The Distribution and Succession of Filamentous Algae in the Southern Taihang Catchment under Different Nutrient Regimes

Human activities have resulted in the eutrophication of rivers, leading to heightened concerns regarding the occurrence of filamentous algal blooms. With the increasing utilization of rivers by humans, the occurrence of these nuisance filamentous algae is expected to increase in frequency in the future. Blooms primarily occur due to energy congestion at the trophic level of primary producers, resulting from inefficient energy flow in both the bottom-up and top-down pathways. To investigate the mechanism underlying the outbreak of filamentous algae, two streams in the southern Taihang catchment with different nutrient conditions were selected for this study. The objective of this study was to understand the effects of nutrient levels and other potential factors on the distribution and succession of filamentous algae. Our findings revealed a positive correlation between nutrient conditions and the biomass of filamentous algae. Cladophora and Spirogyra were identified as the dominant species among filamentous algae, each exhibiting unique distribution patterns in the two streams. Spirogyra thrived predominantly in the Baligou stream, where lower nutrient levels and warmer temperatures prevailed. In contrast, Cladophora flourished in the nutrient-rich Nanping stream at colder temperatures. Results from the generalized linear model indicated that the biomass of Cladophora was influenced by nutrient concentration, water depth, water temperature, and macrobenthic biomass. The biomass of Spirogyra, on the other hand, was primarily determined by water temperature, nutrient concentrations, water depth, and velocity. The positive correlation between Cladophora and macrobenthos revealed a possible mutually beneficial relationship, suggesting that macrobenthos may promote the growth of Cladophora by inhibiting periphytic diatoms. In return, the macrobenthos benefit from a secure refuge and an environment conducive to foraging and reproduction. This study suggested that to alleviate energy flow congestion in the benthic food chain, it is advisable to address this issue by either reducing nutrient loadings in rivers or enhancing the presence of benthivorous fishes in streams.