Studies were carried out on August 14, 2019, in the shallow part of the Kazachya Bay (Sevastopol, Black Sea) under cloudless sky conditions. At the selected point of the Zostera noltii Hornemann canopy, at a depth of 42 cm, with coordinates 44° 57′26″ N, 33° 40′33″ E, measurements of photosynthetically active radiation intensity (IPAR) were taken. During the entire period of research, the plants were in a vertical state. The Z. noltii biomass (mdry) distribution along the canopy height (z) was found to change unevenly, increasing with depth (mdry(z) = 0.0001Z3.881; R2 = 0.95), and this is reflected in the vertical distribution of IPAR. IPAR was observed to decrease with the depth of the canopy, the manner of this decrease being largely dependent on solar altitudes. The measurement results show a significant influence of the Fresnel effect on IPAR values.
Photosynthetically active radiation (PAR) intensity (IPAR) measurements were carried out in a shallow waters section of Tolstiy cape, Sevastopol, the Crimean Peninsula, at a depth of 63 cm along the profile of Cystoseira crinita (Desf.) Bory canopy (canopy height 25-30 cm) at different solar elevation angles in sounding mode on August 27, 2019. During the entire study period the C. crinita thalli were in inclined state. The greater part of the plants mass [67.07% (SD = 9.62, CV = 0.14)] was located in the upper 10 cm layer of the canopy. The PAR vertical intensity profile in the Cystoseira crinita canopy may change during daylight hours. The equations describing the IPAR distribution in the canopy depth at different times of day are provided. Conditions that would typically develop at 9 a.m., made the PAR intensity decrease linearly in the canopy from 657.6 μE . m-2 . s-1 in its upper part up down to 123.45 μE . m-2 . s-1 in its lower part at a depth of 20 cm. At 11 a.m., a high level of PAR intensity (564.98 – 828.12 μE . m-2 . s-1) was observed throughout the canopy. At 6 p.m., with the Sun low on the horizon, the lowest PAR level would be recorded (2.59 – 269.41 μE . m-2 . s-1).
A comparison of phytomass vertical distributions (Wdry(z)/S0) and photosynthetically active radiation (PAR) in Zostera noltii Hornemann canopy in a shallow waters conditions was made. It was found out that between PAR values and Wdry(z)/S0 there is a high inverse relationship of two types – power and exponential. In both cases, the correlation coefficient reaches the value of R2=0.995. The averaged vertical PAR distribution in the canopy is well described by a fourth order polynomial function, with a correlation coefficient of R2=0.998.
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