bioRxiv Science⌕ Search
Home/Archive/bioRxiv

bioRxiv · 10.1101/658591

Incomplete resilience of a shallow lake to a brownification event

Kazanjian, G.·Brothers, S.·Köhler, J.·Hilt, S.
View original source ↗Export metadata ↓

Abstract

Dissolved organic carbon (DOC) concentrations in many freshwater ecosystems of the northern hemisphere have increased in recent decades due to additional terrestrial inputs. This phenomenon, known as brownification, can strongly alter the physical, chemical, and biological traits of aquatic ecosystems. Extreme rainfall can also cause sudden brownification, known as blackwater events in rivers, while longer term effects on lakes are unknown. Here, we investigated the resilience of a small, temperate, shallow lake to a strong natural flooding-induced brownification event in 2011-2012. From initial DOC and total phosphorus (TP) concentrations of ~12 and 0.04 mg L-1, respectively, the lake rapidly reached peak DOC and TP concentrations of 60 and 0.35 mg L-1, respectively. By the following year, water levels had returned close to initial values, yet two additional years of monitoring (until summer 2015) and a more recent sample in spring 2019 showed that the lake did not fully return to its pre-brownification state. Instead, DOC and TP concentrations plateaued at concentrations respectively 1.5-fold and twofold greater than pre-brownification values within less than two years and remained at these concentrations in spring 2019. During this initial recovery period the lake exhibited a decline of phytoplankton and a partial recovery of summer periphyton biomass and production, albeit a full return to pre-brownification values was not recorded in either case. DOC and TP concentrations were positively correlated to phytoplankton biomass and negatively to periphyton. As increases in phytoplankton production outpaced decreasing periphyton production, the net result of this brownification event has been an increase in whole-lake areal summertime primary production. This incomplete resilience to a flooding-induced brownification event implies consequences for several ecological and biogeochemical functions of shallow lakes that warrant further investigation and might contribute to the gradual increase of freshwater DOC concentrations in the northern hemisphere.

Explore related subjects

ecologyPreprint

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Kazanjian, G., Brothers, S., Köhler, J., Hilt, S.. 2019-06-03. Incomplete resilience of a shallow lake to a brownification event. https://doi.org/10.1101/658591

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↗