The effects of bioturbation on particle redistribution in Mediterranean coastal sediment. Preliminary results

In order to quantify bioturbation processes in a coastal Mediterranean ecosystem, experiments were performed to determine sediment mixing rates resulting from macrobenthos activity. Particle flux was measured in situ for 22 days using luminophores, which are colored sediment particles with sizes ranging from 10 to 200 µm.In sediment depths from 0–5 cm, particle mixing was intensive due to high macrobenthos abundance. A small quantity of luminophores was transported down to a depth of 14 ± 2 cm, where the macrofauna was represented principally by Polychetes. In a control experimental structure — without benthic fauna — no transfer of luminophores into the sediment was recorded.Sediment particle mixing measured in the ecosystem studied is intensive, and is the result of high macrobenthos activity. Different mixing modes occur with scales and rates depending on the organisms present. The luminophore profile resulting from bioturbation processes is explained by an intensive bioadvection sediment mixing added to a biodiffusive mixing with an order of magnitude of 10^–6 cm² s^–1. Tracer accumulations between 1 and 2 ± 1 cm and between 4 and 5 ± 1 cm are attributed to bioadvection activity of two or more distinct populations. Studies over a larger time scale have been undertaken to monitor developments in the observed subsurface maxima.     

The influence of sediment composition and leaf litter on the distribution of tubificid worms (Oligochaeta)

Summary The horizontal distribution of three species of tubificid worm (Tubifex tubifex, Limnodrilus hoffmeisteri and L. udekemianus in the sediment of a small stream was examined. Worm distribution was most strongly correlated with the distribution of leaf litter. This relationship was examined in the laboratory by means of choice chambers. It was concluded that; 1) the addition, to an inorganic substratum, of conditioned leaf material, enhanced its attractiveness to the worms; 2) a combination of silt-clay and leaf material was preferred by the worms to mixtures of leaf material and coarser inorganic substrata 3) some leaf species were more attractive to the worms than others; 4) there were differences between the worm species in their preferences for the various leaf species; 5) none of the three tubificid species was exclusively associated with its preferred leaf species; 6) worms would switch to less attractive leaf species if preferred alternatives were unavailable; 7) leaf material only attracted the worms once it had become conditioned; 8) this appeal was lost when the leaves were autoclaved; and 9) substratum choice was independent of worm size.We believe the worms were attracted to the leaves because the associated microfloras provided a concentration of bacterial food. Differences between the three tubificid species in their preferences for the various leaf species probably reduced trophic competition.     

The role of <Emphasis Type="Italic">Campsurus notatus</Emphasis> (Ephemeroptera: Polymitarcytidae) bioturbation and sediment quality on potential gas fluxes in a tropical lake

About 30% of the total area of Lake Batata (Amazon) was impacted by the disposal of bauxite tailings originated from the process of washing bauxite. This effluent, composed by fine particles of clay and water, settled on top of the natural sediment, originating a new substratum with a different physical and chemical composition. This phenomenon created a new distinct habitat (impacted sediment) influencing the benthic community. The aim of this study was to evaluate the impact of bioturbation by Campsurus notatus (Ephemeroptera: Polymitarcytidae) on potential gas fluxes in the sediment of natural and impacted areas of the lake. The natural sediment had a significantly higher methane concentration when compared to the impacted one. In incubated sediment cores, the presence of C. notatus nymphs resulted in a significant increase in oxygen consumption and methane and carbon dioxide release to the water column. The effect of the presence of nymphs on methane was ambiguous. The C. notatus nymphs strongly decreased methane concentration in natural sediment samples, probably because of the enhancement of the oxic sediment area. However, this effect was not observed in impacted samples. Finally, the new substratum of Lake Batata decreased methane concentration in sediment and water column. C. notatus nymphs demonstrated to have a significant role on gas flux (methane and CO₂) from sediment to water column as well as on oxygen consumption in Lake Batata, consequently influencing the carbon cycle in this lake. Handling editor: S. M. Thomaz     

Identification of immature tubificids (Oligochaeta) of Lake Constance and its influence on the evaluation of species distribution

In the course of an extensive taxonomical treatment of Oligochaetes collected from Lake Constance the immature specimens of all species were identified, mainly by setal characters. The method is presented, several hints are given and some characters of additional taxonomic value are described in a comparative way.The large extent to which evaluation of species distribution may be misleading if based only on the mature specimens is demonstrated.     

The impact of sediment reworking by opportunistic chironomids on specialised mayflies

1. Bioturbation, by definition, changes the structure and properties of sediments, thereby altering the environment of the bioturbator and other benthic species. In addition to the indirect effects of sediment reworking (e.g. changes in water quality), bioturbating species may also directly interfere with other species via competition. This study aims, therefore, to examine both the direct and indirect effects of sediment reworking by an opportunistic detritivore on survival and growth of a specialised mayfly species. 2. Bioturbation was imposed by adding different densities of the midge Chironomus riparius to clean and polluted sediments. Changes in water quality and sediment properties, and survival and growth of the mayfly Ephoron virgo were assessed. 3. Chironomid density had a strong negative effect on the concentrations of metals, nutrients and particles in the overlying water, but increased the penetration of oxygen into the sediment. Survival and growth of E. virgo were strongly reduced in the presence of chironomids. In the polluted sediment, the activity of chironomids enhanced the negative effects of pollution on E. virgo. In the clean sediment, inhibition of the mayfly was even more pronounced. 4. This suggests that direct disturbance by C. riparius was more important than indirect changes in water quality, and over‐ruled the potential positive effects of improved oxygen penetration. The results indicated that the distribution of small insects, such as E. virgo, can be limited by bioturbating benthic invertebrates.     

Interactive effects of porewater nutrient enrichment, bioturbation and sediment characteristics on benthic assemblages in sandy sediments

Effective management of eutrophic ecosystems requires an understanding of how nutrient input affects the structure and function of benthic communities. The effects of nutrients in soft sediment habitats can be influenced by a variety of factors including sediment characteristics, hydrodynamic exposure, and the presence of bioturbating macroinvertebrates. We used a large scale exclusion experiment (400 m² areas, n = 6) to test if bioturbating lugworms, Arenicola marina mediate the effects of nutrient enrichment. We incorporated small plots (30 × 30 cm) dosed with household garden fertilizer within the lugworm exclusion and corresponding control areas and predicted that the effects of nutrient enrichment would be greater in the absence of lugworms. We found that the increases in nutrient concentrations were higher in the absence of lugworms, but only in the less permeable sediment in the low intertidal zone compared to the more permeable sediment in the high intertidal. Contrary to expectations, the accumulation of nutrients in the plots did not affect the organic matter and chlorophyll levels in the sediment. Interestingly, there were overall negative effects of nutrient additions on some of the most abundant molluscs, Hydrobia ulvae, Retusa obtusa and juvenile Cerastoderma edule. Possible explanations for these adverse effects such as the changes in the sediment chemistry or the physical presence of the fertilizer in the sediment caused by the nutrient additions are discussed. We conclude that the effects of nutrient enrichment in soft sediment habitats on benthic assemblages are determined by the interplay between the presence of bioturbating macroinvertebrates, tidal height and sediment characteristics.     

The effect of natural populations of the burrowing and grazing soldier crab (Mictyris longicarpus) on sediment irrigation, benthic metabolism and nitrogen fluxes

The aim of this study was to determine the effect of sediment grazing and burrowing activities of natural populations of Mictyris longicarpus on benthic metabolism, nitrogen flux and irrigation rates by comparing sediments taken from minimum disturbance exclusion cages and adjacent sediments subject to M. longicarpus activities. M. longicarpus reduced sediment surface chlorophyll a (approximately 77%), organic carbon (approximately 95%) and total nitrogen concentrations (approximately 99%) in comparison to ungrazed sediments. Consequently, they significantly reduced gross benthic O₂ production (about 71%) and sediment O₂ consumption (approximately 46%). Mean N₂ fluxes showed net effluxes (276-430 μmol m⁻² day⁻¹) in the presences of M. longicarpus and net uptakes (194.09-449.21 μmol m⁻² day⁻¹) where they were excluded. The net uptake of N₂ was most likely due to cyanobacteria fixing of N₂, as dense microbial mats became established over the sediment surface in the absence of M. longicarpus grazing activity. Sediment irrigation/transport rates calculated from CsCl tracer dilution indicated greater irrigation rates in the exclusions (12.12-16.22 l m⁻² h⁻¹) compared to inhabited sediments (6.33-11.73 l m⁻² h⁻¹) and this was again was most likely due to the lack of grazing pressure which allowed large populations of small burrowing polychaetes to inhabit the organic matter rich exclusion sediments. As such, the main influence of M. longicarpus was the interception and consumption of transported organic material, benthic microalgae and other small infaunal organisms resulting in the removal of approximately 0.06 g m⁻² day⁻¹ of nitrogen and 12.12 g m⁻² day⁻¹ of organic carbon. This “cleansing” of the sediments reduced sediment metabolism and the flux of solutes across the sediment water interface and ultimately the heavy predation of M. longicarpus by transient species such as stingrays, results in a net loss of carbon and nitrogen from the system.     

The effect of different submerged macrophyte species and biomass on sediment resuspension in a shallow freshwater lake

Our study aim was to elucidate the effects of different species of submerged macrophytes and biomass levels on sediment resuspension. For this purpose experiments were conducted in four different enclosures (Potamogeton maackianus enclosure-PE, Vallisneria spinulosa enclosure-VE, manipulated enclosure-ME and aquaculture enclosure-AE). A sediment trap method was employed and the experiments were conducted from summer to winter in a shallow freshwater lake located in central China. A total of 813, 1277, 613 and 693 g DW m⁻² of sediment was resuspended in VE, AE, ME and PE, respectively. Our results showed that P. maackianus was more effective than V. spinulosa in restraining sediment resuspension. Macrophytes reached their maximum effectiveness of reducing resuspension at a certain species-specific biomass threshold above which biomass effects on resuspension were negligible. The threshold biomass was estimated as 300 g m⁻² for P. maackianus. Accordingly, within a lake management and aquaculture aspect, we conclude that as long as biomass does not fall below this threshold its consumption will not influence sediment resuspension. In the mid-lower reaches of the Yangtze River macrophyte coverage protects the lake sediment against adverse effects of monsoon wind; if the vegetation is eroded aquaculture sediment resuspension increases significantly.     

Effects of Chironomus tentans larval growth retardation on adult emergence and ovipositing success: implications for interpreting freshwater sediment bioassays

A laboratory study was conducted with Chironomus tentans to assess the significance of growth retardation of third-to fourth-instar larvae over a 10-d test period on long-term survival, adult emergence, and ovipositing success. Data were intended to provide interpretive guidance for the commonly used growth endpoint in 10-d sediment bioassays with C. tentans. Larval growth was controlled by using six feeding levels ranging from 0.2 to 5.9 mg dry weight Tetrafin® fish food per day. Mean 10-d survival was 88% at all feeding levels, but larval growth decreased significantly (p<0.05) with each decrease in feeding level. Cumulative successful emergence of adult C. tentans decreased significantly with decreasing larval growth. Mean times to emergence always increased with decreasing growth rates and effects were generally more pronounced for females than males. At the lowest 10-d mean growth where successful emergence occurred (0.27 mg), the times to emergence doubled relative to the times observed at the highest 10-d mean growth (1.03 mg). Ten-day larval growth retardation was strongly correlated with reduction in adult emergence success (r ² = 0.96). Growth retardations 64% resulted in 86–100% reductions in adult emergence. Growth retardation in the range of 35 to 50% equated with comparable percent reductions in adult emergence success. Although fewer females successfully emerged at 10-d growths of 0.37 and 0.74 mg relative to the highest 10-d growth (1.03 mg), ovipositing success of these females did not appear to be adversely affected by either their slower growth rates or their lower mean dry weights (0.62 and 0.99 mg, respectively). Growth of second generation larvae did not appear to be affected by maternal growth rate, but rather appeared to be solely correlated with their own feeding level.     

A note on the hatching and viability ofCeriodaphnia ephippia collected from lake sediment

Ephippia ofCeriodaphnia pulchella Sars were collected at 2 sites from successive sediment layers. Hatching observed in the laboratory gave information about the duration of their viability. Conclusions about the hatching situation in the lake were drawn from the ratio of intact to total ephippia at various lake depths. The results are discussed.     

Emergence of the midge chironomus tentans when exposed to heavy metal contaminated sediment

This experiment tested the effects of heavy metal contaminated sediment on emergence of chironomids. The number of adults emerging from test chambers containing an uncontaminated sediment and ones with sediment containing 1030 ppm cadmium (Cd), 17,300 ppm zinc (Zn), and 1640 ppm chromium (Cr) were observed for 14 days. It was found that emergence was reduced by over three times and delayed for two days in the heavy metal contaminated sediment.     

Observations of predator-prey interaction on dispersal of an oligochaete prey,Limnodrilus hoffmeisteri

Clumped patches of the oligochaete, Limnodrilus hoffmeisteri, were subjected to predation by the leech, Erpobdella punctata to determine how the dispersion pattern might change. Two separate experiments showed that worms left the patch in 39% and 48% greater numbers when the leech predator was present. This suggests that L. hoffmeisteri uses a antipredatory strategy of dispersal rather than clumping.     

Shading by an invasive macrophyte has cascading effects on sediment chemistry

The submersed freshwater macrophyte Utricularia inflata is a recent invader of Adirondack Mountain lakes (NY, USA). Previous experiments suggested that U. inflata can indirectly change nutrient cycling in Adirondack lake ecosystems by reducing the growth of native isoetid macrophytes, which in turn affects sediment chemistry. A 13-week greenhouse experiment was conducted to test the hypothesis that shading can explain the detrimental effect of U. inflata on the native short-statured isoetid, Eriocaulon aquaticum. Eriocaulon aquaticum has a dense root system that oxidizes sediment by releasing oxygen; it also takes up carbon dioxide from sediment. Growth and asexual reproduction of E. aquaticum grown under shaded conditions was reduced significantly compared to an unshaded control (P < 0.001). Shading resulted in sediment changes: redox potential fell from 216 mV in the absence of shading to 76 mV under four layers of shade cloth (P < 0.0001). Shading also increased the concentration of extractable sediment ammonium (P < 0.01), as well as carbon dioxide concentrations (P < 0.0001) and pH of porewater (P < 0.05). The effect of U. inflata on the native isoetids and consequently on sediment chemistry closely matched the impact of shade cloth with similar light attenuation. Our results indicate that the principal mechanism by which U. inflata affects native isoetids and sediment chemistry is shading.     

An attempt to trace eutrophication in a shallow lake (Balaton,Hungary) using chironomids

Lake Balaton, the largest shallow lake in Central Europe, is about 20 000 years old. An enormous increase in tourism and the disproportionate building development of the last few decades has resulted in the acceleration of eutrophication in the lake. Widespread research to reveal the causes of water-quality deterioration and possible ways of protection against it have recently started. The investigation of the larvae of non-biting midges (Diptera: Chironomidae) in the sediment of the open-water zone has also begun. The contemporary faunal composition strongly correlates with the trophic gradient along the longitudinal axis of the lake. We therefore supposed that the eutrophication process should be identifiable from the analysis of subfossil chironomid head capsules from the upper (15 cm thick) layer of the sediment. We found that quantitative results could only be obtained when fragments as well as relatively intact head capsules are considered. Our data verify that the originally oligo-mesotrophic community has been gradually replaced by eutrophic species in a west to east direction. Large-bodied larvae belonging to the Chironomus plumosus group mix the sediment down to 15 cm as they build their tubes and consequently alter the original proportions of head capsules at the different levels. So the sequence of communities through the sediment-layers is not quite reliable.     

Effects of river sediment elutriates on Daphnia magna

Laboratory sediment bioassays, both acute and chronic, were conducted on sediment elutriates from the River Eurajoki, SW Finland. The river is under impacts of industrial discharges, community effluents and agricultural run-offs. The water flea Daphnia magna Straus was used as a test organism. None of the elutriates tested were acutely toxic. In a long-term bioassay sediment elutriates had effects on survival, body growth and reproduction. Elutriates prepared from samples of a downstream station were characterized by low survival, small body size, reduced total offspring production, and delayed start of reproduction.     

Effects of the burrowing mayfly,Hexagenia, on nitrogen and sulfur fractions in lake sediment microcosms

Effects of the burrowing mayfly, Hexagenia, on nitrogen and sulfur fractions of sediment, and overlying water were determined. Laboratory microcosms were used to reproduce the benthic environment. The activities of Hexagenia increased sediment Eh (1.98 ± 0.486 (22) mV · day ⁻¹), and decreased pH in sediment (−0.007 ± 0.001 (22) day ⁻¹) and overlying water(-0.024 ± 0.004 (10) day⁻¹). In the control, Eh decreased and pH did not change. The presence of Hexagenia also markedly increased ammonia in sediment (5.46 ± 0.14 (22) ppm N · day⁻¹) and overlying water (0.792 ± 0.154 (10) ppm N · day⁻¹), while the control did not change. In addition, the sulfate fraction of sediment (0.177 ± 0.006 (17)% dry mass) and water (50.0 ± 4.9 (5) mg · I⁻¹) in microcosms with Hexagenia was greater than that of the control (0.151 ± 0.005 (16)% dry mass; 14.7 ± 1.71 (3) mg · 1⁻¹) at the termination of the experiment. Hexagenia may also stimulate the mineralization of carbon-bonded sulfur. The general role of Hexagenia in altering sediment chemistry is discussed.     

Effects of sediment anoxia and light on turion germination and early growth of Potamogeton crispus

Potamogeton crispus is a cosmopolitan aquatic species and is widely used as a pioneer species for vegetation restoration of eutrophic lakes. However, many restoration projects applying P. crispus turions have not been successful. Earlier studies focused on effects of light and temperature on turion germination. The purpose of this study was to determine whether sediment anoxia and light interactively affected the turion germination and early growth of P. crispus. Anoxic conditions in the experiment were produced by adding sucrose to the sediment. The germination rate of the turions was 68–73% lower in the highly anoxic condition treatment than in the control. Medium light intensity (10% of natural light at the water surface) was more favorable for germination under slightly anoxic conditions than either low or high light intensity. The growth of newly-formed sprouts was also significantly inhibited by sediment anoxia. Photosynthesis and shoot biomass were reduced under sediment anoxia, whereas total chlorophyll content, root biomass, and soluble protein content were highest in the low anoxic condition treatment. Medium light improved net photosynthesis and biomass production of the sprouts. We conclude that turion germination and sprout growth can be significantly inhibited by sediment anoxia. Medium light intensity may alleviate this inhibition by anoxia, but light has little effect when sediment anoxia is severe. For the purposes of vegetation restoration, more attention should be paid to the role of sediment anoxia, and it is necessary to improve sediment and light conditions for turion germination and early growth of P. crispus in eutrophic lakes. These results will contribute to a more complete understanding of turion germination dynamics of P. crispus and will be useful for future restoration programs. Handling editor: S. M. Thomaz     

Effect of Environmental Pollution on the Chromosomal Variability of Chironomus Riparius

Different frequencies of chromosomal alterations in salivary gland polytene chromosomes AB, CD and EF were described in larvae of Chironomus riparius (syn. Chironomus thummi) from the trace metal-polluted station of Santena on the river Banna, near Turin, and from the unpolluted station of Corio (40 Km from Turin) which was taken as a reference area. In a sample of 56 larvae from Santena, no specimen with the standard karyotype in all cells of the salivary glands was found. Different types of aberrations were found: 33 paracentric and five pericentric inversions, three deficiencies, four amplified sections and one chromatid break. Fifteen out of the 38 inversions and two amplified sections appeared to be inherited, while all the other aberrations were somatic. Most of the aberrations' breakpoints were located on both sides of the centromere regions, where constitutive heterochromatin is present. Also functional alterations were observed (mainly telomere and centromere decondensations and nine novel puffs). In a sample of 49 larvae of a population from the well-preserved area of Corio only six somatic and one inherited paracentric inversions were found. These results suggest that the strong destabilization of the genomes of C. riparius larvae from Santena could be a reaction to the activity of the toxic substances present in the polluted sediments of the river Banna. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetic susceptibilities of lake sediment and soils on the shoreline of Lake Naivasha,Kenya

On steep, unvegetated slopes, sands (particle sizes 0.063 to 2 mm) and gravels (2–64 mm) erode from the shoreline of Lake Naivasha (Kenya) and enter the lake basin. This occurred freely where fringing papyrus (Cyperus papyrus) swamp had been cleared in favour of landing jetties or agriculture. Gravel-sized particles have been recovered up to 60 m offshore and sands to 80 m. In an area where papyrus was undisturbed and the swamp margin was 52 m wide, gravel did not enter the lake and sands penetrated to around 35 m. Large particles are much easier to trace to source and to manage than the finer silts and clays (<0.63 m) that form the bulk of Lake Naivasha's sediment. The pattern of mass specific magnetic susceptibilities for the <63 m fraction of lake sediment around the southern shoreline of the lake suggests that fine particles enter open water directly from the shoreline and are not transported from the lake's only perennial inflow, the River Malewa in the north. Such particles originate from a hinterland that supports high intensity horticulture and are therefore a potential source of contamination. Mean ± SD susceptibility (_If) immediately offshore papyrus fringe was 0.49 ± 0.08 × 10^-6 m³ kg^-1 compared with higher values of 1.33 ± 0.14 × 10^-6 m³ kg^-1 where there was no papyrus barrier (P<0.0001). The value for five sites in the middle parts of the lake was 0.45 ± 0.02 × 10^-6 m³ kg^-1 with 1.38 ± 0.10 × 10^-6 m³ kg^-1 near the mouth of the River Malewa. The results of this study are evidence, therefore, that conservation of a continuous papyrus margin of about 50 m width is a priority for intercepting particulate material.