Release of organic P forms from lake sediments

The effects of different physical and chemical conditions on the decomposition and release of organic and inorganic P compound groups from the sediment of Lake Erken were investigated in a series of laboratory experiments. Conditions investigated were temperature, oxygen level, and the effects of additions of carbon substrate (glucose) and poison (formalin). The effects on the P compound groups were determined by measurements with ³¹P NMR before and after the experiments, as well as analysis of P in effluent water throughout the experiment. Phosphate analysis of the effluent water showed that oxygen level was the most influential in terms of release rates, with the sediments under anoxic conditions generally releasing more phosphate than the other treatments. ³¹P NMR showed that the various treatments did influence the P compound group composition of the sediment. In particular, the addition of glucose led to a decrease in orthophosphate and polyphosphate while the addition of formalin led to a decrease in phosphorus lipids, DNA-phosphate and polyphosphate. Oxic conditions resulted in an increase in polyphosphates, and anoxic conditions in a decrease in these. Temperature did not seem to affect the composition significantly.     

Characterization of soil phosphorus in a fire-affected forest Cambisol by chemical extractions and P-NMR spectroscopy analysis

This study was conducted to investigate the long-term effects of fire on soil phosphorus (P) and to determine the efficiency of different procedures in extracting soil P forms. Different P forms were determined: labile forms (Olsen-P, Bray-P, and P extracted by anion exchange membranes: AEM-P); moderately labile inorganic and organic P, obtained by NaOH-EDTA extraction after removing the AEM-P fraction; and total organic and inorganic soil P. ³¹P-NMR spectroscopy was used to characterize the structure of alkali-soluble P forms (orthophosphate, monoester, pyrophosphate, and DNA). The studied area was a Pinus pinaster forest located at Arenas de San Pedro (southern Avila, Spain). The soils were Dystric Cambisols over granites. Soil samples were collected at 0-2 cm, 2-5 cm, and 10-15 cm depths, two years after a fire in the burned area and in an adjacent unburned forest area. Fire increased the total N, organic C, total P, and organic and inorganic P content in the surface soil layer. In burned soil, the P extracted by the sequential procedure (AEM and NaOH + EDTA) was about 95% of the total P. Bray extraction revealed a fire-induced increase in the sorption surfaces. Analysis by chemical methods overestimated the organic P fraction in the EDTA-NaOH extract in comparison with the determination by ignition procedure. This overestimation was more important in the burned than unburned soil samples, probably due to humification promoted by burning, which increased P sorption by soil particles. The fire-induced changes on the structure of alkali-soluble P were an increase in orthophosphate-P and a decrease in monoester-P and DNA-P.     

Life form dependent impacts of macrophyte vegetation on the ratio of resuspended nutrients

The effects of floating-leaved and submerged macrophytes on sediment resuspension and on the ratio of resuspended nitrogen and phosphorus were studied by sediment traps in the Kirkkojärvi basin in southern Finland. The effect of submerged macrophytes on preventing sediment resuspension was stronger than the effect of floating-leaved plants. On average, among submerged plants the resuspension rate of suspended solids was 43%, and among floating-leaved plants 87% of that in the open water. The floating-leaved Nuphar lutea had a reductive effect on P resuspension but no significant effect on N resuspension. The impact on P resuspension was strong, because root uptake by Nuphar lutea reduced the P content of the sediment. N:P ratio in resuspended nutrients was 6.7 among the plants and 4.1 in the open water. Among suzbmerged plants, sediment N content was strongly increased but P content was not affected due to the pleustophytic life form of the dominant plants (Ceratophyllum demersum, Ranunculus circinatus). The effect of pleustophytes on sediment nutrients was weak, because their nutrient uptake is mostly foliar. The N:P ratio of resuspended nutrients was 7.9 among the submerged plants and 7.0 in the open water. The results suggested that depending on the life form, macrophytes can modify the flux of N and/or P to the water column through their effects on nutrient resuspension and possibly modify phytoplankton communities via their effects on the N:P ratio. If the overall nutrient level is the most important factor for the dominance of cyanobacteria, submerged macrophytes can have stronger effects on phytoplankton community structure than floating-leaved species. If N:P ratio is of importance, the effects of floating-leaved species may be more pronounced.     

Influence of a stormwater sediment deposit on microbial and biogeochemical processes in infiltration porous media

The purpose of this study was to test the relative influence of organic matter quantity and quality and the pollutant content of a stormwater sediment deposit on mineralization processes, microbial characteristics, and the release of solutes in infiltration sediment systems. In microcosm experiments, two other natural sediment deposits (one low and one rich particulate organic matter deposits) were studied to compare their effects with those of the stormwater deposit. The results showed that the biogeochemical processes (aerobic respiration, denitrification, fermentative processes), the microbial metabolism (enzymatic activities), and the releases of several solutes (NH(4)(+) and DOC) were stimulated in presence of the stormwater deposit and the natural particulate organic matter (POM)-rich deposit because of the quantity of the POM in these deposits. In the stormwater deposit, the high availability of the POM (indicated by its low C/N ratio and its high P content) produced a higher stimulation of the microbial metabolism than in presence of the POM-rich deposit (with a high C/N ratio). Pollutant (hydrocarbon and heavy metal) contents of the stormwater deposit did not have a significant effect on microbial processes. Thus, main effects of the stormwater sedimentary deposit on infiltration system were due to its organic matter characteristics (quantity and quality). Such organic matter characteristics need to be considered in future studies to determine the contamination potential of stormwater management practices.     

Historical storage budgets of organic carbon, nutrient and contaminant elements in saltmarsh sediments: biogeochemical context for managed realignment, Humber Estuary, UK

Biogeochemical data from Welwick marsh (Humber Estuary, UK), an actively accreting saltmarsh, provides a decadal-centennial-scale natural analogue for likely future biogeochemical storage effects of managed realignment sites accreting either intertidal muds or saltmarsh. Marsh topographic profiles and progradation history from aerial photographs were combined with (137)Cs and niobium contamination history to establish and verify chronology and sediment mass accumulation. These data, combined with down-core measurements of particulate organic carbon (C(org)), organic nitrogen (N(org)), particle reactive phosphorus and selected contaminant metal (Zn, Pb, Cu, As and Nb) contents were then used to calculate sediment and chemical storage terms and to quantify changes in these over time. These data are used to help predict likely future biogeochemical storage changes at managed realignment sites in the estuary. The net effect of returning some 26 km(2) of reclaimed land to intertidal environments now (about 25% of the maximum possible realignment storage identified for the estuary) could result in the storage of some 40,000 tonnes a(-1) of sediment which would also bury about 800 tonnes a(-1) of C(org) and 40 tonnes a(-1) of N(org). Particulate contaminant P burial would be around 25 tonnes a(-1) along with approximately 6 tonnes a(-1) contaminant Zn, 3 tonnes a(-1) contaminant Pb, and approximately 1 tonnes a(-1) contaminant As and Cu. The study also shows that reclamation activities in the outer estuary since the mid-1700s has prevented, in total, the deposition of about 10 million tonnes of sediment, along with 320,000 tonnes of C(org) and 16,000 tonnes of N(org). The study provides a mid-1990s baseline against which future measurements at the site can determine changes in burial fluxes and improvement or deterioration in contaminant metal contents of the sediments. The data are directly relevant for local managed realignment sites but also broadly indicative for sites generally on the European North Sea Coast.     

Speciation of Al, Fe, and P in recent sediment from three lakes in Maine, USA

Sequential extraction of sediments [Psenner R, Pucsko R. Die Fraktionierung organischer und anorganischer Phosphorverbindungen von Sedimenten. Arch Hydrobiol/Suppl 1988. 70(1): 111-155.] from short, (210)Pb-dated cores from three lakes in Maine USA demonstrates that sediment P is dominantly associated with the NaOH-extractable fraction (P-NaOH(25)) and less with the bicarbonate-dithionite extractable fraction (P-BD). The ratios (Al-NaOH(25))/(Fe-BD) and (Al-NaOH(25))/(P-NH(4)Cl+P-BD) for upper sediment for two oligo-mesotrophic lakes exceeded 3 and 25, the thresholds for preventing substantial release of P from sediments during hypolimnetic anoxia [Kopácek J, Borovec J, Hejzlar J, Ulrich K-U, Norton SA, Amirbahman A. Aluminum control of phosphorus sorption by lake sediments. Environ Sci Technol 2005a;39:8784-8789.]. Hypolimnetic water chemistry verifies this effect. The third lake, currently eutrophic, has values for the ratios that are below the thresholds and this lake has substantial release of P from recent sediment. The sediment characteristics remain relatively constant over the last 150+ years, indicating that the processes responsible for P retention have operated long before atmospheric acidification of watersheds might have influenced the flux of Al and Fe to the lake. In 2002, the pH of inlets and the lakes was generally between 6 and 8. Input to the lakes had high concentrations of acid-soluble particulate and dissolved Al, Fe, and P, and dissolved Al and Fe complexed with dissolved organic carbon (DOC). Lake water column and outlet Al, Fe, and P were typically 90-95% lower than inlet concentrations over a 12 month period. Photo-oxidation of Al-DOC and Fe-DOC in the lake, liberation of inorganic Al and Fe, precipitation of Al(OH)(3) and Fe(OH)(3), adsorption of P by the hydroxides, and sedimentation are responsible for the changes in water quality and long-term sediment characteristics.     

Sediment geochemistry of Al, Fe, and P for two historically acidic, oligotrophic Maine lakes

Phosphorus (P) may be liberated from lake sediments by reductive dissolution of Fe(OH)(3(S)) during periods of hypolimnetic anoxia. P, however, remains adsorbed to Al(OH)(3(S)) regardless of redox conditions. During chronic or episodic acidification of a catchment, ionic Al is mobilized from soils to receiving waters. A fraction of the mobilized Al may precipitate as a consequence of higher pH of the receiving waters. We hypothesized that phosphorus retention in lake sediments is directly related to the magnitude of Al loading in response to low pH in the watershed. We studied cores representing over 200 years of sediment accumulation in historically acidic Mud Pond and Little Long Pond in eastern Maine, USA. Sequential chemical extractions of sediment were used to assess the history of Al, Fe, and P interactions. Mud Pond is a first-order pond with a pH of approximately 4.7, having acidified slightly in response to anthropogenic acidification from approximately 1930. The inlet stream to Mud Pond has dissolved Al concentrations often exceeding 500 microg/L, of which more than half is organically-bound. Mud Pond drains into Little Long Pond, a second-order pond with a historical pH of <6, and which has shown little pH or alkalinity response to increases or decreases in atmospheric SO(4)(2-) input. Sequential extractions show that Al and P are predominantly in the 0.1 M NaOH-extractable fraction in the sediments from both ponds throughout the cores. The concentration of the likely biogenic and non-reactive P within the NaOH fraction increases up core from <30% to approximately 60%. Extractable Fe (<20% of extractable Al) is mainly in the 0.1 M NaOH-extractable fraction, except for the top few cm, which are predominantly in the bicarbonate-dithionite reducible fraction. Accumulation rates of sediment, Al, Fe, and P in both ponds have increased in the last 50-60 yr, but fractions remain in the same proportion. Throughout both sediment cores the molar ratio of specific Al:P fractions greatly exceeds 25, and molar ratio of specific Al:Fe fractions greatly exceeds 3, the thresholds proposed by Kopácek et al. [Kopácek J, Borovec J, Hejzlar J, Ulrich K-U, Norton SA, Amirbahman A. Aluminum control of phosphorus sorption by lake sediments. Environ Sci Technol 2005; 39: 8784-89.] for P release during anoxia. The data illustrate a continuous association of P with Al in both ponds during the last two centuries, likely due to the persistent natural acidity of the catchments.     

Variability in phosphorus binding by aluminum in alum treated lakes explained by lake morphology and aluminum dose

Sediment cores from six aluminum sulfate treated lakes in Minneapolis, MN were analyzed to determine the effectiveness of phosphorus (P) binding by aluminum (Al). Two of the study lakes are polymictic and the remaining four are dimictic. Above background concentrations of Al and Al-bound-P (P_Al) were detected in all six lakes at varying sediment depths. In contrast to previous studies, however, the binding relationship between Al and P was not consistent between lakes and substantial variation was also detected within each sediment profile. Average lake sediment Al:P_Al ratios ranged from 5.6 to 15 (molar) with higher ratios, or less efficient P binding, generally being detected in deep, dimictic lakes with high sediment Al content due to treatment. Multiple linear regression was used to explain the variability among average Al:P_Al ratios detected in each core and a lake morphometry index (Al Depth Index, core collection depth divided by the square root of lake area) along with Al dose described most of the variation (92%). Even though P bound to the added Al appears to be permanently removed from the internal P cycle in each lake (as evidenced by burial with new sediment), the differences in binding efficiency may indicate lower P inactivation, on a per unit Al basis, when elevated amounts of Al are added to the sediment, especially in deeper areas of lakes where sediment focusing may cause elevated Al accumulation to occur.     

Effects of raw water conditions on solution-state aluminum speciation during coagulant dilution

The speciation of aluminum in solutions of alum and various prehydrolyzed, aluminum-based water treatment coagulants was investigated by 27Al NMR at 5 degrees C and 25 degrees C. Alum solutions were seen to contain only mononuclear species including an AlSO4(+) complex, while the prehydrolyzed coagulant solutions contained polynuclear aluminum species, as well. The relative proportions of both polynuclear species and AlSO4(+) complex decreased in cold water. The presence of organic matter had little effect on the speciation of aluminum in diluted alum, but markedly reduced the relative proportion of the tridecamer species in the prehydrolyzed coagulant solutions. The relationship between Al speciation in the coagulants and organic matter removal during jar tests was considered, and the possible role of sulfate in both the formation of the tridecamer species and the effect of organic matter on coagulation efficiency was discussed.     

Metal interactions in contaminated freshwater sediments from the fly river floodplain,Papua New Guinea

Field data for sediment pH, Eh, sulphur and organic matter were analysed to determine their relationship with measured dissolved and particulate metals from sites in the Fly River affected by mine‐derived wastes. The above‐background concentrations of dissolved metals correspond to various concentration groups as demonstrated by copper for background (< 70 mg/kg), moderate (70–500mg/kg) and severe (> 500mg/kg), respectively. Dissolved Cu (r = 0.7431, p < 0.0005) and Mo (r = 0.7133,/> < 0.0005) were significantly correlated with their sediment component. Dissolved Al, Cd, Cu and Mo were positively correlated with sediment pH. Significant negative correlation between dissolved copper and sediment (SOM) organic matter (r = ‐0.3821, p < 0.05), and positive correlation with dissolved Al (r = 0.9358, p < 0.0005) suggest that dissolved Cu is present as a complex with either organic matter, Al/Fe oxyhydroxides, or oxyhydroxide‐organic matter colloids. Significant interrelations between dissolved Al, Cu and Mo with organic matter and the ratio of Fe/SOM also suggests that sediment physico‐chemical characteristics are important in the processes occurring in the Fly River floodplain sediments. These processes appear to be responsible for the significantly increased metal concentration in the water column.     

Using a battery of bioassays, benthic phytoplankton and the AUSRIVAS method to monitor long-term coal tar contaminated sediment in the Cache la Poudre River, Colorado

This survey provides information on sediment toxicity and structural characteristics of the macroinvertebrates and benthic phytoplankton at 10 locations in the Cache la Poudre River after long-term exposure to coal tar residue. The application of the Australian river bioassessment system (AUSRIVAS) as well as a biotest battery was used to evaluate the river ‘health’ condition. Coal tar is a dense nonaqueous-phase liquid of significant environmental concern due to its toxicity and persistence in the subsurface. Organisms like Selenastrum capricornutum, Daphnia magna and Chironomus tentans, representing different complexities in the biosphere, were selected as test systems for ecotoxicological studies. The results obtained in this study indicate that a biotest battery, macroinvertebrate and benthic phytoplankton communities are in principle suitable biological tools for evaluation of toxic oil and coal-derived substances in long-term contaminated river sediment.     

Methylmercury in water, seston, and epiphyton of an Amazonian river and its floodplain, Tapajós River, Brazil

Levels and accumulation of MeHg were characterized in filtered water, suspended organo-mineral matter, phytoplankton, zooplankton and epiphyton during the dry season and the wet season. In open water of the lentic and lotic ecosystems, the MeHg in filtered water (< 0.2 microm) was near or below the detection limit (< 0.02-0.03 ng/l). These concentrations represent < 5% of the Hgtot. content in filtered water. Inundated forests (Igapó) and macrophyte floating mats were the only sites where MeHg was significantly detected (0.07-0.24 ng/l), representing 3-22% of the Hgtot. in filtered water. MeHg concentrations in organo-mineral suspended matter (2-26 ng/g dry wt. representing 0.6-7.3% of Hgtot.) were correlated with the N content but not with the C content. Data suggest that MeHg enrichment of suspended matter is strongly influenced by the presence of degraded planktonic remains relatively rich in N and MeHg. In zooplankton, MeHg concentrations (20-140 ng/g dry wt.) increased from the dry season to the end of the wet season. This increase was followed by higher proportions of MeHg during the wet season in comparison to the dry season (15-40 to 50-70% of the Hgtot.). The epiphytic material collected from the roots of macrophyte floating mats contained 2-8.5 ng/g dry wt. of MeHg. The proportion of MeHg to Hgtot. in epiphyton (1.5-8.3%) correlated with its C and N contents. The data suggest a greater bioavailability of MeHg in the Tapaj6s River ecosystems due to the seasonal increase in water level and the consequent inundation of the floodplain. Inundation favours the development of large macrophyte floating mats which increases the bioavailability of epiphyton to herbivorous/detritivorous fish. The root zone of floating macrophytes and the flooded organic horizon of the Igapó forest are the only sites along the Tapajós River where significant MeHg can be detected in the water column and sediment. This new study supports the hypothesis that MeHg production and transfer to the first link of the food chain in Amazonian river systems is closely related to organic matter biogeochemistry in the floodplain environment.     

Sex- and age-related variation in elemental concentrations of contemporary Japanese ribs

Twenty elements (Al, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Sr, Ti, V, Zn, C and N) in 42 Japanese ribs (forensic medical autopsy cases) were determined using inductively coupled plasma atomic emission spectrometry (ICP-AES), atomic absorption spectrometry (AAS) and carbon and nitrogen analysis to examine sex- and age-related variation in the concentrations of these elements. Bone Fe and Pb concentrations were significantly higher, while P concentrations were lower in males. Elements which showed age-related variation were Ca, P, Al, Fe, Mg, Na, Pb and Zn. Of these, Al, Fe, Pb and Zn linearly accumulate in bone with advancing age. The elements Na and Mg showed the lowest and highest concentrations in the youngest age group (0-19 years), respectively, and reached plateau levels in older age groups. The Ca and P concentrations were highest in the 20-39-year age group, gradually decreasing throughout older age groups, indicating that osteoporotic bone loss occurs in the older subjects. In addition, the results of correlation analysis indicated that the organic matter content of the bone, represented by C or N concentration, was a factor which contributed to the elemental variation of the bone.     

Avian ecological risk potential in an urbanized estuary: Lower Hackensack River, New Jersey, U.S.A.

As part of a comprehensive ecological risk assessment on a broad range of species, the potential for adverse effects in birds was evaluated at a chromate ore processing residue disposal site, Study Area 7, located at the confluence of the Lower Hackensack River, Passaic River, and Upper Newark Bay. Although detection of elevated concentrations of total chromium in sediment prompted the study, it was also necessary to consider potential risks related to other chemicals present in elevated concentrations due to widespread anthropogenic activities in Upper Newark Bay and its watershed. U.S. Army Corps of Engineers' TrophicTrace^® software was used to predict exposure to avian receptors using measured concentrations of chemicals in sediment, measured concentrations of chemicals in benthic invertebrates, and measured site physicochemical parameters. The TrophicTrace^® model was improved as part of the Study Area 7 ecological risk assessment to account for (1) incidental ingestion of sediment by dabbling and diving birds, (2) area use factors for spatial overlap of wide-ranging fish species and piscivorous birds, (3) spatially-explicit utilization of the site by birds with a variety of foraging strategies, and (4) temporal patterns of site utilization by migratory species. The ecological risk assessment demonstrated that chromium in sediment does not pose unacceptable hazards to avian receptors. Potentially unacceptable hazards were indicated for several organic chemicals (i.e., pesticides, polychlorinated biphenyls, and dioxins/furans), with hazard quotients highest for Upper Newark Bay reference conditions, reflecting potential widespread chemical impacts to the estuary. The modifications to TrophicTrace^® conducted for this assessment may be prudent and applicable for improving the accuracy and realism of other assessments involving avian receptors exposed to chemicals via contaminated sediment and transfer through the food web.     

Long-term effects of phosphorus precipitations with alum in hypereutrophic Lake Süsser See (Germany)

Precipitation and inactivation of phosphorus (P) by the addition of aluminum (Al) is a widely applied lake restoration measure. Many studies about short-term effects are reported, but little is known about long-term effects. To reduce this lack of knowledge we investigated the German hardwater lake, Süsser See, which was treated almost annually from 1977 to 1992 with aluminum sulfate (alum). We conducted sediment core experiments in laboratory, as well as in situ investigations of sediment and pore water. The treatment is clearly recognizable in sediment depth profiles as increases of total phosphorus, NaOH-extractable phosphorus, and NaOH-extractable aluminum. The molar ratio of added Al to additionally bound P is approximately 2.1:1. Pore water profiles of soluble reactive phosphorus taken in situ and in sediment core experiments, as well as sorption batch experiments, illustrate that the Al(OH)3 layer's sorptive capacity is still not exhausted with further P sorption occurring in different P fractions. The P release of the sediment is affected by the magnitude of the downward flux into the P sorbing layer. However, sediment core experiments and a modeling exercise indicate that a buried P sorbing layer has little or no effect on the P release of the uppermost fresh sediment layers.     

Mercury and flooding cycles in the Tapajós River basin, Brazilian Amazon: the role of periphyton of a floating macrophyte (Paspalum repens)

Methylmercury (MeHg) increases mercury (Hg) toxicity and is biomagnified in the trophic chain contaminating riverine Amazon populations. Freshwater macrophyte roots are a main site of Hg methylation in different Brazilian environments. Paspalum repens periphyton was sampled in four floodplain lakes during the dry, rainy and wet seasons for measurement of total Hg (THg), MeHg, Hg methylation potentials, %C, %N, δ¹³C, δ¹⁵N and bacterial heterotrophic production as ³H-leucine incorporation rate. THg concentration varied from 67 to 198 ng/g and the potential of Me²⁰³Hg formation was expressive (1-23%) showing that periphyton is an important matrix both in the accumulation of Hg and in MeHg production. The concentration of MeHg varied from 1 to 6 ng/g DW and was positively correlated with Me²⁰³Hg formation. Though methylmercury formation is mainly a bacterial process, no significant correlation was observed between the methylation potentials and bacterial production. The multiple regressions analyses suggested a negative correlation between THg and %C and %N and between methylation potential and δ¹³C. The discriminant analysis showed a significant difference in periphyton δ¹⁵N, δ¹³C and THg between seasons, where the rainy season presented higher δ¹⁵N and the wet period lighter δ¹³C, lower THg values and higher Me²⁰³Hg formation. This exploratory study indicates that the flooding cycle could influence the periphyton composition, mercury accumulation and methylmercury production.     

Assessment of metal mobility in dredged harbour sediments from Barcelona, Spain

In order to assess heavy metal mobility in dredged harbour sediments, six superficial sediment samples covering a range of pollution levels and environments were collected in Barcelona Harbour. Samples were characterised in terms of major compounds (Al, Ca, Fe, Mn, Si, Ti, Mg, K and Na); total C, N and S contents; organic matter; and water content. Pseudo-total trace metal contents were assessed after aqua regia digestion (ISO 11466:1995). The modified BCR three-step sequential extraction procedure (BCR-SEP) was applied, and both major compounds (Al, Ca, Fe and Mn) and trace metals (Cd, Cr, Cu, Ni, Pb and Zn) were determined in the different extracts. Both the pseudo-total digestion method and the BCR-SEP were validated using two sediment certified materials from lakes (BCR CRM 701 and BCR CRM 601). The highest metal concentrations were observed in one of the sampling points which receives an urban discharge. The observed mobility order (percentage of metal extracted in the first step) of the six trace metals studied was Cd>Zn>Pb>Cu>Ni>Cr. The good agreement observed with the results obtained as the sum of the four steps (extractable+residue) and the pseudo-total content shows that laboratory working conditions were under control.     

Composition of particulate and dissolved organic matter in a disturbed watershed of southeast Brazil (Piracicaba River basin)

The elemental and isotopic composition of particulate and dissolved organic matter was investigated in the Piracicaba River basin, S?o Paulo State, Brazil. Comparison of riverine organic matter from the Piracicaba River basin, a region where rivers and streams receive urban sewage and industrial effluents, with data reported for the pristine Amazon system revealed significant differences associated with anthropogenic impacts. One important difference was N enrichment in the particulate organic material of the Piracicaba basin rivers, due to (a) urban and industrial effluents, and (b) enhanced phytoplankton growth, which results from the combination of nutrient enrichment and damming of sections of the rivers. Radiocarbon concentrations were overall more depleted (older 14C age) in the Piracicaba basin rivers than in the Amazon, which may reflect the importance of soil erosion in the former. Analyses of stable and radioactive carbon isotopes and lignin-derived compounds indicated that coarse particulate organic material is composed of a mixture of soil particles and degraded organic matter from C3 and C4 vascular plants. Fine particulate organic material was composed mainly of soil particles and phytoplankton cell remains, the latter especially during low water. Ultrafiltered dissolved organic matter was the most degraded fraction according to its lignin oxidation products, and showed the greatest influence of C4 plant sources.     

Impacts of manipulated regime shifts in shallow lake model ecosystems on the fate of hydrophobic organic compounds

Regime shifts in shallow lakes may significantly affect partitioning of sediment-bound hydrophobic organic chemicals (HOCs) such as polychlorobiphenyls (PCB) and polycyclic aromatic hydrocarbons (PAH). In replicated experimental model ecosystems mimicking the alternative stable states ‘macrophyte-dominated’ and ‘suspended solid – phytoplankton dominated’, we tested the effects of macrophytes and benthivorous fish presence on mass distribution and bioaccumulation of hexachlorobenzene, PCBs and PAHs. HOC mass distributions and lipid-normalized concentrations in sediment (Soxhlet- and 6-h Tenax-extractable), suspended solids, macrophytes, periphyton, algae, zooplankton, invertebrates and carp revealed that mobile, i.e. less hydrophobic or less aged HOCs were more susceptible to ecological changes than their sequestered native counterparts. Macrophytes were capable of depleting considerable percentages of the bioavailable, fast desorbing HOC fractions in the sediment upper (bioactive) layer, but did not have a significant diluting effect on lipid-normalized HOC concentrations in carp. Carp structured invertebrate communities through predation and stimulated partitioning of HOCs to other system compartments by resuspending the sediment. These results show that shifts in ecosystem structure have clear effects on fate, risks and natural attenuation of sediment-bound organic contaminants.     

Historical analysis of salmon-derived polychlorinated biphenyls (PCBs) in lake sediments

Several recent studies have highlighted the importance of salmon as a means to deliver biomagnifying contaminants to nursery lakes. There is a lack of studies, however, which demonstrate empirically how this source has varied through time. This is of great significance because past salmon-derived contaminant loading was potentially greater than it is today. By analyzing radiometrically dated sediment cores collected from ten lakes in Alaska and British Columbia (B.C.), we relate historical numbers of sockeye salmon spawners to ΣPCB concentrations and δ¹⁵N values (a paleolimnological proxy for past salmon-derived nitrogen) in the sediments. The results confirm that sockeye salmon have provided an important route for PCBs to enter the lakes in the past, a finding that is especially evident when the data of all lakes are pooled. Significant relationships between sockeye salmon numbers and δ¹⁵N, as well as ΣPCB concentrations and δ¹⁵N in sediments, were also found. However, it is difficult to establish relationships between salmon numbers, ΣPCBs and δ¹⁵N in individual lakes. This may be due to a number of factors which may influence contaminant loadings to the lakes. The factors include: a) changing salmon contaminant loads over time resulting from a lag in the upper ocean reservoir and/or changing salmon feeding locations; b) greater importance of atmospheric transport in lakes with relatively low salmon returns; and c) increased PCB scavenging due to higher algae productivity in the lakes in recent years.