Campaign #2

On Wednesday 18 October 2023, we headed out to the field for the first day of the second campaign. The experiences of the first campaign came in handy to access the selected sampling sites and organise the logistics of the field visits in an efficient manner. Surprisingly, the study area (and Ecuador in general) is facing the worst drought of the last four decades, causing the levels of the reservoirs to be exceptionally low. Also water levels within the rivers are lower than observed during the first campaign. In the end, 52 accessible sites were selected: 31 river/stream sites and 21 reservoir sites.

We collected information on the abiotic conditions in each of the 52 sampling sites. To get this data, we made use of a multiprobe (a device that measures several conditions at once) on-site and USEPA approved test kits to determine the nutrient concentrations off-site. The collection of this data resulted in some interesting patterns that contrasted the findings of the first campaign. For instance, ammonium and nitrite concentrations directly downstream of the city of Cuenca (site CU03, followed by CU02 and PA01) were almost ten times higher than what we observed in July/August. Also orthophosphate concentrations were clearly higher than before. It is not unthinkable that the extreme drought played a role in these excessive nutrient levels. Equally interesting is the decreasing nutrient levels in the downstream direction, which shows that the Paute river system is able to recover from a signicant pollution event.

In addition to the more standard abiotic conditions, we also collected information on the presence and the emission of greenhouse gases in each of the 52 sampling sites. To get this data, we made use of a the headspace method (mixing 30 mL of water and 30 mL of air) and floating chambers (airtight containers sampled at fixed time intervals) on-site followed by the analysis of the obtained samples off-site. The collection of this data already resulted in some interesting patterns that are in line with the abiotic conditions. For instance, nitrous oxide concentrations and emissions were the lowest in the upstream locations and clearly higher directly downstream of the city of Cuenca. The highest concentration was observed in location CU02, while the highest emission was observed in location PA01 (located closely downstream of CU02). These observations align with the ammonium and nitrogen patterns shown above, illustrating a conversion from ammonium into nitrite in the downstream direction and in the meantime generating the intermediate nitrous oxide.

A total of 52 sampling sites were selected and assessed for a variety of water quality parameters. The abiotic conditions showed a clear contrast with the first campaign, with extremely high nutrient levels directly downstream of the city of Cuenca. Similarly, also the presence and emission of the considered greenhouse gases were clearly higher during this campaign, especially directly downstream of the city of Cuenca.

More information can be found in the short report on the second sampling campaign [link].

We would like to thank K.P. Ramirez Pozo for their help in collecting the samples in the field as well as their subsequent processing in the lab. We also thank D.G. Zuñiga Villegas for providing us with the necessary transport.