Interactive effects of environmental variability and human impacts on the long-term dynamics of an Amazonian floodplain lake and a South Atlantic coastal lagoon

Human activities are exposing freshwater ecosystems to a wide range of stressors, whose direct and indirect effects can be alleviated or exacerbated through interactive effects with dynamic environmental drivers. This study used long-term data from two Neotropical lacustrine freshwater systems (Batata Lake, an Amazonian floodplain lake and Imboassica lagoon, an Atlantic coastal lagoon) subjected to different kinds of environmental fluctuations (i.e., flood pulse and sandbar opening) and anthropogenic impacts (i.e., siltation and eutrophication). Our objective was to determine whether the effects of human perturbations are contingent on modifications of important biotic and abiotic characteristics through environmental variability. For both ecosystems, environmental variability consistently interacted with anthropogenic perturbations to alter most of the variables analyzed, such as nutrient dynamics, chlorophyll-a concentration, zooplankton and benthic invertebrate species richness, and temporal community stability, which indicates that interactive effects between environmental variability and anthropogenic perturbations may impact a myriad of ecosystem properties. Furthermore, the nature of these interactive effects was highly dependent on the variable considered and on the ecosystem analyzed. For example, at Imboassica lagoon, sandbar openings interacted synergistically with trophic state to increase the phosphorus concentration in the water column. At Batata Lake, flooding generally alleviated the negative effects of siltation on species richness by both diluting inorganic suspended material concentration and by promoting local recruitment from the regional species pool. Such results indicate that our ability to understand and predict the outcome of anthropogenic impacts on inland aquatic systems can be hampered if we consider human stressors as “static” phenomena disconnected from dynamic interactions with major local environmental drivers.     

Sustainable impact of mussel farming in the Adriatic Sea (Mediterranean Sea): evidence from biochemical, microbial and meiofaunal indicators

We have investigated the impact of a large mussel farm on the benthic environment using a battery of benthic indicators of environmental quality (including biochemical, microbial and meiofaunal parameters). These were analysed through a multi-control sampling strategy over one year. The differences across the seasons are typically higher than those between the impacted and the control stations. No effects are seen in terms of the sediment oxygen penetration and the downward fluxes (as the total mass, organic and phytopigment fluxes). The indicators based on the biochemical compositions of the sediment organic matter and the microbial parameters also show no evidence of the eutrophication process, except as a slight increase in the bacterial density in the sediments beneath the long-lines of the farm during the period of highest mussel stocks. Finally, no effects are observed in terms of the benthic faunal indicators, as the meiofaunal abundance, the community structure and the taxa richness are all indistinguishable between the farm sediments and the controls. These results show that mussel farming in the investigated system is eco-sustainable and does not significantly alter the coastal marine ecosystem, both in terms of the functioning and the trophic state. The battery of indicators selected in this study represents a useful tool for the monitoring of the potential ecological impact of mussel farms, towards guaranteeing the sustainable development of aquacultures in shallow coastal environments.     

Distribution and ecological relevance of fine sediments in organic-enriched lagoons: the case study of the Cabras lagoon (Sardinia, Italy)

In organic-enriched sedimentary systems, like many Mediterranean coastal lagoons, a detailed analysis of sediment grain size composition and partitioning within the muds is crucial to investigate sedimentological trends related to both hydrodynamic energy and basin morphology. In these systems, sediment dynamics are particularly important because the partitioning and transport of fine sediments can strongly influence the redistribution and accumulation of large amounts of organic matter, and consequently the distribution of benthic assemblages and the trophic status and functioning of a lagoon. Nevertheless, studies on benthic-sediment relationships have been based mainly on a rather coarse analysis of sediment grain size features. In muddy systems, however, this approach may impede a proper evaluation of the relationships and effects of the distribution of fine sediment and organic matter on the biotic benthic components. Here we show that the distribution of sedimentary organic matter (OM) and total organic carbon (TOC) in the Cabras lagoon (Sardinia, Italy) can be explained (i.e., predicted) as a function of a nonlinear increase in the amount of the cohesive fraction of sediments (< or = 8 microm grain size particles) and that this fraction strongly influences the structure, composition and distribution of macrobenthic assemblages. Even in such a homogeneously muddy system, characterized by "naturally" occurring impoverished communities, impaired benthic assemblages were found at < or = 8 microm, OM, TOC contents of about 77%, 11% and 3.5%, respectively. A review of studies conducted in Mediterranean coastal lagoons highlighted a lack of direct integrated analysis of sediment features and the biotic components. We suggest that, especially in organic-enriched coastal lagoons, monitoring programs should primarily investigate and consider the cohesive fraction of sediments in order to allow a better assessment of benthic-sediment relationships and ecological quality of the system.     

Temporal and spatial changes in marine benthic habitats in relation to the EU Water Framework Directive: The use of sediment profile imagery

In 2002 to 2006, sediment profile imagery (SPI) was used to study the environmental impact of eutrophication-induced irregular and seasonal hypoxia on marine benthic habitats in six regions in the Skagerrak and Kattegat (West Sweden). The benthic habitat quality (BHQ) was assessed by parameterisation of biogenic structures observed by the SPI technique, and benthic quality status was related to the EU Water Framework Directive (EU-WFD). The temporal changes were analysed by a 5-factor nested ANOVA and significant temporal differences were recorded within three of the regions. Two of these were affected by hypoxia in the deeper parts and one was probably affected by hypoxia below the halocline. The environmental quality status according to the EU-WFD was bad to high in two regions, moderate to good in three regions, and good to high, i.e., acceptable according to the EU-WFD, in only one region. As BHQ is highly correlated to benthic faunal data, measures have to be taken to improve the coastal water quality in five of the six studied areas.     

The use of the marine biotic index AMBI in the assessment of the ecological status of the Obidos lagoon (Portugal)

This study reports the longitudinal distribution of sediment properties, including inorganic and organic contaminants, and the structure of the benthic community in Obidos lagoon, a coastal system permanently connected to the sea and with negligible freshwater sources. Sediments from the upper to central lagoon consist of fine particles (91%) and from the lower lagoon of sands (94%). Chemical composition is strongly correlated to the percentage of fine particles. Contamination is relatively low in those sediments suggesting the effect of diffuse sources. The increase in organic matter content from down- to upstream areas was associated with the dominance of opportunistic species, while sensitive and indifferent species to organic enrichment were mainly associated to the clean sandy downstream area. The marine biotic index (AMBI) was suitable for the discrimination of the biological and environmental gradients in the Obidos lagoon and was highly related with the gradient of organic matter content in this system.     

Geochemistry of organic carbon and nitrogen in surface sediments of coastal Bohai Bay inferred from their ratios and stable isotopic signatures

Total organic carbon (TOC), total nitrogen (TN) and their δ(13)C and δ(15)N values were determined for 42 surface sediments from coastal Bohai Bay in order to determine the concentration and identify the source of organic matter. The sampling sites covered both the marine region of coastal Bohai Bay and the major rivers it connects with. More abundant TOC and TN in sediments from rivers than from the marine region reflect the situation that most of the terrestrial organic matter is deposited before it meets the sea. The spatial variation in δ(13)C and δ(15)N signatures implies that the input of organic matter from anthropogenic activities has a more significant influence on its distribution than that from natural processes. Taking the area as a whole, surface sediments in the marine region of coastal Bohai Bay are dominated by marine derived organic carbon, which on average accounts for 62±11% of TOC.     

Biodiversity loss in benthic macroinfaunal communities and its consequence for organic mercury trophic availability to benthivorous predators in the lower Hudson River estuary, USA

Organic mercury such as methylmercury is not only one of the most toxic substances found in coastal ecosystems but also has high trophic transfer efficiency. In this study, we examined implications of chronically altered benthic macroinfaunal assemblages for organic mercury trophic availability (based on organic mercury intracellular partitioning) to their predators in the Arthur Kill-AK (New York, USA). Despite low species diversity, both density and biomass of benthic macroinvertebrates in AK were significantly higher than those at the reference site. Disproportionately high biomass of benthic macroinvertebrates (mostly polychaetes) in the northern AK resulted in a more than twofold increase (‘ecological enrichment’) in the trophically available organic mercury pool. These results suggest that altered benthic macroinfaunal community structure in AK may play an important role in organic mercury trophic availability at the base of benthic food webs and potentially in mercury biogeochemical cycling in this severely urbanized coastal ecosystem.     

Benthic microbial abundance and activities in an intensively trawled ecosystem (Thermaikos Gulf, Aegean Sea)

Abundance of benthic bacteria, heterotrophic nanoflagellates and ciliates, extracellular enzymatic activities, bacterial C production, C mineralisation and sediment community oxygen consumption rates were measured in the Thermaikos Gulf (Northeastern Mediterranean), before (September 2001), and during intense trawling activities (October 2001 and February 2002). The biochemical composition of sedimentary organic matter has revealed that bottom trawling had an effect on the trophic state of Thermaikos Gulf. Changes on the benthic microbial food web were also recorded, during the three sampling seasons. Even though trawling-induced sediment resuspension did not alter significantly the abundance of the microbial components, with the exception of the most impacted station, it determined changes regarding their relative importance. Thus, the ratios of bacterium to nanoflagellates and ciliate to nanoflagellates abundance increased in the trawled stations, causing a sudden increase in bacterial C production, in comparison to the non-trawled station. Four months later, the effects of trawling on the microbial food web were less evident, masked possibly by the drastic decrease in the water temperature. The results of the present work suggest that bottom trawling induces alteration of the sedimentological variables and can be considered as a factor affecting the function of the microbial food web in marine coastal ecosystems. These alterations cause faster mobilisation of organic C buried in the sediment and increase nutrient concentrations and availability in the system, thus inducing an effect that could lead to coastal eutrophication.     

Plankton of the Baltic estuarine ecosystems with emphasis on Neva Estuary: a review of present knowledge and research perspectives

Different levels of eutrophication and pollution in the Baltic coastal waters in general, and in estuaries particularly define variations in the buffering capacity of ecosystems of these important filter zones between rivers and the adjacent Baltic Proper. Phyto- and zooplankton in the estuaries form important components of the pelagic food webs that participate in producing and structuring the matter, energy, and information fluxes in the ecosystems. Due to salinity gradients, estuaries provide a large variety of aquatic habitats for native populations of marine, brackish and fresh water plankton species. Non-indigenous planktonic species that expand their bio-geographical range and invade the Baltic coastal ecosystems also find favourable environments, establish permanent populations there, and impact aboriginal ecosystems. The dynamics of abundance, species diversity, population structure, productivity of planktonic communities, and peculiarities of trophic interactions in different Baltic estuaries are influenced by a number of common environmental factors. Being measured on the unified basis and monitored, changes (or stability) of structural and functional parameters of plankton communities can serve as indicators of alterations to the ecosystems. Comparative analyses and quantitative estimates of long-term changes in phyto- and zooplankton can contribute to evaluation of functional response of Baltic coastal ecosystems to anthropogenic stress. Both theoretical (modeling) and empirical studies of interactions within plankton communities aimed at the assessment of the role of planktonic organisms in water quality regulation, and applicability of these data for the evaluation of the status of ecosystems and their management can be considered as major goals for the future investigations in Baltic estuaries.     

Effects of industrial outfalls on tropical macrobenthic sediment communities in Reunion Island (Southwest Indian Ocean)

Temporal changes in the composition of soft bottom macrobenthic assemblages at Reunion Island (Southwest Indian Ocean) were studied in the context of a long-term environmental monitoring programme studying the impacts of effluents of industrial sugar cane refineries that are transferred to shallow and deep coastal environments by different pathways: surface discharge and deep underground injection. Seven stations (between 20 and 160 m depth) were surveyed between 1994 and 2003 on the industrial zone. One additional station was surveyed on a reference site. Spatio-temporal changes in the composition of macrobenthic communities were assessed using several diversity indices, ABC curves, MDS and associated ANOSIM tests and biotic indices. Among the 171 taxa recorded, polychaetes were dominant (89 species), followed by crustaceans and molluscs. The analysis of spatial changes in the composition of macrobenthos showed the existence of distinct benthic communities along the depth gradient. Temporal changes in macrobenthos composition were most prominent at the shallowest station. They mainly corresponded to the decline of several initially dominant taxa and the increase of the Eunicid polychaete Diopatra cuprea. This station further showed increasing macrofaunal abundance, biomass and sediment organic content over time, concomitant with decreasing sediment grain sizes. In deeper environments, temporal changes were much smaller. Macrofaunal abundance and species richness increased progressively, suggesting a moderate impact on benthic ecosystems resulting from slight enrichments due to effluents rich in organic matter. Our results highlight an original response to disturbance pattern involving opportunistic Eunicidae species (D. cuprea) not previously described. Moreover, they allow for the comparison of the impact on macrofauna caused by industrial effluents exported by two distinct and different pathways in a tropical coastal high-energy marine environment.     

Testing the applicability of a Marine Biotic Index (AMBI) to assessing the ecological quality of soft-bottom benthic communities, in the South America Atlantic region

Recently, several monitoring programmes have been undertaken to evaluate the impact of different anthropogenic activities, upon a range of coastal ecosystems located in the South-western Atlantic. In the present contribution, the applicability of the AZTI's Marine Biotic Index (AMBI) is tested, to establish the benthic health of the ecosystem using these data sets. As the AMBI was created previously for use in European estuarine and coastal environments, its general applicability to new geographical locations is discussed. In general, the results are in agreement with those obtained using traditional univariate and multivariate methods. Some inconsistent results are observed, when low abundances and/or number of taxa are recorded in the samples. Moreover, when the macrofauna samples are dominated by large nematodes, the classification of the benthic ecosystem health using AMBI is not consistent with previous results achieved applying other statistical techniques. Thus, parallel to the application of this index to a wider extend, the complementary use of different indices and/or methods is recommended to assess confidently the environmental quality of a coastal area.     

Impact of natural (storm) and anthropogenic (trawling) sediment resuspension on particulate organic matter in coastal environments

In order to assess the impact of natural and anthropogenic sediment resuspension on quantity, biochemical composition and bioavailability of particulate organic matter (POM), two field investigations were carried out in two shallow coastal areas of the Mediterranean Sea. In the Gulf of Lions, we investigated the impact of a storm resuspension of sediment, whereas in the Thermaikos Gulf we investigated the impact of bottom trawling.Resuspension in the Gulf of Lions determined the increase of sedimentation rates, modified the composition of the organic fraction of settling particles and decreased the labile fraction of POM, as indicated by a drop in the enzymatically hydrolysable amino acid fraction. The increase in the refractory fraction, following short-term storm-induced resuspension, increased also the contribution of glycine and decreased the contribution of aspartic acid contents to the total amino acid pools.Trawling activities in Thermaikos Gulf determined a significant increase in suspended POM concentrations and important changes in its biochemical composition. After trawling, the protein to carbohydrate ratio decreased (as a result of a major input of sedimentary carbohydrates at the water–sediment interface) and the fraction of enzymatically hydrolysable biopolymeric C decreased by ≈30%, thus reducing the bioavailability of resuspended organic particles. Results of the present study indicate that changes in suspended POM, induced by storms and trawling activities, can have similar consequences on benthic systems and on food webs. In fact, the potential benefit of increased organic particle concentration for suspension feeders, is depressed by the shift of suspended food particles towards a more refractory composition.     

Sulfate reduction in natural water bodies. 1. The effect of environmental factors and the measured rates of the process

Sulfate reduction is an important oxidation process involving transformation of organic matter and its components and taking place in the aquatic environment and bottom sediments of water bodies (both fresh and marine) under anaerobic conditions. The intensification of sulfate reduction in water bodies is a sign of a stronger anthropogenic impact on the environment and natural water bodies. The development of sulfate reduction under natural conditions reflects the influence of many environmental factors. The effect of the most important factors (the concentration of organic matter and its components and sulfates, the temperature of aquatic environment, and the abundance and activity of sulfate-reducing bacteria) on the process of sulfate reduction in the aquatic environment and bottom sediments in water bodies is considered.     

Does chlorophyllidea reduce reliability of chlorophylla measurements in marine coastal sediments?

Pigment concentrations (chlorophylla, chlorophyllidea and pheopigmentsa) were measured by HPLC and spectrophotometry with acidification on 57 samples collected in different marine coastal sediments, containing autochthonous microphytes, and with various organic matter contents (plant detritus, biodeposits or hydrocarbons). Statistical analysis shows that the spectrophotometry with acidification, as compared to HPLC, gives reliable values for chlorophylla. Chlorophyllidea concentrations may be considered as negligible. Though spectrophotometric methods are sometimes questioned when applied to sediments they appear to give easy, quick and good estimates of Chla contents in benthic microphytes for hydrobiological studies in coastal areas.     

Human health benefits supplied by Mediterranean marine biodiversity

This paper summarizes the overall benefits supplied by Mediterranean marine biodiversity to human health and highlights the anthropogenic and environmental causes that are threatening these benefits. First, the Mediterranean Sea is a valuable source of seafood, which is an important component of the so-called “Mediterranean diet”. This type of diet has several health benefits, including cardio and cancer protective effects, which are attributed to the high intake of seafood-derived n-3 (omega-3) fatty acids. Second, the Mediterranean marine organisms, particularly the benthic ones, have furnished a large variety of bioactive metabolites, some of which are being developed into new drugs to threat major human diseases such as cancer. Third, the Mediterranean coastal areas provide environments for practising maritime leisure activities that provide physical and psychological benefits to users. Despite all this, fishing, tourism, contamination and sea warming are deteriorating this rich marine ecosystem, which needs to be protected to assure human welfare.     

Geophysical and Hydrochemical Identification of Flow Paths with Implications for Water Quality at an ARR Site

Two key challenges regarding the design and operation of aquifer recharge and recovery (ARR) systems are evaluating aquifer heterogeneity and understanding hydrochemical interactions. Uncertainty in this respect can impact the volume of recoverable water and the improvement in water quality. The objective of this research is to leverage the advantages of geophysical measurements and hydrochemical sampling to reveal the properties of an ARR site to inform current ARR system operations and future design decisions. Electrical resistivity tomography was used to image the subsurface below two key infiltration/extraction areas of an ARR site in Colorado, USA. Hydrochemical measurements on transects intersecting the geophysical measurements resolved bulk parameters (i.e., total organic carbon, nitrate, and major cations and anions) and trace organic chemicals (e.g., pharmaceuticals, personal care products). Conservative tracers were also used to estimate degrees of mixing and water travel times and to better assess the performance of the ARR site regarding water quality changes and water recovery. The electrical resistivity measurements suggest that certain areas of the infiltration basins have hydraulic connections to the extraction wells through preferential flow paths, compared with other infiltration basins that are separated by fine‐grained materials from their respective extraction wells. The hydrochemical results indicate that consistent improvements in water quality can be achieved in these preferential flow paths within relatively short travel times (<5 d) at this ARR site.