Exploring the interactions of physical, chemical and biological variables of an Urban river using network analysis

Abstract

Network analysis was used as a method to investigate the relationship between benthic macroinvertebrates in an urban river watershed and physicochemical variables. The measured physicochemical variables were the dissolved oxygen, temperature, nutrients, conductivity, pH, total organic matter, biochemical oxygen demand and river discharge. The metrics applied in the study were the degree of connections between nodes, the number of edges identified for each study location and the functional feeding groups. The river sampling took place over 14 months and sampling took place at five sites, two of which were upstream of a major wastewater treatment works and three sites were downstream of the works. A biological and environmental (BIOENV) analysis was included as part of the overall analysis to compare the variables that influenced the river ecosystem. This study shows that the relationships between benthic macroinvertebrates were stronger at the upstream locations of the watershed, while the downstream locations were controlled by the physicochemical relationships. From this analysis, the river quality and biodiversity were mainly controlled by the discharge, conductivity and availability of relevant organic matter suitable for organisms. Through the network, the degree of connections between the variables revealed the status of the urban river and provided insight into the possible management of vegetation cover across the urban watershed.