Browsing by Author "Rocha, C."
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- Ecosystem-level impact signals of groundwater borne continental nitrate transfer to the Ria Formosa lagoon by Submarine Groundwater Discharge (SGD) traced along the mixing gradient by a multi-indicator approachPublication . Rocha, C.; Veiga-Pires, C.; Wilson, J.; Aníbal, J.; Monteiro, José Paulo; Scholten, J.Recognition of the role played by SGD in the transfer of contaminants to near shore marine enviroments underscores the need for tools and aproaches that will facilitate regional assessments of its environmental impact.
- Effects of early tidal inundation on the cycling of methylamines in inter-tidal sedimentsPublication . Fitzsimons, M. F.; Dawit, M.; Revitt, D. M.; Rocha, C.Methylamine (MA) concentrations were measured at 2 sites in the Ria Formosa, Portugal, including a rearing plot for the clam Ruditapes decussatus (L), Sampling encompassed both sediment exposure and tidal inundation. Porewater MA concentrations at Site 1 (cohesive sediment with low numbers of clams) did not change significantly during sediment exposure, but increased at the onset of inundation, with desorption of solid-phase monomethyldmine (MMA) mainly responsible. Porewater dimethylamine (DMA) did not vary significantly, while porewater trimethylamine (TMA) concentrations decreased after inundation. Solid-phase MA concentrations at Site 1 were more variable, where TMA was consumed at a rate of 60 mu mol kg(-1) bulk sediment h(-1) during the first hour of sampling, suggesting that it was loosely bound to the sediment. The consumption of solid-phase TMA at Site 1 may contradict the notion of adsorption as a preservation mechanism for certain basic analytes. MA concentrations were considerably higher in the sediment and clam samples from Site 2, containing high densities of R. decussatus, where TMA was the most abundant MA, Its concentrations in clam tissue before inundation were 191 decreasing to 36 mmol kg(-1) after inundation. A concurrent increase in sediment solid-phase TMA from 0.1 to 0.9 mmol kg(-1) pointed to release of TMA by the clams. Excretion of TMA from the clam tissue should have increased the sediment concentration by 2.19 mmol kg(-1), but the measured value was 0.84 mmol kg(-1). The low adsorption capacity of sandy sediment and the fact that clams excrete their waste close to the sediment surface should increase the possibility of TMA flushing to the water column. The high density of clams, and the current preference for clam rearing in sandy sediments, could contribute to increased concentrations of dissolved nitrogen in the Ria Formosa lagoon.
- Effects of temperature and salinity on nitrate uptake by green macroalgaePublication . Madeira, Hélder Trindade; Aníbal, J.; Carvalho, Liliana Faia; Esteves, E.; Veiga-Pires, C.; Rocha, C.Temperature, salinity and the availability of dissolved inorganic nutrients are amongst the most important abiotic factors driving macroalgae produstions in estuarine and coastal ecosystems.
- Estimating submarine groundwater discharge into the Ria Formosa lagoon, Portugal: Uncertainties in the lagoon-open ocean radium exchangePublication . Scholten, J.; Rocha, C.; Wilson, J.; Pham, M.; Veiga-Pires, C.; Aníbal, J.The Ria Formosa lagoon is the most important resource for the fishing, aquaculture and tourism industries of southern Portugal. The lagoon expands across an area of approximately 100 km²and about half of its area is intertidal, covered with muddy sand and saltmarshes. The lagoon is shallow (2 m average depth) with semidiurnal tides at amplitudes between 1.3 m and 3 m (during neap and spring tides respectively) causing a relatively rapid renewal of water through three inlets at time scales shorter than 5 days. The hinterland is characterized by intensive agriculture leading to elevated nitrate concentrations in coastal groundwaters. To quantify the amount of submarine groundwater discharge (SGD) and possible associated nutrient fluxes to the lagoon radium concentrations (223Ra, 224Ra, 228Ra, 226Ra) were measured during low and high spring tides in December 2009 and May 2010 using standard techniques (delayed coincidence counting, gamma spectrometry). A radium mass balance model accounting for all major sources and sinks of radium was employed to derive quantitative estimates of SGD. In order to avoid biases due to non-representative sampling, areal average radium concentrations were generated using the ArcGIS spatial analyst interpolation scheme. Radium exchange with the open ocean was the most significant parameter in the mass balance calculations. Three independent models were used to calculate this exchange flux: i) a tidal prism model using radium to calculate the return flow factor, ii) a hydrographic model providing outflow and inflow water fluxes for the Ria Formosa lagoon; and by combining these fluxes with the average concentrations measured at the inlet; iii) a model which estimates the exchange with the ocean based on the radium residence time calculated from the water exposure time in the lagoon. For each of these models we calculated SGD based on 223Ra, 224Ra and 226Ra mass balances the differences being at a maximum no greater than 35 %. However, the results from the models differed up to a factor of 2 with the tidal prism model producing the highest estimate and the residence time model the lowest estimates. We will discuss possible causes for the differences in the model results.
- Impact of the flatworm Symsagittifera roscoffensis on the inorganic nitrogen loading associated with Submarine Groundwater Discharge (SGD): case study from a beach in Southern PortugalPublication . Carvalho, L. F.; Veiga-Pires, C.; Aníbal, J.; Fleming, Alexandra; Rocha, C.Submarine Groundwater Discharge (SDG)is pervasive in coasts worldwide, but focus particulary in interdital areas where they can represent an important source of pollutants to the adjacent coast zone.(...)
- Interception of nutrient groundwater drich submarine discharge seepage on European temperate beaches by the acoel flatworm, Symsagittifera roscoffensisPublication . Carvalho, Liliana Faia; Rocha, C.; Fleming, Alexandra; Veiga-Pires, C.; Aníbal, J.Submarine groundwater discharge (SGD) occurs in intertidal areas, representing a largely unquantified source of solute fluxes to adjacent coastal zones, with nitrogen being constantly the keynote chemical of concern. In Olhos de Água SGD is present as groundwater springs or merely sub-aerial runoff. The occurrence of the flatworm Symsagittifera roscoffensis is described for the first time in Olhos de Água in connection to seepage flows. To assess the impact of this symbiotic flatworm on the nitrogen associated to groundwater discharge flow at the beach, nitrate uptake experiments were conducted in laboratory microcosms. Our results show that S. roscoffensis actively uptakes nitrate at different rates depending on light availability, with rates ∼10 times higher than that of its symbiotic microalgae alone. This supports the hypothesis thatS. roscoffensis could be an important in situ nitrate interceptor, potentially playing a biological role on the transformation of groundwater-borne nitrate loads at the land–ocean boundary.
- Mitigation of nitrogen discharge from fish aquaculture effluents using green macroalgaePublication . Aníbal, J.; Madeira, Hélder Trindade; Carvalho, Liliana Faia; Esteves, E.; Veiga-Pires, C.; Rocha, C.Aquaculture effluents are rich in organic and inorganic nitrogen compounds that may support and enhance local primary productivity, eventualy inducing eutrophication conditions that may lead to the development of harmful algae blooms.
- Mudflat surface morphology as a structuring agent of algae and associated macroepifauna communities: a case study in the Ria FormosaPublication . Aníbal, J.; Rocha, C.; Sprung, MartinAlthough mudflats seem relatively planar, closer inspection reveals a succession of meso-topographical features, including consecutive convex and concave meso- and micro-topographical features. The objective of this study was to determine the influence of meso-scale surface sediment morphology on the dynamics of the macroalgae Ulvales (Chlorophyta) and associated macroepifauna in the Ria Formosa tidal lagoon (southern coast of Portugal). Four sites in the Ria Formosa were sampled monthly. Two were located on convex sections (mounds) of the mudflat and the other two on concave sections (depressions). Macroalgae and related macroepifauna were sampled at each station. Biomass was quantified by determination of the ash-free dry weight (AFDW). Data were analysed using the software package ‘PRIMER’ (Plymouth Routines In Multivariate Ecological Research). Results show a clear distinction between convex and concave areas. In convex sections, Enteromorpha dominated, to the point of being the only algal species present during part of the year. Conversely, biomass and dynamics of Enteromorpha and Ulva were almost the same in concave sections. The associated macroepifauna was also different in protruding or depressed sections of the mudflat. In the convex areas, the macroepifauna population showed less diversity and was dominated by the snail Hydrobia ulvae. In concave areas, the species diversity was larger, but dominated in terms of biomass by the amphipod Melita palmata and the gastropod Nassarius pfeifferi. Results of the study indicate that the benthic communities associated with concave or convex features were different. No relevant differences in texture and sediment physico-chemical characteristics were found between convex and concave sections. The inference is that the morphological nature of the bottom in tidal mudflats can act as a structuring agent of benthic communities.
- Role of transient silicon limitation in the development of cyanobacteria blooms in the Guadiana estuary, south-western IberiaPublication . Rocha, C.; Galvão, Helena M.; Barbosa, Ana B.The Guadiana estuary, located between Portugal and Spain, has the fourth largest drainage basin of Iberian river systems. Up to 75% of the catchment area has been regulated by dams since the early 1970s. During the 1980s and 1990s, an increasing occurrence of summer cyanobacteria blooms dominated by the potentially toxic Microcystis spp. was reported. In an effort to understand the causes of recurrent noxious blooms in the Guadiana estuary, nutrients (phosphorus, nitrogen [nitrate, nitrite and ammonium], and silicon [silicic acid], chlorophyll a and phytoplankton abundance, specific composition and biomass were evaluated during field surveys, from April 1997 to March 1998. A pattern of successive blooms of different phytoplankton assemblages was observed throughout this period. Diatoms (nano-sized, chain-forming) dominated an early spring bloom (max. 18 × 103 cells ml–1) in March and April. Following the decrease in diatom abundance, a chlorophyte bloom (max. 11 × 103 cells ml–1) and then a cyanobacteria bloom (>6 × 104 cells ml–1) quickly followed during late spring through to early summer. From July to September, a major cyanobacteria bloom dominated by the potentially toxic Microcystis spp. (> 4 × 105 cells ml–1) developed in the freshwater zone. The results indicate that high winter loads of nitrogen and phosphorus led to the depletion of silicate (down to as low as 0.2 μM) during the early spring diatom bloom, which conditioned the successive phytoplankton assemblages during the remaining productive period. Low monthly discharge rates during spring and summer further provided an environment with low Si:N and N:P relative availability which, coupled with high water-column temperature (>21°C), seemed to favour the dominance of cyanobacteria over chlorophytes during the summer.
- Seasonal variations in gross biochemical composition, percent edibility, and condition index of the clam Ruditapes Decussatus cultivated in the Ria Formosa (South Portugal)Publication . Aníbal, J.; Esteves, E.; Rocha, C.The grooved carpet shell clam, Ruditapes decussatus (L. 1758), is one of the most popular and profitable molluscs exploited in rearing plots in the Mediterranean. However, annual catch has been declining steadily since the early nineties. In order to understand the seasonality of its nutritional value, thus providing an improved basis for economical valuation of the resource, gross biochemical composition, percentage edibility and condition index were investigated during a year with monthly periodicity in a commercially exploited population of the clam Ruditapes decussatus in the Ria Formosa, a temperate mesotidal coastal lagoon located in the south of Portugal. Our results show that total and non-protein nitrogen co-varied during the year, resulting in a protein content that peaked in the warmest months. Although complementary in summer, carbohydrate and lipid contents showed irregular annual trends. The observed seasonality was comparable to that shown by studies elsewhere at similar latitudes, and are underpinned by the reproductive cycle of the species. Our results show the clams to be at their prime nutritional value at the beginning of summer, when protein content peaks.