Hypertrophic Lagoon Research Articles

Temporal and spatial differences in nitrogen and phosphorus biogeochemistry and ecosystem functioning of a hypertrophic lagoon (Curonian Lagoon, SE Baltic Sea) revealed via Ecological Network Analysis

In coastal lagoons, eutrophication and hydrology are interacting factors that produce distortions in biogeochemical nitrogen (N) and phosphorus (P) cycles. Such distortions affect nutrient relative availability and produce cascade consequences on primary producer's community and ecosystem functioning.In this study, the seasonal functioning of a coastal lagoon was investigated with a multielement approach, via the construction and analysis of network models. Spring and summer networks, both for N and P flows, have been simultaneously compiled for the northern transitional and southern confined area of the hypertrophic Curonian Lagoon (SE Baltic Sea). Ecological Network Analysis was applied to address the combined effect of hydrology and seasonality on biogeochemical processes.Results suggest that the ecosystem is more active and presents higher N and P fluxes in summer compared to spring, regardless of the area. Furthermore, larger internal recycling characterizes the confined compared to the transitional area, regardless of the season. The two areas differed in the fate of available nutrients. The transitional area received large riverine inputs that were mainly transferred to the sea without the conversion into primary producers' biomass. The confined area had fewer inputs but proportionally larger conversion into phytoplankton biomass. In summer, particularly in the confined area, primary production was inefficiently consumed by herbivores. Most phytoplanktonic N and P, in the confined area more than in the transitional area, were conveyed to the detritus pathway where P, more than N, was recycled, contributing to the unbalance in N:P stoichiometry and favouring N-fixing cyanobacteria over other phytoplankton groups. The findings of this study provide a comprehensive understanding of N and P circulation patterns in lagoon areas characterized by different hydrology. They also support the importance of a stoichiometric approach to trace relative differences in N and P recycling and abundance, that promote blooms, drive algal communities and whole ecosystem functioning.

Temporal changes of a food web structure driven by different primary producers in a subtropical eutrophic lagoon

Coastal lagoons are often characterized by eutrophic conditions which are known to impair the structure and functioning of both pelagic and benthic compartments. However, the manner in which eutrophication triggers a series of cascade effects in the whole food web in coastal lagoons has received little attention. Using stable isotope (SI) analyses, we investigated the food web structure in the hypertrophic lagoon of Yundang (Xiamen, China) in two periods of the year characterized by the recurrent alternation of Ulva lactuca and phytoplankton blooms in the cool (March) and warm (September) seasons, respectively. Large temporal fluctuations in the dominance of primary producers (i.e. macroalgae vs. phytoplankton) and, thus, in the available food items, were reflected in major changes in the diet and SI signals of several primary consumers, such as the amphipod Grandidierella japonica, the polychaetes Neanthes japonica and Capitella capitata, and omnivorous fishes (i.e. Mugil cephalus, Oreochromis niloticus, and Sardinella zunasi), while these changes were limited in top carnivorous fishes, such as Lateolabrax japonicus. Furthermore, reduced macrozoobenthic abundance available for omnivores in September was found to force omnivores to switch their feeding habits to those of herbivores. The present study provides evidence that the periodical alternation of macroalgal and phytoplankton blooms throughout the year strongly affect the relations among different trophic levels leading to a cascading effect across the whole food web and to major changes in the lagoon's food web structure. Importantly, our study shows that the lagoon's food web structure under persistent eutrophic conditions can still cope with seasonal changes in primary energy source type from macroalgae to microalgae due to the ability of omnivorous fishes to conduit different food sources up to the highest trophic levels. Thus, this study suggests that in such a highly variable eutrophic system, omnivores play a central role in the lagoon's functioning, and help to sustain the biological resources and the ecosystem services provided by the lagoon.

Drivers of Cyanobacterial Blooms in a Hypertrophic Lagoon

The Curonian Lagoon is Europe’s largest lagoon and one of the most seriously impacted by harmful blooms of cyanobacteria. Intensive studies over the past 20 years have allowed us to identify the major drivers determining the composition and spatial extent of hyperblooms in this system. We summarize and discuss the main outcomes of these studies and provide an updated, conceptual scheme of the multiple interactions between climatic and hydrologic factors, and their influence on internal and external processes that promote cyanobacterial blooms. Retrospective analysis of remote sensed images demonstrated the variability of blooms in terms of timing, extension and intensity, suggesting that they occur only under specific circumstances. Monthly analysis of nutrient loads and stoichiometry from the principal tributary (Nemunas River) revealed large interannual differences in the delivery of key elements, but summer months were always characterized by a strong N (and Si) limitation, that depresses diatoms and favors the dominance of cyanobacteria. Cyanobacteria blooms result in transient (night-time) hypoxia, which stimulates the release of iron-bound P, producing a positive feedback for blooms of N-fixing cyanobacteria. Other biotic factors, such as dreissenid mussels, chironomid larvae, cyprinids and large bird colonies, may also promote P recycling during summer, but their role as drivers of cyanobacteria blooms is understudied.

Evaluation and reformulation of the maximum peak height algorithm (MPH) and application in a hypertrophic lagoon

Evaluation and reformulation of the maximum peak height algorithm (MPH) and application in a hypertrophic lagoon

Zooplankton grazing on natural algae and bacteria under hypertrophic conditions

Zooplankton grazing on natural algae and bacteria under hypertrophic conditions The grazing characteristics of the natural zooplankton community in the shallow hypertrophic lagoon Albufera de Valencia (Spain) were compared in two periods of the annual cycle: (1) at the onset of spring, after a period of increased water flow through the lagoon that reduces phytoplankton density and cyanobacterial prevalence, and (2) in mid-spring, after the spring phytoplankton bloom and under conditions of cyanobacterial dominance. Clearance, ingestion and assimilation rates were measured by labelling natural seston with 14 C-bicarbonate and 3 H-thymidine/leucine. The clearance rates (CRs) of Daphnia magna, the dominant species at the onset of spring, were low, very likely as a consequence of the high abundance of filamentous cyanobacteria in the lagoon. The CRs were nearly equal for phytoplankton and bacteria, corroborating the unselective feeding of Daphnia. Bacteria supplied ≈40 % of the planktoniccarbon ingested byD. magna, and this carbon was assimilated with the same efficiencyas that provided by phytoplankton.This suggests a strong coupling betweenthe microbial loop and the classic grazer trophic web at the onset of spring in the lagoon and, consequently, an important contribution of the microbial loop to energy transfer to higher trophic levels (fish). The CRs of Bosmina longirostris, the dominant species in mid-spring, were also low probably because the food concentrations were well above the incipient limiting level. The CRs were higher for 1-15 µm algae than for <1 µm bacteria, indicating positive selective feeding towards larger cells. Algae sized 3-15 µm provided most of the planktonic carbon ingested by B. longirostris. Similarly, regarding the total mid-spring zooplankton community, phytoplankton contributed 90 % of the planktonic carbon ingested. This suggests that during the spring phytoplankton bloom when cyanobacteria dominate, the energy transferred to zooplankton via bacteria constitutes a smaller fraction than during periods of lower phytoplanktondensity. Finally, our results indicate that zooplankton consumed a very small proportion of phytoplankton and bacterioplankton production during the two studied periods, which highlights the reduced ability of zooplankton to control phytoplankton growth in hypertrophic systems.

Towards the development of a biogeochemical model for addressing the eutrophication problems in the shallow hypertrophic lagoon of Albufera de Valencia, Spain

Our study presents a biogeochemical model that aims to reproduce the ecological processes shaping phytoplankton dynamics in the shallow hypertrophic lagoon of Albufera de Valencia (Spain). The model simulates two elemental cycles (N and P), two phytoplankton groups (cyanobacteria and non-cyanobacteria), and heterotrophic bacteria. First, we examine the capacity to reproduce the observed plankton patterns, while accommodating the uncertainty related to the external forcing factors of our model (hydraulic and nutrient loading, zooplankton grazing). Sensitivity analysis is also performed to identify the most influential parameters and therefore to shed light on the knowledge needed to solidify the model parameter specification. We subsequently utilize the calibrated model to assess the phytoplankton response to potential restoration actions; namely, the interplay between external nutrient loading reductions and variant flushing rates. The model successfully simulates a number of relevant water quality variables in the system, including total chlorophyll a, nitrate, ammonia, total nitrogen and total phosphorus. According to our sensitivity analysis, the credibility of the model as a management tool is primarily dependent upon the characterization of the phytoplankton growth strategies and associated settling rates. External P and N loadings are identified as the predominant driver of the system dynamics and their control should remain the main priority of local management efforts. Finally, we pinpoint future research directions that could advance our understanding of the ecosystem functioning, including an improved quantitative description of the seasonal variability of the hydraulic regime in the studied lagoon.

Recolonization of macrozoobenthos on defaunated sediments in a hypertrophic brackish lagoon: Effects of sulfide removal and sediment grain size

Influences of sediment types on recolonization of estuarine macrozoobenthos were tested using enclosures in a hypertrophic lagoon. Three types of azoic sediment, sand (S), sulfide-rich mud (M), and mud removed of sulfide through iron addition (MFe), were set in field for 35 days during a hypoxic period. A total of 14 taxa including opportunistic polychaetes and amphipods occurred. Infaunal community in S treatment was characterized by highest diversity, total density and biomass, and population density of five dominant taxa, while those parameters were lowest in M treatment. Sulfide removal in MFe treatment achieved much higher density, biomass, and population densities of several taxa in the sediment. Multivariate analyses demonstrated that the established community structure was unique to each treatment. These imply that dissolved sulfide level as well as sediment grain size is a key determinant for the community composition and recolonization speed of early colonists in estuarine soft-bottom habitats.

Patterns of benthic oxygen uptake in a hypertrophic lagoon: spatial variability and controlling factors

Water temperature, organic matter quality and quantity and macrofauna activity generally regulate the seasonal evolution of benthic oxygen uptake in coastal areas. We hypothesize that highly productive lagoons can represent an exception in this respect, due to alternating sequences of phytoplankton bloom, dystrophy and collapse events, coupled with water anoxia and azoic sediments. In order to verify this assumption, total oxygen uptake (TOU) and diffusive oxygen uptake (DOU) were determined during the ice-free period of 2009 in the sediments of a hypertrophic basin (the Curonian Lagoon, Baltic Sea). Seasonal measurements were carried out via sediment incubation and microprofiling in littoral and pelagic areas. TOU increased from spring to summer, but it remained elevated also in autumn likely due to accumulation of labile organic matter after algal blooms. TOU and DOU closely agreed in pelagic areas, while at littoral sites TOU exceeded DOU, suggesting temporal or local importance of bioturbating organisms. Water chlorophyll a and oxygen saturation were likely the most important driving factors for benthic respiration. Very limited oxygen penetration (<1 mm) over a 6-month period possibly enhances nitrogen removal via denitrification and reactive phosphorus efflux.

Hypertrophic lagoon management by sediment disturbance

Experimental control of eutrophication in a small coastal lagoon was attempted by means of sediment disturbance. A specially designed boat was used to resuspend the top 3cm of sediment by a jets of air–water directed towards the bottom. This disturbance was carried out for 3months in each of two areas with a surface area of 24 and 20 hectares respectively. In a total of 80 stations in these two areas and in two undisturbed areas of 16 and 20ha, organic matter, porosity, density and redox potential were monitored in sediment bimonthly and free sulphides were monitored in water close to the bottom. Before, during and after disturbance, the impact of daily sediment resuspension on the water column was monitored monthly, as ammonium nitrogen (N–NH4), soluble reactive phosphorus (SRP), dissolved oxygen (DO) and pH. In the whole lagoon, sediment texture was determined at the start and at the end of the experiment in 120 stations, and seaweed (mainly Chaetomorpha linum and Lophosiphonia subadunca) and seagrass (Ruppia cirrhosa) biomasses were estimated in 42 stations every month. The results showed a stable organic matter content in disturbed areas and an increase in undisturbed areas, as well as an increase in seaweed in areas distant from disturbed areas. No significant effect of sediment resuspension on water column N–NH4, SRP, DO or pH was found.

Enhancement of jellyfish (Aurelia aurita) populations by extensive aquaculture rafts in a coastal lagoon in Taiwan

Abstract Lo, W-T., Purcell, J. E., Hung, J-J., Su, H-M., and Hsu, P-K. 2008. Enhancement of jellyfish (Aurelia aurita) populations by extensive aquaculture rafts in a coastal lagoon in Taiwan. – ICES Journal of Marine Science, 65: 453–461. Blooms of the moon jellyfish, Aurelia aurita, often occur in coastal waters that are heavily affected by human construction, such as harbours. Tapong Bay is a hypertrophic lagoon in southwestern Taiwan that was studied between August 1999 and September 2004. The removal of extensive oyster-culture rafts in June 2002 provided a “natural” experiment to examine the effects of aquaculture on processes and communities in the lagoon. The removal caused many changes in the ecosystem, including increases in flushing, light penetration, dissolved oxygen, salinity, chlorophyll a, primary production, and zooplankton, but decreases in nutrients, periphyton, and dramatically reduced populations of bivalves, zooplanktivorous fish, and jellyfish (A. aurita). We conclude that environmental and trophic conditions were favourable for jellyfish throughout the study period. Therefore, we believe that aquaculture rafts enhanced jellyfish populations by three probable mechanisms: the rafts provided substrate and shading for the larval settlement and polyp colony formation, and the rafts restricted water exchange in the lagoon. Aquaculture is increasing rapidly in Asia, and the problems associated with jellyfish may also increase.

Low filtering rates of Daphnia magna in a hypertrophic lake: laboratory and in situ experiments using synthetic microspheres

Zooplankton grazing was measured in Albufera of Valencia (Spain), a shallow turbid hypertrophic lagoon dominated by filamentous bluegreens, during the period of Daphnia magna growth, to evaluate the role of this cladoceran in maintaining a clear water phase which takes place after flushing for rice cultivation practices. We found extremely low ingestion and clearance rates (CR) on latex beads in situ, using a Haney trap suggesting potentially strong inhibition of grazing by the filamentous cyanobacteria, still flourishing in the lagoon. To test the effect of filaments, we undertook laboratory feeding experiments using six different dilutions of the lagoon water to vary filament concentrations, and four different bead concentrations. A highly significant power function between CR and water dilution associated with filament concentrations was found, indicating that the ability of Daphnia to exploit smaller edible algae and thereby control phytoplankton growth would depend on filament concentration levels in the lagoon. From our results only the two more diluted treatments, 9 × 103 and 18 × 103 filament ml−1 showed CRs not far from the range of what would be normally expected on the basis of the general relationship of feeding rate as a function of total food concentration. This means that at lower food concentrations, filaments reduce D. magna CR by increasing total food concentration beyond the incipient limiting level, as well as by moderate mechanical interference with the animal’s feeding. However, at lagoon water concentrations above 25% (corresponding to filament concentrations of 75 × 105 filaments ml−1), extremely low CR’s, which did not respond to any food addition, were obtained for D. magna. From these results we can infer that at concentrations beyond the above-mentioned critical level, feeding inhibition by filamentous cyanobacteria is most probably due entirely to mechanical interference.

Carbon and nutrient dynamics in a hypertrophic lagoon in southwestern Taiwan

Dissolved and particulate phases of carbon (DIC, DOC, POC) and nutrients (DIN, DIP, DSi, DON, DOP, PN) were investigated bimonthly from August 1999 to August 2000 to study biogeochemical dynamics of carbon and nutrients in Tapong Bay, a small semi-enclosed and hypertrophic lagoon in southwestern Taiwan. The lagoon has only a tidal inlet for exchanging water between Tapong Bay and Taiwan Strait, which may result in low water exchange rates and various oxygen-deficient conditions in bottom water of the inner bay during warm seasons. The water exchange time of Tapong Bay ranges from 7 days (summer) to 13 days (winter) with a mean of 10 days. Nutrient dynamics were largely ascribed to allochthonous inputs, biological and exported removals in the lagoon. Diffusion fluxes from sediments to overlying water accounted for only about 7.6% of annual DIN inputs and 1.0% of annual DIP inputs. High primary productivity (89 mol C m −2 year −1) supported by abundant nutrients primarily drove the lagoon into a hypertrophic condition as particulate organic matter was derived mainly from biological production. Excess of DIP appeared to occur throughout the study period in the lagoon. Temperature, solar radiation and turbidity, rather than nutrients, perhaps controlled seasonal variations of primary productivity. The net ecosystem production (NEP) derived from daily changes of DOC and POC inventories was about 6.3 mmol C m −2 day −1 that was close to 6.7 mmol C m −2 day −1 simulated from the biogeochemical modeling. Therefore, the net ecosystem production (NEP) rate of organic carbon estimated from the biogeochemical model was reliable, and the NEP was temporally variable with an annual mean of 5.8 mol C m −2 year −1, implying that Tapong Bay was an autotrophic system. Although calcification proceeded pronouncedly in warm seasons, an invasion of CO 2 was significant in this system. In terms of nitrogen budget, the annual nitrogen fixation exceeded the annual denitrification with a magnitude of 1.30 mol N m −2 year −1, which may be supported by the abundance of nitrogen fixation microplanktons in the lagoon.

Impact of Commercial Clam Harvesting on Water Column and Sediment Physicochemical Characteristics and Macrobenthic Community Structure in a Lagoon (Sacca Di Goro) of the Po River Delta

The Sacca di Goro is a hypertrophic lagoon of the Po river Delta, which is heavily exploited for rearing ofthe Manila clam, Tapes philippinarum. Harvesting of the clams could add to the general disturbance regime in the lagoon through damage to the benthic community, the release of porewater nutrients which could fuel macroalgal growth and of reduced compounds from the sediment leading to depletion of water column oxygen. We tested these hypotheses during an in situ harvesting experiment. No significant differences were found in population or biomass densities, or community indices between samples collected before and after harvesting. Similarly, no differences were recorded in trophic (food source) availability. Whilst, there was a slight reduction in water column oxygen, pH and Eh values in the plume of suspended sediment, these changes were small. Similarly, increases in water column concentrations of ammonium and reactive phosphorus during harvesting were not significant. Calculations based on profiles of sediment ammonium content, before and after harvesting, demonstrated a release of ammonium equivalent to 13 mmol m−2. In terms of the oxygen and nitrogen budgets of the lagoon the effects of harvesting seem to be of little importance and of the same order of magnitude of sediment-water fluxes driven by clam activity, both terms being subjected to high energy hydrodynarnism.

Changes of life-history traits and size in Daphnia magna during a clear-water phase in a hypertrophic lagoon (Albufera of Valencia, Spain)

(2002). Changes of life-history traits and size in Daphnia magna during a clear-water phase in a hypertrophic lagoon (Albufera of Valencia, Spain) SIL Proceedings, 1922-2010: Vol. 28, No. 3, pp. 1203-1208.

Santa Giusta Lagoon (Sardinia): phytoplankton and nutrients before and after waste water diversion

The purpose of this paper was to assess the effect of the diversion of waste water on the trophic status of the Stagno di Santa Giusta, a hypertrophic lagoon on the centre-western coast of Sardinia. The data available (1990, 1992-1994) before the diversion (1995) were compared with those collected from 1995 to 1999. The lagoon has an area of about 8 km2; its mean depth is about 1 m and is well mixed as regards circulation and stratification. This study examined temperature, salinity, pH, main nutrients (reactive and total phosphorus, nitrate and ammonium nitrogen, reactive silica), chlorophyll-a, phytoplanktonic density and phytobenthic biomass. A comparison of the condition of the water before and after the diversion showed that there was an insufficient reduction in nutrient concentrations. The mean concentrations of nitrate nitrogen and ammonium nitrogen fell from 33 and 87 mg N m-3, respectively, to 28 and 66 mg N m-3, respectively. There was a more marked reduction in phosphorus (from 107 mg P m-3 as reactive phosphorus and from 190 mg P m-3 as total phosphorus to 77 and 127 mg P m-3, respectively), and in reactive silica, from 3 to 1.7 mg l-1. Chlorophyll-a decreased from 11.3 to 10.2 mg m-3; the total density of phytoplankton dropped considerably, but this was due to a different species composition. Phytobenthic biomass showed no particular variations. There were no changes in trophic level, so that dystrophic crises still occurred after the diversion. The results showed that there were no substantial improvements in the trophic status of the lagoon during the years after the diversion, except for some months in 1995. A possible explanation may lie in the structure of the diversion system, which does not completely stop the inflow of sewage into the lagoon.

Seasonal succession of zooplankton populations in the hypertrophic lagoon Albufera of Valencia (Spain)

Seasonal succession of zooplankton populations in the hypertrophic lagoon Albufera of Valencia (Spain)

A multi-temporal study of chlorophyll-a concentration in the Albufera lagoon of Valencia, Spain, using Thematic Mapper data

Abstract A multi-temporal study of chlorophyll-a concentration, has been made by means of Landsat-5 Thematic Mapper (TM) band 1 (0·45-0·52μm) in the Albufera of Valencia, a hypertrophic lagoon of shallow depth. The relationship between this parameter and satellite data was set up from in situ measurements and concurrent satellite data obtained in a campaign from 22 July 1985. This relation has been applied to images of different dates by using a simple procedure of correction, which is based on the use of selected surfaces whose ground reflectance is assumed to be constant with time. Good results were obtained and chlorophyll-a concentrations have been determined with an error of 20 per cent.