Multivariate assessment of spatiotemporal water-quality patterns across anthropogenic-pressure zones in Lake Guamuez, a high- Andean Ramsar wetland
This study utilized multivariate statistical analyses to characterize distinct spatiotemporal water-quality patterns across five anthropogenic-pressure zones in Lake Guamuez, revealing that the navigation channel exhibits the most degraded conditions and highlighting the need for synchronized, source-oriented monitoring in this high-Andean Ramsar wetland.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Freshwater lakes are not just bodies of water; they are living systems that react to the land around them. When people farm, build cities, or move boats across a lake, they change the water's chemistry. These changes often happen in specific spots rather than everywhere at once. A river carrying fertilizer from a farm might make one corner of a lake rich in nutrients, while a nearby area remains clear. Similarly, boats burning fuel or hotels releasing wastewater can create pockets of lower oxygen or higher acidity. Scientists study these patterns to understand how human activity reshapes nature, but it is difficult to tell if a change is caused by a specific activity or simply by the time of year or the weather. To solve this, researchers look at many different measurements at the same time, grouping them to see if they move together like a team, which helps reveal the hidden story of a lake's health.
In the high mountains of southwestern Colombia, Lake Guamuez, also known as La Cocha, faces these exact pressures. It is a protected wetland where people grow crops, live in towns, fish for trout, and navigate the waters for tourism. A team of researchers from the National University of Colombia set out to map how these different human activities affect the water quality in different parts of the lake. They focused on five specific areas: the mouth of a river draining agricultural land, a busy waterfront used by hotels and tourists, a channel used by motorized boats, a zone with floating fish farms, and a central area far from direct human influence that served as a baseline for comparison. Over a period spanning from late 2024 to early 2026, the team visited each zone twice. At every location, they collected water samples from the surface, the middle, and the bottom, taking multiple samples at each depth to ensure accuracy. They measured fourteen different indicators, ranging from the amount of oxygen and the acidity of the water to the levels of nutrients, solids, and organic waste.
The results revealed a clear and distinct pattern across the lake, with the navigation channel showing the most significant signs of stress. In this specific zone, the water held the lowest levels of dissolved oxygen, ranging between 5.57 and 5.58 milligrams per liter, and was the most acidic, with a pH between 5.95 and 6.04. This same area also had the highest levels of electrical conductivity, turbidity, and organic demand, with biochemical oxygen demand reaching 12.38 to 12.43 milligrams of oxygen per liter and chemical oxygen demand hitting 16.57 to 17.19 milligrams per liter. Perhaps most notably, this zone contained the highest concentration of total phosphorus, measuring 0.90 milligrams of phosphorus per liter. In contrast, the central reference zone, far from the main human activities, showed the healthiest conditions, with oxygen levels between 8.13 and 8.21 milligrams per liter and a pH near 8.0. The agricultural zone and the urban waterfront fell somewhere in between, showing moderate levels of change, while the trout farming area surprisingly resembled the healthy central zone more than the busy navigation channel during the times they were measured.
The researchers used advanced statistical methods to confirm that these differences were real and not just random fluctuations. They found that the water in the navigation channel was consistently different from the other zones, forming a distinct group in their analysis. However, the study also highlighted a crucial limitation in how the data was collected. Because the team visited each zone at different times rather than all at once, the differences they saw were a mix of location and timing. The water quality changed as the seasons shifted, and the specific month of sampling was tied to the specific zone visited. This means the researchers could not say with absolute certainty that the boats or the tourism alone caused every single change they observed. They could only confirm that a strong pattern existed where the navigation channel and the urban waterfront showed higher pollution levels and lower oxygen at the times they were measured.
Despite this limitation, the findings offer a clear direction for protecting the lake. The data suggests that the navigation channel and the urban-tourism waterfront are the areas most in need of focused monitoring. The researchers recommend that future studies sample all these zones at the same time to separate the effects of human activity from the natural changes of the seasons. They also suggest tracking specific sources, such as rainfall, boat traffic intensity, and feeding rates at fish farms, to understand exactly what drives the pollution. For now, the study confirms that Lake Guamuez is not uniformly affected by human use; instead, it carries a patchwork of conditions where some sectors remain pristine while others, particularly those used for transport and tourism, show clear signs of environmental strain.
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