If you build it, they will come: rapid colonization by dragonflies in a new effluent-dependent river reach

Abstract

Background Aquatic ecosystems are greatly altered by urban development, including the complete loss of natural habitat due to water diversions or channel burial. However, novel freshwater habitats also are created in cities, such as effluent-dependent streams that rely on treated wastewater for flow. It is unclear how diverse these novel ecosystems are, or how quickly aquatic species are able to colonize them. In this study, we (1) quantify odonate (Insecta, Odonata) colonization of a novel effluent-dependent river reach, (2) examine how drying events affect odonates in these novel habitats, and (3) explore whether effluent-dependent streams can support diverse odonate assemblages. Methods We conducted monthly odonate surveys at three sites along the Santa Cruz River (Tucson, AZ, USA) between June 2019 and May 2020. One site was in a long-established effluent-dependent reach (flowing since the 1970s) that served as a reference site and two sites were in a newly-established reach that began flowing on June 24, 2019 (it was previously dry). We compared odonate species richness, assemblage composition, and colonization patterns across these reaches, and examined how these factors responded to flow cessation events in the new reach. Results Seven odonate species were observed at the study sites in the new reach within hours of flow initiation, and species rapidly continued to arrive thereafter. Within 3 months, species richness and assemblage composition of adult odonates were indistinguishable in the new and reference reaches. However, drying events resulted in short-term and chronic reductions in species richness at one of the sites. Across all three sites, we found over 50 odonate species, which represent nearly 40% of species known from the state of Arizona. Discussion Odonates were surprisingly diverse in the effluent-dependent Santa Cruz River and rapidly colonized a newly established reach. Richness levels remained high at study sites that did not experience drying events. These results suggest that consistent discharge of high-quality effluent into dry streambeds can be an important tool for promoting urban biodiversity. However, it remains to be seen how quickly and effectively less vagile taxa (e.g., mayflies, caddisflies) can colonize novel reaches. Effluent-dependent urban streams will always be highly managed systems, but collaboration between ecologists and urban planners could help to maximize aquatic biodiversity while still achieving goals of public safety and urban development.

How hydrology and landscape shape Odonata assemblages in marshlands crossed by ditches

“…Unlike Bogan et al. (2020), which found that short drying events (i.e., a couple of days) did not impact Odonata assemblages, beta diversity for all species combined increased linearly with drying duration in the present study. To be precise, drying duration varied strongly among sites in the Marais poitevin (on average 23 ± 47 days, range 1–194 days), representing severe conditions.…”

“…This suggests that ditch water management offers clear possibilities to maintain and possibly promote Odonata diversity (see also Herzon & Helenius, 2008; Stratford et al., 2015). For example, water management can be better designed to prevent drying episodes and hence to meet conservation purposes in anthropogenic aquatic systems (Bogan et al., 2020; Mauchamp et al., 2021; Twisk et al., 2000). Indeed, we highlighted that maintaining a water depth of several tens of centimetres throughout the summer might play an essential role for Odonata assemblages.…”

Environmental Determinates of Distribution for Dragonfly Nymphs (Odonata: Anisoptera) in Urban and Non-Urban East Texas Streams, USA

“…In contrast, other dragonfly taxa were less frequently represented in urban streams suggesting intolerance for disturbed systems. Our finding echoes that reported in other studies [30,54]. In contrast, other studies have found that dragonflies were more significantly underrepresented in urban streams [2,3,27] biodiversity with more severely impaired streams having fewer species.…”

“…For example, an urban stream with clear water, sufficient vegetation and shade, and good flow may provide better habitat for some lotic dragonflies than a non-urban stream with turbid water, sluggish flows, and a disturbed shoreline. Moreover, although some species appear to be intolerant of anthropogenic stressors, others readily inhabit disturbed habitats [54]. Many of the previously published tolerance values, which indicate dragonflies are a largely tolerant as a group, are supported by our analysis.…”

Effects of urban spatial and temporal heterogeneity on benthic macroinvertebrate and diatom communities

“…Thus, effluent has been used to restore habitats for species of concern, and urban river food webs and many conservation plans have been created for urban rivers that rely on effluent for habitat creation (Linke et al 2010). Despite research on the effects of urbanization on the physical properties of rivers and the potential for WWTPs to positively and negatively impact biodiversity, no clear picture has emerged about how effluent influences freshwater communities (Hassett et al 2018;Bogan et al 2020;Eppehimer et al 2020;Eppehimer et al 2021).…”