Planktonic Index Research Articles

Depositional environment and stratigraphic framework of the NS- 1 well, Coastal Swamp Depobelt, Niger Delta Basin: a foraminiferal perspective

A comprehensive analysis of 102 ditch-cutting samples from the NS-1 well in Leuma Field, Coastal Swamp Depobelt, Niger Delta Basin, covering depths from 4730 ft to 7790 ft, is presented. Lithologic descriptions revealed eleven lithostratigraphic sub-units within the transitional-paralic sequence of the Agbada Formation, comprising alternating sandstone and shale. The foraminiferal analysis identified 58 species: 14 planktonic, 26 calcareous benthic and 18 agglutinated benthic. Key planktonic index species such as Globigerinoides sp. and Globorotaliacontinuosa indicates a Middle to Late Miocene age. The biozonation correlates with the Blow (1969) Scheme (N7- N9/N10/N11) placing the intervals within the Middle Miocene to Late Miocene epochs. The depositional environment transitioned from Coastal Deltaic to Inner Neritic and Middle Neritic, suggesting a shallow marine setting influenced by a warm, humid climate. The presence of calcareous foraminifera supports a shallow marine deposition above the carbonate compensation depth. This study provides valuable insights into the sedimentological, stratigraphic, and paleoenvironmental history of the NS-1 well during the Miocene.

A Historical Plankton Index: Zooplankton abundance in the North Sea since 800 CE

The North Sea region boasted one of the world’s most important fisheries for many centuries. Climate directly and indirectly influences the development and survival of many important pelagic fish in the North Sea ecosystem. One indirect influence is the food availability in the form of phyto- and zooplankton abundance, which is strongly controlled by environmental factors. One of these environmental factors is local sea surface temperatures. A negative correlation between zooplankton abundance and sea surface temperature is well established for the epeiric sea on the European continental shelf. Continuous temporal observations of North Sea zooplankton production only exist since 1958. Therefore we developed a Historical Plankton Index (HPI) from 800 CE onwards to extend our record of temperature-driven zooplankton abundance in the North Sea over a multi-centennial time scale. For this we used the North Atlantic temperature reconstructions and associations between zooplankton abundance and contemporary sea surface temperatures established applying a General Additive Modelling (GAM) approach. We then examined the association between the HPI and historical landings from the Dutch commercial herring fishery in the 17th century to test the utility of our HPI. We examine the potential influence of food availability (in terms of zooplankton abundance) on the fishery, the evolution of which is often only considered in terms of human influences such as conflict, fishing gear and demand for fish as a commodity. We find that under certain conditions the HPI can explain 20% of the variability in Dutch herring landings. This highlights the importance of developing long-term and large-scale indices of natural marine ecosystem dynamics to understand the historical fortunes of the commercial fishing industry. The results are directly relevant to the United Nations’ sustainable development goal 14 – life below water.

Phytoplankton Community Integrity Index (PCII) – A potential supplementary tool for evaluating nutrient enrichment status of Hong Kong marine waters

Diagnosis of eutrophication requires evidence of disturbance to the balance of organisms. We describe a tool, the Plankton Community Integrity Index (PCII), derived from the Plankton Index (PI) for tracking change in the seasonal patterns of abundance of diatom and dinoflagellate lifeforms when plotted in state space. The tool uses a nutrient-minimum reference period to interpret PCII values as status indicators, with values close to 1 indicating “High” status and 0.6 a Biological Water Quality Criterion (BioWQC) target set at the “Fair”/“Good” status boundary. It has been applied to Hong Kong marine waters, using data from monthly samples from 1995 through 2021. A preliminary analysis, required for the PI method, confirmed monsoonal seasonality in the diatom lifeform. In 5 of the 9 water bodies examined, PCII time series correlated with those of Total Inorganic Nitrogen (TIN). Since 2020, all Water Control Zones met the operationally defined BioWQC target.

Development and testing of a planktonic index of biotic integrity (P-IBI) for Lake Fuxian, China.

Lake Fuxian has the largest reserves of high-quality water resources in China, and understanding its ecological health status is the basis of its environmental protection. Based on a seasonal field investigation of the plankton community, we established a planktonic index of biotic integrity (P-IBI) evaluation system to assess the lake's ecosystem health. The biological integrity of Lake Fuxian was relatively good during winter and spring, but gradually deteriorated from summer to autumn. Areas with poor biological integrity were mainly distributed near tourist attractions along the lake's west coast. Redundancy analysis (RDA) was performed to explore the relationships between the P-IBI, its selected indicators, and the environmental variables. Water temperature (WT), pH, ammonia nitrogen (NH3-N), and dissolved oxygen (DO) significantly influenced the P-IBI and its selected indicators. NH3-N and DO were significantly positively correlated with the P-IBI, indicating that it could be used as a water quality indicator to indirectly reflect lake biological integrity. We demonstrated that the P-IBI can effectively reflect temporal and spatial variations of biological integrity and could be used as a potential tool to evaluate Lake Fuxian ecosystem health.

At what scale should we assess the health of pelagic habitats? Trade-offs between small-scale manageable pressures and the need for regional upscaling

Major planktonic lifeforms such as diatoms, dinoflagellates, meroplankton and holoplankton have recently shown significant and alarming changes in abundance - mainly downwards trends - around the northwest European shelf. This has major implications for food web connections and for ecosystem services including seafood provision and carbon storage. We have quantified these changes in abundance for 2006–2019/20 using a Plankton Index (PI) and show that the scale of spatial aggregation is critical to the ability of the PI to detect change, understand causal mechanisms, and provide advice to policymakers.We derived PI statistics in the Celtic and North Seas from data from the Continuous Plankton Recorder survey offshore and England’s Environment Agency inshore using three sets of spatial units: (i) Ecohydrodynamic (EHD) units based on hydro-biogeochemical modelling, (ii) ‘COMP4′ areas based on cluster analysis of satellite data for chlorophyll a and primary productivity, and (iii) English coastal and estuarine Water Framework Directive (WFD) waterbodies. For the largest scale areas, the EHD units (median size 87,000 km2), we find greater change in plankton communities than previously reported, suggesting that these shifts have continued and possibly intensified in recent years. The smaller-scale COMP4 areas (median size 6,700 km2) appear to encompass more spatially coherent changes in plankton community structure than EHD units; at this scale PI values indicate community shifts of greater magnitude. These COMP4 areas provide a reasonable compromise scale for linking offshore plankton communities to large-scale drivers of change such as climate warming. For inshore plankton communities, larger changes are detected at the smaller WFD waterbody scale (median size 11 km2). This scale allows direct links to coastal management measures and is more suitable for linking to land-sourced pressures.Recent integration of the UK’s OSPAR and WFD plankton monitoring data management enables the exploration of changes across spatial scales to develop a holistic understanding of ecosystem health. Regional-sea scale derivation of the PI for coastal waters provides a clear indication that changes are occurring, at least in phytoplankton communities, while localised PI statistics offer an additional layer of information which can be an important tool for linking to localised drivers of change including coastal anthropogenic pressures. Broadscale inshore zooplankton monitoring is needed to evaluate the coastal plankton community holistically; zooplankton communities offshore are also changing but these changes cannot currently be linked to coastal processes. Layering information across spatial scales provides a breadth of system-level understanding beyond what any one typology can provide.

Impact of agricultural practices on ecosystem health of lagoons: a case study of the Keta Lagoon Complex in Ghana, West Africa

The paper reports on the current ecological health of the Keta Lagoon Complex by analyzing a suite of physical, chemical, and biological environmental conditions prevailing within it. Results are discussed in relation to the main human activity (i.e., agriculture) prevailing in its catchment. The current water quality of the lagoon has declined compared to data collected 20years ago with elevated levels in parameters such as nitrate, phosphate, turbidity, and temperature. Secchi disk depth, salinity, and dissolved oxygen levels in the lagoon have decreased. More than 60% of the total area of the lagoon is predicted to be currently unsuitable to support aquatic life. The Carlson's TSI estimated for the various zones of the lagoon ranged between 72.40 and 80.61 depicting a highly eutrophic lagoon, with about 90% of the total area studied confirmed to be experiencing some degree of eutrophication. The plankton index of biotic integrity also yielded high values of between 3 and 6 in most areas of the lagoon, thereby affirming the poor health of the lagoon. The diversity of phytoplankton and benthic macroinvertebrate species in the lagoon has reduced significantly in the last two decades with about 11 genera of phytoplankton missing in the present study. Benthic macroinvertebrate assemblage richness, evenness, and diversity have decreased from 3.6, 2.0, and 5.8 in 2008 to 1.2, 0.8, and 1.7 respectively, in the present study. Overall, the health of the Keta Lagoon remains poorer and continues to decline with no signs of recovery.

Determining Critical Thresholds of Environmental Flow Restoration Based on Planktonic Index of Biotic Integrity (P-IBI): A Case Study in the Typical Tributaries of Poyang Lake.

Hydropower construction and climate change have aggravated river hydrological changes, which have reduced the water flow regime in the Ruhe River Basin. The reduced flow of the river seriously affected the water supply of nearby residents and the operation of the river ecosystem. Therefore, in order to alleviate the contradiction between water use for hydropower facilities and environmental water use, the urgent need is to explore the ecological flow-threshold of rivers. This study took the Fuhe River Basin as the research object, and summarized the monitoring data of eight hydrological stations from recent decades. Based on this, we explored the response law of P-IBI and flow, a tool to quickly measure the health of the ecosystem. Through the response relationship between alterations in environmental factors of the river and phytoplankton index of biotic integrity (P-IBI), it was determined that environmental flow was the dominant influencing factor of P-IBI. According to P-IBI, the threshold of environmental discharge in the Fuhe River was limited to 273~826.8 m3/s. This study established a regulatory framework for the river flow of large rivers by constructing P-IBI and determining the critical thresholds of environmental flow by constraining the constitution. These results provide a theoretical basis for better planning and improvement of river ecosystem restoration and river utilization.

Ecological Health Status of the Yitong River, China, Assessed with the Planktonic Index of Biotic Integrity

The Yitong River Basin is the main northern urban river basin in China, and its ecological health has become an important issue of public interest. In 2021, the plankton community and main water quality parameters of the Yitong River were monitored quarterly. An evaluation system was established based on the Planktonic Index of Biotic Integrity (P–IBI) to assess the spatial and temporal variability in river health. To verify the feasibility of the P–IBI, its assessment results were compared with those of the water quality index (WQI), and the main factors affecting the P–IBI in different seasons were analyzed using correlation analysis between P–IBI metrics and environmental factors. Seasonal comparisons showed that most sampling sites exceeded the “moderate” level in spring and autumn, followed by winter. The worst assessment results occurred in summer. Urban river reaches were more polluted than reaches in rural areas. Regarding driving factors, hydraulic effects on the P–IBI in spring and autumn were significantly stronger than other environmental factors. In summer and winter, special attention should be paid to the input of nitrogen compounds and organic pollutants. Trends based on the P–IBI and the WQI differed in winter, but site patterns were consistent between both indices. The results provide a theoretical basis and data support for the health maintenance of the Yitong River.

Development and validation of the planktonic index of biotic integrity (P-IBI) for Qin River, a main tributary of the Yellow River in China.

To evaluate the ecosystem health of Qin River, a main tributary of the Yellow River, a planktonic index of biotic integrity (P-IBI) that includes phytoplankton and zooplankton was established based on five metrics using a dataset covering 61 sampling sites in Qin River and its largest tributary the Dan River from October to November 2020. First, an index based on land use pattern and water quality was constructed to select reference sites and impaired sites. Then, five of an initial 38 candidate metrics (phytoplankton density, Palmer algal genus pollution index, zooplankton biomass/phytoplankton biomass, zooplankton Margalef richness index, and zooplankton Simpson diversity index) were selected to establish P-IBI based on their ranges, sensitivity, and redundancy. Finally, five statuses (excellent, good, fair, poor, and very poor) were classified by ratio score method on the basis of their final P-IBI scores. Sites with "excellent and good" and "poor and very poor" status accounted for 26.2% and 49.2%, respectively. "Very poor" sites were mainly located in the Dan River, and "poor" sites were mainly located in the middle reach of the Qin River and upper-middle reach of the Dan River in Jincheng region. Significantly negative correlations between Cl-, SO42-, and F- concentrations and P-IBI values indicated that the P-IBI might reflect domestic and industrial wastewater pollution in the Qin and Dan River in Jincheng region. The P-IBI strongly differentiated reference and impaired sites, suggesting the suitability of the index in the study.

Diagnosis of ecological quality of Dohou Lake on the basis of environmental parameters and phytoplankton community, Western Côte d’Ivoire

The ecological quality of Dohou Lake in Duékoué was determined from the phytoplankton community and physico-chemical parameters. All of the stations in Dohou Lake are dominated by Cyanobacteria and Bacillariophyta individuals, with high monthly proportions observed during the study period. Ecological indicators such as total phosphorus, transparency and chlorophyll made it possible to assess the physico-chemical quality of the environment. Thus, mean total phosphorus values ranged from 970 to 1150 µg/L from station D7 to station D6. Minimum transparency values ranged from 0.1 to 0.5 m from station D7 to D3, and mean values ranged from 0.3 m (station D7) to 0.69 m (station D1). For chlorophyll a, mean values ranged from 3.52 µg/L to 12.98 µg/L from station D7 to station D2, with maximum values for this parameter ranging from 13.4 µg/L (station D7) to 46.73 µg/L (station D2). All of the stations on Dohou lake are therefore in an eutrophic state. The monthly variations in the different proportions of phytoplankton groups observed indicate a clear predominance of Cyanobacteria followed by Bacillariophyta. The values of the Planktonic Index (PI) indicate that the stations are in average ecological condition, except for station D7, which is in poor ecological condition. These ecological qualities are reflected by the spatial and temporal dominance of 4 functional groups which are C, LM, K, and S1.

Development of Ecosystem Health Assessment (EHA) and Application Method: A Review

Human industrialization has caused damage to ecosystems. In this context, researchers have developed several methods to assess the health of various types of ecosystems. In this paper, we evaluated the developmental history and status of ecosystem health (EH) and summarized the concept of EH. We also reviewed ecosystem health assessment (EHA) methods and analyzed the application of EHA methods. EHA methods are generally classified into biological indicator and index system method. The former method is mainly based on the number of dominant species, such as diatom, plankton, and macroinvertebrate. Results indicate that trophic diatom index (TDI), plankton index of biotic integrity (P-IBI), and Ephemeroptera, Plecoptera, and Trichoptera (EPT) are the most commonly used indices. The latter method combines multiple ecosystem metrics and reflects ecosystem processes. The pressure–state–response (PSR) model most commonly uses the index system method. For the application of EHA methods, biological indicator methods are mostly applied in rivers/streams ecosystem, while the index system is primarily involved in urban ecosystems. Therefore, the information presented in this review may be helpful for the modification of EHA methods.

Ecological health assessments of rivers with multiple dams based on the biological integrity of phytoplankton: A case study of North Creek of Jiulong River

North Creek of Jiulong River is characterized by large falls and a high degree of cascade-driven hydropower development. In this paper, ecological health assessments for North Creek of Jiulong River were carried out by a field survey of seasonal phytoplankton community structure dynamics and constructing an index system, the planktonic index of biotic integrity, P-IBI, to compare ecosystem health across different seasons. North Creek were relatively healthy in the summer and fall, but exhibited the worst conditions in the winter. With the exception of fall samples, the assessments for more than 50% of the sites in the dam reservoir area were lower than “moderate.” Further, the ecological health of the mainstream was lower than that of the tributaries. The P-IBI index across different seasons was correlated with some basic water physicochemical parameters (chlorophyll a, COD and DO concentrations). Importantly, these assessment results were consistent with actual water quality monitoring results, indicating that it is feasible to use P-IBI to evaluate river health status. The assessment of seasonal changes in algal community health is helpful for developing management strategies for rivers with multiple dams.

Plankton Index of Biotic Integrity (P-IBI) for assessing ecosystem health within the Ouémé River basin, Republic of Benin

This study aims at assessing the impact of organic pollution on plankton communities of the Ouémé River using a Plankton Index of Biotic Integrity (P-IBI) as a tool for ecological heath assessment. Plankton and other environmental data were collected monthly from October 2014 to September 2015. An Organic Pollution Index (OPI) was calculated to classify the sampling sites, and 18 plankton candidate metrics were used to discriminate among the observed organic pollution levels. From this analysis, seven significant metrics were selected for setting up biotic integrity indices. An indicative value (IndVal) was calculated for each plankton species to identify indicator species characteristic of observed ecological statuses. The OPI shows significant organic pollution at sites, such as Kaboua, Vossa and Atchakpa-rejet, and less organic pollution at Kpassa. The plankton Index of Biotic Integrity (P-IBI) value shows significant correlation (r > 0.75) with organic pollution. Three ecological states were identified: Kaboua and Vossa were in fair condition; Kpassa, Toué, Atchérigbé and Affon in very good condition; and all other sites in good condition. Three phytoplankton and four zooplankton species were significantly associated with good conditions, whereas 108 phytoplankton species and 40 zooplankton species were significantly associated with fair conditions within the River basin.

Joint effects of habitat indexes and physic-chemical factors for freshwater basin of semi-arid area on plankton integrity – A case study of the Wei River Basin, China

As the largest tributary of the Yellow River and a large semi-arid area, the ecological status of the Wei River Basin, China, has become an important issue of concern. Habitat, water quality and biological pressure are the factors affecting the structure and function of rivers. However, it is a challenging task to determine the joint rather than isolated influence of factors on the watershed. Plankton is sensitive to the status of water system, so it is used to analyze the interaction between habitat indexes and physic-chemical parameters of water body. In this study, plankton and water samples were collected from 21 sampling sites in the whole Wei River Basin in October 2019. The planktonic index of biotic integrity (P-IBI), biomass, abundance, diversity index and trophic status were established. The integrity of plankton in the basin was evaluated. Redundancy analysis (RDA) was used to assess the correlation and variability between 23 physicochemical factors and habitat indexes of planktonic community. The results show that the applicability and accuracy of P-IBI are good. The planktonic integrity of the ecosystem in the basin is “critical”. The upper and lower reaches of the main stream are better than those of the middle reaches, while the upper reaches of the two major tributaries are in poor condition due to the influence of cities and industries. Wei River system is better than Jing River and Beiluo River system. Physical and chemical factors, including dissolved oxygen, turbidity, phycocyanin and chlorophyll, are the main driving forces affecting the integrity of plankton in the study area. Relatively speaking, the contribution of physicochemical parameters to P-IBI was greater than that of habitat indexes, and there was a shared explanatory variance between them. The abundance level can best reflect the isolation effect of two aspects of the environment. The results show that the planktonic index of biotic integrity is a potential tool to reflect the interaction of habitat conditions and physical and chemical factors. The whole basin scale research is helpful to promote habitat restoration and water conservation.

Evaluating ecological health in the middle-lower reaches of the Hanjiang River with cascade reservoirs using the Planktonic index of biotic integrity (P-IBI)

Operation of the middle route of the South-to-North Water Diversion Project in the Hanjiang River, China, has made the environmental health downstream of the Danjiangkou Reservoir an important issue for people living along the river. This study used the Planktonic Index of Biotic Integrity (P-IBI) including phytoplankton and zooplankton to evaluate riverine ecological health in an area with cascade reservoirs. Plankton and water samples from 19 sampling sites were collected along the middle-lower reaches of the Hanjiang River in Nov. 2017 and July 2018. To further verify the reliability of the P-IBI results, they were compared with the Saprobic Index (SI) and Comprehensive Water Quality Identification Index (CWQII). Redundancy analysis (RDA) was used to evaluate correlations and variability between P-IBI, SI, CWQII, candidate metrics, and primary environmental factors in the dry and wet seasons. The results showed that the ecological health of the aquatic ecosystem was ‘fair’ in status, oligotrophic, and class II (wet season)-class III (dry season) as evaluated by the IBI, SI, and CWQII, respectively. The ecosystem during the wet season was in better health than that in the dry season: based on CWQII, water quality at 63% of sites was in class III during the dry season, while 79% of sites were in class II in the wet season; and 11% more sites had IBI-A values (the mean values of Phyto-IBI and Z-IBI) less than 3 IBI scores (indicating “fair” status) in the dry season compared to the wet season. Ecological conditions were also poorer in the reservoir backwater area. The main driving forces impacting aquatic ecosystem in the study area were pollutant emissions and dam impacts. This study demonstrated that the P-IBI is a potential tool for evaluating riverine ecological health in areas with cascade reservoirs.

Plankton biodiversity in various typologies of inundation in Paminggir peatland, South Kalimantan, Indonesia on dry season

Abstract. Yunandar, Effendi H, Widiatmaka, Setiawan Y. 2020. Plankton biodiversity in various typologies of inundation in Paminggir peatland, South Kalimantan, Indonesia on dry season. Biodiversitas 21: 1012-1019. The aim of the study was to analyze the typology of inundation areas and plankton biodiversity in Paminggir peatland, South Borneo, Indonesia. Typology of inundation was determined by image processing and spatial analysis using supervised classification method from Landsat 1994, 2014, 2019. Plankton biodiversity was determined using purposive sampling in detected inundation from spatial analysis. Some environmental factors like temperature, Ph and DO were also analyzed. Confirmation of the results of spatial analysis of peatland typology made from overall accuracy and Kappa informed 88.48% and 0.8. The typology of permanent inundation decreased by 30% from 1994 to 2019 during the dry period from June to August of the total study area of 43275,584 hectares due to sedimentation, land conversion for settlement, and increase in water weeds. Inundation criteria with duration throughout the year were was categorized as permanent, whereas temporary inundation was tentative even in certain dry season. Plankton index biodiversity in permanent inundation was more varied compared to temporary inundation. Phytoplankton from the freshwater Chrysophyta group was more dominant, while zooplankton from the Nauplius group, which were the natural food for fish larvae always presented in the typology of permanent inundation.

Freshwater lake ecosystem health assessment and its response to pollution stresses based on planktonic index of biotic integrity.

Based on the planktonic data monitored in Lake Balihe, an ecosystem health assessment system referring to planktonic index of biotic integrity (P-IBI) was constructed to evaluate the lake health status and study the response mechanism of P-IBI to environmental factors. The results showed that a total of 7 phylum 59 species of phytoplankton and 3 phylum 28 species of zooplankton were identified in the lake, and both the plankton density and biomass varied significantly in time and space scales. The significant variation of Protozoa density should be responsible to the inconsistency between the distributions of zooplankton density and biomass, as well as the lowest value of P-IBI in summer. The P-IBI values and therefore the health levels can be seasonally ranked as winter > autumn > spring > summer and found spatially increased along the flow direction. Based on the relationships between P-IBI and the environmental factors, ammonia nitrogen = 0.46 mg/L and Secchi depth = 63 cm were found as the environmental protection thresholds of planktonic biotic integrity for this freshwater lake ecosystem. The findings of the research may provide some guidance to the ecological monitoring and protection of freshwater lake.

Plankton lifeforms as a biodiversity indicator for regional-scale assessment of pelagic habitats for policy

Plankton are sensitive indicators of change and, at the base of marine food webs, they underpin important ecosystem services such as carbon sequestration and fisheries production. In the UK and the Northeast Atlantic region, change in plankton functional groups, or ‘lifeforms’, constructed based on biological traits, is the formally accepted policy indicator used to assess Good Environmental Status (GES) for pelagic habitats under the Marine Strategy Framework Directive (MSFD: 2008/56/EC). To identify changes in UK pelagic habitats, plankton lifeforms, were used from diverse UK data sets collected by different methods, including plankton sampling by nets, water bottles, integrating tube samplers, and the Continuous Plankton Recorder. A Plankton Index approach was used to identify change in plankton lifeforms. This is the first time that the pelagic plankton community has been assessed on a UK-wide scale and forms the foundation of the UK’s 2020 MSFD Assessment for pelagic habitat biodiversity and food webs. This approach revealed that some of the plankton lifeforms used in the assessment displayed spatially-variable changes during the past decade. Assessing plankton community change using a common indicator at the UK scale for the first time is a significant step towards evaluating GES for European seas. Determining GES for pelagic habitats, however, is a challenging process, with additional work required to interpret the assessment results and to identify causation of the changes observed.

A new tool to assess ecosystem health in large subtropical reservoirs: Development and validation of a Planktonic Index of Biotic Integrity

We developed and validated a Planktonic Index of Biotic Integrity for subtropical reservoirs to assess their ecosystem health. For this purpose, we analyzed the phytoplankton and zooplankton communities and determined reservoir trophic status in the Paranapanema River system (Southeast Brazil). Eleven dams were constructed in the main course of this river to supply hydropower plants. Three of the reservoirs are accumulation systems (i.e. with high water retention times), whereas the others are run-of-the-river systems. For the study the three larger reservoirs (Jurumirim, Chavantes and Capivara) were selected. Physical, chemical, and biological (phytoplankton and zooplankton) data were obtained in two sampling campaigns carried out in March (wet season) and October (dry season) of 2011. For each reservoir we sampled six stations, arranged on a gradient established between the lotic (Paranapanema River entrance) and lentic (dam) areas. According to the Trophic State Index for tropical/subtropical reservoirs, the sampling stations were categorized between ultraoligotrophic and mesotrophic. Four metrics achieved significant discrimination (out of a set of 20 candidate metrics). The individual metric scores were summed to provide a Planktonic Index of Biotic Integrity score, which ranged as Mesotrophic (4-9), Oligotrophic (10-14) and Ultraoligotrophic (15-20), corresponding to the classification of fair, good and excellent, respectively. Following the longitudinal sequence, Jurumirim was classified as Oligotophic (Good) and both Chavantes and Capivara as Ultraoligotrophic (Excellent). This study demonstrated that the Planktonic Index of Biotic Integrity is a potential tool for monitoring large subtropical reservoirs, as planktonic organisms are sensitive to environmental changes and this index integrates distinct temporal and spatial scales.

Large rotaliid foraminifera as biostratigraphic and palaeoenvironmental indicators in northwest Borneo: An example from a late Miocene section in Brunei Darussalam

Palaeonvironmental interpretations and biostratigraphic zonations in northwest Borneo are still a matter of debate but are important for petroleum related applications. The outcrop of Ambug Hill, a late Miocene marine siliciclastic sequence in Brunei Darussalam, has been investigated for its foraminifera assemblage. From a 9.5 m clay-rich interval 50 taxa have been recognized and classified, whenever possible to species level. The studied fauna is characterized by mostly hyaline foraminifera, dominated by two rotaliid species: Cavarotalia annectens and Heterolepa dutemplei. Additionally, a number of miliolids, lageniids, bolivinids and also planktonic foraminifera are present but in much lower abundance. The dominance of the rotaliids points to a sea floor rich in organic carbon characterized by muddy substrates with very low light penetration and the possible growth of patchy sea grass or macroalgae in the system, as indicated by epiphytic foraminifera in the samples. The results obtained give additional insights on how the environmental conditions might have been during the deposition of the deltaic sequences very widespread in the region, and how the fauna coped with such settings. Throughout the investigated samples, the dominance of the assemblages clearly shows alternating stress conditions, typical of pro- deltaic environments.The large abundance of rotaliid foraminifera, points toward possible biostratigraphic applications as several taxa within this group have short biozones in the region even though have strong facies dependency. If their role as biostratigraphic indicators could be finally proven, they might be used to date the large depositional sequences occurring in the region, since planktonic index fossils are scarce due to the very proximal settings of the sediments.