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Subterranean estuaries (STEs) are important coastal biogeochemical reactors facilitating unique niches for microbial communities. A common approach in determining STE greenhouse gas and nutrient fluxes is to use terrestrial endmembers, not accounting for microbially mediated transformations throughout the STE. As such, the microbial ecology and spatial distribution of specialists that cycle compounds in STEs remain largely underexplored. In this study, we applied 16S rRNA amplicon sequencing with paired biogeochemical characterisations to spatially evaluate microbial communities transforming greenhouse gases and nutrients in an STE. We show that methanogens are most prevalent at the terrestrial end (up to 2.81% relative abundance) concomitant to the highest porewater methane, carbon dioxide and dissolved organic carbon concentrations (0.41 ± 0.02 µM, 273.31 ± 6.05 µM and 0.51 ± 0.02 mM, respectively). Lower ammonium concentrations corresponded with abundant nitrifying and ammonia-oxidising prokaryotes in the mixing zone (up to 11.65% relative abundance). Methane, ammonium and dissolved organic carbon concentrations all decreased by >50% from the terrestrial to the oceanic end of the 15 m transect. This study highlights the STE's hidden microbiome zonation, as well as the importance of accounting for microbial transformations mitigating nutrient and greenhouse gas fluxes to the coastal ecosystems.
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Compostos de Amônio , Gases de Efeito Estufa , Microbiota , Estuários , Metano , Matéria Orgânica Dissolvida , Nitrogênio , RNA Ribossômico 16S/genética , Microbiota/genéticaRESUMO
Tree stem methane emissions are important components of lowland forest methane budgets. The potential for species-specific behaviour among co-occurring lowland trees with contrasting bark characteristics has not been investigated. We compare bark-mediated methane transport in two common lowland species of contrasting bark characteristics (Melaleuca quinquenervia featuring spongy/layered bark with longitudinally continuous airspaces and Casuarina glauca featuring hard/dense common bark) through several manipulative experiments. First, the progressive cutting through M. quinquenervia bark layers caused exponential increases in methane fluxes (c. 3 orders of magnitude); however, sapwood-only fluxes were lower, suggesting that upward/axial methane transport occurs between bark layers. Second, concentrated methane pulse-injections into exposed M. quinquenervia bark, revealed rapid axial methane transport rates (1.42 mm s-1 ), which were further supported through laboratory-simulated experiments (1.41 mm s-1 ). Laboratory-simulated radial CH4 diffusion rates (through bark) were c. 20-times slower. Finally, girdling M. quinquenervia stems caused a near-instantaneous decrease in methane flux immediately above the cut. By contrast, girdling C. glauca displayed persistent, though diminished, methane fluxes. Overall, the experiments revealed evidence for rapid 'between-bark' methane transport independent from the transpiration stream in M. quinquenervia, which facilitates diffusive axial transport from the rhizosphere and/or sapwood sources. This contrasts with the slower, radial 'through-bark' diffusive-dominated gas transportation in C. glauca.
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Melaleuca , Árvores , Metano , Casca de Planta , Florestas , Dióxido de Carbono , SoloRESUMO
Rivers are often assumed to be the main source of nutrients triggering eutrophication in the Great Barrier Reef (GBR). However, existing nutrient budgets suggest a major missing source of nitrogen and phosphorus sustaining primary production. Here, we used radium isotopes to resolve submarine groundwater discharge (SGD)-derived, shelf-scale nutrient inputs to the GBR. The total SGD was â¼10-15 times greater than average river inputs, with nearshore groundwater discharge accounting for â¼30% of this. Total SGD accounted for >30% of all known dissolved inorganic N and >60% of inorganic P inputs and exceeded regional river inputs. However, SGD was only a small proportion of the nutrients necessary to sustain primary productivity, suggesting that internal recycling processes still dominate the nutrient budget. With millions of dollars spent managing surface water nutrient inputs to reef systems globally, we argue for a shift in the focus of management to safeguard reefs from the impacts of excess nutrients.
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Água Subterrânea , Rios , Monitoramento Ambiental , Eutrofização , NutrientesRESUMO
Knowledge regarding mechanisms moderating methane (CH4 ) sink/source behaviour along the soil-tree stem-atmosphere continuum remains incomplete. Here, we applied stable isotope analysis (δ13 C-CH4 ) to gain insights into axial CH4 transport and oxidation in two globally distributed subtropical lowland species (Melaleuca quinquenervia and Casuarina glauca). We found consistent trends in CH4 flux (decreasing with height) and δ13 C-CH4 enrichment (increasing with height) in relation to stem height from ground. The average lower tree stem δ13 C-CH4 (0-40 cm) of Melaleuca and Casuarina (-53.96 and -65.89) were similar to adjacent flooded soil CH4 ebullition (-52.87 and -62.98), suggesting that stem CH4 is derived mainly by soil sources. Upper stems (81-200 cm) displayed distinct δ13 C-CH4 enrichment (Melaleuca -44.6 and Casuarina -46.5, respectively). Coupled 3D-photogrammetry with novel 3D-stem measurements revealed distinct hotspots of CH4 flux and isotopic fractionation on Melaleuca, which were likely due to bark anomalies in which preferential pathways of gas efflux were enhanced. Diel experiments revealed greater δ13 C-CH4 enrichment and higher oxidation rates in the afternoon, compared with the morning. Overall, we estimated that c. 33% of the methane was oxidised between lower and upper stems during axial transport, therefore potentially representing a globally significant, yet previously unaccounted for, methane sink.
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Metano , Árvores , Atmosfera , Florestas , SoloRESUMO
Growing evidence indicates that tree-stem methane (CH4 ) emissions may be an important and unaccounted-for component of local, regional and global carbon (C) budgets. Studies to date have focused on upland and freshwater swamp-forests; however, no data on tree-stem fluxes from estuarine species currently exist. Here we provide the first-ever mangrove tree-stem CH4 flux measurements from >50 trees (n = 230 measurements), in both standing dead and living forest, from a region suffering a recent large-scale climate-driven dieback event (Gulf of Carpentaria, Australia). Average CH4 emissions from standing dead mangrove tree-stems was 249.2 ± 41.0 µmol m-2 d-1 and was eight-fold higher than from living mangrove tree-stems (37.5 ± 5.8 µmol m-2 d-1 ). The average CH4 flux from tree-stem bases (c. 10 cm aboveground) was 1071.1 ± 210.4 and 96.8 ± 27.7 µmol m-2 d-1 from dead and living stands respectively. Sediment CH4 fluxes and redox potentials did not differ significantly between living and dead stands. Our results suggest both dead and living tree-stems act as CH4 conduits to the atmosphere, bypassing potential sedimentary oxidation processes. Although large uncertainties exist when upscaling data from small-scale temporal measurements, we estimated that dead mangrove tree-stem emissions may account for c. 26% of the net ecosystem CH4 flux.
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Avicennia/metabolismo , Carbono/metabolismo , Florestas , Metano/metabolismo , Caules de Planta/metabolismo , Geografia , Sedimentos Geológicos/química , Oxirredução , Queensland , VolatilizaçãoRESUMO
Atmospheric concentrations of methane have increased â¼2.4 fold since the industrial revolution with wetlands and inland waters representing the largest source of methane to the atmosphere. Substantial uncertainties remain in global methane budgets, due in part to the lack of adequate techniques and detailed measurements to assess ebullition in aquatic environments. Here, we present details of a low cost (â¼$120 US per unit) ebullition sensor that autonomously logs both volumetric ebullition rate and methane concentrations. The sensor combines a traditional funnel bubble trap with an Arduino logger, a pressure sensor, thermal conductivity methane sensor, and a solenoid valve. Powered by three AA batteries, the sensor can measure autonomously for three months when programmed for a sampling frequency of 30 min. For field testing, four sensors were deployed for six weeks in a small lake. While ebullition was spatially and temporally variable, a distinct diurnal trend was observed with the highest rates from mid-morning to early afternoon. Ebullition rates were similar for all four sensors when integrated over the sampling period. The widespread deployment of low cost automated ebullition sensors such as the iAMES described here will help constrain one of the largest uncertainties in the global methane budget.
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Atmosfera , Metano , LagosRESUMO
Estuaries are an important source of greenhouse gases to the atmosphere, but uncertainties remain in the flux rates and production pathways of greenhouse gases in these dynamic systems. This study performs simultaneous high resolution measurements of the three major greenhouse gases (carbon dioxide, methane, and nitrous oxide) as well as carbon stable isotope ratios of carbon dioxide and methane, above and below the pycnocline along a salt wedge estuary (Yarra River estuary, Australia). We identified distinct zones of elevated greenhouse gas concentrations. At the tip of salt wedge, average CO2 and N2O concentrations were approximately five and three times higher than in the saline mouth of the estuary. In anaerobic bottom waters, the natural tracer radon (222Rn) revealed that porewater exchange was the likely source of the highest methane concentrations (up to 1302 nM). Isotopic analysis of CH4 showed a dominance of acetoclastic production in fresh surface waters and hydrogenotrophic production occurring in the saline bottom waters. The atmospheric flux of methane (in CO2 equivalent units) was a major (35-53%) contributor of atmospheric radiative forcing from the estuary, while N2O contributed <2%. We hypothesize that the release of bottom water gases when stratification episodically breaks down will release large pulses of greenhouse gases to the atmosphere.
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Estuários , Gases de Efeito Estufa , Austrália , Dióxido de Carbono , Efeito Estufa , Metano , Óxido Nitroso , Radônio , Análise EspectralRESUMO
Atmospheric radon ((222)Rn) and carbon dioxide (CO2) concentrations were used to gain insight into fugitive emissions in an Australian coal seam gas (CSG) field (Surat Basin, Tara region, Queensland). (222)Rn and CO2 concentrations were observed for 24 h within and outside the gas field. Both (222)Rn and CO2 concentrations followed a diurnal cycle with night time concentrations higher than day time concentrations. Average CO2 concentrations over the 24-h period ranged from ~390 ppm at the control site to ~467 ppm near the center of the gas field. A ~3 fold increase in maximum (222)Rn concentration was observed inside the gas field compared to outside of it. There was a significant relationship between maximum and average (222)Rn concentrations and the number of gas wells within a 3 km radius of the sampling sites (n = 5 stations; p < 0.05). A positive trend was observed between CO2 concentrations and the number of CSG wells, but the relationship was not statistically significant. We hypothesize that the radon relationship was a response to enhanced emissions within the gas field related to both point (well heads, pipelines, etc.) and diffuse soil sources. Radon may be useful in monitoring enhanced soil gas fluxes to the atmosphere due to changes in the geological structure associated with wells and hydraulic fracturing in CSG fields.
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Atmosfera/química , Dióxido de Carbono/análise , Carvão Mineral/análise , Campos de Petróleo e Gás/química , Radônio/análise , Geografia , Modelos Teóricos , Queensland , Análise de Regressão , Fatores de TempoRESUMO
There is growing awareness of the need to better constrain the contribution of atmospheric methane (CH4) fluxes from urbanized estuaries due to the high global warming potential of CH4 and the accelerating growth of urban expansion. This study undertook seasonal sampling campaigns to understand the impact of urbanization on atmospheric CH4 fluxes and their drivers in a large, tropical estuary in India. Overall, the study found that the Cochin estuary emitted large amounts of CH4 (398.8 ± 141.6 µmolm-2d-1) to the atmosphere with CH4 hotspots reaching up to 939.7 µmolm-2d-1 were identified. The strongest drivers of CH4 dynamics in different anthropogenically impacted zones were traced. The source of organic matter for CH4 production was revealed to be terrestrial C3 plants, autochthonous production, marine phytoplankton, and sewage inputs. The study suggests that monsoonal urbanized tropical estuaries may be an important but under-recognized element of the global CH4 budget.
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Estuários , Metano , Metano/análise , Aquecimento Global , Atmosfera , Índia , Dióxido de Carbono/análiseRESUMO
In order to better understand the distribution pattern, pollution degree and the submarine groundwater discharge (SGD) of dissolved heavy metals, 15 subterranean estuaries (STEs) along southwest Indian coast were sampled over three contrasting seasons. The average concentration of metals were ranked as, pre-monsoon > monsoon > post-monsoon with 3 to 12-fold higher groundwater metal concentrations than the adjacent seawater. Average SGD derived essential metal fluxes were five times higher than the toxic metal fluxes of which Fe and Zn together contributed >90 %. Using the Single Factor Contamination Index, the majority of sites were minimally contaminated with only two sites indicating moderate ecological risk due to As. Higher fluxes of Fe, Cu and Zn were likely a result of rising anthropogenic activities. The SGD derived nutrient fluxes were an important source of DIP for primary production in coastal waters and represented 30 % and 44 % of the DIN and DIP inputs respectively.
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Água Subterrânea , Metais Pesados , Estuários , Estações do Ano , Água do Mar , Nutrientes , Índia , Monitoramento AmbientalRESUMO
Fragmented mangroves are generally ignored in N2O flux studies. Here we report observations over the course of a year from the Mangalavanam coastal wetland in Southern India. The wetland is a fragmented mangrove stand close to a large urban centre with high anthropogenic nitrogen inputs. The study found the wetland was a net source of N2O to the atmosphere with fluxes ranging between 17.5 to 117.9 µmol m-2 day-1 which equated to high N2O saturations of between 697 and 1794%. The average dissolved inorganic nitrogen inputs (80.1 ± 18.1 µmol L-1) and N2O emissions (59.2 ± 30.0 µmol m-2 day-1) were highest during the monsoon season when the rainfall and associated river water inputs and terrestrial runoff were highest. The variation in N2O dynamics was shown to be driven by the changes in rainfall, water column depth, salinity, dissolved oxygen, carbon, and substrate nitrogen. The study suggests that fragmented/minor mangrove ecosystems subject to high human nutrient inputs may be a significant component of the global N2O budget.
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Tree stems are an important and unconstrained source of methane, yet it is uncertain whether internal microbial controls (i.e. methanotrophy) within tree bark may reduce methane emissions. Here we demonstrate that unique microbial communities dominated by methane-oxidising bacteria (MOB) dwell within bark of Melaleuca quinquenervia, a common, invasive and globally distributed lowland species. In laboratory incubations, methane-inoculated M. quinquenervia bark mediated methane consumption (up to 96.3 µmol m-2 bark d-1) and reveal distinct isotopic δ13C-CH4 enrichment characteristic of MOB. Molecular analysis indicates unique microbial communities reside within the bark, with MOB primarily from the genus Methylomonas comprising up to 25 % of the total microbial community. Methanotroph abundance was linearly correlated to methane uptake rates (R2 = 0.76, p = 0.006). Finally, field-based methane oxidation inhibition experiments demonstrate that bark-dwelling MOB reduce methane emissions by 36 ± 5 %. These multiple complementary lines of evidence indicate that bark-dwelling MOB represent a potentially significant methane sink, and an important frontier for further research.
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Ciclo do Carbono , Melaleuca/metabolismo , Metano/metabolismo , Methylococcaceae/metabolismo , Microbiota/fisiologia , Melaleuca/microbiologia , Oxirredução , Casca de Planta/metabolismo , Casca de Planta/microbiologia , Árvores/metabolismo , Árvores/microbiologiaRESUMO
Nutrient and pesticide pollution are among the major threats to groundwater quality in agriculturally impacted aquifers. Understanding their legacy effects and drivers are important to protect aquifers from exposures to contamination. However, the complexities of groundwater flowpaths make it difficult to predict the time-scales of groundwater flow and contaminant transport. To determine these controls of groundwater nutrient and pesticides in an aquifer system underlying an intensive agricultural area in the Great Barrier Reef catchment, Australia, we sampled tritium (3H) to estimate groundwater-age, nutrient and pesticide concentrations to investigate groundwater contamination, and nitrogen (áº15N-NO3-) and oxygen (áº18O-NO3-) isotopes to determine groundwater nitrate dynamics. We, then, constructed high-resolution 3D geological and groundwater flow models of the aquifer system to determine the role of the geologic heterogeneity on the observed nutrient and pesticide concentrations. Groundwater 3H derived ages, and nutrient and pesticide concentrations did not follow distinct spatial trends. áº15N-NO3- and áº18O-NO3- values indicated that nitrification and denitrification processes influenced nitrate dynamics in the aquifer system; however, they were not solely able to explain the entire 3D variability. The 3D geologic modelling identified possible preferential flowpaths and perched systems, which helped to explain the observed groundwater-age, nutrient and pesticide variabilities. Old-groundwater (~100-years) was found in shallow depths (<15 m) where perched systems were identified. In areas with preferential flowpaths, young-groundwater (â1-year) with significant nitrate (~12 mg-N/L) and pesticides (up to 315 ng/L) concentrations were detected at deeper depths (>25 m), below perched and locally confined systems. Downward increasing groundwater-age, and decreasing nutrient and pesticide concentrations were detected in the unconfined aquifer, while old-groundwater (~160-years) and lower nitrate (<3 mg-N/L) and pesticides (<2 ng/L) concentrations were detected in the confined systems. This study demonstrates the importance of understanding both the geology and the hydrogeology of an area before deploying monitoring studies and/or making conclusions from tritium, nutrient and pesticide data alone.
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In coastal aquatic ecosystems, prokaryotic communities play an important role in regulating the cycling of nutrients and greenhouse gases. In the coastal zone, estuaries are complex and delicately balanced systems containing a multitude of specific ecological niches for resident microbes. Anthropogenic influences (i.e. urban, industrial and agricultural land uses) along the estuarine continuum can invoke physical and biochemical changes that impact these niches. In this study, we investigate the relative abundance of methanogenic archaea and other prokaryotic communities, distributed along a land use gradient in the subtropical Burnett River Estuary, situated within the Great Barrier Reef catchment, Australia. Microbiological assemblages were compared to physicochemical, nutrient and greenhouse gas distributions in both pore and surface water. Pore water samples from within the most urbanised site showed a high relative abundance of methanogenic Euryarchaeota (7.8% of all detected prokaryotes), which coincided with elevated methane concentrations in the water column, ranging from 0.51 to 0.68 µM at the urban and sewage treatment plant (STP) sites, respectively. These sites also featured elevated dissolved organic carbon (DOC) concentrations (0.66 to 1.16 mM), potentially fuelling methanogenesis. At the upstream freshwater site, both methane and DOC concentrations were considerably higher (2.68 µM and 1.8 mM respectively) than at the estuarine sites (0.02 to 0.66 µM and 0.39 to 1.16 mM respectively) and corresponded to the highest relative abundance of methanotrophic bacteria. The proportion of sulfate reducing bacteria in the prokaryotic community was elevated within the urban and STP sites (relative abundances of 8.0%- 10.5%), consistent with electron acceptors with higher redox potentials (e.g. O2, NO3-) being scarce. Overall, this study showed that ecological niches in anthropogenically altered environments appear to give an advantage to specialized prokaryotes invoking a potential change in the thermodynamic landscape of the ecosystem and in turn facilitating the generation of methane-a potent greenhouse gas.
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Archaea/isolamento & purificação , Estuários , Metano/metabolismo , Methanococcales/isolamento & purificação , Methylocystaceae/isolamento & purificação , Microbiota , Águas Salinas , Microbiologia da Água , Agricultura , Compostos de Amônio/metabolismo , Criação de Animais Domésticos , Archaea/metabolismo , Carbono/metabolismo , Ecossistema , Água Doce/análise , Água Doce/microbiologia , Gases de Efeito Estufa/análise , Habitação , Indústrias , Methanococcales/metabolismo , Methylocystaceae/metabolismo , Nitratos/metabolismo , Oxirredução , Queensland , Águas Salinas/análise , Salinidade , Sulfatos/metabolismo , Temperatura , Termodinâmica , Purificação da ÁguaRESUMO
The role of groundwater in transporting nutrients to coastal aquatic systems has recently received considerable attention. However, the relative importance of fresh versus saline groundwater-derived nutrient inputs to estuaries and how these groundwater pathways may alter surface water N:P ratios remains poorly constrained. We performed detailed time series measurements of nutrients in a tidal estuary (Hat Head, NSW, Australia) and used radium to quantify the contribution of fresh and saline groundwater to total surface water estuarine exports under contrasting hydrological conditions (wet and dry season). Tidally integrated nutrient fluxes showed that the estuary was a source of nutrients to the coastal waters. Dissolved inorganic nitrogen (DIN) export was 7-fold higher than the average global areal flux rate for rivers likely due to the small catchment size, surrounding wetlands and high groundwater inputs. Fresh groundwater discharge was dominant in the wet season accounting for up to 45% of total dissolved nitrogen (TDN) and 48% of total dissolved phosphorus (TDP) estuarine exports. In the dry season, fresh and saline groundwater accounted for 21 and 33% of TDN export, respectively. The combined fresh and saline groundwater fluxes of NO3, PO4, NH4, DON, DOP, TDN and TDP were estimated to account for 66, 58, 55, 31, 21, 53 and 47% of surface water exports, respectively. Groundwater-derived nitrogen inputs to the estuary were responsible for a change in the surface water N:P ratio from typical N-limiting conditions to P-limiting as predicted by previous studies. This shows the importance of both fresh and saline groundwater as a source of nutrients for coastal productivity and nutrient budgets of coastal waters.
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Catchment headwaters comprise the majority of all stream length globally, however, carbon (C) dynamics in these systems remains poorly understood. We combined continuous measurements of pCO2 and radon ((222)Rn, a natural groundwater tracer) with discrete sampling for particulate organic, dissolved organic and inorganic carbon (POC, DOC, and DIC) to assess the short-term carbon dynamics of a pristine subtropical headwater stream in Australia, over contrasting hydrologic regimes of drought, flash-flooding and recovery. Observations over 23days revealed a shift from carbon losses dominated by CO2 outgassing under conditions of low flow (66.4±0.4% of carbon export) to downstream exports of carbon during the flood (87.8±9.7% of carbon export). DOC was the dominant form of downstream exports throughout the study (DOC:DIC:POC=0.82:0.05:0.13). The broadest diel variability among variables occurred during the drought phase, with diel variability up to 662µatmd(-1) (or 27µM[CO2*]d(-1)), 17µMd(-1) and 268Bqm(-3)d(-1) for pCO2, dissolved oxygen and (222)Rn, respectively. Diel dynamics indicated multiple interrelated drivers of stream water chemistry including groundwater seepage and in-stream metabolism. The catchment exported terrestrial carbon throughout the field campaign, with a mean net stream flux of 4.7±7.8mmolCm(-2)(catchment area)d(-1) which is equivalent to 1.4±2.3% of the estimated local terrestrial net primary production. Our observations highlight the importance of accounting for hydrological extremes when assessing the carbon budgets and ecosystem metabolism of headwater streams, and provide a first estimate of aquatic carbon exports from a pristine Australian subtropical rainforest.
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Nitrous oxide (N2O) is an important greenhouse gas, but large uncertainties remain in global budgets. Mangroves are thought to be a source of N2O to the atmosphere in spite of the limited available data. Here we report high resolution time series observations in pristine Australian mangroves along a broad latitudinal gradient to assess the potential role of mangroves in global N2O budgets. Surprisingly, five out of six creeks were under-saturated in dissolved N2O, demonstrating mangrove creek waters were a sink for atmospheric N2O. Air-water flux estimates showed an uptake of 1.52 ± 0.17 µmol m(-2) d(-1), while an independent mass balance revealed an average sink of 1.05 ± 0.59 µmol m(-2) d(-1). If these results can be upscaled to the global mangrove area, the N2O sink (~2.0 × 10(8) mol yr(-1)) would offset ~6% of the estimated global riverine N2O source. Our observations contrast previous estimates based on soil fluxes or mangrove waters influenced by upstream freshwater inputs. We suggest that the lack of available nitrogen in pristine mangroves favours N2O consumption. Widespread and growing coastal eutrophication may change mangrove waters from a sink to a source of N2O to the atmosphere, representing a positive feedback to climate change.
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Atmosfera/química , Água Doce/química , Óxido Nitroso/análise , Áreas Alagadas , Poluentes Atmosféricos/análise , Austrália , Mudança Climática , Monitoramento Ambiental/métodos , Geografia , Nitrogênio/análise , Solo/químicaRESUMO
The remediation of four estrogenic endocrine-disrupting compounds (EDCs), estrone (E1), estradiol (E2), ethinylestradiol (EE2) and estriol (E3), was measured in saturated and unsaturated carbonate sand-filled columns dosed with wastewater from a sewage treatment plant. The estrogen equivalency (EEQ) of inlet wastewater was 1.2 ng L(-1) and was remediated to an EEQ of 0.5 ng L(-1) through the unsaturated carbonate sand-filled columns. The high surface area of carbonate sand and associated high microbial activity may have assisted the degradation of these estrogens. The fully saturated sand columns showed an increase in total estrogenic potency with an EEQ of 2.4 ng L(-1), which was double that of the inlet wastewater. There was a significant difference (P < 0.05) in total estrogenic potency between aerobic and anaerobic columns. The breakdown of conjugated estrogens to estrogenic EDCs formed under long residence time and reducing conditions may have been responsible for the increase in the fully saturated columns. This may also be explained by the desorption of previously sorbed estrogenic EDCs. The effect of additional filter materials, such as basalt sediment and coconut fibre, on estrogenic EDC reduction was also tested. None of these amendments provided improvements in estrogen remediation relative to the unamended unsaturated carbonate sand columns. Aerobic carbonate sand filters have good potential to be used as on-site wastewater treatment systems for the reduction of estrogenic EDCs. However, the use of fully saturated sand filters, which are used to promote denitrification, and the loss of nitrogen as N2 were shown to cause an increase in EEQ. The potential for the accumulation of estrogenic EDCs under anaerobic conditions needs to be considered when designing on-site sand filtration systems required to reduce nitrogen. Furthermore, the accumulation of estrogens under anaerobic conditions such as under soil absorption systems or leachate fields has the potential to contaminate groundwater especially when the water table levels fluctuate.