RC03 - Llangaspalma

Site Code: RC03c. GPS: S12°84368, W75°948578. Elevation: 962m asl.

Water Quality Data

The following river and water quality data was collected from this site:

RC03c July 2019 November 2019
Season: Austral Winter Austral Summer
Date: 10.07.2019 18.11.2019
Time: 8.45am 10.00m
Width (m) 6.5 23
Depth (Av.) (m) 0.506 0.257
CSA (Av.) (m²) 3.293 5.911
Velocity (Av.) (m/s) 1.316 0.496
Discharge (Av.) (m³/s) 4.333 2.932
Riverbed sediment Sand, cobbles & boulders Cobbles & boulders
Temp. (Atmospheric) (°C) 20 29
Temp. (Water) (°C) 17.08 22.01
Atmospheric pressure (mbar) 907 900
Dissolved oxygen (mg/l) 7.31 7.15
Dissolved oxygen (%) 85.47 95.13
pH 5.80 8.76
Conductivity (µS/cm) 432 467
Total Dissolved Solids (ppm) 213 234
ORP (mV) 351.4 132.1
Turbidity Clear Clear: slight green colouration
Alkalinity (mg/l CaCO3) Pink to colourless 168 (1.6N) Pink to colourless 150 (1.6N)

Data Analysis

It is the case that the amount of dissolved oxygen at 100% saturation at sea level and at 20°C would be 9.03 mg/l. However, at 6.99-7.53 mg/l the DO readings in July were on the low side. In November readings were slightly higher at 7.12-7.21 mg/l. In July water temperature was approximately 17°C and in November 22°C which does affect DO saturation capacity. The factors reducing DO levels at this site require further investigation. It is at higher elevation which reduces saturation capacity. There is also little vegetative growth in the river and so little photosynthetic input of oxygen. These factors together may account for the slightly reduced level of oxygen in river water here. At 6 mg/l DO and above aquatic vertebrates do survive and invertebrates thrive. However, conditions are not suitable for many cold-water species, such as Salmonids. High concentrations of nutrients (particularly phosphorus and nitrogen) fuel algae blooms, which initially boosts dissolved oxygen levels but then rapidly reduce DO. It seems unlikely that high nutrient levels from fertilizer runoff or poorly treated waste waters would apply to this site.

The conductivity reading at this site is 409-468 µS/cm with little difference between July and November. The level of conductivity in the Rio Canete at RC03c is an indicator of little contamination from waste waters and agricultural runoff. This is lower than that found at RC00, where sewage would be expected to raise conductivity. Generally, agricultural runoff and sewage will increase conductivity due to the additional chloride, phosphate, and nitrate ions.

pH readings in July 2019 ranged from 5.5-5.85 but need confirming while in November 2019 they ranged from 7.9-9.25. The river is generally slightly alkaline. The range of pH recorded at this site in November, is well within the tolerances for aquatic life, although not ideal for the reproduction of many higher order cold water fish species.

Site Description

Site RC03c is located above the El Platanal reservoir and HEP station at 960m asl. The Rio Canete, at this point is at the beginning of a long deeply incised canyon with little or no intensively cultivated lands in the principal valley. The town of Zuniga lies below this site and Catahuasi above. These settlements are centres of agricultural intensification as a result of raised water abstraction. Above this point the tributaries make a greater contribution to discharge in the main channel. It is in these valleys that agricultural activity is more intense and increasing. In the main valley at this site the valley is narrow and deeply incised. The flood plain is narrow and the river channel braided. Channel flow is highly variable from the dry season to the wet season.

The river holds water year-round with discharge in July recorded as 5.5 m³/s and 2.9 m³/s in November towards the end of the dry season. During the wet season discharge is considerably higher, probably increasing to 18 m³/s. The banks are lined with some river cane and scattered areas of stunted willow. Cultivation is low intensity at this elevation. The production of maize, bananas, ajo (garlic), aji (peppers) and some avocado dominate land use. There are smaller areas of subsistence crops as much agriculture is for household consumption. There is little natural vegetation remaining at this point with some acacia and willow on the narrow flood plain. On the arid slopes columnar cacti are common but these slopes are largely devoid of vegetation. These elevations are typically depauperate but do hold Black-necked Woodpecker, Scrub Blackbird, Blue and Yellow Tanager and Croaking Ground Doves.

RC03 View upstream Site RC03 - Study site location: on the pedestrian accesss to Llangaspalma. (John Forrest)

Site RC03 - the study site. (John Forrest) Site RC03 - the study site. (John Forrest)

RC03 View upstream Site RC03 - View upstream. (John Forrest)

RC03 View downstream Site RC03 - View downstream. (John Forrest)