Rivers affect the biovolume and functional traits of phytoplankton in floodplain lakes

Abstract Aim: We analyzed the temporal distribution (dry and rainy periods) of phytoplankton functional groups (biovolume) from lakes connected to dammed (S1 - Paraná River) and non-dammed rivers (S2 - Baia River and S3 - Ivinhema River) in the upper Paraná River floodplain, Brazil. We also determined the drivers of the phytoplankton community assemblage. Methods Phytoplankton and environmental variables samplings were performed quarterly in dry (2000 and 2001) and rainy (2010 and 2011) periods. We classified the phytoplankton species into seven morphological based functional groups (MBFG). We used analysis of variance to test differences in total phytoplankton biovolume and MBFGs biovolume between lakes and climatic periods. We also used redundancy analysis to determine the MBFGs-environment relation. Results The lake related to the dammed river (S1) presented the lowest species richness. The total phytoplankton biovolume presented differences among the lakes, but we did not register temporal differences associated with water level variation. The lake related to the non-dammed and semi-lentic river (S2) presented the highest biovolume, while S1 (related to the dammed river) and S3 (related to the non-dammed river) exhibited the lowest ones. Filamentous organisms (MBFG III) were associated with poor nutrient conditions and diatoms (MBFG VI) were favored in high water mixing sites. The flagellate groups MBFG II and MBFG V were related to deeper water and lower column mixing conditions, respectively. Conclusions Our results suggest that phytoplankton species with different functional traits drive the primary productivity in the dry and rainy periods. Hence, we highlight the importance of maintaining high functional diversity in lakes to ensure primary productivity. Therefore, we stress the importance of protecting the natural environment such as floodplain lakes because of its contribution to the regional biodiversity and the flow of energy.

**研究目的**：本研究针对巴西巴拉那河上游泛滥平原中，与筑坝河流（S1——巴拉那河）及非筑坝河流（S2——巴亚河、S3——伊维涅马河）相连的湖泊，分析其浮游植物功能群（以生物体积计）的时间分布特征（枯水期与丰水期），同时明确浮游植物群落组成的驱动因子。

**研究方法**：分别于枯水期（2000年、2001年）与丰水期（2010年、2011年）按季度开展浮游植物与环境变量采样。将浮游植物物种划分为7个基于形态学的功能群（MBFG）。采用方差分析检验不同湖泊间、不同气候时期的浮游植物总生物体积及各MBFG生物体积的差异；同时利用冗余分析探究MBFG与环境因子之间的关联。

**研究结果**：与筑坝河流相连的S1湖泊物种丰富度最低。浮游植物总生物体积在不同湖泊间存在显著差异，但未观测到与水位变化相关的时间差异。与非筑坝、半静水水系相连的S2湖泊生物体积最高，而S1（筑坝河流关联湖泊）与S3（非筑坝河流关联湖泊）的生物体积最低。丝状生物（MBFG III）与低营养条件相关，硅藻（MBFG VI）则在水体混合强度较高的生境中占优。鞭毛类功能群MBFG II与MBFG V分别对应深水环境与低水体柱混合条件。

**研究结论**：本研究结果表明，具备不同功能性状的浮游植物物种主导了枯、丰水期的初级生产力。据此，我们强调维持湖泊高功能多样性对保障初级生产力的重要性。同时，鉴于泛滥平原湖泊对区域生物多样性及能量流动的贡献，我们呼吁加强对这类自然环境的保护。