Developing an improved biomonitoring tool for fine sediment: Combining expert knowledge and empirical data

The Proportion of Sediment-sensitive Invertebrates (PSI) index is a biomonitoring tool that is designed to identify the degree of sedimentation in rivers and streams. Despite having a sound biological basis, the tool has been shown to have only a moderate correlation with fine sediment, which although comparable to other pressure specific indices, limits confidence in its application. The aim of this study was to investigate if the performance of the PSI index could be enhanced through the use of empirical data to supplement the expert knowledge and literature which were used to determine the original four fine sediment sensitivity ratings. The empirical data used, comprised observations of invertebrate abundance and percentage fine sediment, collected across a wide range of reference condition temperate stream and river ecosystems (model training dataset n = 2252). Species were assigned sensitivity weights within a range based on their previously determined sensitivity rating. Using a range of weights acknowledges the breadth of ecological niches that invertebrates occupy and also their differing potential as indicators. The optimum species-specific sensitivity weights were identified using non-linear optimisation, as those that resulted in the highest Spearman's rank correlation coefficient between the Empirically-weighted PSI (E-PSI) scores and deposited fine sediment in the model training dataset. The correlation between percentage fine sediment and E-PSI scores in the test dataset (n = 252) was eight percentage points higher than the correlation between percentage fine sediment and the original PSI scores (E-PSI r_s = −0.74, p < 0.01 compared to PSI r_s = −0.66, p < 0.01). This study demonstrates the value of combining a sound biological basis with evidence from large empirical datasets, to test and enhance the performance of biomonitoring tools to increase confidence in their application.     

Microbial carbonate production in a starved basin: The crenistria Limestone of the upper Viséan German Kulm facies

The crenistria Limestone is a set of three autochthonous massive limestone beds occurring with great lithological persistence in the Kulm Facies (cd III , upper Viséan) of the eastern Rheinisches Schiefergebirge. Microfacies analysis reveals mainly minipeloidal fabrics and homogeneous micrite. Uncrushed, sediment-filled conchs of goniatites represent loci of sheltered preservation of primary carbonate textures. Calcified radiolarians are abundant, forming between 20 and 80% of total rock volume. The alleged algal genus Rectangulina is common in the crenistria Limestone. It is reinterpreted to represent the faeces of goniatites. For the first time the presence of in situ preserved sponges is reported. They can be recognized as delicate networks of microsparitic needles embedded in peloidal fabrics. Hexactinellids with primary spicule arrangements can be found embedded in homogeneous micrite. The carbonate forming the limestone beds was produced microbially during decomposition of soft tissue of the radiolarians and sponges. During the cd III , anoxia in the bottom waters of the Kulm Basin persisted for long periods due to stable density stratification of the water column under humid climatic conditions. Oxic conditions in the bottom waters during formation of the limestone are indicated by bioturbation, the presence of sponges and the high Mn-contents of the carbonate. The latter derived from reduction of Mn-oxides during microbial carbonate formation.     

Distribution of microaerophilic bacteria through the oxic-anoxic transition zone of lagoon sediments

In marine sediments, where soluble gases diffuse only very slightly, many organisms struggle for molecular oxygen. Microaerophilic bacteria, able to grow at reduced pO₂ between 0.2 and 12%, have an advantage. Distribution of aerobes, microaerophiles and anaerobes was compared with the oxygen gradient in seawater and sediment samples collected in a northern Mediterranean lagoon. In the near bottom seawater and in the 0–10 mm upperlayer of sediment, the microaerophilic counts were less than 1% of aerobe densities. In the 10–15 mm zone, these two groups were equivalent in density (1 × 10⁵ cells ml^–1). As expected, the microaerophiles took advantage of their low oxygen tension requirements in the subsurface sediments, between the well aerated zone (0–5 mm depth) and the low redox potential zone. Then, beyond a depth of 20 mm, the anaerobes prevailed in this sandy clay.     

Didymosphenia geminata invasion in South America: Ecosystem impacts and potential biogeochemical state change in Patagonian rivers

The diatom Didymosphenia geminata has emerged as a major global concern, as both an aggressive invader of rivers and streams in the southern hemisphere, and for its ability to form nuisance blooms in oligotrophic systems in its native range. South American D. geminata blooms were first documented in Chilean Patagonia in May 2010, and have spread to over five regions and three provinces, in Chile and Argentina respectively. The Patagonian invasion represents a distinct challenge compared to other regions; not only are affected systems poorly characterized, but also a general synthesis of the nature and magnitude of ecosystem impacts is still lacking. The latter is essential in evaluating impacts to ecosystem services, forms the basis for a management response that is proportional to the potentially valid threats, or aids in the determination of whether action is warranted or feasible. Based on a revision of the recent literature, some of the most significant impacts may be mediated through physical changes: substantially increased algal biomass, trapping of fine sediment, altered hydrodynamics, and consequent effects on biogeochemical states and processes such as redox condition, pH and nutrient cycling in the benthic zone. Surveys conducted during the early invasion in Chile show a strong correlation between benthic biomass and associated fine sediments, both of which were one–two orders of magnitude higher within D. geminata blooms. Experimental phosphorous amendments showed significant abiotic uptake, while interstitial water in D. geminata mats had nearly 10–20 fold higher soluble reactive phosphorous and a pronounced pH cycle compared to the water column. A dominant and aggressive stalk-forming diatom with this combination of characteristics is in sharp contrast to the colonial cyanobacteria and bare gravel substrate that characterize many Patagonian streams. The potential displacement of native benthic algal communities with contrasting functional groups, increased primary producer biomass, and fine benthic sediment accumulation, all may have a significant effect on stream nutrient cycling and ecosystem function, in Patagonia and elsewhere where nuisance blooms have been reported.     

Factors influencing the potential mobility and bioavailability of exchangeable ammonium ion in dried lake sediments

Abstract

The effect of drying temperature and oxidation on the level of exchangeable ammonium ion found in sediments has been examined using samples collected from along a polluted creek and from shallow lake bays. The sediments were dried at temperatures between 20°C and 100°C (either in air or under a nitrogen atmosphere), and the ammonium ion content was extracted into 0.1 M KCl prior to analysis using an ion selective electrode. Exposure to air during the drying stage usually resulted in lower ammonium values, while increasing the drying temperature altered the amount of displaceable (i.e. available) ammonium ion extracted, generally in an upward direction. The amount detected (5–25 μ g^?1) varied between sites, and surface sediment values differed from the 10–50 cm core material results. The pH of the extracts varied with the drying temperature used, indicating that the heating process promoted some chemical changes in the test samples. The study has demonstrated that in nutrient level surveys, the analytical data produced can depend greatly on the sample preparation procedure selected. It also indicated the type of changes which could occur when dredged sediments are land dumped.     

Correlation of surface sediment diatoms with the present lake water pH in 28 Algoma lakes,Ontario, Canada

The surface sediment diatom analysis of 28 Algoma lakes (pH 4.40–8.13) indicates that even though each lake has a widely different aquatic environment and characteristic diatom assemblage, a definite relationship exists between the lake water pH and their diatom assemblages. In the acidic lakes acidobiontic and acidophilous diatom species predominate whereas in circumneutral and alkaline lakes circumneutral and alkaliphilous diatoms were most common. Cluster analysis of the pH indicator diatom assemblages grouped the study lakes into three distinct cluster groups. These groups also closely corresponded to lake water pH. On the basis of published ecological information as well as their presence in our study lakes, the pH indicator status of a number of diatom taxa have been discussed. A detailed listing of the diatom taxa identified and their pH indicator status is provided in order to facilitate their use in future diatom-inferred pH studies.     

Modified speciation scheme for inorganic phosphate in lake sediments

Abstract

Speciation schemes for phosphate in soils or sediments tend to yield results which are ‘conditional’ and subject to error. In the proposed modified scheme, secondary phosphate-cation interactions have been minimised by including a cation exchange resin in the extraction system; re-sorption errors have been reduced by using low (1:400) solid to liquid extractant ratios; and slow dissolution rates have been balanced by using longer extraction times (up to 62 h). Variables examined during scheme development included the effect of varying sample weights, extraction time, reagent type, exchanger type, exchanger to sample weight ratios and pH on the amount of phosphate released from a polluted lake sediment. It was found that the amount of inorganic phosphate released by chemical reagents (or by cation exchanger) varied markedly with system pH, being greatest in the pH 2 to 3 region, decreasing to near zero in the pH 4 to 6 zone, and then rising to an intermediate value at pH > 8. Monitoring of the Ca, Mg, Fe and Al released into the various solutions (or transferred into the exchanger phase) indicated that one cannot clearly distinguish between phosphate initially present in association with alkaline earth compounds or iron-rich matrix components. The advantages and limitations of this ‘differential solubility’ scheme have been considered and alternative approaches briefly reviewed.     

Metagenomics reveals sediment microbial community response to Deepwater Horizon oil spill

The Deepwater Horizon (DWH) oil spill in the spring of 2010 resulted in an input of ∼4.1 million barrels of oil to the Gulf of Mexico; >22% of this oil is unaccounted for, with unknown environmental consequences. Here we investigated the impact of oil deposition on microbial communities in surface sediments collected at 64 sites by targeted sequencing of 16S rRNA genes, shotgun metagenomic sequencing of 14 of these samples and mineralization experiments using ¹⁴C-labeled model substrates. The 16S rRNA gene data indicated that the most heavily oil-impacted sediments were enriched in an uncultured Gammaproteobacterium and a Colwellia species, both of which were highly similar to sequences in the DWH deep-sea hydrocarbon plume. The primary drivers in structuring the microbial community were nitrogen and hydrocarbons. Annotation of unassembled metagenomic data revealed the most abundant hydrocarbon degradation pathway encoded genes involved in degrading aliphatic and simple aromatics via butane monooxygenase. The activity of key hydrocarbon degradation pathways by sediment microbes was confirmed by determining the mineralization of ¹⁴C-labeled model substrates in the following order: propylene glycol, dodecane, toluene and phenanthrene. Further, analysis of metagenomic sequence data revealed an increase in abundance of genes involved in denitrification pathways in samples that exceeded the Environmental Protection Agency (EPA)''s benchmarks for polycyclic aromatic hydrocarbons (PAHs) compared with those that did not. Importantly, these data demonstrate that the indigenous sediment microbiota contributed an important ecosystem service for remediation of oil in the Gulf. However, PAHs were more recalcitrant to degradation, and their persistence could have deleterious impacts on the sediment ecosystem.