Decomposition of Hudson estuary macrophytes: Photosynthetic pigment transformations and decay constants

Plant pigment decay constants were determined for four macrophytes collected from the Hudson Estuary.Typha angustifolia andScirpus fluviatilis were used as representatives of emergent aquatic vegetation (EAV), andPotamogeton sp. andVallisneria americana were used to represent submerged aquatic vegetation (SAV). Litter bags were maintained in an environmental chamber in the dark for 104 d. The fastest rate of total mass loss was in the SAVV. americana and slowest in the EAVT. angustifolia. Changes in carotenoid and chloropigment concentration resulting from microbial and meiofaunal heterotrophy in each of the macrophytes were quantified using reverse-phase, high-performance liquid chromatography (RP-HPLC) techniques. Chlorophyllc and the carotenoid, fucoxanthin, provided useful biomarkers in determining the presence of epiphytic diatom growth, which only occurred on the SAV. The highest concentrations of phaeophorbidea, commonly used as an indication of metazoan grazing, were found in the SAVV. americana. Low concentrations of phaeophorbidea in the SAVPotamogeton sp. indicate inefficient use of this SAV by meiofaunal grazers. Lutein decayed slower than all other carotenoids in both EAV and SAV. Microcosm studies such as this are necessary to further understand the mechanisms and kinetics of photosynthetic pigment transformations in natural systems.     

Preservation conditions and the use of sediment pigments as a tool for recent ecological reconstruction in four Northern European estuaries

Down-core sediment pigment concentrations from four Northern European estuaries were measured using high-performance liquid chromatography (HPLC) to investigate phytoplankton community structure and preservation conditions over the last ca. 100 years where all sites have experienced different levels of eutrophication. Phytoplankton pigments have been shown to be useful biomarkers for phytoplankton community structure and abundance due to their taxonomic specificity. The pigment concentrations and sediment pigment inventory showed large variation between the four sites. Concentrations ranged from more than 6000 nmol/g OC to less than 100 nmol/g OC and the inventory integrated over the top 10 cm from more than 300 nmol/cm² to less than 30 nmol/cm² for total identified pigments. Good pigment preservation in Mariager Fjord (Denmark) reflected the almost permanently anoxic conditions. Pigments in Laajalahti (Finland) showed peak concentrations around the time of highest nitrogen loading events known from historical and modelled records over the past 100 years. In contrast, poor down-core preservation of pigments (especially carotenoids) was observed in the Ems-Dollard (The Netherlands) and Himmerfjärden (Sweden) estuaries. The Ems-Dollard site is an intertidal mudflat that experiences daily exposure to light and air, which enhances pigment degradation. In Himmerfjärden, resuspension is an important process affecting both the sedimentation rate and degradation properties. The different preservation conditions at the four sites were supported by the differences in two degradation indicators; the ratio of pheopigment-a to chlorophyll-a and total carotenoids to total pigments. Class-specific carotenoid pigments represented the dominant algal groups reported from each site, however, no distinct down-core changes in the pigment composition were observed at any of the four sites. This indicated that changes in plankton community structure on the group level have been limited over this time period or masked by low preservation of pigments.     

Optimizing interpolation of shoot density data from a Posidonia oceanica seagrass bed

A case study on the optimization of Posidonia oceanica density interpolation, using a data set from a large meadow at Porto Conte Bay (NW Sardinia, Italy), is presented. Ordinary point kriging, cokriging and a weighted average based on inverse square distance were used to interpolate density data measured in 36 sampling stations. The results obtained from different methods were then compared by means of a leave‐one‐out cross‐validation procedure. The scale at which interpolation was carried out was defined on the basis of the Hausdorff dimension of the variogram. Optimizing spatial scale and data points search strategy allowed obtaining more accurate density estimates independently of the interpolation method.     

Particulate and dissolved amino acids in the lower Mississippi and Pearl Rivers (USA)

In this study, we present seasonal changes (monthly samples from September 2001 to August 2003) in the abundance and composition of dissolved and particulate amino acids, at one station in the lower Mississippi and Pearl Rivers (LA, MS: USA). Spatial changes over a 4-day transmit from river km 390 to river mouth (Head of Passes, LA) in the Mississippi River, and a two-day downstream sampling from Jackson (MS) to Stennis Space Center (MS) were also determined. Temporal data in the lower Mississippi River showed significantly lower concentrations of dissolved combined amino acids (DCAA, 0.8 to 2.2 μM) and dissolved amino acids in high molecular weight fraction (HMW DAA, 0.2–0.4 μM) than in the Pearl River (DCAA, 1.4–4.3 μM; HMW DAA, 0.4–1.4 μM). Dissolved free amino acids (DFAA) were significantly lower than DCAA in both rivers, and displayed minimal seasonal variability. DCAA, HMW DAA, and particulate amino acids (PAA) were generally higher during high-flow periods, which may have suggested dominance in terrestrial sources. Carbon-normalized yield of PAA (%C-PAA) was generally higher during low-flow conditions and positively correlated with chlorophyll-a (chl-a), reflective of in situ sources. Downstream variability in the lower Mississippi River showed stable DCAA concentrations, a decline in PAA (from 1.06 to 0.43 μM), and a gradual increase in mole percent of non-protein amino acids (%NPAA). This likely reflected bacterial degradation of phytoplankton biomass during falling discharge. Nitrogen-normalized yield of PAA (%N-PAA) was inversely correlated with PAA (R = − 0.7, n = 48), indicative of short-term sedimentation and resuspension events. Conversely, downstream decreases in DCAA and middle-reach peaks of PAA and %N-PAA in the Pearl River, likely resulted from photochemical degradation of DOM as well as algal production during base-flow conditions. The comparisons in abundance and composition of DAA and PAA in these different river systems provides important information on in situ nitrogen and carbon cycling as related to riverine inputs of organic matter to coastal ocean.     

The bimodal rift-related Juscelândia volcanosedimentary sequence in central Brazil: Mesoproterozoic extension and Neoproterozoic metamorphism

The Barro Alto Complex and Juscelândia volcanosedimentary sequence are exposed in the central part of the Neoproterozoic Brasília belt of central Brazil. The former is a large (approximately 150 km long), boomerang-shaped, mafic-ultramafic, layered complex formed by two different intrusions metamorphosed under granulite facies. These rocks are tectonically overlain by rocks of the Juscelândia volcanosedimentary sequence, represented mainly by biotite-gneiss and amphibolite, or amphibolite facies metamorphic equivalents of rhyolite and basalt, respectively. New SIMS U–Pb zircon data and Sm–Nd isochron data presented herein help clarify the igneous and metamorphic evolution of the Juscelândia volcanosedimentary sequence, as well as its relationship with the Barro Alto Complex. Zircon grains from two biotite gneisses were analyzed by SIMS (SHRIMP) and indicate Mesoproterozoic dates, approximately 1.28 Ga, interpreted as the time of bimodal volcanism in a tectonic setting transitional between a continental rift and an ocean basin. Metamorphism is constrained by Sm–Nd garnet-whole-rock isochrons for garnet amphibolite and pelitic schists of the Juscelândia sequence, as well as for clinopyroxene-garnet amphibolite and garnet granulite of the Barro Alto Complex, which give ages between 0.74 and 0.76 Ga, in agreement with SIMS dates for metamorphic zircon rims. These new data are significant, because they establish that a single metamorphic event affected both the Barro Alto Complex and the Juscelândia sequence. Based on these new data, we present a modified tectonic model for the Brasília belt.     

Carbon cycling in a shallow turbid estuary of southeast Texas: The use of plant pigment biomarkers and water quality parameters

Particulate organic carbon (POC), dissolved organic carbon (DOC), and plant pigments (chlorophylls and carotenoids) were measured approximately bimonthly from March 1992 to October 1993 in the Sabine-Neches estuary (Sabine Lake region), located on the Texas-Louisiana border. High freshwater inflow into this shallow turbid estuary results in the shortest hydraulic residence time (ca. 7 d) of all Texas estuaries (Baskaran et al. in press). Annual averages of chlorophyll-a (3.0 μg l^?1) and particulate organic carbon (1.1 mg l^?1) in the water column were extremely low in comparison to other shallow estuaries. The highest chlorophyll-a concentrations were observed in October 1993, in the mid and lower regions of the estuary, during the lowest river discharge. Zeaxanthin and fucoxanthin concentrations suggested that much of the chlorophyll-a during this low flow period was represented by cyanobacteria and diatoms that entered from the Gulf of Mexico. The range of DOC concentrations was generally high (4.4–20.9 mg l^?1) and were significantly correlated with POC, but not with chlorophyll-a concentrations. When total suspended particulate (TSP) concentrations were below 20 to 30 mg l^?1, there were significant increases in %POC and %PON of the TSP. The unusually high POC: chlorophyll-a ratios (highest value of 1423) suggested that much of the POC contained low concentrations of chlorophyll-a that had degraded during transport from wetlands in the Sabine and Neches rivers. Based on these data, this estuary can be characterized as a predominantly heterotrophic system, with low light penetrance, short particle-residence times, high DOC, and low inputs from autochthonous carbon sources.     

Seismic studies of the Brasília fold belt at the western border of the São Francisco Craton, Central Brazil, using receiver function, surface-wave dispersion and teleseismic tomography

The Tocantins Province in Central Brazil is composed of a series of SSW–NNE trending terranes of mainly Proterozoic ages, which stabilized in the Neoproterozoic in the final collision between the Amazon and São Francisco cratons. No previous information on crustal seismic properties was available for this region. Several broadband stations were used to study the regional patterns of crustal and upper mantle structure, extending the results of a recent E–W seismic refraction profile. Receiver functions and surface wave dispersion showed a thin crust (33–37 km) in the Neoproterozoic Magmatic Arc terrane. High average crustal Vp/Vs ratios (1.74–1.76) were consistently observed in this unit. The foreland domain of the Brasília foldbelt, on the other hand, is characterized by thicker crust (42–43 km). Low Vp/Vs ratios (1.70–1.72) were observed in the low-grade foreland fold and thrust zone of the Brasília belt adjacent to the São Francisco craton. Teleseismic P-wave tomography shows that the lithospheric upper mantle has lower velocities beneath the Magmatic Arc and Goiás Massif compared with the foreland zone of the belt and São Francisco craton. The variations in crustal thickness and upper mantle velocities observed with the broadband stations correlate well with the measurements along the seismic refraction profile. The integration of all seismic observations and gravity data indicates a strong lithospheric contrast between the Goiás Massif and the foreland domain of the Brasília belt, whereas little variation was found across the foldbelt/craton surface boundary. These results support the hypothesis that the Brasília foreland domain and the São Francisco craton were part of a larger São Francisco-Congo continental plate in the final collision with the Amazon plate.     

Geochronology of granulites from the south Itabuna-Salvador-Curaçá Block,São Francisco Craton (Brazil): Nd isotopes and U–Pb zircon ages

This work provides five new U–Pb zircon dating and the corresponding Nd isotope data for felsic granulites from the south Itabuna-Salvador-Curaçá Block (ISCB), in the São Francisco Craton, Brazil. Three major sets of felsic granulites can be recognised. The oldest set is tonalitic in composition and of TTG affinity. It is Archaean in age with magmatic zircon cores dated at 2675 ± 11 Ma by LA-ICPMS and up to ca 2.7–2.9 Ga by SHRIMP on an other sample. It exhibits epsilon Nd values between ?8 and ?11 at 2.1 Ga. This Nd signature is similar to that of granulites found in the western Archaean Jequié Block. Cartographically, this set of Archaean terrains represents at least 50% of the granulites in the studied area. The second set corresponds to a Palaeoproterozoic calc-alkaline tonalitic suite with zircon ages from 2019 ± 19 Ma to 2191 ± 10 Ma and epsilon Nd values between ?3 and ?4 at 2.1 Ga, corresponding partially to a newly formed crust. The third set of granulites is also Palaeoproterozoic. It is shoshonitic to monzonitic in composition and synchronous with the high grade metamorphism dated by metamorphic zircons at 2086 ± 7 Ma (average of five samples). The Nd isotope signature for this alkaline set is similar to that of the Palaeoproterozoic calc-alkaline one. Nd isotopes appear to be a very efficient tool to distinguish Archaean from Palaeoproterozoic felsic protoliths in granulitic suites of the Itabuna-Salvador-Curaçá Block (ISCB). Finally, the southern part of the ISCB is composed of a mixture of Archaean and Palaeoproterozoic protoliths, in similar amounts, suggesting that it was probably an active margin between 2.1 and 2.2 Ga located on the eastern border of the Archaean Jequié Block. A major crustal thickening process occurred at ca 2.09 Ga in the ISCB and seems significantly younger towards the west, in the Jequié granulites, where an average of 2056 ± 9 Ma is determined for the high grade event.