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Invasive dreissenid mussels have altered plankton abundance and nutrient cycling in the Great Lakes. In this study, a 1-D hydrodynamic-biogeochemical coupled model is developed to investigate their effects at a mid-depth offshore site in Lake Michigan. Model simulation shows that water surface temperature and vertical thermal structure can be well reproduced. Driven by the simulated vertical mixing, the biological model solves the transport and transformation of nutrients, plankton and detritus in the water column. Mussel grazing and excretion are added at the bottom boundary. The biological model predicts a notable decline of phytoplankton biomass and considerable increase of dissolved phosphorus (DP) in the entire water column at the end of spring. However, the reduction of phytoplankton and the increase of DP are limited to the bottom 20 m in summer as a result of the strong stratification. Model results also show that mussels can maximize particle delivery to the benthos, as the modeled benthic diffusive flux of particulate phosphorus exceeds the passive settling rate by 4.2× on average. Model simulation over a 10-month period indicates that profundal mussels have the potential to significantly change the distribution of energy and nutrients in the water column, even in a deep and stratified environment. [ABSTRACT FROM AUTHOR]

The ongoing restoration of the Florida Everglades has changed the hydrology in south Florida and increasing freshwater discharge has contributed to a shift in nutrients and phytoplankton in northern Florida Bay. To understand the effect of the changing nitrogen (N) forms and nitrogen:phosphorus (N:P) ratios on phytoplankton biomass and assemblage composition, five mesocosm experiments were conducted. Nutrient additions included a matrix of different forms of N (NO 3 − , NH 4 + , and DON) and P (as sodium β-glycerophosphate pentahydrate) in differing N:P molar ratios (4, 16, 32), a P alone addition, and a control. In general, chlorophyll a increased three-fold in the + P treatments and ten-fold in the + N + P treatments, while it did not increase in the + N treatments. Typically the + N + P treatments, particularly the + NO 3 − +P at the N:P molar ratio of 32, promoted high concentrations of fucoxanthin (generally indicative of diatoms) relative to chlorophyll a . While chlorophyll a did not increase significantly in the + N alone treatments, there was a change in the phytoplankton assemblage. The + N treatments, when N was in the form of + NH 4 + yielded proportionally higher zeaxanthin (generally indicative of picocyanobacteria). When the + N:P ratio increased, the relative concentrations of fucoxanthin and alloxanthin (generally indicative of cryptophytes) to chlorophyll a increased, whereas the relative concentrations of zeaxanthin and dinoflagellates (generally indicative of photosynthetic dinoflagellates) declined. This study highlights the importance of dual P and N control, particularly N in the forms of NH 4 + and DON if picocyanobacterial blooms are to be controlled. [ABSTRACT FROM AUTHOR]

We discuss a mathematical model of growth of two types of phytoplankton, non-nitrogen-fixing and nitrogen-fixing, that both require light in order to grow. We use general functional responses to represent the inhibitory effect their biomass has on the exposure to light. We give conditions for the existence and local stability of all of the possible steady-states (die out, single species survival, and coexistence). We derive conditions for global stability of the die out and single-species steady-states and for persistence of both species when the coexistence steady-state exists. Numerical investigation illustrates the qualitative dynamics demonstrating that even under constant environmental conditions, both stable intrinsic oscillatory behavior and a period doubling route to chaotic dynamics are possible. We also show that competitor-mediated coexistence can occur due to the positive feedback resulting from recycling by the nitrogen-fixing phytoplankton. To show the impact of seasonal change in water depth, we also allow the water depth to vary in an annual cycle and discuss echo blooms in this context. [ABSTRACT FROM AUTHOR]

Abstract: Species composition and biomass of phytoplankton assemblages of a heavily impacted lake (Lake Illawarra) and a less impacted lake (Burrill Lake) in the South-Eastern region of Australia were compared based on bimonthly samples from three sites in each lake collected between April 2005 and April 2007. Lake Illawarra was generally characterized by higher nutrient concentrations and lower salinity than Burrill Lake. Phytoplankton assemblages displayed significant differences between the two lakes in terms of the dominant species composition and patterns of seasonal change rather than biomass. Diatoms were the dominant species in Lake Illawarra on most sampling occasions. In contrast, dinoflagellates (including toxic species) dominated in Burrill Lake during most seasons. Seasonal succession of phytoplankton in the two lakes did not follow the strict spring maximum that is generally observed in temperate waters. In Burrill Lake, maximum phytoplankton biomass often occurred in winter, while the maximum biomasses in Lake Illawarra occurred in autumn, winter and spring. The significant difference of nutrient structure between two lakes and warm temperate regime was regarded as important factors to affect these results. The results suggested care should be taken when relying on estuary health “indicators”, such as chlorophyll a, rather than more detailed investigations of phytoplankton species compositions. [Copyright &y& Elsevier]

• Prominent seasonality in spatial variation of hydro-biological parameters. • Cold-core eddy fuelled higher pre-southwest monsoon chlorophyll- a levels. • Lower surface chlorophyll- a levels despite higher nutrient during post-southwest monsoon. • Potential role of nutrient stoichiometry in determining chlorophyll- a seasonality. • Post-southwest monsoon phosphate-limitation induced lower chlorophyll- a levels off Godavari. The hydro-biological parameters such as thermohaline structure, nutrients, and chlorophyll- a (chl- a) during pre-southwest monsoon (PRSWM) and post-southwest monsoon (POSWM) periods of 2017, was investigated and compared along a coastal transect in the western Bay of Bengal (BoB). The impact of cold-core and warm-core eddies on chl- a in the very near coastal waters of the western BoB was analyzed. During PRSWM period, the water column was recharged with phytoplankton growth-promoting nutrients entrained by cold-core eddies that resulted in an increment in chl- a concentration. A three-times increase in chl- a concentration was observed due to the cold-core eddy, whereas the presence of warm-core eddy reduced the chl- a concentration by 87%. However, during POSWM period, despite having higher nitrate concentration and adequate light in the water column, the surface chl- a was substantially lesser than PRSWM. The molar ratio of ambient inorganic macronutrients during POSWM period played a significant role resulting in lower chl- a concentration. Nitrogen to phosphate (N:P) and nitrogen to silicate (N:Si) ratios were less than the Redfield values. The chl- a concentration off Godavari, a biological hotspot, was the lowest during POSWM period. This study highlights phosphate limitation off Godavari during the high river discharge period. [ABSTRACT FROM AUTHOR]

İzmir Bay has been one of most polluted bays of the Mediterranean for a long time. When the "Big Channel Project" was completed in 2000, sewage flow into the bay ended. Hence, the influence of creeks, which are the only source of water transportation to the inner bay, was investigated in the current study. Monthly samples of creek water and seawater were taken. Basic water quality variables and nutrients were measured. In addition, the phytoplankton community was arrayed into size fractions to assess the contribution of each size fraction to biomass and pigment concentrations. Analyses showed that the creek waters had very high nutrient concentrations. Although decreasing nutrient concentrations of the sea as compared to past years were detected, results of the analyses showed that the phytoplankton biomass was increased. Minimum and maximum values of nutrient concentrations and chlorophyll-a were 0.23-22.28 µM for ammonium, 1.54-11.77 µM for nitrate, 0.00-3.51 µM for nitrite, 1.99-41.94 µM for silicate, 0.00-5.96 µM for phosphate, and 5.03-30.26 µg/L for chlorophyll-a. Nanoplankton was the dominant phytoplankton group in the inner bay. An increment in picoplankton was detected towards the outer part of the bay. The microplankton biomass was correlated with NH+4-N, [Si(OH) 4-Si], and o.PO4-P. [Si(OH) 4-Si], o.PO4-P, and microplankton were the most important constituents in the inner bay. Consequently, controlling nutrient concentrations in the creeks might contribute to the cleaning process in İzmir Bay. [ABSTRACT FROM AUTHOR]

Diel vertical migration (DVM) of zooplankton is commonly considered an adaptation for feeding in food-rich and warm surface waters at night and avoiding visual predators during the day. However, the critical assessment of migration patterns frequently suggests that: (i) zooplankton may leave deeper waters with rich, deep-chlorophyll layers and move into the epilimnion where food resources are lower and/or (ii) the night-time increase in epilimnetic plankton abundance is not matched by a density decrease in deeper strata. To study these discrepancies, we measured DVM of zooplankton in a 1.3-ha Spanish karst lake (Laguna del Tejo) where the phytoplankton in the deep chlorophyll layer had been labelled with the isotopic tracer 15N. There were only limited changes in the vertical distribution patterns of rotifers and copepods over the diel cycle, but night-time biomass (mg L−1) of the cladoceran, Diaphanosoma brachyurum in the water column of the oxic zone increased 168% in the central area of the lake but there was not a parallel reduction in their density in the metalimnion or hypolimnion. Additionally, the isotopic signatures of the zooplankton in the epilimnion stayed constant from day to night, suggesting that there was little vertical migration. The results suggest that horizontal movements rather than vertical migration explain the increasing abundance of zooplankton in the central epilimnion of Laguna del Tejo during the night and that low food resources in this layer provide no incentive for DVM. [ABSTRACT FROM AUTHOR]

Phytoplankton biomass-nutrient relationship is widely used by lake managers to assess the eutrophication impact and to set the nutrient targets. Submerged vegetation and large zooplankton grazing have long been identified as factors weakening the relationship by decoupling phytoplankton from nutrients. Proving this decoupling unambiguously is difficult because, in natural systems, many factors act together, blurring each other's effect. In this article, we present the results of continuous monitoring of 13 ponds where the effects of submerged vegetation and zooplankton grazing were enhanced by biomanipulation (fish removal). The monitoring allowed these effects to be assessed and compared with the pre-biomanipulation situations when phytoplankton biomass was mainly nutrient driven. The comparison showed a strong weakening effect of submerged vegetation and large zooplankton grazing on the chlorophyll a-total phosphorus relationship suggesting that a considerable degree of ecological quality of ponds affected by eutrophication can be restored even when nutrient-loading reduction is not feasible. [ABSTRACT FROM AUTHOR]

Abstract: Recent characterizations of atmospheric conditions favorable to upwelling events in the Western Cantabrian Sea have stressed the need to analyze the significance of the orientation of the coast on the phenomenon of upwelling. Surface-wind fields for the northwestern Galician marine area were provided by the QuikSCAT satellite and an SST map was elaborated using the NASA GHRSST satellite data. A cruise was conducted aboard the RV Lura in June 2009 during northern prevailing winds. Data of thermohaline variables, concentration of dissolved oxygen, dissolved inorganic nitrogen, chlorophyll, dissolved and particulate organic carbon and nitrogen and phytoplankton abundances were obtained. When the upwelling developed west of the Cape Ortegal was strong, the Eastern North Atlantic Central Water mixed with coastal water eastward of the Cape and the upwelled seawater reached the westernmost of the Northern Galician Rias, the Ria of Ortigueira. Incoming seawater was poor in nitrate and chlorophyll concentrations when compared to that of the upwelling events in the Western Galician Rias. The phytoplankton assemblages were typical of summer upwelling blooms in the latter Rias but phytoplankton biomass was lower in the Ria of Ortigueira and the species were indicatives of initial (inner ria under continental influence) and advanced (outer ria under upwelling inputs) stages of phytoplankton succession. The observed process arose when the upwelling edge-zone reaches a change of coastal orientation as may also occur in other upwelling regions. [Copyright &y& Elsevier]

Abstract: The aim of this study was to investigate the cycling of dissolved inorganic and organic nutrients using moored instrumented buoys (SmartBuoys) during the spring bloom in the North Sea. The instrumentation on the buoys enabled high frequency measurements of water-column integrated irradiance and in situ chlorophyll to be made, and also preserved water sample collection which were used for dissolved inorganic and organic nutrient analyses. The SmartBuoys were located in the year-round well-mixed plume zone associated with the River Thames and in the summer stratified central North Sea. These site locations allowed comparison of nutrient concentrations and cycling, and spring bloom development at two contrasting sites. The spring bloom was expected to be initiated at both stations due to increasing insolation and decreasing suspended load leading to higher water-column integrated irradiance. Due to differences in suspended load between the sites, the spring bloom started ∼2 months earlier in the central North Sea. The spring bloom in the Thames plume also resulted in higher maximum phytoplankton biomass due to the higher pre-bloom nutrient concentrations associated with riverine input. The use of SmartBuoys is also shown to allow the cycling of dissolved organic nutrients to be examined over the critical, and often undersampled, spring bloom period. Dissolved Organic Nitrogen (DON) clearly increased during the spring bloom in the central North Sea compared to winter concentrations. DON also increased in the Thames plume although showing greater winter variability related to higher riverine and sedimentary dissolved organic matter input at this shallow (∼18 m) coastal site. DON increase during the spring bloom was therefore related to primary production at both sites probably due to active release by phytoplankton. At both stations DON decreased to pre-bloom concentrations as the bloom declined suggesting the released DON was bioavailable and removed due to heterotrophic uptake and production. The preserved nutrient samples from the central North Sea site were also suitable for Dissolved Organic Phosphorus (DOP) analysis due to their low suspended load with similar trends and cycling to DON, albeit at lower concentrations. This suggested similar processes controlling both DON and DOP. The variable timing of short term events such as the spring bloom makes sampling away from coastal regions difficult without the use of autonomous technology. This study demonstrates for the first time the applicability of using preserved samples from automated buoys for the measurement of dissolved organic nutrients. [Copyright &y& Elsevier]

This paper provides a synthesis of current knowledge on phytoplankton production, seasonality, and stratification in tropical African lakes and considers the effects of nutrient enrichment and the potential impacts of climate warming on phytoplankton production and composition. Tropical African lakes are especially sensitive to climate warming as they experience wide fluctuations in the thermocline over a narrow range of high water temperatures. Recent climate warming has reduced phytoplankton biomass and production in the lakes. A decline in the production of palatable chlorophytes and an increase in cyanobacteria has led to reduced zooplankton production and a consequent decline in fish stocks, all of which can be associated with the elevated water temperatures. This indicates that even moderate climate warming may destabilise phytoplankton dynamics in tropical African lakes, thereby reducing water quality and food resources for planktivorous fish, with consequent negative impacts on human livelihoods. [ABSTRACT FROM AUTHOR]

Stoichiometric nutrient ratios are the consequence of myriad interacting processes, both biotic and abiotic. Theoretical explanations for autotroph stoichiometry have focused on species' nutrient requirements but have not addressed the role of nutrient availability in determining autotroph stoichiometry. Remineralization of organic N and P supplies a significant fraction of inorganic N and P to autotrophs, making nutrient recycling a potentially important process influencing autotroph stoichiometry. To quantitatively investigate the relationship between available N and P, autotroph N : P, and nutrient recycling, we analyze a stoichiometrically explicit model of autotroph growth, incorporating Michaelis-Menten-Monod nutrient uptake kinetics, Droop growth, and Liebig's law of the minimum. If autotroph growth is limited by a single nutrient, increased recycling of the limiting nutrient pushes autotrophs toward colimitation and alters both autotroph and environmental stoichiometry. We derive a steady state relationship between input stoichiometry, autotroph N : P, and the stoichiometry of organic losses that allows us to estimate the relative recycling of N to P within an ecosystem. We then estimate relative N and P recycling for a marine, an aquatic, and two terrestrial ecosystems. Preferential P recycling, in conjunction with greater relative P retention at the organismal and ecosystem levels, presents a strong case for the importance of P to biomass production across ecosystems. [ABSTRACT FROM AUTHOR]

The ratio of the amount of treated wastewater to river water is increasing in urban areas due to the spread of sewage systems. Treated wastewater is also sometimes extensively used to create streams and other water environments in urban areas. Rivers, streams and other water environments provide valuable habitats for all kinds of aquatic species, but the relationship between such aquatic species and the quality of treated wastewater they inhabit is not clearly understood. This study was carried out to clarify the effect of the water quality of treated wastewater such as nutrients and residual chlorine on periphytic algae grown in a stream receiving treated wastewater using laboratory-scale experimental channels. The following results were obtained. (1) When the range of phosphate (PO4-P) concentration was 0. 04 to 0. 09 mg/L, the higher the PO4-P concentration, the higher the biomass of periphytic algae and the more dominant the Chlorophyceae. (2) When the range of total residual chlorine (TRC) concentration was 0. 07 to 5. 8 mg/L, the higher the TRC concentration, the lower the biomass of periphytic algae. When the range of TRC concentration was 0. 93 to 5. 8 mg/L, this tendency was more pronounced. [ABSTRACT FROM AUTHOR]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.

Abstract: This study was carried out on the qualitative and quantitative characteristics of phytoplankton community structure and the environmental factors that affect its distribution and the changes in İzmit Bay, which is an eutrophic bay of Marmara Sea. The water samples were collected bimonthly between February 1999 and September 2000 from the 10 sampling sites (from surface, −5m, −10m, and −20m). Phytoplankton densities were calculated as cellsl−1, biomass was estimated by biovolumes and chlorophyll a content. During the study period, a total of 77 taxa from five algal classes, Bacillariophyceae, Dinophyceae, Chrysophyceae, Haptophyceae and Dicthyochophyceae were determined. Species composition of phytoplankton was typical of eutrophic conditions and was frequently characterized by the presence of Dinophyceae. In general, the most important groups were Dinophyceae and Bacillariophyceae in species numbers and density. The bay was characterized by intensive dinoflagellate (mainly Prorocentrum spp.) dominated bloom in all sampling periods, while the diatoms (shifts were observed in dominant diatoms) contributed most to the settling phytoplankton biomass. Differences among sampling sites and depths were recorded in terms of phytoplankton density, biovolume and chlorophyll a values. Correlation between chlorophyll a, cell count and biomass was significant. In general, the bay sustained a poor phytoplankton community with higher diversity relatively towards the outer than the interior zone in terms of Shannon-Weaver diversity index (H′). Some environmental parameters seem to play an important role in determining the phytoplankton community succession and then diversity, favoring or limiting the growth of the different groups of the phytoplankton. The Secchi disc depth, an indicator of primary production in the marine environment was comparatively low and limited vertical distribution of phytoplankton. The results indicate that primary production of the bay may be limited by nitrogen and silicate in some periods. [Copyright &y& Elsevier]

A nutrient–phytoplankton–zooplankton–detritus (1D-NPZD) `phytoplankton {Phyt} and Pseudocalanus elongatus {Zoop} dynamics in the spring bloom time in the Gdańsk Gulf. The 1D-NPZD model consists of three coupled, partial second-order differential equations of the diffusion type for phytoplankton {Phyt}, zooplankton {Zoop}, nutrients {Nutr} and one ordinary first-order differential equation for benthic detritus pool {Detr}, together with initial and boundary conditions. In this model, the {Zoop} is presented by only one species of copepod (P. elongatus) and {Zoop} is composed of six cohorts of copepods with weights (Wi) and numbers (Zi); where Zoop=∑lower limit i=1, upper limit 6 WiZi. The calculations were made for 90 days (March, April, May) for two stations at Gdańsk Gulf with a vertical space step of 0.5m and a time step of 900 s. The flow field and water temperature used as the inputs in the biological model 1D-NPZD were reproduced by the prognostic numerical simulation technique using hydrographic climatological data. The results of the numerical investigations described here were compared with the mean observed values of surface chlorophyll-a and depth integrated P. elongatus biomass for 10 years, 1980–1990. The slight differences between the calculated and mean observed values of surface chlorophyll-a and zooplankton biomass are ca. 10–60 mg C m-3 and ca. 5–23 mg C m-2, respectively, depending on the location of the hydrographic station. The 1D-NPZD model with a high-resolution zooplankton module for P. elongatus can be used to describe the temporal patterns for phytoplankton biomass and P. elongatus in the centre of the Gdańsk Gulf. [Copyright &y& Elsevier]

The response of phytoplankton development to an increased nutrient input in deep canyon-shaped stratified reservoirs was shown in four case studies. In contrast to lakes, specific features were described: longitudinal succession of phytoplankton development along the valley, transport of algal biomass and the peculiarities of P loading to epilimnion during summer stratification. Long term studies in two reservoirs showed the fluctuations of particular plankton components due to variations in flushing rate on the one hand and fish succession leading to prevalence of planktivorous species on the other. [ABSTRACT FROM AUTHOR]