State Key Laboratory of Marine Resource Utilization in South China Sea, Hainan University, Haikou 570228, China.
College of Ecology and Environment, Hainan University, Haikou 570228, China.
Sci Total Environ. 2021 Nov 10;794:148673. doi: 10.1016/j.scitotenv.2021.148673. Epub 2021 Jun 24.
Tropical and subtropical rivers are being subjected to multiple stressors from human disturbance (e.g., water pollution and habitat degradation). Understanding the relationship between environmental conditions and the river ecosystem is important for improving river management. We built 14 Ecopath models composed of 28 functional groups (trophic levels [TLs] of 1.0-3.8) along a subtropical urban river to explore the influence of environmental changes on system attributes. From headwaters to downstream, the model outputs showed that the transfer efficiency (TE), energy flow parameters, and ecosystem theory indices exhibited significant (P < 0.05) differences across a longitudinal gradient of disturbance, indicating heterogeneous attributes of local river segments. The high TE values of TLs I, II, and III separated the upper, middle, and lower reaches, respectively, which could be attributed to the shift in dominant consumption flows from upstream 'periphyton - aquatic insects - insectivorous fish' to midstream 'detritus - shrimp - crustaceavorous fish' and to downstream 'phytoplankton - filter-feeding invertebrates/fish'. Structural equation modelling was used to test the causal relationships among environmental variables and demonstrated that abiotic factors directly influenced biomass composition and indirectly influenced trophic networks. Water quality, including dissolved oxygen and flow velocity; habitat characteristics, such as riffles, cobble-gravel substrate, and seasonal floodplain; and biological indicators, including the relative contributions (%) of decapods, insectivorous fish, and insect scrapers to biomass composition, had significant (P < 0.05) positive impacts on system maturity (evaluated by omnivory, connectance, and cycling indices). In the future, it will be possible to evaluate the health of river ecosystems by monitoring representative environmental factors, which could be a cost-effective approach to system-level improvement.
亚热带和热带河流受到人类干扰（如水污染和栖息地退化）的多种胁迫。了解环境条件与河流生态系统之间的关系对于改善河流管理至关重要。我们沿着一条亚热带城市河流构建了 14 个包含 28 个功能组（营养级 [TL] 为 1.0-3.8）的 Ecopath 模型，以探索环境变化对系统属性的影响。从源头到下游，模型输出表明，传递效率（TE）、能量流参数和生态系统理论指数在干扰的纵向梯度上存在显著（P<0.05）差异，表明局部河流段具有异质属性。TLs I、II 和 III 的高 TE 值分别分隔了上游、中游和下游，这可能归因于主导消费流从上游的“周丛生物-水生昆虫-食虫鱼类”向中游的“碎屑-虾类-甲壳类食鱼动物”以及下游的“浮游植物-滤食性无脊椎动物/鱼类”的转变。结构方程模型用于检验环境变量之间的因果关系，并表明非生物因素直接影响生物量组成，间接影响营养网络。水质（包括溶解氧和流速）、栖息地特征（如急流、卵石-砾石基质和季节性洪泛区）和生物指标（包括十足目甲壳动物、食虫鱼类和昆虫刮食者对生物量组成的相对贡献（%））对系统成熟度（通过杂食性、连通性和循环指数来评估）具有显著（P<0.05）的积极影响。未来，通过监测有代表性的环境因素来评估河流生态系统的健康状况将成为可能，这可能是一种具有成本效益的系统水平改善方法。
