Agricultural Irrigation Canals Threaten Wild Terrestrial Vertebrates in Northern Chile

Simple Summary

Agriculture in arid ecosystems depends on the availability of water, which is often transported through large open irrigation canals. Although essential to improve productivity, these waterways pose a threat to terrestrial vertebrates living in the surrounding areas. Here, we conducted a survey looking for fallen animals in a dry irrigation canal located near Ovalle, in northern Chile. Our observations unveiled 100 native rodents or reptiles dead along a transect of 900 m. Few alive live specimens were rescued and relocated in the neighboring area. We conclude that measures to mitigate detrimental effects are needed for the conservation of terrestrial vertebrates that inhabit ecosystems disrupted by agriculture agricultural irrigation canals in northern Chile.

Abstract

Irrigation canals are essential for agriculture in semi-arid regions like northern Chile, yet their ecological impacts on wildlife remain underexplored. Here, we assessed the effects of a 900 m transect of a dry, polyethylene-covered irrigation canal in the Coquimbo region on local terrestrial fauna. A total of 121 reptiles, marsupials, and rodents were found in the canal, with 82.64% mortality. Our evidence suggests that the animals drowned when the water flux stopped or perished because of the extreme heat irradiated by the polyethylene geomembrane once the canal became empty. We highlight that these canals act as lethal pitfall traps for terrestrial vertebrates, as seen in other countries. Given the ecological impact that these waterways impose on local fauna, the implementation of mitigation strategies such as physical barriers, escape aids, and connectivity structures to reduce mortality is urgent in the region.

1. Introduction

Irrigation canals are the most cost-effective way to transport water in agriculture [1] and are essential in semi-arid regions worldwide, particularly in areas where water scarcity limits productivity [2]. In fact, channeling water by gravity is an efficient way to distribute the resource in the arid north of Chile (roughly 18–33° S). The water is accumulated in dams constructed in the Andes Mountains and downloaded through kilometric open canals that irrigate plantations [3]. Despite its vital role in agriculture, the ecological implications of these waterways on wildlife remain largely understudied in the region, which is home to native rodents (Abrocomidae: Abrocoma, Chinchilla; Cricetidae: Abrothrix, Phyllotis; Octodontidae: Ctenoyms, Octodon, Spalacopus), marsupials (Didelphidae: Thylamys), and reptiles (Squamata: Callopistes, Galvarinus, Homonota, Liolaemus, Philodryas) [4,5].

Open irrigation canals provide inadvertent access for invasive species, alter natural habitats, and disrupt local rivers [6]. More critically, water channeling systems can lead to direct mortality, displacement, and fragmentation of habitats for terrestrial vertebrates [7,8]. Ecological disruptions of this nature have far-reaching consequences for species persistence and for the broader biodiversity of a given region [9]. This note highlights the impact that irrigation canals pose to terrestrial vertebrate assemblages of the Coquimbo region in northern Chile, with the aim to inform national stakeholders.

2. Materials and Methods

On 27 December 2024 (austral summer), we conducted a convenience survey to inspect a 900 m transect of a 26 km long irrigation canal for fallen animals (top width: 5 m; bottom width: 2 m; depth: 3.2 m) at El Guindo Alto, Ovalle (−30.6430618; −71.1096796; 780 m), Coquimbo Region (Figure 1). The canal had 57° angled sides and was partially dry, with scattered pools of water along its bottom. Covered by high-density polyethylene (HDPE) geomembrane, the canal conducts water from “La Paloma” dam to local crops and fruit tree plantations. The survey was performed between 17:00 and 22:00 h. All the observed animals were identified using taxonomic field guides [4,5]. The canal is surrounded by xeric vegetation composed of trees (Acacia cavens), shrubs (Gypothamnium pinifolium, Heliotropium linariifolium, Nolana villosa, Oxyphyllum ulicinum, Polyachryus fuscus), and cacti (Austrocactus coquimbensis, Copiapoa hypogea, Eriosyce curvispina, Eulychnia acida) [10]. The region lies within a transitional zone between desertic and Mediterranean climates, characterized by arid conditions and limited oceanic moisture influence [10].

3. Results

Although brief, our survey revealed the detrimental effects of open-channel irrigation systems in the area. A total of 121 specimens were observed, 21 of which were successfully removed from the channel and released in the neighboring area. One hundred specimens were found dead. The affected taxa included two reptiles, one marsupial and two rodent species (Figure 2,

Table 1. Total accounts of live/dead vertebrate species observed during the survey of a dry irrigation canal at El Guindo Alto, Ovalle, Coquimbo Region, northern Chile.

Class	Order	Species	Alive	Dead	Total
Mammalia	Rodentia	Phyllotis darwini	10	95	105
		Spalacopus cyanus	1	4	5
	Didelphimorphia	Thylamys elegans	1	0	1
Reptilia	Squamata	Callopistes maculatus	7	1	8
		Philodryas chamissonis	2	0	2
Total			21	100	121

). Phyllotis darwini comprised 87% of specimens. Overall, 82.64% of the animals were dead and were not removed from the canal.

4. Discussion

Due to the low water storage levels (10%) currently observed at La Paloma dam [11], water distribution is being rationed according to pre-scheduled periods with farmers, including during the Christmas holidays. This fact likely explains why the canal was dry on 27 December. Although the exact time required for the canal to empty is unknown to us, it takes around 30 h according to local people’s observations. Therefore, we hypothesize that dead animals either drowned after falling into the stagnant water or may have fallen in while water was still flowing and were carried by the current to these areas. Consequently, that was the reason why some of the carcasses were still wet (Figure 2). Moreover, once completely dry, the heat radiated by the canal’s HDPE geomembrane could have posed an additional hazard to any animal falling in. In fact, under direct solar exposition, black geomembranes can reach temperatures over 70 °C [12], which is enough to cause death by heat exhaustion and heatstroke in small mammals [13]. Noteworthy, some of the rescued reptiles exhibited pododermatitis, possibly due to prolonged exposure to the hot surface. Although we are not aware of the total quantity of animals that fall into the canal when the water is flowing, the data from our survey along 900 m could be extrapolated to the total extension of the channel. However, while the 26 km-long canal passes through environments similar to the site where we conducted the survey, extrapolating the data would still require additional information for validation, such as the number of scavenger species removing prey items before specimen encounters [7,8].

The high mortality rate that we observed (82.64%) highlights the significant threat these canals pose as pitfall traps for terrestrial vertebrates, a fact also documented in other countries [7,8]. This underscores the need for mitigation strategies, such as fences to prevent access, bridges to maintain landscape connectivity, and escape aids like stairs, ropes, or ramps [14,15,16]. Moreover, covering the canals with textured geomembranes featuring raised bumps may facilitate the grip of the animals, enabling them to exit the canals when these are empty. While some of these measures have shown promising results elsewhere, their implementation in northern Chile’s irrigation canals remains pending and should be considered in environmental policies aimed at conserving local fauna. As irrigation canals expand, addressing the ecological consequences of these waterways is critical to preserving the country’s biodiversity.

5. Conclusions

Irrigation infrastructure in arid regions can unintentionally threaten local wildlife by creating hazardous conditions that trap and kill small vertebrates. The findings from our short field survey revealed a high proportion of animal mortality within a limited section of a water channel, suggesting a broader, unaddressed conservation issue. Contributing factors likely include extreme surface temperatures and physical barriers that prevent escape. Simple structural adaptations and preventive strategies could significantly reduce these impacts. Incorporating ecological safeguards into the design and management of these systems is essential to support biodiversity in vulnerable landscapes.