Ratios Of Suspended Particulate Matter Research Articles

Sustained stoichiometric imbalance and its ecological consequences in a large oligotrophic lake

Considerable attention is given to absolute nutrient levels in lakes, rivers, and oceans, but less is paid to their relative concentrations, their nitrogen:phosphorus (N:P) stoichiometry, and the consequences of imbalanced stoichiometry. Here, we report 38 y of nutrient dynamics in Flathead Lake, a large oligotrophic lake in Montana, and its inflows. While nutrient levels were low, the lake had sustained high total N: total P ratios (TN:TP: 60 to 90:1 molar) throughout the observation period. N and P loading to the lake as well as loading N:P ratios varied considerably among years but showed no systematic long-term trend. Surprisingly, TN:TP ratios in river inflows were consistently lower than in the lake, suggesting that forms of P in riverine loading are removed preferentially to N. In-lake processes, such as differential sedimentation of P relative to N or accumulation of fixed N in excess of denitrification, likely also operate to maintain the lake's high TN:TP ratios. Regardless of causes, the lake's stoichiometric imbalance is manifested in P limitation of phytoplankton growth during early and midsummer, resulting in high C:P and N:P ratios in suspended particulate matter that propagate P limitation to zooplankton. Finally, the lake's imbalanced N:P stoichiometry appears to raise the potential for aerobic methane production via metabolism of phosphonate compounds by P-limited microbes. These data highlight the importance of not only absolute N and P levels in aquatic ecosystems, but also their stoichiometric balance, and they call attention to potential management implications of high N:P ratios.

Time-series variations in 129I concentrations and 129I/137Cs ratios in suspended particulate matter collected in eastern Japan immediately after the 2011 nuclear accident in Fukushima, Japan

We have determined the hourly atmospheric concentrations of 129I in aerosols dispersed into the atmosphere by the nuclear accident at the Fukushima Daiichi Nuclear Power Plant (FD1NPP) on March 11, 2011. Data were obtained by measuring the quantity of 129I in suspended particulate matter (SPM) collected on filter tapes at 41 SPM monitoring stations in Fukushima and other prefectures in eastern Japan, including the metropolitan area of Tokyo and the surrounding area. After scrutiny, 500 out of 920 hourly SPM samples were determined to be reliable (i.e., devoid of cross-contamination), and these were subjected to further analysis and discussion. Based on the data from these samples, especially data from the four SPM sampling sites located close to the FD1NPP (Futaba, Naraha, Haramachi and Nihonmatsu), the time-series variations in the atmospheric concentration of 129I and the activity ratio of 129I/137Cs were reconstructed by using 137Cs concentration data in the literature. 129I and 137Cs were observed to be continuously and sometimes explosively dispersed into the atmosphere in aerosols transported by radioactive plumes from the FD1NPP. The highest activity concentrations of 129I and 137Cs were observed in the SPM sample at the Futaba SPM station (3.2 km west-northwest of the FD1NPP) at 14:00–15:00 on March 12 after the venting of Unit 1. Systematically high 129I/137Cs activity ratios were observed at the Futaba and Haramachi stations from March 12 to 14, suggesting that radioactive masses released from the FD1NPP during the first few days after the nuclear accident were relatively enriched in radioiodine. High activity ratios of 129I/137Cs were also measured starting on March 21 at Naraha (17.5 km south of FD1NPP) and from March 22–23 in the metropolitan area which must have been caused by a different type of emission event(s) on those days at the FD1NPP, as previously reported. The 129I data from this study are highly effective in the validation and elaboration of the modelling of the atmospheric dispersion of radioiodine. They further contribute to assessing the internal exposure due to inhalation of 131I estimated by means of such elaborate atmospheric diffusion models.

Distribution and fractionation of rare earth elements in suspended particulate matter in a coastal river, Southeast China.

BackgroundIn the river system, the geochemistry of rare earth elements (REEs, a series of elements from La to Lu) in suspended particulate matter (SPM) is generally controlled by rock weathering processes and hydrochemical characteristics, as well as being affected by anthropogenic activities. However, the variations of geochemical characteristics and behaviors of REEs in SPM with a salinity gradient from the inland river to the estuary have been short of a systematic understanding.MethodsThe REE concentrations, Post Archean Australia Shale (PAAS)-normalized REE, La/Yb, La/Sm, and Sm/Yb ratios of SPM were investigated in the Jiulongjiang River, which is a coastal river mainly flowing through granite rocks in Southeast China. The correlation relationships between physicochemical parameters (including water pH, total dissolved solids (TDS), HCO3– concentrations, and the concentrations of major elements of SPM) and PAAS-normalized REE ratios of SPM were analyzed to determine the factors that affect the REE concentration and fractionation of SPM in the different regions of Jiulongjiang River, including the main stream and tributary of Beixi River, Xixi River, Nanxi River, and estuary. Additionally, the Ce, Eu, and Gd anomalies of SPM were estimated.ResultsThe average ∑REE concentration of SPM (352 mg/kg) in the granite rock basin was twice higher than the mean value (175 mg/kg) of the world’s rivers. The PAAS-normalized REE ratios of SPM in the main rivers including Beixi River (main stream), Xixi River, and Nanxi River were near due to the same lithologic distribution. In the tributary of Beixi River, the input of low-weathered carbonate minerals which contain very few REE caused the lower REE concentrations of SPM. The PAAS-normalized REE ratios of SPM in the estuary were significantly lower than those in the main rivers, which was mainly attributed to the significant REE removal with the increment of salinity. The enrichment of LREE relative to HREE in SPM increased with decreasing water pH in the main rivers. In the estuary, the preferential removal of dissolved LREE occurred compared to HREE with the increment of salinity. The negative Ce and Eu anomalies of SPM occurred in both the main rivers and estuary region and rare Gd pollution was present in the basin. Additionally, human activities caused the increment of REE concentrations and more negative Ce anomaly at some specific sites, such as dam effect and agricultural pollution.ConclusionsThe REE concentrations and fractionations of SPM in river water mainly depend on lithologic distribution and riverine pH, while they are affected by salinity in the estuary.

Distribution of C/N/P stoichiometry in suspended particulate matter and surface sediment in a bay under serious anthropogenic influence: Daya Bay, China.

The C/N/P stoichiometry of organic matter can provide useful information for better understanding of the effects of human activities on aquatic ecosystems. The Daya Bay is a semi-closed bay under serious anthropogenic influences in the southeastern China. This study investigated the contents and ratios of C, N, and P in suspended particulate matter (SPM) and surface sediment in Daya Bay during the spring of 2017. Average C/N/P ratios were 139/17/1 in the surface SPM, 129/16/1 in the bottom SPM, and 61/8/1 in the surface sediment. The C/N ratio of SPM was significantly lower in the western inner bay, suggesting that eutrophication can reduce this ratio. The N/P ratio of SPM was slightly higher in the inner bay, while no clearly distribution pattern was found in the C/P ratio of SPM. Compared with SPM, surface sediment showed significantly lower N/P and C/P ratios. The C/N, N/P, and C/P ratios and contents of total organic C, N, and P were higher in the surface sediment in the inner bay. Our results suggested that the distribution of C/N/P stoichiometry was uncoupled between SPM and surface sediment. The C/N/P stoichiometry of surface sediment can effectively reflect the regional variation of terrigenous input and the influence of nuclear power plant thermal effluent.

Short-term changes in the quality of suspended particulate matter in a human impacted and mangrove dominated tropical estuary (Can Gio, Vietnam)

Suspended particulate matter (SPM) is a key component of coastal food webs and a key variable of nutrient budgets. Understanding its variability across short time scales in estuaries may help ecologists understand seasonal and diurnal migration of estuarine organisms, and answer how their nutritional requirements are fulfilled. It may also inform biogeochemists regarding the factors that influence import and export of nutrients between terrestrial and coastal ecosystems. This study aimed to link the dynamics of fatty acids, stable isotopes (δ13C and δ15N) and C/N ratios of SPM, revealing organic matter quality, to rapidly varying factors (SPM concentration, salinity and presence of daylight) and comparing this variability to the seasonal variation induced by the alternation of dry and wet seasons in the studied region. Our results revealed that these rapidly varying factors had a strong influence on the bacterial and the phytoplanktonic compartments of SPM. They suggest that tidally resuspended particles are the site of intense heterotrophic activity and that estuarine phytoplankton store lipids during the daytime up to substantially modifying SPM quality. Our study also shows higher freshness of SPM during the wet season. We expect this study to raise the interest of both biologists and biogeochemists to introduce daily variability of SPM in food webs and nutrient budgets modelling.

Crucian Carp (Carassius carassius) Strongly Affect C/N/P Stoichiometry of Suspended Particulate Matter in Shallow Warm Water Eutrophic Lakes

Crucian carp (Carassius carassius) is a key fish species in most Chinese subtropical and tropical shallow lakes. Through sediment feeding, crucian carp could greatly change water turbidity and nutrient levels, as well as the abundance of herbivorous consumers, which may have important influences on seston element stoichiometry. However, so far, experimental studies on this topic are lacking. We conducted a 36-day mesocosm experiment to explore the effects of crucian carp on water physicochemical and biological properties, and C/N/P ratios in suspended particulate matter (SPM) under eutrophic conditions. Our results provided three major findings: (1) Crucian carp resuspended sediments and along with them, reduced light penetration and lower light/total phosphorus (TP) ratios. (2) Crucian carp reduced biomasses of both zooplankton and macrozoobenthos, whereas their effect on phytoplankton was weak, potentially because of resuspension-induced light limitation. (3) Both C/P and N/P ratios in SPM were significant lower in mesocosms with crucian carp than in fish-free controls, which may be attributed to the high contribution of P-rich sediments and low light to nutrient supply caused by fish-induced resuspension. Our results suggest that besides planktivorous fish, benthivore (e.g., crucian carp) in warm shallow waters could also affect pelagic C/N/P stoichiometry via sediment feeding, which may further influence energy transfer efficiency in lake food chain.

SEDIMENT AND SUSPENDED PARTICULATE MATTER OF JAKARTA BAY, INDONESIA

Jakarta Bay is a semi enclosed bay located in the northern coast of Jakarta Metropolitan City. Hydrologically 13 rivers flowing in the Jakarta region and there are three big rivers with significant discharge to the Jakarta Bay namely Citarum, Ciliwung, and Cisadane Rivers. Jakarta, as Indonesian capital city with population of 8.725.630 inhabitants, and another 15 million people live in the surrounded suburban of Jakarta, creates a significant anthropogenic impact to the environmental system. Limited infrastructures, such as no sewerage system and lack of industrial waste management, cause the rivers in this region have over their carrying capacity.Seventeen sampling stations were determined in the Jakarta Bay, consisting of 5 stations at the river mouths (estuaries) and other 12 stations in the bay spreading from the coastal to offshore areas. Water and sediment samples were taken during 2 monsoonal or seasonal variations, August 2006 for dry season and February 2007 for rainy season respectively. Additionally, samples were also taken in May 2007.Sediment distribution in the estuary consists mostly of black clay. The sediments clays were bad smell. In the coastal region and in the dry season, the sediments consists of black clay and at one sampling site (station S3) the sediment was bad smell. However, all sampling sites became bad smell in the rainy season. In the inner bay area, sediments were greyish green sandy clay with some shell fragments. In the outer bay, the sediments were dominated by greyish green clayey sand with some shell fragments. The black clay with bad smell is indicative of anthropogenic influence from Jakarta River Basin. C/N ratio of the sediments in the dry season ranged from 1 to about 4.2 where in the estuaries (at stations M1, M2 and M4) the ratio were higher compared to the inner and outer bays. The C/N ratio of suspended particulate matter ranged from the lowest ratio of 0.7 to the highest ratio of 17.7 at the bottom layer and lesser ranged of 0.7 to 9.8 at surface layer. POC concentrations ranged between 50-650 µM and 50-900 µM, in February and May, respectively. High concentrations of POC exists along the coastline or estuaries then decreasing toward the sea. POC is distributed widely in February than that in May due to higher discharge from the rivers. The average TOC concentrations in February is lower than that in May, but the TOC load in February was much higher than that in May due to the big differences of river discharge and because the samples were taken a week after the big flood in Jakarta area (February 4th - 6th, 2007). Total organic carbon fluxes from the river to the bay in February and May 2007 were 107.6 T /day C and 42.7 T /day C, respectively. Key words : sediment, anthropogenic influence, C/N Ratio, POC, TOC, flux

Nature and source of suspended particulate matter and detritus along an austral temperate river–estuary continuum, assessed using stable isotope analysis

Ecologists are interested in the factors that control, and the variability in, the contributions of different sources to mixed organic materials travelling through lotic systems. We hypothesized that the source matter fuelling mixed organic pools in a river–estuary continuum varies over space and time. Samples of the mixed organic pools were collected along a small temperate river (Kowie River) in southern Africa during early and late spring, summer and winter. The C:N ratios of suspended particulate matter (SPM) collected during summer and winter indicated that the lower reaches of the system had similar organic matter contributions. Stable isotope analysis in R revealed that aquatic macrophytes were significant contributors to SPM in the upper reaches. Bulk detritus had large allochthonous matter components in the lower reaches, and contributions of aquatic macrophytes and benthic algae were high (>50%) in the upper to middle reaches. The evaluation of organic matter contributions to SPM and detritus along the river–estuary continuum provided a baseline assessment of the nature and sources of potential food for consumers inhabiting different locations during different seasons. Incorporating SPM and detritus spatio-temporal variations in food web studies will improve our understanding of carbon flow in aquatic systems.

Contrasting controls on the phosphorus concentration of suspended particulate matter under baseflow and storm event conditions in agricultural headwater streams

Whilst the processes involved in the cycling of dissolved phosphorus (P) in rivers have been extensively studied, less is known about the mechanisms controlling particulate P concentrations during small and large flows. This deficiency is addressed through an analysis of large numbers of suspended particulate matter (SPM) samples collected under baseflow (n=222) and storm event (n=721) conditions over a 23-month period across three agricultural headwater catchments of the River Wensum, UK. Relationships between clay mineral and metal oxyhydroxide associated elements were assessed and multiple linear regression models for the prediction of SPM P concentration under baseflow and storm event conditions were formulated. These models, which explained 71–96% of the variation in SPM P concentration, revealed a pronounced shift in P association from iron (Fe) dominated during baseflow conditions to particulate organic carbon (POC) dominated during storm events. It is hypothesised this pronounced transition in P control mechanism, which is consistent across the three study catchments, is driven by changes in SPM source area under differing hydrological conditions. In particular, changes in SPM Fe–P ratios between small and large flows suggest there are three distinct sources of SPM Fe; surface soils, subsurface sediments and streambed iron sulphide. Further examination of weekly baseflow data also revealed seasonality in the Fe–P and aluminium oxalate–dithionate (Alox–Aldi) ratios of SPM, indicating temporal variability in sediment P sorption capacity. The results presented here significantly enhance our understanding of SPM P associations with soil derived organic and inorganic fractions under different flow regimes and has implications for the mitigation of P originating from different sources in agricultural catchments.

Mineralogy and Sr–Nd isotopes of SPM and sediment from the Mandovi and Zuari estuaries: Influence of weathering and anthropogenic contribution

Clay minerals and Sr–Nd isotopes of suspended particulate matter (SPM) and bottom sediment were investigated along transect stations of the Mandovi and Zuari estuaries, western India to determine the provenance and role of estuarine processes on their distribution. Kaolinite and illite, followed by minor goethite, gibbsite and chlorite were present in SPM and bottom sediment at all stations, both during monsoon and pre-monsoon. Smectite occurred in traces at river end stations but its contents increased downstream in both estuaries. Smectite contents were much higher in Zuari than in Mandovi estuary. The 87Sr/86Sr ratios and ɛNd of SPM were higher than those in hinterland rocks and laterite soils. The Sr ratios were highest at river end stations of both estuaries and decreased sharply seaward. The Sm/Nd ratios of SPM and sediment were close to that of iron ore material flushed into the estuaries. The mean ɛNd of SPM and sediment were similar in both estuaries. It is suggested that the smectite is formed in coastal plains and its distribution downstream is controlled by lithology and drainage basin of rivers. Abundant kaolinite and high Sr ratios reflect chemical weathering and lateritization of source rocks. Sr isotopic ratios along transects are influenced by changes in salinity, organic matter and turbidity. High and near identical ɛNd values along transect stations of both estuaries suggest that the Nd isotopic compositions are influenced by the lateritization of source rocks and anthropogenic contribution of ore material.

Spatial variation of biogenic and crustal elements in suspended particulate matter from surface waters of the North Pacific and its marginal seas

The physical and chemical properties of oceanic suspended particulate matter (SPM) reflect the characteristics of the water mass, including marine biological activity and riverine and/or atmospheric inputs, and provide a clue to understanding the ocean biogeochemical processes. Detailed data mapping of particle number concentration, particle volume concentration and elemental composition (Si, Ca, Ti and Fe) were obtained from surface waters of the North Pacific and its marginal seas (the Sea of Okhotsk, the Bering Sea and the Chukchi Sea) during summer and autumn based on bulk and single particle analyses of the SPM. In the Bering Sea and Chukchi Sea, the mean concentration of particle number and volume were 35×106particlesL−1 and 960ppbv, respectively, and more than 10 times higher than those in the North Pacific (2.1×106particlesL−1 and 39ppbv). The mean concentrations of both biogenic (Si and Ca) and crustal (Ti and Fe) elements in the SPM from the Bering Sea and Chukchi Sea were also approximately 10 times higher than those from the North Pacific and the Sea of Okhotsk. The high concentrations of crustal elements in the continental shelf region of the Bering Sea appear to be sustained by riverine input from the Yukon River. Nutrients transported together with crustal material from the river could contribute to high primary productivity of the Bering Sea, and result in the high concentrations of biogenic SPM. The Fe to Ti ratios in SPM varied among the ocean regions; the ratios in the Bering Sea and the Chukchi Sea were 5 times higher than those in the North Pacific. Individual particle analysis also revealed the spatial difference in size and chemical compositions of aluminosilicate-type particles. These evidences indicate that the difference in origins and/or oceanic processes of crustal particles among the ocean regions affects the spatial variation of elemental ratio in crustal SPM.

Fe/Al ratios of suspended particulate matter from intermediate water in the Okhotsk Sea: Implications for long-distance lateral transport of particulate Fe

We have found that the ratio of Fe to Al in suspended particulate matter (SPM) in the intermediate layer of the Okhotsk Sea increases to the open ocean from the dense shelf water on the northwestern continental shelf, which is the source of southward-flowing Okhotsk Sea Intermediate Water (OSIW). The SPM concentration and the Al content of the SPM decrease along the course of the OSIW, whereas the ratios of Ba and Mn to Al increase. The SPM samples on the continental shelf were collected in waters characterized by low N⁎ (the deviation from the stoichiometric relationship between nitrogenous nutrients and phosphate). These low N* values imply that sedimentary denitrification occurs on the continental shelf, and both Fe and Mn are concomitantly reduced in the sediments and diffuse from the sediments to the overlying waters, where they are subsequently oxidized and precipitate. We assume that the SPM in the intermediate layer is influenced mainly by horizontal transport from the continental shelf to the ocean interior and that Ba can be used as a proxy for organic matter. Based on these assumptions, the results could reflect the following processes: 1) a gradual loss of denser lithogenic matter, evidenced by the decreases of the SPM concentration and of the Al content of the SPM, and 2) a relative increase of the Fe and Mn fractions associated with the organic matter in the SPM, which is derived from the continental shelf. The organic matter-related Fe and Mn could also be affected by the precipitation of both Fe and Mn just above the reduced sediments of the continental shelf. Our results show that the particulate Fe associated with organic matter is preferentially transported from the northwestern continental shelf to the open ocean.

Isotopic indicators of source and fate of particulate organic carbon in a karstic watershed on the Yunnan-Guizhou Plateau

The studied watershed is a Karst-dominated area on the Yunnan-Guizhou Plateau. The local karstic environment might cause the biogeochemical processes involving POC to be different from those in non-karstic regions. Isotopic composition of particulate organic C (POC) and total N (TN) (δ13CPOC, δ15NTN) and C/N ratios (atomic) were used to identify sources and fates of POC in suspended particulate matter (SPM) and sediments over space and time in the karstic watershed. Distributions of POC in SPM and sediments show great seasonal and spatial variations. The δ13CPOC in SPM ranges from −27.4 to −19.0‰ and −33.4 to −22.3‰ in summer and winter, respectively. The C/N ratios in SPM in both seasons are lower than 12 and most are around 7. The surface and core sediments have lower δ13CPOC but higher C/N ratios than those of SPM. According to source analysis using C/N ratios, δ13CPOC and δ15NTN, the major source for POC in SPM is phytoplankton, while POC in surface sediments are attributed to land-derived and aquatic sources. Core sediments in the region affected by less anthropogenic impact have a similar POC source to surface sediment. However, in regions with intense deforestation and farming, land-derived sources may be major contributors to POC in core sediments. Calculated contributions from these sources to POC in the riverine-lacustrine system confirm the above observation. The flux and export rate of POC in SPM are 7.85×108ga−1 and 492mgm−2a−1, respectively. In contrast to some world rivers, POC output from the karstic watershed is mainly from in-stream photosynthesis. Land-derived POC is merely redistributed in river and lake beds and sediments in the karstic riverine-lacustrine system act as an organic C pool. The observed features are likely due to intense anthropogenic impact and particular geomorphology of the karstic environment.

Modeling the effects of near-surface plumes of suspended particulate matter on remote-sensing reflectance of coastal waters

A radiative transfer model was applied to examine the effects of vertically stratified inherent optical properties of the water column associated with near-surface plumes of suspended particulate matter on spectral remote-sensing reflectance, R(rs)(λ), of coastal marine environments. The simulations for nonuniform ocean consisting of two layers with different concentrations of suspended particulate matter (SPM) are compared with simulations for a reference homogeneous ocean whose SPM is identical to the surface SPM of the two-layer cases. The near-surface plumes of particles are shown to exert significant influence on R(rs)(λ). The sensitivity of R(rs)(λ) to vertical profile of SPM is dependent on the optical beam attenuation coefficient within the top layer, c(1)(λ), thickness of the top layer, z(1), and the ratio of SPM in the underlying layer to that in the top layer, SPM(2)/SPM(1), as well as the wavelength of light, λ. We defined a dimensionless spectral parameter, P(λ)=c(1)(λ)×z(1)×(SPM(2)/SPM(1)), to quantify and examine the effects of these characteristics of the two-layer profile of SPM on the magnitude and spectral shape of R(rs)(λ). In general, the difference of R(rs)(λ) between the two-layer and uniform ocean decreases to zero with an increase in P(λ). For the interpretation of ocean color measurements of water column influenced by near-surface plumes of particles, another dimensionless parameter P'(λ) was introduced, which is a product of terms representing homogenous ocean and a change caused by the two-layer structure of SPM. Based on the analysis of this parameter, we found that for the two-layer ocean there is a good relationship between R(rs)(λ) in the red and near-infrared spectral regions and the parameters describing the SPM(z) profile, i.e., SPM(1), SPM(2), and z(1).

Assimilation of Oil-Derived Elements by Oysters Due to the Deepwater Horizon Oil Spill

During and after the Deepwater Horizon Oil Spill (DWHOS), oysters (Crassostrea virginica) were exposed to oil and susceptible to incidental consumption of surface and subsurface oil materials. We determined the contribution of oil materials from the DWHOS to diet of oysters by comparing carbon (C) and nitrogen (N) stable isotope ratios in oyster shell to ratios in suspended particulate matter (SPM) and in fresh and weathered oil. Average δ(13)C and δ(15)N values in oyster shell (-21 ± 1‰ and 9-11‰, respectively) were consistent with consumption of naturally available SPM as opposed to values in oil (-27 ± 0.2‰, 1.6 ± 0.4‰). Stable isotope ratios in oyster adductor muscle were similar to shell for δ(15)N but not δ(13)C, suggesting either a recent shift in diet composition or differential assimilation of C between tissue types. We found no evidence of assimilation of oil-derived C and N and, therefore, no evidence of an oyster-based conduit to higher trophic levels. Trace elements in shell were inconclusive to corroborate oil exposure. These findings are not an indication that oysters were not exposed to oil; rather they imply oysters either did not consume oil-derived materials or consumed too little to be detectable compared to natural diet.

Decrease in anthropogenic nutrients and its effect on the C/N/P molar ratio of suspended particulate matter in hypertrophic Dokai Bay (Japan) in summer

Biologically important nutrient concentrations in Dokai Bay have declined as a result of reductions in anthropogenic inputs of total nitrogen and total phosphorus. A decrease in nutrient concentrations affects phytoplankton growth, thereby changing the biochemical characteristics of autochthonous particulate matter. We therefore investigated changes in the C/N/P molar ratio of suspended particulate matter (SPM) in the summer, when phytoplankton growth is vigorous, before environmental quality standards (EQSs) were attained (1995–1998) and afterward (2006–2009). We found that the ratio of particulate organic nitrogen (PON) to particulate phosphorus (PP) changed in conjunction with changes in the ratio of dissolved inorganic nitrogen to dissolved inorganic phosphorus (DIP) that resulted from reductions in nutrient loading. Furthermore, we suggest that because the DIP concentration in seawater was high before EQSs were attained, inorganic phosphorus was possibly adsorbed onto SPM. After the attainment of EQSs, however, the DIP concentration fell, and PON/PP was high. Phosphorus limitation of phytoplankton growth in the mouth of the bay may explain the high PON/PP ratios after EQS attainment.

Estimation of suspended sediment concentration based on bio-optical mechanism and HJ-1 image in Chaohu Lake

Synchronization experiment was conducted in June, 2009 to get Inherent Optical Properties (IOP) of water component in Chaohu Lake. Water bio-optical mechanism was studied combined with multispectral data of Environmental Satellite 1 (CCD), and then inversion models of total suspended matter (TSM), inorganic suspended matter (ISM) and organic suspended matter (OSM) concentration were built. The data indicated that: the absorption ratio of suspended particulate matter and CDOM to total were almost no change from band 1 to band 2 with about 85% and 9%, respectively. The ratio of pure water to total increased from 0.4% to 5.6%. Water reflectance in these two bands were influenced by absorption of three kinds of components: algae particles absorption surpassed non-algal particles in band 3, and so played an important role in total absorption with about 35.7%; the proportion of pure water absorption and particles matter backscattering both were 99% in band 4, so these two components decided the main inherent optical properties in band 4. The models of TSM and ISM concentration inversion based on band combination (band 3 + band 4)/(band 1 + band 2) were built, while OSM concentration was estimated by band 4/(band 1 + band 2) index. Inversed by image data, RE of TSM concentration between modeled and measured was 33.4%, and RMSE was 18.68 mg/L. RE of ISM and OSM concentration were 39.9% and 35.2% respectively. The inversion was more accurate when satellite-ground data were just in the same day. At this situation, RE of ISM concentration dropped to 25.4%, and that of TSM and OSM reduced to 26.5% and 26.8% as well.

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 (δ 13C and δ 15N) 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 δ 13C, δ 15N, 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.

Metal and nutrient dynamics in a eutrophic coastal lagoon (Óbidos, Portugal): the importance of observations at different time scales

Water and sediment quality was monitored at four sites of Obidos coastal lagoon (Portugal) in February, May, July and October 2006, covering different hydrological conditions. Concentrations of nutrients and metals increased in autumn/winter, particularly in an inner branch with symptoms of eutrophication that receives a small tributary contaminated by agro-industrial activities. Moreover, concentrations of PO(4)(3-), Si(OH)(4) and Mn (diffusive gradients of thin films (DGT)-measured) varied inversely with salinity. Additionally, that branch was monitored over 26-h in July 2006 to assess variations of water quality parameters, nutrients and metals on short timescale. During the night, O(2) in water reached a minimum of 40% saturation followed by a pronounced increase of DGT-measured metals and nutrients in water column: Fe and Mn (ten times); Cr, Co, PO(4)(3-) and Si(OH)(4) (six times). Enhancements were also registered for metal/Al ratios in suspended particulate matter: Mn, Cr and Cd (four to six times); Fe, Ni and Co (1.5 times). The metal distribution coefficients calculated along the 26-h survey showed a maximum at daylight suggesting a preferential association of metals with suspended particles. Data recorded under different hydrological conditions and over the 26-h survey allowed to address the influence of external and internal sources on water quality. The results of this study highlight the importance of day/night cycles on the availability of nutrients and metals in eutrophic environments.

Temporal and spatial variability in stable isotope ratios of SPM link to local hydrography and longer term SPM averages suggest heavy dependence of mussels on nearshore production

Temporal changes in hydrography affect suspended particulate matter (SPM) composition and distribution in coastal systems, potentially influencing the diets of suspension feeders. Temporal variation in SPM and in the diet of the mussel Perna perna, were investigated using stable isotope analysis. The δ13C and δ15 N ratios of SPM, mussels and macroalgae were determined monthly, with SPM samples collected along a 10 km onshore–offshore transect, over 14 months at Kenton-on-Sea, on the south coast of South Africa. Clear nearshore (0 km) to offshore (10 km) carbon depletion gradients were seen in SPM during all months and extended for 50 km offshore on one occasion. Carbon enrichment of coastal SPM in winter (June–August 2004 and May 2005) indicated temporal changes in the nearshore detrital pool, presumably reflecting changes in macroalgal detritus, linked to local changes in coastal hydrography and algal seasonality. Nitrogen patterns were less clear, with SPM enrichment seen between July and October 2004 from 0 to 10 km. Nearshore SPM demonstrated cyclical patterns in carbon over 24-h periods that correlated closely with tidal cycles and mussel carbon signatures, sampled monthly, demonstrated fluctuations that could not be correlated to seasonal or monthly changes in SPM. Macroalgae showed extreme variability in isotopic signatures, with no discernable patterns. IsoSource mixing models indicated over 50% reliance of mussel tissue on nearshore carbon, highlighting the importance of nearshore SPM in mussel diet. Overall, carbon variation in SPM at both large and small temporal scales can be related to hydrographic processes, but is masked in mussels by long-term isotope integration.