The effects of water chemistry and lock-mediated connectivity on macroinvertebrate diversity and community structure in a canal in northern England

Freshwater ecosystems are under threat from habitat loss, partly due to urban expansion. However, some elements of urban freshwaters are already integral parts of the urban landscape and so are more resilient to loss, representing opportunities for the enhancement of freshwater resources within cities. This study investigated the biodiversity value of the Leeds-Liverpool Canal in Leeds, UK, in relation to its landscape context. Specifically, we tested the hypotheses that (i) biodiversity value is lowest nearest to the urban core, and (ii) the pattern of canal locks structured ecological communities. Nutrients, metals and dissolved carbon all existed at relatively low concentrations, contrary to what is often seen in urban water bodies, although concentrations were higher in the urban core. This gradient of chemical stress was associated with a decline in macroinvertebrate diversity towards the city centre, which manifested as pollution-sensitive taxa being excluded from this area. Community structures were found to vary between groups of sampling sites separated by locks, suggesting that locks may act as barriers for aquatic invertebrates by restricting dispersal. The results in this study indicate that canals in urban areas can be high-quality habitats, despite the associated anthropogenic stressors, and locks may represent a unique model for researching relationships between connectivity and community structure.