Biotic Uptake Research Articles

Biomonitoring of rare earth elements in Southern Norway: Distribution, fractionation, and accumulation patterns in the marine bivalves Mytilus spp. and Tapes spp.

Growing extraction and usage of rare earth elements and yttrium (REY) for medical and industrial applications has resulted in increased discharges into the marine environment. Using Mytilus spp. Mussels and Tapes spp. clams as bioindicator organisms, we analyzed 15 REY in soft tissues of specimens collected at two potentially polluted sites in Southern Norway: in the vicinity of an industry producing gadolinium-based MRI contrast agents (GBCAs) (Lindesnes) and in an industrially-affected fjord (Porsgrunn). The spatial distribution of REY and shale-normalized fractionation patterns were determined to assess the potential anthropogenic contribution of REY at the sites. At both sites, the REY fractionation pattern in soft tissue was characterized by enrichment of light rare earth elements (LREE) over heavy rare earth elements (HREE), while also displaying negative cerium and small positive gadolinium (Gd) anomalies. LREEs contributed to over 80% of the total REY concentrations, with increasing relative enrichment following higher total REY. Gd anomalies remained conserved in most sites despite significant differences in total REY; however, a high Gd anomaly (Gd/Gd* = 4.4) was found downstream of the GBCA industry spillwater outlet, indicating biotic uptake of excess anthropogenic Gd at this site. Total REY concentrations in clams in Porsgrunn were one order of magnitude higher than in mussels in Lindesnes. This may be attributable to freshwater influences in Porsgrunn, where clams collected closer to the river mouth had significantly higher total REY concentrations. This study constitutes the first assessment of REY concentrations in marine bivalves in Norway and can provide useful information for future biomonitoring studies on REY contamination.

Physical and biogeochemical drivers of solute mobilization and flux through the critical zone after wildfire

A nine-year time series of nutrient cation and anion concentration and efflux from three forested catchments in the Jemez River Basin Critical Zone Observatory (JRB-CZO) in northern New Mexico was used to quantify the pulse of chemical denudation resulting from varying levels stand-replacing wildfire intensity in May-June of 2013. The 3 years of pre-fire and 6 years of postfire data were also probed to shed light on the mechanisms underlying the pulsed release and the subsequent recovery. The initial large solute pulse released to the streams—K+, Ca2+, Mg2+, SO42-, Cl−, dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and total dissolved nitrogen (TDN)—was caused by leaching of hillslope ash deposits during the first monsoon storms post-fire. Debris flow following the wildfire likely redistributed much of the ash-containing sediments along streams and valley bottoms. Sustained elevated solute concentrations observed in the surface waters throughout the post-fire period relative to pre-fire baselines is consistent with these soluble materials being periodically flushed from the soils during wet seasons, i.e., snowmelt and summer monsoons. As microbial mediated reactions and biotic uptake—due to plant regrowth—recover after fire, nutrient ion export (e.g., NO3-, Cl− and SO42-) steadily decreased toward the end of the post fire period, but remained above pre-fire levels, particularly for NO3- and SO42-. Surface water concentrations of polyvalent cations (e.g., Al and Fe) decreased significantly after the fire. Our observations suggest that changes in organic matter composition after fire (e.g., increased humification index—HIX) and the presence of pyrogenic carbon may not favor organo-metal complexation and transport. Finally, differences in burn severity among the three watersheds presented in this study, provide insights of the relative impact of solute exports and resilience. The catchments that experienced high burn severity exhibited greater solute fluxes than the less severely burn. Moreover, despite these differences, toward the end of the post-fire period these surface waters presented low and similar solute effluxes, indicating system recovery. Nonetheless, magnitudes and rebounds were solute and process specific. The results of this study highlight the importance of surface and near surface physical and biogeochemical processes on the long-lasting geochemical denudation of forested catchments following wildfires of varying intensities.

Effects of biochar on the fate of conazole fungicides in soils and their bioavailability to earthworms and plants.

The study showed novel findings about changes in the fate and bioavailability of conazole fungicides (CFs) after biochar (BC) addition to soil. Two contrasting soils (low- and high-sorbing of CF; L soils, H soils) were amended by three BCs (low-, moderate-, and high-sorbing of CF; L-BC, M-BC, H-BC) at 0.2% and 2% doses. Epoxiconazole (EPC) and tebuconazole (TBC) were then added to the soil-BC mixtures, and their degradation, bioaccumulation in earthworms (Eisenia andrei), and bioconcentration in lettuce (Lactuca sativa) were studied for three months. Also, stir bar sorptive extraction (SBSE) was performed to determine CF (bio)accessibility. The EPC and TBC degradation in the soil-BC mixtures followed usually the first-order decay kinetics. The BC addition prevalently decreased the pesticides degradation in the L soil mixtures but often increased it in the H soil mixtures. In general, EPC degraded less than TBC. BC type and dose roles in the pesticides degradation were unclear. The BC addition significantly reduced pesticide uptake to the earthworms in the L soil mixtures (by 37-96%) and in the H soil mixtures (by 6-89%) with 2% BC. The BC addition reduced pesticide uptake to the lettuce roots and leaves significantly-up to two orders of magnitude, and this reduction was strong in H soil mixtures at 2% of BC. The BC addition reduced the CF (bio)accessibility measured by SBSE in all L soil mixtures and some H soil mixtures with 2% BC. Although not significant, it also seems that the pesticide bioaccumulation, bioconcentration, and (bio)accessibility were decreasing according to the BC type (L-BC > M-BC > H-BC). The pesticide concentrations in the earthworms and lettuce correlated significantly to the SBSE results, which indicates this technique as a possible predictor of biotic uptake. Our results showed that the interactions were hard to predict in the complex soil-BC-pesticide system.

Effects of effluents from wastewater treatment plants on the abiotic and biotic uptake of phosphorus by streambed sediments

Sustained inputs of nitrogen and/or phosphorus from wastewater treatment plants (WWTPs) to aquatic environments lead to an increased risk of eutrophication. The purpose of this study was to analyze the relative proportions of biotic and abiotic processes in the uptake of phosphorus by streambed sediments and their response to exogenous carbon (sodium acetate) concentration gradients, as well as explore the effects of WWTP effluent discharges on the biotic and abiotic uptake potential of phosphorus by streambed sediments in the receiving streams. Experiments were undertaken with streambed sediments collected from four different sites in different seasons, with or without the addition of a chloroform solution (biological inhibitor), to which were added different concentrations of a source of carbon (sodium acetate). After completing the indoor simulation culture, the total uptake potential (SPUlive), abiotic uptake potential (SPUabiotic), and biotic uptake potential (SPUbiotic) of phosphorus by the sediments were calculated. The SPUlive values of the sediments in the receiving section of the WWTP effluent were higher than those at the control site and gradually decreased with the flow direction. A larger amount (c. 79.04–98.11%) of the added phosphorus was taken up abiotically by the sediments with no added carbon. The SPUbiotic value of all sampling sites increased with the increase in exogenous carbon concentration by the addition of acetate, and accordingly the maximum contribution rate of the biotic uptake of phosphorus in sediments was 14.83–36.40%. Although WWTP effluents can increase the risk of release of phosphorus from sediments to the overlying water, the abiotic and biotic uptake potential of phosphorus by sediments is significantly increased by sediment–nutrient interactions. There may be more serious carbon limitations in the uptake of phosphorus by streambed sediments downstream of WWTPs than those at the reference site.

Iron Speciation and Physiological Analysis Indicate that Synechococcus sp. PCC 7002 Reduces Amorphous and Crystalline Iron Forms in Synthetic Seawater Medium

Cyanobacteria have high iron requirements due to iron-rich photosynthetic machineries. Despite the high concentrations of iron in the Earth’s crust, iron is limiting in many marine environments due to iron’s low solubility. Oxic conditions leave a large portion of the ocean’s iron pool unavailable for biotic uptake, and so the physiochemical properties of iron are hugely important for iron’s bioavailability. Our study is the first to investigate the effect of iron source on iron internalization and extracellular reduction by Synechococcus sp. PCC 7002. The results indicated that the amorphous iron hydrolysis species produced by FeCl3 better support growth in Synechococcus through more efficient iron internalization and a larger degree of extracellular reduction of iron than the crystalline FeO(OH). An analysis of dissolved iron (II) indicated that biogenic reduction took place in cultures of Synechococcus grown on both FeCl3 and FeO(OH).

Environmental archives of atmospheric Hg deposition – A review

Environmental archives offer an opportunity to reconstruct temporal trends in atmospheric Hg deposition at various timescales. Lake sediment and peat have been the most widely used archives; however, new records from ice, tree rings, and the measurement of Hg stable isotopes, are offering new insights into past Hg cycling. Preindustrial Hg deposition has been studied over decadal to millennial timescales extending as far back as the late Pleistocene. Exploitation of mercury deposits (mainly cinnabar) first began during the mid to late Holocene in South America, Europe, and Asia, but increased dramatically during the Colonial era (1532–1900) for silver production. However, evidence for preindustrial Hg pollution is restricted to regions directly downwind or downstream of cinnabar or precious metal mining centers. Excluding these areas, there has been an approximately four-fold increase in atmospheric deposition globally over the industrial era (i.e., since 1800–1850), though regional differences exist, especially during the early 20th Century. Lake sediments, peat, ice, and tree rings are all influenced by (and integrate) a range of processes. For example, lake sediments are influenced by atmospheric deposition, sediment focusing, and the input of allochthonous material from the watershed, peat records reflect atmospheric deposition and biotic uptake, ice cores are a record of Hg scrubbed during precipitation, and tree rings record atmospheric concentrations. No archive represents an absolute record of past Hg deposition or concentrations, and post-depositional transformation of Hg profiles remains an important topic of research. However, natural archives continue to provide important insight into atmospheric Hg cycling over various timescales.

Enantioselective degradation of dufulin pesticide in water: Uptake, thermodynamics, and kinetics studies.

Kudzu (Pueraria thunbergiana) plant extract impregnated sediments were used for abiotic and biotic uptakes and biodegradation. The optimized conditions were 25 μg L-1 concentration, 7 days for abiotic uptake and 56 days for biotic uptake and biodegradation, dose 2 g L-1 , 7 pH, and 35°C temperature. The amount removed of dufulin was 32.6% in abiotic conditions while these were 90% in the case of biotic uptake and biodegradation. Enantioselective biodegradation indicated that S-(+)-enantiomer degraded faster (90%) than R-(-)-enantiomer (87%). The data for abiotic and biotic uptakes and biodegradation followed well Langmuir, thermodynamics, and kinetics models. All these processes followed pseudo first-order kinetics. It was observed that biodegradation was three times responsible for dufulin removal than simple sorption uptake (abiotic and biotic). The abiotic and biotic uptakes and biodegradation were quite fast and endothermic nature. The developed method may be used to remove the racemic and enantiomeric dufulin in water.

Patterns of blood mercury variation in two long-distance migratory thrushes on Mount Mansfield, Vermont.

We investigated mercury (Hg) blood concentrations in Bicknell's thrush (Catharus bicknelli) and Swainson's thrush (C. ustulatus), congeneric long-distance migratory songbirds, from 2000-2017 at a montane forest site in north-central Vermont. We analyzed variation in blood Hg of both species using mixed-effects models, incorporating atmospheric wet Hg deposition data from a nearby sampling location. Although Hg deposition varied among years and seasonally, we detected no temporal trend in either atmospheric deposition or blood Hg, nor evidence of a relationship between the two. Sampling date had the strongest effect on blood Hg concentration, which declined seasonally, followed by age and sex of the individual. The data did not support an effect of species. We believe that the absence of a clear relationship between local atmospheric deposition and thrush blood Hg concentrations suggests that Hg cycling dynamics, mechanisms of transfer, and timing of uptake by montane forest biota are complex and poorly understood. The blood Hg concentrations of ~0.07-0.1 μg/g we documented in Bicknell's and Swainson's thrush are below those found to negatively impact physiological or reproductive endpoints in other invertivorous terrestrial passerines. To better evaluate the validity of Bicknell's thrush as a bioindicator of MeHg availability in montane forest ecosystems, we recommend (1) effects-based investigations, (2) a more robust understanding of Hg and MeHg cycling, (3) more clear geospatial and temporal links between Hg deposition and biotic uptake, and (4) more thorough documentation of Hg burdens across the species' annual cycle.

Seasonality of Phosphorus and Nitrate Retention in Riparian Buffers.

Measurement of the retention of dissolved nutrients in riparian areas with snowmelt runoff are much less common than for rainfall runoff, but low rates of uptake or the release of nutrients with snowmelt have been attributed to frozen soils, lower biotic uptake, and release of nutrients from senesced vegetation. In the research presented here, we evaluate whether the potential for uptake of dissolved reactive phosphorus (DRP) and NO differ significantly between snowmelt and summer seasons with flow through 13 riparian buffers downstream of cropland in Manitoba, Canada. Flow-through buffers in small channels are typical in this landscape, and pulsed releases of a conservative tracer and dissolved nutrients were used to measure uptake rates. Although mean uptake rates of NO were higher in summer than for snowmelt, responses varied widely. Aerial uptake rate of DRP showed a significant negative relationships with soil Olsen-P ( = 0.54, < 0.001) and a P saturation index ( = 0.48, < 0.001) across both seasons. Biological processes may be of greater importance for NO retention, but DRP retention appears to be driven by adsorption-desorption regardless of season. Olsen-P is identified as a good indicator of potential for release or retention of DRP in riparian buffers with fine-textured calcareous soils, for both snowmelt and summer seasons. Soil testing may be a good tool to aid in the siting of new buffers and to track the effectiveness of management interventions to remove P from riparian areas, such as harvest of vegetation.

Potential for Phosphorus Uptake by Bed Sediments and Its Response to Carbon Additions in the Shiwuli River, Chaohu Lake Basin

Surficial sediments were collected from five sampling sites in the mainstream of the Shiwuli River along an urban-rural gradient in the Chaohu Lake basin during July 2017 (summer) and January 2018 (winter). The total uptake (SPUlive), abiotic uptake (SPUkill), and biotic uptake (SPUbiotic) of phosphorus by sediments were measured, and uptake responses to different carbon sources (i. e., sodium acetate, glucose, and a mixture of both) were explored quantitatively through incubation experiments. The results showed that SPUlive had obviously spatiotemporal variations across the five sites, and SPUkill was higher than that of SPUbiotic. Under no carbon added, the mean values of SPUkill were 3.016 μg·(g·h)-1 and 3.368 μg·(g·h)-1, and the average values of SPUbiotic were 0.784 μg·(g·h)-1 and 0.323 μg·(g·h)-1 in summer and winter, respectively. Moreover, significant differences were found in abiotic phosphorus uptake between the two months. In the presence of carbon addition, both the value of SPUbiotic and the contribution rate of biotic phosphorus uptake showed a distinct increase. In general, the magnitude and rate of biotic uptake of phosphorus by sediments was highest when sodium acetate was added, followed by glucose, while the effect of mixed carbon was the worst. The responses of biotic phosphorus uptake to carbon addition suggested that the uptake potential of phosphorus by sediments in Shiwuli River was restricted by the carbon availability to some degree.

Spiraling Down Hillslopes: Nutrient Uptake from Water Tracks in a Warming Arctic

Hydrologic flowpaths might propagate biogeochemical signals among connected ecosystems or alter and dampen signals because of reactions or retention occurring during transport. In the Arctic, experimentally warmed terrestrial tundra releases inorganic nitrogen (N), but the fate of this newly released N remains unclear. Nitrogen could be passively transported downslope in flowing water, or retained when flowpaths intercept N-limited ecosystems. We applied nutrient spiraling theory to simultaneously measure reaction and transport of ammonium (NH4+) and phosphate (PO43−), nutrients limiting primary productivity in Arctic ecosystems. Pulse fertilization experiments were focused on flowpaths known as water tracks that hydrologically connect soils to receiving streams and lakes in upland tundra of Alaska. Water tracks typically retained PO43−, but passively transported NH4+, thus potentially propagating NH4+ produced by warming tundra soils to downstream ecosystems. Nutrient uptake was uncorrelated with the relative proportion of downslope transport in transient storage zones, but greater NH4+ uptake occurred as advective hydrologic flux increased relative to dispersion. Phosphate uptake declined as thaw depth increased over the summer season likely because of declining capacity for biotic uptake or sorption in deeper soils. Phosphorus limitation in fluvial ecosystems of the Arctic might result in efficient transport of inorganic N to N-limited lentic and coastal ecosystems, where increasing subsidies furnished by N loss from warming terrestrial tundra could support enhanced primary production.

Partitioning assimilatory nitrogen uptake in streams: an analysis of stable isotope tracer additions across continents

AbstractHeadwater streams remove, transform, and store inorganic nitrogen (N) delivered from surrounding watersheds, but excessive N inputs from human activity can saturate removal capacity. Most research has focused on quantifying N removal from the water column over short periods and in individual reaches, and these ecosystem‐scale measurements suggest that assimilatory N uptake accounts for most N removal. However, cross‐system comparisons addressing the relative role of particular biota responsible for incorporating inorganic N into biomass are lacking. Here we assess the importance of different primary uptake compartments on reach‐scale ammonium (NH4+‐N) uptake and storage across a wide range of streams varying in abundance of biota and local environmental factors. We analyzed data from 17 15N‐NH4+ tracer addition experiments globally, and found that assimilatory N uptake by autotrophic compartments (i.e., epilithic biofilm, filamentous algae, bryophytes/macrophytes) was higher but more variable than for heterotrophic microorganisms colonizing detrital organic matter (i.e., leaves, small wood, and fine particles). Autotrophic compartments played a disproportionate role in N uptake relative to their biomass, although uptake rates were similar when we rescaled heterotrophic assimilatory N uptake associated only with live microbial biomass. Assimilatory NH4+‐N uptake, either estimated as removal from the water column or from the sum uptake of all individual compartments, was four times higher in open‐ than in closed‐canopy streams. Using Bayesian Model Averaging, we found that canopy cover and gross primary production (GPP) controlled autotrophic assimilatory N uptake while ecosystem respiration (ER) was more important for the heterotrophic contribution. The ratio of autotrophic to heterotrophic N storage was positively correlated with metabolism (GPP: ER), which was also higher in open‐ than in closed‐canopy streams. Our analysis shows riparian canopy cover influences the relative abundance of different biotic uptake compartments and thus GPP:ER. As such, the simple categorical variable of canopy cover explained differences in assimilatory N uptake among streams at the reach scale, as well as the relative roles of autotrophs and heterotrophs in N storage. Finally, this synthesis links cumulative N uptake by stream biota to reach‐scale N demand and provides a mechanistic and predictive framework for estimating and modeling N cycling in other streams.

Measurements of windblown dust characteristics and ocean fertilization potential: The ephemeral river valleys of Namibia

Abstract Delivery of nutrients to the ocean by mineral aerosol deposition involves complex biogeochemical interactions that include atmospheric processing, dissolution and biotic uptake of available nutrients in the surface waters. Research into the fertilization potential of aeolian dust is currently constrained by a lack of understanding of the nutrient composition and bioavailability in dust source areas. Further, research into hot-spots of dust emission has largely focused on paleo-lacustrine sources and pans, to the detriment of other potential sources such as ephemeral river valleys in desert regions. Here, we investigate the sediment characteristics and nutrient content of windblown and surface sediments of a largely overlooked southern African dust source, Namibia’s ephemeral river valleys. We deployed monitoring equipment in three river valleys to capture deflated sediments and monitor airborne dust concentration and meteorological conditions throughout an annual dust season. Our results show that windblown dust within the river valleys is easily transportable offshore from Namibia over the Benguela Upwelling System, an intensely productive region of the South Atlantic Ocean. We demonstrate that the windblown dust contains iron, phosphorus and nitrogen nutrients, each of which may positively impact primary production rates when deposited in the complex upwelling system. The river valley dust has a significantly higher content of nutrients than either of southern Africa’s major dry lake bed dust sources, Etosha and Makgadikgadi Pans. This aeolian work builds on previous source sediment findings proposing the ephemeral river valleys of Namibia as regionally important sources of dust with enhanced ocean fertilisation potential.

Quantifying components of the phosphorus cycle in temperate forests

We review the state‐of‐the‐art of cross‐disciplinary knowledge on phosphorus (P) cycling in temperate forest ecosystems, focused at studies from hydrology, biology, biogeochemistry, soil‐, and geosciences. Changes in soil P stocks during long‐term ecosystem development are addressed briefly; the general ranges of specific P pools and P fluxes within the ecosystem and the presumed underlying processes are covered more in depth. Wherever possible, we differentiate between coniferous and deciduous forests. As the most important P pools, mineral soil, forest floor, vegetation, and microbial biomass are described in terms of pool size, molecular composition, and turnover. Litterfall, soil water seepage, atmospheric deposition, and biotic uptake as the most studied P fluxes in the forest ecosystem are discussed in detail, spotlighting biogeochemical processes relevant for mobilization and retention of P in the rooting zone. Through a meta‐analysis of available literature, we build a dataset that allows the quantification of major P‐cycle components in temperate forests in terms of range and distribution, highlighting similarities and differences between coniferous and deciduous forests. The two forest types are notably distinct in their distribution of P within compartments of the plant biomass and forest floor. The possibility to construct closed local P balances is often hindered by missing information on fluxes of dissolved and particulate P across the ecosystem boundary, be it in the atmosphere, soil, or on the surface. These fluxes are irregular in space and time and feature large overall mass fluxes but comparatively small P fluxes, making the latter one difficult to quantify.WIREs Water2017, 4:e1243. doi: 10.1002/wat2.1243This article is categorized under:Water and Life &gt; Nature of Freshwater EcosystemsScience of Water &gt; Water Quality

Biotic and Abiotic Uptake of Phosphorus in Benthic Sediments of Suburban Streams Under Intense Human Disturbance Scenario

To reveal the impact of land use change on the phosphorus uptake in benthic sediments of suburban streams, a headwater stream in the urban fringe of Hefei City was selected and a set of benthic sediments was collected monthly from the chosen stream reach from June to November 2016. An incubation method was applied to explore the biotic and abiotic uptake of phosphorus in benthic sediments under intense human disturbance scenario. Results showed that the uptake potentials in summer were higher than those in autumn, both for total (including biotic and abiotic) and abiotic uptake of phosphorus. Furthermore, both of these uptakes were distinctly higher for the third sampling site, which is adjacent to the sewage outlet, than those for the other sites. For all six sampling sites, the contribution rate of biotic uptake of phosphorus was significantly greater than that of abiotic uptake, both in summer and autumn. The monthly variations in potentials and contribution rates of phosphorus uptake indicated that intense human disturbance via land use change had a great impact on the biotic uptake of phosphorus in benthic sediments of the suburban stream.

Changes in carbon and nutrient fluxes from headwaters to ocean in a mountainous temperate to subtropical basin

AbstractWater erosion provides major links in global cycles of carbon (C), nitrogen (N) and phosphorus (P). Although significant research on erosion mechanisms has been done, there is still little knowledge on C, N and P fluxes across landscapes to the ocean and their controlling factors in subtropical climates. A four‐year study quantifying and comparing particulate and dissolved C, N and P from multiple scales (microplot, plot, microcatchment, subcatchment, catchment, sub‐basin and basin) was performed in Thukela basin (≈30 000 km2), South Africa. The basin climate was largely subtropical‐humid [mean annual precipitation (MAP) &gt; 980 mm yr‐1], but temperate (MAP &gt;2000 mm yr‐1) on the highlands. Open grassland, cropland and bushland were the major land uses. On average, 65, 24 and 4 g m‐2 yr‐1 C, N and P were displaced from original topsoil positions, but only 0.33, 0.005 and 0.002 mg m‐2 yr‐1 were, respectively, exported to the ocean. The fluxes decreased by 95, 97 and 84%, respectively, from plot to microcatchment outlet; and decreased further in downstream direction by &gt;99% from microcatchment to basin outlet. The hillslope (microplot to microcatchment) fluxes correlated strongly with rainfall parameters. Particulate contributions dominated hillslope fluxes at 73, 81 and 76% of total annual C, N and P, respectively. Although particulate C dominated in the microcatchment‐catchment reach (55%), N (54%) and P (69%) were dominated by dissolved forms. The lower basin zone was dominated by dissolved flux contributions at 93, 81 and 78% for C, N and P for the sub‐basin outlet. These results suggested spatially varying drivers of C, N and P losses from the landscape to the ocean, via the river network. Deposition was envisaged the dominant hillslope level loss process, which gradually gave way to mineralization and biotic uptake in the river network as flux contributions shifted from being predominantly particulate to dissolved forms. Copyright © 2017 John Wiley &amp; Sons, Ltd.

Sources and transformations of anthropogenic nitrogen along an urban river–estuarine continuum

Abstract. Urbanization has altered the fate and transport of anthropogenic nitrogen (N) in rivers and estuaries globally. This study evaluates the capacity of an urbanizing river–estuarine continuum to transform N inputs from the world's largest advanced (e.g., phosphorus and biological N removal) wastewater treatment facility. Effluent samples and surface water were collected monthly along the Potomac River estuary from Washington D.C. to the Chesapeake Bay over a distance of 150 km. In conjunction with box model mass balances, nitrate stable isotopes and mixing models were used to trace the fate of urban wastewater nitrate. Nitrate concentrations and δ15N-NO3− values were higher down-estuary from the Blue Plains wastewater outfall in Washington D.C. (2.25 ± 0.62 mg L−1 and 25.7 ± 2.9 ‰, respectively) compared to upper-estuary concentrations (1.0 ± 0.2 mg L−1 and 9.3 ± 1.4 ‰, respectively). Nitrate concentration then decreased rapidly within 30 km down-estuary (to 0.8 ± 0.2 mg L−1), corresponding to an increase in organic nitrogen and dissolved organic carbon, suggesting biotic uptake and organic transformation. TN loads declined down-estuary (from an annual average of 48 000 ± 5000 kg day−1 at the sewage treatment plant outfall to 23 000 ± 13 000 kg day−1 at the estuary mouth), with the greatest percentage decrease during summer and fall. Annually, there was a 70 ± 31 % loss in wastewater NO3− along the estuary, and 28 ± 6 % of urban wastewater TN inputs were exported to the Chesapeake Bay, with the greatest contribution of wastewater TN loads during the spring. Our results suggest that biological transformations along the urban river–estuary continuum can significantly transform wastewater N inputs from major cities globally, and more work is necessary to evaluate the potential of organic nitrogen and carbon to contribute to eutrophication and hypoxia.

Improving our capacity to manage hypoxic blackwater events in lowland rivers: The Blackwater Risk Assessment Tool

Blackwater events occur when returning floodwater contains elevated levels of dissolved organic carbon. Normally the export of carbon from floodplains to a river channel is a beneficial process, providing sustenance to lowland river ecosystems. However if the rate of oxygen consumption during decomposition of the organic carbon is faster than it can be replenished from the atmosphere, this can cause hypoxia, with catastrophic short-term consequences for aquatic fauna. Because river regulation has disconnected many floodplains from their source rivers, floodplain inundation is increasingly being actively managed specifically for the benefit of the environment. However, the risk of hypoxic blackwater generation must be considered during such managed floods. This paper describes a new tool for predicting dissolved oxygen and dissolved organic carbon in flood return water, using minimal data inputs. The Blackwater Risk Assessment Tool (BRAT) is based on the same conceptual framework underpinning an earlier, geographically specific, blackwater model. However BRAT differs in a number of significant ways from the earlier model. The BRAT is based on a generic, rather than site-specific, inundation model; and users have the option to use actual hydrographs if these are available. Furthermore, most of the algorithms used to model blackwater generation processes have been refined, reflecting new knowledge generated since the original model was constructed. This includes changes to floodplain litter load estimation methods, algorithms for the temperature dependence of dissolved organic carbon leaching and biotic uptake, and re-aeration rate calculation. Finally, unlike the earlier model, all the algorithms and constants in BRAT are readily accessible so that the model can be customized to suit floodplain ecosystems other than the ones for which it was developed. The model was validated using flood events in Koondrook–Perricoota and Gunbower forests, Australia. Model outputs were in good agreement with observed dissolved oxygen during these flood events with root mean square variation as low as 1.2mgO2L−1.

A dynamic marine iron cycle module coupled to the University of Victoria Earth System Model: the Kiel Marine Biogeochemical Model 2 for UVic 2.9

Abstract. Marine biological production as well as the associated biotic uptake of carbon in many ocean regions depends on the availability of nutrients in the euphotic zone. While large areas are limited by nitrogen and/or phosphorus, the micronutrient iron is considered the main limiting nutrient in the North Pacific, equatorial Pacific and Southern Ocean. Changes in iron availability via changes in atmospheric dust input are discussed to play an important role in glacial–interglacial cycles via climate feedbacks caused by changes in biological ocean carbon sequestration. Although many aspects of the iron cycle remain unknown, its incorporation into marine biogeochemical models is needed to test our current understanding and better constrain its role in the Earth system. In the University of Victoria Earth System Climate Model (UVic) iron limitation in the ocean was, until now, simulated pragmatically with an iron concentration masking scheme that did not allow a consistent interactive response to perturbations of ocean biogeochemistry or iron cycling sensitivity studies. Here, we replace the iron masking scheme with a dynamic iron cycle and compare the results to available observations and the previous marine biogeochemical model. Sensitivity studies are also conducted with the new model to test the sensitivity of the model to parameterized iron ligand concentrations, the importance of considering the variable solubility of iron in dust deposition, the importance of considering high-resolution bathymetry for the sediment release of iron, the effect of scaling the sedimentary iron release with temperature and the sensitivity of the iron cycle to a climate change scenario.

Dissolved organic carbon biolability decreases along with its modernization in fluvial networks in an ancient landscape

The metabolism of dissolved organic carbon (DOC) along fluvial networks determines what fraction of organic matter is exported to the ocean. Although it is thought fresh rather than older DOC is preferred by bacteria, old DOC can also be highly bioavailable to stream bacterial communities. In strongly seasonal and oligotrophic regions, we argue that groundwater inputs of old DOC may increase the bioavailability of stream organic matter. We sampled 22 streams along a gradient of size (wetted widths from 1 to 60 m) and one groundwater spring in the Kimberley region of northwest Australia to determine how the age and bioavailability of streamwater DOC varied with stream size. Our hypothesis was that stream DOC would become more enriched in 14C (younger) and less bioavailable as streams increased in size and depleted 14C‐DOC was metabolized by stream microbial communities. We also used fluorescence characterization of DOC, ultraviolet absorbance at 254nm (SUVA254), δ13C‐DOC and lignin phenol yields to assess how these indicators of DOC character influenced the bioavailability and age of stream DOC. Stream evaporation/inflow ratios (E/I, used as a proxy for catchment water residence time), determined from changes in stream δ18O along the gradient of stream size, were positively related to DOC concentration and carbon‐normalized lignin yields, while δ13C‐DOC became more depleted with increasing E/I. Stream Δ14C‐DOC varied from −452.1‰ (groundwater) to 48.9‰ and showed progressive enrichment as streams increased in size and accumulated DOC mainly from terrestrial plant material. Older DOC corresponded to higher bioavailability (R2 = 0.67, P &lt; 0.01), suggesting that old bioavailable DOC, which has escaped from subterranean food webs utilizing 14C‐depleted carbon, is common to one of the oldest landscapes on earth. Therefore, rapid biotic uptake of old bioavailable DOC originating in groundwater springs and the accumulation of modern, terrestrially derived DOC work in opposite directions affecting DOC dynamics along fluvial networks. We suggest the metabolism of old DOC along fluvial networks provides a biogeochemical link between non‐contemporary carbon fixation and modern river productivity.