With global warming and increased erratic and severe weather events, our world is changing. Understanding aquatic ecosystem health, e.g., the mechanisms that sustain biodiversity and ecosystem functions, in a world with which we are familiar is difficult, let alone in a constantly changing world. Generations of aquatic ecologists have produced knowledge showing linkages between inflows (hydraulic displacement and resource loading), temperature, stratification, irradiance, conductivity, biodiversity, and ecosystem functions. With this understanding, our power to predict ecosystem health remains limited and our ability to manage aquatic ecosystems tenuous. In an unfamiliar and changing world, other processes that are currently not considered in management decisions are likely to become more important. For example, increased propagule pressure on the early-season plankton community from the previous year’s late-season plankton community will likely occur with milder winters. It is possible that less palatable assemblages will occur earlier in the season, which might sequester resources and prevent them from moving up the food web at a time when many organisms are spawning. In addition, microbially-driven ecosystem processes and interactions between microbes and other plankton taxa are likely to change. Erratic weather might lead to greater stochasticity and magnitude in disturbances causing local extinctions of rare species, thereby decreasing richness and destabilizing ecosystem functions. In this session, we welcome presentations that explore the issue of how to better understand aquatic ecosystem health (including, but not limited to, microbes and plankton) in a changing world with which we are unfamiliar. Presentations that are based on patterns observed across environmental gradients (e.g., latitudinal, precipitation, temperature, disturbance frequency, etc.) are particularly welcome.
Lead Organizer: Daniel Roelke, Texas A&M University Galveston (droelke@tamu.edu)
Co-organizers:
Jessica Labonte, Texas A&M University Galveston, USA (labontej@tamug.edu)
Simon Mitrovic, University of Technology Sydney, Australia (Simon.Mitrovic@dnr.nsw.gov.au)
Robert Ptacnik, WasserCluster Lunz, Austria (Robert.Ptacnik@wcl.ac.at)
Sierra Cagle, Texas A&M University Galveston (sec1414@tamu.edu)
Presentations
02:00 PM
Freshwater planktonic cyanobacterial blooms in rivers; a review of species, toxins, causes and possible changes due to climate change and river flow management (8310)
Primary Presenter: Simon Mitrovic, University of Technology Sydney (simon.mitrovic@uts.edu.au)
In freshwaters, much of the focus on cyanobacterial harmful algal bloom (cHAB) research has centred around lakes and reservoirs. However, blooms of riverine planktonic cHABs are also common in many areas of the world and may increase with climate change. To date there has been no comprehensive world-wide review of planktonic cyanobacterial blooms in rivers and their toxins, and the factors contributing to bloom formation. This review examines and summarises the available published literature on riverine planktonic cHABs including information on the bloom forming species, toxins produced and conditions contributing to bloom formation. We develop conceptual models of planktonic cHAB river bloom formation and discuss the possible influence of climate change on the main drivers of blooms and possible management strategies to control riverine blooms. We use historic river flow and air temperature changes to illustrate how river systems have changed over time due to development and climate change and examine how this may influence bloom occurrence.
02:15 PM
INFERRING CLIMATE CHANGE EFFECTS ON LAKES THROUGH COMPARISON OF PHYTOPLANKTON AND PHYTOTOXINS FROM TWENTY LAKES SPANNING A PRONOUNCED PRECIPITATION GRADIENT (7938)
Primary Presenter: Daniel Roelke, Texas A&M University Galveston (droelke@tamu.edu)
With global warming, there is need for better understanding of mechanisms that sustain ecosystem health, specifically biodiversity and ecosystem functioning. In this research, we infer climate change effects on lakes, specifically altered hydrology, through comparison of phytoplankton and phytotoxins from lakes that span a pronounced precipitation gradient. The lakes are warm-monomictic systems of the southcentral USA. In-lake conditions, phytoplankton composition, microcystin concentrations, and microbial functions were explored. Our data revealed widespread microcystins in lakes across this region, some of which exceeded regulatory limits. Microcystins were higher in the spring than summer, indicating that these lakes, even across a large range of precipitation, do not follow the trends of temperate dimictic lakes. Microcystins were found in surface waters and bottom waters well below the photic zone, reflecting the persistence of these toxins in the environment. Our analyses showed strong association between microcystins, nitrate + nitrite, Planktothrix abundance, and transcriptional activity. Many systems exhibited strong denitrification in the spring, perhaps contributing to the decreased toxin concentrations in the summer. Counter to most of the lakes, one lake, positioned on the drier end of our precipitation gradient and which had the highest microcystin concentrations, indicated nitrogen cycle disruption, including inhibited denitrification. These findings suggest that with climate change in this area, ecosystem health is likely to change for the worse.
02:30 PM
Modeling cyanobacteria bloom formation and toxin production as a function of environmental N:P stoichiometry and hydraulic displacement (8318)
Primary Presenter: Sierra Cagle, Texas A&M University at Galveston (sec1414@tamu.edu)
Cyanobacteria harmful algal blooms (HABs) are major disruptors of ecosystem functioning and are becoming increasingly problematic in some aquatic systems as climate change related impacts alter water column processes. In the work presented here, we focus on how N:P stoichiometry and hydraulic displacement, two lake characteristics influenced by anthropogenic activity and climate change, regulate cyanobacteria population dynamics and toxin production within a process driven numerical model. We also examine how phytoplankton diversity is altered under bloom conditions or periods of elevated toxin production to better understand the complex interplay between diversity, competition, interference strategies (e.g. toxin production) and environmental conditions that influence ecosystem functioning or loss thereof via bloom occurrence. For this work, we used a previously published plankton model, which produces seasonal phytoplankton dynamics and includes a population rich phytoplankton assemblage, allowing us to examine biotic interactions across a range of environmental gradients. The model was altered to include environmental conditions typical of warm monomictic systems in the southcentral USA, and a cyanobacteria state variable. Incorporation of the cyanobacteria state variable was coupled with production of cyanotoxins which negatively affected other biotic model populations. And, as part of model tailoring, we compared the usefulness of two equations which differently represent the relationship between toxin production and nutrient concentrations versus nutrient stoichiometry. Using both equations, we ran simulations over a gradient of N:P conditions using hydraulic displacement rates typical of systems spanning an East-West precipitation gradient in Texas (calculated using the Hydrologic and Water Quality System (HAWQS) for Texas reservoirs). Lakes in this region were the focus of previous work which produced empirical data against which the model results will be compared. This study will provide insight to factors important for maintenance of ecosystem health and functioning in the face of cyanobacteria HABs.
02:45 PM
Environmental factors associated with toxic cyanobacterial proliferations in a Central Texas reservoir (8453)
Primary Presenter: Brent Bellinger, City of Austin (brent.bellinger@austintexas.gov)
Cyanobacterial harmful algal proliferations are increasingly associated with dog and livestock deaths when benthic mats break free of their substrate and float to the surface. Fatalities have been linked to neurotoxicosis from anatoxins, potent alkaloids produced by certain genera of filamentous cyanobacteria. After numerous reports of dog illnesses and deaths at a popular recreation site on Lady Bird Lake, Austin, Texas in late summer 2019, water and floating mat samples were collected from several sites along the reservoir. Water quality parameters were measured and mat samples were maintained for algal isolation and DNA identification. Samples were also analyzed for cyanobacterial toxins using LC-MS. Dihydroanatoxin-a was detected in mat materials from two of the four sites (0.6 – 133 ng/g wet weight) while water samples remained toxin free over the course of the sampling period; no other cyanobacterial toxins were detected. DNA sequencing analysis of cyanobacterial isolates yielded a total of 11 genera, including Geitlerinema, Tyconema, Pseudanabaena, and Phormidium/Microcoleus, taxa known to produce anatoxins, including dihydroanatoxin, among other cyanotoxins. Analyses support low daily upriver dam discharge, higher TP and NO3 concentrations, and day of the year were the main parameters associated with the presence of toxic floating cyanobacterial mats.
03:00 PM
SPATIOTEMPORAL PATTERNS IN pCO2 IN AN IMPOUNDED URBAN STREAM SYSTEM WITH A HISTORY OF HARMFUL ALGAL BLOOMS (7780)
Primary Presenter: Reynaldo Patino, U.S. Geological Survey (at Texas Tech University) (reynaldo.patino@ttu.edu)
Intense photosynthesis-driven carbon fixation can cause CO2 undersaturation in eutrophic surface waters, potentially turning them into air CO2 sinks especially in summer. In the context of rising air CO2 levels and associated gains in air-to-water CO2 flux over time, an increased carbon supply from air could be a contributing factor to positive trends in harmful algal bloom intensities. We determined spatiotemporal patterns in surface pCO2 in an impounded, eutrophic, urban stream system in West Texas with a history of harmful algal blooms. We took monthly measurements (early-to-mid afternoon) over two years above the dam spillways of four artificial lakes and used field water temperature and pH and lab-measured total alkalinity (Alk) to estimate pCO2. Alk was moderate-to-high in all lakes (overall lake medians, ~1200-1800 μmol/L). Three of the lakes had overall and seasonal median pCO2 values well below air pCO2 values (lowest individual lake values ranged from 6 to 37 μatm), and their seasonal median values of dissolved oxygen showed oversaturation year-round. The overall median pH in these three lakes ranged from 8.6 to 8.9. These observations indicate that eutrophic urban lakes can maintain high levels of productivity and be daytime sinks of air CO2 year-round. Although algal communities may take carbon directly from Alk (bicarbonate), the severity of CO2 depletion in three of the study lakes suggests they are carbon-limited, and therefore that the ongoing increase in air CO2 levels could potentially lead to the intensification of their algal blooms.
03:15 PM
EXPLORING SEDIMENT STABILITY, TURBIDITY, AND NUTRIENT FLUX USING EROSION MESOCOSMS (7966)
Primary Presenter: Marissa Kneer, US Army Corps of Engineers - Engineering Research and Development Center (marissa.l.kneer@usace.army.mil)
The UMCES Gust Erosion Microcosm System (U-GEMS) is a tool for assessing the erodibility of aquatic sediments and can be adapted to a wide variety of applications and research questions. To date, the U-GEMS has been used in studies ranging in topic from erodibility and suspended solids loading to contaminant mobilization from sediments. Here, we present two case studies highlighting the adaptability of this tool and its utility for studying aquatic health in response to ecosystem changes affecting sediment erosion or resuspension. The first case study details how the U-GEMS was used to measure internal phosphorus loading related to sediment resuspension in several reservoirs experiencing harmful algal blooms (HABs). Sediments with the highest potential for resuspension, as determined by the U-GEMS experiments, also contained the highest concentrations of total phosphorus, which will have consequences for long-term lake health and HAB mitigation. In the second case study, the U-GEMS was used to assess the stability of sediments within wildrice stands in northern Michigan. Wildrice is susceptible to sediment disturbance via uprooting in low density sediments. Sediment cores were collected from five lakes with variable amounts of wildrice to investigate the relationship between wildrice plant density and sediment stability. Generally, results indicated that lakes with less erodible sediments had higher densities of wildrice and more consistent wildrice densities from year-to-year.
SS16B - Understanding Aquatic Ecosystem Health in a Changing World
Description
Time: 2:00 PM
Date: 6/6/2024
Room: Hall of Ideas I