Nutrient dynamics and ecosystem metabolism in the Bay of Blanes (NW Mediterranean)

The dynamics of the nutrient pools and their stoichiometry as well as their control by ecosystem metabolism (benthic and planktonic) and benthic–pelagic exchanges (sedimentation rates and sediment waterfluxes) were examined in the Mediterranean littoral (Blanes Bay, NE Spain). Dissolved organic nitrogen comprised about half of the nitrogen present in the water column and the carbon pool was dominated by the inorganic pool (95% of the carbon present in the water column). The dissolved and particulate organic pools were deficient in P relative to C and N, indicating a rapid recycling of P from organic matter. The pelagic compartment was heterotrophic, supported by significant allochthonous inputs of land material, which also contributed greatly to the sedimentary inputs (37% of total sedimenting carbon). In contrast, the benthic compartment was autotrophic, with the excess net benthic community production balancing the deficit in pelagic community production, leading to metabolic equilibrium at the station studied. Sedimentary inputs of nitrogen, phosphorus and silicon exceeded the benthic release, indicating that the benthic compartment acted as a sink for nutrients, consistent with its autotrophic nature. Carbon inputs to the benthic compartment also exceeded requirements, due to the allochthonous subsidies to the system, so that the benthic compartment stored or exported organic carbon. An erratum to this article can be found at .     

A revision of the genus Neoneuromus in China (Megaloptera: Corydalidae)

Lake Illawarra, is a typical shallow intertidal coastal barrier lagoon in New South Wales, Australia. This paper reports the first examination of photosynthetic characteristics of benthic microalgae and seagrass in this lake by measuring the oxygen exchange procedure (flux) using sediment-core incubations in the laboratory. Photosynthesis vs irradiance relationships (P–I curves) were generated from measurements made at nine irradiances for microphytobenthos (MPB) at five different water depths (sites) during September 2002. Maximum benthic gross primary production (GP_max) for MPB in this lake tended to decrease with the increasing water depth from Site 5 (about 0.2 m deep) to Site 1 (about 3.0 m deep), and was correlated with decreasing surface sediment Chl-a concentrations.     

Contribution of benthic microalgae to the temporal variation in phytoplankton assemblages in a macrotidal system

Suspended marine benthic microalgae in the water column reflect the close relationship between the benthic and pelagic components of coastal ecosystems. In this study, a 12‐year phytoplankton time‐series was used to investigate the contribution of benthic microalgae to the pelagic system at a site along the French‐Atlantic coast. Furthermore, all taxa identified were allocated into different growth forms in order to study their seasonal patterns. The highest contribution of benthic microalgae was observed during the winter period, reaching up to 60% of the carbon biomass in the water column. The haptobenthic growth form showed the highest contribution in terms of biomass, dominant in the fall‐winter period when the turbidity and the river flow were high. The epipelic growth form did not follow any seasonal pattern. The epiphytic diatom Licmophora was most commonly found during summer. As benthic microalgae were found in the water column throughout the year, the temporal variation detected in the structure of pelagic assemblages in a macrotidal ecosystem was partly derived from the differentiated contribution of several benthic growth forms.     

Estuarine intertidal sandflat benthic microalgal responses to in situ and mesocosm nitrogen additions

Benthic microalgal communities are important components of estuarine food webs and make substantial contributions to coastal materials cycling. Nitrogen is generally the limiting factor for marine primary production; however other factors can limit benthic primary producers because of their access to the additional nutrients found in sediment porewater. Field and laboratory experiments were conducted to test the hypothesis that water column nitrogen supply affects estuarine sandflat benthic microalgal community structure and function. Our field and mesocosm experiments assessed changes at both the population and functional group levels. Simulated water column nitrogen additions increased maximum community photosynthesis in most cases (Pb_max from photosynthesis vs. irradiance curves). Additional changes that resulted from nitrogen additions were decreases in porewater phosphate, increases in porewater ammonium, shifts in community composition from N₂ fixing cyanobacteria toward diatoms, and detectable, though not statistically significant increases in biomass (as chlorophyll a). Results from field and laboratory experiments were quite similar, suggesting that laboratory experiments support accurate predictions of the response of intertidal benthic microalgae to changes in water column nutrient conditions.     

Environmental heterogeneity patterns and predictive models of chlorophyll a in a Brazilian coastal lagoon

The spatial and temporal patterns of environmental heterogeneity in a Brazilian coastal lagoon were described by means of principal component analysis. Carapebus Lagoon has been subject to eutrophication, due to increased nutrient loading from domestic and industrial sewage. Spatial variations in the trophic state and temporal variations in the degree of marine influence are the major sources of environmental heterogeneity in this lagoon. The close and significant relation between total phosphorus and chlorophyll a (r² = 60, p <0.05), and the high TN:TP ratios (up to 50:1) suggest that phosphorus might be the major nutrient controlling phytoplankton biomass in this lagoon. However, nitrogen might be more important as a growth-limiting nutrient in the eutrophic site of the lagoon, where high total phosphorus concentration (up to 338 μg l-1) and low TN:TP mass ratios (<10:1) were found. In a multiple regression model, total phosphorus and electric conductivity explained together a high and significant (R²=0.86, p < 0.001) amount of variance in chlorophyll yields. This predictive model of chlorophyll a is important as a tool for Carapebus lagoon management because it allows one to predict the algal biomass development of the lagoon in response to nutrients and marine water inputs resulting from man's activities. This revised version was published online in July 2006 with corrections to the Cover Date.     

Variability of nutrients and phytoplankton biomass in a shallow brackish water ecosystem (Chilika Lagoon, India)

Seasonal and spatial variations in water quality parameters, such as nutrients [NH₄ ⁺–N, NO₂⁻–N, NO₃⁻–N, PO₄³⁻–P, total nitrogen (TN) and total phosphorus (TP)], Secchi disc depth, salinity, dissolved oxygen, chlorophyll a, primary productivity and phytoplankton standing stock, were studied in Chilika Lagoon (from 27 sampling locations) during 2001–2003 to assess the present ecological status. The study was undertaken after a major hydrological intervention in September 2000, which connected the lagoon body and the Bay of Bengal via a manmade opening (new mouth). Current and old data on water quality were also compared to establish the changes that had occurred after the hydrological intervention. Multivariate techniques and gridding methods were used to investigate the spatial and seasonal variability of the data and to characterize the trophic evolution of the basin. Results of principal component analysis (PCA) indicated that the 27 stations can be classified into five groups based on similarities in the temporal variation of nutrients, chlorophyll a concentration, salinity, and other physicochemical parameters. The tributaries and the exchange of lagoon water with the Bay of Bengal most probably determine the water quality and the dynamics of the ecosystem. Hydrodynamics of the lagoon, weed coverage, input of urban sewage through tributaries and agricultural runoff are probably the key factors controlling the trophic conditions of the lagoon. An increase in salinity and total phosphorus was noted after the new mouth was opened, while the total suspended sediment load, the water column depth, and nitrogenous nutrients decreased. The new mouth opening also brought changes in the phytoplankton species composition.     

Modeling eutrophication and oligotrophication of shallow-water marine systems: the importance of sediments under stratified and well-mixed conditions

A one-dimensional model that couples water-column physics with pelagic and benthic biogeochemistry in a 50-m-deep water column is used to demonstrate the importance of the sediment in the functioning of shallow systems, the eutrophication status of the system, and the system’s resilience to oligotrophication. Two physical scenarios, a well-mixed and a stratified water column, are considered and both are run along a gradient of increasing initial pelagic-dissolved inorganic nitrogen (DIN) concentration. Where the mixed layer extends to the bottom, more nutrients and less light are available for growth. Under low to moderately eutrophic conditions (pelagic DIN <30 mmol m⁻³), this leads to higher productivity in well-mixed waters, while the stratified system is more productive under highly eutrophic conditions. Under stratification, the build-up of nitrate and depletion of oxygen below the mixed layer does not notably change the functioning of the sediment as a sink for reactive nitrogen. In sediments underlying well-mixed waters, sedimentary denitrification, fueled mainly by in situ nitrification, is slightly more important (8–15% of total benthic mineralization) than under stratified waters (7–20%), where the influx of bottom-water nitrate is the most important nitrate source. As a consequence of this less efficient removal of reactive nitrogen, the winter DIN concentrations are higher in the stratified scenario. The model is used to estimate the long-term benefits of nutrient reduction scenarios and the timeframe under which the new steady-state condition is approached. It is shown that a 50% reduction in external nitrogen inputs ultimately results in a reduction of 60–70% of the original pelagic DIN concentration. However, as the efflux of nitrogen from the sediment compensates part of the losses in the water column, system oligotrophication is a slow process: after 20 years of reduced inputs, the pelagic DIN concentrations still remain 2.7 mmol m⁻³ (mixed) and 3.9 mmol m⁻³ (stratified) above the ultimate DIN concentrations. Guest editors: J. H. Andersen & D. J. Conley Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark     

Nitrogen cycling in coastal marine ecosystems

It is generally considered that nitrogen availability is one of the major factors regulating primary production in temperate coastal marine environments. Coastal regions often receive large anthropogenic inputs of nitrogen that cause eutrophication. The impact of these nitrogen additions has a profound effect in estuaries and coastal lagoons where water exchange is limited. Such increased nutrient loading promotes the growth of phytoplankton and fast growing pelagic macroalgae while rooted plants (sea-grasses) and benthic are suppressed due to reduced light availability. This shift from benthic to pelagic primary production introduces large diurnal variations in oxygen concentrations in the water column. In addition oxygen consumption in the surface sediments increases due to the deposition of readily degradable biomass. In this review the physico-chemical and biological factors regulating nitrogen cycling in coastal marine ecosystems are considered in relation to developing effective management programmes to rehabilitate seagrass communities in lagoons currently dominated by pelagic macroalgae and/or cyanobacteria.     

Effects of nutrient enrichments on primary production in the Ria Formosa coastal lagoon (Southern Portugal)

Small-scale, short-term enrichment experiments were conducted in the Ria Formosa coastal lagoon (southern Portugal), to assess the effects of nutrient availability on primary productivity, biomass (as chlorophyll a), and algal composition. Samples were collected from natural communities at three different sites in the western lagoon: Barra, oceanic inlet; Ramalhete, adjacent to a urban waste water treatment plant; and Ponte, an upstream channel used for recreation and bivalve farming. These samples were enriched separately with nitrogen and phosphorous during the extreme neap tides of the summer solstice at both high (HW) and low water (LW). The experiment was repeated during the autumnal equinox to test for seasonality, and during the following summer solstice to test for replication. The addition of nitrogen consistently stimulated the productivity and biomass during summer experiments at the two sites within the lagoon, identifying N as the most likely primary “potentially limiting nutrient” in the western part of the lagoon for this period. No stimulation of biomass and productivity occurred in September at the same two sites indicating the importance of other factors such as light, sedimentation or grazing pressure, as controlling the pelagic community. However, these outcomes were reversed at the oceanic inlet (Barra-HW) where there was no stimulation by nitrogen during the summer months, but there was in September, suggesting that there is a different nutritional requirement for the coastal community in comparison with the lagoon community. In samples where productivity was stimulated, diatoms were the group most sensitive to enrichment.     

Spatial variability of benthic-pelagic coupling in an estuary ecosystem: consequences for microphytobenthos resuspension phenomenon

The high degree of physical factors in intertidal estuarine ecosystem increases material processing between benthic and pelagic compartments. In these ecosystems, microphytobenthos resuspension is a major phenomenon since its contribution to higher trophic levels can be highly significant. Understanding the sediment and associated microphytobenthos resuspension and its fate in the water column is indispensable for measuring the food available to benthic and pelagic food webs. To identify and hierarchize the physical/biological factors potentially involved in MPB resuspension, the entire intertidal area and surrounding water column of an estuarine ecosystem, the Bay des Veys, was sampled during ebb tide. A wide range of physical parameters (hydrodynamic regime, grain size of the sediment, and suspended matter) and biological parameters (flora and fauna assemblages, chlorophyll) were analyzed to characterize benthic-pelagic coupling at the bay scale. Samples were collected in two contrasted periods, spring and late summer, to assess the impact of forcing variables on benthic-pelagic coupling. A mapping approach using kriging interpolation enabled us to overlay benthic and pelagic maps of physical and biological variables, for both hydrological conditions and trophic indicators. Pelagic Chl a concentration was the best predictor explaining the suspension-feeders spatial distribution. Our results also suggest a perennial spatio-temporal structure of both benthic and pelagic compartments in the ecosystem, at least when the system is not imposed to intense wind, with MPB distribution controlled by both grain size and bathymetry. The benthic component appeared to control the pelagic one via resuspension phenomena at the scale of the bay. Co-inertia analysis showed closer benthic-pelagic coupling between the variables in spring. The higher MPB biomass observed in summer suggests a higher contribution to filter-feeders diets, indicating a higher resuspension effect in summer than in spring, in turn suggesting an important role of macrofauna bioturbation and filter feeding (Cerastoderma edule).     

Contrasting responses of intertidal microphytobenthos and phytoplankton biomass and taxonomic composition to the nutrient loads in the Jiulong River Estuary

Microphytobenthos (MPB) and phytoplankton are important primary producers in the estuarial ecosystem, and their functions are critical to the ecosystem's biodiversity and environmental safety. The aim of this study was to compare the response of MPB and phytoplankton to the nutrient loads in a eutrophic estuary, which has seldom been studied. We used high‐performance liquid chromatography (HPLC) and CHEMTAX software to examine the biomass and taxonomic composition of both MPB and phytoplankton at Da‐yu Island (DYI) and Ji‐yu Island (JYI) in the Jiulong River Estuary from July 2010 to March 2012. The results showed that MPB chlorophyll a was low in the summer and high in the winter at both DYI and JYI, indicating a unimodal pattern. However, the phytoplankton chlorophyll a showed a mirrored pattern. Diatoms were the dominant class in both benthic and pelagic environments. Although redundancy analysis indicated that the effects of different environmental factors could not be easily separated, it is likely that phosphate and temperature were the most important factors regulating the seasonal patterns of MPB and phytoplankton diatoms, respectively. MPB and phytoplankton cyanobacteria was co‐limited by salinity and temperature. The high N/P ratio and low phosphate favored chlorophytes and cyanobacteria. Our study demonstrates the use of HPLC and CHEMTAX in an integrated survey of the spatial and temporal distribution patterns of MPB and phytoplankton in an estuarial ecosystem. The contrasting responses of MPB and phytoplankton to nutrient loads indicate the critical role of MPB in subtropical estuarial ecosystem function. The relationship between nutrients and MPB may indicate a significant contribution to carbon and nutrient cycling.     

Fish Reliance on Littoral–Benthic Resources and the Distribution of Primary Production in Lakes

Pelagic, littoral, and terrestrial resources can all play a role in supporting consumers in lakes. The role of benthic algal-derived food web pathways in lakes is perhaps the least understood because limnologists have historically focused on pelagic (open-water) production and processes. We compiled carbon stable isotope data from 546 fish populations (75 lakes), and used a two end-member mixing model to calculate littoral–benthic reliance for each fish species in each lake. Fish littoral–benthic reliance values were averaged by lake to assess overall fish species benthic reliance for each lake. Lake-specific mean littoral reliance (BR_L; fish species not weighted according to production or biomass) averaged 57% and was independent of lake morphological and limnological attributes. For these same lakes, water column nutrients, light, and morphometry data were used to estimate whole-lake benthic algal and phytoplankton primary production. On average, benthic algae comprised 36% of whole-lake primary production (BP_f = 0.36). BP_f and BR_L were weakly correlated: BR_L tends to be high even in large/deep lakes in which benthic algae is a minor contributor to whole-lake primary production. The high littoral–benthic contribution to individual fish species appears to reflect the high concentration of fish species diversity in the littoral zone. Our work cannot be extrapolated to whole-lake fish production. However, the result is consistent with other work indicating that most fish species inhabit the littoral zone, whereas relatively few exclusively inhabit the pelagic. Our results suggest that it takes less primary production to support a single fish species in the littoral zone than is required to support a species in the pelagic.     

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.     

Coupled energy pathways and the resilience of size-structured food webs

Size-based food-web models, which focus on body size rather than species identity, capture the generalist and transient feeding interactions in most marine ecosystems and are well-supported by data. Here, we develop a size-based model that incorporates dynamic interactions between marine benthic (detritus-based) and pelagic (primary producer based) pathways to investigate how the coupling of these pathways affects food web stability and resilience. All model configurations produced stable steady-state size spectra. Resilience was measured by the return speed obtained from local stability analysis. Return times following large perturbations away from steady-state were also measured. Resilience varied nonlinearly with both predator and detrital coupling, and high resilience came from predators (1) feeding entirely in the slow benthic zone or (2) feeding across the two energy pathways, with most food coming from the fast pelagic pathway. When most of the energy flowed through the pelagic pathway, resilience was positively related to turnover rate. When most of the energy flowed through the benthic pathway, resilience was negatively related to turnover rate. Analysis of the effects of large perturbations revealed that resilience for pelagic ecosystems depended on the nature of the perturbation and the degree of benthic–pelagic coupling. Areas with very little or no benthic–pelagic coupling (e.g. deep seas or highly stratified water columns) may return more quickly following pulses of detrital fallout or primary production but could be much less resilient to the effects of human-induced mortality (harvesting).     

Sedimentation modified by wind induced resuspension in a shallow tropical lagoon (Cote d'Ivoire)

In shallow environments, under certain conditions of fetch, wind velocity, bathymetry and bottom characteristics, resuspension can be generated by wind induced waves. In the tropical Ebrié lagoon, austral trade winds are dominant almost all year long, and their velocity shows a marked diel pattern with maximum speed between noon and midnight. Only austral trade winds with a speed >3 m s⁻¹ allow particle resuspension which is effective for depths<1.5 m. In these areas, significantly higher values of chlorophyll biomass and mineral seston are noted during the windy sequences. Granulometric and mineralogical analyses showed that only the surficial sediment (0–3 cm) was involved in resuspension. This process induces several effects: 1) an increase of the suspended matter concentration in the water and thus a light attenuation due to a higher turbidity, 2) a redistribution in the whole water column of nutrients from the pore water and 3) a removal of the finer fractions from the superficial sediment. On the contrary, for depths>1.5 m, particle sinking is permanent in depressions which are spontaneously transformed into anoxic systems. At the lagoon scale, sedimentation is significantly modified by wind induced resuspension. According to the bathymetry and the distance from a river, three sedimentary facies are recognized. Their grain size distributions are parabolic in areas where resuspension occurs, logarithmic in areas where no resuspension is possible and hyperbolic in the hollows and the main channels. Finally, a large part of the allochthonous inputs (from drainage and rivers) and autochthonous pelagic production is trapped into the Ebrié lagoon and less than 10% of the particles entering the lagoon are exported toward the Atlantic Ocean.     

Increasing nitrogen limitation during summer in the List Tidal Basin (Northern Wadden Sea)

The European Wadden Sea is characterized by high nutrient loads and turbid waters. Riverine nutrient input showed a gradual decrease since the mid 1980s. In the List Tidal Basin (Northern Wadden Sea) the frequency of low NO₃ values in summer has increased and decreasing mean annual suspended matter concentrations indicate an increasing underwater irradiance. We used an approach developed by Cloern (Aquat Ecol 33:3–16, 1999) to analyze resource limitation of nitrogen (DIN) and underwater irradiance for phytoplankton growth in the List Tidal Basin between 1985 and 2005. Comparing our results to other studies suggests that the List Tidal Basin is one of the most nitrogen sensitive areas of the European Wadden Sea. In 2005, phytoplankton growth was light limited from January to May and in November and December, co-limited by both resources in June, July and October, and nitrogen limited in August and September. Comparing phytoplankton growth limitation in the periods 1985–1991 and 1999–2005, the duration of nitrogen limitation during summer is significantly longer in the second period (2.1 ± 0.9 months) than in the first (0.7 ± 0.5). Moreover, light limitation in September and October has decreased in the second period. A decreasing phytoplankton growth during summer is in line with former studies from the List Tidal Basin, which showed that summer chlorophyll concentrations have decreased since the mid 1980s. We suggest that nowadays less food is available for higher pelagic and benthic trophic levels due an increased nitrogen limitation during summer.     

Annual cycle of the planktonic phytocenosis in the Ob-Enisei shallow zone of the Kara Sea

This paper analyzes data on the state of the pelagic microalgae community of the Kara Sea for all hydrological seasons. The data were obtained during complex in situ observations in 1996–2006. Four phases in the annual succession cycle of the phytoplankton of the nearshore continental area of the Kara Sea were identified: a prevernal phase (cryoflora bloom), vernal phase (ice-edge bloom), summer-fall phase (mixed synthesis phase), and winter phase (dormant phase). These periods are clearly distinguished from each other in their composition of dominating species complexes and quantitative characteristics, i.e., the numbers and biomasses of microalgae. In the investigated region, which is completely covered by ice during most of the year, the primary production processes begin at the same time as in ice-free coastal areas. Growth and blooming of cryoflora occur under the ice cover long before it breaks down. The peak development of the pelagic microalgae community, which is comparable to the spring peak of microalgae in ice-free coastal areas, is observed in the summer, when freshwater runoff from large rivers increases sharply.     

Water Quality Trends in a Coastal Lagoon Impacted by Non-point Source Pollution after Implementation of Protective Measures

Water quality data from two different monitoring periods are used to evaluate the trophic state and effectiveness of various protective measures on the restoration of a eutrophic, coastal Mediterranean lagoon. Main protective measures included elimination of municipal/industrial raw wastewater discharges in the rivers outflowing to the lagoon, sediment/erosion control practices in the lagoon’s drainage basin (i.e., construction of sediment/debris dams and grade control structures, reforestation and ban on livestock grazing), and reduction of fertilizer application quantities as a result of changes in crops. Water quality data include, among others, chlorophyll a, dissolved oxygen and nutrient concentrations, various physicochemical parameters, and transparency, measured during two monitoring periods, i.e., before (1983–84) and after (1998–99) implementation of protective measures. Rainfall depth for the two time periods was also available. Empirical equations were developed, from statistical analyses of the data, relating the water quality parameters during the two monitoring periods. These models help identify water quality trends. Based on the analyses, it seems that measures were effective in reducing sediments transported into the lagoon. However, the lagoon remains eutrophic to hypereutrophic, mostly due to phosphorus released in the water column from bottom sediments. Therefore, future restoration efforts should be directed towards the management of bottom sediments.