Water quality of limnological stations

Prepared by Viviana Cruz Hernández (physico-chemistry, phytoplankton),

William Lanza Aguilar (periphyton, statistical analysis)

& Xavier Lazzaro (sondes, databases)

Characteristics of  a network of limnological stations 

We conducted the periodic campaigns between 2018 and 2021, monitoring 41 stations during 45 field campaigns, in 4 zones of the Titicaca Minor Lake ('Lago Menor'). In each zone we monitored physicochemical and biological indicators (communities) to evaluate the state of water quality and the level of eutrophication. We monitored 11 physicochemical variables at each station: pH, conductivity (µS/cm), dissolved oxygen (DO, mg/L), turbidity (NTU Nephelometric Turbidity Unit), nitrates (mg/L), nitrites (mg/L), ammonium (mg/L), phosphates (mg/L), fluorescent dissolved organic matter (fDOM, RFU Relative Fluorescence Unit), chlorophyll-a (Chl-a, RFU) and Phycocyanin (RFU).  

We evaluated 139 phytoplankton samples, by inverted microscopy, identified according to the traditional Taxonomic Classification and by Functional Groups (MBFG) according to their morphology (Kruk et al. 2010), to estimate density (org/mL) and biovolume (mm3/L) represented by bar graphs, by season, zone, and sampling time.  We identified 59 genera among the phyla: Bacilliarophyta (20), Chlorophyta (20), Charophyta (7), Euglenozoa (= Euglenophyta) (3), Cyanobacteria (4), Myozoa (= Dinophyta) (2), Cryptophyta (2) and Ochrophyta (1). The MBFG classification groups microalgae according to functional morphology, considering physiological, morphological and phenological characteristics related to the environment. This classification takes into account volume, maximum linear dimension (MDL), area, and the presence of mucilage, flagellum, gas vesicles, and silicon structures. Thus, microalgae were differentiated into 7 functional groups. Zooplankton were identified and quantified to genus level. Twenty genera of rotifers, 13 of cladocerans and 7 of copepods were recorded, as well as juvenile individuals of the 3 orders of copepods (calanoid, cyclopoid and harpacticoid copepods) and nauplii. We performed an Analysis of Similarity (ANOSIM) to identify differences in the composition of functional groups between zones, and representative groups in each zone. The analysis showed significant differences between the different zones (p-value ≤ 0.05); with the exception of the zones Northwest (NW) vs Katari system (SK), (p-value = 0.44), suggesting a high similarity between them.

In order to simplify the initial monitoring network, cluster analysis was performed to identify stations with similar conditions, thus having a criterion to reduce the number of stations. The PAST application, https://past.en.lo4d.com/windows , was used for the analysis of scientific data in statistical form, which draws graphs and diagrams with an interface similar to that of other spreadsheet programs. For each zone (Northeast, Central, Katarí System), 4 cluster analyses were performed (see our OLT book on pages 192-208): 

(a) a cluster considering basic parameters* (pH, DO = dissolved oxygen, EC = Conductivity, SAL = Salinity); 

b) a cluster with data on pigments (Chlorophyll-a = Chl-a and Phycocyanin = FC) and dissolved organic matter (fDOM); 

c) a cluster considering nutrients (nitrates and phosphates); and 

d) a cluster based on the composition of biological communities  (phytoplankton and zooplankton).

From the cluster analysis, we suggested 3 stations in the Northeast zone (BH, NE3 and NE7); 5 stations in the Central zone (CE4, CE8, CE14, CE16 and CE18); 4 stations in the Katari water system zone (SK4, SK5, SK7 and SK10). The Northwest zone has only one LC station (Chúa Trench), for which the cluster analysis could not be performed. Due to the experience in binational expeditions between Peru and Bolivia, it will also be important to consider the monitoring of the Fish Farm Center ('Centro Piscícola') in charge of IPD-PACU, where trout farming is carried out, and can be considered a source of contamination. Therefore, 2 stations were proposed in the Northwestern zone.

The southern area of Lake Titicaca was not monitored as part of the permanent Lake Titicaca Observatory project. We have as background the binational expeditions of 2015 and 2016 where we observed a degradation of water quality in the sectors of Tiahuanaco, Guaqui and Desaguadero. Thus, for the minimum monitoring network covering the entire Bolivian sector of 'Lago Menor', we propose 3 additional stations in the Southern zone: S1, S2 and S3, respectively in front of Tiahuanaco and Guaqui river mouths, and Desaguadero river outlet.

The next 37 sub-pages present the results obtained using the submersible FluoroProbe BBE fluorometer, the Biospherical C-OPs spectroradiometer, and the YSI EXO2 multiparameter sonde, at the stations  along the 37 campaigns in the different zones of the study site in Lago Menor.