HydroMet buoy 2023-2024 water quality at 1-m

EXO2 probe depth

From November 15 to 20, the EXO2 probe remained at the bottom. Thus, the corresponding parameter values are useless. The rest of time the probe remained at about 1 m depth (as programed). Yet, the profiling was not yet setup because the depth sensor has to be calibrated to the new bottom depth of 9 m (instead of 10 m previously).

Chlorophyll-a

During the 1980', the average Chl-a concentration in the Minor Lake was 3 µg/L (oligorophic condition). During the 2019 to early 2023 period, the average Chl-a reached 10 µg/L (eutrophic condition). Since we resumed the buoy monitoring in November, Chl-a oscillated between 10 to 20 RFU (relative fluorescence unit), i.e. 40 to 80 µg/L, which is highly eutrophic. From November 28 to December 6, we observed a micro-algae efflorescence (bloom) with 17 to 36 RFU, i.e. 68 to 145 µg/L of Chl-a. These concentrations are equivalent to those during the 2015 bloom. Additionally, the dominant micro-alga is the green (Chlorophyte) unicellular harmless Carteria sp. that also dominated in 2015. Since December, Chl-a stabilized around 4-8 µg/L.

Phycocyanin (cyanobacteria)

Phycocynin is the main photosynthetic pigment of cyanobacteria. Until now, phycocyanin concentration represented ≤ 1% of Chl-a concentration. Yet, since November it reached 1 RFU = 1 µg/L of phycocyanin, compared to 4-8 µg/L of Chl-a, it is a worrying increase! Indeed, if cyanobacteria become dominant (such as in internal Puno bay), they would be difficult to eradicate, and blooms could occur repeatedly, then becoming chronicle.

Dissolved organic matter

During 2019-2022, the average concentration in dissolved organic matter (fDOM) was about 1 RFU, occasionally up to 4.5 RFU during the 2021-2022 rainy seasons. Yet, since November 2023, fDOM ranged 3.1-3.5 RFU. This probably not due to the Katari watershed discharges (rains are scarce), but may be to the reduction in water depth (water column more susceptible to wind mixing) and also stronger winds, as compared to previous years.

Dissolved oxygen saturation

During 2019-2022, dissolved oxygen saturation (DO%) ranged 80-110%. Since November 2023, DO% is slightly lower 70-100%, with a slight increase through time. This may be due to higher organic matter decomposition.

Dissolved oxygen concentration

As a consequence, dissolved oxygen concentration (DO) ranged only 7-10 mg/L, as compared to 7-12 mg/L during 2019-2022.

Turbidity

During 2019-2022, turbidity ranged 0.2-0.6 NTU, occasionally 1.4 NTU in November 2021. Since November 2023, turbidity is much higher 2-4 NTU. Probably due to the discharges of more concentrated wastewaters (less rain) from the Katari watershed, a lower lake level that improves the water column mixing by stronger winds.

Conclusion

As compared to the 2019-2022 period, since we resumed the buoy monitoring in November 2023, the pelagic water quality at the HydroMet buoy site, in the northern region of Titicaca Minor Lake, is increasingly deteriorated, passing from an olgotrophic-mesotrophic state to a eutrophic-highly eutrophic state, with bloom occurrence.

The increased speed of Lago Menor eutrophication, illustrated by the concentrations of chloorophyll-a and phycocyanin, is extremely worrying!

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