AndesFlux PE-TNR Tower

Greenhouse gas flow measurement tower in the Tambopata National Reserve

AmeriFlux, a network of towers that measures evapotranspiration in order to fine-tune the water balance and understand short- and long-term carbon flows between terrestrial ecosystems and the atmosphere in the Americas, is part of FluxNet, a congregation of regional networks of America, Europe, Asia, Africa and Australia. For its part, AndesFlux corresponds to the network of towers operated by the Pontifical Catholic University of Peru (PUCP), at the national level, which studies ecohydrological impacts on the western Amazon.

The PE-TNR Flow Tower is located in the Tambopata National Reserve and is part of AndesFlux, a western Amazon network of towers equipped with eddy covariance systems (covariance of turbulent flows), which have instrumentation consisting mainly of gas analyzers and three-dimensional ultrasound anemometer, which is complemented by meteorological sensors of temperature, humidity, precipitation, radiation, etc. This entire system is powered by photovoltaic energy, provides data in real time and allows monitoring and investigating the exchange of greenhouse gases (carbon, water and methane) between the forest and the atmosphere, as well as the energy balance coming from the sun and captured through the forest for the photosynthetic process.

Tropical forests: carbon sinks and water regulators

Tropical forests constitute one of the most important carbon stores and sinks of terrestrial biomass due to their capacity to capture atmospheric carbon (CO2). Thanks to this process, forests play an important role in balancing the carbon cycle and mitigating the effects of climate change. Additionally, they are important in the hydrological cycle, as water intercepted by vegetation evaporates and forms moisture-laden air currents, which helps govern wind and rain patterns.

Evaluating carbon in forests: plots, towers, satellites?

The western Amazon forests present complex and particular climatic, biotic patterns due to their proximity to the Andes, conditioning their response to climate change and deforestation. There are several methods to evaluate the flow and balance of carbon between the forest and the atmosphere and see its contribution as a mitigating agent of the greenhouse effect:

1.- Allometric methods that consist of carrying out evaluations of in situ biomass in a certain area (1ha)

2.- Flow covariance method. Evaluation of carbon, methane and water flows between the forest and the atmosphere through the information collected by the flow towers.

3.- Remote sensing. Evaluation carried out using drones, small planes or satellites implemented with LIDAR or other technology.

Methodology:

The eddy covariance method is a technique based on atmospheric measurements of vertical air flows, which allow calculating gas emissions and consumption between the forest and the atmosphere. Additionally, it estimates the exchange of carbon and other greenhouse gases, as well as the energy balance of terrestrial and aquatic ecosystems.

In its beginnings, 40 years ago, this method was used in the field of micrometeorology. Today it has multiple applications including agriculture and scientific research.

To study the carbon, water and energy balances in western tropical forests, flow measurement towers have been implemented that have sensors that work at high and low frequencies. The high-frequency sensors generate 10 measurements per second and are made up of the CO2, CH4 and H2O gas analyzers, and the three-dimensional ultrasound anemometer. For their part, low-frequency sensors generate one measurement per minute and include meteorological sensors such as temperature, humidity, precipitation, long and short wave radiation, photosynthetically active radiation, soil temperature, etc.

The data generated by the towers are subsequently processed through the use of specialized software, which allows the calculation of important variables such as the net flow of carbon, water, energy, gross primary productivity, water efficiency, etc.

The PE-TNR Tower was the first metal infrastructure instrumented for research purposes in Peru (2015) and is 54 meters high. In addition, it is the third in South America to carry out calibrated measurements of atmospheric CO2 as part of NASA’s OCO-2 (orbital carbon observatory) project.

This tower is the result of collaborative work between the Scottish Alliance for Geoscience, Environment and Society – SAGES (for its acronym in English), the University of Edinburgh, the NGO AIDER, the company Peruvian Safaris, the National Service of Protected Areas by the State (SERNANP) and the Pontifical Catholic University of Peru (PUCP).

Nationally, AndexFlux has four towers located in:

PE-BRE, in the concession for conservation BREO (San Martin).

PE-PAN, at the Biological Station and the Panguana Private Conservation Area (Huánuco).

PE-AMG, at The Friends (Mother of God) Biological Station.

Results and conclusions:

The PE-TNR Tower allows you to see the flows of CO2 and H2O on a fine time scale. In both graphs represented on a chromatic intensity scale, it can be seen that the blue color corresponds to low or negative values; while the color red, high or positive values. In terms of fluxes, negative values indicate that the forest behaves as a carbon sink. For its part, positive values require the emission of gases:

a.- We can appreciate the behavior of CO2 flows through the circadian cycles in the years 2017, 2018 and 2019. The forest exerts its greatest capacity to absorb CO2 from the atmosphere between 6:00 a.m. and 4:00 p.m. , which is represented in blue colors.

b.- Regarding H2O, the behavior is opposite, since, according to the photosynthetic process, while CO2 flows from the atmosphere into the leaf, H2O moves from the leaf towards the atmosphere. This process is known as evapotranspiration. In the graph, we observe that between 6:00 and 16:00, the forest reaches its maximum evapotranspiration values; that is, water loss through the leaves

The rainy and dry seasons also show different flow patterns:

a. The humid or rainy season (green) reaches lower values in the fluxes, which indicates that it is during this time that the forest exerts its greatest CO2 sink capacity.

b. Evapotranspiration also becomes greater in the rainy season, when it reaches the highest values of H2O flux, since greater CO2 fixation involves greater evapotranspiration or loss of H2O.