High Nutrient Input Research Articles

Diversity and species composition of diatom communities of Ardley Island, South Shetland Islands

The Antarctic diatom flora has been at the centre of interest of many studies in past decades. The present paper brings new information on the species richness, biogeography and community composition of diatoms on the Ardley Island, South Shetland Islands. One fresh-water and ten soil samples had been collected from the Antarctic Special protected area (ASPA) in the spring of 2019. The following analysis revealed eighty-six diatom taxa in well-developed communities, dominated by Luticola muticopsis, L. truncata, Pinnularia australoschoenfelderi, P. austroshetlandica and P. borealis. According to the current biogeographical knowledge, the majority of species have restricted distribution among the Antarctic Realm; 46.5% of them are reported from various islands of the Maritime Antarctic Region. Based on the dominance of species as Luticola muticopsis and L. truncata and their ecological preferences, we concluded that the species composition of the diatom communities is driven by high nutrient input from breeding seabirds and the moisture availability during the austral summer.

Danish wetlands remained poor with plant species 17-years after restoration

For more than two decades, wetland restoration has been successfully applied in Denmark as a tool to protect watercourses from elevated nutrient inputs from agriculture, but little is known about how the flora and fauna respond to restoration. The main objective of this study was therefore to: (1) examine plant community characteristics in 10 wetland sites in the River Odense Kratholm catchment, restored between 2001 and 2011 by re-meandering the stream and disconnecting the tile drains, and (2) explore whether the effects of restoration on plant community characteristics change with the age of the restoration. Specifically, we hypothesised that plant community composition, species richness and diversity would improve with the age of the restoration and eventually approach the state of natural wetland vegetation. We found that the prevailing plant communities could be characterised as humid grasslands, moist fallow fields and improved grasslands, whereas the abundance of natural wetland plant communities (e.g., rich fens, fen-sedge beds and humid grasslands) was lower in both the recently restored as well as in older restored wetlands. Additionally, species richness and diversity did not seem to improve with the age of the restoration. We suggest that the continued high nutrient input at the restored sites in combination with restricted dispersal of wetland plant species may hamper the recovery of natural plant communities and that the sites therefore may stay botanically poor for many decades.

Unusually Warm Summer Temperatures Exacerbate Population and Plant Level Response of Posidonia oceanica to Anthropogenic Nutrient Stress.

Posidonia oceanica is a key foundation species in the Mediterranean providing valuable ecosystem services. However, this species is particularly vulnerable towards high coastal nutrient inputs and the rising frequency of intense summer heat waves, but their combined effect in situ has received little attention so far. Here, we investigated the effects of in situ nutrient addition during an unusually warm summer over a 4-month period, comparing different morphological, physiological and biochemical population metrics of seagrass meadows growing in protected areas (Ischia) with meadows already exposed to significant anthropogenic pressure (Baia – Gulf of Pozzuoli). Our study highlights that the effects of warmer than usual summer temperatures on the population level of seagrass meadows can be exacerbated if the plants are already exposed to higher anthropogenic pressures. Morphological and population level indicators mainly changed over time, possibly impacted by season and the warmer temperatures, and displayed more pronounced reductions in seagrasses from impacted sites. The additional nutrient supply had even more deleterious effects, as shown by a decrease in approximately 67% in cover in fertilized plots at high impacted sites and 33% at low impacted sites. Moreover, while rhizome starch concentration showed a seasonal increase in plants from low impacted sites it displayed a trend of a 27% decrease in fertilized plots of the high impacted sites. Epiphyte biomass was approximately four-fold higher on leaves of plants growing in impacted sites and even doubled with the additional nutrient input. Predicting and anticipating stress in P. oceanica is of crucial importance for conservation and management efforts, given the limited colonizing and reproductive ability and extremely slow growth of this ecosystem engineer. Our results suggest that monitoring efforts should focus especially on leaf area index (LAI), carbohydrate concentrations in the rhizomes, and epiphyte cover on leaves as indicators of the onset of stress in Posidonia oceanica, which can be used by decision makers to take appropriate measures before damage to the ecosystem becomes irreversible, minimize future human interference and strengthen the resilience of these important ecosystems.

Land-use intensity affects the potential for apparent competition within and between habitats.

Arthropod communities dwelling in adjacent habitats are able to impact one another via shared natural enemies. In agricultural landscapes, drastic differences in resource availability between crop and non-crop habitats cause variation in insect herbivore densities over short distances, potentially driving inter-habitat effects. Moreover, the composition of the landscape in which the habitats are embedded likely affects realised attack rates from natural enemies via impacts on local arthropod community structure. Here, we examine indirect effects between herbivore species within and between habitat types by calculating the potential for apparent competition between multiple populations. Firstly, we aim to determine how disparities in resource availability impact the strength of the potential for apparent competition occurring between habitats, secondly to examine the impact of landscape composition upon these effects, and finally to couch these observations in reality by investigating the link between the potential for apparent competition and realised attack rates. We used DNA metabarcoding to characterise host-parasitoid interactions within two habitat types (with divergent nutrient inputs) at 11 locations with variable landscape composition within an agroecosystem context. We then used these interaction networks to estimate the potential for apparent competition between each host pair and to compare expected versus realised attack rates across the system. Shared natural enemies were found to structure host herbivore communities within and across habitat boundaries. The size of this effect was related to the resource availability of habitats, such that the habitat with high nutrient input exerted a stronger effect. The overall potential for apparent competition declined with increasing land-use intensity in the surrounding landscape and exhibited a discernible impact on realised attack rates upon herbivore species. Thus, our results suggest that increasing the proportion of perennial habitat in agroecosystems could increase the prevalence of indirect effects such as apparent competition among insect herbivore communities, potentially leading to enhanced population regulation via increased attack rates from natural enemies like parasitoid wasps.

Seasonal and spatial dynamics of selected pesticides and nutrients in a small lake catchment – Implications for agile monitoring strategies

Intensive anthropogenic pressure such as high inputs of nutrients and pesticides severely threaten most European water bodies. Small catchments ≤10 km2 are not monitored under the Water Framework Directive but play an important role in freshwater ecosystems. The high complexity in seasonal and spatial dynamics require more than a one-size-fits-all approach in water quality monitoring. Often located in rural areas with a high agricultural activity, small catchments often carry high amounts of nutrients, pesticides and their transformation products affecting drinking water resources. With a low-cost approach of a monthly sampling campaign over the course of one year combined with meaningful indicators for potential pollution sources within the catchment this study could elucidate catchment dynamics and two hotspots for pesticides and nutrients. Two different groups of pesticides were observed (I) pesticides on long-term use which were applied in high amounts over the last decades (e.g., chloridazon and its transformation products) and (II) pesticides on short-term use, newly introduced into the market. Especially transformation products of pesticides from group (I) together with nitrate showed a steady release from two fields into the receiving water bodies over the year, probably being stored in the soil layers over the years of application slowly leaching out. Pesticides from group (II) showed a strong seasonality, released from another hotspot area probably due to run-off shortly after application. Streamlining this knowledge into targeted measures and an agile monitoring strategy for the respective catchments may allow a sustainable improvement of water quality and a better ecosystem protection.

Bryozoan‐rich stromatolites (bryostromatolites) from the Silurian of Gotland and their relation to climate‐related perturbations of the global carbon cycle

ABSTRACTBryozoan–stromatolite associations (bryostromatolites) formed conspicuous reef structures throughout the Sheinwoodian (Wenlock) to Ludfordian (Ludlow) stratigraphy on Gotland but have not been described so far. They are mainly composed of encrusting bryozoans forming a complex intergrowth with porostromate and spongiostromate microbes and are different from the abundant stromatoporoid–coral–algal reefs with respect to their composition. In the bryostromatolite different growth stages can be identified. The observed succession can be taken as evidence for cyclic environmental changes during reef formation. Stenohaline reef‐dwelling organisms, such as echinoderms, sponges, corals and trilobites, indicate fully marine salinities. Ten localities exposing bryostromatolites were discovered. Individual bryostromatolites are small with few decimetres up to one metre in size, and occur solely in shallow marine areas. Common features of these reefs on Gotland are cauliflower‐like growth, a high bryozoan diversity, a high abundance of phosphatic fossils and components such as bryozoan pearls and inarticulate phosphatic brachiopods, enhanced bioerosion, Palaeomicrocodium crusts, vadose silt and gypsum pseudomorphs. The high abundance of Palaeomicrocodium, as well as the alternation with other crust‐forming contributors, suggest that it could have been formed directly at the palaeo‐sea surface, probably in times of minor but high‐frequency sea‐level fluctuations. Vadose silt and pseudomorphs after gypsum in reef cavities indicate subaerial exposure shortly after reef growth. The high amount of phosphatic components indicates a high nutrient input, probably by dust. All bryostromatolites were formed in times of strongly elevated δ13C values. The unusual combination of sedimentological and palaeoecological features, as well as their occurrence exclusively during strong positive δ13C excursions, are evidence that the bryostromatolite development responded to climatic/oceanographic changes, which may have played an important role in reef control.

Organic Farming Practices and Shade Trees Reduce Pest Infestations in Robusta Coffee Systems in Amazonia.

Coffee agroforestry systems could reconcile agricultural and environmental objectives. While pests and diseases can reduce yield, their interactions with shade and nutrition have been rarely researched, and are particularly lacking in perennial systems. We hypothesized that intermediate shade levels could reduce coffee pests while excess shade could favor fungal diseases. We hypothesized that organic rather than mineral fertilization would better synchronize with nutrient uptake and higher nutrient inputs would be associated with reduced pest and disease damage due to higher plant vigor, yet effects would be less obvious in shaded plots as coffee growth would be light-limited. Using three-year-old trees of Coffea canephora var. Robusta (robusta coffee) in the Ecuadorian Amazon, we compared a full-sun system with four shading methods creating different shade levels: (1) Myroxylon balsamum; (2) Inga edulis; (3) Erythrina spp.; or, (4) Erythrina spp. plus Myroxylon balsamum. Conventional farming at either (1) moderate or (2) intensified input and organic farming at (3) low or (4) intensified input were compared in a split-plot design with shade as the main plot factor and farming practice as the sub-plot factor. The infestation of the following pests and disease incidences were evaluated monthly during the dry season: brown twig beetle (Xylosandrus morigerus), coffee leaf miner (Leucoptera coffeella), coffee berry borer (Hypothenemus hampei), anthracnose disease (Colletotrichum spp.), thread blight (Pellicularia koleroga), and cercospora leaf spot (Cercospora coffeicola). Coffee berry borer and brown twig beetle infestation were both reduced by 7% in intensified organic treatments compared to intensified conventional treatments. Colonization of coffee berry borer holes in coffee berries by the entomopathogenic fungus Beauveria bassiana was also assessed. Brown twig beetle infestation was significantly higher under full sun than under Inga edulis, yet no other shade effects were detected. We demonstrate for the first time how intensified input use might promote pest populations and thus ultimately lead to robusta coffee yield losses.

Increasing nutrient influx trends and remediation options at Hartbeespoort Dam, South Africa: a mass-balance approach

The Hartbeespoort Dam, located 40 km west of Tshwane on the Crocodile River, is an extremely eutrophic water body. Situated in one of the most economically active areas of South Africa, it receives a high nutrient input from wastewater treatment works (WWTW), leaking sewers, as well as urban and agricultural runoff. The Metsi a Me programme, which ran from 2006 to 2016, aimed to mitigate in-lake nutrient stocks using biomanipulation, including the physical removal of Eichhornia crassipes (water hyacinth) and Microcystis aeruginosa (blue-green algae). Using Department of Water and Sanitation water quality and flow data, the annual influxes and outfluxes of total nitrogen (TN) and total phosphorus (TP) to the Hartbeespoort Dam were calculated. Through literature review and comparison with previous studies, the relative importance of nutrient removal from biomass harvesting in relation to retained nutrients was assessed. The average nutrient influx from rivers during hydrological years 2010/11 to 2016/17 was 582 t∙a−1 TP and 4 687 t∙a−1 TN, with trends for both TN and TP being significantly positive over this period. TP influx increased by 77.8 t∙a−1 every year and TN influx increased by 456 t∙a−1, reversing a long-term negative trend. Average annual dam retention + removal (calculated as the difference between river inputs and outputs, i.e., including sedimentation, biomass removal and denitrification losses) was 358 t P and 2 195 t N. A best estimation of nutrient removal from water hyacinth and algal harvesting was 2.1 t∙a−1 P and 11.5 t∙a−1 N, and 3.9 t∙a−1 P and 40 t∙a−1 N, respectively. An estimated 341 t∙a−1 P and 674–1 288 t∙a−1 N was sedimented. Denitrification losses are poorly quantified but are possibly comparable to sedimentation. River outfluxes increased by 28.4 t∙a−1 TP and 110 t∙a−1 TN, smaller rates than the influxes, suggesting increasing retention per annum. Upgrading WWTWs in the catchment and refurbishing leaking and overflowing sewers is the most appropriate long-term solution.

Crop diversity enriches arbuscular mycorrhizal fungal communities in an intensive agricultural landscape.

Summary Arbuscular mycorrhizal fungi (AMF) are keystone symbionts of agricultural soils but agricultural intensification has negatively impacted AMF communities. Increasing crop diversity could ameliorate some of these impacts by positively affecting AMF. However, the underlying relationship between plant diversity and AMF community composition has not been fully resolved.We examined how greater crop diversity affected AMF across farms in an intensive agricultural landscape, defined by high nutrient input, low crop diversity and high tillage frequency. We assessed AMF communities across 31 field sites that were either monocultures or polycultures (growing > 20 different crop types) in three ways: richness, diversity and composition. We also determined root colonization across these sites.We found that polycultures drive the available AMF community into richer and more diverse communities while soil properties structure AMF community composition. AMF root colonization did not vary by farm management (monocultures vs polycultures), but did vary by crop host.We demonstrate that crop diversity enriches AMF communities, counteracting the negative effects of agricultural intensification on AMF, providing the potential to increase agroecosystem functioning and sustainability.

Anthropogenic nutrient loads and season variability drive high atmospheric N2O fluxes in a fragmented mangrove system

Fragmented mangroves are generally ignored in N2O flux studies. Here we report observations over the course of a year from the Mangalavanam coastal wetland in Southern India. The wetland is a fragmented mangrove stand close to a large urban centre with high anthropogenic nitrogen inputs. The study found the wetland was a net source of N2O to the atmosphere with fluxes ranging between 17.5 to 117.9 µmol m−2 day−1 which equated to high N2O saturations of between 697 and 1794%. The average dissolved inorganic nitrogen inputs (80.1 ± 18.1 µmol L−1) and N2O emissions (59.2 ± 30.0 µmol m−2 day−1) were highest during the monsoon season when the rainfall and associated river water inputs and terrestrial runoff were highest. The variation in N2O dynamics was shown to be driven by the changes in rainfall, water column depth, salinity, dissolved oxygen, carbon, and substrate nitrogen. The study suggests that fragmented/minor mangrove ecosystems subject to high human nutrient inputs may be a significant component of the global N2O budget.

Opportunities of Reduced Nitrogen Supply for Productivity, Taste, Valuable Compounds and Storage Life of Cocktail Tomato

Vegetable production requires high nutrient input for ensuring high quality and high yield. As this is ecologically disadvantageous, it is necessary to determine if nitrogen (N) fertilization can be reduced without negative effects on productivity. For quality reasons, the effects of reduced N supply on taste, valuable compounds and storage life must be elucidated in parallel. This study examines whether reducing the N supply of cocktail tomatoes by 50% to recommendations affects the yield and quality of tomato fruits. Three varieties with different skin colors, yellow-orange (‘Apresa’), red (‘Delioso’) and brown (‘Bombonera’), were grown in soil in a greenhouse and harvested at the red-ripen stage. Quality parameters were assessed at harvest and after eight-day storage. Total yield decreased exclusively with ‘Bombonera’ due to reduced fruit weight. Firmness of the fruit pulp, concentrations of minerals, soluble solid contents, total acidity, total phenolics and liposoluble pigments of fruits were not influenced. However, storage affected chemical compositions positively, as shown by increased antioxidants. Descriptive sensory analyses revealed no impact of reduced N supply. From the perspective of the yield, quality and shelf life of fruits, reducing the N supply by 50% offers opportunities for the three cocktail tomato varieties in soil cultivation.

Insolation vs. meltwater control of productivity and sea surface conditions off SW Greenland during the Holocene

We address here the specific timing and amplitude of sea‐surface conditions and productivity changes off SW Greenland, northern Labrador Sea, in response to the high deglacial meltwater rates, the Early Holocene maximum insolation and Neoglacial cooling. Dinocyst assemblages from sediment cores collected off Nuuk were used to set up quantitative records of sea ice cover, seasonal sea‐surface temperature (SST), salinity (SSS), and primary productivity, with a centennial to millennial scale resolution. Until ~10 ka BP, ice‐proximal conditions are suggested by the quasi‐exclusive dominance of heterotrophic taxa and low dinocyst concentrations. At about 10 ka BP, an increase in species diversity and abundance of phototrophic taxa marks the onset of interglacial conditions at a regional scale, with summer SST reaching up to 10 °C between 8 and 5 ka BP, thus in phase with the Holocene Thermal Maximum as recorded in the southern Greenlandic areas/northern Labrador Sea. During this interval, low SSS but high productivity prevailed in response to high meltwater discharge and nutrient inputs from the Greenland Ice Sheet. After ~5 ka BP, a decrease in phototrophic taxa marks a two‐step cooling of surface waters. The first started at ~5 ka BP, and the second at ~3 ka BP, with a shift toward colder conditions and higher SSS suggesting reduced meltwater discharge during the Neoglacial. This second step coincides with the disappearance of the Saqqaq culture. The gap in human occupation in west Greenland, between the Dorset and the Norse settlements from 2000 to 1000 years BP, might be linked to high amplitude and high frequency variability of ocean and climate conditions.

The Genomic Capabilities of Microbial Communities Track Seasonal Variation in Environmental Conditions of Arctic Lagoons.

In contrast to temperate systems, Arctic lagoons that span the Alaska Beaufort Sea coast face extreme seasonality. Nine months of ice cover up to ∼1.7 m thick is followed by a spring thaw that introduces an enormous pulse of freshwater, nutrients, and organic matter into these lagoons over a relatively brief 2–3 week period. Prokaryotic communities link these subsidies to lagoon food webs through nutrient uptake, heterotrophic production, and other biogeochemical processes, but little is known about how the genomic capabilities of these communities respond to seasonal variability. Replicate water samples from two lagoons and one coastal site near Kaktovik, AK were collected in April (full ice cover), June (ice break up), and August (open water) to represent winter, spring, and summer, respectively. Samples were size fractionated to distinguish free-living and particle-attached microbial communities. Multivariate analysis of metagenomes indicated that seasonal variability in gene abundances was greater than variability between size fractions and sites, and that June differed significantly from the other months. Spring (June) gene abundances reflected the high input of watershed-sourced nutrients and organic matter via spring thaw, featuring indicator genes for denitrification possibly linked to greater organic carbon availability, and genes for processing phytoplankton-derived organic matter associated with spring blooms. Summer featured fewer indicator genes, but had increased abundances of anoxygenic photosynthesis genes, possibly associated with elevated light availability. Winter (April) gene abundances suggested low energy inputs and autotrophic bacterial metabolism, featuring indicator genes for chemoautotrophic carbon fixation, methane metabolism, and nitrification. Winter indicator genes for nitrification belonged to Thaumarchaeota and Nitrosomonadales, suggesting these organisms play an important role in oxidizing ammonium during the under-ice period. This study shows that high latitude estuarine microbial assemblages shift metabolic capabilities as they change phylogenetic composition between these extreme seasons, providing evidence that these communities may be resilient to large hydrological events in a rapidly changing Arctic.

Climate and Human-Driven Variability of Summer Hypoxia on a Large River-Dominated Shelf as Revealed by a Hypoxia Index

Coastal hypoxia has become common especially in large river dominated coastal ecosystems. To better quantify the severity of hypoxia and the contribution of hypoxia drivers, we applied principal component analysis (PCA) on observable properties from eight summer hypoxia events in the East China Sea and defined the first principal component as the hypoxia index (HI). Multiple linear regression showed that the HI significantly correlated with three direct hypoxia drivers including water column stratification, subsurface water residence time, and respiration rates, which accounted for 5.7, 55.3, and 34.5%, respectively, of the total variance of PCA derived HI. We further reconstructed the HI over the past 60 years using available long-term data of stratification, model-derived residence times and respiration rates. The results show that summer hypoxia has become more severe since the 1960s. ENSO and global warming may have exacerbated hypoxia by affecting the river discharge, resulting in freshening in the plume-impacted shelf area, while anthropogenic activities may have exacerbated hypoxia by elevating fluvial nutrient concentrations, resulting in higher respiration rates. In addition, warming of the bottom water from the Kuroshio Current accounts for an additional increasing rate for HI, which made hypoxia more severe by means of decreasing oxygen solubility. Overall, our results indicate that stratification, water residence and oxygen solubility resulting from climate change can explain about 80% while higher respiration resulting from higher nutrient inputs can explain about 20% of the variation in the severity of hypoxia during the past half century.

Short-Term Effect of Biochar on Microbial Biomass, Respiration and Enzymatic Activities in Wastewater Irrigated Soils in Urban Agroecosystems of the West African Savannah

Irrigated urban agriculture (UA) supports the economy and health of urban inhabitants in low-income countries. This system is often characterized by high nutrient inputs and mostly utilizes wastewater for irrigation. Biochar has been proposed to increase crop yields and improve soil properties. In this study, we assessed the transient effect of rice husk biochar (20 t ha−1) and/or fertilizer (NPK: 15-15-15) on microbial respiration, microbial biomass carbon and enzyme activities of irrigated (wastewater and tap water) soil from an UA field experiment in the Guinea savannah zones of Ghana. Our results showed an increase by up to 123% in soil organic carbon (SOC) after a year of biochar application, while hot water extractable carbon (HWEC) was increased by only 11 to 26% and microbial biomass carbon (MBC) by 34%. Basal respiration was significantly increased in mineral fertilized soil by up to 46% but decreased by 12–45% under wastewater irrigation. Overall, the metabolic quotient (qCO2) indicated less stress for the microbial community and increased carbon use efficiency with biochar application and wastewater irrigation. Total enzymes activity was increased under wastewater irrigation and biochar treated soils exhibit a more diverse composition of C-cycling enzymes and a higher activity of aminopeptidases. Biochar and wastewater showed positive effects on biological soil properties and contributed to soil fertility. Our results suggest beneficial effects of biochar on non-biochar SOC stocks in the long term.

Microbial carbon-use efficiency and straw-induced priming effect within soil aggregates are regulated by tillage history and balanced nutrient supply

Soil samples from an Alfisols with long-term (> 12 years) contrasting tillage intensities (i.e., no-till versus plow-till) were first divided into three distinct dry aggregate-size classes (i.e., mega-, macro-, and microaggregates) and then incubated with 13C-labeled wheat residue at three input levels of balanced nutrients supply under controlled laboratory conditions. Across all the treatments, from 55.1 to 83.4% of total straw-C was mineralized within the incubation period. The microaggregates significantly increased the straw-C mineralization rate by 3.6 and 3.1 mg C g−1 straw-C day−1 compared to the mega- and macroaggregates respectively, mainly due to the higher microbial biomass. The high input of balanced nutrients enhanced the straw-C mineralization. Moreover, the microbial C-use efficiency (CUE) of straw residue in the microaggregates was 25.1% and 7.3% higher than that in the mega- and macroaggregates, respectively. Legacy effect of the long-term no-till increased microbial CUE, mainly by reducing the C-nutrient stoichiometric imbalance. In contrast, straw addition to the microaggregates resulted in the lowest positive priming effect (PE) of SOC compared to that added to the mega- and macroaggregates. Both the nutrient input and no-till treatments positively contributed to the decrease in positive PE. The negative correlation between the microbial CUE of the straw residue and the positive PE was reported for the first time, and the inputs of straw residue and high-level nutrients to the microaggregates from the no-till treatment increased CUE but decreased positive PE.

Harmful micro-algal blooms and local environmental conditions of the coastal fringe: Moroccan Mediterranean coasts as a case study

The dynamic study of harmful phytoplankton, conducted from June 2013 to May 2014, has tracked the evolution of the microalgae community at four sites located along the Moroccan western Mediterranean coast. 91 species and genera of phytoplankton were identified, 8 of which are recognized as potentially toxic. The genus Pseudo-nitzschia, a diatom known to produce domoic acid, is quite prevalent in all four sites, particularly in spring. The toxic dinoflagellate species detected in our study are Gymnodinium catenatum, Alexandrium sp PSP producers, Prorocentruml Lima, Dinophysis acuminata, D. caudata, D. fortii DSP producer, and Ostreopsis sp known palytoxin producer. The species Gymnodinium catenatum proliferates intensively from S1 to S3 in winter and S4 in summer, while Alexandrium sp proliferates mainly during spring and late summer with an exceedance of the threshold. Significant blooms of Dinophysis sp were recorded during the summer at all sites. On the other hand, the abundance of Ostreopsis sp was noted during the spring summer period with low concentrations. Discriminant analysis (DFA) of nutrients, toxic species identifies perfect seasonal discrimination. Winter and fall are characterized by high nutrient inputs, but algal biomass is low. On the contrary, spring and summer are characterized by a depletion of nutrients in the environment following the assimilation of these elements by phytoplankton.

Hyperspectral Reflectance Characteristics of Cyanobacteria

Potentially harmful cyanobacterial blooms are an emerging environmental concern in freshwater bodies worldwide. Cyanobacterial blooms are generally caused by high nutrient inputs and warm, still waters and have been appearing with increasing frequency in water bodies used for drinking water supply and recreation, a problem which will likely worsen with a warming climate. Cyanobacterial blooms are composed of genera with known biological pigments and can be distinguished and analyzed via hyperspectral image collection technology such as remote sensing by satellites, airplanes, and drones. Here, we utilize hyperspectral microscopy and imaging spectroscopy to characterize and differentiate several important bloom-forming cyanobacteria genera obtained in the field during active research programs conducted by US Geological Survey and from commercial sources. Many of the cyanobacteria genera showed differences in their spectra that may be used to identify and predict their occurrence, including peaks and valleys in spectral reflectance. Because certain cyanobacteria, such as Cylindrospermum or Dolichospermum, are more prone to produce cyanotoxins than others, the ability to differentiate these species may help target high priority waterbodies for sampling. These spectra may also be used to prioritize restoration and research efforts to control cyanobacterial harmful algal blooms (CyanoHABs) and improve water quality for aquatic life and humans alike.

Trophic status index and natural fisheries potential of some Iranian reservoirs.

The Iran Water Resources Management Company constructs many dams to control surface water that provide a new potential for aquaculture activities. Trophic status index and natural potential for fish production were investigated in nine small dam reservoirs from northwest of Iran. Prediction of fish productivity was calculated based on phytoplankton biomass (using chlorophyll a concentration in water; p Chl-a) and benthic macro invertebrate biomass (p BMI). Average p Chl-a and p BMI of reservoirs were estimated as 233.9±479.4 kg ha-1yr-1 and 14.76±19.18 kg ha-1yr-1 respectively. Concentrations of total phosphorus and total nitrogen varied between 0.023-0.345 and 0.42-3.58 mgl-1, respectively. According to Carlson's transformed model (TSIPN) the mesotrophic status was dominant in reservoirs in which TSIPN varied between 38.7 and 51.2. The eutrophication trend seems to be very fast in these reservoirs because of high nutrient input by aquacultures activities. The usage of fertilizers and amounts of food for aquaculture proposes and expansions of exotic species decline the natural fisheries potential of these reservoirs. Maintenance of water quality and investigation of native species should be planned to preserve sustainable fisheries activities in these reservoirs.

Interplay between the paradox of enrichment and nutrient cycling in food webs

Nutrient cycling is fundamental to ecosystem functioning. Despite recent major advances in the understanding of complex food web dynamics, food web models have so far generally ignored nutrient cycling. However, nutrient cycling is expected to strongly impact food web stability and functioning. To make up for this gap, we built an allometric and size structured food web model including nutrient cycling. By releasing mineral nutrients, recycling increases the availability of limiting resources for primary producers and links each trophic level to the bottom of food webs. We found that nutrient cycling can provide a significant part of the total nutrient supply of the food web, leading to a strong enrichment effect that promotes species persistence in nutrient poor ecosystems but leads to a paradox of enrichment at high nutrient inputs. The presence of recycling loops linking each trophic level to the basal resources weakly affects species biomass temporal variability in the food web. Recycling loops tend to slightly dampen the destabilising effect of nutrient enrichment on consumer temporal variability while they have opposite effects for primary producers. By considering nutrient cycling, this new model improves our understanding of the response of food webs to nutrient availability and opens perspectives to better link studies on food web dynamics and ecosystem functioning.