Browsing by Author "Mudge, S."
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- Identifying the source of nutrient contamination in a lagoon systemPublication . Wayland, D.; Megson, D.; Mudge, S.; Icely, John; Newton, AliceNutrient concentrations within watercourses are often associated with the input of sewage or the runoff of fertilizers. Due to population increases, there has been a dramatic rise in the amount of fertilizer applied to land, as well as in the further development of sewage treatment plants (STPs), both of which can lead to significant discharges with associated eutrophication risks in coastal waters. The implementation of the European Union Water Framework Directive (EU-WFD) should improve the management and quality of European water bodies. The Ria Formosa Lagoon, Portugal, is one such water body monitored under the WFD where two inter-calibration sites have been developed, that of the Anc˜ao Basin, which has a status of “high/good,” and that of the Ramalhete Channel, with a status of “good/moderate.” Spatial nutrient concentrations (NH+ 4 , NO–2 , NO–3 , PO3–4 ) and lipids were measured in two areas that were thought to contribute nutrients into the Anc˜ao Basin; a river that flows through several golf courses and the Ramalhete Channel, which receives discharge from both Faro Airport and a STP. Nutrient analyses showed that waters from the Ramalhete Channel had substantial concentrations, the highest of which was ammonium, which exceeded 180 μM near the sewage discharge site; however, concentrations diminished towards the sea, reaching 2.7 μM suggesting the utilization of NH+4 by seagrasses (Zostera noltii).The Atlantic Ocean was also a source of nitrate, contributing 1.8 μM, whereas sources of phosphate originated in the Anc˜ao Basin catchment and included a commercial horticulture site,several golf courses, and the STP. Principal component analysis (PCA) and cross plots of the 5β-coprostanol/cholesterol and 5β-coprostanol/(5β-coprostanol + 5α-cholestanol) ratios identified areas of fecal contamination, highlighting several sites previously unknown to contain sewage matter. In general, nitrogen sources were associated with agriculture and phosphate originated from the golf complex and sewage discharges. These effects were partly mitigated, however, by eutrophic ponds between the river and the lagoon.
- Lagoon-sea exchanges, nutrient dynamics and water quality management of the Ria Formosa (Portugal)Publication . Newton, Alice; Mudge, S.Historical data from the Ria Formosa lagoon are classified according to the EEA 2001 guidelines to provide a frame of reference to evaluate the effect of management during the implementation of the environmental legislative Directives. Water samples from the Ria Formosa lagoon were significantly enriched in nitrogen (NH4 NO2 and NO3) with respect to the adjacent coastal waters indicating that inputs from sewage, agricultural runoff and benthic fluxes were not fully assimilated within the lagoon. Tidal flushing was insufficient in the inner areas of the lagoon to remove or effectively dilute these inputs. Enrichment was most severe close to the urban centres of Faro and Olhão, as well as in the Gilão Estuary and the shallow extremities. Dissolved oxygen undersaturation (mean 75% during daylight hours) was associated with the area close to the sewage outlets of Faro. In the shallow west end of the lagoon during summer, dissolved oxygen supersaturation reached 140% during the day but fell to 50% at night. Classification using the EEA (2001) guidelines suggests the system is ‘‘poor’’ or ‘‘bad’’ with respect to phosphate concentrations for the majority of the year and ‘‘poor’’ in nitrogen contamination during the autumn rainy period. Due to the high overall nitrogen load in the lagoon, there is a net export to the coastal waters, especially during November and December, and phosphate only becomes limiting briefly during the spring bloom (April). Therefore, substantial phytoplankton populations may be supported year-round in the lagoon. The consequences of water quality deterioration in the Ria Formosa would negatively affect the lagoon as a regional resource, important for its ecological, economic and recreational value. The industries most affected would be tourism, fisheries and aquaculture. Management options include Urban Waste Water Treatment, dredging, artificial inlets, limits on urban development and changes in agricultural practices.
- Oxygen depletion in relation to water residence timesPublication . Mudge, S.; Icely, John; Newton, AliceThe relationship between residence time and oxygen saturation was investigated in a mesotidallagoon in southern Portugal. The system receives no significant freshwater input during the summer months and has a high evaporation rate. These features enable an estimate of residence time from the salinity differences between ocean water entering the system and lagoon water. More than 10 000 GPS referenced measurements of oxygen saturation, temperature and salinity were made during large spring tides in September, 2006. The lowest oxygen saturation (B44%) was measured in the waters with the highest calculated residence times (7 days). There was a significant linear decrease in the oxygen saturation with increasing residence time of B16% per day. This was similar to the rate measured on a neap tide in August, 2005. The high salinity, low oxygen saturated water was spatially confined to one inner channel, except at high water when this water was pushed into other channels. Although the tides investigated were the largest for several years, the oxygen saturation did not exceed 70% in this inner region. It is proposed that the direct discharge of oxygen consuming effluent, including domestic sewage, into this inner channel is responsible for this persistent oxygen deficit.
- Residence times in a hypersaline lagoon: using salinity as a tracerPublication . Mudge, S.; Icely, John; Newton, AliceGenerally the waters of the Ria Formosa Lagoon, Portugal have a short residence time, in the order of 0.5 days (Tett, P., Gilpin, L., Svendsen, H., Erlandsson, C.P., Larsson, U., Kratzer, S., Fouilland, E., Janzen, C., Lee, J., Grenz, C., Newton, A., Ferreira, J.G., Fernandes, T., Scory, S., 2003. Eutrophication and some European waters of restricted exchange. Continental Shelf Research 23, 1635e1671). This estimation is based on the measurements of currents and the modelling of water exchange at the outlets to the ocean. However, observations of the temperature and salinity in the inner channels imply that residence time is greater in these regions of the lagoon. To resolve this apparent contradiction, spatial measurements of the temperature and salinity were made with a meter for conductivity, temperature and depth along the principal channels of the western portion of the lagoon, with a sampling frequency of two per second. Evaporation rates of 5.4 mm day 1 were measured in a salt extraction pond adjacent to the lagoon and used to determine the residence time through salinity differences with the incoming seawater. In June 2004, the water flooding in from the ocean had an average salinity of 36.07 which contrasted with a maximum of 37.82 at mid ebb on a spring tide, corresponding to a residence time of >7 days; the mean residence time was 2.4 days. As the tide flooded into the channels, the existing water was advected back into the lagoon. Although there was a small amount of mixing with water from another inlet, the water body from the inner lagoon essentially remained distinct with respect to temperature and salinity characteristics. The residence time of the water was further prolonged at the junction between the main channels, where distinct boundaries were observed between the different water masses. As the water ebbed out, the shallow Western Channel was essentially isolated from the rest of the outer lagoon, and the water from this channel was forced down the Ramalhete Channel, from where it was unable to exit the lagoon in one tidal cycle due to the extensive path length of w14 km to the sea. Although the overall exchange rate of water is short in the outer lagoon, this study emphasizes that management models should take into account additional complexities that might arise from the much longer exchange rates of the inner lagoon. For example, the principal sewage discharge for the urban area of Faro is into the section of the Ramalhete Channel where efficient flushing is impeded by the relatively high residence times of the water body in this channel. The implementation of the techniques used for this study are a quick and relatively cost effective approach to testing assumptions about water quality and exchange in shallow coastal systems.
- Temperature and salinity regimes in a shallow, mesotidal lagoon, the Ria Formosa, PortugalPublication . Newton, Alice; Mudge, S.In a recent study of the mesotidal Ria Formosa, a coastal lagoon in southern Portugal, water temperature in the channels ranged from 12 C in winter to 27 C in summer and salinity from 13 to 36.5, although much higher values were observed in saltpans. Conditions in the Ria Formosa were not homogeneous despite a large tidal exchange of water; the inner channels of the Ria Formosa were brackish in winter but hypersaline in summer. Water in inner areas of lagoon had significantly different temperature and salinity characteristics compared to the inflowing coastal water, both in winter and in summer. Areas with these differences in temperature and salinity were detectable both at low water and at high water neaps. Deterioration of water quality is therefore more probable in these areas. The waters went through a complex heating and cooling cycle in summer with diurnal difference of 6 C and 2 in temperature and salinity, respectively. The lack of freshwater input and high insolation meant the outflowing water of the lagoon was more saline that the inflowing coastal waters. In summer, the temperature controlled density with the least dense waters also being the most saline, whereas in winter salinity was the major density controlling parameter. The effects of these freshwater inputs were localised to the vicinity of the Gila˜o River. No evidence was found of persistent or widespread temperature or salinity stratification in the Ria Formosa and so this shallow lagoon appears to be vertically well mixed. Vertical mixing does not allow a dense, stagnant, bottom layer of water to form that would aggravate a deterioration of water quality. The net effect of these processes is a parcel of water that moves through the lagoon with minimal dilution and potentially receiving waste discharges.
- Temporal and spatial variation of phytopigments in the Western part of the Ria Formosa lagoon, Southern PortugalPublication . Pereira, M.; Icely, John; Mudge, S.; Newton, Alice; Rubina, R.The spatial and temporal variation of phytoplankton pigments in the western part of Ria Formosa, Portugal, was investigated between September 2000 and July 2002. Sampling stations included the ocean boundary (Anc˜ao inlet) and two different landward boundary situations: 1) the shallow westernmost “blind end” of the lagoon (Ponte) and 2) near a main sewage outlet (Ramalhete). Nutrient concentrations were higher during the first year of sampling but were lower than those recorded in previous studies. This decrease in the concentration of nutrients was possibly the result of the 1997 relocation of the Anc˜ao inlet, which allowed better water circulation in the lagoon. Throughout this study, concentrations of chlorophyll a determined by high-performance liquid chromatography were consistently low. Inter-annual variability in the pattern of chlorophyll a concentration was observed in the form of a bimodal peak (spring/summer and autumn) between September 2000 and June 2001 and more uniformconcentrations from September 2001 until July 2002. Principal component analysis of the concentrations of all pigments did not indicate any spatial- or tidal-related variations but did show that pigment concentrations varied over time. Partial least squares analysis corroborated this temporal shift of the phytoplankton pigment abundance and composition and showed that these shifts could be linked to certain environmental variables. Fucoxanthin was the dominant accessory pigment and was strongly correlated with chlorophyll a. Other marker pigments present in lower concentrations included chlorophyll b, 19′-hexanoyloxyfucoxanthin, neoxanthin, alloxanthin, diadinoxanthin, lutein, zeaxanthin, and beta-carotene. PLS analysis was used to infer the dominant phytoplanktonic groups in the lagoon. This analysis established that diatoms and other algal groups with a similar pigment profile dominated the phytoplankton community throughout the year. Cryptophytes were the second most abundant group in the lagoon. The remaining groups, including dinoflagellates, cyanophytes, and chlorophytes, contributed much less to the total algal biomass (generally <10%).
- The effect of benthic sediments on the dissolved nutrient concentrations and fluxes sediment-seawater nutrient exchange in the Ancão basin, Ria Formosa, Portugal.Publication . Murray, L.; Mudge, S.; Newton, Alice; Icely, JohnThe Ria Formosa is a meso-tidal coastal lagoon experiencing enhanced nutrient concentrations. Assessment of sediment–seawater interaction is essential if nutrient dynamics and the risk of eutrophication are to be fully understood. Pore water concentrations of dissolved inorganic and organic phosphorus, ammonium, nitrate and nitrite were determined in cores from six sites. Changes in nutrients concentrations were measured in intertidal pools on sand and mud between tides. Dissolved inorganic phosphorus (DIP) concentrations (~200 lmol l–1) and effluxes (123 ± 14 lmol m–2 h–1) were greater from sand than mud (37 ± 10 lmol m–2 h–1), possibly due to the binding of P with the <63 lm fraction. NH4+ effluxes were high outside the Ancão Basin(821 ± 106 lmol m–2 h–1) and were associated with Enteromorpha sp. mats. The greatest NO3 – efflux was from sediments near a salt marsh (170 ± 67 lmol m–2 h–1). These sediment fluxes of P were not sufficient to account for elevated P concentrations seen by other workers on the ebb tide from the Anca˜o Basin. Intertidal pools were sinks for Dissolved Inorganic Nitrogen (DIN) and DIP over the 6 h exposure period. Thus, tidepools may be an important route of nutrients into sediments that enhances the effects of sediments on seawater nutrient concentrations.