# Three-Year Follow-Up Assessment of Anthropogenic Contamination in the Nichupe Lagoon
## 3 Results and Discussion
Therefore, the spatial and temporal distribution of caffeine in the NLS (Figure 3) clearly shows that touristic activity and the inefficiency of treatment promote the presence of wastewater, but the concentration and dispersion will be altered by the hydrological conditions related with anomalous precipitation events. In terms of nutrients in 2019 (see Table 2 and Figure 4a-e), compared with data from the previous year, there is also an increasing tendency in nitrate and nitrite concentrations and variability in the quantification of ammonia, phosphate, and silicate. However, from 2019 to 2020, there was a decrease in nutrients, while the chlorophyll concentration increased (Figure 4f). This could be the result of the infiltration of rainwater because of the Cristobal storm that lasted 9 days in the Yucatan Peninsula [28]. This could have favored the dilution of nutrients in the lagoon and the suspension of particles that increased the concentration of chlorophyll-a. Also, the previously discussed effect of the anomalous rain/higher  
Figure 3: Distribution of caffeine throughout the zones of the NLS in the three-year follow-up. groundwater input in the area is observed for salinity levels in 2018 and 2020, as can be seen in Figure 4h where values as low as 23.8 ppt were detected. Figure 4: _Cont._  
Also, groundwater inputs to the NLS in the same years promote a decrease in oxygen levels as seen in Figure 4g [10], although oxic values prevail. Our results are comparable with the values presented in Table 3 for similar systems during rainy seasons: coastal lagoons also in the Yucatan. Moreover, this information is essential to assess the anthropogenic contamination in the area. Results from the Kruskal-Wallis test are shown in Table 4; this nonparametric test was carried out after the results of non-normally distributed data were given by the Shapiro  
Figure 4: Spatial and temporal variations in the NLS of (**a**) NO\({}_{3}\)\({}^{-}\), (**b**) NO\({}_{2}\)\({}^{-}\), (**c**) NH\({}_{4}\)\({}^{+}\), (**d**) SRP, (**e**) SRSi, (**f**) Cha-a, (**g**) salinity, and (**h**) DO. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Salinity** & **DO** & **NO\({}_{3}\)\({}^{-}\)** & **NO\({}_{2}\)\({}^{-}\)** & **NH\({}_{4}\)\({}^{+}\)** & **PO\({}_{4}\)\({}^{3-}\)** & **SiO\({}_{4}\)\({}^{-}\)** & **Study Area** & **Reference** \\ \multicolumn{1}{c}{**(PSU)**} & **(mg L\({}^{-}\)1)** & **(\#g L\({}^{-}\)1)** & **(\#g L\({}^{-}\)1)** & **(\#g L\({}^{-}\)1)** & **(\#g L\({}^{-}\)1)** & **(\#g L\({}^{-}\)1)** & **Study Area** & **Reference** \\ \hline
25.8 & & 180 & 381 & 173 & & & Dzilam Lagoon & [31] \\
33.2 & 3.2 & 471 & 93.0 & 657 & & & Chelem Lagoon & [32] \\
33.3 & 3.99 & 236 & 52.1 & 225 & 41.54 & 8476 & Celestun Lagoon & [33] \\
28.4 & 4.07 & 691 & 54.7 & 195 & 1410 & 4680 & Nichupté mangroves & [3] \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Overview of nutrient comparison data from coastal zones in the Yucatan Peninsula. Wilk test. Significant differences were observed between the salinity (\(p<0.05\)). Most of the zones remained classified as polyhaline (18-30 PSU) throughout the three years of the study. The distinguishing aspect of the NLS is the interaction with groundwater flows and the pressure gradient oriented from the mainland to the lagoon system; thus, the salinity values suggest that near the coast, there is a process of mixing due to the known limestone and cavernous structure of the subsoil between the fresh water and seawater [17]. Zone I (Bojorquez) presents a direct influence of the water of the Caribbean Sea and long residence times; therefore, in this zone, the salinity was above 30 PSU. For dissolved oxygen, no significant differences were observed over the years (\(p=0.109\)) but the range of variation in dissolved oxygen indicates intense metabolic activity in the water column [34]. Finally, for caffeine and nutrients, it shows significant differences (\(p<0.05\)).