T. Ortega

Anthropogenic effects on greenhouse gas (CH4 and N2O) emissions in the Guadalete River Estuary (SW Spain)

Coastal areas are subject to a great anthropogenic pressure because more than half of the worlds population lives in its vicinity causing organic matter inputs, which intensifies greenhouse gas emissions into the atmosphere. Dissolved concentrations of CH4 and N2O have been measured seasonally during 2013 in the Guadalete River Estuary, which flows into the Cadiz Bay (southwestern Spanish coast). It has been intensely contaminated since 1970. Currently it receives wastewater effluents from cities and direct discharges from nearby agriculture crop. Eight sampling stations have been established along 18 km of the estuary. CH4 and N2O were measured using a gas chromatograph connected to an equilibration system. Additional parameters such as organic matter, dissolved oxygen, nutrients and chlorophyll were determinate as well, in order to understand the relationship between physicochemical and biological processes. Gas concentrations increased from the River mouth toward the inner part, closer to the wastewater treatment plant discharge. Values varied widely within 21.8 and 3483.4 nM for CH4 and between 9.7 and 147.6 nM for N2O. Greenhouse gas seasonal variations were large influenced by the precipitation regime, masking the temperature influence. The Guadatete Estuary acted as a greenhouse gas source along the year, with mean fluxes of 495.7 μmol m(-2)d(-1) and 92.8 μmol m(-2)d(-1) for CH4 and N2O, respectively.

Using a laboratory simulator in the teaching and study of chemical processes in estuarine systems

The teaching of Chemical Oceanography in the Faculty of Marine and Environmental Sciences of the University of Caidiz (Spain) has been improved since 1994 by the employment of a device for the laboratory simulation of estuarine mixing processes and the characterisation of the chemical behaviour of many substances that pass through an estuary. The equipment comprising the simulator is controlled by a computer system running the program OLE (Oceanography and LEarning), which was developed originally as a research tool in Chemical Oceanography (under Windows® environment). Later, on the initiative of several teachers, the handling of the simulator was simplified to allow its use as a didactic resource for teaching the various processes that take place in littoral systems.Since its initial development, many different natural environmental conditions have been simulated, and the behaviour of many chemical pollutants has been studied. On the basis of this favourable experience, the simulator designed appears to be a versatile tool that can be usefully employed in both academic learning and research work.

Temporal and spatial variation of N2O production from estuarine and marine shallow systems of Cadiz Bay (SW, Spain)

There is still much uncertainty regarding the global oceanic emissions of N2O, and particularly emissions from coastal regions, because spatio-temporal datasets have limited coverage. The concentration of dissolved N2O in surface waters and the associated fluxes to the atmosphere have been studied in three coastal systems located near Cadiz Bay (southwestern coast of Spain) over different time scales. The three systems present different hydrodynamic characteristics (an estuary and two marine systems) that influence the distribution of N2O in the water column. Nutrients, oxygen, and particulate organic nitrogen were also measured to investigate the processes responsible for N2O production in the water column. Data on dissolved N2O has been obtained in each system from i) two-year monitoring at fixed station; ii) four seasonal samplings along the longitudinal length of the system; and iii) daily sampling in summer. The concentration of N2O ranges between 1.1 and 292.0nM indicating very high spatio-temporal variability. In general, the concentration of N2O increased during the rainy season associated with the precipitation regime that, in turn, increases the lateral inputs of organic matter and nutrients from both natural sources (discharges into rivers and adjacent marshes) and anthropogenic activities (agriculture, urban effluents and fish farming). Dissolved N2O also varied with the tides: the highest concentrations were measured during the ebb, which suggests that the systems export N2O to the Bay and adjacent Atlantic Ocean. In addition nitrification seems to be an important process for N2O formation in the water column, which also explains some of the variability in the dataset. The mean atmospheric flux of N2O reveals that entire study area was a net source of N2O to the atmosphere. The fluxes ranged between 0.5 and 313.2μmolm-2day-1 in the estuarine system, and between -7.2 and 97.8μmolm-2day-1 in the two marine systems.

Inorganic carbon fluxes at the water-sediment interface in five littoral systems in Spain (Southern Europe)

The benthic fluxes of dissolved inorganic carbon have been measured in five different littoral ecosystems in Spain (Southern Europe). The values measured by means of benthic chambers ranged between 30 and 378 mmol m−2 d−1 and may be considered relatively high. They were linearly correlated with the organic carbon content in surface sediments. The concentration of dissolved inorganic carbon in interstitial water presents a strong vertical gradient (30 mM at 25 cm), with diffusive fluxes between 0.1 and 14.1 mmol m−2 d−1. The comparison between diffusive fluxes and benthic chamber (in situ) fluxes shows the important role of the benthic macrofauna irrigation processes in relation to species exchange across the sediment-water interface.

Distribution of N2O in the eastern shelf of the Gulf of Cadiz (SW Iberian Peninsula)

Distribution of N2O has been determined in eight cruises along three transects (Guadalquivir, Sancti Petri and Trafalgar) in the Gulf of Cadiz, during 2014 and 2015. The mean N2O value for this area was 10.0±0.9nM, with large spatial and temporal variations. Stratification in the water column has been observed; the concentration of this gas increases with the depth, because of the presence of the Eastern North Atlantic Central Water (ENACW) and the Mediterranean Outflow Waters (MOW). The N2O production measured in this study is mainly due to nitrification. N2O yields from nitrification were estimated from the linear correlation of the excess of N2O (ΔN2O) with Apparent Oxygen Utilization (AOU) and nitrate (NO3-), with values of their slopes ranged between 0.010 and 0.021% and 0.017-0.025% respectively. There is an onshore - offshore gradient of N2O; the highest values were found at the shallower stations, indicating coastal input and benthic remineralization. The seawater-air flux of N2O is affected by several variables (temperature, AOU and NO3-), and the average flux calculated is 2.7±2.0μmolm-2d-1. The fluxes show a decrease with increasing distance from the coast, and with proximity to the Strait of Gibraltar. The study area behaves as a source of N2O to the atmosphere, with a global emission of 0.18Ggyear-1.