Understanding Of Biogeochemical Cycles Research Articles

Tree-mycorrhizal associations detected remotely from canopy spectral properties.

A central challenge in global ecology is the identification of key functional processes in ecosystems that scale, but donot require, data for individual species across landscapes. Given that nearly all tree species form symbiotic relationships with one of two types of mycorrhizal fungi - arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi - and that AM- and ECM-dominated forests often have distinct nutrient economies, the detection and mapping of mycorrhizae over large areas could provide valuable insights about fundamental ecosystem processes such as nutrient cycling, species interactions, and overall forest productivity. We explored remotely sensed tree canopy spectral properties to detect underlying mycorrhizal association across a gradient of AM- and ECM-dominated forest plots. Statistical mining of reflectance and reflectance derivatives across moderate/high-resolution Landsat data revealed distinctly unique phenological signals that differentiated AM and ECM associations. This approach was trained and validated against measurements of tree species and mycorrhizal association across ~130000 trees throughout the temperate United States. We were able to predict 77% of the variation in mycorrhizal association distribution within the forest plots (P<0.001). The implications for this work move us toward mapping mycorrhizal association globally and advancing our understanding of biogeochemical cycling and other ecosystem processes.

Assessment of Heavy Metal Contamination and Wetland Management in a Newly Created Coastal Natural Reserve, China

ABSTRACT Xie, Z.; Zhang, H.; Zhao, X.; Du, Z.; Xiang, L., and Wang, W., 2016. Assessment of heavy metal contamination and wetland management in a newly created coastal natural reserve, China. The investigation of the content and distribution of heavy metals in coastal soils is useful for improving our understanding of biogeochemical cycles and their potential feedback to global environmental change. The accumulation of heavy metals in the Yellow River Delta (YRD) was investigated using 43 sampling sites to determine the concentrations and vertical distribution of heavy metals. Factor analysis, contamination factors, and the geoaccumulation index were applied to evaluate the contamination condition. The contamination factors and geoaccumulation index clearly indicated that the coastal ecosystems are still in their pristine state with respect to metal pollution. Factor loadings reveal that the first principal component was strongly and positively related to arsenic, chromium, copper, nickel, lead, and zinc,...

Patterns of distribution of inorganic nutrients in Red Sea and their implications to primary production

This paper presents data on inorganic nutrients obtained in several transects within Saudi Arabian waters of the Red Sea in 2012–2015. Increase in their concentrations from north to south is not monotonously linear but is punctuated by regions of high concentrations alternating with those of low concentrations, regardless of the type of nutrient (N, P or Si), season and location. Such a type of distribution could be only explained in terms of eddy circulations within the Red Sea basin. The enrichment with nutrients of the boundary currents of the eddies could be explained partly by entrainment of Gulf of Aden Intermediate Water in the eddies and the mixing of the latter with the underlying Red Sea Deep Water, and partly by a higher biological productivity in the peripheries of the eddies. These results have two major implications for our understanding of biogeochemical cycles in the Red Sea. The first is that the eddy-associated injection of nutrients into the euphotic zone could cause higher levels of production over a substantial spread of the Red Sea. The second is that the anticyclonic eddies may function as traps of nutrients and in that event, their peripheries and centers may function as independent mesocosms.

Transcriptional activity of the giant barrel sponge, Xestospongia muta Holobiont: molecular evidence for metabolic interchange.

Compared to our understanding of the taxonomic composition of the symbiotic microbes in marine sponges, the functional diversity of these symbionts is largely unknown. Furthermore, the application of genomic, transcriptomic, and proteomic techniques to functional questions on sponge host-symbiont interactions is in its infancy. In this study, we generated a transcriptome for the host and a metatranscriptome of its microbial symbionts for the giant barrel sponge, Xestospongia muta, from the Caribbean. In combination with a gene-specific approach, our goals were to (1) characterize genetic evidence for nitrogen cycling in X. muta, an important limiting nutrient on coral reefs (2) identify which prokaryotic symbiont lineages are metabolically active and, (3) characterize the metabolic potential of the prokaryotic community. Xestospongia muta expresses genes from multiple nitrogen transformation pathways that when combined with the abundance of this sponge, and previous data on dissolved inorganic nitrogen fluxes, shows that this sponge is an important contributor to nitrogen cycling biogeochemistry on coral reefs. Additionally, we observed significant differences in gene expression of the archaeal amoA gene, which is involved in ammonia oxidation, between coral reef locations consistent with differences in the fluxes of dissolved inorganic nitrogen previously reported. In regards to symbiont metabolic potential, the genes in the biosynthetic pathways of several amino acids were present in the prokaryotic metatranscriptome dataset but in the host-derived transcripts only the catabolic reactions for these amino acids were present. A similar pattern was observed for the B vitamins (riboflavin, biotin, thiamin, cobalamin). These results expand our understanding of biogeochemical cycling in sponges, and the metabolic interchange highlighted here advances the field of symbiont physiology by elucidating specific metabolic pathways where there is high potential for host-prokaryote interactions.

Distribution of Arsenite-Oxidizing Bacteria and its Correlation with Temperature in Hot Springs of the Tibetan-Yunnan Geothermal Zone in Western China

The distribution of arsenite-oxidizing bacteria in response to temperature is of great importance to an understanding of biogeochemical cycling of arsenic in geothermal features. The abundance and diversity of arsenite-oxidizing bacteria were investigated in the geothermal features of Tengchong County of Yunnan Province, Dachaidan County of Qinghai Province, and Tibet. The abundance of aioA genes, which encode the large subunit of arsenite oxidase, was determined by quantitative polymerase chain reactions. The diversity of aioA genes was studied by PCR-cloning-based phylogenetic analyses. The results showed that the aioA gene abundance increased as temperature decreased, whereas its diversity at the OTU level (97% cutoff) increased with increasing temperature. This suggests that temperature played an important role in affecting aioA gene distribution and thus arsenic speciation. The aioA gene population (at OTU level) differed among the studied regions, indicating geographic isolation may be an important factor controlling aioA gene distribution in hot springs.

Influence of natural organic matter on the bioavailability and preservation of organic phosphorus in lake sediments

Information about the bioavailability and sequestration of organic phosphorus (Po) in sediments is fundamental to understanding biogeochemical cycling of phosphorus (P) in eutrophic lakes. However, the processes governing preservation of Po in sediments are still poorly understood. Sequential extraction of Po by H2O (H2O-Po) and NaOH–EDTA (NaOH–EDTA Po), in combination with enzymatic hydrolysis/31P NMR, was applied to estimate the bioavailability of Po in sediments of Lake Tai (Ch: Taihu), China. Of H2O-Po and NaOH–EDTA Po, 45.5–89.4% and 30.4–71.3% respectively were hydrolyzed by phosphatase, and therefore considered to be biologically available. Of NaOH–EDTA Po, 28.7–69.6% could not be hydrolyzed by phosphatase; this portion was characterized by 31P NMR as monoester P and/or diester P. Simulation experiments of hydrolysis of model Po compounds in the presence of humic acids (HA), which were used as a model for natural organic matter (NOM), and metals, including Al, Ca, and Fe, have demonstrated that enzymatic hydrolysis of labile monoester P was weakly reduced by HA or metal ions. Condensed phosphate (e.g., pyrophosphate) and phytate-like P (e.g., inositol phosphates) were resistant to enzymatic hydrolysis in the presence of HA and/or metal ions, which indicated that they may be possibly preserved in sediments. These observations suggest that NOM in sediments can be a significant factor determining the bioavailability and preservation of Po in sediments. The presence of metals would enhance the effect of NOM on preservation of Po in sediments. Formation of Po–metal–HA or Po–metal complexes might be mechanisms responsible for these processes.

Contrasting biogeochemical characteristics of the Oubangui River and tributaries (Congo River basin).

The Oubangui is a major tributary of the Congo River. We describe the biogeochemistry of contrasting tributaries within its central catchment, with watershed vegetation ranging from wooded savannahs to humid rainforest. Compared to a 2-year monitoring record on the mainstem Oubangui, these tributaries show a wide range of biogeochemical signatures, from highly diluted blackwaters (low turbidity, pH, conductivity, and total alkalinity) in rainforests to those more typical for savannah systems. Spectral analyses of chromophoric dissolved organic matter showed wide temporal variations in the Oubangui compared to spatio-temporal variations in the tributaries, and confirm that different pools of dissolved organic carbon are mobilized during different hydrological stages. δ13C of dissolved inorganic carbon ranged between −28.1‰ and −5.8‰, and was strongly correlated to both partial pressure of CO2 and to the estimated contribution of carbonate weathering to total alkalinity, suggesting an important control of the weathering regime on CO2 fluxes. All tributaries were oversaturated in dissolved greenhouse gases (CH4, N2O, CO2), with highest levels in rivers draining rainforest. The high diversity observed underscores the importance of sampling that covers the variability in subcatchment characteristics, to improve our understanding of biogeochemical cycling in the Congo Basin.

Phenology as a strategy for carbon optimality: a global model

Abstract. Phenology is essential to our understanding of biogeochemical cycles and the climate system. We develop a global mechanistic model of leaf phenology based on the hypothesis that phenology is a strategy for optimal carbon gain at the canopy level so that trees adjust leaf gains and losses in response to environmental factors such as light, temperature and soil moisture, to achieve maximum carbon assimilation. We fit this model to five years of satellite observations of leaf area index (LAI) using a Bayesian fitting algorithm. We show that our model is able to reproduce phenological patterns for all vegetation types and use it to explore variations in growing season length and the climate factors that limit leaf growth for different biomes. Phenology in wet tropical areas is limited by leaf age physiological constraints while at higher latitude leaf seasonality is limited by low temperature and light availability. Leaf growth in grassland regions is limited by water availability but often in combination with other factors. This model will advance the current understanding of phenology for ecosystem carbon models and our ability to predict future phenological behaviour.

Soil organic carbon and nutrients along an alpine grassland transect across Northern Tibet

Abstract Soil carbon and nutrient contents and their importance in advancing our understanding of biogeochemical cycling in terrestrial ecosystem, has motivated ecologists to find their spatial patterns in various geographical area. Few studies have focused on changes in the physical and chemical properties of soils at high altitudes. Our aim was to identify the spatial distribution of soil physical and chemical properties in cold and arid climatic region. We also tried to explore relationship between soil organic carbon (SOC) and total nitrogen (TN), total phosphorus (TP), available nitrogen (AN), available phosphorus (AP), soil particle size distribution (PSD). Samples were collected at 44 sites along a 300 km transect across the alpine grassland of northern Tibet. The study results showed that grassland type was the main factor influencing SOC, TN and TP distribution along the Gangdise Mountain-Shenzha-Shuanghu Transect. SOC, TN and TP contents were significantly higher in alpine meadow than alpine steppe ecosystems. SOC, TN, TP and AN contents in two soil layers (0–15 cm and 15–30 cm) showed no significant differences, while AP content in top soil (0–15 cm) was significantly higher than that in sub-top soil (15–30 cm). SOC content was correlated positively with TN and TP content (r = 0.901 and 0.510, respectively). No correlations were detected for clay content and fractal dimension of particle size distribution (D). Our study results indicated the effects of vegetation on soil C, N and P seem to be more important than that of rocks itself along latitude gradient on the northern Tibetan Plateau. However, we did not found similar impacts of vegetation on soil properties in depth. In addition, this study also provided an interesting contribution to the global data pool on soil carbon stocks.

Weathering and soil formation rates based on geochemical mass balances in a small forested watershed under acid precipitation in subtropical China

Abstract Accurate weathering and soil formation rates in natural environment and their quantitative dependences on environmental factors remain poorly understood, despite their significance in the understanding of biogeochemical cycling and for the development of sustainable land-use strategies. In the present study, rates of weathering and soil formation on granite and their dependences on acid precipitation were studied in a small forested watershed, Fengxingzhuang (FXZ), in subtropical China using geochemical mass balance equations and multiple regression analysis. Atmospheric input from wet and dry deposition, and stream output through runoff were monitored from March, 2007 to February, 2010. The physical and chemical properties of soil and granite rock were also determined. The results show that acid precipitation is very severe in the FXZ forested watershed by bringing in H + both directly from strong acids (741 mol ha − 1 yr − 1 ) and indirectly from nitrogen and sulfur transformations (831 mol ha − 1 yr − 1 ), which serves as an important driving force for weathering and soil formation. The FXZ forested watershed currently remains as a net sink for hydrogen ion, inorganic nitrogen, sulfur, potassium, and aluminum, with a mean of 0.07, 1.60, 1.48, 0.10, and 0.44 g m − 2 yr − 1 , respectively, and a net source for dissolved silicon, sodium, calcium, and magnesium, with a mean of 5.33, 2.95, 1.04, and 0.34 g m − 2 yr − 1 , respectively. Based on geochemical mass balance equations, the weathering rate of granite (R) in the FXZ forested watershed is 1.04 ± 0.65 t ha − 1 yr − 1 , but varying according to the changes in environmental conditions such as rainfall amount, air temperature, and H + input within different seasons. Correspondingly, soil formation rate (S) is 0.95 ± 0.69 t ha − 1 yr − 1 , which equals to 0.066 ± 0.048 mm yr − 1 of soil depth, suggesting a base for establishing the soil loss tolerance value in the granitic region of subtropical China. Acid precipitation significantly promotes weathering and soil formation by the input of rainfall and H + , although air temperature effects occur simultaneously. A proposed model that quantitatively describes weathering and soil formation rates is a combined product of rainfall amount ( x 1 ), H + input ( x 2 ) and air temperature ( x 3 ) resulting from multiple regressions: R = 0.00045 ∗ x 1 + 0.026 ∗ e 0.0022 x 2 + 0.012 ∗ e 0.0459 x 3 ; S = 0.00035 ∗ x 1 + 0.029 ∗ e 0.002 x 2 + 0.016 ∗ e 0.0424 x 3 , which improves the prediction from simple linear regression.

Oceanografia e Química: unindo conhecimentos em prol dos oceanos e da sociedade

The marine environment is certainly one of the most complex systems to study, not only because of the challenges posed by the nature of the waters, but especially due to the interactions of physical, chemical and biological processes that control the cycles of the elements. Together with analytical chemists, oceanographers have been making a great effort in the advancement of knowledge of the distribution patterns of trace elements and processes that determine their biogeochemical cycles and influences on the climate of the planet. The international academic community is now in prime position to perform the first study on a global scale for observation of trace elements and their isotopes in the marine environment (GEOTRACES) and to evaluate the effects of major global changes associated with the influences of megacities distributed around the globe. This action can only be performed due to the development of highly sensitive detection methods and the use of sampling and handling techniques, together with a joint international program working toward the clear objective of expanding the frontiers of the biogeochemistry of the oceans and related topics, including climate change issues and ocean acidification associated with alterations in the carbon cycle. It is expected that the oceanographic data produced this coming decade will allow a better understanding of biogeochemical cycles, and especially the assessment of changes in trace elements and contaminants in the oceans due to anthropogenic influences, as well as its effects on ecosystems and climate. Computational models are to be constructed to simulate the conditions and processes of the modern oceans and to allow predictions. The environmental changes arising from human activity since the 18th century (also called the Anthropocene) have made the Earth System even more complex. Anthropogenic activities have altered both terrestrial and marine ecosystems, and the legacy of these impacts in the oceans include: a) pollution of the marine environment by solid waste, including plastics; b) pollution by chemical and medical (including those for veterinary use) substances such as hormones, antibiotics, legal and illegal drugs, leading to possible endocrine disruption of marine organisms; and c) ocean acidification, the collateral effect of anthropogenic emissions of CO2 into the atmosphere, irreversible in the human life time scale. Unfortunately, the anthropogenic alteration of the hydrosphere due to inputs of plastics, metal, hydrocarbons, contaminants of emerging concern and even with formerly exotic trace elements, such us rare earth elements is likely to accelerate in the near future. These emerging contaminants would likely soon present difficulties for studies in pristine environments. All this knowledge brings with it a great responsibility: helping to envisage viable adaptation and mitigation solutions to the problems identified. The greatest challenge faced by Brazil is currently to create a framework project to develop education, science and technology applied to oceanography and related areas. This framework would strengthen the present working groups and enhance capacity building, allowing a broader Brazilian participation in joint international actions and scientific programs. Recently, the establishment of the National Institutes of Science and Technology (INCTs) for marine science, and the creation of the National Institute of Oceanographic and Hydrological Research represent an exemplary start. However, the participation of the Brazilian academic community in the latest assaults on the frontier of chemical oceanography is extremely limited, largely due to: i. absence of physical infrastructure for the preparation and processing of field samples at ultra-trace level; ii. limited access to oceanographic cruises, due to the small number of Brazilian vessels and/or absence of clean laboratories on board; iii. restricted international cooperation; iv. limited analytical capacity of Brazilian institutions for the analysis of trace elements in seawater; v. high cost of ultrapure reagents associated with processing a large number of samples, and vi. lack of qualified technical staff. Advances in knowledge, analytic capabilities and the increasing availability of analytical resources available today offer favorable conditions for chemical oceanography to grow. The Brazilian academic community is maturing and willing to play a role in strengthening the marine science research programs by connecting them with educational and technological initiatives in order to preserve the oceans and to promote the development of society.

Microbial enzymes that oxidize hydrocarbons

EDITORIAL article Front. Microbiol., 13 November 2013Sec. Microbiological Chemistry and Geomicrobiology https://doi.org/10.3389/fmicb.2013.00338

Correlating microbial community profiles with geochemical data in highly stratified sediments from the Arctic Mid-Ocean Ridge.

Microbial communities and their associated metabolic activity in marine sediments have a profound impact on global biogeochemical cycles. Their composition and structure are attributed to geochemical and physical factors, but finding direct correlations has remained a challenge. Here we show a significant statistical relationship between variation in geochemical composition and prokaryotic community structure within deep-sea sediments. We obtained comprehensive geochemical data from two gravity cores near the hydrothermal vent field Loki's Castle at the Arctic Mid-Ocean Ridge, in the Norwegian-Greenland Sea. Geochemical properties in the rift valley sediments exhibited strong centimeter-scale stratigraphic variability. Microbial populations were profiled by pyrosequencing from 15 sediment horizons (59,364 16S rRNA gene tags), quantitatively assessed by qPCR, and phylogenetically analyzed. Although the same taxa were generally present in all samples, their relative abundances varied substantially among horizons and fluctuated between Bacteria- and Archaea-dominated communities. By independently summarizing covariance structures of the relative abundance data and geochemical data, using principal components analysis, we found a significant correlation between changes in geochemical composition and changes in community structure. Differences in organic carbon and mineralogy shaped the relative abundance of microbial taxa. We used correlations to build hypotheses about energy metabolisms, particularly of the Deep Sea Archaeal Group, specific Deltaproteobacteria, and sediment lineages of potentially anaerobic Marine Group I Archaea. We demonstrate that total prokaryotic community structure can be directly correlated to geochemistry within these sediments, thus enhancing our understanding of biogeochemical cycling and our ability to predict metabolisms of uncultured microbes in deep-sea sediments.

The MIRACLE Project: An integrated approach to understanding biogeochemical cycling of mercury and its relationship with lagoon clam farming

The “MIRACLE” Project was aimed at two specific issues: understanding Hg biogeochemical cycling in the Marano and Grado Lagoon and testing the coexistence of clam farming with Hg contamination in the sediments. Mercury contamination was measured in several matrices (water, sediment, biota) and its mobility was tested along with its speciation in relation to biogeochemical processes occurring in the lagoon environment, where bacterial communities have a primary role in converting Hg to its more toxic form, methylmercury (MeHg). Bioaccumulation of the Hg species was investigated on natural and seeded clams (Ruditapes philippinarum), the most important commercial bivalves in the Lagoon. The Editorial summarizes the main results obtained from this multidisciplinary study and reported in the Special Issue.

Improving biogeochemical knowledge through technological innovation

The understanding of biogeochemical cycles has benefited from technological advances facilitating new kinds of measurements and observations. Satellite‐borne ocean‐color sensors that assess the physiological status of phytoplankton have led to improved estimates of oceanic productivity, as have micrometeorological approaches measuring terrestrial photosynthesis and respiration. The advent of satellites fitted with synthetic aperture radar (a specialized sensor used to determine inundation extent and vegetation types in wetlands) has revealed large fluxes of carbon dioxide and methane from these areas. Advances in the measurement of chemical constituents and turbulence have allowed the detection of high‐resolution coupling between physical and biogeochemical processes. Genomics and proteomics – the study of genes and of an organism's complement of proteins, respectively – have revolutionized our understanding of the types of cells present in the environment and their ability to transform elements by allowing direct assessment of gene and protein sequences.

Dust Thou Art Not &amp; unto Dust Thou Shan't Return: Common Mistakes in Teaching Biogeochemical Cycles

When describing biogeochemical transfers, textbook authors have often overstated the role of soil while neglecting the role of carbon dioxide. Unfortunately, these errors align with naive biogeochemical intuitions. This article aims to increase awareness of the prevalence of such misconceptions and offers countermeasures. Avoiding these misconceptions becomes increasingly important as concerns over carbon emissions grow. In addition, because an accurate understanding of biogeochemical cycles can transform deeply held beliefs, successfully teaching this topic can have the collateral benefit of inspiring lasting interest in science.

Diel biogeochemical processes and their effect on the aqueous chemistry of streams: A review

This review summarizes biogeochemical processes that operate on diel, or 24-h, time scales in streams and the changes in aqueous chemistry that are associated with these processes. Some biogeochemical processes, such as those producing diel cycles of dissolved O 2 and pH, were the first to be studied, whereas processes producing diel concentration cycles of a broader spectrum of chemical species including dissolved gases, dissolved inorganic and organic carbon, trace elements, nutrients, stable isotopes, and suspended particles have received attention only more recently. Diel biogeochemical cycles are interrelated because the cyclical variations produced by one biogeochemical process commonly affect another. Thus, understanding biogeochemical cycling is essential not only for guiding collection and interpretation of water-quality data but also for geochemical and ecological studies of streams. Expanded knowledge of diel biogeochemical cycling will improve understanding of how natural aquatic environments function and thus lead to better predictions of how stream ecosystems might react to changing conditions of contaminant loading, eutrophication, climate change, drought, industrialization, development, and other factors.

Isoscapes: Spatial Pattern in Isotopic Biogeochemistry

Isotope ratios of actively cycled elements vary as a function of the biogeochemical processes in which they participate and the conditions under which those processes occur. The resultant spatiotemporal distribution of isotopes in environmental materials can be predicted using models of isotope-fractionating processes and data describing environmental conditions across space and time, and it has been termed an isoscape, or isotopic landscape. Analysis of isoscapes and comparison of isoscape predictions with observational data have been used to test biogeochemical models, calculate aerially integrated biogeochemical fluxes based on isotope mass balance, and determine spatial connectivity in biogeochemical, ecological, and anthropological systems. Isoscape models of varying quality are available for stable H, C, N, and O isotopes in a range of Earth surface systems, but significant opportunities exist to refine our understanding of biogeochemical cycles and our ability to predict isoscapes through the development of more mechanistic and more comprehensive isoscape models.

Limitations of the ferrozine method for quantitative assay of mineral systems for ferrous and total iron

The quantitative assay of clay minerals, soils, and sediments for Fe(II) and total Fe is fundamental to understanding biogeochemical cycles occurring therein. The commonly used ferrozine method was originally designed to assay extracted forms of Fe(II) from non-silicate aqueous systems. It is becoming, however, increasingly the method of choice to report the total reduced state of Fe in soils and sediments. Because Fe in soils and sediments commonly exists in the structural framework of silicates, extraction by HCl, as used in the ferrozine method, fails to dissolve all of the Fe. The phenanthroline (phen) method, on the other hand, was designed to assay silicate minerals for Fe(II) and total Fe and has been proven to be highly reliable. In the present study potential sources of error in the ferrozine method were evaluated by comparing its results to those obtained by the phen method. Both methods were used to analyze clay mineral and soil samples for Fe(II) and total Fe. Results revealed that the conventional ferrozine method under reports total Fe in samples containing Fe in silicates and gives erratic results for Fe(II). The sources of error in the ferrozine method are: (1) HCl fails to dissolve silicates and (2) if the analyte solution contains Fe 3+, the analysis for Fe 2+ will be photosensitive, and reported Fe(II) values will likely be greater than the actual amount in solution. Another difficulty with the ferrozine method is that it is tedious and much more labor intensive than the phen method. For these reasons, the phen method is preferred and recommended. Its procedure is simpler, takes less time, and avoids the errors found in the ferrozine method.

The Influence of Organic Acids on Mercury Bioavailability: Insight from an Earthworm Assessment Protocol

Between 10 and 15 million artisanal and small-scale miners in more than 50 countries directly rely on gold mining for their livelihoods. Mainly due to the rudimentary techniques that characterize artisanal mining, these activities are frequently accompanied by extensive environmental degradation and deplorable socio-economic conditions. Mercury, cheap, easy-to-use and effective, is commonly used to recover gold through amalgamation. Due to its misuse, between 800 and 1000 tonnes of mercury are released into the air, water, and soils by artisanal gold miners every year. This generates serious health hazards for miners involved in gold extraction, as well as for surrounding community inhabitants, who may be exposed via high levels of mercury in fish they consume. The metallic mercury discharged by miners into the environment has the potential to undergo many changes, including the transformation to a readily bioavailable and highly toxic form of mercury, methylmercury. A laboratory methodology using the earthworm Eisenia foetida was developed to assess mercury bioavailability in mine tailings and aqueous solutions and examine the influence of certain factors, in particular organic acids, on the transformation of metallic mercury into bioavailable forms. The earthworm protocol provides a quick, inexpensive and simple means to examine the role of specific factors on mercury transformations and is a valuable tool for prioritizing contaminated sites based on the potential for mercury incorporation into biota. Through a series of tests using metallic mercury dissolved in humic, tannic and fulvic acids and mine tailings and soils saturated with organic acids, this research indicates that earthworms (E. foetida) are capable of accumulating Hg from solutions and the reaction of mercury with organic acids is an important pathway for the incorporation of mercury into the food chain. This finding is significant in terms of understanding biogeochemical cycling of Hg in darkwaters and assessing ecological and human health risks from Hg in these aquatic systems. The influence of organic acids on Hg bioaccumulation and intestinal methylation is extremely significant in terms of understanding biogeochemical cycling of Hg in darkwaters and assessing ecological and human health risks from Hg in these aquatic systems.