Engineered ponds as environmental and ecological solutions in the urban water cycle: A case study in Patagonia

Abstract

Environmentally sound solutions such as engineered ponds have primarily been established for waste water treatment and flood control in urban areas. However, there is a lack of comprehensive understanding of the factors that influence the aquatic biodiversity of these artificial water bodies, and it has been questioned whether ponds that are designed for water treatment are also able to enhance or support regional biodiversity. The present study (1) examined the water management function of two constructed wetland systems in the urban water cycle: flood prevention ponds (FP) and waste water treatment ponds (WT); (2) analysed their role to enhance local and regional biodiversity (macrophytes and invertebrates); and (3) assessed the functioning of a waste water treatment plant (WTP) in view of regional regulations. As expected, strong differences were found in water quality conditions between FPs and WTs, mostly in terms of nutrients, conductivity, suspended solids and oxygen levels. FPs created optimal environments harboring several species of macrophytes and supporting diverse invertebrate assemblages, comparable to those recorded at natural ponds. On the contrary, WTs sustained three times less taxa, with Psychoda sp. and Chironomus sp., (dipterans indicators of poor ecological conditions) dominating the assemblage. The waste water treatment plant was partially successful with regards to domestic effluent processing. Nutrient values for treated effluents exceeded the permissible standards for receiving surface waters in the region. Constructed ponds offer an opportunity for managers and environmental regulators to conserve and enhance aquatic biodiversity in ecologically poor environments. In addition to other ecosystem services (sociocultural), FPs also promoted biotic biodiversity. WTs functioned as nutrient sinks rather than as biodiversity spots, but their biodiversity and functioning could be enhanced through proper design and management. Some feasible solutions to improve WTP functioning are itemized and discussed.