University of Wisconsin–Madison

Research Themes in NTL-8

Our vision is to gain a predictive understanding of the ecology of lakes at longer and broader scales than has been traditional in limnology. Our conceptual framework uses a nested set of spatial scales, from individual lakes and their watersheds, to hydrologically-linked sets of lakes, entire lake districts, multiple lake districts within the Great Lakes region, and comparative studies of lakes and lake districts around the globe. Our research program is interdisciplinary and aims to understand the ecology of lakes in relation to relevant atmospheric, geochemical, landscape and human processes. Within the NTL domain, we have observed shifts in driver and response variables that are both gradual and abrupt on time scales of years to decades. Examples of rapid changes in lake responses that have been particularly conspicuous to both researchers and many Wisconsin residents include the collapse of valuable Walleye fisheries; increasing fluctuations in lake levels; arrival of new aquatic invaders; and sudden declines in lake water clarity, among others. At the same time, we are also seeing changes in drivers that can cause abrupt change, but abrupt changes have not followed, leading us to ask why. Our research activities are inspired by these observations and are organized around the overarching question: What are the causes and consequences of abrupt ecological change in lakes and their surrounding landscapes?

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What are lake phenological responses to a warmer and more variable climate that may lead to abrupt ecological change?

We’re investigating how increasing climate variability shifts winter and spring phenology, triggering abrupt ecological responses (Dugan 2021; Feiner et al. 2022). Analyses of long-term data showed that increasing variability in ice-off timing disrupts walleye recruitment due to photoperiod spawning cues, limiting adaptation to changing spring conditions and contributing to population declines (Barta et al. 2024; Feiner et al. 2025). Complementary work revealed how species invasions can trigger abrupt responses in organic matter cycling (Rohwer et al. 2023, 2025), as the timing of stratification, primary production, and invasive species interact to drive the spring clearwater phase and summer anoxia (Ladwig et al. 2021; Rohwer et al. 2024). Bacteria, viruses, and protists in Lake Mendota undergo predictable phenological cycles along with abrupt shifts in species composition (Rohwer et al. 2023, 2025; Zhou et al. 2025). These findings demonstrate that variability in winter and spring weather propagates through food webs and biogeochemical processes.

Representative Publications from this Research Theme

How do interactions of land use/land cover and climate affect urban aquatic ecosystems?

We’re examining how climate variability interacts with spatial gradients in urban areas to drive ecosystem change. In the Yahara watershed, abrupt canopy loss from emerald ash borer infestation did not uniformly intensify the urban heat island (Berg and Kucharik 2022, 2024); however, tree canopy cover does regulate runoff through plant water use and interception, with implications for urban flooding (Voter and Loheide 2021). High-frequency measurements in stormwater ponds showed that precipitation can trigger abrupt increases in water level and subsequently primary production (Briggs 2025; Curtis 2025) whereas summer productivity legacies control winter oxygen and greenhouse gases flux (Gorsky et al. 2024). Surveys across land-use gradients revealed lower species richness but high beta diversity in urban ponds and strong effects of habitat complexity and connectivity (Sauer et al. 2022; Trovillion et al. 2023). Together, these studies show how climate and land-use interact to generate diverse, and sometimes abrupt, ecological responses in urban waterbodies.

Representative Publications from this Research Theme

How do external drivers interact with aquatic invasive species to regulate water quality?

We’re examining how external drivers including extreme precipitation and spatial variation in watershed inputs interact to regulate water quality in Lake Mendota. Analysis of long-term high frequency sensor data showed that cyanobacterial blooms lag storms by 1–60 days due to internal processes of grazing and nutrient recycling (Carpenter et al. 2022). Modeling further demonstrated the effects of nutrient loading can persist for decades even if external P loading was abruptly eliminated (Hanson et al. 2023). Spatial surveys of water quality after storms revealed that moderate precipitation produces only weak immediate changes in nutrients and phytoplankton (Kibler 2026; Ortiz 2026), but storms may contribute to sediment nutrient pools that are later mobilized by wind-driven mixing, generating lagged effects, while wind-driven waves influence bloom initiation and senescence (Gushulak et al. 2025). These studies of Mendota demonstrate that abrupt shifts in water quality of large lakes arise from lagged interactions among watershed forcing and climate variability.

Representative Publications from this Research Theme

What causes intentional ecosystem manipulations to persist, revert, or lead to novel states?

We used invasive species management as ecosystem-scale experiments to examine how induced abrupt changes persist, revert, or lead to novel states (Perales et al. 2021; Carpenter 2026). Removal of common carp in Lake Wingra triggered a rapid shift from turbid water to dense macrophytes and filamentous algae that has persisted for over 15 years (Gorsky et al. 2026). Parallel fish manipulations in Crystal and Sparkling Lakes tested whether restructuring food webs could suppress invasive rainbow smelt and promote native fish recovery. After concurrent smelt removal and cisco reintroduction, smelt remain rare while native fishes have increased (Mrnak et al. 2023, 2025). These experiments show how management can trigger abrupt shifts while hinting at the feedbacks that influence persistence. A synthesis of decades of NTL research further articulated general principles of aquatic invasions (Vander Zanden et al. 2024).

Representative Publications from this Research Theme