Dissolved inorganic carbon dynamics and CO₂ atmospheric exchanges in the inner and outer Scheldt estuary

Since 1992, the Chemical Oceanography Unit of the University of Liège has carried out on a regular basis field cruises in the Scheldt inner estuary and the river plume (outer estuary), during which were measured: pH, total alkalinity, dissolved inorganic carbon, partial pressure of CO2 (pCO2), dissolved oxygen and atmospheric flux of CO2. In the inner Scheldt estuary, pCO2 values in the upper estuary can be as high as 9000 ppm that is about 25 times the value of atmospheric equilibrium (presently around 370 ppm). These high pCO2 values induce a high CO2 efflux and the entire Scheldt can emit up to 790 tons of carbon per day (tC day-1) to the atmosphere. The annually integrated CO2 emission is estimated to 456 tC day-1 (Frankignoulle et al 1998 Science 282: 434-436). Along the salinity gradient, dissolved inorganic carbon dynamics are dominated on one hand by nitrification at salinities around 5 and on the other hand by dilution. Total alkalinity is not conservative in the upper estuary (salinity 0 to 5) due to intense nitrification which produces H3O+ and leads to a decrease of total alkalinity and a minimum of both pH and oxygen saturation level. For salinities higher than 5, total alkalinity has a conservative behaviour (Frankignoulle et al 1996 Limnol. Oceanogr. 41: 365-369). A simple carbon budget shows that aerobic heterotrophic activity and nitrification produce similar amounts of CO2 and can explain most of the CO2 emission from the inner estuary to the atmosphere. The input of CO2 from fresh water inputs represents only 10% of aerobic heterotrophic activity and nitrification and 10% of the estuarine emission to the atmosphere. The advective flux of CO2, from the river to the estuary and from the estuarine mouth to the North Sea are one order of magnitude lower than atmospheric exchange in the estuarine zone (Abril et al 2000 Comptes Rendus de l'Académie des Sciences Paris 330: 761-768). In the outer Scheldt estuary, pCO2 shows a distinct seasonal evolution related to the cycle of biological activity. Throughout the year, the river plume is over-saturated (average pCO2 value of about 450 ppm) except during the Phaeocystis bloom when values of pCO2 as low as 50 ppm are observed (Borges and Frankignoulle 1999 J. Mar. Syst. 19: 251-266). The outer Scheldt estuary emits CO2 on an annual basis at a rate of about 110 tC day-1 that corresponds to about 25% of the emission of CO2 by the inner estuary. A simple carbon budget shows the input of CO2 from the inner estuary contributes to about 30% of the emission of CO2 from the outer estuary. The remaining emission of CO2 is from the net heterotrophic activity fuelled by organic carbon inputs from the inner Scheldt estuary and the Belgian coast (Borges and Frankignoulle 2002 Biogeochemistry 59: 41-67)

Dissolved inorganic carbon cycle in the maximum turbidity zone of the upper Scheldt estuary

The Scheldt Estuary is one of the most polluted macro-tidal European estuaries due to a high anthropogenic pressure around its catchment area. High load of suspended organic matter (with at least two third directly related to human activities) associated to a long residence time within the estuary (three months) contribute to an intense bacterial degradation (Wollast, 1988). The most striking feature of this work, compared to the previous studies carried on the Scheldt (Frankignoulle et al.,1996, 1998; Abril et al., 2000) is the continuous measurement of the CO2 partial pressure of the surface brackish water in the maximum turbidity zone of the inner Scheldt Estuary since November 2002 to nowadays. Our results show that pCO2 in the surface brackish water is outstandingly high, ranging from 2000 to 10000 ppm, which represents up to 2700% of the CO2 atmospheric pressure. CO2 also shows strong meso- and macroscale variabilities and on an annual scale it appears that pCO2 is mainly controlled by temperature and heterotrophy

The Azorean Biodiversity Portal: an internet database for regional biodiversity outreach

Copyright © 2010 The Natural History Museum.There is a growing interest in academia to provide biodiversity data to both the scientific community and the public. We present an internet database of the terrestrial lichens, bryophytes, vascular plants, molluscs, arthropods, vertebrates and coastal invertebrates of the Azores archipelago (Portugal, North Atlantic): the Azorean Biodiversity Portal (ABP, http://www.azoresbioportal.angra.uac.pt/). This is a unique resource for fundamental research in systematics, biodiversity, education and conservation management. The ABP was based on a regional species database (ATLANTIS), comprised of grid-based spatial incidence information for c. 5000 species. Most of the data rely on a comprehensive literature survey (dating back to the 19th century) as well as unpublished records from recent field surveys in the Azores. The ABP disseminates the ATLANTIS database to the public, allowing universal, unrestricted access to much of its data. Complementarily, the ABP includes additional information of interest to the general public (e.g. literature on Macaronesian biodiversity) together with images from collections and/or live specimens for many species. In this contribution we explain the implementation of a regional biodiversity database, its architecture, achievements and outcomes, strengths and limitations; we further include a number of suggestions in order to implement similar initiatives

Two alien insect species are new records at the family-level to the Azores archipelago (Portugal)

Species introductions are a major issue for biodiversity conservation and human well-being worldwide, but their impact can be particularly severe in oceanic island ecosystems. Here, we report the occurrence of two alien species on Terceira island, Rivellia syngenesiae (Fabricius, 1781) (Diptera: Platystomatidae) and Sceliphron caementarium (Drury, 1773) (Hymenoptera: Sphecidae), being the first reports of these insect families to the Azores archipelago. We provide the diagnosis of each species, information on their distribution and ecology, and discuss their potential impact on native biodiversity. Furthermore, we anticipate the spread of these species through the Azores islands, benefiting from the high increase in commerce and tourism, and stress the need to set a program for the early detection of alien species in the archipelago.info:eu-repo/semantics/publishedVersio

Biodiversity patterns of macroinvertebrate assemblages in natural and artificial lentic waters on an Oceanic Island

The Azorean islands have been historically affected by human activities, mainly due to the combined effects of habitat degradation and fragmentation, and the introduction of exotic species. We here aim to analyze the role of environmental characteristics and spatial descriptors in supporting regional biodiversity of macroinvertebrates by considering natural ponds and artificial tanks. After the monthly variation of macroinvertebrate assemblages was assessed in three temporary and two permanent ponds in the Azorean island of Terceira during a complete inundation-desiccation annual cycle, the assemblage differences of 12 ponds (three temporary and nine permanent ponds) and 8 closely-located artificial tanks were analyzed across a range of landscape disturbances. Macroinvertebrate assemblages were found to differ according to hydroperiod and sampled months. Although the former explained the highest variance, macroinvertebrate differentiation by hydroperiod was also dependent on the study month. Our results also revealed a consistent monthly pattern of species replacement. However, the contribution of nestedness to the macroinvertebrate β-diversity was notable when temporary ponds were close to desiccation, probably indicating a deterministic loss of species due to the impoverished water conditions of the ponds facing desiccation. When the macroinvertebrate assemblages were analyzed in relation to physico-chemical variations and spatial descriptors, the artificial tanks were not clearly segregated from the natural ponds, and only differentiated by pH differences. In contrast, those natural ponds exhibiting high concentrations of total phosphorous (likely signs of anthropization) also discriminated the ordination of ponds in a distance-based redundancy analysis, and showed impoverished assemblages in comparison with well-preserved ponds. The macroinvertebrate assemblages of the natural ponds showed a significant spatial pattern, but this spatial influence was not significant when tanks and ponds were considered together. Our results suggest that tanks may act as possible reservoirs of biodiversity during the desiccation period of temporary ponds, but are unable to establish successful populations. These fishless permanent tanks can complement the conservation of a biodiversity that is largely maintained by the pristine high-altitude natural ponds. The establishment of a guideline for conservation management that also considers the artificial tanks is necessary to benefit the local and regional Azorean macroinvertebrate diversit

Pelagic metabolism of the Scheldt estuary measured by the oxygen method on an annual scale

Pelagic gross primary production (GPP), community respiration (CR) and nitrification were measured in the turbid Scheldt Estuary by the oxygen Winkler method from January to December 2003 at monthly intervals (EUROTROPH EU project). Five stations along the estuary were investigated, corresponding to a salinity (S) range of 0-25. Water was sampled and incubated until sunset in 60 ml glass bottles stored in a 5 compartment incubator kept at in situ temperature by flowing water. Irradiance was controlled in each compartment by filters having a shading capacity ranging from 0 to 100%. In order to estimate the oxygen consumption due to the respiration and nitrification processes, samples were incubated, in the dark compartment, with and without addition of nitrification inhibitors. Net community production (NCP) was most of the time negative in the estuary with values ranging from -275 to +31mmol O2.m-2.d-1 and the lowest values were found near Antwerp (S = 2). Strong pelagic GPP and positive NCP rates were observed in the freshwater part during summer with a maximal value in June (+373mmol O2.m-2.d-1), corresponding to an increase of the O2 concentration and a decrease of the partial pressure of CO2 (pCO2) in the water column during this period. Nitrification contributes 5 to 60% of the oxygen consumption in the water column with highest values measured in the inner part of the estuary due to high ammonium and suspended matter concentrations. Assuming a C/O2 molar ratio of 0.07, we estimated that nitrification represents on an annual scale 35% of organic matter production at salinity 2 which is consistent with previous estimates. NCP rates measured in 2003 are among the lowest reported in the literature and confirm the strong heterotrophic status of the Scheldt Estuary

Biogeochemical cycle in a coccolithophorid bloom

The biogeochemical properties of an extensive bloom of the coccolithophore, Emiliania huxleyi, at the shelf break in the northern Gulf of Biscay was investigated in June 2006. Total Alkalinity (TA) values in the water column showed strong non-conservative behaviour indicative of the impact of calcification, with the highest TA anomalies (up to 26μmol.kg-1) in the high reflectance coccolith patch. Partial pressure of CO2 (pCO2) values ranged from 250 to 338μatm and the area was found to act as a sink for atmospheric CO2.Overall, pCO2@13°C (pCO2 normalized at a constant temperature of 13°C) in the water column was negatively related to TA anomalies in agreement with an overall production of CO2 related to calcification. Hence, the calcifying phase of the E. huxleyi bloom decreased the sink of atmospheric pCO2, but did not reverse the direction of the flux. Rates of pelagic respiration up to 5.5mmol O2.m-3.d-1 suggested a close coupling between primary production and respiration and/or between organic carbon content and respiration. Benthic respiration rates were quite low and varied between 2 and 9mmol O2.m-3.d-1, in agreement with the fact that the study area consists of sandy sediments with low organic matter content. Benthic respiration was well correlated to the chlorophyll a content of the top 1cm of the sediment cores. Evidence was found for dissolution of CaCO3 due to the acidification of superficial sediments in relation to the production of CO2 and the oxidation of H2S in the oxic layers