Abstract
The fragility of geographically isolated islands stresses the necessity of evaluating the current situation, identifying temporal trends and suggesting appropriate conservation measures. To support this, we assessed the freshwater quality of three stream basins on San Cristóbal (Galapagos) for two consecutive years. Abiotic conditions generally complied with existing guidelines, except for the pH in the Cerro Gato basin (<6.5) and orthophosphate concentrations in 2016 (>0.12 mg P L−1). Macroinvertebrate communities were characterized by low family richness (3–11) and were dominated by Atyidae or Chironomidae, thereby causing low diversity (0.33–1.65). Spatial analysis via principal component analysis (PCA) illustrated that abiotic differences between stream basins were mostly related to turbidity, pH, dissolved oxygen (DO), and conductivity. Biotic differences were less clear due to masking by anthropogenic disturbances and dispersal limitations, yet indicated a negative effect of reduced pH and DO on Atyidae presence. In 2017, significantly narrower ranges were found for turbidity, temperature, pH, and diversity (p < 0.01), suggesting a decrease in habitat variability and a need for conservation measures, including mitigating measures related to dam construction for water extraction. As such, further follow-up is highly recommended for the sustainable development and environmental protection of this unique archipelago.
Highlights
Freshwater systems located on geographically isolated islands represent sensitive environments prone to irreversible changes when experiencing an unexpected disturbance [1]
principal component analysis (PCA) and Redundancy analysis (RDA) were preferred over correspondence analysis (CA) and canonical CA (CCA), as (1) a preliminary detrended correspondence analysis (DCA) resulted in an axis length shorter than 3 units, suggesting the use of a linear ordination [38]; (2) the Hellinger distance provides a better trade-off between resolution and linearity, compared to chi-squared-based techniques [37]; and (3) CCA is not recommended to be used if data richness covers a wide range [39]
The lowest dissolved oxygen (DO) concentration (4.62 mg O2 L−1 ) was observed in site G1 in 2017, but it was mostly higher than 6 mg O2 L−1
Summary
Freshwater systems located on geographically isolated islands represent sensitive environments prone to irreversible changes when experiencing an unexpected disturbance [1]. Human colonization of these remote areas has occurred throughout history, relying on ground- and/or rainwater to provide for daily freshwater needs. Population growth, tourism, and climate change are major factors affecting both freshwater quantity and quality [2,3,4,5]. Land conversion for human purposes limits rainwater interception and replenishment of water resources, while allowing evaporation to occur at higher rates, altering water quantity [3,6]. Freshwater diversity on islands is often unbalanced in terms of macroinvertebrate communities and characteristically different from the mainland, especially when considering volcanic islands (e.g., Macaronesia, Galapagos) that have never been in physical contact with the mainland [1,9]
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