Bastiaan A. Knoppers

Trophic state and water turn-over time in six choked coastal lagoons in Brazil

Comparison of total phosphorus and chlorophyll-a concentration, nutrient loading, and water turn-over time in six shallow choked lagoons along the coast of the state of Rio de Janeiro, Brazil, established that water turn-over time is related to the trophic state of the lagoons with additional anthropogenic nutrient loading affecting this relationship. Turnover time was calculated as a flushing half-life from rainfall, evaporation, runoff, and tidal exchange data, and trophic state was calculated from the quantity and quality of dissolved inorganic nutrients, total phosphorus, and chlorophyll-a standing stock. Flushing half-life of the lagoons ranged between 1 and 27 days, annual phosphorus areal loading from 3 to 18 mg m−2d−1, and chlorophyll-a standing stock from 6 to 160 mg M−2

A 21 000 cal years paleoclimatic record from Caçó Lake, northern Brazil: evidence from sedimentary and pollen analyses

Abstract Sedimentological studies including seismic profiles, mineralogy and organic geochemistry on two cores from the center and margin of Caco Lake, Maranhao State, northern Brazil, revealed variable climatic and environmental conditions during the last 21 cal kyr BP. Between 21 and 17 cal kyr BP, during the Late Glacial Maximum, regional climate was predominantly dry, interrupted by short humid phases, as reflected by a succession of very thin layers of sand and organic matter. The Late Pleistocene climate was relatively wet as is suggested by rapid lake-level rise and forest expansion. The Late Pleistocene humid climate differed significantly from present conditions. We suggest that Late Glacial humid conditions were the consequence of intensification of the Inter-Tropical Convergence Zone or shifts of its position, resulting in Antarctic cold-front occurrences. The abrupt climatic changes during this period were marked by siderite deposition into Caco Lake, which appears to be related to regional hydrologic changes linked to global/Northern Hemisphere events. The Holocene was characterized by lower moisture availability and a distinct dry period until 7 cal kyr BP, in response to South American insolation conditions.

Chapter 9 Aquatic Primary Production in Coastal Lagoons

Measurements of hourly, daily and annual rates of aquatic primary production in coastal lagoons are now numerous, but the mechanisms that regulate primary production are still difficult to assess. Short term dynamics in functioning and diversity in geomorphological configuration, hydrodynamics, nutrient supply, and autotrophic populations, as well as the usage of various methods in primary production measurements, are among some reasons. Mesotrophic to eutrophic choked lagoons with depths exceeding about two meters and light limitation at the bottom are commonly phytoplankton based. In shallower choked to restricted lagoons with high nutrient loading perennial macroalgae appear in succession with phytoplankton. Restricted to leaky lagoons harbor more macrophytes and species predominance is selected by a combination of depth, tidal flushing, and nutrient loading. Nutrient budgets for coastal lagoons are still lacking, but external inorganic nitrogen loading seems to supply 5-20% and sediment release 5-30% of primary production demand. Regenerated production is thus high and its largest fraction is maintained by nutrient recycling in the water column. In comparison to primary production yield, approximately 10-25% of carbon is accumulated in lagoon sediments. Many tropical and sub-tropical lagoons particularly those with typical dry/wet seasons are marked by seasonal shifts between autotrophic and heterotrophic metabolism Beholding exceptions, annual primary production ranges from 200 to 500 g Cm −2 year −1 , and is highest in tropical choked phytoplankton based lagoons and those governed by macrophytes. Global coastal lagoon primary production is estimated at 10 11 kg C year −1 and is similar to the contribution by upwelling areas and by a factor of four less than estuaries where primary production per unit area is similar to that in lagoons.

Sedimentary sterols as indicators of environmental conditions in Southeastern Guanabara Bay, Brazil

The interconnected Icarai and Jurujuba embayments, set within the lower south-eastern portion of Guanabara Bay, SE-Brazil, have been subject to the direct input of domestic effluents and other associated contaminants from human activities in their watersheds. This study addresses the composition of carbon, nitrogen and molecular steroid markers of surface sediments (n = 24) and a short core (L = 47 cm), in order to evaluate the impact by sewage, the contribution between allochthonous and autochthonous derived organic matter and eutrophication of the embayments. Coprostanol concentrations revealed, when compared to other regions in Guanabara Bay, high contamination by sewage close to the point of sewage discharge in Icarai embayment. In contrast, the more enclosed and eutrophic Jurujuba embayment exhibited a larger contribution of autochthonous organic matter, as shown by the combination of cholesterol, dinosterol and, partially, also brassicasterol. The presence of stigmasterol and b-sitosterol also indicated a minor contribution of organic matter from terrestrial plants, as revealed by principal component analysis. The sedimentary record of the Jurujuba embayment exhibited highest concentrations of all sterol markers in the top layer, corroborating the recent increase in the accumulation of sewage, plankton derived organic carbon and also eutrophication. Trend in degradation of organic matter was evidenced by sterol/stanol ratios and the behavior of dinosterol indicated that the embayment has been dominated by the accumulation of phytoplankton derived organic matter since earlier times.

Coastal Lagoons of Southeastern Brazil: Physical and Biogeochemical Characteristics

Coastal lagoons are one of six categories of inland coastal ocean-connected systems (Kjerfve 1994). Coastal lagoons are shallow water bodies, with depths usually less than 5 m, oriented parallel to the shoreline, separated from the ocean by a barrier, and connected to the ocean by one or more inlets (Phleger 1969). According to their geomorphology and water exchange with the coastal ocean, they are conveniently subdivided into choked, restricted, and leaky lagoon systems (Kjerfve 1986) (Fig. 3.1). Choked lagoons have the longest and leaky lagoons the shortest water residence times (Kjerfve and Magill 1989). Tidal mixing maybe negligible or intense, and salinity may vary from that of a fresh water coastal lake to a hypersaline lagoon.

Particle Fluxes and Bulk Geochemical Characterization of the Cabo Frio Upwelling System in Southeastern Brazil: Sediment Trap Experiments between Spring 2010 and Summer 2012

Physical and biogeochemical processes in continental shelves act synergistically in both transporting and transforming suspended material, and ocean dynamics control the dispersion of particles by the coastal zone and their subsequent mixing and dilution within the shelf area constrained by oceanic boundary currents, followed by their gradual settling in a complex sedimentary scenario. One of these regions is the Cabo Frio Upwelling System located in a significantly productive area of Southeastern Brazil, under the control of the nutrient-poor western boundary Brazil Current but also with a wind-driven coastal upwelling zone, inducing cold-water intrusions of South Atlantic Central Water on the shelf. To understand these synergic interactions among physical and biogeochemical processes in the Cabo Frio shelf, a series of four experiments with a total of 98 discrete samples using sediment traps was performed from November 2010 to March 2012, located on the 145 m isobath on the edge of the continental shelf. The results showed that lateral transport might be relevant in some cases, especially in deep layers, although no clear seasonal cycle was detected. Two main physical-geochemical coupling scenarios were identified: singular downwelling events that can enhance particles fluxes and are potentially related to the Brazil Current oscillations; and events of significant fluxes related to the intrusion of the 18°C isotherm in the euphotic zone. The particulate matter settling in the Cabo Frio shelf area seems to belong to multiple marine and terrestrial sources, in which both Paraiba do Sul River and Guanabara Bay could be potential land-sources, although the particulate material might subject intense transformation (diagenesis) during its trajectory to the shelf edge.

Nutrients, heavy metals and organic micropollutants in an eutrophic Brazilian lagoon☆

Abstract This article documents the environmental quality with respect to nutrients, heavy metals, and organic micropollutants at Lagoa de Guarapina, a tropical eutrophic lagoon of Rio de Janeiro State, Brazil. Concentrations of nutrients and heavy metals in the lagoon and its tributaries were low, closely resembling natural conditions. However, Pb formed the exception, and its presence in conjunction with detectable concentrations of organic micropollutants suggest that minor pollution effects are occurring via atmospheric inputs.

The Plankton Tower. IV. Interactions Between Water Column and Sediment in Enclosure Experiments in Kiel Bight

Neritic ecosystems in the boreal zone generally maintain more plankton biomass over a longer period of the year than off-shore systems in the same latitude. Productivity is higher particularly during the summer stratification, between the spring and autumn phytoplankton blooms brought about by nutrients from sources other than pelagic remineralization. Plankton biomass levels maintained by recycling within a pelagic system tend to decrease with time if limiting nutrients bound in sedimenting particles are not replenished. In neritic environments, surface waters can receive nutrients from the land, but depending on water depth and local weather and geomorphology, replenishment can also come from nutrient-rich subthermocline water and sediments. In deeper bodies of water with a steep coastline, such as fjords, the sediment contribution will be less important (Takahashi et al. 1977) than in shallow water systems with more of their sediment surface within the euphotic zone (von Bodungen et al. 1975, Rowe et al. 1975).

In situ measurements of benthic primary production, respiration and nutrient fluxes in a hypersaline coastal lagoon of SE Brazil

Bentbic oxygen and nutrient ftuxes were measured in a section of the hypersaline carbonate-rich coastal lagoon of Araruama, SE-Brazil. In situ incubations of the sediment surface (Zm - 1.5) were performed at one station with light/dark chambers during september 1993 (early spring period) and april 1995 (earlyautumn period). The carbonate..rich aediments were covered by 1-3 mm thick microalgal mats, dominated by the cyanobaeteria Phormidium sp, Oscillatoria sp, and Lyngbya sp. Benthic net primary production rates were 15.4 ± 0.7 mmolC/m2/d in early spring and 33.8 ± 8.8 mmolC/m2/d in early autumn, total community respiration rates attained 35.3 ± 7.2 and 65.7 ± 16.9 mmolC/m2/d, and pelagic primary production rates 1.7 ± 0.7 and 4.0 ± 1.4 mmolC/m2/d, respectively. Total community metabolism was thus heterauophic and mainly driven by benthic metabolism. The benthic release rates af ammonia were 0.65 ± 0.32 mmolC/m2/day in early spring and 0.58± 0.42mmoVm ldaym early autumn, butwere near to negligible for orthophosphate. Pelagic primaryproduction was limited byphosphorous, in part, by the preferential release of etmmonia over orthophosphate from the sediment-water interface. The benthic primary production and nutrient release rates were within the range of other eury-to hypersaline carbonate-rich environments characterized by non- consolidated algat rats.

Triazines in the tropical lagoon system of Mundaú-Manguaba, NE-Brazil.

This study addresses triazines in the tropical and eutrophic Mundau-Manguaba estuarine-lagoon system (MMELS) located in the State of Alagoas, NE-Brazil, affected by sugar-cane monoculture in its lower drainage basin. Water and sediment samples from MMELS were collected during the wet post-harvest season (August/2006) and the dry harvest season (February/2008). Trace analysis of the triazines atrazine, simazine, deethylatrazine, deisopropylatrazine and deethyldeisopropylatrazine were performed in surface sediments, suspended particulate matter and in the dissolved fraction in water. Water samples were filtered and after the analytical procedures, the resulting extracts were analyzed by gas chromatography-mass spectrometry. Additionally, the analytical method for suspended particulate matter was evaluated, the recovery being between 72-123 % with relative standard deviations of 4.2-22 % and limits of detection around 0.2-0.3 ng L-1. Sediments fortified at 10, 20 and 50 ng g-1 were extracted with the ASE system and recovery experiments lied between 68-133 % with relative standard deviations of 2-34 %. The limits of detection were of 0.6-1.2 ng g-1. Atrazine was the sole triazine detected and only in suspended particulate matter during the wet season at four sites, with low concentrations of 3.1, 2.7, 1.6 and 0.7 ng L-1. This suggests that triazines are either largely retained and transformed within the sugar-cane fields and/or are readily diluted in the waters and degraded due to the intense metabolism of MMELS.