Kettle holes are glaciofluvially created depressional wetlands that collect organic matter (OM) and nutrients from their surrounding catchment. Kettle holes mostly undergo pronounced wet-dry cycles. ...Fluctuations in water table, land-use, and management can affect sediment biogeochemical transformations and perhaps threaten the carbon stocks of these unique ecosystems. We investigated sediment and water of 51 kettle holes in NE Germany that differ in hydroperiod (i.e. the duration of the wet period of a kettle hole) and land-use. Our objectives were 1) to test if hydroperiod and land management were imprinted on the isotopic values (δ13C, δ15N) and C:N ratios of the sediment OM, and 2) to characterize water loss dynamics and kettle hole-groundwater connectivity by measuring the stable δ18O and δD isotope values of kettle hole water over several years. We found the uppermost sediment layer reflected recent OM inputs and short-term processes in the catchment, including land-use and management effects. Deeper sediments recorded the degree to which OM is processed within the kettle hole related to the hydroperiod. We see clear indications for the effects of wet-dry cycles for all kettle holes, which can lead to the encroachment of terrestrial plants. We found that the magnitude of evaporation depended on the year, season, and land-use type, that kettle holes are temporarily coupled to shallow ground water, and, as such, kettle holes are described best as partially-closed to open systems.
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•Kettle holes lie on the boundary of the aquatic and terrestrial domains.•Surface sediments reflect surrounding land-use and management.•Deeper sediments reflect past organic matter sources and the hydroperiod.•The onset of evaporation and lateral flow partly determine kettle hole hydroperiod.•Strong links between land use and hydroperiod drive kettle hole biogeochemistry.
Municipal solid waste (MSW) landfill is regarded as an important emission source of atmospheric mercury (Hg), which is associated with potential health and environmental risks, as outlined by the ...Minamata Convention on Hg. This review presents the current state of knowledge with regards to landfill Hg sources, Hg levels in MSW and cover soils, Hg emission to the atmosphere, available Hg biogeochemical transformations, research methods for Hg emission, and important areas for future research. In addition, strategies for controlling landfill Hg emissions are considered, including reducing the Hg load in landfill and in situ controls. These approaches mainly focus on Hg source reduction, Hg recycling programs, public education, and in situ technology such as timely soil cover, vegetation, and end-of-pipe technology for controlling Hg emission from landfill gas.
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•Hg release from landfill poses a series health and environmental risk.•We review Hg sources, levels, emissions, and biogeochemical transformations.•We consider research methods for Hg emissions and identify future research areas.•Strategies for reducing Hg emissions include reducing Hg load and in situ control.•Recycling, education, soil, vegetation, and technology can control Hg emissions.
Clay minerals are very common in nature and highly reactive minerals which are typical products of the weathering of the most abundant silicate minerals on the planet. Over recent decades there has ...been growing appreciation that the prime involvement of clay minerals in the geochemical cycling of elements and pedosphere genesis should take into account the biogeochemical activity of microorganisms. Microbial intimate interaction with clay minerals, that has taken place on Earth’s surface in a geological time-scale, represents a complex co-evolving system which is challenging to comprehend because of fragmented information and requires coordinated efforts from both clay scientists and microbiologists. This review covers some important aspects of the interactions of clay minerals with microorganisms at the different levels of complexity, starting from organic molecules, individual and aggregated microbial cells, fungal and bacterial symbioses with photosynthetic organisms, pedosphere, up to environmental and biotechnological implications. The review attempts to systematize our current general understanding of the processes of biogeochemical transformation of clay minerals by microorganisms. This paper also highlights some microbiological and biotechnological perspectives of the practical application of clay minerals–microbes interactions not only in microbial bioremediation and biodegradation of pollutants but also in areas related to agronomy and human and animal health.
Animals are a critical component of biogeochemical cycles. While animal mediated fluxes of nutrients and energy have received considerable attention, the impacts of these fluxes on microbial ...community structure and function are comparatively understudied. Here, we investigated if freshwater mussel influences on biogeochemical cycling in stream sediment are accompanied by changes in sediment microbial community composition and ecoenzymatic activity, and if these relationships change under different nutrient regimes.
We predicted that mussel effects on ecosystem function are reflected by modified sediment microbial communities. We hypothesized that if changes in either sediment ecoenzymatic function or microbial community composition are driven by mussel‐derived nutrient amendments, we should see muted changes in microbial community assemblages or function when a given nutrient is abundant. However, if microbial communities and function are influenced by other mussel functions, then we should see uniform changes regardless of nutrient availability.
We transplanted freshwater mussels and natural river sediment to flow‐through mesocosms and monitored changes in microbial community composition over 1 week. Our results indicate that mussels always changed sediment microbial community composition, but the way communities changed was dependent on ambient nutrient concentrations.
On the final day we measured the activity of ecoenzymes known to correlate to microbial function and nutrient availability. Mussels homogenized the stoichiometric ratios of ecoenzyme activities, indicating a consistent function of sediment microbes associated with freshwater mussels. Our results suggest that mussels may promote functional redundancy in sediment microbial communities and highlight the importance of animals in controlling biogeochemical transformations under changing nutrient conditions.
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Read the free Plain Language Summary for this article on the Journal blog.
Hyporheic exchange plays a key role in the biogeochemical evolution of water and in ecosystem functioning at the local, reach, and watershed scales. Residence time is a fundamental metric to describe ...the possible transformation taking place in this exchange zone. With this in mind, we use a simple conceptual model to explore the residence time distributions (RTDs) of sinuosity‐driven hyporheic zones (HZs) and to discriminate the individual effect of sinuosity (σ), valley slope (Jx), hydraulic conductivity (K), aquifer dispersivity (αL), and the biogeochemical timescales (BTSs) that characterize the degradation of dissolved organic carbon in these hydrologic systems. We find that RTDs are characterized by one early mode and a late time power law behavior. For a given aquifer dispersivity, the shape of these distributions is stretched or compressed by changes in Jx, K, and σ, having a strong influence on the net biogeochemical transformations within the HZ. Using BTSs proposed in previous studies and sensitivity analyses, we show the potential of σ, Jx, and K to classify meander HZs as net sinks of nitrates or only modulators of the residence times in the subsurface where nitrate reduction is negligible. These findings can be used as predictive tools to quantify the potential of meanders as biogeochemical reactors at the watershed scale with the aid of remote sensing data and GIS processing techniques. These tools can guide experimental design, suggesting important locations to visit, sample, and/or instrument. Also, hyporheic restoration projects can use them for initial site selection and design of channel modifications.
Key Points
RTDs characterize the biogeochemical potential in the meander hyporheic zone
We propose tools to predict the biogeochemical potential of meander HZs
Valley slope, sinuosity, and hydraulic conductivity dictate the shape of the RTD
In this study we evaluated the magnitude and seasonal variations of natural and anthropogenic fluxes of inorganic (NO⁻₃, NH ⁺₄, and PO₄³⁻) and organic (DON and dissolved organic carbon) nutrients ...delivered by submarine groundwater discharge (SGD) and rivers to the fourth largest estuary in the USA, Mobile Bay in Alabama. To identify the sources of SGD-nutrient in the estuary and their subsurface biogeochemical transformation, we applied a multimethod approach that combines geochemical nutrient (N and P) mass-balances, stable isotopes (nitrate δ¹⁵NNO3 and δ¹⁸ONO3 and sediment organic matter δ¹³Corg and δ¹⁵Norg) signatures, microbial sequencing analyses, dissolved organic matter source-composition, and shallow estuarine sediment lithological analyses. We found that during dry seasons SGD delivered nearly a quarter of the total nutrient inputs to Mobile Bay. These SGD fluxes were anoxic and N was delivered to the bay almost entirely as NH₄⁺ and DON, which represented more than half of the total NH₄⁺ and almost one fifth of the total DON inputs to the bay. We further observed that these significant SGD-derived N fluxes occurred exclusively to the east shore of Mobile Bay, historically impacted by hypoxia and large-scale fish kills known as “Jubilees”. We demonstrate here that although the Mobile Bay coastal area is largely developed and anthropogenic influences are well documented, a shallow peat layer identified only on the east shore serves as the main source of the exceptionally high NH₄⁺ and DON fluxes. We found that the high groundwater NO₃⁻ concentrations observed further inland from overfertilization also identified by previous studies, decreased dramatically as groundwater percolated through the intertidal zone of the coastal aquifer. The microbial community identified in the coastal sediments suggests that denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were the main processes responsible for this extensive removal and transformation of anthropogenic N, respectively. Furthermore, we found no significant anthropogenic inputs from manure or sewage waste to the bay. These findings show that natural sources of nutrients can outcompete anthropogenic inputs despite extensive development of the coastal area. We hypothesize that similar subsurface biogeochemical nutrient transformations can occur in other shallow estuaries of the northern Gulf of Mexico and worldwide.
Inland waters are hotspots for biogeochemical activity, but the environmental and biological factors that govern the transformation of organic matter (OM) flowing through them are still poorly ...constrained. Here we evaluate data from a crowdsourced sampling campaign led by the Worldwide Hydrobiogeochemistry Observation Network for Dynamic River Systems (WHONDRS) consortium to investigate broad continental-scale trends in OM composition compared to localized events that influence biogeochemical transformations. Samples from two different OM compartments, sediments and surface water, were collected from 97 streams throughout the Northern Hemisphere and analyzed to identify differences in biogeochemical processes involved in OM transformations. By using dimensional reduction techniques, we identified that putative biogeochemical transformations and microbial respiration rates vary across sediment and surface water along river continua independent of latitude (18°N−68°N). In contrast, we reveal small- and large-scale patterns in OM composition related to local (sediment vs. water column) and reach (stream order, latitude) characteristics. These patterns lay the foundation to modeling the linkage between ecological processes and biogeochemical signals. We further showed how spatial, physical, and biogeochemical factors influence the reactivity of the two OM pools in local reaches yet find emergent broad-scale patterns between OM concentrations and stream order. OM processing will likely change as hydrologic flow regimes shift and vertical mixing occurs on different spatial and temporal scales. As our planet continues to warm and the timing and magnitude of surface and subsurface flows shift, understanding changes in OM cycling across hydrologic systems is critical, given the unknown broad-scale responses and consequences for riverine OM.
The stable isotope compositions of nitrogen-nitrate (
15
N-NO
3
) and oxygen-nitrate (
18
O-NO
3
), and concentration of nutrients (NO
3
−
, NH
4
+
, NO
2
−
, PO
4
3−
) for water samples collected ...from springs, shallow wells and boreholes during dry and wet seasons were used to investigate sources and biogeochemical transformation of NO
3
−
in groundwater along the slopes of Mount Meru. About 80 % of all water sources had nitrate concentration higher than background concentration of 10 mg/l during both seasons, while NH
4
+
and NO
2
−
concentrations were very low probably due to nitrification. Concentrations of NO
3
−
above 50 mg/l were observed in some water sources. Concentrations of PO
4
3−
in all groundwater sources were very low during the two seasons owing to dilution and adsorption. The δ
15
N-NO
3
−
for boreholes waters averaged +11.6 ± 2.1 and +10.7 ± 2.1 ‰ during dry and wet seasons, respectively. Similarly, the δ
18
O-NO
3
−
of borehole waters for the wet and dry seasons averaged +5.2 ± 1.3 and +4.6 ± 1.9 ‰, respectively. With regard to dug wells, the δ
15
N-NO
3
−
of well water averaged +13.3 ± 2.5 and +12.5 ± 2.3 ‰ during dry and wet seasons, respectively, while the δ
18
O-NO
3
−
for the wet and dry seasons averaged +7 ± 2.3 and +6.4 ± 2.1 ‰, respectively. The δ
15
N-NO
3
−
, for springs averaged +11.2 ± 2.2 ‰ during dry season and +11.7 ± 3.5 ‰ during wet season whereas the δ
18
O-NO
3
−
for the wet and dry seasons averaged +7.3 ± 3.6 and +5.9 ± 2.6 ‰, respectively. The isotopic data suggested that the source of NO
3
−
in the water sources are dominated by sewage and/or animal manure and to less extent, soil organic N. Few samples collected in close proximity of manure heaps and sanitary facilities had δ
15
N values between 16 and 20 ‰ suggesting occurrence of denitrification.
Hyporheic flow and nutrient turnover in hyporheic systems are strongly influenced by in-stream bedforms. An accurate representation of topographical variations of the stream-streambed interface is ...therefore essential in analytical models in order to represent the couplings between hydrological and biogeochemical processes correctly. The classical Toth approach replaces the streambed surface topography by a flat surface which is identical to a truncation of the original physical flow domain into a rectangle. This simplification can lead to biased estimates of hyporheic flow and nutrient cycling within hyporheic systems. We present an alternative analytical modeling approach for solving hyporheic problems without domain truncation that explicitly accounts for topographical variations of the streambed. The presented approach is based on the application of perturbation theory. Applications of the method to hyporheic systems, ranging from the centimeter-scale of rippled bedforms to riffle structures of 10 m and larger scale, indicate a high accuracy of the approach.
•Analytical modelling approach based on perturbation theory.•Representation of potential flow and biogeochemical nutrient turnover in hyporheic systems.•Accurate and flexible analytical solutions.
The most important biogeochemical transformations and boundary exchanges in the Indian Ocean seem to occur in the northern region, where the processes originating at the land-ocean boundary extend ...far beyond the continental margins. Exchanges across the eastern and western boundaries are generally less significant. However, several important biogeochemical fluxes (e.g. exchanges across the air-sea, sedimentwater, land-sea and continental shelf-open ocean) remain to be quantified for most biogenic elements in the latter two areas. Some of these fluxes are expected to be substantial in the case of Indonesian continental margins and probably also across the eastern coasts of Africa not covered in this chapter. However, a dearth of information makes these margins some of the least known in the world calling for concerted research efforts, involving regional/international initiatives with emphasis on local capacity building, in future.
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