Bogan Michael T, Eppehimer Drew, Hamdhani Hamdhani, Hollien Kelsey
School of Natural Resources and the Environment, University of Arizona, Tucson, AZ, USA.
Department of Aquatic Resources Management, University of Mulawarman, Samarinda, Indonesia.
PeerJ. 2020 Sep 16;8:e9856. doi: 10.7717/peerj.9856. eCollection 2020.
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.
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.
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.
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.
城市发展极大地改变了水生生态系统，包括因引水或河道掩埋导致自然栖息地完全丧失。然而，城市中也创造了新的淡水栖息地，例如依赖废水排放的溪流，这些溪流依靠经处理的废水来维持水流。目前尚不清楚这些新型生态系统的多样性如何，或者水生物种能够多快地在其中定殖。在本研究中，我们（1）量化了一个新型依赖废水的河段豆娘（昆虫纲，蜻蜓目）的定殖情况，（2）研究了干旱事件如何影响这些新型栖息地中的豆娘，以及（3）探讨了依赖废水的溪流是否能够支持多样的豆娘群落。
我们于2019年6月至2020年5月在美国亚利桑那州图森市的圣克鲁斯河沿岸的三个地点每月进行一次豆娘调查。一个地点位于一个长期存在的依赖废水的河段（自20世纪70年代以来一直有水流），作为参考地点，另外两个地点位于一个新形成的河段，该河段于2019年6月24日开始有水流（此前为干涸状态）。我们比较了这些河段之间豆娘的物种丰富度、群落组成和定殖模式，并研究了这些因素如何响应新河段的水流停止事件。
在新河段水流开始后的数小时内，就在研究地点观察到了7种豆娘物种，此后物种仍在迅速持续到达。在3个月内，新河段和参考河段中成年豆娘的物种丰富度和群落组成已无明显差异。然而，干旱事件导致其中一个地点的物种丰富度出现短期和长期下降。在所有三个地点，我们发现了超过50种豆娘物种，这几乎占亚利桑那州已知物种的40%。
在依赖废水的圣克鲁斯河中，豆娘的多样性惊人，并且迅速在一个新形成的河段定殖。在没有经历干旱事件的研究地点，丰富度水平仍然很高。这些结果表明，持续向干涸的河床排放高质量的废水可能是促进城市生物多样性的一个重要工具。然而，较不具迁移性的类群（例如蜉蝣、毛翅目昆虫）能够多快且有效地在新河段定殖，仍有待观察。依赖废水的城市溪流将始终是高度管理的系统，但生态学家和城市规划者之间的合作有助于在实现公共安全和城市发展目标的同时，最大限度地提高水生生物多样性。
