Resilience Of Aquatic Ecosystems Research Articles

Assessing Ecosystem Health: A Comparative Study Using Water Quality Index Analysis across Ten Lotic System in the Cross River System

This review synthesizes findings from 10 scientific publications utilizing the weighted arithmetic Water Quality Index (WQI) to assess the status of diverse water bodies (Ikpa River, Lower Enyong Creek, Nwaniba River, Imo River, Etim Ekpo River, Lower Qua Iboe River, Ibeno Estuary, Cross River, Ikot Ebak River and Oboroenyin River) all within the Cross River System. The Analysis reveals that 6 out of 10 sampled water bodies are moderately polluted, while the remaining 4 exhibit slight pollution levels. These findings underscore significant concerns regarding water quality degradation, predominantly attributed to industrial effluents, agricultural runoff and urban contaminants. The WQI proves effective in consolidating multiple water quality parameters into a comprehensive index, facilitating a holistic assessment of pollution levels and guiding management strategies. Moving forward, concerted efforts are imperative to enhance monitoring efforts, implement stringent regulatory measures, and adopt sustainable practices to safeguard freshwater resources globally. This review underscores the urgency of integrated approaches to mitigate pollution and ensure resilience of aquatic ecosystems and public health.

Exploring the nexus between water quality and land use/land cover change in an urban watershed in Uruguay: a machine learning approach.

The expansion of urban areas contributes to the growth of impervious surfaces, leading to increased pollution and altering the configuration, composition, and context of land covers. This study employed machine learning methods (partial least square regressor and the Shapley Additive exPlanations) to explore the intricate relationships between urban expansion, land cover changes, and water quality in a watershed with a park and lake. To address this, we first evaluated the spatio-temporal variation of some physicochemical and microbiological water quality variables, generated yearly land cover maps of the basin adopting several machine learning classifiers, and computed the most suitable landscape metrics that better represent the land cover. The main results highlighted the importance of spatial arrangement and the size of the contributing watershed on water quality. Compact urban forms appeared to mitigate the impact on pollutants. This research provides valuable insights into the intricate relationship between landscape characteristics and water quality dynamics, informing targeted watershed management strategies aimed at mitigating pollution and ensuring the health and resilience of aquatic ecosystems.

Diel temperature signals track seasonal shifts in localized groundwater contributions to headwater streamflow generation at network scale

Groundwater contributions to streamflow sustain aquatic ecosystem resilience; streams without significant groundwater inputs often have well-coupled air and water temperatures that degrade cold-water habitat during warm low flow periods. Widespread uncertainty in stream-groundwater connectivity across space and time has created disparate predictions of energy and nutrient fluxes across headwater networks, hindering predictions of cold-water habitat resilience under climate change scenarios. Recently, annual paired air and water temperature signals have been harnessed to indicate stream water thermal sensitivity and the dominance of deep versus shallow groundwater influence, although the utility of diel air–water temperature signal metrics for hydrologic inference has remained unexplored. Here we analyzed two consecutive years of locally paired, air–water temperature data from 47 headwater stream sites in the Catskill Mountains, New York, USA, and discovered characteristic seasonal patterns in diel temperature signal sinusoid metrics (amplitude ratio, phase lag, and mean ratio) driven by shifts in streamflow generation mechanisms and stream network position. Hydrologic interpretations of observed patterns were supported by stream heat budget model scenarios and additional analysis of paired air–water temperature data from two streams in Shenandoah National Park, Virginia, USA, with well characterized stream-groundwater connectivity. We found that within smaller tributaries, streamflow generation transitions from runoff to groundwater dominance were driven by hillslope drying during seasonal periods of lower precipitation. This was evidenced by significant correlations (p < 0.01) between daily water:air temperature signal amplitudes (non-linear decreases of ∼ 50 %) and derived baseflow index at 22 of the 28 sites, indicating enhanced local groundwater influence on streamflow promotes decoupling of diel air–water temperature signals. Additionally, ratios between daily water:air temperature signal means were lower in tributaries (∼0.68) when compared to main-stem (∼0.8) sites, increasing linearly throughout the observational period. In conceptual stream heat budget models, groundwater inflow had minimal effects on daily phase lags (∼0.2 hr), but increases in fractional groundwater discharge (0–50 %) depressed daily amplitude (∼20 % to 50 %) and mean ratios (∼15 %), supporting the sensitivity of daily metrics to interpreted changes in seasonal groundwater contributions to streamflow. During observational periods (i.e., April through October 2021 and 2022), significant differences (p < 0.01) between tributary and main-stem air–water metrics occurred when baseflow contributions were highest (∼0.93 vs. ∼ 0.68), as sites lower in the network had daily temperature metrics dominated by stream channel thermal inertia, rather than local groundwater connectivity, showing enhanced air–water diel signal coupling during warmer, drier periods. Divergent air temperature coupling across the network was interpreted as being driven by distance from local groundwater source zones, as additional lateral groundwater inflows do not contribute a meaningful fraction to channel discharge lower in the network. Given the growing footprint of stream temperature observations, diel air–water temperature signals can provide distributed metrics sensitive to upstream groundwater discharge. Consequently, these metrics can support ongoing efforts by resource managers and researchers seeking to forecast the resilience of cold-water habitat to climate warming and changing precipitation regimes in mountain headwater streams.

Investigating the Acute Cardiac Restoration for Rescuing Daphnia Magna Stressed from Environmental Disturbances Using Antioxidants

Freshwater ecosystems face a significant challenge with the pervasive oxidative stress induced by pollution with global warming and ozone layer depletion. Amidst this concern, various companies assert their products' antioxidant properties to restore them to normal. Elevated oxygen species, identified as a pivotal contributor to heightened cardiac functionality, particularly impact crucial organisms such as Daphnia Magna within aquatic environments. This study proposes a proactive approach to mitigate oxidative stress by introducing antioxidants into water, aiming to offer insights into fortifying the health and resilience of aquatic ecosystems confronting oxidant escalation. The primary. Objective: of this research was to assess the impact of commercially available "antioxidants" on the heart rates of Daphnia Magna during the recovery phase from oxidative stress. As. Methods: the investigation unfolds in two phases: an initial toleration study to gauge Daphnia reactions to selected chemicals, followed by a recovery study where Daphnia was exposed to the oxidizing agent H2O2 for 30 minutes and subsequently immersed in antioxidant solutions as well as in culturing water for a comparison purpose. The central methodology revolves around comparing the heart rates of Daphnia exposed to H2O2 and analyzing their recovery in different solutions. Heart rate serves as a chosen metric due to its reliability as an indicator of stress and its non-invasive measurement, ensuring minimal harm to the organisms. A newly defined parameter, relative restoration power (RRP) as mean heartbeat %change, was estimated and compared. Our Conclusions: revealed that certain antioxidants exhibit a modest yet noteworthy impact on enhancing the recovery of Daphnia magna. Consequently, the study concludes that improving antioxidant uptake or finding less intrusive delivery methods may be viable strategies to mitigate oxidative stress in Daphnia magna.

Linking ecological niches to bacterial community structure and assembly in polluted urban aquatic ecosystems.

Bacterial communities play crucial roles in the functioning and resilience of aquatic ecosystems, and their responses to water pollution may be assessed from ecological niches. However, our understanding of such response patterns and the underlying ecological mechanisms remains limited. In this study, we comprehensively investigated the effects of water pollution on the bacterial structure and assembly within different ecological niches, including water, sediment, submerged plant leaf surfaces, and leaf surfaces, using a 16S high-throughput sequencing approach. Ecological niches had a greater impact on bacterial community diversity than pollution, with a distinct enrichment of unique dominant phyla in different niches. This disparity in diversity extends to the bacterial responses to water pollution, with a general reduction in α-diversity observed in the niches, excluding leaf surfaces. Additionally, the distinct changes in bacterial composition in response to pollution should be correlated with their predicted functions, given the enrichment of functions related to biogeochemical cycling in plant surface niches. Moreover, our study revealed diverse interaction patterns among bacterial communities in different niches, characterized by relatively simply associations in sediments and intricate or interconnected networks in water and plant surfaces. Furthermore, stochastic processes dominated bacterial community assembly in the water column, whereas selective screening of roots and pollution events increased the impact of deterministic processes. Overall, our study emphasizes the importance of ecological niches in shaping bacterial responses to water pollution. These findings improve our understanding of the complicated microbial response patterns to water pollution and have ecological implications for aquatic ecosystem health.

Unleashing the power of acetylacetone: Effective control of harmful cyanobacterial blooms with ecological safety

Harmful algal blooms resulting from eutrophication pose a severe threat to human health. Acetylacetone (AA) has emerged as a potential chemical for combatting cyanobacterial blooms, but its real-world application remains limited. In this study, we conducted a 42-day evaluation of AA's effectiveness in controlling blooms in river water, with a focus on the interplay between ecological community structure, organism functional traits, and water quality. At a concentration of 0.2 mM, AA effectively suppressed the growth of Cyanobacteria (88 %), Bacteroidia (49 %), and Alphaproteobacteria (52 %), while promoting the abundance of Gammaproteobacteria (5.0 times) and Actinobacteria (7.2 times) that are associated with the degradation of organic matter. Notably, after dosing of AA, the OD680 (0.07 ± 0.02) and turbidity (8.6 ± 2.1) remained at a satisfactory level. AA induced significant disruptions in two photosynthesis and two biosynthesis pathways (P < 0.05), while simultaneously enriching eight pathways of xenobiotics biodegradation and metabolism. This enrichment facilitated the reduction of organic pollutants and supported improved water quality. Importantly, AA treatment decreased the abundance of two macrolide-related antibiotic resistance genes (ARGs), ereA and vatE, while slightly increased the abundance of two aminoglycoside-related ARGs, aacA and strB. Overall, our findings establish AA as an efficient and durable algicide with favorable ecological safety. Moreover, this work contributes to the development of effective strategies for maintaining and restoring the health and resilience of aquatic ecosystems impacted by harmful algal blooms.

Fishing triggers trophic cascade in terms of variation, not abundance, in an allometric trophic network model

Trophic cascade studies often rely on linear food chains instead of complex food webs and are typically measured as biomass averages, not as biomass variation. We study trophic cascades propagating across a complex food web including a measure of biomass variation in addition to biomass average. We examined whether different fishing strategies induce trophic cascades and whether the cascades differ from each other. We utilized an allometric trophic network (ATN) model to mechanistically study fishing-induced changes in food web dynamics. Different fishing strategies did not trigger traditional, reciprocal trophic cascades, as measured in biomass averages. Instead, fishing triggered a variation cascade that propagated across the food web, including fish, zooplankton and phytoplankton species. In fisheries that removed a large amount of top-predatory and cannibalistic fish, the biomass oscillations started to decrease after fishing was started. In fisheries that mainly targeted large planktivorous fish, the biomass oscillations did not dampen but slightly increased over time. Removing species with specific ecological functions might alter the food web dynamics and potentially affect the ecological resilience of aquatic ecosystems.

Impacts of sugarcane (Saccharum sp.) soil and fertiliser management practices on nutrients and sediment in plot-scale runoff from simulated rainfall

Runoff of nutrients and sediment from agricultural catchments can impair the health and resilience of aquatic ecosystems in receiving waterbodies. The sugarcane (Saccharum sp.) industry in Australia has adopted strategies to improve farm runoff water quality. Rainfall simulation trials were conducted to quantify the relative effectiveness of some sugarcane soil and fertiliser management practices on nutrient and sediment loss in runoff. The trials were conducted within the Herbert River catchment in the Wet Tropics of Queensland. Simulated rainfall (~76 mm h–1) was used to generate runoff from 1.70 m2 plots in first ratoon sugarcane on well-drained Ferralsols at Abergowrie and from 1.55 m2 plots in sugarcane planted into furrows and mound beds on an imperfectly drained Luvisol at Trebonne. At Abergowrie, the practices studied were; crop residue retention after harvest (green cane trash blanketing), applying a liquid rather than a granular fertiliser, and applying fertiliser to the sub-surface rather than to the surface on ratoon phase sugarcane. At Trebonne, sub-surface fertiliser placement was studied on plant cane and after varying amounts of time and repeated rainfall after fertiliser application. Comparisons were made with a similar study in plant cane at Macknade. Particulate nitrogen (N), particulate phosphorus (P), and suspended sediment losses in runoff were reduced by crop residue retention, which was expected. Dissolved inorganic N (DIN) loads (but not concentrations) were also reduced by residue retention. Dissolved inorganic N and filterable reactive P concentrations in runoff were reduced by sub-surface fertiliser placement, as expected, and by the liquid fertiliser that was studied. In contrast to expectations, DIN concentrations increased in mound beds (but not in furrows) with increasing time and rainfall after fertiliser application. The increase was attributed mainly to increases in soil mineral N and runoff volume. The practice that was most effective at reducing DIN loads in runoff (64–85% reduction) was sub-surface rather than surface placement of fertiliser.

Resilience of terrestrial and aquatic fauna to historical and future wildfire regimes in western North America.

Wildfires in many western North American forests are becoming more frequent, larger, and severe, with changed seasonal patterns. In response, coniferous forest ecosystems will transition toward dominance by fire‐adapted hardwoods, shrubs, meadows, and grasslands, which may benefit some faunal communities, but not others. We describe factors that limit and promote faunal resilience to shifting wildfire regimes for terrestrial and aquatic ecosystems. We highlight the potential value of interspersed nonforest patches to terrestrial wildlife. Similarly, we review watershed thresholds and factors that control the resilience of aquatic ecosystems to wildfire, mediated by thermal changes and chemical, debris, and sediment loadings. We present a 2‐dimensional life history framework to describe temporal and spatial life history traits that species use to resist wildfire effects or to recover after wildfire disturbance at a metapopulation scale. The role of fire refuge is explored for metapopulations of species. In aquatic systems, recovery of assemblages postfire may be faster for smaller fires where unburned tributary basins or instream structures provide refuge from debris and sediment flows. We envision that more‐frequent, lower‐severity fires will favor opportunistic species and that less‐frequent high‐severity fires will favor better competitors. Along the spatial dimension, we hypothesize that fire regimes that are predictable and generate burned patches in close proximity to refuge will favor species that move to refuges and later recolonize, whereas fire regimes that tend to generate less‐severely burned patches may favor species that shelter in place. Looking beyond the trees to forest fauna, we consider mitigation options to enhance resilience and buy time for species facing a no‐analog future.

Non-additive effects of foundation species determine the response of aquatic ecosystems to nutrient perturbation.

Eutrophication is a persistent threat to aquatic ecosystems worldwide. Foundation species, namely those that play a central role in the structuring of communities and functioning of ecosystems, are likely important for the resilience of aquatic ecosystems in the face of disturbance. However, little is known about how interactions among such species influence ecosystem responses to nutrient perturbation. Here, using an array (N=20) of outdoor experimental pond ecosystems (15,000L), we manipulated the presence of two foundation species, the macrophyte Myriophyllum spicatum and the mussel Dreissena polymorpha, and quantified ecosystem responses to multiple nutrient disturbances, spread over two years. In the first year, we added five nutrient pulses, ramping up from 10 to 50μg P/L over a 10-week period from mid-July to mid-October, and in the second year, we added a single large pulse of 50μg P/L in mid-October. We used automated sondes to measure multiple ecosystems properties at high frequency (15-minute intervals), including phytoplankton and dissolved organic matter fluorescence, and to model whole-ecosystem metabolism. Overall, both foundation species strongly affected the ecosystem responses to nutrient perturbation, and, as expected, initially suppressed the increase in phytoplankton abundance following nutrient additions. However, when both species were present, phytoplankton biomass increased substantially relative to other treatment combinations: non-additivity was evident for multiple ecosystem metrics following the nutrient perturbations in both years but was diminished in the intervening months between our perturbations. Overall, these results demonstrate how interactions between foundation species can cause surprisingly strong deviations from the expected responses of aquatic ecosystems to perturbations such as nutrient additions.

Building and Restoring a Healthy Aquatic Ecosystem

Cities are suffering from more floods than ever, causing huge loss of life and property. The reason is that modern cities often lack resilience to the uncertainty of natural disasters. Aquatic ecosystems on the whole are unhealthy. As global climate change intensifies, aquatic ecosystems are facing more severe challenges. The author explains the necessity to cope with water-related issues holistically, and contends that aquatic ecosystems should be evaluated, protected, and restored based on the understanding of ecosystem services they provide. The water security patterns at macro, medium, and micro levels help improve the resilience of aquatic ecosystems, restore the aquatic and hydrophytic habitats, reconstruct the harmony and symbiosis between water systems and humans, and nourish the health and prosperity of ecological civilization.

Effects of microplastics and their adsorption of cadmium as vectors on the cladoceran Moina monogolica Daday: Implications for plastic-ingesting organisms

As pervasive and resilient contaminants, microplastics (MPs) have potential to interact with the toxicity of metals through adsorption on the surface. In this study, we focused on 7-day adsorption of cadmium (5, 10 μg/L) to aged polyethylene-MPs particles (300 μg/L), and further examined 21-day chronic effects of MPs and MPs-Cd on cladoceran Moina monogolica Daday. The effects criteria selected were physiological changes (e.g., parental survival time, somatic growth and reproductive parameters) and nutritional profiles in offspring. Exposure of M. monogolica to both MPs and MPs-Cd can impair the development, reproductive output and fecundity across treatment groups, ultimately leading to parental mortality and poor nutritional status in progeny. Importantly, MPs with adsorbed Cd showed greater adverse dose-dependent effects than bare MPs, likely due to the mechanisms of physico-chemical interactions related to the Cd release from MPs-Cd inside organisms. MPs can pose not only a direct harm to the organisms but also an indirect hazard via adsorption as “transport vector”, having implications for the function and resilience of aquatic ecosystems. Our findings experimentally highlight the importance of characterizing chemical profiling of contaminants adsorbed to field plastics in order to better assess environmentally relevant risks associated with MPs and metals in coastal areas.

The Shewanella genus: ubiquitous organisms sustaining and preserving aquatic ecosystems.

The Gram-negative Shewanella bacterial genus currently includes about 70 species of mostly aquatic γ--proteobacteria, which were isolated around the globe in a multitude of environments such as surface freshwater and the deepest marine trenches. Their survival in such a wide range of ecological niches is due to their impressive physiological and respiratory versatility. Some strains are among the organisms with the highest number of respiratory systems, depending on a complex and rich metabolic network. Implicated in the recycling of organic and inorganic matter, they are important components of organism-rich oxic/anoxic interfaces, but they also belong to the microflora of a broad group of eukaryotes from metazoans to green algae. Examples of long-term biological interactions like mutualism or pathogeny have been described, although molecular determinants of such symbioses are still poorly understood. Some of these bacteria are key organisms for various biotechnological applications, especially the bioremediation of hydrocarbons and metallic pollutants. The natural ability of these prokaryotes to thrive and detoxify deleterious compounds explains their use in wastewater treatment, their use in energy generation by microbial fuel cells and their importance for resilience of aquatic ecosystems.

Recovery of acidified Sudbury, Ontario, Canada, lakes: a multi-decade synthesis and update

The Sudbury region of northeastern Ontario, Canada, provides one of the world’s best examples of the resilience of aquatic ecosystems after reductions in atmospheric contaminant deposition. Thousands of lakes around the Sudbury metal smelters were badly damaged by acid deposition. Lakes closest to the smelters were also contaminated by metal particulates. However, large reductions in atmospheric SO2and metal emissions starting in the early 1970s have led to widespread chemical improvements in these lakes, and recovery has been observed for various aquatic biota. Studies of Sudbury-area lakes are advancing our understanding of chemical and biological lake recovery; however, recovery is a complicated process and much remains to be learned. Biological recovery has often been slow to follow chemical recovery, and it has become apparent that the recovery of lakes from acidification is closely linked to interactions with other large-scale environmental stressors like climate change and Ca declines. Thus, in our multiple-stressor world, recovery may not bring individual lakes back to their exact former state. However, with time, substantial natural biological recovery toward typical lake communities can be reasonably expected for most but not necessarily all biota. For organisms with limited dispersal ability, particularly fish, human assistance may be necessary to re-establish typical communities. In lakes where food webs have been severely altered, re-establishment of typical diverse fish communities may in fact be an important element aiding the recovery of other important components of aquatic ecosystems including zooplankton and benthic macroinvertebrates. In the lakes closest to the smelters, where historically watersheds as well as lakes were severely damaged, the recovery of aquatic systems will be closely linked to ongoing terrestrial recovery and rehabilitation, particularly through the benefits of increased inputs of terrestrially derived organic matter. The dramatic lake recovery observed in the Sudbury area points to a brighter future for these lakes. However, continued monitoring will be needed to determine future changes and help guide the management and protection of Sudbury-area lakes in this multiple-stressor age.

Looking beyond fishing: Conservation of keystone freshwater species to support a diversity of socio‐economic values

Abstract Keystone species can provide a focal point for designing conservation and management strategies that protect a diversity of social–ecological values in aquatic ecosystems; however, to avoid bias towards a subset of values associated with a single activity, such as fishing, stakeholder consultations must cover a spectrum of social perspectives. Using the Murray crayfish (Euastacus armatus) as a model, this study explored how Aboriginal Traditional Owners, landowners, tourism businesses, scientific researchers, non‐governmental organizations, and government agencies valued this threatened freshwater species across south‐east Australia. Qualitative methods revealed that E. armatus is a culturally significant species, targeted for fishing, but is also valued for a range of non‐extractive reasons that support social–ecological linkages between people and freshwater ecosystems. Perceived as an iconic species by most stakeholders, there was general support for E. armatus to be used as a flagship for conserving a spectrum of social–ecological values (e.g. Aboriginal Traditional Owner totem species), attached to their local freshwater ecosystems. Although stakeholders were conflicted over whether fishing should continue, four themes emerged on how to develop more equitable and effective conservation and management strategies: increased public education, co‐management with non‐government stakeholders, federal government co‐ordination, and spatial protection of critical areas. The protection of aquatic species in ways that support their full range of cultural, economic, and ecological values will require more bottom‐up (i.e. stakeholder‐led) approaches to conservation and management design. Broader stakeholder engagement and co‐management should reduce perceptions that local stakeholders are isolated from management processes, while increasing the capacity and confidence of managers to implement strategies that bolster both the social and ecological resilience of aquatic ecosystems.

Effective restoration of aquatic ecosystems: scaling the barriers

The focus of ecosystem restoration has recently shifted from pure rehabilitation objectives to both improving ecological functioning and the delivery of ecosystem services. However, these different targets need to be integrated to create a unified, synergistic, and balanced restoration approach. This should be done by combining state‐of‐the‐art knowledge from natural and social sciences to create manageable units of restoration that consider both the temporal and multiple spatial scales of ecosystems, legislative units, and policy agendas. Only by considering these aspects combined can we accomplish more cost‐efficient restoration resulting in resilient ecosystems that provide a wealth of ecosystem services and the possibility for sustainable economic development in the future. We propose a novel conceptual framework that will yield more effective ecosystem restoration: the Operational Restoration Unit. This is based on scale‐dependent restoration actions that can adhere easily to the relevant environmental legislation, encompass the spatial and temporal resilience of aquatic ecosystems, and consider the sum of human pressures acting on water bodies. This opens up possibilities for an effective integration of the restoration agenda into the delivery of major policy objectives of economic growth, regional development, and human security. WIREs Water 2017, 4:e1190. doi: 10.1002/wat2.1190This article is categorized under: Water and Life &gt; Conservation, Management, and Awareness Human Water &gt; Water Governance

Sedimentation in dryland river waterholes: a threat to aquatic refugia?

In dryland river systems subject to prolonged low and no flow periods, waterholes, or sections of river channel that are deep relative to the rest of the channel and that retain water for longer periods of no flow, provide refugia for aquatic biota and hence are critical to the resilience of aquatic ecosystems. This study examined physical, chemical and bio-stratigraphy in refugial waterholes situated along four distributaries of the Lower Balonne River system in semi-arid Australia. In doing so we reconstructed environmental histories for the waterholes, calculated how sedimentation rates have changed in response to land use change over the past two centuries, and assessed whether they are threatened by increased sedimentation through potential effects on waterhole depth and hence persistence times and habitat quality. Our study found that sedimentation rates have increased substantially since European settlement, most likely in response to removal of groundcover by grazers. The increased sediment accumulation rates are estimated to have reduced persistence times during low and no flow periods of the waterholes by 2–4 months. Despite evidence from other similar systems in Australia that increased influx of sediment coincided with loss of submerged macrophytes, stratigraphic records of preserved pollen and diatoms did not provide consistent evidence of biotic or habitat quality changes within the waterholes associated with European settlement.

Longitudinal trends in water chemistry and phytoplankton assemblage downstream of the Riverview WWTP in the Upper Olifants River

Aquatic ecosystem resilience is an integral part of sustainable development for numerous economic, social and culture reasons. The regulation of nutrient inputs into rivers and the capacity of rivers to retain and transform excess nutrients is an important aspect of ecological resilience of aquatic systems and the management of river water quality. The primary production by algae in the selected Olifants River reach, dominated by a cobble or bedrock substrate, had been highly effective in assimilating phosphate concentrations (PO4) during low river flow regimes in winter months. However, the assimilation of PO4 by phytoplankton was temporary and caused changes in the phytoplankton community structure, reducing the diversity and degrading habitat downstream. The ecological impact of the Riverview wastewater treatment plant (WWTP) was detectable over a distance of 40km downstream from the plant. The chloride concentration below the WWTP in July during low flow regimes decreased from 33mgL−1 to 21mgL−1 at 0.1–40km downstream from the WWTP. During benthic algae mat senescence and flood disturbance during the high flows of the summer months, displaced nutrients accumulated in these filamentous algae mats and was then displaced further downstream to Lake Loskop where they fuelled the development of cyanobacterial blooms in the riverine zone of this man-made lake.

Strengthening the link between climate, hydrological and species distribution modeling to assess the impacts of climate change on freshwater biodiversity

To understand the resilience of aquatic ecosystems to environmental change, it is important to determine how multiple, related environmental factors, such as near-surface air temperature and river flow, will change during the next century. This study develops a novel methodology that combines statistical downscaling and fish species distribution modeling, to enhance the understanding of how global climate changes (modeled by global climate models at coarse-resolution) may affect local riverine fish diversity. The novelty of this work is the downscaling framework developed to provide suitable future projections of fish habitat descriptors, focusing particularly on the hydrology which has been rarely considered in previous studies. The proposed modeling framework was developed and tested in a major European system, the Adour–Garonne river basin (SW France, 116,000km2), which covers distinct hydrological and thermal regions from the Pyrenees to the Atlantic coast. The simulations suggest that, by 2100, the mean annual stream flow is projected to decrease by approximately 15% and temperature to increase by approximately 1.2°C, on average. As consequence, the majority of cool- and warm-water fish species is projected to expand their geographical range within the basin while the few cold-water species will experience a reduction in their distribution. The limitations and potential benefits of the proposed modeling approach are discussed.

The periphyton as a multimetric bioindicator for assessing the impact of land use on rivers: an overview of the Ardières-Morcille experimental watershed (France)

Developing new biological indicators for monitoring toxic substances is a major environmental challenge. Intensive agricultural areas are generally pesticide-dependent and generate water pollution due to transfer of pesticide residues through spray-drift, run-off and leaching. The ecological effects of these pollutants in aquatic ecosystems are broad-ranging owing to the variety of substances present (herbicides, fungicides, insecticides, etc.). Biofilms (or periphyton) are considered to be early warning systems for contamination detection and their ability to reveal effects of pollutants led researchers to propose a variety of methods to detect and assess the impact of pesticides. The present article sought to provide new insights into the ecological significance of biofilm microbial communities and to discuss their bioindication potential for water quality and land use by reporting on 4 years of research performed on the French Ardieres-Morcille experimental watershed (AMEW). Various biological indicators have been applied during several surveys on AMEW, allowing the characterisation of (i) the structure and diversity of biofilm communities [community level finger printing (CLFP) such as PCR–DGGE and pigment classes], (ii) functions associated with biofilm [community level physiological profiles (CLPP) such as extracellular enzymes, pesticides biodegradation or carbon sources biodegradation] and (iii) biofilm tolerance assessment (pollution-induced community tolerance, PICT) of the main contaminant in the AMEW (copper and diuron). Approaches based on CLFPs and PICT were consistent with each other and indicated the upstream–downstream impact due to the increasing land use by vineyards and the adaptation of algal and bacterial communities to the pollution gradient. CLPPs gave a contrasted bioindication because some parameters (most of the tested extracellular enzymes activities) did not detect a pollution gradient. Such CLPPs, CLFPs and PICT methods applied to biofilm could constitute the basis for a relevant in situ assessment both for chemical effects and aquatic ecosystem resilience.