Stream bioassessment using benthic macroinvertebrate assemblages is widely implemented by regulatory agencies, yet a critical question regarding spatial autocorrelation and sample independence remains: How much of a stream network does a point sample represent? Macroinvertebrate assemblages vary along a longitudinal gradient, likely due to a combination of natural and anthropogenic factors that alter water physiochemistry and habitat. A better understanding of how these gradients affect macroinvertebrate assemblage variance could prevent spatial over- and under-sampling within bioassessment efforts. This project investigated longitudinal patterns (10 s of km) of macroinvertebrate assemblages in 14 Wisconsin streams. Spatial autocorrelation was assessed using Moran’s I and other multivariate methods with an emphasis on estimating the distance at which assemblages no longer display spatial correlation. Within most streams, there was a linear, direct relationship between assemblage dissimilarity and longitudinal distance, with distance to independence (DTI) ranging from 1.7–13.5 km. DTI was most strongly affected by conductivity, which is often a surrogate for a suite of anthropogenic effects. With increasing conductivity, DTI increases, suggesting more homogenous assemblages in disturbed streams. Natural factors like watershed size, channel gradient, and riparian slope also affected DTI. Considering spatial correlation in monitoring designs could improve the efficiency and application of regulatory bioassessment programs.

监管机构广泛采用底栖无脊椎动物组合进行河流生物评估，但是关于空间自相关和样本独立性的关键问题仍然存在：点样本代表多少河流网络？无脊椎动物的集合体沿纵向梯度变化，这可能是由于自然和人为因素共同作用，改变了水的生理化学和栖息地。对这些梯度如何影响大型无脊椎动物集合方差的更好理解可以防止生物评估工作中空间过采样和欠采样。该项目研究了威斯康星州14条河流中大型无脊椎动物组合的纵向模式（10 s km）。使用Moran's I和其他多变量方法评估了空间自相关，重点是估计装配不再显示空间相关性的距离。在大多数溪流中，组合差异与纵向距离之间存在线性直接关系，独立距离（DTI）为1.7-13.5 km。DTI受电导率的影响最大，电导率通常是一系列人为效应的替代物。随着电导率的增加，DTI增大，表明受干扰的流中的组合更加均匀。分水岭大小，河道坡度和河岸坡度等自然因素也影响了DTI。在监测设计中考虑空间相关性可以提高监管生物评估计划的效率和应用。