Jargal Namsrai, Lee Eui-Haeng, An Kwang-Guk
Department of Bioscience and Biotechnology, Chungnam National University, Daejeon, 34134, South Korea.
Department of Bioscience and Biotechnology, Chungnam National University, Daejeon, 34134, South Korea; Korea Rural Community Corporation, Naju, 58327, Republic of Korea.
J Environ Manage. 2023 Jul 1;337:117737. doi: 10.1016/j.jenvman.2023.117737. Epub 2023 Mar 16.
Eutrophication management is one of the greatest environmental challenges for lacustrine systems worldwide. The empirically predicted models between algal chlorophyll (CHL-a) and total phosphorus (TP) provide a basis for managing eutrophication in lakes and reservoirs, but other environmental factors influencing the empirical relations must be considered. Here, we tested the impacts of morphological and chemical variables, as well as the effect of the Asian monsoon, on the functional response of CHL-a to TP using two-year data of 293 agricultural reservoirs. This study was based on the approaches of empirical models (linear and sigmoidal), CHL-a:TP ratio, and trophic state index deviation (TSID). Algal CHL-a exhibited a strong log-linear relation with TP on the basis of 2-year average data (R = 0.69, p < 0.001), whereas it had a more sigmoidal relation in terms of monsoon-seasonal averages (R = 0.52, p < 0.001). The linear segment of the CHL-a-TP relation aligned with the gradient of TP (10 mg/L < TP < 100 mg/L) from mesotrophic to eutrophic conditions. The transfer efficiency of TP to CHL-a based on the 2-year mean CHL-a:TP was high (0.6 <) across all assessed agricultural systems. CHL-a:TP showed insignificant correlations with reservoir morphological variations, but it decreased (<0.5) in eutrophic and hypereutrophic systems during the monsoon season (July-August). Because TP and total suspended solids (TSS) have become increasingly abundant, light conditions become insufficient for algal growth during and after the monsoon season. Light-limited conditions become more prevalent in hypereutrophic systems with shallow depth and high dynamic sediment ratio (DSR) because of the intense rainfall inputs and wind-induced sediment resuspension of the post-monsoon season. TSID reflected the degree of phosphorus limitation and the reduction in underwater light corresponding to changes in reservoir water chemistry (ionic content, TSS, and TN:TP ratio), trophic state gradient, and morphological metrics (mainly mean depth and DSR). Our findings suggest that monsoon-induced changes in water chemistry and light attenuation, which are also associated with anthropogenic pollutant runoffs and reservoir morphology, are critical factors that influence the functional response of algal CHL-a to TP in temperate reservoirs. Modeling and assessing eutrophication should therefore take into account monsoon seasonality along with individual morphological features further.
富营养化管理是全球湖泊系统面临的最大环境挑战之一。藻类叶绿素（CHL-a）与总磷（TP）之间的经验预测模型为湖泊和水库的富营养化管理提供了基础，但必须考虑影响这种经验关系的其他环境因素。在此，我们利用293个农业水库的两年数据，测试了形态和化学变量的影响以及亚洲季风的影响，对CHL-a对TP的功能响应。本研究基于经验模型（线性和S形）、CHL-a:TP比值和营养状态指数偏差（TSID）方法。基于两年平均数据，藻类CHL-a与TP呈现出很强的对数线性关系（R = 0.69，p < 0.001），而在季风季节平均值方面则呈现出更明显的S形关系（R = 0.52，p < 0.001）。CHL-a-TP关系的线性部分与中营养到富营养条件下TP的梯度（10 mg/L < TP < 100 mg/L）一致。基于两年平均CHL-a:TP，TP向CHL-a的转移效率在所有评估的农业系统中都很高（>0.6）。CHL-a:TP与水库形态变化的相关性不显著，但在季风季节（7月至8月），在富营养和超富营养系统中其值下降（<0.5）。由于TP和总悬浮固体（TSS）越来越丰富，在季风季节期间及之后，光照条件对藻类生长变得不足。由于季风后季节强烈的降雨输入和风致沉积物再悬浮，光照受限条件在深度浅且动态沉积物比率（DSR）高的超富营养系统中更为普遍。TSID反映了磷限制程度以及与水库水化学（离子含量、TSS和TN:TP比值）、营养状态梯度和形态指标（主要是平均深度和DSR）变化相对应的水下光照减少情况。我们的研究结果表明，季风引起的水化学和光衰减变化，这也与人为污染物径流和水库形态有关，是影响温带水库中藻类CHL-a对TP功能响应的关键因素。因此，在对富营养化进行建模和评估时，应进一步考虑季风季节性以及个体形态特征。
