Effects of Water Velocity and Specific Surface Area on Filamentous Periphyton Biomass in an Artificial Stream Mesocosm

Accounting for effects of growth rate when measuring ecological stability in response to pulse perturbations

Ecological stability is a vital component of natural ecosystems that can inform effective conservation and ecosystem management. Furthermore, there is increasing interest in making comparisons of stability values across sites, systems and taxonomic groups, often using comparative synthetic approaches, such as meta-analysis. However, these synthetic approaches often compare/contrast systems where measures of stability mean very different things to the taxa involved. Here, we present results from theoretical models and empirical data to illustrate how differences in growth rates among taxa influence four widely used metrics of ecological stability of species abundances responding to pulse perturbations: resilience, recovery, resistance and temporal stability. We refer to these classic growth-rate-dependent metrics as 'realised' stability. We show that realised resilience and realised temporal stability vary as a function of organisms' growth rates; realised recovery depends on the relation between growth rate and sampling duration; and realised resistance depends on the relation between growth rate and sampling interval. To account for these influences, we introduce metrics intended to be more independent of growth rates, which we refer to as 'intrinsic' stability. Intrinsic stability can be used to summarise the overall effects of a disturbance, separately from internal recovery processes - thereby allowing more general comparisons of disturbances across organisms and contexts. We argue that joint consideration of both realised and intrinsic stability is important for future comparative studies.

Local and landscape factors influencing mercury distribution in water, bottom sediment, and biota from lakes of the Araguaia River floodplain, Central Brazil

Mercury (Hg) is a chemical element widely present in the Earth's crust. However, its high toxicity and ability to accumulate in organisms and biomagnify through food chains characterize it as a global pollutant of primary control. We assessed total mercury concentrations ([THg]) in abiotic and biotic compartments from 98 floodplain lakes associated with the Araguaia River and six tributaries (Midwest Brazil). [THg] quantification in water was performed by cold vapor atomic fluorescence spectroscopy. [THg] in bottom sediment was assessed using cold vapor generation atomic absorption spectrophotometry, while [THg] in macrophyte, periphyton, and plankton were quantified by thermal decomposition atomic absorption spectrometry. Hotspots of [THg] in water, bottom sediment, and macrophytes were determined in areas impacted by pasture and urban areas. In contrast, hotspots of [THg] in periphyton and forest fires were determined in preserved areas downstream. [THg] in plankton did not show a clear spatial distribution pattern. The mean bioaccumulation factor order was plankton (2.3 ± 1.8) > periphyton (1.3 ± 0.9) > macrophytes (0.7 ± 0.4) (KW = 55.09, p < 0.0001). Higher [THg] in water and bottom sediment were associated with high pH (R2adj = 0.118, p = 0.004) and organic matter (R2adj = 0.244, p < 0.0001). [THg] in macrophytes were positively influenced by [THg] in water (R2adj = 0.063, p = 0.024) and sediment (R2adj = 0.105, p = 0.007). [THg] in periphyton are positively related to forest fires (R2adj = 0.156, p = 0.009) and [THg] in macrophytes (R2adj = 0.061, p = 0.03) and negatively related to lake depth (R2adj = 0.045, p = 0.02). The transfer of Hg from water and sediment to the biota is limited. However, the progressive increase of the bioaccumulation factor between macrophyte, periphyton, and plankton may indicate Hg biomagnification along the food chain of the Araguaia River floodplain.

Effects of operational parameters on the performance of unialgal Oedogonium sp. filamentous algae nutrient scrubbers under controlled environmental conditions

Filamentous algae nutrient scrubber (FANS) operating parameters can strongly influence algal biomass productivity and nutrient removal. However, few studies to date have investigated the effects of FANS operating parameters such as initial standing crop, harvesting frequency and influent flow rate on biomass productivity and nutrient removal performance, especially for FANS that cultivate a single species of algae. Therefore, the overall aim of this study was to investigate how operating parameters affect the biomass productivity and nutrient removal performance of Oedogonium sp. - a promising species for unialgal FANS. The initial standing crop had a significant effect on biomass productivity, with productivities being highest (8.6 ± 0.5 g DW biomass m^-2day^-1) when the initial standing crop was 60-70 g DW m^-2. However, the daily nutrient removal rate was highest (0.47 ± 0.06 g N m^-2 day^-1and 1.24 ± 0.13 g P m^-2 day^-1) at the highest initial standing crop (100-110 DW m^-2). Biomass productivity was highest with a three-day growth period, regardless of size of the initial standing crop. Therefore, a four-day harvesting interval was selected as the optimal harvesting regime to promote exponential growth and high biomass production. Influent flow rate had a significant effect on biomass productivity, which was highest (9.3 ± 1.7 g DW m^-2 day^-1) for the 1 L min^-1 flow rate. This flow rate also gave the highest instantaneous nutrient removal rate (0.05 ± 0.02 g N m^-3 and 0.14 ± 0.05 g P m^-3). Current results suggest that an optimum initial standing crop of 70-80 g DW m^-2, harvesting frequency of four days and influent flow rate of 1 L min^-1 (16.7 L min^-1 m^-1 width) were optimal for Oedogonium sp. cultivated on FANS to maximize their biomass production and nutrient removal under controlled laboratory conditions. These results contribute to understanding the impacts of operating parameters on optimizing unialgal Oedogonium sp. FANS biomass production and nutrient removal performance.

Recent advances in the bio-application of microalgae-derived biochemical metabolites and development trends of photobioreactor-based culture systems

Microalgae are microscopic algae in sizes ranging from a few micrometers to several hundred micrometers. On average, half of the oxygen in the atmosphere is produced by the photosynthetic process of microalgae, so the role of these microorganisms in the life cycle of the planet is very significant. Pharmaceutical products derived from microalgae and commercial developments of a variety of supplements extracted from them originate from a variety of their specific secondary metabolites. Many of these microalgae are a reservoir of unique biological compounds including carotenoids, antioxidants, fatty acids, polysaccharides, enzymes, polymers, peptides, pigments, toxins and sterols with antimicrobial, antiviral, antifungal, antiparasitic, anticoagulant, and anticancer properties. The present work begins with an introduction of the importance of microalgae in renewable fuels and biodiesel production, the development of healthy food industry, and the creation of optimal conditions for efficient biomass yield. This paper provides the latest research related to microalgae-derived substances in the field of improving drug delivery, immunomodulatory, and anticancer attributes. Also, the latest advances in algal biocompounds to combat the COVID-19 pandemic are presented. In the subject of cultivation and growth of microalgae, the characteristics of different types of photobioreactors, especially their latest forms, are fully discussed along with their advantages and obstacles. Finally, the potential of microalgae biomass in biotechnological applications, biofuel production, as well as various biomass harvesting methods are described.

Stream algal biomass response to experimental phosphorus and nitrogen gradients: A case for dual nutrient management in agricultural watersheds

Watershed managers generally focus on P reduction strategies to combat freshwater eutrophication despite evidence that N co-limits primary production. Our objective was to test the role of P in limiting stream periphyton biomass within the Buffalo River watershed in Arkansas by conducting a 31-d streamside mesocosm experiment. To represent potentially different starting states, cobbles were transplanted from two different tributary streams and initially exposed to a range of P (0, 0.012, 0.025, 0.05, 0.1, and 0.2 mg L^-1 P) to assess benthic ash-free dry mass (AFDM) and chlorophyll-a (chl a) and responses during a P only enrichment period. Later, the experiment was continued under a N/P (10:1 molar ratio) enrichment gradient to examine co-limitation. Mean AFDM was higher on Day 31 of the N+P enrichment compared with Day 17 of the P-only enrichment (p < .001). Overall differences in AFDM and chl a were observed between cobbles from different stream sites. Phosphorus enrichment stimulated benthic chl a biomass, but enrichment effects were greater when streams were enriched with N+P (p < .001). Chlorophyll-a increased (4.4-57.9 mg m^-2 ) with increasing P concentrations (p < .001) after P enrichment but was threefold greater after N+P enrichment, increasing from 13.3 to 171.1 mg m^-2 across the enrichment gradient. Results support the need to consider both N and P limitation in freshwater systems and demonstrate that potential increases in nutrient concentrations may influence accumulation of algae on cobble substrates from the Buffalo River watershed.

Water quality in simulated eutrophic shallow lakes in the presence of periphyton under different flow conditions

Although the effects of periphyton on water quality and its relationship with flow conditions have been studied by researchers, our understanding about their combined action in eutrophic shallow lakes is poor. In this research, four aquatic model ecosystems with different water circulation rates and hydraulic conditions were constructed to investigate the effect of periphyton and flow condition on water quality. The concentrations of NH₄⁺, TP, and chlorophyll-a and flow conditions were determined. The results show that, as a result of the rising nutrient level at the early stage and the decline in the lower limit, the presence of periphyton can make the ecosystem adaptable to a wider range of nutrients concentration. In terms of the flow condition, the circulation rate and hydraulic condition are influential factors for aquatic ecosystem. Higher circulation rate in the ecosystem, on one hand, facilitates the metabolism by accelerating nutrient cycling which is beneficial to water quality; on the other hand, high circulation rate leads to the nutrient lower limit rising which is harmful to water quality improvement. At low velocities, slight differences in hydraulic conditions, vertical velocity gradient and turbulence intensity gradient could affect the quantity of phytoplankton. Our study suggests that, considering environmental effect of periphyton, flow conditions and their combined action is essential for water quality improvement and ecological restoration in eutrophic shallow lakes.

Advanced nutrient removal from surface water by a consortium of attached microalgae and bacteria: A review

Innovative and cost-effective technologies for advanced nutrient removal from surface water are urgently needed for improving water quality. Conventional biotechnologies, such as ecological floating beds, or constructed wetlands, are not effective in removing nutrients present at low-concentration. However, microalgae-bacteria consortium is promising for advanced nutrient removal from wastewater. Suspended algal-bacterial systems can easily wash out unless the hydraulic retention time is long, attached microalgae-bacteria consortium is more realistic. This critical review summarizes the fundamentals and status of attached microalgae-bacteria consortium for advanced nutrient removal from surface water. Key advantages are the various nutrient removal pathways, reduction of nutrients to very low concentration, and diversified photobioreactor configurations. Challenges include poor identification of functional species, poor control of the community composition, and long start-up times. Future research should focus on the selection and engineering of robust microbial species, mathematical modelling of the composition and functionality of the consortium, and novel photobioreactor configurations.

Nutrient removal from horticultural wastewater by benthic filamentous algae Klebsormidium sp., Stigeoclonium spp. and their communities: From laboratory flask to outdoor Algal Turf Scrubber (ATS)

Benthic filamentous algae have evident advantages in wastewater treatment over unicellular microalgae, including the ease in harvesting and resistance to predation. To assess the potentials of benthic filamentous algae in treating horticultural wastewater under natural conditions in Belgium, three strains and their mixture with naturally wastewater-borne microalgae were cultivated in 250 ml Erlenmeyer flasks in laboratory as well as in 1 m(2) scale outdoor Algal Turf Scrubber (ATS) with different flow rates. Stigeoclonium competed well with the natural wastewater-borne microalgae and contributed to most of the biomass production both in Erlenmeyer flasks and outdoor ATS at flow rates of 2-6 L min(-1) (water velocity 3-9 cm s(-1)), while Klebsormidium was not suitable for growing in horticultural wastewater under the tested conditions. Flow rate had great effects on biomass production and nitrogen removal, while phosphorus removal was less influenced by flow rate due to other mechanisms than assimilation by algae.