Temperature and manganese as determining factors in the presence of diatom or blue-green algal floras in streams

Functional and compositional responses of stream microphytobenthic communities to multiple stressors increase and release in a mesocosm experiment

Field observations form the basis of the majority of studies on microphytobenthic algal communities in freshwater ecosystems. Controlled mesocosm experiments data are comparatively uncommon. The few experimental mesocosm studies that have been conducted provide valuable insights into how multiple stressors affect the community structures and photosynthesis-related traits of benthic microalgae. The recovery process after the stressors have subsided, however, has received less attention in mesocosm studies. To close this gap, here we present the results of a riparian mesocosm experiment designed to investigate the effects of reduced flow velocity, increased salinity and increased temperature on microphytobenthic communities. We used a full factorial design with a semi-randomised distribution of treatments consisting of two levels of each stressor (2 × 2 × 2 treatments), with eight replicates making a total of 64 circular mesocosms, allowing a nuanced examination of their individual and combined influences. We aimed to elucidate the responses of microalgae communities seeded from stream water to the applied environmental stressors. Our results showed significant effects of reduced flow velocity and increased temperature on microphytobenthic communities. Recovery after stressor treatment led to a convergence in community composition, with priority effects (hypothesized to reflect competition for substrate between resident and newly arriving immigrant taxa) slowing down community shifts and biomass increase. Our study contributes to the growing body of literature on the ecological dynamics of microphytobenthos and emphasises the importance of rigorous experiments to validate hypotheses. These results encourage further investigation into the nuanced interactions between microphytobenthos and their environment and shed light on the complexity of ecological responses in benthic systems.

Mediterranean springs: Keystone ecosystems and biodiversity refugia threatened by global change

Mediterranean spring ecosystems are unique habitats at the interface between surface water and groundwater. These ecosystems support a remarkable array of biodiversity and provide important ecological functions and ecosystem services. Spring ecosystems are influenced by abiotic, biotic, and anthropogenic factors such as the lithology of their draining aquifers, their climate, and the land use of their recharge area, all of which affect the water chemistry of the aquifer and the spring discharges. One of the most relevant characteristics of spring ecosystems is the temporal stability of environmental conditions, including physicochemical features of the spring water, across seasons and years. This stability allows a wide range of species to benefit from these ecosystems (particularly during dry periods), fostering an unusually high number of endemic species. However, global change poses important threats to these freshwater ecosystems. Changes in temperature, evapotranspiration, and precipitation patterns can alter the water balance and chemistry of spring water. Eutrophication due to agricultural practices and emergent pollutants, such as pharmaceuticals, personal care products, and pesticides, is also a growing concern for the preservation of spring biodiversity. Here, we provide a synthesis of the main characteristics and functioning of Mediterranean spring ecosystems. We then describe their ecological value and biodiversity patterns and highlight the main risks these ecosystems face. Moreover, we identify existing knowledge gaps to guide future research in order to fully uncover the hidden biodiversity within these habitats and understand the main drivers that govern them. Finally, we provide a brief summary of recommended actions that should be taken to effectively manage and preserve Mediterranean spring ecosystems for future generations. Even though studies on Mediterranean spring ecosystems are still scarce, our review shows there are sufficient data to conclude that their future viability as functional ecosystems is under severe threat.

Anticipated impacts of climate change on the structure and function of phytobenthos in freshwater lakes

Climate change threatens surface waters worldwide, especially shallow lakes where one of the expected consequences is a sharp increase in their water temperatures. Phytobenthos is an essential, but still less studied component of aquatic ecosystems, and it would be important to learn more about how global warming will affect this community in shallow lakes. In this research, the effects of different climate change scenarios (SSP2-4.5 and SSP5-8.5, as intermediate and high emission scenarios) on the structure and function of the entire phytobenthos community using species- and trait-based approaches were experimentally investigated in an outdoor mesocosm system. Our results show that the forecasted 3 °C increase in temperature will already exert significant impacts on the benthic algal community by (1) altering its species and (2) trait composition (smaller cell size, lower abundance of colonial and higher of filamentous forms); (3) decreasing Shannon diversity; and (4) enhancing the variability of the community. Higher increase in the temperature (+5 °C) will imply more drastic alterations in freshwater phytobenthos by (1) inducing very high variability in species composition and compositional changes even in phylum level (towards higher abundance of Cyanobacteria and Chlorophyta at the expense of Bacillariophyta); (2) continuing shift in trait composition (benefits for smaller cell volume, filamentous life-forms, non-motile and weakly attached taxa); (3) further reducing the functional diversity; (4) increasing biofilm thickness (1.4 μm/°C) and (5) decreasing maximum quantum yield of photosystem II. In conclusion, already the intermediate emission scenario will predictably induce high risk in biodiversity issues, the high emission scenario will imply drastic impacts on the benthic algae endangering even the function of the ecosystem.

Responses of periphyton communities to abrupt changes in water temperature and velocity, and the relevance of morphology: A mesocosm approach

Sudden instream releases of water from hydropower plants (hydropeaking [HP]) can cause abrupt temperature variations (thermopeaking [TP]), typically on a daily/sub-daily basis. In alpine rivers, hydropeaking and thermopeaking waves usually overlap, which leads to a multiple stressor of flow velocity pulses and temperature alteration. Periphytic communities could give important insights into the effects of combined thermo- and hydropeaking (THP) in stream ecosystems. Thus, the study's first aim was to assess the combined effects of thermo-hydropeaking on structural (composition, biomass) and functional (photosynthesis, enzyme activity) properties of periphyton. The second aim was to assess the interaction between periphytic algae and the heterotrophic communities (bacteria) and determine how biotic and abiotic factors explain the variability of bacterial enzymatic activities in the periphyton. We assessed the effects of repeated cold and warm thermo-hydropeaking for 24 days on periphyton, by manipulating discharge and temperature in six experimental flumes directly fed by an Alpine stream. Our study revealed that THP had structural and functional effects on periphyton in oligotrophic streams, where the effects depending on the direction of the temperature change (cold/warm) and on the morphological setting (pool/riffle). The results showed that even a short-term increase in flow velocity and temperature decrease could induce better growth conditions for diatoms. Additionally, an increase in the interaction between periphytic algae and bacteria during thermo-hydropeaking was also shown, this coupling being more pronounced in pool than in riffle sections. Our results clearly showed that riffle sections develop less periphytic algal biomass and activity and therefore, THP can reduce biomass availability for primary consumers in large areas of impacted streams. These findings highlight the importance of mitigation measures, focusing on establishing heterogeneous stream bed areas, with frequent pool and riffle sequences.

Redefining Boundaries: Ruth Myrtle Patrick's Ecological Program at the Academy of Natural Sciences of Philadelphia, 1947-1975

Ruth Myrtle Patrick (1907-2013) was a pioneering ecologist and taxonomist whose extraordinary career at the Academy of Natural Sciences of Philadelphia spanned over six decades. In 1947, an opportunity arose for Patrick to lead a new kind of river survey for the Pennsylvania Sanitary Water Board to study the effects of pollution on aquatic organisms. Patrick leveraged her already extensive scientific network, which included ecologist G. Evelyn Hutchinson, to overcome resistance within the Academy, establish a new Department of Limnology, and carry out the survey, which was a resounding success and brought much needed money to the Academy. As demand for her expertise grew among industrial companies, such as the chemical company DuPont, Patrick became more active in the world of applied science. She repurposed data and instruments from her river surveys to run new experiments, test ecological theories, and conduct long-term ecological studies. Through these studies, she advanced an argument that biologist Thomas Lovejoy dubbed the "Patrick principle," the idea that the ecological health of a body of water could be measured by the relative abundance and diversity of species living there. Patrick was elected to the National Academy of Sciences in 1970, became a board member of DuPont in 1975, and received two of the most prestigious awards in ecology: the Eminent Ecologist Award from the Ecological Society of America in 1972 and the Tyler Ecology Award in 1975. This article analyzes Patrick's unusual success in bridging the worlds of science and industry and her unusual ability to cross, and redefine, the perceived boundary between basic and applied fields in biology. It argues that Patrick's position at the Academy, an institution of natural history that was both willing and able to accept money from industrial corporations, is key to understanding her success in, and influence on, the field of river ecology.

Biological Characterization of Water in Damietta Branch of the Nile River, Egypt

BACKGROUND AND OBJECTIVE

Damietta branch is one of the two main branches of the Nile River (Egypt), that often inhabited by many aquatic organisms, which affect and reflect its water characteristics. This study examine the relation between submerged macrophytes, their epiphytic microalgae and bacterial communities as well as the variations in their distribution and species composition with respect to season and location.

MATERIALS AND METHODS

Macrophytes, epiphytes and water samples were collected from 5 sites distributed along Damietta branch. Macrophytes, epiphytes and bacterial indicators of pollution were identified using standard methods.

RESULTS

Three submerged macrophytes (Myriophyllum spicatum, Ceratophyllum demersum L. and Potamogeton crispus) and 191 epiphytic algal taxa dominated by 87 Bacillariophyta and 62 Chlorophyta were recorded with significance seasonal and spatial variations. Myriophyllum spicatum was the most frequent macrophyte (p = 100%) and represent about 100, 100, 97.4 and 64.9% kg DW m-2 of the total collected macrophytes biomass during autumn, winter, spring and summer respectively. The relation between some epiphytic algal species and specific macrophytes was evident and the high organic pollution tolerant algal species like, Melosira granulata, Nitzschia palea, Synedra ulna, Oscillatoria limosa, Microcystis aeruginosa were recorded. Results of bacteriological analysis revealed a significance difference in total viable bacterial counts developed on either 22 or 37°C, total coliform, fecal coliform, fecal streptococci and Escherichia coli attributed to the seasons and sites.

CONCLUSION

The results indicated different relations between macrophytes, epiphytes and bacteria, which is a useful biological tool for characterization of water quality in Damietta branch for different purposes.

The population and production dynamics of benthic algae in an artificial recirculating hard-water stream

An artificial stream has been used to examine the population and production dynamics of benthic algae that grow in the hard-water, nutrient-rich streams of southern England. The channel, made of glass-reinforced plastic is 60 m in circumference and filled with flints ca . 40 mm in diameter. Water 0.3 m deep above the gravel was recirculated at 0.4 m s -1 by an archimedean screw pump. Water was supplied from the aquifer at a rate of 4.2 m 3 h -1 and left the channel from an overflow notch. The chemical composition of the inflow water was relatively constant so that differences between inflow and outflow could be directly related to biological and non-biological changes in the channel. Experiments in the dark showed that calcium carbonate precipitated, reducing calcium concentration and alkalinity to 80% of inflow values. Reactive phosphate precipitated to 28% of inflow concentrations. Preliminary experiments were done in the light between April and December 1976 and detailed experiments between April 1977 and July 1978. The initial colonization phase, in both 1976 and 1977, was dominated by diatoms. Chlorophyll densities increased by over 300-fold in 14 days in 1977. The change in cell numbers of four dominant species, over a 7 day period, confirmed doubling times of less than 2 days. Maximum densities of 500-600 mg chl a m -2 were reached 5 weeks after the dark covers had been removed. The biomass remained constant for the next 14 days and during this phase the rate of silicon uptake was 4.5 g m -2 day -1 . Substantial uptake was also recorded, while the biomass was declining, between the seventh and ninth weeks. Over a period of 60 days, 107 gSi m -2 were taken up and photosynthetic studies indicated that 137 gC m -2 has also been taken up. In terms of biomass this would correspond to 2.3-4.6 g chl a m -2 , whereas the maximum observed biomass was 0.5-0.6 g m -2 . Loss of fine particulate material over 60 days was 0.0558 g of pigment per square metre and sedimentation into the lower layers of the gravel was 0.735 g of pigment per square metre. During weeks 10, 11 and 12 substantial quantities of silicon and phosphorus were released into the water and for a brief period calcium bicarbonate concentrations in the channel approached inflow concentrations. The diatoms of the initial colonization phase were succeeded by a lime-encrusted growth of blue-green and green algae ( Lyngbya kützingii , Chamaesiphon polymorphus and Gongrosira incrustans ) with densities through the winter of 1977 of 200 mg chi a m -2. Cladophora glomerata developed in the autumn of 1977 and its epiphytic algal flora was substantially different from the epilithic flora. Diatoms recurred in large numbers in the spring of 1978. In terms of biomass the principal diatoms were Achnanthes minutissima , Fragilaria virescens , Gomphonema rhombicum , Meridion circulare , Nitzschia fonticola and Synedra ulna . Regression analysis showed that suspended chlorophyll a concentration was not related to benthic algal biomass (estimated as chlorophyll a) but more closely related to benthic diatom volume or dissolved silicon concentration. The seasonal succession of algae in the channel was very similar to that which occurs in local streams. The initial colonization phase by diatoms bears a striking resemblance to the spring outburst of benthic diatoms in local streams. In the channel (and in natural streams, by inference) this succession cannot be controlled by changes in discharge, water velocity or chemical composition of the water. The onset of diatom growth in the spring in streams is probably largely controlled by light intensity. The absence of large numbers of insect larvae, until mid-April, probably allows the biomass-to develop. After April the impact of insect larvae on diatom populations may be considerable.

Use of artificial streams for toxicological research

A review of the literature pertaining to the use of artificial streams as research tools in both toxicant and nontoxicant studies was conducted. This document summarizes that review and provides an assessment of the value of artificial streams in toxicological research. Descriptions are presented of the major types of artificial streams including considerations for the physical design of those streams based on their intended use. Research representative of nontoxicant behavioral, productivity, and trophic relationship studies is summarized to provide a background for the more in-depth discourse on toxicant research. Toxicant research is reviewed in relation to environmental factors such as physical type of artificial stream, light, water, and substrate and experimental conditions including biota tested, method of biota introduction, measured parameters, and toxicant. Comparisons and assessment are presented concerning the use of the appropriate artificial system for addressing various types of toxicant research emphasizing simple vs. complex systems.