface that is present in-situ. This research explores the use of mesocosms (core samples to be manipulated by a flow-through design in such a way as to preserve the sediment-water interface disturbing the microbial community as little as possible. The adsorption information gleaned from this type of experiment is then be combined with broader molecular approaches that address microbial function in the sediments at the interface via RNA-sequencing, such as metagenomics. 

Point Source Nutrient Load into Lake Erie

Lake Erie has long faced environmental challenges due to toxic cyanobacteria blooms, largely driven by nutrient pollution from agricultural and urban sources. In collaboration with Environment and Climate Change Canada (ECCC) and the Ontario Greenhouse Vegetable Growers (OGVG), this study investigates Sturgeon Creek, a tributary of Lake Erie, to assess pollution sources and nutrient inputs. Through seasonal sampling and analyses—including chemical analysis, microbial community profiling, isotopic signatures, and qPCR—pollution hotspots will be identified and further examined to determine their sources and extent. The goal is to quantify and characterize nutrient contributions to Lake Erie, informing mitigation strategies. Additionally, local horticulturists are exploring and testing green solutions to address these issues, integrating sustainable practices into water quality management. 

The Role of Microbes in Nutrient Release from Sediments in Lake Erie

Eutrophication, driven by excessive nutrient loads, threatens aquatic ecosystems, public health, and causes significant economic losses, with over 60% of lakes globally at risk. Lake Erie, the most nutrient-sensitive of the Laurentian Great Lakes, is a prime example of eutrophication. Although both Canada and the United States have committed to reducing external nutrient loads to Lake Erie, eutrophication-related issues, such as cyanobacterial blooms, continue to worsen in frequency and extent. As external nutrient inputs decrease, internal nutrient release from sediments becomes a dominant driver of eutrophication, sustaining water quality degradation for years. This internal loading is driven by sediment microorganisms, which respond to environmental changes and influence nutrient release through shifts in community composition and functional gene expression. However, previous studies on internal loading have mainly focused on nutrient release from sediments, with limited attention given to the role of microorganisms. In Lake Erie, variations in water flow direction and significant physical and chemical differences across zones may result in distinct microbial functional responses, which, in turn, affect nutrient release. The mechanisms linking microbial functional responses to internal loading and their role in the development of cyanobacterial harmful algal blooms (cHABs) in Lake Erie remain poorly understood. This study aims to assess the functional response of sediment microbial communities and their impact on internal loading in Lake Erie. The findings will enhance our understanding of sediment microbial responses to eutrophication, their role in internal loading, and provide valuable insights for lake management strategies.  

Exploring the Land to Lake connection linking nutrient dynamics, source identification and ecological function using advance genomics in the western Lake Ontario watershed 

Some areas of the Great Lakes experience nutrient eutrophication that impair beneficial use and result in harmful effects on ecosystem functions. Challenged by rapid population growth and land use changes, there is pressing need to safeguard water quality in the western Lake Ontario watershed.  There is limited scientific information on the influence of the existing microbial consortia and their contributions to nutrient dynamics in Great Lake watersheds for informed effective management decisions. Efforts are underway to understand both nutrient dynamics and loading to the western basin of Lake Ontario. Currently, target tributaries are sampled for a range of general water quality parameters (e.g., nutrients, E. coli, pH, turbidity) and collected year-round, during base- and event-flow conditions. These tributaries span a range of land-use, including large urban areas and Canada’s only urban national park. To augment this monitoring work 16S rRNA metabarcoding analysis targeting both the total DNA and active RNA component was applied to water samples collected within a spatial gradient of 11 tributaries. From these samples baseline microbial bioindicators for each large tributary were identified and potential changes in community structures after large rain/precipitation events were compared. Integrating this large genomic data set to understand the land to lake connection will provide additional insight to improve nutrient management for healthy Great Lakes ecosystems. 

Great Lakes Recreational Water Security

Recreational water usage is a major tourist attraction within the Laurentian Great Lakes, where pathogenic bacterial levels have increased substantially compared to historic trends. Freshwater quality assessments commonly rely on CFUs of broad or ambiguous taxa (i.e. enterococci) found within the water column and are only performed occasionally. Further, sampling protocols do not take into account the energy dynamics of the system (waves, currents, swimmer density) and often rely on assessments of planktonic populations sampled during calm low activity periods. It has been shown that sediment resuspension, transport, and deposition influence both the temporal and spatial variation in microbial communities within both the sediments and water compartments. The labs approach links aspects of biogeochemical regulation to pathogen emergence in these systems to such environmental issues concerning recreational water security and addresses a need for modern evaluations and solutions to microbial contamination in large lake systems.