Resilience of an aquatic macrophyte to an anthropogenically induced environmental stressor in a Ramsar wetland of southern Chile

Abstract

In mid-2004, anthropogenically induced changes in water quality of the Río Cruces wetland, a Ramsar site located in southern Chile (ca. 40°S), enhanced the resuspension of iron-enriched sediments, which were subsequently deposited over the most abundant aquatic macrophyte of the wetland (Egeria densa Planch. 1849). This event triggered the formation of brownish, necrotic patches and increased iron contents in the leaves and stems of E. densa, which contributed to a significant demise of the plant within the wetland. In this study, we estimate the recovery time as a proxy for resilience of this macrophyte at organismal and population levels. Macro- and micro-optical characteristics, as well as iron contents in tissues of E. densa, were documented in four time windows (2004, 2008, 2012, and 2014). In addition, the size of the macrophyte population and its spatial occurrence were monitored from 2008 to 2016 across 36 study sites within the wetland. Our results suggest necrotic patches and high iron contents in E. densa persisted at least until 2008. After 2013, a significant increase in the spatial occurrence of E. densa was observed within the wetland, reaching full recovery of the population during 2015. The health of plant tissues and iron contents in leaves and stems showed recovery period close to 4 years, while the recovery of the spatial occurrence of E. densa took approximately 9 years. While the monitoring of plant health was not performed on a strict annual basis, the recovery rates estimated here are slower than those described for other macrophytes. This finding might reflect the long-lasting effects of the disturbance from 2004 and the interaction with biotic processes, such as foraging by waterbirds recolonizing the Río Cruces wetland. These results show that full recovery of E. densa was achieved through a cascade of effects starting with abiotic factors (water quality) and passing through physiological and individual levels, to finally reach the population level. A key aspect of this response is the invasive nature of the macrophyte, which likely contributed to its recovery as a consequence of improved water quality. Less successful macrophyte species in other systems may not reach the specific population recovery, and become subdominant species instead, or even be eradicated from the wetland either as the result of herbivory or due to competition with other macrophytes.

Ecosystem processes, management and human dimension of tectonically-influenced wetlands along the coast of central and southern Chile

“…consequence from a pulse disturbance event caused by the initial industrial operations of a pulp mill plant located upstream from the Río Cruces wetland (Escaida et al 2015;UACh 2015). The recovery processes begun in 2012 (Jaramillo et al 2018a(Jaramillo et al , 2018b and today, nearly 14 years after the disturbance, the population abundances and health conditions of swans, the spatial cover of the aquatic plant E. densa, and the transparency of waters across the wetland have recovered to their initial undisturbed state. The abundance of the affected biotic components of the wetland appear to be healthy (UACh, 2015(UACh, , 2017 and include biotic components such as macrophytes, fi shes, and river shrimps, amongst others (Lagos et al 2008).…”

“…Furthermore, the importance of tidal variability in coastal wetlands was emphasized in the workshop by Dr. Mario Pino (Universidad Austral de Chile). Associated studies from this research group along the Río Cruces wetland (UACh 2015) addressed the re-suspension of iron-enriched sediments causing deterioration of sanitary conditions in aquatic macrophytes during the pulse disturbance event of 2004 and subsequent cascading effects on population abundances, body weights and liver conditions of Black-necked swans (Jaramillo et al 2018a(Jaramillo et al , 2018b.…”

Dietary habits of the black-necked swan Cygnus melancoryphus (Birds: Anatidae) and variability of the aquatic macrophyte cover in the Río Cruces wetland, southern Chile

“…densa , Potamogeton pusillus and Potamogeton lucens were recorded and used to fit the SDMs. For those five years, SDMs were fit using remote sensing layers extracted from a Landsat 8 Operational Land Imager (OLI) scenes recorded on location 233/88 of the path/row of Worldwide Reference System 2 (WRS-2) [26,28,38] (S2 Table). For each OLI scene, bands 2 through 7 were processed as described by [39] and yielded top-of-atmosphere reflectance percentage values (RTOA).…”

“…Since 2012, a gradual recovery of E . densa was observed across the wetland, followed by a gradual recovery of the population of swans [26,27,28] reaching numbers as high as 16,000 birds in early 2019 (https://www.conaf.cl).…”

Consumption of aquatic macrophytes by the Red-gartered Coot Fulica armillata (Aves: Rallidae) in a coastal wetland of north central Chile

“…Jaramillo et al 2007;Lagos et al 2008). Only eight years later, macrophytes begun to recover and a concomitant increase in the abundance of coots was observed (Jaramillo et al 2018a(Jaramillo et al , 2018b, although the mechanisms underlying their decline and subsequent recovery remain not fully understood.…”