Because WSPV systems are an important avenue for future clean energy use (Almeida et al., 2022), it is essential to understand their potential impacts on ecology and biodiversity. Our surveys on 26 WSPV systems in the Yangtze River basin in China indicated that WSPV systems led to decreases in the UCA, T, DO, and plankton diversity of waterbodies. The overall species richness and individual densities of birds were lower in the PA-NPAs than in the CAs, and waterbirds were not seen nesting in waterbodies with WSPV systems. Moreover, the plankton and bird communities in the waterbodies with WSPV systems significantly differed from those in the CAs. These results suggest that WSPV systems have profound impacts on the water environment and biodiversity and that the impacts were not limited within the area covered by the PV panels but expanded to surrounding areas in the same waterbody.
We found that WSPV systems led to decreases in the T and DO of waterbodies in both seasons, which is consistent with previous experimental studies and model predictions (Château et al., 2019; Wang et al., 2022). The decreased light radiation due to shading from the PV modules (Armstrong et al., 2016) might be the main cause of decreased T around WSPV systems. Temperature impacts the growth and reproduction of plankton, and we found a significant relationship between T and the plankton densities in this study. DO in water comes from the diffusion of oxygen in the air and photosynthesis by aquatic plants (Neal et al., 2006). PV modules in FPV or PMPV systems can attenuate the turbulence of wind moving across water, and FPV modules can also reduce the contact area between air and water; both of these phenomena reduce the transfer of oxygen from air into the water. The shading created by PV modules also reduces the oxygen produced by photosynthesis in aquatic plants (Haas et al., 2020).
Our results indicated that the species richness and densities of phytoplankton, microzooplankton, and macrozooplankton decreased in the PAs, and these decreases were closely related to the environmental changes induced by the WSPV systems, including decreased UCA, T and DO. All of these changes could affect the growth and reproduction of plankton (Thackeray et al., 2008; Mette et al., 2011). We found that UCA was generally negatively related to the phytoplankton densities, but not all phytoplankton groups had reduced in the PAs with low UCA. This may be related to the different light demands between phytoplankton groups: the dominant phytoplankton groups with significantly lower density in the PAs than CAs (e.g., Microcystis, Cryptomonas, and Coelastrum) were those with high light demands, while the groups with non-significantly differences in density between the PAs and CAs (Pseudanabaena, Oscillatoria, and Merismopedia) were those with low light demands (Singh and Singh, 2015; Gao et al., 2019. Fig. S1). Moreover, changes in phytoplankton communities can also be transferred along food chains, impacting microzooplankton and macrozooplankton at higher trophic levels.
In our study area, nutrient concentration weakly impacted plankton diversity. This may be because of the nutrient enrichment of the waterbodies from the well-developed agriculture and aquaculture in the study area (Huo et al., 2021), thus nutrients were not the main limiting factor for the growth and reproduction of plankton. Although the species richness and individual densities of all three plankton groups were low in the PAs, the Shannon‒Wiener diversity and Pielou evenness indices were generally higher in the PAs than in the NPAs or CAs in summer. This may be attributed to the fact that adverse water conditions created by WSPV systems suppress the population growth of dominant groups (e.g., cyanobacteria) (Bockwoldt et al., 2017; Haas et al., 2020), thus resulting in higher abundance-based Shannon‒Wiener diversity and Pielou evenness indices in the PAs. In the three areas, the dominant species and groups in the three plankton communities (e.g., Microcystis spp., Diurella stylata, and Daphnia pulex) were all indicators of eutrophic conditions (Lin et al., 2003), which is associated with the nutrient enrichment of the waterbodies in the study area (Huo et al., 2021). Although WSPV systems have the potential to mitigate the risk of bloom outbreaks to some extent (Liu et al., 2020), WSPV systems do not decrease the nutrient concentrations in waterbodies, therefore cannot solve the problem of eutrophication.
We found that both FPV and PMPV systems caused a decrease in T, DO, UCA, and plankton diversity of waterbodies, and a more sharply decrease in the FPV than PMPV systems. This could be because the pontoon and mooring components of the FPV system are placed on the water surface, which impedes contact between the air and water and thereby reduces the effect of wind turbulence on the water, thus reducing the transfer of oxygen from the air into the water (Neal et al., 2006; Exley et al., 2021). In addition, compared with PMPV systems, FPV systems have additional components, including pontoons, floats, mooring systems and connectors, and thus have higher coverage, reducing the amount of light radiation that enters the water (Sahu et al., 2016). The T, DO and UCA in the water largely affect the reproduction and growth of aquatic organisms, and thus affect the diversity and composition of aquatic communities.
Earlier model simulations have predicted that the impacts of WSPV systems can be limited when PV panel coverage is low (Château et al., 2019; Haas et al., 2020). However, we found the impacts of WSPV systems were not related to the UCA, even low coverage can significantly affect water physicochemical traits and plankton communities. This could be because most PV panels are not arranged flat but with a southward inclination angle to maximize solar radiation conversion and power generation per unit area of the PV system; thus, PV panels can be vertically illuminated by sunlight (Xu et al., 2017). This arrangement greatly increases the shading of PV panels, resulting in the sunlight shining area on waterbodies being much smaller than the UCA. This suggests that the UCA largely underestimates the effects of WSPV systems on waterbodies. The shading area of the PV panels on water surfaces is the most suitable metric to measure the effects of WSPV systems.
Waterbirds are highly dependent on wetlands for nesting, feeding, and resting (Wang et al., 2018) and thus are susceptible to wetland habitat changes by the introduction of WSPV systems. In the PV areas, we found decreased species richness and individual densities of waterbirds, no nesting waterbirds, and altered community composition. These changes may be related to habitat occupation and landscape changes due to the presence of PV modules and disturbances from routine PV management. The increased land bird abundance in the PV areas may be attributed to the attractiveness of the dark-coloured solar panels to insects (Horváth et al., 2010), providing prey for insectivorous land birds. This is consistent with the foraging behaviour of birds on PV panels. The decreased waterbird diversity suggests that WSPV systems largely impact waterbirds. Thus, WSPV systems should not be constructed in critical habitats for waterbirds.
The changed water physicochemical traits and plankton and bird communities can further impact ecosystem stability and resiliency. WSPV systems are often situated in waterbodies with limited flow, such as lakes, reservoirs, and coal mining subsidence wetlands (Sahu et al., 2016; Li et al., 2023), making it difficult to mitigate the impacts of WSPV systems through water exchange. Therefore, the cumulative effects of these impacts are likely to intensify over time. While flowing waterbodies, such as rivers, may mitigate the cumulative effects of WSPV systems, they are often unsuitable for WSPV system installation due to their size or management requirements (e.g., flooding). Additionally, waterbodies serve various functions, such as water supply, aquaculture, recreation, and flood control. Although WSPV systems can spatially coexist with other functions, such as aquaculture (Pringle et al., 2017; Château et al., 2019), our study showed that WSPV systems impact the physicochemical traits and biological communities of waterbodies, which may weaken their suitability for other functions. For instance, WSPV systems reduced the DO of waterbodies, which is detrimental to aquaculture. Moreover, the electromagnetic fields produced by PV cabling and the potential diffusion of pollutants (e.g., microplastics) from PV modules into water may have long-term effects on aquatic environments (Lovich and Ennen, 2011; Da Silva and Branco, 2018), which are still unknown and require further studies. Therefore, the compatibility of WSPV systems with other functions should be considered.
As an emerging mode of solar energy utilisation, WSPV systems have developed in a short period of about 10 years. The WSPV systems in the study have operated for 3–5 years, thus the long-term impacts are uncertain, requiring long-term monitoring. The region of this study is in the subtropics, and the degree of impacts of WSPV systems may vary between climate zones with different temperatures and light radiations. In addition, the areas of waterbodies and the coverage proportion of WSPV systems can be a key factor in the degree of photovoltaic impacts, on which further research is required.
Expanding the scope of light energy use, WSPV systems have broad development prospects in the future from the perspective of water resource availability (Jin et al., 2023). However, this study reveals that WSPV systems have significant impacts on the water environment and biodiversity that could be long-lived. Since the cover created by the PV modules is the cause of the series of impacts we observed, we suggest that WSPV systems should be installed at suitable sites and scales. It is also necessary to conduct long-term monitoring to understand the impacts of WSPV systems on ecological and environmental conditions; such monitoring is currently lacking but critical for targeted measures to mitigate adverse impacts. Our study provides important insights into the ecological and environmental consequences of WSPV systems and addresses the implications of the development of WSPV systems as part of the sustainable use of water resources.