Sustainable Solutions for Environmental Pollution, Volume 2. Группа авторов

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Figure 1.6 (a) The 2-ha FSF-CW (Reims, France) in March 2020; (b) the UAV (Spyboat, CT2MC), Petite-bourgeoise, France collecting samples and monitoring dissolved oxygen and temperature.

Figure 1.7 Monitoring the Reims FSF-CW with an aquatic drone. (a) Dissolved organic carbon (DOC, ) and dissolved total nitrogen (o) in discrete samples collected by the UAV; (b) dissolved oxygen saturation at sampling points; (c) dissolved oxygen concentration as registered by the UAV dissolved oxygen probe.

UASs (Unmanned Aerial Systems, i.e., aerial drone) have also been proposed to collect water samples from the sky (Lally et al., 2019). The payload is still rather limited (200 to 300 ml approximately), especially for small UASs and the success rate of water capture needs to be increased. Nevertheless, development is progressing in that field: Benson et al. have reported the successful collection of small sterile water samples (50 ml) for microbial identification in water bodies (Benson et al., 2019).

      1.13.2 Vegetation Monitoring

      Aquatic plants are an essential element of CW but the monitoring of their development (e.g., growth, senescence) is not easy, especially on large-scale systems. Accurate field surveys can be organized from the ground but there are time-consuming and labour-intensive. Very large systems cannot be monitored completely. Depending upon the water depth, some areas might not be accessible by boat. Recent progress in aerial imagery by UAS (i.e., aerial) can be a solution to these problems. UAS can be fitted with classical RGB cameras as well as more sophisticated sensors to cover the light spectrum down to NIR: they can detect free water areas, emerged as well as submerged aquatic plants (Chabot et al., 2017; Chabot et al., 2018). After calibration with ground sensors, an estimation of dissolved oxygen, turbidity (Wang et al., 2020a) or Chlorophyll-a (Gitelson et al., 2007) can also be provided. However, dedicated flights should be organized with licensed UAS pilots and under proper weather conditions (no rain and low wind). Furthermore, wildlife disturbance and even collisions with birds should be considered (Jarrett et al., 2020). Satellite images can also be used even if the spatial resolution is lower.

      Saberioon et al. (2020) have successfully monitored Chlorophyll-a and total suspended solids in fishponds and sandpit lakes of various surfaces (tens to hundreds of hectares) and depths (from 2 m for fishponds to 10 m for sandpit lakes) using the Sentinel-2 constellation. The two Sentinel-2 satellites are working at high spatial resolution (10 to 60 m) with a revisit cycle of 5 days. Sentinel-2 satellites are fitted with a multi-spectral imager working with 13 bands (from visible to mid-infra-red) and provide a high temporal resolution series of images, if the sky is cloud-free (Saberioon et al., 2020). These images are freely available on the Copernicus-ESA website (https://scihub.copernicus.eu/).

In spite of its small size, the development of the vegetation in the 1.5-ha CW constructed downstream the St Just–St Nazaire de Pézan wastewater treatment plant (5,000 persons equivalent) in France can be monitored using the Sentinel-2 constellation true colour images (Figure 1.8).

The intensity of the green channel (560 nm) reflects the development of emerged and free-floating vegetation, as shown in Figure 1.9. It is a global assessment as the CW is composed of different zones (e.g., phytoplankton, reedbeds, or free-surface area) (pole-zhi.org, 2013). The vegetation starts to grow at the end of March and reaches its maximum (as monitored though the green channel) early June.

Figure 1.8 Sentinel-2 True colour images of the St Just–St СКАЧАТЬ