Productivity Of Algal Communities Research Articles

LATE GLACIAL AND HOLOCENE HISTORY OF LAKE BOLSHOE MIASSOVO (SOUTHERN URALS) BASED ON DIATOM ANALYSIS OF BOTTOM SEDIMENTS<a href="#FN1"><sup>1</sup></a>

Bottom sediments are the most important “archive” containing information about the development of lake ecosystems. One of the most reliable and widely used methods of studying bottom sediments is diatom analysis (Juze et al., 1949). Currently, it is part of a group of guiding methods used to reconstruct the historical dynamics of the environment and climate (Rudaya et.al., 2012; Palagushkina et.al., 2018). In this work, the history of development of Lake Bolshoe Miassovo (Southern Urals) reconstructed using the taxonomic composition of diatoms found in the 526 cm long sediment core is presented. The maximum age of the sediments in the column was 13 500 years BP. According to the results of the study, 123 taxa of diatoms belonging to 47 genera were identified in the lake sediments. Diatom analysis of the bottom sediments of the studied lake allowed us to identify the main stages of the evolution of the reservoir during the Late Glacial and Holocene. During ~13 200–11 700 yr BP, in the period of a cool climate, the lake was a deep body of water with a constant water level and an extensive zone of shallow waters overgrown with macrophytes; then ~11 700–8500 cal. years BP against the background of cooling, the water level decreased; from ~8500–4600 cal. years BP was the stage of increasing water level in the lake in a warmer and wetter climate; in the period ~4600–2500 cal. years BP there was an increase in productivity of algal communities; during ~2500–800 cal. years BP against the background of decreasing temperature, a deep lake with low mineralized water, and presence of swampy shallow waters with acidification processes in them is finally formed.

Responses of benthic algae to nutrient enrichment in a shallow lake: Linking community production, biomass, and composition

Abstract Understanding how nutrient limitation affects algal biomass and production is a long‐standing interest in aquatic ecology. Nutrients can influence these whole‐community characteristics through several mechanisms, including shifting community composition. Therefore, incorporating the joint responses of biomass, taxonomic composition, and production of algal communities, and relationships among them, is important for understanding effects of nutrient enrichment. In shallow subarctic Lake Mývatn, Iceland, benthic algae compose a majority of whole‐lake primary production, support high secondary production, and influence nutrient cycling. Given the importance of these ecosystem processes, the factors that limit benthic algae have a large effect on the function and dynamics of the Mývatn system. In a 33‐day nutrient enrichment experiment conducted in Lake Mývatn, we measured the joint responses of benthic algal biomass, primary production, and composition to nitrogen (N) and phosphorus (P) supplementation. We enriched N and P using nutrient‐diffusing agar overlain by sediment, with three levels of N and P that were crossed in a factorial design. We found little evidence of community‐wide nutrient limitation, as chlorophyll‐a concentrations showed a negligible response to nutrients. Gross primary production (GPP) was unaffected by P and inhibited by N enrichment after 10 days, although the inhibitory effect of N diminished by day 33. In contrast to biomass and primary production, community composition was strongly affected by N and marginally affected by P, with some algal groups increasing and others decreasing with enrichment. The taxa with the most negative and positive responses to N enrichment were Fragilariaceae and Scenedesmus, respectively. The abundances of particular algal groups, based on standardised cell counts, were related to GPP measured at the end of the experiment. Oocystis was negatively associated with GPP but was unaffected by N or P, while Fragilariaceae and Scenedesmus were positively associated with GPP but had opposite responses to N. As a result, nutrient‐induced compositional shifts did not alter GPP. Overall, our results show that nutrient enrichment can have large effects on algal community composition while having little effect on total biomass and primary production. Our study suggests that nutrient‐driven compositional shifts may not alter the overall ecological function of algal communities if (1) taxa have contrasting responses to nutrient enrichment but have similar effects on ecological processes, and/or (2) taxa that have strong influences on ecological function are not strongly affected by nutrients.

PRIMARY PRODUCTIVITY AND ENERGY RELATIONSHIPS IN ARTIFICIAL STREAMS1

The productivity of algal communities was investigated in two recirculating artificial streams. Emphasis was placed on a study of the effects of various factors on energy flow and on the characterization of artificial streams as a research tool. Productivity was measured by pH and carbon dioxide changes, upstream‐downstream oxygen changes, and the biomass of algae collected on artificial substrata.A temperature increase caused a small, but insignificant, increase in net productivity, while increased light intensity caused an increase in net productivity. A higher current velocity caused an increase in net productivity, significant as shown by riffle vs. pool communities, but not significant between a fast and a slow stream. A shorter, but more frequent photoperiod did not change the rate of production significantly. High chelate concentration caused a reduction in net productivity.Estimates of net productivity by the carbon dioxide and oxygen methods were in agreement for two out of five studies, while estimates by the biomass of algae on substrata were consistently lower than estimates by the gas methods. Net production varied from 2,815 to 5,565 cal m−2 day−1, resulting in efficiencies from 3.8 to 9.8%. Efficiencies of gross productivity varied from 6.4 to 16.1%.