Spatial pattern of K_d(PAR) and its relationship with light absorption of optically active components in inland waters across China

Abstract. The spatial distribution of the attenuation of photosynthetic active radiation (K_d(PAR)) was routinely estimated in China lakes and reservoirs. Higher mean value of K_d(PAR) was observed in Northeastern plain and mountainous region (NER). A linear model is used to predict K_d(PAR), as a function of light absorption coefficient of pigment particulates (a_phy), colored dissolved organic matters (a_CDOM), and inorganic particulate matters (a_NAP): K_d(PAR) = 0.41 + 0.57 × a_CDOM + 0.96 × a_NAP + 0.57 × a_phy (R² = 0.87, n = 741, p < 0.001). Spatial K_d(PAR) was relatively dependent on the inorganic particulate matters (average relative contribution of 57.95 %). When only consider the contribution of absorption of a_OACs to K_d(PAR), the results found that the a_OACs could explain 70 %–87 % of K_d(PAR) variations. In the lakes with low TSM concentration and non-eutrophic lakes with high TSM, a_CDOM was the most powerful predicting factor on K_d(PAR). In eutrophic lakes with high TSM, a_NAP had the most significant impact on K_d(PAR). This study allowed K_d(PAR) to be predicted from a_OACs values in the inland waters. Besides, results of this study are suggesting that new studies on the variability of K_d(PAR) in inland waters must consider the hydrodynamic conditions, trophic status and the distribution of optically active components within the water column.