| 01 Sep 2025
The Loobos ecosystem first tower dataset: meteorology, turbulent fluxes and net ecosystem exchange (1996 to 2021)
Abstract. We describe a 25 years (1996–2021) observational dataset of meteorology, turbulent fluxes and net ecosystem exchange collected from the first tower at the Loobos site, the Netherlands (NL). This is one of the 17 first FLUXNET sites globally. The presented dataset contains six data streams, namely (1) the NL-Loo_BM stream including meteorological data: four-component radiation (radiation balance), air temperature and relative humidity, wind information, precipitation and throughfall, photosynthetic active radiation, bole temperature and soil heat flux), (2) the NL-Loo_Profile stream containing vertical profiles of CO2 mole fraction, H2O pressure, air temperature and relative humidity, (3) the NL-Loo_ST stream derived from the aforementioned two streams including total stored heat flux, H2O and CO2 fluxes below the canopy, (4) the NL-Loo_EC stream including EC measurements of CO2 flux, sensible heat and latent heat fluxes, (5) the NL-Loo_Soil stream including vertical profiles of soil moisture and temperature and ground water level data, and (6) ancillary data including soil respiration, vegetation properties (i.e., tree height, stem width and dry aboveground biomass, Leaf Area Index, sap flow, needle foliage properties and the associated nutrient analysis) and ground water level. The data quality of these data streams is assured through standard operating procedures. To show the utility of gathering long-term and comprehensive measurements, we present analyses of mean diurnal storage CO2 flux, the trend of NEE over the last 25 years and the energy balance closure. Being one of the longest datasets of its kind in a temperate forest, this valuable dataset is anticipated to be used for investigating the performance of various gap-filling algorithms, semi-climatological trends including extreme climatic events (such as the heatwave of 2003 and the drought of 2018) and the role of forest ecosystem in the carbon, water and energy cycle. Meanwhile, it is expected to be employed for validating modelled land-atmosphere CO2 and turbulent exchange fluxes, verifying model assumptions and serving as ground truth for satellite data retrievals. The dataset is accessible at https://doi.org/10.5281/zenodo.15721310 under a CC-BY4 open use license, where it is published as an associated station-like site and the same data will also be available at the European Fluxes Database Cluster. Hence, the data will be committed to the FLUXNET Data System Initiative too. It is noted that in 2021 a second tower was erected next to the first tower, which 40 was labelled as an ICOS Ecosystem Class 2 site in 2023 (van der Molen et al., 2025). Here we describe the first tower’s instrumentation and data processing up to a Level 1 product (derived variables and quality checks, but not gap-filled).
General comments.
The manuscript “The Loobos ecosystem first tower dataset: meteorology, turbulent fluxes and net ecosystem exchange (1996 to 2021)” by Zhao et al. describes an impressive bulk of data collected over 25 years at one of the earliest micrometeorological towers installed in Europe for the systematic monitoring of CO2 and energy fluxes. The dataset includes, beyond flux variables, numerous parallel measurements of biophysical parameters and biological processes of the forest ecosystem such as LAI, foliage chemistry, biomass carbon stocks, sap flow density and water table depth.
A dedicated section explains in detail the flux data processing pipeline and the quality check procedures for flux and partly for meteorological variables. Finally, a synthesis of the dataset is illustrated by plots showing the consistency of the flux data, the mean diurnal variation and in particular the mean monthly NEE fluxes from which the trend towards a stronger carbon sequestration can be observed.
The presented dataset is undoubtedly of interest to the readers of ESSD and the well-structured manuscript delivers an overall clear and detailed description of it. Said that, I recommend the publication of the manuscript but only after a minor revision mainly to : (i)fix some issues concerning the terminology used to describe the ecosystem-atmosphere CO2 exchanges,; (ii) provide more information about the quality of meteorological measurements and the instruments maintenance routines.
Specific comments.
Introduction section (ca. L60): I suggest including a map of the area showing the location of the measurements (eddy covariance, meteorological, forest transects, sap flow, etc.).
Introduction – par 2.1.1: Some instruments were operated continuously for long periods of time (eg. pyranometers, quantum sensors, etc.). Report about the maintenance routine and its frequency to ensure accurate measurements, mentioning if the sensors were periodically calibrated and if the calibration drift was accounted for in processing the data.
L223: I guess that the “depth of 15 cm” refers to insertion of the collar into the soil and not to the depth of the chamber which would be placed on top of the collar. Please confirm.
L444: the negative storage at sunrise should not be associated only to a “release of carbon dioxide” to the atmosphere, but also to the photosynthetic uptake of CO2 by the vegetation below the eddy covariance sensors height.
L460: fig. 8 shows mean monthly NEE, that is, by definition, the net flux resulting from the difference between the processes of photosynthesis and respiration. Therefore, in the case of this evergreen needle forest, I would not talk about a decrease of “winter respiration” but rather of the intensity of the CO2 source.
Appendix (L570-571): Replace “left photo” and “ right photo” with “photo on the right” and “photo on the left” respectively.