Recovery of black-necked swans, macrophytes and water quality in a Ramsar wetland of southern Chile: Assessing resilience following sudden anthropogenic disturbances

Exploring the recovery of a large wetland using black-necked swan blood parameters and body condition 16 years after a pollution-induced disturbance

Resilience theory has taken center stage in tackling the challenge of wetland recovery on a fast-changing planet. Because of waterbirds' enormous dependence on wetlands, their numbers have long been used as surrogates for wetland recovery over time. However, immigration of individuals can mask actual recoveries at a given wetland. One alternative to expanding the knowledge of wetland recovery is the use of physiological parameters from aquatic organism populations. We explored the variations in the physiological parameters of black-necked swan (BNS) before, during, and after a 16-year period of a pollution-induced disturbance that originated in a pulp-mill wastewater discharge. This disturbance triggered the precipitation of iron (Fe) in the water column of the Río Cruces Wetland in southern Chile, one of the main sites for the global population of BNS Cygnus melancoryphus. We compared our recent (2019) original data (body mass index [BMI], hematocrit, hemoglobin, mean corpuscular volume, blood enzymes, and metabolites) with available datasets from the site obtained before the pollution-induced disturbance (2003) and immediately after the disturbance (2004). Results indicate that, 16 years after the pollution-induced disturbance, some important parameters of animal physiology did not return to their pre-disturbance state. For instance, BMI, triglycerides, and glucose were significantly higher in 2019 than in 2004, right after the disturbance. By contrast, the hemoglobin concentration was significantly lower in 2019 than in 2003 and 2004, and uric acid was 42% higher in 2019 than in 2004. Our results demonstrate that, despite higher BNS numbers with larger body weights present in 2019, the Río Cruces wetland has only partially recovered. We suggest that the impact of megadrought and wetland disappearance far from the site results in high rate of swan immigration, casting uncertainty about using the number of swans alone as honest indicators of wetland recovery after a pollution disturbance. Integr Environ Assess Manag 2023;19:663-675. © 2023 SETAC.

Land reclamation pattern and environmental regulation guidelines for port clusters in the Bohai Sea, China

Coastal land reclamation (CLR), particularly port reclamation, is a common approach to alleviating land shortages. However, the spatial extent, percentages, and processes of these newly reclaimed ports are largely unknown. The Bohai Sea is the most concentrated area of port reclamation worldwide. Thus, this study addresses the changes in the different coastline types and port reclamation process in the area. The reclamation area of the 13 ports in the Bohai Sea in 2002-2018 was 2,300 km2, which decreased the area of the sea by 3%. The natural coastline length in Tianjin decreased by 47.5 km, whereas the artificial coastline length increased by 46.6 km. Based on the port boundary, however, only 26.3% of the reclaimed areas have been used for port construction, which concentrates in the Tianjin and Tangshan ports. The ratio of built-up area within the ports is only 32.5%, and approximately 48.3% of the reclaimed areas have no construction projects. The port land reclamation in the Bohai Sea has been undergoing periods of acceleration, peak, deceleration, and stagnation since 2002. Hence, future port reclamation should not be totally prohibited, and fine management should be conducted based on the optimization of the reclaimed port area. The innovation of this research is its analysis of the port internal land use pattern, the percentage of built-up area in the ports, and the sustainability of port reclamation policies. The findings have vital implications for scientifically regulating the spatial pattern and exploring the utility of port reclamation.

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

The black-necked swan Cygnus melancoryphus is an aquatic herbivorous bird whose dietary habits depend on the dominance and accessibility of macrophyte banks in shallow areas of coastal and limnetic wetlands in southern South America. The swans from the Río Cruces wetland in southern Chile (ca. 39°S) feed mainly on the macrophyte Egeria densa from the water column between depths from less than 0,5 and 2,0 m. A micro- histological analysis of black-necked swan feces (N = 152) collected during six sampling occasions between 2012 and 2017 confirms the preferred consumption of E. densa and highlights the impact of temporal changes in the cover of these macrophytes on the swan's diet. The dietary composition of black-necked swans appears as a reliable proxy for temporal changes in the distribution of the most common aquatic macrophytes in the Río Cruces wetland. These results highlight the importance of preserving shallow wetlands as the habitat for aquatic macrophytes that provide the main food source for these herbivorous water birds.

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

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.