Growing water quality impairment represents a global scale problem threatening human development and ecosystem integrity. Alterations of water can pose a threat to public health and affect human access to safe water for drinking and domestic purposes, food production, and recreation [1
]. In aquatic ecosystems, poor water quality can lead to detrimental effects such as the increase in algal blooms, aquatic species mortality, increase in fish disease, among others [2
]. Within the Galapagos Islands, human activities have contributed to major alterations in coastal and ground water quality [4
], resulting in public health problems such as a high incidence of respiratory and gastrointestinal parasitic infection in residents and tourists [4
]. In addition, as observed in other parts of the world, poor water quality can be impaired further by natural-climate driven processes [7
]. This study seeks to evaluate coastal and ground water quality on the Pelican Bay watershed in Santa Cruz Island to gain a better understanding of the current status of water quality along with seasonal and spatial variations.
Increasing permanent human population and tourism in the Galapagos exerts a significant pressure over the fragile ecosystem of the islands and enhances water degradation [5
]. Main groundwater sources for Santa Cruz Island are contaminated due to several factors such as the location of the basal aquifer beneath dense urban settlements, the lack of effective wastewater treatment plants, and seawater intrusion [12
]. In fact, seawater may be migrating inland due to overexploitation of the aquifer [5
]. In particular, malfunctioning septic tanks are responsible for most of the fecal contamination in the island [4
]. Main sources of fecal contamination for coastal marine waters in Puerto Ayora, the main urban area on Santa Cruz Island, include: land runoff of sewage waters during wet weather, submarine and boat discharges, and overland pipe sewage effluents [5
]. Additionally, high levels of E. coli
in the coastal waters seem to be related to groundwater leachate flowing seaward during low tide [15
]. Yet, more specific monitoring is needed to understand the complete picture of potential water impairment in the Galapagos Islands and to identify the implications of basin sensitivity on water quality to increases in tourism and residents.
Besides the anthropogenic factors, water quality can be directly affected by several climate-related mechanisms in both the short and long term. For example, water quality variation in the Huai River Basin in China is significantly correlated with precipitation and strongly affected by air temperature [7
]. Other studies [8
] found that intense rainfalls and runoff make pathogens more susceptible to rise in concentration in superficial waters. Moreover, water temperature increases reduce gases solubility and favors many physical-chemical processes such as dissolution, solubilization, complexation, nitrification, degradation, and evaporation occurring in water bodies, leading to elevated levels of dissolved substances found in temperate and tropical regions [10
]. Additionally, mineralization increases leads to a greater release of nitrogen, phosphorus, and carbon from soil that is then transported by runoff [16
]. Warmer temperatures may also impact water bodies with long residence times, which would imply eutrophication problems in the future [16
]. Regarding precipitation, literature studies have demonstrated that pollutant transport is enhanced by heavy rainfall events, which increase runoff and erosion, and in many cases cause higher levels of turbidity and organic matter [10
]. Therefore, similar climate-related processes as those described herein may affect water quality in the Galapagos Islands. Although, other factors, such as the direction of the groundwater flow, the distance from the sea, and changes in altitude, have been observed to influence changes in water temperature, pH, conductivity, and dissolved oxygen (DO) in Santa Cruz Island [13
], there is still the need to investigate water quality variability due to seasonal and natural processes in the Galapagos.
Determining environmental background levels constitutes a helpful comparative tool that can be utilized to define thresholds values for specific water bodies [17
] and defines if water characteristics are influenced by either natural processes or human activities. Background concentration is defined as “a concentration of a substance in a particular environment that is indicative of minimal influence by human (anthropogenic) sources” [19
]. Therefore, the environmental background levels can reveal natural conditions unaffected by anthropogenic influence [17
]; thus, it enables us to distinguish values of a particular parameter that are product of natural processes from anthropogenic impacts [20
]. Environmental background levels and the upper limit background levels (or thresholds) have been established worldwide for many waterbodies [17
]. However, the application of large-scale background values to evaluate local status of water quality can lead to misunderstandings because local background is constrained by local conditions [17
] such as water–rock interactions, chemical and biological processes, residence time of water, recharge inputs and transport processes [18
]. For that reason, statistical methods are preferred for the calculation of local background levels.
This study evaluates coastal and ground water status in Pelican Bay, a human-influenced watershed in Santa Cruz Island, using a 9-year (2007–2015) dataset obtained during a local water quality monitoring program conducted by the Galápagos National Park. Physical-chemical and microbiological parameters were used to assess water quality and its suitability for designated purposes at each study site, such as potable water, irrigation and/or recreation based on national and international guidelines. Additionally, environmental background levels were calculated to reveal natural conditions unaffected by anthropogenic contributions within the 9-year study period. To evaluate whether or not changes in tourism and residents are responsible for degradation of the water sources between 2007 and 2015, a sensitivity analysis was conducted. Finally parameters were analyzed to describe their seasonal and spatial variations.