Rapid colonization of aquatic communities in an urban stream after daylighting

Didier L. Baho,Karoline D. Myrstad,Therese F. Moe,David Arnott,Susanne C. Schneider

doi:10.1111/rec.13394

Abstract

Restoring aquatic ecosystems is still at an early stage and the outcomes of the remediation techniques used are often not reported, which limit opportunities to learn and further improve these methods. One common remediation technique in urban areas is daylighting, which involves the re‐opening of once buried streams with the aim of restoring ecosystem functions and services. In this study, we monitored the colonization of two important aquatic communities, benthic algae and macroinvertebrates, and assessed the nutrient retention capacity of a recently daylighted urban stream in the city of Oslo, Norway. The approach used involved transforming a buried channel into an open stream consisting of interconnected riffles and ponds seeded with aquatic and terrestrial plants. Benthic algal and macroinvertebrate communities begun to colonize the restored stretch within a relatively short time, 9 months following daylighting. The dynamics of the two aquatic communities differed, indicating that spatial processes are influential in determining the establishment of benthic algae, whereas time is more important for macroinvertebrate communities. The observed net nutrient retention from the daylighted stretch for phosphate, total nitrogen, total phosphorus, and calcium were 226, 128, 38 and 14%, respectively. However, the efficiency of the daylighted stretch to sequester nutrients was limited by the lack of controlling nutrient inputs from diffuse sources. This highlights the importance of addressing the influence of broader‐scale processes, extending beyond the boundaries of the restored reach, which can otherwise demise the success of daylighting.

Highlights

Streams and rivers were previously considered as obstacles for urban development and were subsequently culverted (Paul & Meyer 2001)
Restoring urban stream using daylighting by policies such as the Habitats Directive (92/43/EEC) and the Water Framework Directive (2000/60/EC), which encouraged the use of various rehabilitation techniques (Clarke et al 2003; Smith et al 2014)
Average water temperatures followed patterns associated with seasonal variations, with maximum and minimum temperatures observed in August and November, respectively (Fig. S3A)

Summary

Introduction

Streams and rivers were previously considered as obstacles for urban development and were subsequently culverted (Paul & Meyer 2001). 2021 Restoration Ecology Vol 29, No 5, e13394 through completely enclosed man-made channels built from impermeable material, and these culverts were buried to gain land (Elmore & Kaushal 2008; Wild et al 2011) Such practices substantially impact streams (Elmore & Kaushal 2008; Beaulieu et al 2014) and lead to alterations in hydrology (Walsh et al 2005), decreased nutrient retention (Hope et al 2014), impaired biodiversity (Neale & Moffett 2016), and reduced cross-habitat interactions between land and water due to loss of riparian vegetation (Paul & Meyer 2001; Roy et al 2003). Empirical evaluations of daylighting (i.e. de-culverting; (Wild et al 2011) of urban streams are still scarce, in particular during the early (re)colonization of aquatic communities (Neale & Moffett 2016; Lorenz et al 2018)

Methods

Results

Conclusion