Short report on campaign 02

Last update: 25/06/2024

Introduction

The collection of field data is an important element of the HydroCORE project. It allows to make an assessment of the state of the Paute river system and to identify patterns in both space and time. It is expected that these conditions change along the path of the Paute river due to a variety of human and natural influences. For instance, the city of Cuenca is situated in the upstream part of the basin, while two reservoirs are present in the downstream part prior to entering the Amazon region.

To characterise the Paute river system, the HydroCORE project foresees a total of eight sampling campaigns over a period of two years. Abiotic conditions are recorded every three months and supplemented with the collection of macroinvertebrates every six months. At the spatial level, the project aims to include 20 reservoir sites and 30 river sites (totaling 50 sampling sites). These also include sites that are part of a reference system in which no artificial reservoirs are present, being the Jubones river system.

The second sampling campaign was performed from 17 October 2023 until 10 November 2023. During this period, a total of 52 sampling sites were visited. The results of the abiotic analyses performed both on-site (observations of the field conditions, probe readings) as off-site (nutrient analyses) are reported here in a concise manner. More results (e.g., gas samples) will be added later.

Map of the sampling sites

A total of 52 sampling sites were visited and distributed as follows: (1) 20 river sites, (2) 21 reservoir sites, and (3) 11 reference system sites. The majority of the river sites (N = 14) is located upstream of the two reservoirs, while the majority of the reservoir sites (N = 16) is located in the largest reservoir (called Mazar). Relatively few reservoir sites (N = 4) were visited in the smaller reservoir (called Amaluza) due to accessibility reasons. There are hardly roads leading to the reservoir due to the steep mountains and a large fraction of the water surface is overcrowded by water hyacinth (E. crassipes). The map shows where the sampling sites are situated:

Figure 1: Map of the sampling locations.

Physicochemical conditions

At every sampling site, a series of water quality parameters were recorded. In addition, water samples were collected in plastic bottles for nutrient analysis in the lab at UCuenca. Within this section, the results of these analyses are presented in a concise manner and further explored through principal component analysis and hierarchical clustering. Through this exploration, similarities and dissimilarities between sampling sites can be observed.

Statistical summary

A first step in the data exploration is looking at the characteristic statistics of the considered variables. This provides an idea of the range of the obtained values and indicates if (and where) data is missing. For this overview, a distinction is made between the parameters measured on-site and off-site.

An overall summary of the parameters that were measured on-site is given in Table 1, showing an altitude range between 915 m and 3105 m above sea level. Dissolved oxygen levels ranged from 2.29 mg/L up to 18.03 mg/L, averaging at 11.02 mg/L (SD = 2.81 mg/L). Also turbidity and chlorophyll a displayed a rather wide range (0.50 NTU up to 128 NTU and 6.13 µg/L up to 342.63 µg/L, respectively), while salinity showed to be more constant.

In addition, Table 1 also contains a summary of the parameters that were measured off-site. Nutrient concentrations below the quantification limit were replaced by the quantification limit (worst-case approach), resulting in similar values for both the first and second quartile (i.e. median) when assessing nitrate and orthophosphate levels. The highest nutrient levels were 2.56 mg/L nitrate-nitrogen, 0.60 mg/L nitrite-nitrogen, 7.18 mg/L ammonium-nitrogen, 10.07 mg/L total nitrogen, 0.80 mg/L orthophosphate-phosphorus, and 0.93 mg/L total phosphorus.

Table 1: Summary of the on- and off-site variables
	Min	Q1	Median	Q3	Max	Mean	SD	#NA
Altitude [m a.s.l.]	915.00	2003.50	2145.00	2206.00	3105.00	2082.06	413.65	0
Distance	0.35	38.30	47.16	64.07	143.08	54.85	32.89	0
Temperature [oC]	12.76	16.78	18.52	19.87	22.89	18.12	2.45	0
pH [-]	6.33	7.02	7.59	7.84	8.72	7.47	0.58	0
Conductivity [mS/cm]	0.00	0.09	0.16	0.21	0.59	0.17	0.11	0
Salinity [ppt]	0.00	0.00	0.10	0.10	0.30	0.09	0.07	0
Oxygen saturation [%]	24.60	107.95	128.95	137.55	207.80	120.72	32.53	0
Oxygen [mg/L]	2.29	10.13	11.60	12.59	18.03	11.02	2.81	0
Total dissolved solids [g/L]	0.00	0.06	0.10	0.13	0.38	0.11	0.07	0
Oxidation reduction potential [ORPmV]	208.00	272.50	284.50	318.00	364.00	289.79	34.89	0
Turbidity [NTU]	0.50	4.40	8.20	18.40	128.00	17.88	27.43	0
Chlorophyll a [ug/L]	6.13	15.81	28.90	54.80	342.63	50.42	63.68	0
Average flow [m/s]	0.00	0.00	0.13	0.34	0.91	0.19	0.23	1
Nitrate-N [mg/L]	0.50	0.50	0.50	0.50	2.56	0.65	0.41	0
Nitrite-N [mg/L]	0.00	0.00	0.01	0.07	0.60	0.07	0.13	0
Ammonia-N [mg/L]	0.00	0.03	0.24	0.79	7.18	0.68	1.39	0
Total-N [mg/L]	0.50	0.61	0.95	1.87	10.07	1.67	2.08	0
Orthophosphate-P [mg/L]	0.00	0.01	0.01	0.06	0.80	0.09	0.20	0
Total-P [mg/L]	0.00	0.03	0.04	0.14	0.93	0.14	0.21	0

Correlation analysis

The different variables of the previous sections were used as a basis for a correlation analysis (see Figure 2). From this analysis, it is clear that some variables are more correlated than others (as is expected). Salinity, conductivity, and total dissolved solids show a higher-than-average correlation as they more or less reflect the amount of dissolved chemicals in the water column. Also the different nutrients display a higher correlation, with the exception of nitrate-nitrogen. The latter might be related to the relatively low variability in the observed value due to the quantification limit of 0.5 mgN/L used during the analysis (see Table 1).

Figure 2: Correlation analysis of the various variables.

Principal component analysis

From previous sections it is clear that various water quality parameters were assessed in the selected sampling sites. These parameters can be analysed individually to identify (dis)similarities between sampling sites, though that will lead to an overly extensive list of observations. As an alternative, dimensionality reduction can be applied on the data by extracting the most informative patterns and representing them as part of a new set of variables. Principal component analysis (PCA) allows to perform such a dimensionality reduction and shows that the first component is mostly determined by nutrient levels and salinity/conductivity/total dissolved solids. The second principal component is mostly determined by alitude/flow and oxygen/temperature/chlorophyll a.

The PCA shows that the majority of sampling sites cluster together (see Figure 3), which is partially in line with the observed nutrient levels (see Table 1). Sites that showed discrepancy from the majority of the sites included the Paute river (code ‘PA’) and Giron sites (code ‘GI’), displaying relatively higher nutrient levels.

Figure 3: PCA of the physicochemical data.

Supervised clustering

In addition to the unsupervised analysis provided by PCA, a supervised cluster analysis can be performed to identify (dis)similarities between sampling sites. These (dis)similarities can be calculated through distances, with the Euclidean distance being the most frequently used. Subsequently, clusters are created based on these distances by using a specific linkage technique. Here, Euclidean distances and a complete linkage is being used.

The resulting hierarchical tree displays the closeness of the different sampling sites and shows that spatially close sites do not always cluster together (see Figure 4). Some closely situated sites do cluster together (e.g., MA11/27, RI01/02, AM04/05, AM06/07), while others end up further away in the tree (e.g., MA11/13, GI02/03, RI01/02). Some overlap with the PCA result can also be seen, including the similarity between GI03 and GI04 and the discrepancy with the majority of sampling sites.

Figure 4: Hierarchical clustering of the sample sites.

Summary

A total of 51 sampling sites were selected and assessed for a variety of water quality parameters. Surprisingly, nutrient levels were higher than observed during the first sampling campaign (July-August 2023), though nitrate levels were often too low to be quantified. Several sampling sites seem to show different conditions, most of them located near/downstream of urbanisation. For example, the Cuenca (CU02/03) and Paute (PA01/02/03) sites are situated downstream of Cuenca, while the Giron sites are situated in and downstream of the town of Giron.

Acknowledgement

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.

Reference

Van Echelpoel, W. (2024). Short report on campaign 02. HydroCORE project. Online: https://wvechelp.github.io/HydroCORE/Reports/ShortReportCampaign02.html