Pressures on aquatic ecosystems, such as rising nutrient emissions, more extreme weather patterns, permafrost thaw, land use changes, water diversions, and intensified coastal shoreline erosion, are accompanied by regional to continental scale alterations of the biogeochemical cycles of carbon and nutrients, from land to the coastal ocean. Given the complexity of the interactions between climate change, human activities, and ecosystem responses, integrated data acquisition and modeling tools are required to assess and predict the sources and sinks of carbon and nutrients, including phosphorus, nitrogen, silicon, and iron, along the aquatic continuum. This session will highlight advances, as well as remaining knowledge gaps, in our qualitative and quantitative understanding of the evolving speciation, loadings, transport pathways, retention mechanisms of carbon and nutrients in inland waters and nearshore marine environments. An important outcome will be to evaluate the extent to which our current scientific understanding can guide the management of aquatic ecosystems and reduce the risks associated with, for example, the strengthening of water column stratification, nutrient enrichment, and changes in nutrient limitation patterns of lakes and coastal marine systems. Further topics of interest include but are not limited to: the coupling of physical and biogeochemical processes controlling nutrient retention along the aquatic continuum; projected terrestrial carbon and nutrient inputs to aquatic systems under variable climate change scenarios; greenhouse gas emissions from aquatic ecosystems; nearshore-offshore and inter-basin exchanges in large lakes; aquatic photosynthesis, sediment and water column respiration as sentinels of aquatic food web perturbations and drivers of biogeochemical cycling; elemental and material mass balances and related modeling and accounting approaches; estimating chemical loadings to rivers; environmental indicators; environmental management and policies for mitigation and adaptation to climate change. The session will be open to research contributions ranging from field observations and experimental studies, to data-driven machine learning and mechanistic modeling of nutrient and carbon dynamics in aquatic environments, and from local to global scales. We especially welcome presentations that address the responses of the aquatic carbon and nutrient cycles to climate change and other anthropogenic forcings and interventions in the hydrological cycle.
Lead Organizer: Serghei Bocaniov, University of Waterloo, Ontario, Canada (sbocaniov@uwaterloo.ca)
Co-organizers:
Serghei Bocaniov, Department of Earth and Environmental Sciences, University of Waterloo, Waterloo, Ontario, Canada (sbocaniov@uwaterloo.ca)
Zahra Akbarzadeh, Department of Earth and Environmental Sciences, University of Waterloo, Waterloo (zahra.akbarzadeh@gmail.com)
Sergei Katsev, Large Lakes Observatory, University of Minnesota at Duluth (skatsev@d.umn.edu)
Philippe Van Cappellen, Department of Earth and Environmental Sciences, University of Waterloo (pvc@uwaterloo.ca)
Presentations
02:00 PM
CHANGING AQUATIC CARBON AND NUTRIENTS WITH HYDROLOGIC PRESSES AND PULSES IN COASTAL WETLANDS (7688)
Primary Presenter: John Kominoski, Florida International University (jkominos@fiu.edu)
Climate change is increasing storms and sea levels throughout coastal regions. Humans can both increase and decrease freshwater presses (long-term patterns) and pulses (episodic fluctuations). How freshwater and marine hydrologic presses and pulses are impacting aquatic carbon and nutrients in ecosystems is uncertain. We measured long-term (2000-2022) changes in precipitation and surface water chemistry [salinity, dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorus (TP) concentrations] in subtropical wetlands in the Everglades (Florida, USA). Precipitation pulses (i.e., rainfall at a site exceeding 2.5 cm h-1) were variable over space and time (< 2 to 24 cm d-1). Pulses both increased and decreased TN (from -100 to +170 μMol L-1) and TP (from -1 to 5 μMol L-1) above mean monthly concentrations. Pulsed increases in TN and TP were higher at brackish than freshwater sites, and changes in TN and TP were greatest from 5-10 cm d-1 rainfall. Hurricane storm surge and freshwater flooding increased DOC concentrations in mangrove estuaries and reduced DOC aromaticity (SUVA254). Long-term freshwater restoration is reducing salinities in brackish estuaries, and freshwater DOC concentrations declined at brackish salinities above 10 ppt. Sea-level rise is increasing saltwater intrusion and carbon losses in brackish wetlands, but freshwater restoration is reducing peak dry-season salinities. Hydrologic changes from storms and sea-level rise are mobilizing fluxes of aquatic carbon and nutrients, requiring long-term research to understand net ecosystem effects.
02:15 PM
TERRESTRIAL LINKAGES TO EARLY SUCCESSIONAL PONDS FOLLOWING THE 1980 MOUNT ST. HELENS ERUPTION (7870)
Primary Presenter: Katey Queen, Western Washington University (queenk3@wwu.edu)
Ponds created by the 1980 Mount St. Helens eruption are still in their early successional stages. As climate change warms the region, an increase in terrestrial organic carbon, i.e. brownification, is expected to alter pond habitats. Zooplankton communities in these ponds may experience profound habitat and resource changes due to terrestrial forest communities shifting from deciduous to coniferous vegetation. Eighteen mesocosms were established in 300-L cattle tanks near three perennial ponds in the Mount St. Helens National Volcanic Monument, Washington, USA. Using a factorial design, mesocosms were treated with deciduous or coniferous leaf litter crossed with a browning agent (i.e., humic acid). Ponds and mesocosms were sampled weekly for five weeks to examine zooplankton communities (abundance, biomass, richness), as well as trends in temperature, dissolved oxygen, pH, and nutrients. After three weeks, dissolved organic carbon (DOC) concentrations in mesocosms averaged four times higher in browning-deciduous treatments compared to deciduous treatments alone and eight-fold higher than the untreated controls, with DOC concentrations in coniferous mesocosms slightly lower than deciduous. There were differences in zooplankton community composition and biomass between the mesocosm treatments, with the largest abundance and diversity shifts from the control in browning-deciduous treatments. This study aims to understand the terrestrial-aquatic linkages in an early successional landscape and provide insight into zooplankton community structure and function.
02:30 PM
Long-term changes in precipitation drive DOC and phytoplankton dynamics in oligotrophic boreal lakes (7980)
Primary Presenter: Scott Higgins, IISD Experimental Lakes Area (shiggins@iisd-ela.org)
Dissolved organic carbon (DOC) influences a wide range limnological properties and processes, including potentially large effects on productivity at the base of lake food webs. This study evaluated the effects of DOC on phytoplankton communities and primary production using long-term observations and space-for-time substitutions for a series of unmanipulated lakes at the IISD-Experimental Lakes Area, Canada. Spatially, elevated DOC corresponded with substantial declines (c. -70%) in phytoplankton biomass and productivity among lakes. Temporally, long-term changes in precipitation were correlated with increased DOC loads and lake concentrations. Consistent with spatial surveys, increased DOC within lakes over time was associated with reduced water clarity and large declines (c. -18-30 %) in thermocline and euphotic depths and phytoplankton biomass (c. -40 %) within deeper stratified lakes. However, within a shallow polymictic lake increased DOC appeared to drive a shift in alternate stable states resulting in large increase (c. +300 %) in phytoplankton biomass. The use of chlorophyll a (chl) as an indicator of phytoplankton biomass across gradients of DOC and water clarity was highly misleading due to the capacity for algae to alter their pigment concentrations in response to light conditions. Ratios of chl:carbon and chl:biomass systematically increased with DOC. Moreover, relying on volumetric units of epilimnetic biomass or productivity was also misleading. Given that epilimnetic and euphotic zone volumes systematically declined with increases in DOC, employing areal or volume weighted units was more appropriate for evaluating ecosystem-level effects of DOC.
02:45 PM
SEDIMENT SOURCE SHAPES INTERACTIONS BETWEEN DISSOLVED AND PARTICULATE PHOSPHORUS DURING HIGH FLOW EVENTS IN AN AGRICULTURAL WATERSHED (8380)
Primary Presenter: Morgan Shaw, The Ohio State University (shaw.759@buckeyemail.osu.edu)
Eutrophication of freshwater ecosystems is a global environmental problem often caused by excess bioavailable phosphorus (P). Thus, it is important to understand the sources and sinks of bioavailable P in a watershed. Previous work suggests that during high-flow events, which dominate annual P and sediment loads, exchange of P between dissolved and particulate forms affects the bioavailability of P exports to recipient ecosystems. Yet, suspended sediment is derived from many sources on the landscape, which can differ in composition and likely, affinity for P sorption. Because human activities can affect sediment source, it is important to understand how source influences sediment-P (sedP)-dissolved P (DP) interactions during high flow. To address this, we collected seven distinct sources (four streambank soils, two cropland soils, and streambed sediment) from a Maumee River tributary, the Maumee watershed being the main source of P fueling Lake Erie cyanobacteria blooms. Using source material collected in May, June, and December, we conducted three experiments which examined sedP-DP interactions in a simulated high-flow environment for 120 hours. Streambed and streambank sources sorbed P, with most P sorption occurring during the first day, while cropland soils did not absorb additional P. Our results indicate that sediment source likely influences sedP-DP interactions during high flows, suggesting that changes in land management that alter the relative balances of sediment sources may influence in-stream P transformations and bioavailability of P to recipient ecosystems.
03:00 PM
Filling the gap: Estimating Australia’s riverine carbon gas emissions (8018)
Primary Presenter: Adam Rexroade, Charles Darwin University (rexroadea@gmail.com)
In order to understand aquatic carbon export in a changing world, we must first understand the baseline. Compared to North America and Europe, Australia has significantly fewer observations of CO2 and CH4 in streams and rivers, particularly in the tropical regions. We used synoptic sampling of 164 different headwater streams in three tropical sub-climates (humid, wet-dry and semi-arid) and the temperate region of Australia to try to better quantify the greenhouse gas (GHG) emissions from headwater streams in both spatial and temporal contexts. Across all four regions, CO2 and CH4 concentrations were 163.8 and 1.7 μmol L-1, significantly higher than previously reported global medians for all stream orders, respectively. Significant spatial variation occurred between the tropical and temperate zones as well as across the tropical sub-climates. Temporally, while gas concentration varied only minimally, gas evasion varied significantly between seasons in the tropics, particularly in the semi-arid and wet-dry tropics where at least 85% and 54% of streams were seasonally ephemeral, respectively. This seasonal change in flow regime not only reduces surface areas of streams but the lower flow rate and velocity reduce the gas transfer velocity. These changes in surface area and gas transfer velocity show that hydrology drives seasonal changes rather than the availability of either gas. These data both demonstrate the need for spatially and temporally diverse (at both global and regional scales) training data for global upscaling efforts, as well as highlight Australia as a potential hotspot for GHG emissions on a global scale.
03:15 PM
The Metabolic Balance of Lake Superior’s Mixed Layer (7864)
Primary Presenter: Panditha Gunawardana, Trent University (sasindugunawardana@trentu.ca)
Understanding carbon (C) dynamics in large lake ecosystems presents significant challenges due to their size, limiting our understanding of their role in the global C cycle. Here, we used autonomous underwater vehicles (gliders) to calculate metabolism in Lake Superior, the world’s largest freshwater lake by surface area. We used seven years of high-resolution limnological data from 17 glider missions, including dissolved oxygen and temperature, along with wind data from the National Data Buoy Center, to calculate daily epilimnetic gross primary production (0.32 ± 0.49 g O2 m-3 day-1) and ecosystem respiration (0.50 ± 0.60 g O2 m-3 day-1) using established methods. Our findings revealed net heterotrophy dominated in the epilimnion of Lake Superior, with net ecosystem production recorded at 0.17 ± 0.53 g O2 m-3 day-1, displaying spatial and temporal variations. Despite relatively lower metabolic rates than other lake ecosystems, Lake Superior's substantial size significantly contributes to the global C cycle. This study showcases the unexploited potential of gliders in advancing our understanding of C dynamics in large lake ecosystems.
SS37A - Carbon and Nutrient Fluxes Under Climate Change: Cycling, Retention, and Impacts Along the Aquatic Continuum from Land to Coastal Ocean
Description
Time: 2:00 PM
Date: 7/6/2024
Room: Meeting Room KL