Phosphorus fractionation in soil and sediments along a continuum from agricultural fields to nearshore lake sediments: Potential ecological impacts

The movement of phosphorus (P) from agricultural fields to streams and deposition in the nearshore of the lake presents a continuum of related physical and chemical properties that act to partition P into different physico-chemical fractions. We investigated changes in soil and sediment P fractionation as material was eroded from predominantly agricultural fields, transported via stream sediments, and deposited in a nearshore lake environment. Total phosphorus content of the soils and sediment decreased from field soils with an average concentration of 553.81 mg P kg^? 1 to 202.28 mg P kg^? 1 in stream sediments to 67.47 mg P kg^? 1 in lake sediments. Significant changes in P fractionation occurred during erosion, transport, and deposition of the particulate or sediment phase. The fractionation of P within the soils and sediments changed significantly from aluminum and organic matter associated P dominant in field soils to calcium associated P dominant in nearshore lake sediments. Various physical and chemical processes appear to be responsible for these transformations which impact the mobility and bioavailability of P. A significant amount of P was lost from field soils as they were transported and deposited. This P has either become available to biota or deposited in deeper portions of the lake system. Ultimately, the impact of P export on the nearshore lake environment may be influenced by the changes in P fractionation that occurred during transport and deposition and by the influence of macrophytes on the biogeochemical cycling of P in the sediment.     

Sediment Toxicity from Copper in the Torch Lake (MI) Great Lakes Area of Concern

Torch Lake (MI) is a Federal Superfund Site and a Great Lakes Area of Concern. Torch Lake was impacted by over 200 million tons of copper rich mine tailings that were deposited in and along the shores of the lake. Twenty percent of the volume of the lake was displaced and the sediments have high concentrations of copper (1,000 mg/kg dry weight on average).Pore water from four sediment cores was analyzed at incremental depths for copper, total organic carbon, and toxicity using the Microtox^® 90% Comparison Test. Cores were also analyzed for copper and organic matter in the dry sediments. Statistical evaluation of data indicated that the upper sediments compared to the deeper sediments: 1) were less toxic (49% light loss versus 68%); 2) contained less pore water copper (0.59 mg/L vs. 0.81 mg/L); 3) had a higher percent organic matter (2.2% vs. 1.6%); and, 4) had no difference in the solid phase copper concentrations.Further evaluation of the sediment toxicity through direct comparison to copper chloride standards demonstrated that all pore water samples had reduced toxicity. The reduced toxicity of the pore water samples was reproduced by adding synthetic organic carbon to the copper chloride standards. These findings have implications for the EPA's No Action alternative for the sediments of Torch Lake. In making their recommendation, the EPA cites that preliminary data (believed to be obtained from nearby Portage Lake) shows that the sediments of Torch Lake are being covered and detoxified by natural sedimentation. However, total copper concentrations in the sediments from the south basin of Torch Lake do not indicate that the sediments are being covered and diluted by natural organic matter laden particles. Also, detoxification may be difficult to demonstrate without a baseline of sedimentation readings for comparison. In fact, solid phase copper concentrations may remain high due to scouring and erosion of surrounding stamp sand beaches or the steep side walls of the lake. This instability of particles has important implications for future restoration and monitoring activities in Torch Lake.     

Stable carbon and nitrogen isotopic signatures of organic matter sources in near-shore areas of Lake Victoria,East Africa

Stable isotope ratios of organic carbon and nitrogen (δ¹³C and δ¹⁵N) were measured in suspended particulate matter (SPM) and sediment in the near-shore areas of Tanzanian waters of Lake Victoria (LV) to identify the various sources of organic matter in different areas of the lake. Spatial variations in δ¹³C, δ¹⁵N, and C/N ratios in SPM and sediments in inshore areas were due to differences in the proportions and sources of autochthonous or allochthonous matter. Watershed characteristics, such as urbanization, and lake characteristics, such as algal blooms, also immensely influenced the stable isotope signal of the organic matter in sediments. Stable C and N ratios showed that inshore areas in bays without pronounced fluvial input were dominated by autochthonous planktonic organic matter; conversely, for bays receiving significant fluvial inflows, the composition of organic matter depended on the extent of preservation of shoreline vegetation. Signals resulting from input of anthropogenic organic waste as a result of urbanization were distinguishable from natural sources. This work demonstrates the potential to discriminate between input sources of organic material into lakes using stable isotope signals in sediment and suspended particulate matter.     

Estimates of the remineralization and burial of organic carbon in Lake Baikal sediments

Sediment cores collected from several stations throughout Lake Baikal in water depths from 100 m off the Selenga River delta to the deepest basin of the lake (~1640 m), have been analyzed for sedimentary organic carbon, nitrogen, and the remineralized components in pore water. The organic carbon content of surface sediments generally varied from 2.3 to 3.2% by weight, and profiles typically showed an exponential decrease in both organic carbon and nitrogen in the upper 20–30 cm of the sediment column. Steady state models of organic matter diagenesis yield first order decomposition rate constants which range from 0.0009 to 0.022 y⁻¹. The calculated residence times for the metabolizable fraction of the organic matter in these sediments increases roughly with increasing water depth and is on the order of 50–300 years. Pore water concentration profiles were determined for dissolved inorganic carbon, dissolved organic carbon (DOC), methane, and dissolved ammonium. At depth (25–30 cm) methane concentrations ranged from 50 to 800 μmol L_pw⁻¹ and DOC from 400 to 900 μmol L_pw⁻¹. Estimation of carbon recycling rates based upon diffusion along pore water concentration gradients at the sediment-water interface, indicate that combined DOC and methane fluxes generally contribute <15% of the overall turnover of sedimentary organic carbon. Comparisons to Laurentian Great Lakes environments show trends in sediment deposition, organic matter remineralization, and the time scales of carbon recycling across nearly two orders of magnitude with the fraction of organic content buried generally decreasing with decreasing sedimentation rates.     

宜兴三氿沉积物氮形态分布及其影响因素

为了解宜兴三氿(西氿、东氿和团氿)沉积物氮形态分布及其影响因素,采用连续分级提取法对三氿12个采样点表层沉积物样品中各种形态氮含量进行测定,探讨了不同形态氮的空间分布特征及影响因素。结果表明:总氮的空间分布与沉积物有机质分布存在明显的一致性,团氿含量较高,东、西氿含量较低且基本持平;可转化态氮含量占总氮的59.5%,对水体潜在危害较大,空间分布呈现出西氿最大、东氿次之、团氿最低的趋势;可转化态氮中4种形态氮含量大小顺序为弱酸可提取态氮、离子交换态氮、强碱可提取态氮、强氧化剂可提取态氮,弱酸可提取态氮为可转化态氮的优势形态;沉积物有机质与总氮和强氧化剂可提取态氮呈极显著正相关关系(P 0.01),pH值与总氮呈显著负相关关系(P 0.05);上覆水总氮与离子交换态氮呈极显著正相关关系(P 0.01),与可转化态氮呈显著正相关关系(P 0.05)。     

Temporal and spatial patterns based on sediment and sediment–water interface characteristics along a cascade of reservoirs (Paranapanema River, south-east Brazil)

Physical and chemical characteristics of the sediments in a cascade of eight reservoirs located in the Paranapanema River (south‐east Brazil) were analysed during two consecutive years during summer (January), autumn (April), winter (July) and spring (October) of 2000 and 2001, respectively. The granulometric texture, organic matter content and nutrient concentration (total nitrogen and phosphorus) were determined in the superficial sediment of 19 sampling stations, as well as the temperature, dissolved oxygen, pH, conductivity and redox potential in the bottom layer of the water column. Seasonal and spatial changes were observed for both years, especially for organic matter and nutrient concentrations. Three different areas could be identified along the river, which corresponded to the upper, middle and lower Paranapanema basin. The first area was characterized by an increase of nutrients and organic matter in the sediments and a decrease of temperature and dissolved oxygen in the downstream direction. The second one represented a region where fluctuations in nutrient and organic matter concentrations and a reduction in dissolved oxygen were observed. In the third area, there was an increase in nutrient and organic matter in the sediments and also an increase in temperature and dissolved oxygen towards the river mouth. The results of the principal components analysis, using water and sediments variables, showed the ordination of sampling stations by periods: wet (January–April) and dry (July–October) during 2000. This pattern was also verified during 2001, but with slight changes, probably due to the increase in the rains which would have produced certain homogenization effects along the river.     

Sediment distribution and accumulation in Lake Naivasha,Kenya over the past 50 years

Although surface waterbodies are water sources for socio‐economic activities and ecosystems, their functions are threatened by sedimentation. Sedimentation of lakes and reservoirs can result in a loss of storage capacity and altered water quality. The present study assessed the sedimentation status of Lake Naivasha, Kenya, based on sediment distribution and accumulation over the past 50 years, using a Bathymetric Survey System (BSS). The BSS uses multi‐frequency Acoustic Profiling System (APS) to map recently deposited sediments. Sediment core samples were collected with a vibe‐ coring device and dated. Sediment layers corresponding to a period of the past 20 and 50 years were identified. Sediment cores and acoustic images were subsequently used to determine sediment thickness within the lake. The collected depth data from multi‐frequency APS, and dated cores were processed in DepthPic and Surfer software. The sediment depth was extracted in DepthPic, while the sediment volume and distribution were generated from Surfer software. The results from present study indicated that sediment distribution varied from one part of the lake to another for the past 20 and 50 years. High sediment thickness observed in the south‐west and eastern parts of the lake. Between 1996–2016 and 1966–2016 periods, the maximum accumulated sediment thickness was found to be about 0.55 and 1.9 m, with an average sediment thickness of 0.25 and 0.56 m, respectively. The mean sediment load corresponding to the 1966–1996 and 1996–2016 periods was 2.78 × 10⁵ and 4.61 × 10⁵ t/year, respectively. It was found that sediment load into Lake Naivasha has been increasing in the recent past. Based on the present the study, it was found that combined use of BSS, sediment cores and dating can be adopted in many lakes and reservoirs to determine sediment thicknesses even where no prior bathymetric surveys exist for comparison.     

Early Diagenesis of Mercury in the Laurentian Great Lakes

The early diagenesis of mercury in deep lake environments was investigated by examining the distribution of mercury among waters and sediments from several depositional basins in the Laurentian Great Lakes. Partitioning of mercury among different sediment phases was examined by sequential chemical extraction (using procedures specifically designed for mercury). Mercury in porewaters and sediment extracts was analyzed by flow-injection/hydride-generation atomic absorption spectroscopy.Results indicate that mercury is affected by early diagenesis at all of the sites studied. Much of the mercury is enriched in the surface layer of sediments, where it is primarily associated with organic matter and iron oxides. The redox cycling of iron and manganese influences the behavior of mercury; concentration profiles suggest that as oxides begin to dissolve in reduced sediments, nearly all of the adsorbed mercury is released. Organic matter decay also appears to release significant amounts of mercury. Porewater profiles suggest that most of the dissolved mercury released from decaying organic matter or from dissolving iron oxides may be taken up by freshly deposited organic matter and iron oxides in the near-surface layers. Much of the mercury that reaches the sediment column is thus recycled near the sediment-water interface, increasing both the residence time and the concentrations of mercury in surface sediments of these deep lake basins.     

Sedimentation,Resuspension, and Oxygen Depletion in Lake Erie (1979)

Oxygen depletion in Lake Erie's central basin hypolimnion is ultimately sustained by the respiration rate of organisms using organic matter which is produced in the trophogenic zone. Although other transformations are certainly important, they are nevertheless driven by the decomposition of organic carbon both in the water column and in the sediments. Rates of transport of particulate organic carbon to the hypolimnion and sediments were estimated using sediment traps. Corrections for sediment resuspension were necessary even during the summer period when the lake is stratified. Particulate organic carbon concentrations in the hypolimnion were partially independent of short-term variations in chlorophyll concentration. The net downflux of carbon to the hypolimnion appeared less than that required to support the observed oxygen depletion. Sediment resuspension accounted for much of the particulate material caught by the sediment traps in the central basin. It is concluded that organic material stored in the surficial sediments is made available to the water column through frequent resuspension. Of total phosphorus in the trap samples, an average of 42% was potentially bioavailable (NaOH extraction).     

Nutrient concentrations in the surface sediments of Lake Chivero,Zimbabwe: A shallow,hypereutrophic, subtropical artificial lake

A lake‐wide survey in Lake Chivero, Zimbabwe, was performed to (i) examine the spatial distribution of three sediment grain sizes; (ii) determine their nutrient concentrations; and (iii) analyse the relationships between the measured surface sediment variables in the three sediment grain sizes. The results of this study indicated sand, silt and mud sediments occupied about 24, 22 and 54%, respectively, of the lake area. All the measured physicochemical variables varied significantly among the three sediment grain sizes (P < 0.05, anova ). High values for pH, dissolved oxygen and NO₃ were observed in the sand sediments, while water depth, electrical conductivity, soluble reactive phosphorus, NH₄, total phosphorus, total nitrogen and total organic carbon were observed in the mud sediments. In the silt sediments, most measured variables showed intermediate values. Intervariable correlation indicated varied correlation patterns among the three sediment grain sizes. Information generated in this study is essential for an accurate delineation of the spatial extent of nutrient and contaminant distribution in the sediment of Lake Chivero and will facilitate the ability of lake managers to derive a comprehensive nutrient budget of the lake as a means of establishing realistic target conditions for lake restoration.     

Quantification of soil erosion and sediment yield for ungauged catchment using the RUSLE model: Case study for Lake Basaka catchment in Ethiopia

Soil erosion is a monumental land degradation problem in many parts of the world, threatening the well‐being of humans and ecosystems. The Lake Basaka catchment is heavily affected by serious land degradation problems related to land use–land cover changes (LULC), population dynamics and settlement, introduction of large‐scale irrigation schemes, etc. Accordingly, the objective of the present study was to quantify the magnitude of soil lost from the Lake Basaka catchment and the sediment subsequently delivered to the lake on the basis of the limited available dataset in a distributed manner using the RUSLE model in a GIS environment. The results indicated about 36 million m³ of soil were lost from the catchment between 1973 and 2007. Soil erosion and sedimentation in the lake catchment continue to increase from time to time, being attributed to the significant LULC occurring in the catchment. About 23 cm of the economically productive top soil in the catchment was lost during the study period (1960–2015), which translates into a significant degradation of the catchment (e.g. further reduction of infiltration capacity, thereby accelerating run‐off and erosion rates). Similarly, about a 1.3 m deep sediment layer was deposited in the lake during the same period. The computed sediment yield indicates about 14% of the lake incremental volume and depth in recent periods (post‐2000s) is attributable to sedimentation. Certain coincidental changes are also occurring in the catchment, including organic matter declines, soil nutrient depletion and soil depth decrement, which may lead to decreased production and productivity and associated ecosystem imbalances. The present study identified the potential areas that contribute significantly to erosion and sedimentation, thereby providing guidance regarding where land use/cover practices must be implemented to limit/reduce, if not avoid, the impacts of erosion and subsequent sedimentation in Lake Basaka.     

Sedimentation dynamics within a large shallow lake and its role in sediment transport in a continental-scale watershed

A comprehensive understanding of the sedimentation dynamics within Lake Winnipeg (surface area: 23,750 km²) and its role in sediment transport in the downstream river system was achieved by determining the properties of lake bottom sediment and patterns of sediment accumulation rates and by constructing a conceptual total (i.e., organic and inorganic) sediment budget. Net deposition was the governing process in the South and North Basins, whereas transportation dominated in the Narrows. The largest fluvial source of sediments to the lake, the Red River, supplies 35% of the total sediment load. Although accumulation rates in profundal zones progressively decreased northward from this source at the south end of the lake, high accumulation rates with low inventories of fallout radionuclides in the northern margin of the North Basin indicate a second sediment source, which was determined to be erosion of north shore banks, which accounts for up to 50% of the total sediment load to the lake. The nearshore-offshore gradient in bottom sediment properties in the North Basin confirmed that the signature of this source can reach at least 20 km southward into the lake. However, the properties of bottom sediments, sedimentation dynamics, and sediment budget suggested that some of the materials eroded from the north shore are exported without interaction with the lake bottom and this local sediment source is the dominant source for the downstream river system. It was concluded that Lake Winnipeg effectively disconnects the downstream Nelson River from sediment transport processes in its upstream watershed (953,250 km²).     

The distribution and turnover of benthic organic matter in a lowland river: influence of hydrology,seston load and impoundment

The standing stocks of benthic organic matter (BOM) and some of its biochemical compounds (particulate organic carbon, particulate nitrogen, protein, and chlorophyll a) were investigated in the upper 12 cm of the sediments at several sampling sites in a free‐flowing and in an impounded river section of the lowland River Spree (Germany). Several environmental variables were recorded, in order to determine their potential influence on the organic matter content in the sediments. It was shown that the organic matter content in the upper sediment layers was mainly determined by the local hydrological regime, which was best reflected by the particle size distribution at the sampling sites. For the deepest investigated sediment strata, no influencing factors could be determined. The amount and quality of suspended matter was of minor importance to sediment composition. Also seasonal effects could not be detected. The impounded river section exhibited less seasonal variation in organic matter storage, as well as shorter carbon turnover lengths, longer carbon turnover times and lower rates of annual organic matter recycling than the free‐flowing river section, which indicates that changes in river hydraulics result in alterations to the organic matter budget. These alterations could be related to the changed mesohabitat composition and to the higher standing stocks of organic matter in the impounded river reach. We conclude that both morphological and hydrological alterations affect the structure and function of running water ecosystems because of their negative effect on the organic matter cycling. Copyright © 2002 John Wiley & Sons, Ltd.     

The effect of Lake Erie water level variations on sediment resuspension

Variability in Lake Erie water levels results in variations of the fluid forces applied to the lake bed by free-surface gravity wind-waves. An increase in the bed stress may re-suspend sediment deposited years earlier. This study identifies areas of possible non-cohesive sediment mobilization in response to the forcing conditions and water levels present in Lake Erie. Observations from NOAA buoy 45005 were used to identify wave events generated by a variety of atmospheric forcing conditions. For each event, numerical predictions of significant wave height, wave period, and water level from the Great Lakes Forecasting System (GLFS) were used to characterize the wave event variability over the lake. The Shields parameter was estimated at each 2 km × 2 km grid cell with the local wave forcing as predicted by GLFS assuming an estimate of the wave-induced friction factor. In the Cleveland harbor region of the central basin, the Shields parameter was also estimated by assuming uniform wave conditions as observed by NOAA buoy 45005. The “contour of incipient motion” for both variable and uniform wave events was defined as the offshore contour where the Shields parameter exceeds the critical limit for motion. Comparisons with a radiometrically corrected image from Landsat-7 showed that the spatially varying wave events from GLFS were in qualitative agreement with the satellite observations. A sensitivity analysis of wave height, wave period, and grain size showed the contour of incipient motion to be the most sensitive to wave period. Calculations performed for record high and low water levels showed that the incipient motion of non-cohesive sediments in the relatively flat central basin to be the most sensitive to the historic hydrologic variability present in Lake Erie.     

洪湖沉积物碳氮磷分布特征及污染评价

洪湖是中国第七大淡水湖,富营养化问题日益突出。全面了解洪湖沉积物氮、磷、有机质的含量及分布特征,对掌握其富营养化现状与氮磷污染生态风险具有重要意义。在湖区布设了8个采样点,2019年10月采集50 cm柱状沉积物,分别测定不同深度沉积物总氮(TN)、总磷(TP)以及有机质(OM)含量,分析了TN、TP 和OM 含量的空间分布特征及相关性,并运用综合污染指数法评价其对应的污染程度。结果表明:洪湖沉积物TN含量在467.8~8 454.5 mg/kg之间,平均值2 167 mg/kg,为重度污染,其中近一半的采样点表层沉积物TN含量>5 000 mg/kg;TP含量在502.7~1 252.4 mg/kg之间,平均值693.8 mg/kg,除杨柴湖为重度污染外,其他大部分地区为中度污染;有机质含量占比在5.0%~24.9%之间,平均值9.6%,为重度污染。在垂直空间上,TN、TP 和OM 均在沉积物表层垂向深度0~20 cm存在明显的积累,其含量随垂向深度的增加而迅速降低。研究成果可为洪湖富营养化的控制与治理提供科学数据支撑。     

The role of wind-wave related processes in redistributing river-derived terrigenous sediments in Lake Turkana: A modelling study

A complete annual cycle of the dynamics of fine-grained sediment supplied by the Omo and smaller rivers is simulated for Lake Turkana, one of the world’s large lakes, with the hydrodynamic, wave and sediment transport model Delft3D. The model is forced with river liquid and solid discharge and wind data in order to simulate cohesive sediment transport and resuspension. It simulates stratification due to salinity, wave generation and dissipation, and sediment advection and resuspension by waves and currents, with multiple cohesive sediment fractions. A comparison of the simulation results with remotely-sensed imagery and with available in-situ sediment deposition rates validates the model. By devising simulation scenarios in which certain processes were switched on or off, we investigated the contribution of waves, wind-induced surface and bottom currents, salinity-induced stratification and river jet, in resuspending and transporting fine sediments in the lake basin. With only the wind or river influence, most of the sediment deposition occurs in the first 10 km off the Omo River mouth and at a depth < 10 m. When waves are switched on, increased bed shear stresses resuspend most of the fine sediments, that are then deposited further and deeper in the first 30 km, in water depths > 30 m. This study sheds new light on sediment transport in Lake Turkana and in great lakes in general, favouring the view that wind-waves can be the main agent that transports sediment away from river mouths and to deeper areas, as opposed to river-plume or gravity-driven transport.     

Polycyclic aromatic hydrocarbon residues in the sediments of a dune lake as a result of power boating

The potential chemical effects of motorized recreational activities (power boating, water skiing, jet skiing) on Brown Lake, an Australian perched, acid dune lake, were investigated. The objective of this study was to identify and quantify polycyclic aromatic hydrocarbon compounds (PAHs) that may have accumulated in the water and/or the organic bottom sediments of the test lake as a result of the operation of powered recreational watercraft, and to evaluate any risk to aquatic biota. To achieve this, a detailed sampling and analysis programme of the lake water and sediments was implemented. Basic water quality, ionic and nutrient data gave no indication of any deterioration in the water quality of the lake, which was attributable to human usage in general or motorized recreational activities in particular. However, analysis of samples taken from the organic bottom sediments of the lake revealed the presence of 10 PAH, including benzo(a)pyrene, chrysene, fluoranthene, phenanthrene and pyrene, which are known to be indicative of fossil fuel combustion processes. Three PAH compounds were found at all survey sites: benzo(a)pyrene (in 46% of samples), fluoranthene (in 53% of samples) and pyrene (in 44% of samples). Results of the analyses were compared with values from published guidelines for residues in freshwaters and sediments, as well as with previous studies dealing with the effects of fossil fuel combustion products on lakes. The highest PAH concentrations in sediments were recorded for benzo(a)pyrene, with three values (830, 955 and 1070 μg kg^–1 dryweight) exceeding the upper threshold recommended in the draft Canadian freshwater sediment quality guidelines. Benzo(a)pyrene also exceeded the lower Canadian sediment threshold in 51 (40%) samples. These results indicate a significant level of chemical contamination of Brown Lake as a consequence of four decades of motorized recreational activities and present a significant risk to aquatic biota, particularly benthic and littoral invertebrates associated with the contaminated sediments.     

Diagenesis of Organic Matter in the Sediments of Lakes Ontario,Erie, and Huron

The organic matter in the modern sediments of Lakes Ontario, Erie, and Huron is composed of humic compounds (68 to 83%), amino acids (19 to 20%), lipids (2 to 8%), carbohydrates (2 to 6%), and amino sugars (0.5 to 4%). Amino acid and carbohydrate concentrations are high in plankton samples, which are the primary source of the sedimentary organic matter. These compounds are decomposed during their passage through the food chains and while resting at the sediment-water interface with the concurrent formation of humic compounds. The degree of diagenesis of the modem sedimentary organic matter is related to both the trophic state of the lake and to the water depth, with the greatest amount in the most eutrophic lake basins and in the shallowest water depths. Diagenesis of the organic matter is rapid prior to burial in the sediments and is slow after burial. The decomposition rates of the sedimentary organic matter are in the following order: amino acids>>amino sugars>carbohydrates>humic compounds>lipids.     

Sediment phosphorus characteristics in the clearwater state of Lake Mogan, Turkey

This study examined the vertical distributions of total phosphorus (TP) and phosphorus fractions, and the iron and organic matter, in the littoral sediment in a macrophyte‐dominated, clearwater state in Lake Mogan between September 2005 and August 2006. Benthic macroinvertebrates and total bacteria in the sediment also were determined. No clear seasonal or depth‐related (0–20 cm) patterns were found in sediment concentrations for the measured parameters. The phosphorus release was quantitatively very low, and a negative phosphorus release (–0.132 µg m^?2 day^?1) was measured during the summer months. The TP concentrations of the sediment samples ranged between 675.00 and 1463.80 µg g^?1 dry weight (DW), and the trophic level of the lake was eutrophic. On average, inorganic phosphorus fractions comprised the largest fraction (63%), while organic‐bound phosphorus (Org ≈ P) constituted 37% of the TP in Lake Mogan. The most important phosphorus‐immobilizing factors are high iron content (14 200–47 750 µg g^?1 DW), the sediment's clay content (47.80–51.80%), and an abundance of macrophytes at the sampling station. The low abundance of benthic macroinvertebrates (510–850 individuals m^?2), which depend on sediments with high iron and low organic matter (5.42–13.30%), played a role in the sediment phosphorus retention. Although bacterial abundance in the surficial sediment appeared to be positively correlated to temperature, the overlying water did not experience anoxic conditions, supporting a state in which bacteria were able to retain phosphorus in their cell structures. Long‐term changes in the sediments of Lake Mogan must be monitored lake. In order to optimize the management of the lake, and to determine the longevity of a clearwater state following management measures and continued external phosphorus loading, long‐term changes in the sediments of Lake Morgan must be monitored.     

Benthic Bioaccumulation and Bioavailability of Polychlorinated Dibenzo-p-Dioxins/Dibenzofurans from Surficial Lake Ontario Sediments

The benthic bioavailability of surface sediment-associated polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) was quantified and assessed in Lake Ontario. Bottom sediments were collected from three areas along the Lake Ontario southern shoreline near Olcott, Rochester, and Oswego, New York. The sediment samples were subjected to 28-day, PCDD/F bioaccumulation experiments using the aquatic oligochaete Lumbriculus variegatus. Empirical data including only detectable PCDD/F tissue residues were used to quantify the benthic bioavailability of 11 PCDD/F congeners through the calculation of biota-sediment accumulation factors (BSAFs). BSAFs calculated for at least two lake areas were combined as Lake Ontario BSAFs for those specific congeners. Variability of the BSAFs was estimated by propagated error (PE) terms. Mean Lake Ontario BSAFs (±PE) ranged from 0.04±0.02 for octachlorodibenzofuran (OCDF) to 2.42±1.32 for 1,2,3,6,7,8-hexachlorodibenzofuran (HxCDF). Tetrachlorodibenzo-p-dioxin (TCDD) and 1,2,3,4,7,8-HxCDF, shown to be among the highest toxic equivalencies (TEQs) in lake sediments, yielded BSAFs of 0.51±0.18 and 0.22±0.12, respectively. Statistical comparison of the TCDD BSAFs showed no significant differences among the lake areas. The benthic bioavailability of TCDD appeared lower than the results of other investigators. While hydrophobicity and degree of chlorination play some role, other factors, such as steric properties, and composition of organic carbon and matter, may have had a greater influence on the benthic bioavailability of PCDD/F congeners. Comparisons of these benthic BSAFs to fish BSAFs suggest that the bioaccumulation of PCDD/F congeners by fish is more related to water solubility and degree of chlorination than to sediment concentration.