# Three-Year Follow-Up Assessment of Anthropogenic Contamination in the Nichupe Lagoon
## 1 Introduction  
The tourism industry has promoted direct and massive alteration of the coastal environment [1]. The state of Quintana Roo, Mexico, has been economically dependent on the tourism industry since the mid-1970s when Cancun and the Rivera Maya were created. Up to the late 1960s, Cancun was an uninhabited barrier island formed by dunes and unexplored beaches, within a landscape of mangroves and virgin rainforests [2]. The city of Cancun, State of Quintana Roo, is now a major hub for tourism activities, where many of them are carried out in natural protected areas, which are particularly vulnerable owing to the proximity of urban zones [3]. The Cancun hotel zone was built on a small spit, a relic fringing reef, separating the mainland of the peninsula with a shallow coastal lagoon: the Nichupte Lagoon [4; 5]. The Nichupte Lagoon System (NLS) is an oligotrophic system that embraces an area of about 48 km\({}^{2}\), with depths varying between 0.3 and 4.5 m. It is located on the northeast coast of the Yucatan Peninsula on the coastline corresponding to the Caribbean Sea [6] it contains marine water and sandy sediments covered by seagrass and algae and is one of the attractions that has made Cancun an important tourist place in Mexico [7]. Dismally, the NLS is subject to all the environmental negative changes typical of the urban development and recreational activities on the coastline, coupled with the growing urban expansion in the surroundings. Due to the hydrological connectivity underground that prevails in this karst system, it receives continental water discharges year round with a higher volume during the rainy season [8; 9; 10]. Incoming water carries out substances produced by land-based activities that have the potential to negatively change the water quality and ecosystem function [11]. The population growth in Quintana Roo state has caused an increase in the concentration of nutrients in the coastal aquifer, which are subsequently discharged into the coastal ecosystems of the area through the discharge of groundwater that maintains connectivity between inland anthropogenic activities and marine aquatic ecosystems [12]. One of the main activities that has affected Nichupte is the continual discharge of sewage, which has increased the amount of nutrients resulting in eutrophication [7]. This intense tourist activity gave rise to major environmental problems: loss of mangrove forests, swamps, sand dunes, and beaches; eutrophication of coastal lagoons; degradation of water quality; and changes in the coastline due to harbor and marina construction [13]. General changes in land use from the construction of hotels on these fragile coastal lands have resulted in increased sediment run-off, to which coral reefs are particularly sensitive, extensive deforestation, and the underground supply of water enriched with nitrogen and phosphorus from wastewater generated by hotels and golf courses, which result in alterations affecting the health of the ecosystem [1]. Currently, many parts of the NLS are seriously polluted and give off foul odors derived from the discharging of wastewater from hotels and shopping malls throughout Cancun [14]. Wastewater treatment plants in the hotel zone are on the island next to the lagoon, along with the rainwater drainage conducted to discharge over the lagoon. About 80% of the area of the island has been paved, which prevents the penetration of water from rain on the ground. Thus, when it drains, the same water carries heavy metals with it and other chemical compounds soluble or insoluble in the lagoon [15]. A great vulnerability of the Nichupte lagoon is the high residence time of the water and the fact that it only has two narrow inlets located as the only ways to communicate with the sea. This implies a restricted circulation pattern that allows the accumulation of organic matter, nutrients, and some other contaminants [11].