A literature review on the effects of high ammonium concentrations on the growth of 6 classes of microalgae suggests the following rankings. Mean optimal ammonium concentrations were 7600, 2500, 1400, 340, 260, 100μM for Chlorophyceae, Cyanophyceae, Prymnesiophyceae, Diatomophyceae, Raphidophyceae, and Dinophyceae respectively and their tolerance to high toxic ammonium levels was 39,000, 13,000, 2300, 3600, 2500, 1200μM respectively. Field ammonium concentrations <100μM would not likely reduce the growth rate of most microalgae. Chlorophytes were significantly more tolerant to high ammonium than diatoms, prymnesiophytes, dinoflagellates, and raphidophytes. Cyanophytes were significantly more tolerant than dinoflagellates which were the least tolerant. A smaller but more complete data set was used to estimate ammonium EC50 values, and the ranking was: Chlorophyceae>Cyanophyceae, Dinophyceae, Diatomophyceae, and Raphidophyceae. Ammonia toxicity is mainly attributed to NH3 at pHs >9 and at pHs <8, toxicity is likely associated with the ammonium ion rather than ammonia.

Given the authoritative and well-documented publication records that crenic habitats support the substantial aquatic biodiversity, understanding of algal dynamics in response to anthropogenic and natural stressors in these crenic systems seems paramount. We sampled and monitored twelve freshwater springs for a period of 2 years from 2014 to 2015 to observe algal dynamics and the factors govern the distribution and dynamics. We used ANOVA, nMDS, PCA, ANOSIM, SIMPER, and BIOENV to reveal the key physicochemical variables influencing the distributional pattern and dynamics of algae. The analysis of variance (ANOVA, Tukey’s post hoc test) revealed significant difference among the springs with dominance of Bacillariophyceae (62%) followed by Chlorophyceae (18%) whereas nMDS ordination of abundance data in two-dimensional space resulted in a significant separation between spring sites (stress value of 0.13). One-way nested ANOSIM produced a significant distinction between periphytic algal communities in springs (global test R = 0.928, p = 0.001). The results of SIMPER revealed the highest average dissimilarity (60.95%) between springs S4 and S5, with the top five contributing families including Cyanophyceae (30.25%), Bacillariophyceae (25.98%), Rhodophyceae (16.74%), Chlorophyceae (13.64%), and Chrysophyceae (13.39%). BIOENV analysis of the periphytic algal data suggested that the assemblage pattern in all crenic habitats were controlled by discharge, conductivity, dissolved oxygen, total alkalinity, and total phosphorus. Since, springs are groundwater-dependent ecosystems acting as ecohydrologic refugia, any small change in groundwater discharge could strongly influence the ambient conditions (including water quality and temperature), which in turn influences the biological assemblage patterns and ecosystem services. Therefore, changes in discharge may provide information on possible future ecological change in the springs in relation to rising aridification.

Assessment of water resources requires interdisciplinary studies that include multiple ecosystem aspects. This study evaluated the water quality of Juara Lagoon (ES, Brazil) based on physical and chemical variables, cytogenetic responses in Allium cepa and phytoplankton dynamics. Three sampling sites were defined and water samples were collected during two sampling periods. Analyses such as determination of photic zone, conductivity, and concentrations of nutrients and metals were conducted as well as cytotoxic, mutagenic, and genotoxic potentials using A. cepa test. The main attributes of phytoplankton community, such as total richness, total density, density by class, dominance, and diversity, were also evaluated. Results have revealed that Juara Lagoon has signs of artificial eutrophication at two sampling sites due to high levels of total phosphorus and ammonia nitrogen. Cytotoxic, genotoxic, and mutagenic potentials were detected as well as high concentrations of Fe and Mn. Furthermore, 165 phytoplankton taxa were recorded, with highest richness in Chlorophyceae and Cyanophyceae classes. In addition, Cyanophyceae presented as the highest density class. A. cepa test and phytoplankton community evaluation indicated that the ecological quality of Juara Lagoon is compromised.