ABSTRACT

The effects of salinity (as chloride [Cl] at 600, 1000, 1600, and 2500 mg L⁻¹) and nitrate (as nitrogen [N] loading rates using concentrations of 1, 2, 5, and 10 mg L⁻¹) additions on phytoplankton communities (as chlorophyll and carotenoid pigments) were determined using a fully factorial 3 m³ mesocosm pond experiment. Redundancy analysis followed by variance partitioning analysis (VPA) statistically compared phytoplankton with water chemistry, zooplankton, phytobenthos (aquatic plants and periphyton), and zoobenthos to understand relationships among benthic and pelagic components. Repeated measures analysis of variance (RM-ANOVA) indicated no interactive effects of the 2 treatments. In VPA, physicochemical variables explained the most variance (33.6%) in the phytoplankton pigment dataset relative to benthic primary producers (0.4%) and invertebrates (2.3%). Salinisation led to an increase in biomass of planktonic siliceous algae (Cl ≥1600 mg L⁻¹) and chlorophytes and cyanobacteria (Cl ≥2500 mg L⁻¹), which we infer was caused by increased phosphorus release from sediments while aquatic plants and periphyton declined. Nitrate additions increased the biomass of cryptophytes and chlorophytes at intermediate N loading rates using concentrations of 5 mg L⁻¹ (associated with greater ammonium [NH₄-N] availability and shifts in aquatic plant composition). These findings support the hypothesis that the relative availability of reduced versus oxidised N forms is an important driver of phytoplankton composition. Together, these results suggest that pelagic biota are highly sensitive to salinity and nitrate increases, and that the phytoplankton compositional shifts are driven by indirect effects on water chemistry (bioavailable P mobilisation, changes in N forms), which are mediated by benthic processes.

摘要

盐度（以600、1000、1600和2500 mg L ^-1的氯化物[Cl]的形式）和硝酸盐（以1、2、5和10 mg L ^-1的浓度的氮[N]的负载率）的影响使用全因子3 m ³确定浮游植物群落的添加量（如叶绿素和类胡萝卜素色素）中观池塘实验。冗余分析后再进行方差分区分析（VPA），对浮游植物与水化学，浮游动物，浮游底栖动物（水生植物和周生浮游动物）和浮游底栖动物进行统计学比较，以了解底栖和浮游成分之间的关​​系。重复测量方差分析（RM-ANOVA）表明2种处理均无交互作用。在VPA中，相对于底栖初级生产者（0.4％）和无脊椎动物（2.3％），理化变量解释了浮游植物色素数据集的最大差异（33.6％）。盐碱化导致浮游硅质藻类生物量的增加（CL≥1600毫克的L ^-1）和绿藻和蓝藻（CL≥2500毫克的L ^-1），我们推测是由于沉积物中磷的释放增加而水生植物和附生植物减少了。硝酸盐的添加使用5 mg L ^-1（与更大的铵[NH ₄有关]的浓度在中等的N加载速率下增加了隐藻类植物和绿藻类的生物量。-N]的可用性和水生植物组成的变化）。这些发现支持以下假设：还原态氮和氧化态氮的相对利用率是浮游植物组成的重要驱动因素。总之，这些结果表明，浮游生物对盐度和硝酸盐含量高度敏感，而浮游植物的组成变化是由对水化学的间接影响（生物利用磷的动员，N形式的变化）驱动的，而间接作用是由底栖生物过程介导的。