Porewater Nutrient Concentrations Research Articles

The porewater nutrient and heavy metal characteristics in sediment cores and their benthic fluxes in Daya Bay, South China

Nutrient and heavy metal (Fe, Mn, Ni, Cu, Pb, Zn, Cr, Cd and As) concentrations in porewater in sediment cores and their diffusive benthic fluxes were investigated in Daya Bay, South China, to study the accumulation and transfer of nutrients/metals at the sediment-water interface, and to discuss the impact of human activities on nutrients/metals. Nutrients and heavy metals displayed different profiles in porewater, which was mainly attributed to the distinct biogeochemical conditions in sediments. Total mean fluxes of nutrients (except NO3 and NO2) and metals in study area were positive, indicating nutrients and metals diffused from the sediment to overlying water, and sediment was generally the source of nutrients/metals. Human activities and the weak hydrodynamic force made nutrients/metals accumulate in sediment, so the sediment should be paid more attention to as the endogenesis of contamination in Daya Bay waters.

Sediment Biogeochemistry of Mesophotic Meadows of Calcifying Macroalgae

Mesophotic (low light) sands were studied in Hawaiian coastal waters (39–204 m water depth) from O‘ahu to Kaho‘olawe by sampling inside and outside of extensive macroalgal meadows of chlorophytes Halimeda kanaloana and Udotea sp. during September 2004, December 2004, and November 2006. Porewater nutrient concentrations in these permeable sediments were comparable to those in nearshore sands and were highly elevated at sediment depths available to holdfasts of some algae (5–10 cm); maximum levels were 3.0 µM reactive phosphorus, 33 µM nitrate, 0.70 µM nitrite, 38 µM ammonium, and 130 µM silicic acid. Benthic material is calculated to be the major source of organic matter driving diagenesis in these sediments. Vegetated sediments appeared more oxidizing than unvegetated sediments, and the presence of macroalgae, particularly Halimeda, was generally associated with higher sediment dissolved inorganic carbon levels. Halimeda-vegetated sediments generally had low dissolved inorganic nitrogen (DIN) levels compared to the Udotea-vegetated and non-vegetated sediments, consistent with the net N loss indicated by sediment stoichiometric relationships. In contrast, Udotea-vegetated sediments showed minimal apparent algal DIN uptake.

九龙江河口区养虾塘沉积物-水界面营养盐交换通量特征

PDF HTML阅读 XML下载 导出引用 引用提醒 九龙江河口区养虾塘沉积物-水界面营养盐交换通量特征 DOI: 10.5846/stxb201603130448 作者: 作者单位: 福建师范大学,福建师范大学,湿润亚热带生态-地理过程教育部重点实验室,福建师范大学 作者简介: 通讯作者: 中图分类号: 基金项目: 福建省基本科研专项重点资助项目（2014R1034-1）；国家自然科学基金资助项目（41671088，41371127）；福建师范大学校级创新团队资助项目（IRTL1205）；福建师范大学地理科学学院研究生出国（境）访学资助计划和地理科学学院研究生科研创新资助项目（GY201601） Temporal variation of nutrients fluxes across the sediment-water interface of shrimp ponds and influencing factors in the Jiulong River Estuary Author: Affiliation: Key Laboratory of Humid Sub-tropical Eco-geographical Process of Ministry of Education,School of Geographical Sciences,Research Centre of Wetlands in Subtropical Region,Fujian Normal University,Key Laboratory of Humid Sub-tropical Eco-geographical Process of Ministry of Education,School of Geographical Sciences,Research Centre of Wetlands in Subtropical Region,Fujian Normal University,Key Laboratory of Humid Sub-tropical Eco-geographical Process of Ministry of Education,School of Geographical Sciences,Research Centre of Wetlands in Subtropical Region,Fujian Normal University,Key Laboratory of Humid Sub-tropical Eco-geographical Process of Ministry of Education,School of Geographical Sciences,Research Centre of Wetlands in Subtropical Region,Fujian Normal University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:通过对九龙江河口区陆基养虾塘水样和沉积物样品采集分析及结合室内模拟实验，探讨了虾塘在不同养殖阶段沉积物-水界面营养盐通量时间变化特征及其主要影响因素。虾塘沉积物向上覆水体释放NOx--N（NO2--N和NO3--N）、NH4+-N和PO43--P能力均呈现随养殖时间推移而降低的特征。沉积物在养殖中期和后期分别呈现对上覆水体NOx--N和PO43--P的吸收现象，但总体表现为释放（平均通量分别为（1.87±1.15）、（1.58±0.52）mg m-2 h-1和（1.22±0.62）mg m-2 h-1）。沉积物-水界面溶解无机氮交换以NH4+-N为主（沉积物平均释放通量为（46.18±13.82）mg m-2 h-1）。沉积物间隙水与上覆水间的营养盐浓度差（梯度）及温度对上述交换通量的时间动态特征具有重要调控作用。研究结果表明养殖初期或中期沉积物较高的无机氮（尤其是NO2--N和NH4+-N）释放是养殖塘水质恶化的一个极具潜力的污染内源，可能会对虾的健康生长产生负面效应，控制沉积物无机氮释放是养虾塘养殖初期和中期重要的日常管理活动之一。 Abstract:Eutrophication is increasingly challenging the sustainability and healthy development of aquaculture. The effects of variations in nutrient dynamics remain unclear, including porewater nutrient concentrations and nutrient fluxes at the sediment-water interface (SWI), from aquaculture ponds globally, and particularly in China. In this study, temporal variation of the concentrations of nitrogen and phosphorus in porewater and their fluxes across the interface of sediment-water was investigated in the Jiulong River estuary, a subtropic estuary on the southeast coast of China. Overlying water, intact sediments, and sediment porewater were collected using sediment samplers from three shrimp ponds in June, August, and October 2015. Overlying water and sediment porewater nutrient analyses were performed using an automatic continuous flow analyzer. SONE (sediment oxygen and nutrient exchanges) incubation techniques were used to measure rates of nutrient fluxes (NO2--N, NO3--N, NH4+-N, and PO43--P). NO2--N, NO3--N, NH4+-N, and PO43--P concentrations in porewater ranged from 0.01 to 0.06, 0.06 to 0.22, 10.31 to 14.13, and 0.05 to 0.35 mg/L, respectively, with mean values of 0.04, 0.15, 11.83, and 0.17 mg/L. Higher NO2--N and NO3--N concentrations in porewater occurred during June and higher NH4+-N and PO43--P concentrations occurred during August. The NO2--N, NO3--N, NH4+-N, and PO43--P fluxes across the interface of sediment-water ranged from -2.96 to 7.60, -1.00 to 3.15, -0.79 to 4.95, and 19.23 to 91.73 mg m-2 h-1, respectively. The fluxes of nitrogen and phosphorus nutrients across the interface of sedimentwater showed significant temporal variation, with higher nutrient release fluxes during June and lower fluxes during October. The mean fluxes of NO2--N, NO3N, and PO43--P from the sediment to overlying water were (1.87±1.15), (1.58±0.52), and (1.22±0.62) mg m-2 h-1, respectively, indicating that the shrimp pond sediment acted as a nitrogen and phosphorus release source. Dissolved inorganic nitrogen (DIN) release dominated by excess NH4+-N, and the NH4+-N flux from sediment was (46.18±13.82) mg m-2 h-1. Pearson's correlation analysis showed that the temporal variation of nitrogen and phosphorus fluxes were significantly positively correlated with sediment temperature (P < 0.05), but significantly negatively correlated with shrimp biomass (P < 0.05). The results suggest that the temporal variation of nutrients fluxes across the sediment-water interface in shrimp ponds was controlled by the nutrient concentration gradient, sediment temperature, and the foraging and metabolic activity of shrimp. This study highlighted that the relatively high DIN (NO2--N and NH4+-N) release from sediment during the initial and middle stages of aquaculture could be a potential pollution source in shrimp ponds, which might increase the risk of shrimp mortality. 参考文献 相似文献 引证文献

Varying Inundation Regimes Differentially Affect Natural and Sand-Amended Marsh Sediments.

Climate change is altering sea level rise rates and precipitation patterns worldwide. Coastal wetlands are vulnerable to these changes. System responses to stressors are important for resource managers and environmental stewards to understand in order to best manage them. Thin layer sand or sediment application to drowning and eroding marshes is one approach to build elevation and resilience. The above- and below-ground structure, soil carbon dioxide emissions, and pore water constituents in vegetated natural marsh sediments and sand-amended sediments were examined at varying inundation regimes between mean sea level and mean high water (0.82 m NAVD88 to 1.49 m NAVD88) in a field experiment at Laws Point, part of the Plum Island Sound Estuary (MA). Significantly lower salinities, pH, sulfides, phosphates, and ammonium were measured in the sand-amended sediments than in the natural sediments. In natural sediments there was a pattern of increasing salinity with increasing elevation while in the sand-amended sediments the trend was reversed, showing decreasing salinity with increasing elevation. Sulfide concentrations generally increased from low to high inundation with highest concentrations at the highest inundation (i.e., at the lowest elevations). High pore water phosphate concentrations were measured at low elevations in the natural sediments, but the sand-amended treatments had mostly low concentrations of phosphate and no consistent pattern with elevation. At the end of the experiment the lowest elevations generally had the highest measures of pore water ammonium. Soil carbon dioxide emissions were greatest in the sand-amended mesocosms and at higher elevations. Differences in coarse root and rhizome abundances and volumes among the sediment treatments were detected with CT imaging, but by 20 weeks the natural and sand-amended treatments showed similar total belowground biomass at the intermediate and high elevations. Although differences in pore water nutrient concentrations, pH, salinity, and belowground root and rhizome morphology were detected between the natural and sand-amended sediments, similar belowground productivity and total biomass were measured by the end of the growing season. Since the belowground productivity supports organic matter accumulation and peat buildup in marshes, our results suggest that thin layer sand or sediment application is a viable climate adaptation action to build elevation and coastal resiliency, especially in areas with low natural sediment supplies.

Experimental test of N-limitation for Zostera nigricaulis seagrass at three sites reliant upon very different sources of N

The hypothesis that seagrasses may be nitrogen-limited has been examined in a number of studies, particularly in oligotrophic waters where nutrients are typically scarce. Here we examined nitrogen-limitation for the temperate seagrass, Zostera nigricaulis, at three sites where seagrasses use very different sources of nitrogen (N) based on stable isotopes of N: Swan Bay - fixed and recycled N, Kirk Point - N from treated sewage, and Blairgowrie - N from catchment. Dramatic changes to source inputs during a recent prolonged drought were linked to seagrass loss in parts of the bay dependent on catchment inputs. Here we test to what extent seagrasses dependent on different sources of N are N-limited, by enriching sediment pore water levels. Sediment pore water nutrient levels varied naturally between the sites by a factor of 14, from Swan Bay (highest) to Blairgowrie (lowest), and were much higher than water column levels. There was a detectable enrichment effect for pore water nutrient concentrations within the treatment plots after one month, although the effect was greatest for the Blairgowrie site, and was most pronounced for NH4 levels. There was a significant enrichment effect for seagrass growth after 5months, but only at a single site, Blairgowrie. Seagrass cover, above-ground biomass and mean leaf length were substantially higher in the treatment than control plots at the Blairgowrie site, but not at the other two sites. Higher %N content and lower δ15N in the leaf tissues at Blairgowrie and Kirk Point indicated that N released from the fertilizer had been assimilated by the seagrass at both these sites, but in the case of Kirk Point this did not translate into greater seagrass growth. The results suggest that seagrasses at Blairgowrie, in the southern part of the bay, are highly N-limited. This is a region that is isolated from the major source of N (the catchment) utilised by seagrass in this part of the bay. The pattern of N-limitation in this and a previous study is consistent with regions that displayed major fluctuations in seagrass cover during the ‘Millennium’ drought from 1997 to 2009. Consequently, predicted decreases in long-term rainfall in south-eastern Australia could have negative consequences for seagrass extent in areas that are N-limited.

Rapid colonization of degraded mangrove habitat by succulent salt marsh

Long-term closure of the Kobonqaba Estuary mouth to the sea resulted in high water levels, inundation of pneumatophores and die-back of the mangroves specifically, Avicennia marina. The recovery of the mangroves was measured by assessing changes in vegetation cover and sediment characteristics along transects and all mangroves present in the estuary were described in terms of height, diameter at breast height and phenology. Measurements were made in 2011, 2012, 2013 and 2015. Surviving adult trees were producing propagules and showed that the forest would be able to regenerate if the seedlings established and were able to survive the environmental conditions. However there may be competition from salt marsh plants which increased in average cover from 0% in 2011 to 18.9% (2013) and 50% in 2015. Sediment characteristics changed over the study period with more oxic conditions in 2013 and 2015 (57.6 and 62.3mV) compared to 2011 and 2012 (−189 to −148mV) and organic matter decreased from 18.4% in 2011 to 9.8% in 2015. High initial porewater nutrient concentrations in 2013 promoted salt marsh growth. A particular sequence of events was recorded for the establishment of salt marsh in this previous mangrove habitat where stabilization of sediment by microphytobenthos and macroalgae was the key to further colonization by emergent macrophytes.

Biogeochemistry and Nutrient Limitation of Microbial Biofilms in Devils Hole, Nevada

Abstract Little is known about the role of microbial biofilms in nutrient cycling and ecosystem processes within desert springs. However, biofilms produce microscale physicochemical variation important to ecosystem function. We used microelectrodes to measure microscale physicochemical (temperature, pH, O2, and H2S) heterogeneity in biofilms at Devils Hole, Nevada. Additionally, we measured water column and pore water nutrient concentrations in 2 autotrophic (Spirogyra, cyanobacteria) and 1 heterotrophic (Beggiatoa) biofilm types. Spirogyra and cyanobacteria followed similar physicochemical trends; however, Spirogyra had more pronounced diurnal and seasonal variation. Oxygen concentrations within the biofilms varied with sample month, light availability, and biofilm type. We also assessed the nutrient limitation of desert spring microbial biofilms using a nutrient-diffusing substrata experiment. Autotrophic and heterotrophic biofilms responded differently to nutrient treatments. The differences between cy...

Biogeochemistry of dissolved inorganic carbon and nutrients in seagrass (Zostera noltei) sediments at high and low biomass

Nutrient recycling is highly controlled by benthic macrophytes in shallow coastal zones. In seagrass bed, this recycling mainly occurs in sediment porewater, which is considered to be the main source of nutrients for plant growth. This work investigated the effect of a Zostera noltei meadow on the biogeochemistry of inorganic nutrients and carbon in vegetated sediments of the Arcachon Bay. We characterized the vertical distributions of dissolved inorganic C (DIC), NH4+, dissolved inorganic P (DIP) and redox-sensitive particulate inorganic P in bare sediments and in sediments heavily or sparsely colonised by Z. noltei. The obtained concentration profiles were used to calculate benthic production rates or particulate stocks. The porewater nutrient concentrations measured in vegetated sediments were depleted by a factor of 10–100 compared to bare sediments. The concentrations of NH4+, DIP and DIC exhibited a strong vertical zonation reflecting successive layers of intense production or consumption within the root zone often considered and sampled as a homogeneous zone. The deeper root zone showed higher consumption rates of dissolved inorganic nutrients compared to the upper root zone as young roots growing deeper in the sediment played a major role in nutrient plant uptake. A consumption of DIC was consistently recorded in the root zone. We hypothesized that this could result from a transport of CO2 from roots to leaves supporting photosynthetic activity as suggested for freshwater plants. We pointed out to what extent the influence of seagrasses changed between sparse and dense meadows. This work emphasizes the high spatial variability in biogeochemical processes occurring at small scale within the root zone or between dense and sparse seagrass patches. Such a variability should be considered when dealing with the role of seagrass in biogeochemical cycles, especially in the context of global decline of seagrass.

Herbicide management of invasive cattail (Typha × glauca) increases porewater nutrient concentrations

Invasive wetland plants are the primary targets of wetland management to promote native communities and wildlife habitat, but little is known about how commonly implemented restoration techniques influence nutrient cycling. We tested how experimental mowing, herbicide application, and biomass harvest (i.e., removal of aboveground biomass) treatments of Typha-invaded mesocosms altered porewater nutrient (NO3 −, NH4 +, PO 4 −3 ) concentration and supply rate, vegetation response, and light penetration to the soil surface. We found that while herbicide application eliminated the target species, it also reduced native plant density and biomass, as well as increased porewater nutrient concentration (PO 4 −3 , NO3 −) and supply rates (N, P, K) up to a year after treatments were implemented. Because herbicide application promotes nutrient enrichment, it may increase the likelihood of reinvasion by problematic wetland invaders, as well as cause eutrophication and deleterious algal blooms in adjacent aquatic systems. Our data suggest that biomass harvest should be considered by managers aiming to reduce Typha abundance without eradicating native diversity, avoid nutrient leaching, as well as possibly utilizing biomass for bioenergy.

Sedimentary organic matter contents and porewater chemistry at upper bathyal depths influenced by the 2011 off the Pacific coast of Tohoku Earthquake and tsunami

Sedimentary organic matter and porewater geochemistry at upper bathyal depths off Tohoku, Japan, were investigated 1 year after the 2011 off the Pacific coast of Tohoku Earthquake. Total organic carbon (TOC) and total nitrogen (TN) concentrations, organic carbon and nitrogen isotopic compositions, dissolved oxygen (DO) concentrations, and bottom water and porewater nutrient concentrations were examined in sediment core samples collected from eight upper bathyal stations. Event deposits 1 to 7 cm thick were observed at all sampling stations, indicating that a vast area off Tohoku has been influenced by sedimentological events caused by the earthquake or subsequent tsunami. Both TOC and TN concentrations were lower in coarse-grained event deposits. Carbon and nitrogen isotopic composition, together with the C/N ratio, suggested that the event deposits, including turbidites, were composed of local sediments that had been transported relatively short distances. Nutrient fluxes across the sediment–water interface correlated with surface TOC and bottom water DO concentrations. However, event deposit thickness showed no correlation with oxygen or nutrient fluxes. The organic matter content of the event deposits was similar to that in the underlying sediments at each site, and thus no apparent effect of event deposits on nutrient fluxes was observed. Our results suggest that biogeochemical cycles in sediments of disturbed areas are affected not only by event deposit thickness, but also by the source of the event deposits.

Underestimation of nutrient fluxes due to possible bacterial activity during a core incubation experiment

Examinations of sediment core incubation and calculations of diffusive nutrient fluxes based on the difference between the nutrient concentration in pore water and that in the overlying water were carried out to evaluate the benthic fluxes of nutrients such as phosphate (PO4), ammonium (NH4), and silicic acid [Si(OH)4] from the sediment–water interface. Test surface-sediment samples were collected in the western area of the Seto Inland Sea in October 2013 and January 2014. They were incubated onboard the ship for intervals of approximately 40–90 h, and changes in the concentrations of nutrients in the overlying water with incubation time were monitored. Furthermore, in order to inhibit bacterial activity, sodium azide (NaN3) was added to the overlying water of another incubation system, whereupon nutrient concentrations in the overlying water were observed to increase linearly with incubation time. On the other hand, when NaN3 was not added, a linear increase was observed in the Si(OH)4 concentration but not in those of PO4 and NH4. The calculated diffusive fluxes generally agreed with those obtained from core incubation with the addition of NaN3. These findings suggest that the elution of PO4 and NH4 from the sediment–water interface during a core incubation experiment can be affected by bacterial activity, which could potentially lead to the underestimation of benthic fluxes. Therefore, great care should be taken when carrying out incubations of surface sediment, and they should be performed along with calculations of diffusive fluxes.

Embayment scale assessment of submarine groundwater discharge nutrient loading and associated land use

A shoreline survey of porewater nutrient concentrations and 222Rn surface water activities was performed in Port Jefferson Harbor, NY, an embayment of Long Island Sound. Submarine groundwater discharge (SGD) was calculated for individual shoreline segments; shallow porewater nutrient concentrations were applied to calculated groundwater flux values in order to spatially depict the nutrient flux to overlying harbor water. Nitrate was the dominant form of inorganic nitrogen as porewater concentrations of ammonium were negligible. Land use analysis showed that nitrate to phosphate ratios (N:P) in SGD were positively correlated with medium to high development of inland aquifer watersheds. A multivariate regression model was developed which describes 79% of the variability in shoreline nitrate discharge. Three modes of nutrient transport were observed; 1) High SGD rates coupled with nutrient rich groundwater derived from high density development, 2) moderate SGD rates coupled with low nutrient groundwater from low density development/forested watersheds and 3) negligible SGD rates associated with recirculated seawater adjacent to low density development areas. Transport mode 1 dominated total SGD nitrate inputs primarily due to steep hydraulic gradient, a characteristic of tunnel valleys in glacial deposits, which highlights the critical role hydrogeology plays in groundwater nitrogen loading to surface water. Total nitrate inputs to the harbor from shoreline SGD alone are 980 mol d−1, similar to average daily sewage treatment plant nitrogen inputs of 870 mol d−1. The techniques used in this study represent an effective methodology for calculating SGD derived nutrient loads where a surface water nutrient source is present.

Interlinked seasonal variation in biogenic nutrient fluxes and pore-water nutrient concentrations in intertidal sediments

The seasonal variation in biogenic fluxes of NH4 +, PO4 3− and SiO2 calculated from the nutrient excretion rates of dominant bivalves (Ruditapes philippinarum and Arcuatula [=Musculista] senhousia), and pore-water nutrient (NH4 +, PO4 3−, SiO2 and NO3 − + NO2 −), sedimentary acid-volatile sulfide (AVS) and benthic chlorophyll-a (Chl-a) concentrations was assessed on an intertidal sandflat in the Seto Inland Sea (Japan) from summer 1994 to autumn 1995. In spite of the large variability between sampling dates and stations, significant correlations between biogenic nutrient fluxes and pore-water nutrient concentrations were found, suggesting a seasonal linkage between bivalve-mediated biological processes and chemical features of sediments. This linkage was stronger in surface (0–0.5 cm) than subsurface (0.5–2 cm) sediments, consistent with the autoecological characteristics of R. philippinarum and A. senhousia inhabiting the uppermost sediment layer. Significant temporal variation in pore-water NO3 − + NO2 −, sedimentary AVS and benthic Chl-a concentrations was also found, which was related to both occasional extreme events (e.g., dystrophy) and alternating periods of production and decomposition. This study may serve twofold in (1) contributing to unravel the ecological structure and functioning of natural tidal flats, and the scale of seasonal variability in biotic and sedimentary parameters and (2) providing useful information for assessing the effectiveness of the physico-chemical and biological structure of artificial tidal flats which are growing in number and extension worldwide.

Eutrophication threatens Caribbean seagrasses – An example from Curaçao and Bonaire

Seagrass beds are globally declining due to human activities in coastal areas. We here aimed to identify threats from eutrophication to the valuable seagrass beds of Curaçao and Bonaire in the Caribbean, which function as nursery habitats for commercial fish species. We documented surface- and porewater nutrient concentrations, and seagrass nutrient concentrations in 6 bays varying in nutrient loads. Water measurements only provided a momentary snapshot, due to timing, tidal stage, etc., but Thalassia testudinum nutrient concentrations indicated long-term nutrient loads. Nutrient levels in most bays did not raise any concern, but high leaf % P values of Thalassia in Piscadera Bay (∼0.31%) and Spanish Water Bay (∼0.21%) showed that seagrasses may be threatened by eutrophication, due to emergency overflow of waste water and coastal housing. We thus showed that seagrasses may be threatened and measures should be taken to prevent loss of these important nursery areas due to eutrophication.

The Trophic State of Patagonian Argentinean Lakes and its Relationship with Depth Distribution in Sediment Phosphorus

The parameters used to determine the trophic state of a water body are: total phosphorus (TP),transparency (Secchi disk depth) and chlorophyll a. However, these parameters show strong seasonalfluctuations which may hinder the estimation of trophic state. Some authors have proposed that sediments be used as an additional tool to evaluate the trophic state of a water body. The aim of this study was to determine the depth distribution of sediment TP in relation with the lake trophic state. Nine sediment corers from water bodies located in Patagonian Region (Argentina) were studied. The nutrient concentrations in pore water and in sediments were analyzed. The results obtained showed that there is a relationship between the depth distribution of sediment TP and the trophic state for all studied environments. Two exceptions were noted to this general pattern (Lakes Caviahue and Lacar). Our findings indicate that both pore water and sediments could be considered as the best parameters to estimate the tropic state of a water body compared to the water column.

BIOB: A mathematical model for the biodegradation of low solubility hydrocarbons

Modeling oil biodegradation is an important step in predicting the long term fate of oil on beaches. Unfortunately, existing models do not account mechanistically for environmental factors, such as pore water nutrient concentration, affecting oil biodegradation, rather in an empirical way. We present herein a numerical model, BIOB, to simulate the biodegradation of insoluble attached hydrocarbon. The model was used to simulate an experimental oil spill on a sand beach. The biodegradation kinetic parameters were estimated by fitting the model to the experimental data of alkanes and aromatics. It was found that parameter values are comparable to their counterparts for the biodegradation of dissolved organic matter. The biodegradation of aromatics was highly affected by the decay of aromatic biomass, probably due to its low growth rate. Numerical simulations revealed that the biodegradation rate increases by 3–4 folds when the nutrient concentration is increased from 0.2 to 2.0mgN/L.

Spartina alterniflora and invasive Phragmites australis stands have similar greenhouse gas emissions in a New England marsh

Salt marshes are critically important for a range of ecosystem services including nutrient filtration and carbon sequestration. Despite this, salt marshes are subjected to a variety of anthropogenic impacts, many with negative consequences. One impact is the introduction and subsequent proliferation of invasive species. An exotic strain of Phragmites australis has invaded salt marshes on the U.S. East Coast, affecting biodiversity, hydrology, and biogeochemistry. We quantified the difference between P. australis and native S. alterniflora in greenhouse gas emissions, net primary productivity, and biogeochemical parameters in sediment and porewater. Although we observed differences between the species (P. australis had greater biomass, drier and cooler sediments, and lower porewater nutrient concentrations), we observed no differences in greenhouse gas emissions. Vegetated and unvegetated plots had similar fluxes of methane (CH4) and nitrous oxide (N2O), but very different fluxes of carbon dioxide (CO2) due to photosynthesis. Fluxes of the three gases examined were related to sediment temperature and live biomass. In addition, CH4 fluxes were linked to salinity while N2O fluxes were linked to photosynthetically active radiation. CO2 fluxes varied as expected over the seasons. Rates of CH4 production were generally low and typical of salt marshes, but showed a wide variation demonstrating the high spatial heterogeneity of CH4 production. The marsh in this study was not a significant sink or source of N2O, although small fluxes of N2O were detected on occasion. This study confirms that salt marshes with relatively low nitrogen impacts are not important contributors of N2O to the atmosphere.

Spatial and seasonal variations of nutrients in sediment profiles and their sediment-water fluxes in the Pearl River Estuary, Southern China

Three cruises were launched in the Pearl River Estuary (PRE) in 2005 to investigate the biogeochemical cycling of nutrients associated with early diagenesis related to degradation of organic matter. Seasonal and spatial variations of pore water nutrient concentrations and profile patterns in sediments were studied. Nutrient fluxes at the sediment-water interface (SWI) were measured by incubation experiments, and we here discussed the accumulation and transformation processes of nutrients at the SWI. The nutrients generally decreased from the Pearl River outlets downstream, indicating anthropogenic influences on the nutrient inputs in the estuary. NO3-N concentration was the highest of the three forms of DIN (dissolved inorganic nitrogen, the sum of NH4-N, NO3-N and NO2-N) in the overlying water, and NH4-N was the main component of DIN in pore water. The gradual increase of NH4-N and the rapid decrease of NO3-N with sediment depth provided the evidence for anaerobic conditions below the SWI. Negative fluxes of NO3-N and positive fluxes of NH4-N were commonly observed, suggesting the denitrification of NO3-N at the SWI. The DIN flux direction suggested that the sediment was the sink of DIN in spring, however, the sediment was generally the source of DIN in summer and winter. PO4-P distribution patterns were distinct while SiO4-Si inconspicuously varied in sediment profiles in different seasons. The flux results indicated that PO4-P mainly diffused from the water column to the sediment while SiO4-Si mainly diffused from the sediment to the water column. Generally, the incubated fluxes were the coupling of diffusion, bioturbation and biochemical reactions, and were relatively accurate in this study.

Biogeochemical effects of simulated sea level rise on carbon loss in an Everglades mangrove peat soil

Saltwater intrusion and inundation can affect soil microbial activity, which regulates the carbon (C) balance in mangroves and helps to determine if these coastal forests can keep pace with sea level rise (SLR). This study evaluated the effects of increased salinity (+15 ppt), increased inundation (−8 cm), and their combination, on soil organic C loss from a mangrove peat soil (Everglades, Florida, USA) under simulated tides. Soil respiration (CO2 flux), methane (CH4) flux, dissolved organic carbon (DOC) production, and porewater nutrient concentrations were quantified. Soil respiration was the major pathway of soil organic C loss (94–98%) and was approximately 90% higher in the control water level than the inundated treatment under elevated salinity. Respiration rate increased with water temperature, but depended upon salinity and tidal range. CH4 flux was minimal, while porewater DOC increased with a concomitant, significant decline in soil bulk density under increased inundation. Porewater ammonium increased (73%) with inundation and soluble reactive phosphorus increased (32%) with salinity. Overall, the decline in soil organic C mineralization from combined saltwater intrusion and prolonged inundation was not significant, but results suggest SLR could increase this soil’s susceptibility to peat collapse and accelerate nutrient and DOC export to adjacent Florida Bay.

Biogeochemical Recovery of Oligohaline Wetland Soils Experiencing a Salinity Pulse

Oligohaline wetlands exist at a dynamic interface along a river-to-estuary gradient where salinity changes frequently due to fluctuating tidal cycles and weather events. Large storms can cause short-term saltwater intrusion into these low-lying coastal areas, exposing oligohaline wetland plants and soils to above-normal salinities and severe stress on wetland organisms. The objective of this study was to determine how oligohaline wetland soils respond to a single pulse saltwater intrusion, similar to what may occur during hurricane-associated storm surge. Soil response variables were measured in intrusion-Impacted and Reference soils before, during, and after a 6-wk saltwater intrusion event to determine potential impacts on microbial biomass and activity and associated nutrient dynamics. We observed no significant change in basal CO₂ or CH₄ production in oligohaline soils (interstitial salinity = 1.3 ± 0.1 practical salinity units [psu]; mean ± 1 SD) exposed to 20 psu saltwater, while substrate-induced methanogenesis was negatively correlated with salinity. Microbial biomass C (MBC) responded positively to saltwater intrusion by doubling in concentration at the 0- to 5-cm depth interval. Saltwater intrusion had no impact on porewater nutrient concentrations; however, extractable NH₄⁺ decreased as salinity increased. Although some significant changes in microbial activity, abundance, and nutrient availability occurred due to saltwater intrusion, these impacts were generally transient, with post-intrusion conditions resembling pre-intrusion conditions. These results suggest that short-term and transient saltwater intrusion may have little longer-term effect on wetland soil biogeochemistry. However, compounding effects of frequent saltwater intrusion pulses due to strong, regularly occurring storm events could cause longer-lasting shifts in biogeochemical functioning of these wetlands.