Urban Ecosyst (2012) 15:285–291 DOI 10.1007/s11252-012-0227-6
Positioning urban rivers within urban ecology Robert A. Francis
Published online: 1 March 2012 # Springer Science+Business Media, LLC 2012
Abstract Rivers are important components of many urban systems, and research into urban rivers is increasing internationally, both in scope and intensity. As an introduction to a special section on urban rivers, this short article briefly highlights some key trends in urban river research based on a survey of published articles from Web of Knowledge, before summarising the contributions made by the special section papers. In particular, there has been a general increase in work on urban rivers since the 1990s, with a more dramatic increase from 2001. Most published research has concentrated on water quality and its wider environmental implications; ecologically, many studies have focused on autecology, community ecology or river restoration/rehabilitation, with the main emphasis on macroinvertebrates or fish. Geographically, most studies have taken place in North America (mainly the US) and Asia (mainly China). In the large majority of cases research has been on relatively small rivers within urbanised catchments rather than large, heavily urbanised systems within major towns or cities. Given the wide range of topics and studies relating to urban river research, a detailed meta-analysis of the urban river ecology literature would be a useful endeavour. The six papers included in the special section of this issue provide a sample of some of key and emerging themes within recent urban river research, and originate from a session on the understanding and management of urban rivers held at the Royal Geographical Society (with IBG) Annual Meeting in 2010, at Imperial College London. Keywords Urban river . Urban stream . Urban ecology . Review . Synthesis . Freshwater As we pass the point in history where the majority of the people on the planet live in urban areas (UNFPA 2007), it is heartening that the scientific study of urban ecosystems continues to gain momentum within a range of disciplines and across a broad geographical spectrum (e.g. Forman 2008; Pickett et al. 2011a, b; Kowarik 2011; Francis et al. 2012). Recent studies have moved beyond the presentation of case studies to present increasingly broad R. A. Francis (*) Department of Geography, King’s College London, Strand, London WC2R 2LS, UK e-mail:
[email protected]
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syntheses. This has helped to highlight the challenges and benefits of studying urban systems not just for urban planning and management, but for understanding fundamental aspects of ecosystem structure and process, resource use and metabolism, species–environment interactions, and the explicit and intrinsic interrelationships between humans and their environment (Grimm et al. 2008; Pickett et al. 2011a, b; Ramalho and Hobbs 2012; Francis et al. 2012). Urban rivers have key ecological and societal roles within broader urban systems. Indeed, most urbanisation has historically begun at locations where key resources and services are found, including fresh water, food, transportation links, ease of defence and waste disposal (Grimm et al. 2008). River systems generally provide all of these, and prior to the development of extensive and dedicated transport networks that allowed the movement of people and goods (such as the railway and highway networks that allowed the development of many towns and cities throughout the US; Anas et al. 1998), river and estuarine/coastal systems were the foci for most urban development. The legacy of this often unchecked development is widespread degradation and destruction of riverine habitats coupled with impacts to hydrological regimes, alluvial aquifer storage, water quality, geomorphological patterns and processes, and fluvial/riparian ecotones. Taken as a whole, these impacts have resulted in declines in riverine ecological quality and precipitous losses of biodiversity at both local and regional scales (Groffman et al. 2003; Gurnell et al. 2007; Wenger et al. 2009; Everard and Moggridge 2012). Nevertheless, urban rivers continue to be important features within both the physical and cultural landscapes of urbanised areas. Rivers are central to the identity of many towns and cities (e.g. the Thames in London, the Seine in Paris, the Hudson in New York, the Yarra in Melbourne). Further, waterfront areas often represent desirable areas for urban development and gentrification (e.g. Breen and Rigby 1994; Chang and Huang 2011), and are the aquatic ecosystems that the majority of urban populations most commonly see and reflect upon in their daily lives (e.g. Gabr 2004). Research interest in urban river systems began to increase notably in the early 1990s, with a more dramatic increase from 2001 (Fig. 1). Based on a survey of articles from Web of Knowledge using the search terms “urban stream” OR “urban river” and scrutinised 13 5 13 0 12 5 12 0 11 5 11 0 10 5 10 0 95 90 85 80 75 70 65 60 55 50 45 40 35 30 25 20 15 10 5 2011
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Fig. 1 Publications including the search terms “urban river*” or “urban stream*” included in Web of Knowledge, arranged according to year published. Search conducted on 14 January 2012
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Fig. 2 Breakdown of a subsample of articles published in relation to urban rivers from Web of Knowledge. In November 2011, 1,184 articles were found using the search terms “urban river*” OR “urban stream*”. This was reduced to 753 articles for individual scrutiny by using the more restrictive terms “urban river” OR “urban stream”. Of the 753 articles, 68 were found to be repeat or incomplete entries, leaving 685 articles for further analysis. These were classified according to a primary focus, b organisms studied (of which only the most common six are presented) and c broad geographical location (including ‘general’ studies that include conceptual or review work across geographical regions). All values are rounded to the nearest whole number
individually, most studies have focused on water quality and its wider environmental (including human health) implications (Fig. 2a). Other studies have focused on topics ranging from river restoration, hydrogeomorphology, biogeochemical processes, and autecology or community ecology/biodiversity of aquatic organisms (usually macroinvertebrate or fish taxa; Fig. 2b). Unsurprisingly, bacteria are commonly studied, but mainly as indicators of water quality. These results are comparable to Wenger et al.’s (2009) review of key research questions for urban streams; though differences between the brief literature summary presented here (Fig. 2) and Wenger et al. (2009) will inevitably result from the different timescales reported (1988–2008 by Wenger et al. 2009, 1968–2011 here), and the search terms used. In Wenger et al.’s (2009) study, the search terms “urban*” and “stream* OR river*” were disaggregated, meaning that rivers and streams within a broadly urbanised catchment, or downstream of an urban area for example, may have been included, whereas the search terms here were “urban stream OR urban river”, potentially restricting the publications extracted to more specifically urban foci. Nevertheless, a more complete meta-analysis or systematic review of urban river ecology seems like a worthwhile exercise to establish the current state of knowledge in more depth.
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It is certainly clear that ecological research on urban rivers is increasing, particularly following key advances such as the quantification of urbanization impacts and development of the urban stream syndrome (USS) concept (Paul and Meyer 2001; Walsh et al. 2003), and progress in rehabilitation efforts (e.g. Booth 2005). Wenger et al. (2009) identified key research foci for urban rivers, with priorities ranging from fundamental linkages between urbanisation and biotic response at differing scales, to the development of appropriate ecosystem indicators and communication tools to facilitate river management and improvement. There is also something of a research gap for work on major urban systems; most ecological studies on urban rivers have focused on smaller systems within urbanised catchments, rather than heavily urbanised and engineered rivers, in part because the investigation of such systems can be problematic. However, some notable exceptions include bodies of work on the River Thames through London (e.g. Attrill 1998; Francis and Hoggart 2009, 2012; Hoggart et al. 2012) and the lower Passaic River in New Jersey (e.g. Iannuzzi et al 2005; Kinnell et al 2007; Conder et al. 2009). Geographically, the large majority of work on urban rivers has taken place in North America (mainly the US), Asia (mainly China), and Europe (mainly western Europe) (Fig. 2c). South America (mainly Brazil), Australia and New Zealand have fewer studies, while urban Africa is clearly underresearched and this is likely to be a major research gap given the potential for urbanisation in Africa (Wisner and Pelling 2008; though see Potts 2012). The low number of articles from some parts of the world may reflect a reduced tendency for research to be published in international English language journals, and it is likely that many more studies, particularly from China, exist but are not included in Web of Knowledge. Increased interest in urban rivers has in part been driven by an increasing acknowledgement of the importance of such systems (both ecologically and socially), but also by the need to comprehensively understand and manage them in order to address international legislation. An example is the EU Water Framework Directive (2000/60/EC), which requires all European water bodies to achieve ‘good ecological status’ by 2015, or in the case of heavily modified water bodies (which includes many urbanised systems), ‘good ecological potential’ (see Borja and Elliott 2007 for further definition and discussion). Despite this, fundamental questions remain regarding urban rivers, from what an ‘urban’ river actually is (linked perhaps to wider discussions on the definition of ‘urban’; see MacGregor-Fors 2011; Francis and Chadwick 2012), and what their defining characteristics and range of variation might be (e.g. Gurnell et al. 2007; Wenger et al. 2009) to how they may be rehabilitated, restored or otherwise improved (e.g. Booth 2005; Findlay and Taylor 2006; Francis 2009; Wenger et al. 2009). There is also greater engagement with societal parameters and values in order to more fully understand and manage urban rivers, with some recent studies in particular highlighting the importance of the social dimension (e.g. Eden and Tunstall 2006; Lundy and Wade 2011; Pickett et al. 2011b). This special section results from a session dedicated to the understanding and management of urban rivers held at the Royal Geographical Society (with IBG) Annual Meeting in 2010, at Imperial College London. The papers presented here provide a sample of some of the key themes within recent urban river research, though necessarily only begin to touch upon some of the unknowns (Wenger et al. 2009). The place of urban rivers with the framework of ecosystem services is addressed by Everard and Moggridge (2012), who note that service concepts, particularly those associated with recreation and education, are increasingly being used to justify restoration efforts and are often reported in grey literature. Despite this, methodologies for applying the ecosystem services framework to urban rivers vary, for example in what may be considered an appropriate level of monetisation of services, in comparison to non-economic stakeholder valuation. Although various tools
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exist for ecosystem service applications, they often require a level of understanding of the urban river context that is frequently lacking; this highlights the need for greater investigation and consideration of the processes driving such services. Everard and Moggridge (2012) further review aspects of the application of ecosystem services to urban rivers, drawing on examples from the UK, and conclude that where possible a holistic ecosystem approach is perhaps the best way of unifying the different stakeholders of urban river systems. Ramírez et al. (2012) consider urban rivers on tropical islands and how they may present characteristics that differ from urban river generalities and the urban stream syndrome paradigm, with a focus on Puerto Rico and Hawaii. They note in particular that tropical island streams are often dominated by diadromous fish and shrimp species, which may display increased tolerance to urbanisation and associated impacts due to their utilisation of both freshwater and marine ecosystems, as long as longitudinal connectivity of the river is maintained to facilitate movement. Consequently, although macroinvertebrates in such systems (which are not diadromous) may respond to urban conditions as predicted by the urban stream syndrome, fish and shrimp communities may not, further illustrating differential responses to the syndrome according to the biological assemblage and geographical region under consideration. Two field studies included here consider macroinvertebrates in urban rivers, but in very different systems. Hoggart et al. (2012) look at the macroinvertebrate diversity of flood defence walls along the heavily engineered River Thames through central London (UK), finding that wall construction material and position relative to flow disturbance influence the level of diversity and the biotic communities found. Chadwick et al. (2012) examine the effects of urbanisation on headwater tributaries of the St. Johns River in Florida (US). They find an unexpected positive relationship between urbanisation and macroinvertebrate richness, possibly in relation to altered flow regimes that create intermediate disturbance conditions and thereby support a range of different species. The research further suggests that river ecosystems may respond in a variety of ways to urbanisation, and that further work is needed to elucidate the range and variation of responses. The final two papers in this special section focus on UK rivers. Cockel and Gurnell (2012) investigate the riparian seed bank of the River Brent in London, in comparison with several rural systems. Among other things, they find that, along with the expected reduction in species diversity found along the urban compared to the rural systems, the Brent contains a substantially higher proportion of alien species (21% compared to 4–5%). This further highlights the role that urban ecosystems may play in the establishment and spread of both terrestrial and aquatic invasive plant species; a concern also noted by Klotz and Kühn (2010). The complex issues surrounding urban river assessment and restoration in the UK are considered by Shuker et al. (2012), focusing on the communication of biophysical river conditions to a range of stakeholders. They present an urban river survey toolkit and illustrate how it may be used for concise but informative comparisons of urban river stretches to allow for more effective decision-making, thereby supporting resource use and management efforts. Although these papers represent only a limited snapshot of the sort of research being conducted in urban river systems, they help to demonstrate the range of interdisciplinary work needed to successfully understand and manage such systems; from concept development, refinement and validation to robust river assessment and rehabilitation techniques applied across the ecology/society interface. With growing pressure on freshwater systems throughout the world (e.g. Dudgeon et al. 2006; Vörösmarty et al. 2010) urban river systems are, and will remain, an important focus for ecological research.
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