bioRxiv Science⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/658799

Long-term influence of climate and experimental eutrophication regimes on phytoplankton blooms

Salk, K. R.·Venkiteswaran, J. J.·Couture, R.-M.·Higgins, S. N.·Paterson, M. J.·Schiff, S. L.
View original source ↗Export metadata ↓

Abstract

Phytoplankton blooms respond to multiple drivers, including climate change and nutrient loading. Here we examine a long-term dataset from Lake 227, a site exposed to a fertilization experiment (1969-present). Changes in nitrogen:phosphorus loading ratios (high N:P, low N:P, P-only) did not impact mean annual biomass, but blooms exhibited substantial inter- and intra-annual variability. We used a process-oriented lake model, MyLake, to successfully reproduce lake physics over 48 years and test if a P-limited model structure predicted blooms. The timing and magnitude of blooms was reproduced during the P-only period but not for the high and low N:P periods, perhaps due to N acquisition pathways not currently included in the model. A model scenario with no experimental fertilization confirmed P loading is the major driver of blooms, while a scenario that removed climate-driven temperature trends showed that increased spring temperatures have exacerbated blooms beyond the effects of fertilization alone.\n\nSignificance StatementHarmful algal blooms and eutrophication are key water quality issues worldwide. Managing algal blooms is often difficult because multiple drivers, such as climate change and nutrient loading, act concurrently and potentially synergistically. Long-term datasets and simulation models allow us to parse the effects of interacting drivers of blooms. The performance of our model depended on the ratio of nitrogen to phosphorus inputs, suggesting that complex biological dynamics control blooms under variable nutrient loads. We found that blooms were dampened under a \"no climate change\" scenario, suggesting that the interaction of nutrient loading and increased temperature intensifies blooms. Our results highlight successes and gaps in our ability to model blooms, helping to establish future management recommendations.\n\nData Availability StatementData and metadata will be made available in a GitHub repository (https://github.com/biogeochemistry/Lake-227). Upon manuscript acceptance, the repository will be made publicly available and a DOI will be provided. We request that data users contact the Experimental Lakes Area directly, per their data use policy (http://www.iisd.org/ela/wp-content/uploads/2016/04/Data-Terms-And-Conditions.pdf).

Source connections

Explore related subjects

ecologyPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Salk, K. R., Venkiteswaran, J. J., Couture, R.-M., Higgins, S. N., Paterson, M. J., Schiff, S. L.. 2019-06-03. Long-term influence of climate and experimental eutrophication regimes on phytoplankton blooms. https://doi.org/10.1101/658799

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related preprints

bioRxiv2026

Human-caused ignitions and plant invasion drive fire-regime change in a dryland biodiversity hotspot

Dryland ecosystems cover much of Earths terrestrial surface and are increasingly affected by climate warming, land-use change, and biological invasion. The Sonoran Desert of western North America, a biodiversity hotspot that historically experienced infrequent fire, exemplifies how these global-change processes are driving ecosystem transformation through the emergence of novel disturbance regimes. Using records of more than 73,000 wildland fire events, we quantified anthropogenic and environmental controls on fire ignition, size, and spread across the Sonoran Desert. Human-caused ignitions accounted for 95.5% of all recorded fires since the early 1990s and were concentrated near roads, buildings, and other areas of human activity, particularly during late spring. In contrast, lightning-caused ignitions were rare within the Sonoran Desert and occurred primarily in adjacent montane forests during late summer months. Consistent with broader trends across the western United States, fires were typically largest when they ignited far from roads, where access is limited, and fire management often relies on indirect attack strategies. Pre-fire annual and perennial herbaceous vegetation both promoted fire spread, with detectable effects at cover values as low as 5%, while bare ground reduced fuel connectivity and constrained fire growth. Rather than exhibiting a distinct threshold response, fire spread increased linearly with herbaceous cover, suggesting that even modest increases in fine fuels can alter fire behavior in this historically fuel-limited ecosystem. Together, our results illustrate that human ignitions determine where fires occur, whereas herbaceous fuels determine whether those ignitions spread, driving fire-regime transformation across an iconic North American desert. Managing and adapting to this novel fire regime will require coordinated efforts to reduce human-caused ignitions, limit invasive herbaceous fuels, maintain bare-ground interspaces, and rapidly suppress fires. More broadly, our findings identify the mechanisms controlling fire regime change in dryland ecosystems and provide a framework for anticipating ecosystem transformation under ongoing global change.

ecology↗
bioRxiv2026

Hidden infections: Linking parasite ecology, fish health and stakeholder perceptions in Nile tilapia aquaculture in central Kenya

Parasite infections in farmed fish may remain unrecognised when fish-health assessment relies mainly on visible signs. We investigated metazoan parasite occurrence, parasite diversity and community composition, associations between gill-parasite burden and histological alterations, and stakeholder recognition of fish-health problems in Nile tilapia (Oreochromis niloticus) aquaculture in central Kenya. We examined 157 fish from 20 farms, assessed gill histology in 137 fish, measured water quality once per farm, and collected questionnaire and interview data from 48 stakeholders. Five metazoan parasite groups were recorded, with monopisthocotylans the most prevalent (36.3%). Higher monopisthocotylan burden was associated with a greater cumulative number of gill lesion types (odds ratio 1.86, 95% CI 1.43-2.42, p < 0.001), whereas copepod burden was not. Parasite diversity was higher in the larger operational pond category across all three Hill-number orders (p = 0.006-0.008), and parasite-community composition differed between categories (PERMANOVA, p = 0.034), although these comparisons were exploratory because only four farms were in the larger category and farm category overlapped with county. Single-time-point water-quality measurements showed no clear associations with parasite burden, diversity or community composition after multiple-testing correction. Farmers and fisheries or extension officers recognised signs of poor fish health but rarely identified parasites as a specific cause, and routine diagnostic confirmation was uncommon. The findings reveal a gap between laboratory detection of parasite-associated gill alterations and farm-level recognition and diagnosis.

ecology↗
bioRxiv2026

Habitat degradation destabilizes complex metacommunities by disrupting dispersal

Habitat loss and fragmentation are rapidly reshaping ecosystems worldwide, yet their consequences for ecological stability remain unresolved. Classical theory, pioneered by Robert May, established rigorous criteria for stability; however, these apply to spatially well-mixed communities, limiting their relevance to habitat degradation. Here, we develop a metacommunity framework that integrates classical stability theory with spatial dynamics to determine how anthropogenic habitat degradation reshapes ecosystem stability. We show that metacommunities exhibit three distinct dynamical regimes following a perturbation (e.g., drought or forest fire): stable regime (perturbations decay and species persist), reactive regime (perturbations are transiently amplified, which increases extinction risk under repeated disturbances), and unstable regime (perturbations grow, causing extinctions even after a single disturbance). Dispersal fundamentally reshapes these stability transitions, converting unstable communities into reactive ones and reactive communities into stable ones. While homogeneous dispersal progressively stabilizes communities, heterogeneous dispersal maximizes stability at intermediate strengths. We further show that habitat loss and fragmentation can be comparably effective at driving species extinctions by shifting metacommunities from stable to reactive and ultimately unstable regimes, demonstrating that fragmentation per se can be as important as habitat loss. Our findings reveal that reactivity is both an early-warning signal of impending instability and a state of elevated extinction risk under recurrent disturbances. By linking stability transitions to changes in population persistence under nonlinear dynamics, our results bridge classical stability theory with spatial ecology and provide a general framework for predicting how ecological complexity and dispersal jointly govern both ecosystem stability and population persistence under habitat degradation.

ecology↗