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.     

The structure,diversity and somatic production of the fish community in an estuarine coastal lagoon,Ria de Aveiro (Portugal)

The present study aims to determine biological fish production of a lagoon and relate this to the commercial fisheries yield. The fish community of an estuarine lagoon in the west coast of Portugal was sampled between November 1998 and November 2000 to estimate the production ecology of the community, including somatic production, population size, species richness, species diversity, and biomass. Using the Allen curve method of determination, the total annual fish production of all fish species in the lagoon was calculated at 90.3 tonnes or 2.1 g m⁻² year⁻¹ in the first year and 106.7 tonnes or 2.5 g m⁻² year⁻¹ in the second year. The marine seasonal migrant species, sardine, Sardina pilchardus, which colonises the lagoon during the juvenile period of its life stages, produced more than 35 tonnes in each year and accounted for >39 and >33%, in the first and second year respectively, of the total fish production in this lagoon. Sardine was numerically more abundant (18,217 specimens) but due to their small size contributed only 13% to the total biomass. Sardine was thus the most important fish species in terms of the consumption and production processes of the whole fish community in this system. Commercial fisheries’ records indicate that approximately 300 tonnes per annum of fish are taken from the lagoon, which corresponds to three times more than the estimated production in the lagoon. Thus, if it exists, the sustainability of the fishery appears to depend on the immigration of fish from the adjacent coastal area and it is questioned whether the fishery is sustainable in the long-term. The findings indicate that careful and effective management of the lagoon is required to ensure a long-term healthy aquatic environment and sustainable catches in the future.     

Changes in the fish fauna of the Ria de Aveiro estuarine lagoon (Portugal) during the twentieth century

The fish biodiversity of the Ria de Aveiro has been analysed during the 20th century, as an indicator of the biological integrity of the ecosystem. Ninety-two distinct species and 38 families of Agnatha, Chondrichthyes and Osteichthyes occurred during the period. The family and species richness showed two levels of magnitude, from the 1910s, with high values (26–28 families and 51–52 species), and during the last two decades with more variable values (20–27 families and 38–55 species). A total of 13 species (four non-sporadic species) have disappeared recently. The lagoon system has been affected by large-scale anthropogenic influences mainly the substantial development of industries and the increasing population in the watershed, in addition to overfishing, climatic changes and dredging. In general, as shown by an analysis of the ecotrophic guilds present, the area maintained a similar structure during the whole period. No significant differences in time were recorded for any of the designated guilds. The twenty-two frequent species, which occurred in six or seven surveys, were mainly estuarine resident species or marine adventitious species, living in the substratum (benthic fish), on soft substratum and vegetated bottoms. They were feeding either on invertebrates alone or on invertebrates and fish, and producing pelagic or benthic eggs. The 19 sporadically-recorded species, recorded only once, were mostly marine adventitious, demersal fishes, living above rough bottom and vegetation, feeding strictly on invertebrates, and producing eggs benthically or deposited into vegetation. It is concluded that the Ria de Aveiro estuarine coastal lagoon has supported similar fish communities during the past century and that these comprise representatives of various ecological types.     

Seasonal variability in mercury inputs into the Ria de Aveiro,Portugal

Water, suspended particulate matter (SPM) and sediments were collected from the Esteiro de Estarreja (Ria de Aveiro, Portugal), which receives considerable quantities of waste mercury from a chlor-alkali plant. Dissolved and particulate Hg concentrations in the effluent ranged between 4 –167 g I^–1 and 141–3144 g g^–1, respectively, at pH values of >10. The effluent plume undergoes significant chemical changes during advection downestuary. The evidence suggested that adsorption of dissolved Hg onto organic-rich SPM was an important process. A maximum sediment Hg concentration of 500 g g^–1 was found about 1.5 km from the discharge, as a result of the settling of Hg-rich SPM. Downestuary Hg concentrations in sediments decline to about 100 g g^–1 at the mouth of the Esteiro. The particle-water interactions are discussed in terms of the transport of dissolved and particulate Hg into the Ria de Aveiro.     

Evidence of a planktonic food web response to changes in nutrient input dynamics in the Mar Menor coastal lagoon,Spain

Nutrient input dynamics in the Mar Menor coastal lagoon has recently changed as a consequence of changes in agricultural practises. An interannual comparison of the environmental variables and the planktonic biomass size-spectra was performed between 1988 and 1997. While nitrate concentration was low in 1988, the values in 1997 increased considerably. Since 1995, two alloctonous jellyfish species (Rhyzostoma pulmo and Cotylorhiza tuberculata) occurred in large numbers in summer time and reached peak abundance in summer of 1997. The size-spectra analysis comparison revealed that, in spite of changes in nutrient input that stimulated the growth of larger phytoplankton cells, there were no significant differences in the spectra slope which followed a similar seasonal trend in both years. However, the plankton biovolume considered under the size range compared (between 2 and 1000 m diameter) was, paradoxically, always lower in 1997. Given that there were higher nutrient levels in 1997, this finding suggest a strong top-down control mechanism of size structure. Gut contents of jellyfishes showed their preference for large diatoms, tintinnids, veliger larvae and copepods, corroborating that size structure in these assemblages can be subject to top-down control. The implication of these results is that the feeding activities of large gelatinous zooplankton (jellyfishes) may play an important role controlling the consequences of eutrophication within the Mar Menor coastal lagoon.     

Evaluation of a eutrophic coastal lagoon ecosystem from the study of bottom sediments

Morphological reconstruction and biogeochemical characterisation of the lagoon of Comacchio (Italy) were carried out in order to provide recommendations for the recovery, conservation and sustainable management of the Fattibello-Spavola coastal lagoon ecosystem. Samples were taken in two seasons: July 1997 and November 1998. The irregular morphology of the Fattibello lagoon affects depositional processes and seawater exchange (tidal currents). Several depressions retain part of the dense water of the saline wedge; these stagnant waters became sinks for fine terrigenous and organic matter. The basin is already extensively supplied with N and P compounds from land. The inflow is demonstrated by the large quantity of organic C, N and organic and inorganic P compounds in the superficial sediment. The ratios between the various forms of macronutrients indicate that the organic matter is primarily of autochthonous origin, with relatively low C/N ratios (8.4±0.6 and 8.1±0.6 in July and November, respectively). Shallow areas were almost always oxygenated by tidal currents and thus rich in organisms, with a predominance of molluscs and Ficopomatus enigmaticus. However, the trophic equilibrium of the ecosystem was affected by the accumulation of organic matter in the depressions, favoured by the increased hydrodynamics during the autumn. These accumulations generate high oxygen consumption and release considerable quantities of nutrients into the water column, with the risk of serious dystrophy throughout the basin during the summer. Local dredging and an improvement of the circulation have been suggested and carried out to contain these processes. Reclamation measures in the longer term were proposed.     

Mercury in Plants from Fields Surrounding a Contaminated Channel of Ria de Aveiro,Portugal

Samples of plants and soil were collected in March and June 1995 at 12 sites in fields surrounding the Estarreja Channel (Ria de Aveiro), where the mercury-rich effluent of a chlor-alkali plant has been discharged since the 1950s. Mercury concentrations in soil ranged from 0.64 to 182 μ g g^?1. The highest values were attributed to soil contaminated with sediments dredged from the Estarreja Channel. Plant roots contained between 0.03 and 3.2 μ g g^?1 of total mercury, and there is evidence that root systems uptake mercury from the soil. The linear relationship between mercury concentrations in the roots of Holcus lanatus and in soil over a wide range of mercury concentrations suggests that mercury uptake depends on the element's concentration in the soil. The ratio root:soil concentrations for the analyzed plants varied between 0.003 and 0.199, indicating varying mercury uptake by the root systems. Levels of mercury in the aerial parts of plants showed no clear relationship with the values found in soil or in roots, presumably being influenced mostly by the atmospheric deposition of airborne particles or absorption of atmospheric mercury.     

Effects of sand bar openings on some limnological variables in a hypertrophic tropical coastal lagoon of Brazil

This study describes the spatial and temporal dynamics of several physical, chemical and biological variables in the Grussai lagoon, and their relationship to ephemeral sand bar openings and to a constant in natura waste water input. The spatial variation in pH, dissolved oxygen, electrical conductivity, total alkalinity and nutrients (e.g. soluble reactive silicate, soluble reactive phosphate and ammonium) was associated to the anoxic and nutrient rich groundwater discharge, the development of aquatic macrophytes, the biological activities of phytoplanktonic community and the marine influence. During the period when the sand bar was closed (isolated), the lagoon water was supersaturated with dissolved oxygen and exhibited high values of pH (8–10), total alkalinity (3.000–5.000 μeq l^-1), and chlorophyll a contents (60-300 μg l^-1), and had low values of dissolved nutrients (nearly undetectable). These suggest a biological processes dominance. When the sand bar was opened, there was an enrichment with dissolved inorganic nutrients (e.g. ammonium and soluble reactive phosphorus up to 120 and 5 μM, respectively) and a decrease in pH (below 8), total alkalinity (below 3.000 μeq l^-1) and dissolved oxygen during the initial second to eight days. Subsequently there was a period when the physical and chemical characteristics of seawater prevailed. The lagoon returned chemical to the pre-opening water conditions in a few days (∼ 10–20). This quick return implies highly efficient biological mechanisms. The high levels of chlorophyll a, total nitrogen and phosphorus in the water column indicate a high eutrophication stage in the Grussai lagoon during the sand bar closed periods. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Microbiological and environmental variables involved in the sulfide buffering capacity along a eutrophication gradient in a coastal lagoon (Bassin d'Arcachon,France)

Microbiological and environmental variables involved in the removal of free sulfide were studied along an eutrophication transect in the Bassin d'Arcachon (France). At four sites, analyses were carried out on reduced sulfur compounds, iron species and total numbers of viable sulfur bacteria (sulfide-producing bacteria, colorless sulfur bacteria and purple sulfur bacteria). In addition, the chemical buffering capacity towards free sulfide and the potential microbiological sulfide oxidation rates were determined.In the ecosystem, no free sulfide occurs in the top layers of the sediment at all four sites, despite a high nutrient load and hence favourable conditions for sulfide-producing bacteria. The explanation of this apparent discrepancy was shown to be the high biological sulfide oxidizing capacity in combination with a high chemical buffering capacity.The data presented illustrate that the buffering capacity of sediments towards free sulfide is the combined result of the chemical and biological processes. The ratio between these were found to depend on the degree of eutrophication. It was shown that the chemical buffering capacity towards sulfide is severely overestimated when based on the pool of chemically reactive iron, a more realistic value is obtained by estimating the total amount of sulfide that can be added before free sulfide can be detected. A clear difference was observed between the numbers of colorless sulfur bacteria and the activity of the entire population. For a proper quantification of the sulfide buffering capacity of sediments, it is essential to estimate the concentration of iron and sulfur compounds that actually can react with sulfide, as well as to analyze the activities of sulfide-oxidizing microbes.     

Macroinvertebrates associated with Chara in a tropical coastal lagoon (Imboassica lagoon,Rio de Janeiro,Brazil)

Imboassica lagoon is an urban coastal lagoon located in the municipality of Macaé (RJ), which has been exposed to a process of artificial eutrophication through the inflow of untreated sewage, as well as artificial openings of the sandbar that separates it from the ocean, provoking drastic modifications in this ecosystem. The sampling for the analysis of the community of macroinvertebrates associated with Charopyceae (Chara angolensis e C. fibrosa) were performed between October 1995 and October 1997, with a total of 9 samplings at two sampling stations: one located in the innermost area of the lagoon and another at the mouth of the main sewage channel, close to the sandbar. Throughout this period, four artificial sandbar-opening events were recorded, resulting in changes in the biomass of the macroalgae and in the densities of the macroinvertebrate populations. Through the analysis of the density of organisms per square meter, and density of organisms per 100 g dry weight of Chara, it was established that the biomass of the macroalgae has a direct influence on the density of the associated macrofauna. The greater development of the periphytic community in the area close to the inflow of sewage allows for the development of a community of macroinvertebrates with high densities, composed mainly of scraping organisms, such as the mollusc Heleobia australis (Hidrobiidae).     

Trophic status based on nutrient concentration scales and primary producers community of tropical coastal lagoons influenced by groundwater discharges

Changes in the rate of primary production as an indication of trophic status of aquatic ecosystems have been one of the major indicators of their health. Despite different approaches been devised for evaluating this process, few are useful for comparison and generalization of their results. The coastal zone ecosystems of Yucatan (SE Mexico) exhibit hydrological variability closely associated with the groundwater discharges, which are the only freshwater sources in the coastal ecosystems. In order to learn about the trophic status of karstic tropical coastal lagoons, three of them (Celestun, Chelem and Dzilam) located in Yucatan (SE, Mexico) were monitored for inorganic nutrients, Chl-a, phytoplankton and macrophyte productivity. The nitrate concentrations suggest that the trophic status was influenced by fresh water springs, being meso-eutrophic in Celestun, oligotrophic in Chelem, and mesotrophic in Dzilam. In the case of ammonium ions, the three lagoons were mesotrophic, indicating that processes such as remineralization play an important role in the trophic dynamic of these shallow ecosystems. According to phosphate concentrations, Celestun and Dzilam were mesotrophic, and Chelem was oligotrophic. External inputs of phosphate and bioturbation by waterfowl may be responsible of these differences. Primary productivity at Celestun was greater than at Chelem and Dzilam lagoons and the contribution by seagrasses was significant in all three. It is found that indices based on nutrient concentration and phytoplankton biomass are useful as an indication of trophic status in groundwater influenced coastal lagoons. Moreover, estimations on the total system productivity, and the relative contribution of each primary producer, is a holistic approach useful for understanding trophic dynamic in shallow tropical coastal ecosystems.     

Littoral macrofauna (secondary) responses to experimental nutrient addition to rocky shore mesocosms and a coastal lagoon

Macrofauna secondary responses to controlled eutrophication within two MARICULT/MAST-III projects, EULIT and COMWEB, are compared. EULIT utilises a nutrient gradient established in eight hard bottom mesocosms, whereas the data from COMWEB originate from a whole-ecosystem study – the case of experimental nutrient addition to Hopavågen lagoon. In both systems, nutrient addition started in May 1998, after initial studies of the background macrofauna communities, thus allowing application of Before-After-Control-Impact-Pairs techniques (BACIP). The main objectives have been to investigate the macrofauna responses to eutrophication in littoral rocky shore ecosystems and to evaluate if similar responses could occur in mesocosm and `field' systems, despite their inherent differences. Apart from a distinct increase in numbers of Littorina littorea L. and some indications of increased abundance of the genus Jaera, no significant changes, caused by 2.5 years of nutrient addition, could be detected in the mesocosm fauna. It is interesting, however, that these two possibly stimulated animal groups have two things in common: (1) both belong to the rather few mobile taxa, which are not flushed out of the system through the mesocosm outlets, (2) both feed on microalgae and green algae in the upper littoral zone, i.e., algal groups that have shown the clearest response to the nutrient addition. In Hopavågen, 1.5 years of nutrient addition only caused modest plant and animal responses in the rocky shore ecosystem, although there was a markedly increased settlement of Mytilus edulis L. at one lagoon site. This increase was probably due to elevated levels of digestible particles (increased phytoplankton production) caused by the nutrient addition. There were also some indications of increased production of filamentous algae at this same lagoon site. All in all, both studies demonstrate only minor responses to increased nutrient levels within the littoral community (both plants and animals). One explanation to this may be that longer time-scales are needed in order for clear-cut changes to occur. Several observations also indicate that wave exposure (significant in both systems) may largely modulate the impact of increased nutrient load on the structure of littoral communities. Another explanation is the high degree of stability among littoral macroalgae-dominated communities with internal biological regulation factors (like grazing) possibly being able to counteract effects.     

Study of the Ria Formosa ecosystem: benthic nutrient remineralization and tidal variability of nutrients in the water

Exchange of nutrients across the sediment-water interfaces of Ria Formosa was studied in the laboratory. In the field, water samples were collected (i) fortnightly, at low and high tide over one year, and (ii) semi-diurnally, over three neap-spring tidal cycles in winter. Results from both laboratory experiments and field collection were quite variable. Higher liberation rates of silicates, phosphates and ammonium occurred in chambers whose bottom was formed by mixtures of mud and sand covered by vegetation with clams. The bottom took up nitrates from the overlying water. Nutrient variations in the lagoon water were controlled both seasonally and tidally. Higher concentrations of silicates were found at low tide independently of the season; phosphates in spring/summer at low tide; nitrates in winter/spring at high tide. Tidal flushing appears to be an important removal-mechanism in this lagoon.     

Clear water associated with biomass and nutrient variation during the growth of a Charophyte stand after a drawdown,in a tropical coastal lagoon

The community of Charophytes in the Imboassica coastal lagoon in Brazil (22° 24 S and 42° 42 W) sometimes occupies almost the entire benthic region, and presents a large variation in C:N:P ratio. The effect of drawdown on the regeneration and buildup of biomass and on the nutrient concentration of these macroalgae was studied at three different sampling sites. Drawdown results in a high level of mortality in the macroalgae stands and after the water level later rises, the process of oospore germination begins. The drawdowns occurred in November 96 and January 97, and after March 97 we took samples in order to determine biomass values and the concentration of carbon, nitrogen and phosphorus. The results indicate that the fast growth of Charophytes may absorb a great amount of the nutrients entering the lagoon. The biomass reached maximum values of between 400 and 600 g DW m^–2, and the C:N:P ratio varied from 51:7:1 to 1603:87:1, indicating that this macroalgae may grow in a wide range of nutrient concentration. The presence of this community in the Imboassica lagoon may act as one of the limiting factors controlling phytoplanktonic primary production, decreasing nutrient availability in the water column (`bottom-up' control) and keeping the water clear after drawdowns. Probably through the habitat structure produced by the great biomass reached, they provide substrate and shelter for the structuring of a community with grazing zooplankton, which acts as a `top-down' controlling mechanism on the phytoplankton.     

Modern benthic diatom distribution in a hypersaline coastal lagoon: the Lagoa de Araruama (R.J.), Brazil

Diatom assemblages identified in 75 surface sediment samples in a shallow hypersaline coastal lagoon (Lagoa de Araruama, R.J., Brazil) are mainly composed of holo-euryhaline and marine euryhaline benthic taxa. The lagoon is characterized by an assemblage dominated by Cocconeis placentula var. euglypta, associated with Catenula adhaerens and Cocconeis diminuta. However, different areas, characterized by specific assemblages, have been identified. Their distribution seems to be related to (1) fluctuations in bathymetry, influenced by water inputs from the ocean and from rivers adjacent to the lagoon; (2) fluctuations in salinity through the influence of marine water and the precipitation–evaporation rate. Moreover, the distribution of associations characterized by the presence of Nitzschia palea, N. pusilla and Fallacia cryptolyra suggests the influence of man-induced activities. Although these diatoms are not dominant, their wide distribution inside the lagoon, favored by local wind-hydrodynamics, suggest a large impact of anthropic activities (e.g. freshwater and organic sewages).     

Seasonal and areal features of the lagoonal environment in Lake Nakanoumi,a shallow coastal lagoon in Japan

Lake Nakanoumi is a shallow coastal lagoon connected with the Japan Sea by a narrow channel. Over the past decade, land reclamation resulted in a 33% reduction of the lagoon's surface area. The remaining water basin of Lake Nakanoumi is scheduled to be artificially freshened to supply irrigation water for the newly reclaimed lands. This paper deals with the seasonal and areal features of the lagoonal environment prior to the beginning of the artificial desalinization.     

Storage and export of mercury from a contaminated bay (Ria de Aveiro,Portugal)

Mercury has been determined in water, suspended particulate matter (SPM)and sediments (solid fraction and pore water) collected in a heavilycontaminated confined area (Largo do Laranjo) of the Ria de Aveiro.Mercury has been analysed in seabass (Dicentrarchus labrax) capturedin several locations of the lagoon. The levels of mercury in water and SPMin the contaminated sampled places fluctuated daily with the tide (from 10to 53 ng.dm^-3 and 3.5 to 26 g.g^-1, respectively),indicating the export at the tidal rhythm. Bottom sediments exhibitedhigher concentrations, the maximum (48 g.g^-1) occurringnear the anthropogenic source at depths corresponding to the periods ofhigher industrial discharges. Mercury concentrations in pore waters (max.80 ng.dm^-3) exceed the values found in the water column and werehigher at depths where Acid Volatile Sulphides (AVS) presented broadmaximums. This implies a remobilization at anoxic conditions. However theexport across the sediment-water interface predicted through moleculardiffusion is low (between 1 to 4 × 10^-3 ng.cm^-2.h^-1) incomparison to the industrial input. The anthropogenic mercury appears tobe rapidly accumulated in seabass, a predator fish that enter seasonally inLargo do Laranjo.     

Diatom ecological preferences in a shallow temperate estuary (Ria de Aveiro,Western Portugal)

The study of the diatom ecological preferences was conducted from January 2002 to June 2003 in Canal de Mira, Ria de Aveiro, Western Portugal. Three sampling stations along a salinity gradient were sampled monthly, in new moon, at high and low tide. Salinity, temperature, pH, dissolved oxygen and nutrient contents were measured for each sampling station; chlorophyll a and diatom diversity and abundance were also evaluated. Canonical correspondence analysis was used to identify the environmental variables governing the composition and structure of diatom assemblage. The variation in the species data among the different reaches was strongly determined by the salinity spatial gradient and by the temperature temporal gradient. The lower reaches were dominated by marine species (e.g. Auliscus sculptus, Chaetoceros densus, Fallacia forcipata,Licmophora flabellata, L. grandis, Surirella comis), while in the most upstream station typical freshwater species dominated (e.g. Caloneis permagna, Cymatopleura solea, Cymbella tumida, Gomphonema longiceps, Pinnularia stommatophora, Stauroneis smithii). Weighted averaging was used to estimate optima and tolerances of some diatom taxa for the most influential variables. It was possible to establish groups oftaxa with defined and distinctive salinity and temperature preferences.