Fergus C Emi, Brooks J Renée, Kaufmann Philip R, Herlihy Alan T, Hill Ryan A, Mitchell Richard M, Ringold Paul
Oak Ridge Institute for Science and Education, U.S. Environmental Protection Agency, Corvallis, Oregon, USA.
US EPA, Office of Research and Development, Center for Public Health and Environmental Assessment, Pacific Ecological Systems Division, Corvallis, Oregon, USA.
Ecosphere. 2023 Nov 9;14(11):1-24. doi: 10.1002/ecs2.4688.
Stream macroinvertebrate assemblages are shaped by natural and human-related factors that operate through complex hierarchical pathways. Quantifying these relationships can provide additional insights into stream ecological assessment. We applied a structural equation modeling framework to evaluate hypothesized pathways by which watershed, riparian, and in-stream factors affect benthic macroinvertebrate condition in the Western Mountains (WMT) and Xeric (XER) ecoregions in the United States. We developed a conceptual model grounded in theory, empirical evidence, and expert opinion to evaluate the following hypotheses: (1) macroinvertebrate assemblages are primarily driven by proximal, in-stream factors (e.g., water quality and physical habitat); (2) anthropogenic land uses affect macroinvertebrates indirectly by altering in-stream characteristics; and (3) riparian vegetation cover attenuates land use effects. We tested our model separately on three measures of benthic macroinvertebrate assemblage condition: ratio of observed-to-expected taxonomic richness (O/E); a multimetric index (MMI); and richness of Ephemeroptera, Plecoptera, and Trichoptera taxa (EPT). In the WMT, site-level riparian cover, in-stream physical habitat (relative bed stability), and water chemistry (total nitrogen) were the top three predictors of macroinvertebrate assemblages, each having over two times the magnitude of effect on macroinvertebrates compared with watershed-level predictors. In the arid XER, annual precipitation and stream flow characteristics were top predictors of macroinvertebrate assemblages and had similar magnitudes of effect as in-stream water chemistry. Path analyses revealed that land use activities in the watershed and at the stream site degraded macroinvertebrate assemblages indirectly by altering relative bed stability, water quality, and riparian cover/complexity. Increased riparian cover was associated with greater macroinvertebrate condition by reducing land use impacts on stream flow, streambed substrate, and water quality, but the pathways differed among ecoregions. In the WMT, site-level riparian cover affected macroinvertebrate assemblages partly through indirect pathways associated with greater streambed stability and reduced total nitrogen concentrations. In contrast, in the XER, watershed-level riparian cover affected macroinvertebrate assemblages through greater specific stream power. Identifying the relative effects of and pathways by which natural and anthropogenic factors affect macroinvertebrates can serve as a framework for prioritizing management and conservation efforts.
溪流大型无脊椎动物群落受自然因素和人为因素影响，这些因素通过复杂的层级路径发挥作用。量化这些关系有助于深入了解溪流生态评估。我们应用结构方程模型框架来评估流域、河岸带和溪流内部因素影响美国西部山区（WMT）和干旱地区（XER）生态区底栖大型无脊椎动物状况的假设路径。我们基于理论、实证证据和专家意见构建了一个概念模型，以评估以下假设：（1）大型无脊椎动物群落主要受溪流近端因素驱动（如水质和物理栖息地）；（2）人为土地利用通过改变溪流特征间接影响大型无脊椎动物；（3）河岸植被覆盖减轻土地利用的影响。我们分别用底栖大型无脊椎动物群落状况的三种衡量指标对模型进行了检验：观察到的分类丰富度与预期分类丰富度之比（O/E）；多指标指数（MMI）；蜉蝣目、襀翅目和毛翅目分类单元的丰富度（EPT）。在西部山区，场地层面的河岸植被覆盖、溪流内部物理栖息地（相对河床稳定性）和水化学（总氮）是大型无脊椎动物群落的前三大预测因子，与流域层面的预测因子相比，它们对大型无脊椎动物的影响程度均超过两倍。在干旱的XER地区，年降水量和溪流流量特征是大型无脊椎动物群落的主要预测因子，其影响程度与溪流内部水化学相似。路径分析表明，流域和溪流场地的土地利用活动通过改变相对河床稳定性、水质和河岸植被覆盖/复杂性间接降低了大型无脊椎动物群落质量。河岸植被覆盖增加与大型无脊椎动物状况改善相关，这是通过减少土地利用对溪流流量、河床基质和水质的影响实现的，但不同生态区的路径有所不同。在西部山区，场地层面的河岸植被覆盖部分通过与更大的河床稳定性和降低的总氮浓度相关的间接路径影响大型无脊椎动物群落。相比之下，在干旱地区，流域层面的河岸植被覆盖通过更大的特定水流功率影响大型无脊椎动物群落。确定自然和人为因素影响大型无脊椎动物的相对影响和路径可为管理和保护工作的优先排序提供框架。
