Ecological hallmarks of our entry into the Anthropocene include shifts in current drivers, emergence of new drivers of ecosystem structure and function, and accelerating change in many ecological patterns and processes. These include abrupt changes- that is, changes that are fast in time or fast relative to their drivers. These rapid and often unexpected dynamics have been described among lakes and rivers as well as coastal and pelagic marine environments, and across levels of organization from populations to ecosystems. From a human perspective, abrupt changes in aquatic ecosystems are rarely viewed as positive. And because of their speed, adapting to or managing these changes is difficult and may thus compromise ecosystem goods and services, and, more broadly, human well-being. This session invites contributions that report on abrupt changes in aquatic ecosystems at the population, community, or ecosystem scale; about responses to an abrupt change in a key driver; or that explore the causes and consequences of these rapid changes. Contributions are also welcome on research to manage aquatic ecosystems and adjacent human communities in the face of potential for abrupt change.
Lead Organizer: Emily Stanley, University of Wisconsin - Madison (ehstanley@wisc.edu)
Co-organizers:
Mike Pace, University of Virginia (pacem@virginia.edu)
Jake Vander Zanden, University of Wisconsin (mjvanderzand@wisc.edu)
Presentations
02:00 PM
Forecasting coral reef dynamics using scientific machine learning (7767)
Primary Presenter: Zechariah Meunier, Oregon State University (meunierz@oregonstate.edu)
Ecological monitoring often does not produce the high-resolution data necessary for forecasting ecosystem states under future environmental conditions. To address this issue, we leveraged scientific machine learning (SciML) techniques to integrate theoretical models with time series data to detect alternative states and predict their long-term dynamics. Our SciML approach utilized two frameworks: neural ordinary differential equations (NODEs) and universal differential equations (UDEs). NODEs use a neural network to approximate a system of differential equations, and UDEs extend this method by incorporating known dynamics. We applied both methods to time series of coral, turf algae, and macroalgae coverage spanning up to 21 years on 25 reefs across the US Virgin Islands (USVI) to answer several research questions. First, which SciML framework provides more accurate estimates of long-term benthic coverage? Second, can UDEs reliably estimate grazing rates on algae? Finally, what are the near-term forecasts for benthic coverage on these reefs? We found that UDEs performed better than NODEs (had lower normalized RMSE) for modeled reefs. In addition, UDEs yielded grazing rates in the range of 0 to 35% of the reef, which is lower than thresholds that would produce coral-dominated reefs. Consequently, near-term forecasts indicated either macroalgae or turf algae would continue to dominate USVI reefs. Through application of SciML, our study enhances understanding of alternative state maintenance and provides valuable tools for ecosystem management and conservation on coral reefs.
02:15 PM
ABRUPT CHANGE IN LONG-TERM LAKE DATA: DETECTION AND PATTERNS (7957)
Primary Presenter: Allison Kneisel, University of Wisconsin - Madison (ankneisel@wisc.edu)
Understanding mechanisms of abrupt ecological change is increasingly important as climate change places novel pressures on system drivers. However, the effectiveness of detection techniques and the patterns of abrupt change detection across and within ecosystems are unknown. We simulated abrupt changes in time-series to test the sensitivity of detection methods and applied those methods to lake monitoring data from the North Temperate Lakes (NTL) Long-Term Ecological Research site. In 1000 simulations of Gaussian time-series data with constant mean and standard deviation (0 and 1 respectively), Pettitt’s test for change-point detection found a change (p < 0.05) in 2% of the datasets, less than expected by chance. When the mean increased from 0 to 1 or 2 halfway through the time-series, simulating abrupt change, detection rose to 68% and 100% respectively. Detection of abrupt change was slightly lower when the mean changed gradually. When fitting simulations to abrupt and gradual change curves, the gradual model rarely outperformed the abrupt model, even when the change was gradual. Of 169 seasonal average time-series collected by NTL (8 variables, 7 Wisconsin lakes, 1 - 4 seasons), 49 had significant change points, with 24 fitting the abrupt model and 9 fitting the gradual change model. There was no distinct pattern in changes among biological, physical, and chemical lake variables. Testing abrupt change detection methods with simulations that reflect the types of data collected by the NTL will strengthen our ability to quantify patterns of abrupt change in lake ecosystems.
02:30 PM
MULTI-DECADAL INCREASE IN ALGAL ORGANIC MATTER PRODUCTION IN TROPICAL LAKES ACROSS CENTRAL MEXICO (7904)
Primary Presenter: Marttiina Rantala, University of Liège (marttiina.rantala@gmail.com)
Global changes have a strong influence on lake algal communities and the major biogeochemical cycles that they shape. Growing evidence illustrates unprecedented algal community reorganizations and disruptions to lake carbon and nutrient cycles over past decades driven by myriad global and local human stressors; however, comparably little is known of such transitions at lower latitudes. We explored patterns and drivers of algal organic matter production and related biogeochemical cycles in five tropical crater lakes spanning central Mexico. To overcome long-term data limitations, we utilized information preserved in dated lake sediments, employing an array of biogeochemical and ecological indices tracking changes in algal production and community dynamics, and overall ecosystem state, over the past century. In two lakes, we extended our analysis further back in time to assess how ecosystem changes driven by major climate transitions of the past millennium compare with those of recent decades. Preliminary results indicate a distinct increase in algal organic matter production in recent decades across the region, and an enhanced carbon sink in the sediments of some of the lakes. These changes appear to be linked to increased evaporative forcing on lake levels as well as to local watershed disturbances. Our results further depict a similar period of increased organic matter production coincident with an earlier warm period; however, the pace and nature of the recent changes appear unparalleled.
02:45 PM
AQUATIC PLANT COMMUNITIES AND RAPID WATER LEVEL CHANGE: EXAMINING LONG-TERM PATTERNS IN FISH LAKE, WISCONSIN, USA (8412)
Primary Presenter: Cassandra Ceballos, University of Wisconsin-Madison (ceceballos@wisc.edu)
Fish Lake, a core study site in southern Wisconsin for the North Temperate Lakes Long-Term Ecological Research (NTL-LTER) program, provides an extreme example of lake level rise. Surface water elevation has steadily risen >5m since the 1960s then rapidly increased by 3m from 2017 to 2021. Rising water has displaced the littoral zone upwards and inundated houses, roads, trees, and other terrestrial substrates to create novel littoral habitats in the lake. Our objectives were to determine how macrophyte communities have responded to water level fluctuations and which species have established in the novel nearshore habitats. An analysis of NTL-LTER data from 1995 to 2023 shows that species richness declined by at least 50% in 2008 and 2019 and coincided with dramatic increases in lake level. Submersed plants growing entirely below the water surface or rooted in the sediment including Potamogeton crispus and Vallisneria americana declined in years following a rise in water level while species that became more common can employ fast growth or possess flexible stems such as Stuckenia pectinata and Ceratophyllum demersum, respectively. Species that propagate by fragmentation or cloning such as Persicaria amphibia and Chara spp. were present in 2023 when lake levels reached record highs. We hypothesize that changes in macrophyte communities are being driven by water level fluctuations through unknown mechanisms and that some species may be better at colonizing the newly flooded substrate through an advantageous growth form, morphological feature, or reproductive strategy.
03:00 PM
WITHIN A DECADE, TWO INVASIVE SPECIES ALTER KEY ECOSYSTEM FUNCTIONS IN LAKE CONSTANCE (8248)
Primary Presenter: Piet Spaak, Eawag (spaak@eawag.ch)
Lake Constance, one of the largest Alpine lakes on the border between Germany, Austria and Switzerland, has undergone major changes over the past century. From the 1950s to the 1980s, Lake Constance experienced a period of severe eutrophication, resulting in significantly elevated nutrient levels. Although the natural trophic state of the lake has been restored, irreversible changes in the aquatic communities have occurred. In addition to eutrophication, climate change and in particular the invasion of non-native plant and animal species are threatening natural biodiversity. This leads to changes in food webs and affects the functioning of the ecosystem in Lake Constance. In particular, the three-spined stickleback (Gasterosteus aculeatus) and the quagga mussel (Dreissena bugensis) are causing major problems. Stickleback and quagga mussel populations have exploded in recent years, with sticklebacks becoming the most abundant pelagic fish species. Quaggas can settle in all water depths, causing problems with intake pipes and other structures. Quaggas are also an important competitor for zooplankton, which feed on phytoplankton. We hypothesise that these two invasive species are responsible for the decline in fish yields and fisheries in Lake Constance. We present a large EU-funded project (www.seewandel.org) that investigates the causes and consequences of such invasions for Lake Constance. We present the latest results on these invasive species and their consequences for the lake.
SS09A - Abrupt Change in Aquatic Ecosystems
Description
Time: 2:00 PM
Date: 7/6/2024
Room: Hall of Ideas G