Search Results (9)

Abundant large organic aggregates, which form mucous webs up to a few decimeters in length, have been observed in Baía de Todos os Santos (BTS), northeastern Brazil. This communication presents preliminary results from field (February 2015) and laboratory (June 2015) experiments that aimed to determine preliminary values for respiration and near-maximum photosynthesis and the impact of macroaggregates on respiration rates. The experiments included the determination of respiration in controls, with the mechanical removal and addition of macroaggregates. The field experiment during a flood tide presented the lowest respiration rate (−7.0 ± 0.7 µM L⁻¹ d⁻¹), average net primary production (8.9 ± 4.5 µM L⁻¹ d⁻¹), and gross primary production (16.0 ± 10 µM L⁻¹ d⁻¹), with a ratio of gross primary production to respiration of 2.3. The control experiments during an ebb tide showed a mean respiration rate of 8.7 ± 2.3 µM L⁻¹ d⁻¹, whereas, after macroaggregate removal, this was 9.5 ± 4.5 µM L⁻¹ d⁻¹. In the laboratory experiments, the control sample respiration rate of 18.4 ± 1.4 µM L⁻¹ d⁻¹ was slightly increased to 20.6 ± 0.1 µM L⁻¹ d⁻¹ after aggregate removal. The addition of aggregates to the control sample increased the respiration rate by approximately 3-fold, to 56.5 ± 4.8 µM L⁻¹ d⁻¹. These results indicate that macroaggregates could have an important role in pelagic and benthic respiration, as well as in the whole bay’s metabolism. Full article

As a result of climate change, the Mediterranean Sea has been exposed to an increase in the frequency and intensity of marine heat waves in the last decades, some of which caused mass mortality events of benthic invertebrates, including sponges. Sponges are an important component of benthic ecosystems and can be the dominant group in some rocky shallow-water areas in the Mediterranean Sea. In this study, we exposed the common shallow-water Mediterranean sponge Chondrilla nucula (Demospongiae: Chondrillidae) to six different temperatures for 24 h, ranging from temperatures experienced in the field during the year (15, 19, 22, 26, and 28 °C) to above normal temperatures (32 °C) and metabolic traits (respiration and clearance rate) were measured. Both respiration and clearance rates were affected by temperature. Respiration rates increased at higher temperatures but were similar between the 26 and 32 °C treatments. Clearance rates decreased at temperatures >26 °C, indicating a drop in food intake that was not reflected by respiration rates. This decline in feeding, while maintaining high respiration rates, may indicate a negative energy balance that could affect this species under chronic or repeated thermal stress exposure. C. nucula will probably be a vulnerable species under climate change conditions, affecting its metabolic performance, ecological functioning and the ecosystem services it provides. Full article

Benthic diatom communities dominate sheltered shallow inner coastal waters of the atidal Southern Baltic Sea. However, their photosynthetic oxygen production and respiratory oxygen consumption is rarely evaluated. In the Baltic Sea carbon budget benthic diatom communities are often not included, since phytoplankton is regarded as the main primary producer. Therefore, two wind-protected stations (2–49-cm depths) were investigated between July 2010 and April 2012 using undisturbed sediment cores in combination with planar oxygen optodes. We expected strong fluctuations in the biological activity parameters in the incubated cores over the course of the seasons. The sediment particles at both stations were dominated by fine sand with a median grain size of 131–138 µm exhibiting an angular shape with many edges, which were less mobile compared to exposed coastal sites of the Southern Baltic Sea. These sand grains inhabited dense communities of rather small epipsammic diatoms (<10 µm). Chlorophyll a as a biomass parameter for benthic diatoms fluctuated from 64.8 to 277.3-mg Chl. a m⁻² sediment surface. The net primary production and respiration rates exhibited strong variations across the different months at both stations, ranging from 12.9 to 56.9 mg O₂ m⁻² h⁻¹ and from −6.4 to −137.6 mg O₂ m⁻² h⁻¹, respectively. From these data, a gross primary production of 13.4 to 59.5 mg C m⁻² h⁻¹ was calculated. The results presented confirmed strong seasonal changes (four-fold amplitude) for the activity parameters and, hence, provided important production biological information for sheltered sediments of the Southern Baltic Sea. These data clearly indicate that benthic diatoms, although often ignored until now, represent a key component in the primary production of these coastal habitats when compared to similar studies at other locations of the Baltic Sea and, hence, should be considered in any carbon budget model of this brackish water ecosystem. Full article

The two-stage ditch is a river restoration technique that aims at improving the sediment regime and lateral channel connectivity by recreating a small floodplain alongside a stream reach. This study aimed to analyze the efficiency of a two-stage ditch in improving the stream sediment structure and functions under different hydrological conditions (baseflow, post-bankfull, post-flood). Stream sediments were collected in channel sections adjacent to the two-stage ditch, adjacent to a natural floodplain along channelized reaches without inundation areas. Grain sizes, organic matter content and phosphorous (P) fractions were analyzed along with functional parameters (benthic respiration rate and P adsorption capacity, EPC₀). The reach at the two-stage ditch showed no changes in sediment texture and stocks, while the floodplain reach showed higher fines and organic matter content under all hydrological conditions. The sediments in degraded reaches were more likely to be P sources, while they were more in equilibrium with the water column next to the natural floodplains and the two-stage ditch. Only functional parameters allowed for assessing the restoration effects on improving the sediment stability and functionality. Due to its sensitivity, the use of P adsorption capacity is recommended in future studies aiming at evaluating the response of river sediments to restoration measures under different hydrological conditions. Full article

Lampreys spend their larval stage within fine sand fluvial sediments, where they burrow and act as filter feeders. Lamprey larvae (ammocoetes) can significantly affect benthic-pelagic coupling and nutrient cycling in rivers, due to high densities. However, their bioturbation, feeding and excretion activities are still poorly explored. These aspects were investigated by means of laboratory incubations of intact sediments added with ammocoetes and of animals alone. Oxygen respiration, nutrient fluxes and excretion rates were determined. Individual ammocoete incubations suggested that biomass-specific oxygen consumption and ammonium, reactive phosphorus and silica excretion were size-dependent, and greater in small compared to large individuals. The comparison of ammocoetes metabolic rates with rates measured in intact sediments revealed that ammocoetes activity decreases significantly when they are burrowed in sediments. Furthermore, results suggest that a major fraction of ammonium excreted by ammocoetes was assimilated by benthic microbes or microalgae to overcome in situ N-limitation. Alternatively, part of the excreted ammonium was oxidized and denitrified within sediments, as nitrate uptake rather increased along with ammocoetes density. Ammocoetes excreted reactive phosphorus and silica but such production was not apparent in bioturbated sediments, likely due to microbial or microalgal uptake or to immobilization in sediments. Full article

Macrofauna can produce contrasting biogeochemical effects in intact and reconstructed sediments. We measured benthic fluxes of oxygen, inorganic carbon, and nitrogen and denitrification rates in intact sediments dominated by a filter and a deposit feeder and in reconstructed sediments added with increasing densities of the same organisms. Measurements in reconstructed sediments were carried out 5 days after macrofauna addition. The degree of stimulation of the measured fluxes in the intact and reconstructed sediments was then compared. Results confirmed that high densities of bioturbating macrofauna produce profound effects on sediment biogeochemistry, enhancing benthic respiration and ammonium recycling by up to a factor of ~3 and ~9, respectively, as compared to control sediments. The deposit feeder also increased total denitrification by a factor of ~2, whereas the filter feeder activity did not stimulate nitrogen removal. Moreover, the effects of deposit feeders on benthic fluxes were significantly higher (e.g., on respiration and ammonium recycling) or different (e.g., on denitrification) when measured in intact and reconstructed sediments. In intact sediments, deposit feeders enhanced the denitrification coupled to nitrification and had no effects on the denitrification of water column nitrate, whereas in reconstructed sediments, the opposite was true. This may reflect active burrowing in reconstructed sediments and the long time needed for slow growing nitrifiers to develop within burrows. Results suggest that, in bioturbation studies, oversimplified experimental approaches and insufficient preincubation time might lead to wrong interpretation of the role of macrofauna in sediment biogeochemistry, far from that occurring in nature. Full article

The integrated crop–livestock system (ICLS) is a farming strategy that helps to sustain agrobiodiversity, ecosystem services, and restores environmental sustainability. Furthermore, ICLS provides food and nutritional security to the small and marginal farmers in developing nations. In this context a mass-balanced ecosystem model was constructed for a smallholder ICLS along the Indian west coast to analyze the agro-ecological performance in terms of sustainability, resource use, nutrient balance and recycling. Thirteen functional groups were defined in the ICLS model with trophic levels ranging from 1.00 (detritus and benthic nitrogen fixers) to 3.00 (poultry and ruminants). The total system throughput index was estimated to be 1134.9 kg N ha⁻¹ year⁻¹ of which 60% was from consumption, 15% from exports, 10% from respiration, and the remaining 15% eventually flowing into detritus. The gross efficiency of the ecosystem was estimated to 0.3, which indicated higher growth rates and low maintenance energy costs. The higher food self-sufficiency ration of 7.4 indicated the integration of crop–livestock as an imperative system to meet the food and nutritional requirement of the farm family. The indices such as system overhead (60%), Finn’s cycling index (16.6) and mean path length (3.5) denoted that the ICLS is a small, resource-efficient, stable, maturing and sustainable ecosystem in terms of the ecosystem principles and recycling. The present model will serve as the first model on the ICLS from the humid tropics and will help in the evaluation of the other agro-ecological systems using the Ecopath modelling approach. In conclusion, farm intensification through crop and animal diversification has the highest impact on farm productivity, food self-sufficiency and resource-use-efficiency of the smallholder’s livelihood security. Full article

Suspended, organic matter, especially in the form of adhesive extracellular polymers (EPS), tends to form flocs, which may also incorporate suspended lithogenic particles in coastal environments. With an increased settling velocity, these ballasted flocs form in a narrow zone along the coast and potentially represent a major source of pelagic primary production for the benthic community. We sought support for this hypothesis by examining our measurements of the mud content, porosity, permeability, pigment content, and specific respiration rate of sediment from the German Bight (North Sea) for signs that the pelagic zone of ballasted floc formation is affecting the local sediment characteristics. Based on a simple bottom-shear stress model and by employing empirical correlations of sediment characteristics we were able to find strong indications that this is actually the case. Our results demonstrate how ballasted flocs contribute to the benthic pelagic coupling in a high turbulence environment. Full article

The North American oligochaete Sparganophilus tamesis is widespread in European freshwaters. Its ecological effects on benthic nitrogen (N) biogeochemistry were studied in two contrasting environments: the organic-rich muddy sediments of the eutrophic Mincio River (Italy) and the organic-poor sandy sediments of the oligotrophic Cazaux-Sanguinet Lake (France). Oxygen and inorganic N fluxes and denitrification rates (IPT) were measured by dark incubation of intact cores with different worm biomass. Sediment oxygen demand and denitrification were higher in muddy than in sandy sediments; however, at the two sites, bioturbation by the oligochaetes stimulated differing microbial O₂ and NO₃⁻ respiration and NH₄⁺ production. In particular, the relative effect of S. tamesis on sediment metabolism was greater in Cazaux-Sanguinet Lake than in the Mincio River. As a result, S. tamesis favored net N loss in the Mincio River, whereas it increased NH₄⁺ recycling and lowered denitrification efficiency in the Cazaux-Sanguinet Lake. Our results suggest that the effects of S. tamesis on N biogeochemistry might differ depending on local trophic settings. These results have implications for the conservation of isoetids in the French Lake, whose persistence can be menaced by oligochaete-induced nutrient mobilization. Full article