Aquatic ecosystems are varied and complex, and cannot be described in a single unified manner. However, each system, whether it is a pelagic, coastal marine or riverine, still follows certain patterns of energy and nutrient transfer. The field of Ecological Stoichiometry aims at understanding the balance of energy and chemical elements in ecological interactions. It examines the trophic relationships linking the elemental physiology of organisms with their food web interactions and ecosystem function. In particular, it explores nutrient dynamics with concepts such as stoichiometric food quality imposed by elemental co-limitation, consumer-driven nutrient recycling or the growth rate hypothesis. Ecological Stoichiometry has been applied on different levels of biological organization, from organelle biochemistry to ecosystems and across diverse organisms from bacteria to plants and animals. In this session, we welcome contributions from the broad community to show how Ecological Stoichiometry can improve our understanding in diverse fields, including studies on individuals, populations, communities, ecosystems, and even human alteration to the Earth system. This session also calls for contributions from across the range of approaches (theoretical, experimental, observational, and modelling) that can be used to investigate the effects of changing environments with the help of Ecological Stoichiometry on all aspects of aquatic ecosystems.
Lead Organizer: Cecilia Laspoumaderes, Univ. Nac. del Comahue - INIBIOMA- CONICET (claspoumaderes@comahue-conicet.gob.ar)
Co-organizers:
Cedric Meunier, Biologische Anstalt Helgoland, Alfred Wegener Institut, Germany (Cedric.Meunier@awi.de)
Maarten Boersma, Biologische Anstalt Helgoland, Alfred Wegener Institut, Germany (Maarten.Boersma@awi.de)
Erik Sperfeld, Universität Greifswald, Germany (erik.sperfeld@uni-greifswald.de)
Presentations
08:30 AM
Stoichiometric Symptoms of the Urban Stream Syndrome (7238)
Primary Presenter: Eric Moody, Middlebury College (ekmoody@middlebury.edu)
The urban stream syndrome describes a set of interacting stressors that define the conditions that control biological function in urbanized streams, particularly those in the Global North. While one well-studied “symptom” of the urban stream syndrome is increased nutrient loading, the relative stoichiometry of these nutrients (e.g., nitrogen (N) and phosphorus (P)) may also be unique in urban streams due to organismal responses to other urban stressors. Urbanization may alter the stoichiometric traits of aquatic organisms by selecting for sets of traits with a common stoichiometric signature, which may in turn alter the relative storage and fluxes of key elements like N and P in urban streams. We hypothesize that unpredictable hydrology, elevated maximum temperatures, and increased concentrations of salts associated with urbanization select for taxa with low body C:P and N:P because these taxa must exhibit rapid growth rates and/or come from marine-derived lineages with greater salt tolerance. Both rapidly growing insects and salt-tolerant crustaceans have relatively low body C:P and body N:P, albeit for different biological reasons. We also suggest that the effects of urbanization on stoichiometric traits should be strongest at high latitudes, where urban heat island effects and use of deicing salts create a strongly differentiated fitness landscape. We use a recently developed stoichiometric diversity framework to analyze benthic invertebrate assemblages across urban gradients in Vermont and Arkansas (USA) to test these hypotheses.
08:45 AM
REACTIVE MACRONUTRIENT RATIOS DETERMINE BENTHIC AND HYPORHEIC BIOFILM STRUCTURE AND FUNCTION IN A STREAM MESOCOSM EXPERIMENT (5137)
Primary Presenter: Anika Grosse, Helmholtz Centre for Environmental Research - UFZ (anika.grosse@ufz.de)
Benthic and hyporheic biofilms play a key role in stream nutrient cycling, ecosystem metabolism and greenhouse gas emissions. However, the relative roles of dissolved organic carbon (DOC), inorganic carbon (via light availability for photosynthesis), nitrogen (N) and phosphorus (P) availability for biofilm properties and the associated control of C, N and P assimilation by biofilms remain poorly understood. Here we present results from a full factorial stream mesocosm experiment to investigate how reactive DOC:N:P ratios (as DOC, nitrate-N (NO3-N) and phosphate-P (PO4-P)) and light availability (10 and 46 µmol/m2/s) affect the heterotrophic and autotrophic structure and function of benthic and hyporheic biofilms. Due to high NO3-N concentrations, the background reactive DOC:N:P ratio was 317:1572:1, indicating low relative availability of DOC and P. The addition of reactive C and P sources resulted in a reactive DOC:N:P ratio of 97:47:1, more similar to typical ratios of bacteria and algae. Altered reactive nutrient ratios increased bacterial density and heterotrophic functional diversity in both benthic and hyporheic biofilms, whereas light increased autotrophic functional diversity only when combined with altered DOC:N:P ratios. Our data confirm that the ratio of reactive macronutrients is an important driver of benthic and hyporheic biofilm composition and function, and interacts differently with autotrophic and heterotrophic components. These results highlight the need for coupled C:N:P studies to better assess stream ecosystem responses to human impacts.
09:00 AM
Response of lake metabolism to catchment inputs inferred using high-frequency lake and stream data from across the northern hemisphere (5946)
Primary Presenter: Jessica Corman, University of Nebraska-Lincoln (jcorman3@unl.edu)
In lakes, the rates of gross primary production (GPP), ecosystem respiration (R), and net ecosystem production (NEP) are often controlled by resource availability. Herein, we explore how catchment vs. within lake predictors of metabolism compare across lake types. We combined stream loads of dissolved organic carbon (DOC), total nitrogen (TN), and total phosphorus (TP) with lake DOC, TN, and TP concentrations and high frequency in situ monitoring of dissolved oxygen from 16 lakes spanning 39 to 64 oN, a range of inflowing streams, and trophic status. We found that stream load stoichiometry was indicative of lake stoichiometry for C:N and C:P (R2=0.74 and R2=0.84, respectively), but not for N:P (R2=0.04). As we found a strong positive correlation between TN and TP, we only used TP in our statistical models. For the catchment model, GPP and R were best predicted by DOC load, TP load, and load N:P (R2=0.85 and R2 = 0.82, respectively). For the lake model, GPP and R were best predicted by TP concentrations (R2=0.86 and R2=0.67, respectively). The inclusion of N:P in the watershed model, but not the lake model, suggests that both N and P regulate metabolism and that organisms may be responding more strongly to catchment inputs than lake resources. Our models predicted NEP poorly, though it is unclear why. Overall, our work stresses the importance of characterizing lake catchment loads to predict metabolic rates, a result that may be particularly important in watersheds experiencing changing hydrologic regimes related to global environmental change.
09:15 AM
Only A Multiannual Perspective Reveals Globally Ubiquitous Stoichiometric Relationships Between Nutrients And Chlorophyll-a In Shallow Lakes (6766)
Primary Presenter: Daniel Graeber, Helmholtz-Centre for Environmental Research - UFZ (daniel.graeber@ufz.de)
Nutrients enhance phytoplankton growth in shallow lakes, but lake-specific responses to nutrient changes are highly variable. Here, we hypothesize that this large variability results from stochastic changes in short-term drivers, which obscure a ubiquitous and predictable, long-term stoichiometric relationship between phytoplankton and nutrients. To test this hypothesis, we extracted long-term variation in multiannual time series by calculating 5-year simple moving averages (SMAs) based on growing season averages of total nitrogen (TN), total phosphorus (TP), and chlorophyll a (Chla, as a phytoplankton biomass surrogate) concentrations for 159 shallow lakes from around the globe. The residuals of these 5-year SMAs represent short-term variability. For both datasets, we calculated regressions between TN, TP, and Chla along a gradient of molar TN : TP. Using a rigorous bootstrap approach, we show that regressions between nutrients and Chla are highly robust for 5-year SMAs (median R² = 0.87), where we find predictable, ubiquitous relationships between nutrients and Chla along the TN : TP gradient. The remaining short-term variation in Chla was not related to nutrients. This ubiquitous, stoichiometric, long-term relationship between nutrients and phytoplankton provides a new approach for developing effective management strategies for nutrients in shallow lakes and catchments.
09:30 AM
The C:N:P of nanoplanktonic diatoms (7202)
Primary Presenter: Ishari Nuwanthi Samarasinghe Gunasekara Liyanage, Dahousie University (nuwanthisamarasinghe89@gmail.com)
Nano-sized diatoms are common members of phytoplankton communities and may play a significant role in export. Compared to micro-sized diatoms, little is known about their physiological responses, elemental, and biochemical composition of nano-sized diatoms in response to environmental conditions. To add to the small but growing database of knowledge of this group, Minidiscus trioculatus (CCMP 496) and Minutocellus polymorphus (CCMP 501) were acclimated and grown under a range of irradiances (15 to 480 μmol photons m-2 s-1 and temperatures (5 to 25 0C) to determine their the growth rate, photophysiological response, and C:N:Si:P content under optimal and sub-optimal growth conditions. Both species exhibit: increases in C: N irradiance between 15 to 250 but a small decrease at 480 μmol photons m-2 s-1 (perhaps due to higher maintenance costs associated with photoinhibition), decreases in N:P with increasing temperature, and no clear trend in N:P with changes in growth rate due to irradiance or temperature. These results suggest that neither the growth rate hypothesis or the temperature compensation hypotheses apply to these small diatoms.
09:45 AM
NITROGEN FIXATION AND C:N:P RATIOS IN AN EXTREMELY PHOSPHATE-RICH SODA LAKE (7183)
Primary Presenter: Sebastian Haas, University of Washington (s.haas@dal.ca)
Carbonate-rich alkaline lakes (“soda lakes”) often have very high phosphate but low inorganic nitrogen (N) concentrations. These unusual systems provide insights into mechanisms underlying biogeochemical nutrient cycling and are also interesting analogs for research on the origin of life, for which high concentrations of phosphorus (P) are required. Across a seasonal wet-dry cycle, we sampled the water columns and sediments of two neighboring (~100 m apart) shallow soda lakes in British Columbia, Canada. We measured 15N2 fixation rates, nutrient limitation, stable isotope signatures (δ15N, δ13C), as well as concentrations of various P, N and C phases. Last Chance Lake’s water column appears to be the most phosphate rich (up to 37 mM) on Earth and N is limiting its primary productivity, yet biological N2 fixation (BNF) rates were low to moderate (≤30 nM d-1). Goodenough Lake also has unusually low inorganic N:P ratios but is considerably less phosphate-rich (~0.1 mM) and contains cyanobacterial benthic mats fixing N2 at high rates (115.3 ±6.6 µM d-1), which may cause higher particulate N:P ratios and lower phosphate concentrations by creating P demand. Conversely, in Last Chance Lake, BNF limitation likely contributes to the remarkably conservative behavior of phosphate, and, together with geochemical mechanisms, explains why so much phosphate remains dissolved. We will present insights on the interactions of extremely high phosphate concentrations, low BNF rates, particulate C:N:P ratios, and primary production based on the natural experiment provided by these neighboring lakes.
SS040C Ecological Stoichiometry in a Dynamic World: Exploring the Ecology of Changing Environments Through Theory, Patterns, Processes and Experiments.
Description
Time: 8:30 AM
Date: 7/6/2023
Room: Auditorium Mallorca