Attachment patterns and influencing factors of Limnoperna fortunei in a large hydropower station on the Jinsha River

The invasion and attachment of the golden mussel (Limnoperna fortunei) in hydropower engineering structures pose a significant threat to the safe and efficient operation of power stations. Biofouling caused by this species leads to obstruction of trash racks, blockage in cooling water pipes, corrosion of metal structures, and risks of unplanned shutdowns. However, existing studies primarily focus on biofouling in single engineering components, lacking a systemic understanding of the attachment characteristics and diffusion laws across the entire hydraulic system of large hydropower stations. Furthermore, the regulatory mechanisms of engineering scheduling, such as unit start-stop frequency and flow velocity thresholds, on biofouling remain unclear. Taking a large hydropower station in the Jinsha River Basin as the study object, this paper aims to systematically investigate the spatiotemporal distribution, growth rhythm, and reproductive patterns of Limnoperna fortunei in the complex hydraulic environment. Moreover, it seeks to quantitatively reveal the synergistic regulation mechanisms of hydrodynamic conditions, environmental factors, and engineering operations, thereby providing a scientific basis for constructing a comprehensive prevention and control strategy.

A systematic field investigation and sampling campaign were conducted during the maintenance periods of the study area in February and April 2024. Three key engineering structures prone to biofouling were selected for the study: trash racks, quick gate slots, and main transformer cooling water pipes. Belt transect sampling with 15 cm×15 cm quadrats was employed. For the trash racks, vertical sampling covered the intermittent submersion, stable submersion, and deep-water zones. For the quick gate slots, samples were taken from the bottom sedimentation zone and sidewalls at different elevations. For the cooling water pipes, sampling was performed in enclosed pipelines. The FiSAT Ⅱ software suite was employed for population parameter analysis. Specifically, the Bhattacharya method was used to separate cohorts from length-frequency data to identify reproductive groups. The annual reproductive pattern was inferred based on growth rates and validated by monitoring synchronous planktonic larvae from 2024 to 2025. The von Bertalanffy growth function parameters (asymptotic length L_∞ and growth coefficient K) were estimated using the ELEFAN I module to assess growth potential. In addition, the correlation between biological data and environmental/operational variables, including water level fluctuations, flow velocity, water temperature, and the start-stop records of generating units (specifically comparing Units 6 and 7), was analyzed.

The results revealed considerable spatial heterogeneity and gradient diffusion characteristics of Limnoperna fortunei attachment. 1) In terms of spatial distribution, a clear "source-sink" pattern was observed. The attachment density follows the order: cooling water pipes> trash racks> quick gate slots. In the trash racks, the density showed a vertical single-peak distribution, with the peak located 5-20 m below the minimum operating water level, shaped by the tradeoff between desiccation stress in the upper fluctuation zone and high flow shear in the deep zone. In the quick gate slots, the bottom density was markedly higher than that of the sidewalls due to gravity settlement during shutdowns. Notably, the attachment density in the gate slot of Unit 7 (66 start-stop/year) was markedly lower than that of Unit 6 (21 start-stop/year), indicating that frequent hydraulic disturbance inhibits colonization. An extreme disparity was found in the cooling water pipes; the left and right bank pipes had a density of 31 400 and 0 ind./m², respectively, attributable to a flow velocity threshold effect. The right bank velocity (0.23-0.28 m/s) was below the critical threshold (~0.3 m/s) required for maintaining sufficient food flux, whereas the left bank velocity (0.45-0.58 m/s) was optimal. 2) The population exhibited a "parent-offspring-grandspring" structure in terms of growth and reproduction, confirming a reproductive pattern of three generations per year. Growth showed strong seasonality, accelerating during the high-temperature season (June-October) and stagnating in the low-temperature season (February-April). Spatially, the growth potential (represented by L_∞ and growth performance index ϕ') decreased along the flow path from the trash racks to the cooling water pipes. Despite their high density, the number of individuals in the cooling water pipes was considerably less, attributable to metabolic inhibition due to the consistently lower water temperature (15.5-16.0 ℃) in the deep-water intake.

This study confirms that the distribution and growth of Limnoperna fortunei in large hydropower stations are co-regulated by hydrodynamic conditions, physiological metabolism, and engineering scheduling. The trash rack area serves as the core colonization "source, " continuously supplying larvae to downstream "sinks, " such as quick gate slots and cooling water pipes. Two key physical regulatory mechanisms were identified: the "start-stop frequency effect, " in which frequent hydraulic disturbance and scouring effectively limit colonization, and the "flow velocity threshold effect, " where velocities below ~0.3 m/s inhibit survival due to insufficient trophic flux. Furthermore, low water temperature in deep intakes restricts somatic growth through metabolic suppression. On the basis of these findings, a comprehensive control strategy of "engineering protection as the main measure and operational optimization as auxiliary" is proposed. Recommendations include applying long-acting antifouling coatings in core colonization zones (trash racks), implementing UV/heat treatment and mechanical cleaning for closed systems (cooling water pipes), and attempting intermittent increases in unit start-stop frequency during noncritical periods to use hydraulic disturbance to suppress biofouling.