Evaluation of phosphorus bioavailability in sediments of the shallow lakes in the middle and lower reaches of the Yangtze River region,China

Phosphorus (P) fractions and their bioavailability in the sediments from the middle and lower reaches of the Yangtze River region were investigated using different chemical extraction methods. The results show that the contents of bioavailable P in the sediments extracted by different extraction procedures varied greatly. But their rank order was similar. Potentially releasable P (PRP) was the largest, followed by algal available P (AAP), NaHCO₃ extractable P (Olsen-P), water soluble P (WSP), and readily desorbable P. PRP contributed approximately 60% to total P (TP) in most sediments, AAP 20%, Olsen-P 15%, WSP 2%, and readily desorbable P (RDP) 0.5%. For the heavily polluted sediments, their bioavailable P extracted from TP mainly originated from inorganic P (IP), IP mainly originated from NaOH–P, the bioavailable P concentrations can be evaluated by measuring the concentrations of TP, NaOH–P, and IP. For the slightly polluted sediments, the bioavailable P can only be evaluated by different chemical extractable methods.     

太湖入湖河道沉积物中生物利用磷和营养水平分析

为了解太湖入湖河道的营养状况,研究了太湖西部河流沉积物生物利用磷的组成与分布。研究结果显示,北部沉积物中营养元素较高,南部较低;沉积物中生物利用磷的含量次序为藻类可利用磷(AAP)>NaHCO3提取磷(OLP)>水溶性磷(WSP)>易解吸磷(RDP),其中AAP是重要的生物利用磷,AAP的比例越高,富营养化程度越高。AAP与营养元素的相关性在不同区域河道有所不同,北部河道与总氮(TN)、总磷(TP)相关性较好,中部和南部河道与沉积物有机质总量(TOM)相关性较好。沉积物的生物利用磷受不同污染源影响较大。对比河道沉积物与湖泊沉积物的特征,发现湖泊沉积物中生物利用磷(BAP)/总磷(TP)、藻类可利用磷(AAP)/总磷(TP)都高于河道沉积物,表明湖泊沉积物中的磷更容易被植物吸收。     

Sediment phosphorus fractions and profile distribution at different vegetation growth zones in a macrophyte dominated shallow Wuliangsuhai Lake,China

Sediment phosphorus (P) fractions and profile distribution at submerged macrophyte growth zone, emergent macrophyte growth zone and open-water zone were studied in Wuliangsuhai Lake, China, as well as the correlations among water content, grain size, and organic matter and P fractions. Among the three surveyed zones, the highest concentrations of most P forms occurred in the surface sediment and the lowest between a depth of 12 and 22 cm, except HCl-P and NaOH-P. Sediment phosphorus was mainly associated to inorganic forms (>50%) in three surveyed areas, and the highest value of inorganic phosphorus (IP) in the surface sediment was obtained from submerged macrophyte growth zone. Submerged and emergent macrophytes increased the IP content by 107 and 44 μg/g, respectively, in the surface sediment compared with open-water zone. Vertical profiles of IP in the three surveyed zones showed that the concentrations decreased from surface to 12 cm depth and then increased. There was a similar trend in the sediment profiles of organic phosphorus (OP) and total phosphorus (TP), but the highest concentration of OP and TP in surface sediment was obtained from the emergent macrophyte growth zone. Compared with open-water zone, the emergent macrophyte increased TP content in surface sediment by 1.73 times to 1,320 μg/g, while submerged macrophyte enhanced TP content in the surface sediment by 1.13 times to 865 μg/g. It was observed that in macrophyte growth zones, a strong linear correlation existed between organic matter and OP (r > 0.98), and the maximum concentrations of OP were present in the areas with maximum concentrations of organic matter. Results show that, although rooted macrophyte could uptake directly P from sediments, it is responsible for increasing the internal P loading especially OP by reducing current velocities, attenuating wave energy and generating organic residue in Wuliangsuhai Lake.     

不同干燥方式对湖泊沉积物磷提取的影响

以滇池5个典型区域表层沉积物为例,研究了自然风干、低温烘干和真空冻干等3种干燥方式对沉积物中磷的形态含量及其生物有效性测定的影响。结果表明：烘干、风干过程促进了沉积物有机磷的降解转化和微生物磷的释放,导致有机磷的含量偏低,总磷含量却比冻干高。各形态磷受不同干燥方式的影响程度不同,风干样品中BD-P较高,冻干样品中NaOH-rP含量最高,NH4Cl-P、HCl-P、残渣磷（Residual-P）由于含量较低或其化学性质比较稳定而差异不大。冻干样品中生物可利用磷分别比风干、烘干高26.7%、20.2%,表明冻干处理能较为真实地反映沉积物中磷的组成特征,是比较理想的样品干燥方式。各形态含量顺序为：藻类可利用磷（AAP）〉NaHCO3可提取磷（Olsen-P）〉水溶性磷（WSP）〉易解吸磷（RDP）。沉积物中Olsen-P与NH4Cl-P、BD-P、NaOH-rP、活性磷及上覆水体总磷水平呈显著正相关,因此可作为评价滇池沉积物磷的生物有效性的重要指标。     

Organic phosphorus fractionation in wetland soil profiles by chemical extraction and phosphorus-31 nuclear magnetic resonance spectroscopy

Organic P (OP) plays an important role in soil P cycling and is a potential P source for wetland plants. In this study, a modified chemical sequential fractionation method and ³¹P nuclear magnetic resonance spectroscopy (³¹P NMR) of NaOH–EDTA extracts were used to examine the distribution of organic P fractions and compounds in soil profiles of the Beijing Yeyahu Wetland, China. The influence of acid treatment prior to NaOH–EDTA extraction on ³¹P NMR spectra was also investigated. Results show that highly resistant OP was the major class of organic P. The rank order of organic P fractions was highly resistant OP (on average accounting for 68.5% of total OP) > moderately resistant OP (15.8%m of total OP) > moderately labile OP (11.4% of total OP) > labile OP (4.3% of total OP). Most of the organic P fractions decreased with soil depth due to the accumulation of plant residues in surface soils and the deposition and diagenesis of soils. Moderately (r = 0.586, p < 0.01) and highly (r = 0.741, p < 0.01) resistant OP fractions were positively correlated with soil organic matter. Phosphorus compounds including orthophosphate (23–74.6% of total P in spectra), monoester phosphate (18.6–76%), diester phosphate (nil-7.8%) and pyrophosphate (nil-6.7%) were characterized using ³¹P NMR. Monoester-P was the dominant soil organic P compound identified. The proportion of monoester-P increased significantly in NaOH–EDTA extracts with HCl pretreatment and it was confirmed by chemical analysis. Therefore, it can be concluded that HCl pretreatment can remove more than half of the inorganic P and increase the overall recovery rate of organic P during subsequent NaOH–EDTA extraction, which might be a new approach for organic P detection. Furthermore, the OP chemical sequential fractionation method presented in this study is an integrated and comprehensive approach which can be used for further verification.     

Factors affecting the internal loading of phosphorus from calcareous sediments of Baiyangdian Lake in North China

Phosphorus (P) is the limiting macronutrient for primary production in most lakes. Sediment characteristics are strongly correlated to the internal P loading in lakes. This study investigated speciation of P, Fe, Al, and Ca in sediments of six sampling sites with varying trophic status in Baiyangdian Lake of North China during the period of July 2008 and March 2009. The results of sequential extraction experiments of the top sediments showed that total extractable P ranged approximately from 13 to 28 μmol g⁻¹ for all sampling sites and the rank order of P-fractions was HCl–P > NaOH₈₅–P > NaOH₂₅–P > BD–P > NH₄Cl–P. BD–P and BD–Fe had a consistent change with seasons. Their concentrations were both much higher in early spring and mid-autumn. BD–Fe, Al extracted with NaOH at 25°C and 85°C affected corresponding P concentration in sediments, while high concentration of extractable Ca from sediments showed no direct effects. According to the Kopáček et al. model of the molar ratios of Al:Fe and [NaOH₂₅–Al]:[NH₄Cl–P + BD–P], there was potential P release from sediments twice a year for some hypereutrophic sites in early spring and mid-autumn, especially in the former season.     

Phosphorus fractions and bioavailability in relation to particle size characteristics in sediments from Lake Hongfeng, Southwest China

Information on the chemical composition of phosphorus (P) fractions in sediments is fundamental to understanding P bioavailability and eutrophication in lake ecosystems. Phosphorus fractions and its bioavailability in sediments cores of Lake Hongfeng, southwest China, were investigated using a chemical sequential extraction scheme. Relationships between P fractions, P bioavailability and particle sizes were discussed. P fractions concentrations were ranked in the order: Residual-P > NaOH–rP > NaOH–NRP > HCl–P > BD–P > NH₄Cl–P, and all of them decreased with increasing sediment depth. Statistical analysis showed that concentrations of bioavailable P (BAP) which includes the NH₄Cl–P, BD–P, NaOH–rP and NaOH–NRP fractions ranged from 404.68 to 1,591.99 mg/kg and accounted for 26.8–71.8 % of the concentrations of total phosphorus (TP) in the top 5 cm sediments, whereas in the whole sediment cores, their concentrations ranged from 239.70 to 1,591.99 mg/kg and accounted for 26.8–76.0 % of TP. The results suggested that the sediments were a large potential source of P for algae blooms in Lake Hongfeng. Phosphorus fractions and their potential bioavailability were influenced by the sediment particle sizes, especially the bioavailability of the NH₄Cl–P fraction, which was strongly affected by the presence of fine particle sizes in the sediments.     

Concentration, Molecular Weight Distribution and Neutral Sugar Composition of DOC in Maritime Antarctic Lakes of Differing Trophic Status

The molecular weight distributions and hydrolysable neutral sugar composition of dissolved organic carbon (DOC) was investigated in four maritime Antarctic lakes on Signy Island of different trophic status; Heywood Lake (eutrophic), Light Lake (oligo-mesotrophic), Sombre Lake and Moss Lake (both oligotrophic). Tangential flow ultra-filtration (TFU) was used to separate DOC into high molecular weight (HMW; >1000 Da) and low molecular weight (LMW; < 1000 Da) size fractions. Pulsed amperometric detection-high performance liquid chromatography (PAD-HPLC) was used to determine the hydrolysable neutral sugar molecular composition of each size fraction. Total DOC concentrations defined the trophic trend in the four lakes and ranged from 8 to 303 μM. The <1000 Da fraction of all the lakes dominated the DOC distribution, comprising 76% in Light Lake which also had the highest chl-a concentrations. Heywood Lake was relatively enriched in >1000 Da total organic carbon and had extremely high concentrations of total hydrolysable neutral sugars (11 μM) corresponding to 43% of total DOC. However, no clear pattern was apparent with regard to lake trophic status and potential sources of DOC, and the measured variations in individual aldose concentration, composition and their various molecular weight fractions.     

Application of allochthonous organic carbon and phosphorus forms in the interpretation of past environmental conditions

Organic matter in sediments, for instance, carbon, nitrogen and phosphorus, can be used to reconstruct the paleoecological and pollution history of lakes and their catchment basins. In this paper, the contents of allochthonous organic carbon (allochthonous OC) and autochthonous organic carbon (autochthonous OC) in sediment cores taken from Wuliangsuhai Lake and Daihai Lake in northern China are quantified by using a binary model, and phosphorus forms in the sediment cores from the two lakes are extracted by sequential extraction techniques. The results indicate that the palaeoenvironment and paleoclimate of Daihai Lake and its catchment basin in the recent 250 years can be well reconstructed based on the content of allochthonous OC. The climate was relatively humid and warm in the period of 1865–2005, while relatively dry and cold in the period of 1765–1865. The sedimentary information of allochthonous OC in the 22–42-cm portion of the sediment cores in Daihai Lake corresponds to the final cold fluctuation of the Little Ice Age that occurred since the Middle Holocene. The difference of phosphorus forms in the sediment cores between the two lakes indicates that phosphorus input to the lakes and the correlation between phosphorus forms and distribution and the changes of environment are influenced by the eutrophication mechanisms and environmental conditions of the two lakes.     

Study on vertical distribution and activity factor of P forms in sediments of three urban shallow lakes in People’s Republic of China

The vertical variation of P forms in sediments of urban shallow lakes in China, Xuanwu Lake, Daming Lake and Mochou Lake, were sequentially extracted and measured with the method of SEDEX. The results indicated the TP content in the sediment profiles ranged from 371.94 to 777.25 mg kg⁻¹ for Xuanwu Lake, 1,308.14 to 4,632.63 mg kg⁻¹ for Daming Lake, and 995.49 to 1,860.71 mg kg⁻¹ for Mochou Lake. The results of sequential extraction showed that Ca-P and Fe-P were the main fractions. Meanwhile, the proportions of Bio-P to TP were 35.24% for Xuanwu Lake, 29.57% Daming lake, and 25.26%, for Mochou Lake, indicating a high potential of P releasing. The content of Bio-P was significantly and positively correlated with TP (r = 0.978, P < 0.01). Lake hydrations conditions played an important role in the distribution and contents of Bio-P and TP. In the region with macrophytes, the contents of TP and Bio-P were relatively low. Physicochemical properties of sediments were significantly related to the fraction distribution and P contents, and might play an important role in controlling P activity and mobility. Moreover, Fe showed an evident influence on P fraction and the ratio Fe/P might be good indicator to the contents and composition of active P in sediments.     

Phosphorus distribution in the sediments of a shallow eutrophic lake,Lake Chaohu,China

In this study, the sediment profiles of total phosphorus (TP), inorganic phosphorus (P_i), organic phosphorus (P_o), C/P and N/P were used to investigate time-dependent P distribution changes in Lake Chaohu. The characteristics of P_i and P_o fractions in the surface sediments were studied and the difference between east and west lake region was also discussed. The P_i and P_o contents displayed a clear gradient from east to west in sediments of Lake Chaohu, and the P_o/P ratios were lower in sediments with industrial and urban pollution sources input in west lake region. The study indicated that different sediments area had diverse concentrations and distributions of P_o fractions due to their different drainage basin and pollution sources. The profile distribution of the C/P and N/P ratios decreased with increasing depths and stayed relatively constant ratios at the depths of 15–30 cm. The C/P and N/P ratios were always below Redfield ratios in sediment profile, indicating P enrichment but likely due to the preferential loss of carbon in respect to phosphorus. The rank order of P_i-fractions extracted was HCl-P_i > NaOH-P_i > NaHCO₃-P_i in surface sediments. The relative distribution of NaHCO₃-P_i and HCl-P_i was in agreement with the trophic conditions of the regions studied. Among the sequentially extracted P_o forms, the rank order of P_o fractions was residual P_o > HCl-P_o > fulvic acid-P > humic acid-P > NaHCO₃-P_o, with mean relative proportion of 5.4:3.4:2.2:1.1:1.0.     

Effect of addition of organic residues on phosphorus release kinetics in some calcareous soils of western Iran

We investigated the effects on phosphorus (P) release of the addition of potato, wheat, and sunflower residues and fruit compost to five calcareous soils. Residue was added at the rate of 20 g kg⁻¹. After 2 months of incubation, P values in control and amended soils were used for kinetic studies and fractionated by a sequential extraction procedure. The relative contribution of available P fraction (KCl-P) increased from 1.4% in control soils to 1.8%, 1.9%, 2.2%, and 2.3% in soils amended by fruit, wheat, potato, and sunflower residue addition, respectively, indicating that organic residues increased P in this fraction. In soils amended with different residues, the percentage of Olsen-P released over 86-h successive extractions with 0.01 M CaCl₂ ranged from 57.6% for fruit residue addition (average of five soils) to 60.5% for potato residue addition. The ability of residues to release P depended on the soil properties, with 21.9 mg kg⁻¹ (average of all residues) released to soil 2 and 77.4 mg kg⁻¹ released to soil 4. Also residues behaved differently, with 31.5 mg kg⁻¹ (average of five soils) released by fruit residues and 40.0 mg kg⁻¹ released by sunflower residues. Release of P was best described by a parabolic diffusion model. The corresponding rate constant (mg kg⁻¹ h^−1/2) for P release for amended soils, defined as the release rate averaged for five soils, was found to decrease in the order: potato (2.73) > sunflower (2.61) > wheat (2.56) > fruit (2.50). The present study demonstrates that addition of residues improves P availability of these calcareous soils by increasing extractable P and the release rate and could be an alternative, indigenous source of P. However, the increase in P availability and the release rate following organic residue application suggests high potential mobility to water sources.     

Characteristics and Influence of Phosphorus Accumulated in the Bed Sediments of a Stream Located in an Agricultural Watershed

We investigated the accumulation and influence of bioavailable P (BAP) in sediments of a stream located in an agricultural area of the Lake Mendota watershed in Wisconsin, USA. During hydrologic events, the stream carried high concentrations of suspended sediment (up to 250 mg/l) and BAP (up to 2.5 mg/l). Bed sediments were highly enriched in BAP, as inventories of BAP in the top 10 cm of sediment ranged from 143 to 14,500 μg P/cm². Space variations in BAP inventories were related to site-specific hydrodynamics and geochemical factors, including iron (Fe; r ² = 0.71) and aluminum (Al; r ² = 0.54) concentrations. Most sites behaved as potential sinks for dissolved reactive phosphate during hydrologic events and potential sources during base-flow periods. Through the combination of site-specific factors and geochemical controls, Dorn Creek modifies the amount, timing, and composition of P delivered from the watershed to downstream sites and water bodies.     

Impact of municipal compost on soil phosphorus availability and mineral phosphorus fractions in some calcareous soils

The phosphorus (P) resources worldwide are limited, and the prices of commercial P fertilizer continue to increase. Therefore, the use of P containing wastes is important for P recycling in agriculture. The P fractionation methods have been widely applied to characterize the effect of land use practice on soil P dynamics. Information about effect of organic manures on available P and inorganic P (P_i) fractions in calcareous soils of Chaharmahal va Bakhtiari province is limited. The objectives of this research were to study the effect of municipal compost (MC) on available P and P_i forms in five calcareous soils. Municipal compost was applied at the rates of 0, 0.5, 1.0, 1.5 and 2.0% (w/w). Samples were incubated at 25?±?1°C and 20% moisture content for 150?days. At the end of incubation, available P in MC-treated soils was extracted by Olsen, AB-DTPA and 0.01?M CaCl₂ methods. Also, phosphorus was fractionated chemically into labile P (LP), non-occluded P(NP), re-adsorbed P (RP), occluded P (OP), calcium phosphates (CaP) and residual P. The results showed that there was a linear increase in soil available P with MC application. There was a significant positive relationship between Olsen-P, AB-DTPA-P and 0.01?M CaCl₂-P, and MC additions with slopes ranged from 0.471 to 0.583, 0.032 to 0.106, and 0.033 to 0.081, respectively. The increase in soil test P (STP) from MC additions was not related to the initial STP of the soils. A sharp increase in LP, NP and CaP and decrease in residual P concentration occurred in all soils with MC application. It can be concluded that MC applied to calcareous soils may enhance P nutrition of plants. Furthermore, applied P partitioning into the relatively available forms means the potential erosion losses of P to streams and other bodies of water.     

Distribution and speciation of phosphorus in sediments of Dongping Lake,North China

Dongping Lake is an important regulator for the Eastern Route of South-to-North Water Diversion Project in China, and the water quality assurance of it is of great importance. To investigate the distribution characteristics and burial process of phosphorus (P) in Dongping Lake as well as their relationship with regional economic development and human activities, 33 spatially distributed surface sediment samples and one lake sediment core were extracted from Dongping Lake. A harmonized procedure for the P forms in freshwater sediments developed by the European Programme, Standards, Measurements, and Testing was used in this paper. The results show that NaOH–P (P bound to Al, Fe, Mn oxides or hydroxides), HCl–P (Ca-bound P), inorganic phosphorus (IP), organic phosphorus (OP), and total phosphorus (TP) in the surface sediments show a strong spatial variability. The highest NaOH–P and OP concentrations were observed in the eastern and south-eastern region of the lake and decreased gradually away from the mouth area of Dawen River. We deduced that anthropogenic input via the Dawen River is the main contributor. The higher concentration of HCl–P occurred in the north-west region of the lake and increased in a gradient away from the mouth area of Dawen River, and this pattern of distribution could be related to grain-size effects and higher transport energies close to riverine inlets. Pollution reflected by phosphorus in the core sediments of Dongping Lake is well consistent with the economic development history of Dongping County. From the beginning of the 20th century to the middle 1970s, the concentrations of each P speciation did not vary largely and runoff of the Yellow River mainly contributed to the P accumulation in the sediment, which might reflect the background values of them in the lake in pre-industrial period. The stable Mz (mean grain size), low loss-on-ignition (LOI), and high sedimentary flux also support this. The rapid increase of NaOH–P and OP at 10–0 cm (especially 5–0 cm) indicates the enhancing anthropogenic eutrophication since the middle 1970s. The LOI peak period and a coarsening of particle size also support this interpretation. However, the decreasing of TP and HCl–P was attributed to the change in sediment supply. As due to construction of dams around the lake, runoff of the Dawen River mainly contributed to the P accumulation in the sediment during this period.     

Alpine lake sediment records of the impact of glaciation and climate change on the biogeochemical cycling of soil nutrients

Lake sediment cores from the Coast Mountains of British Columbia were analyzed using chemical sequential extractions to partition the dominant geochemical fractions of phosphorus (P). The P fractions include mineral P (the original source of bioavailable P), occluded P (bound to soil oxides), and organic P (remains of organic matter). By comparing P fractions of soil and recent lake sediment samples, these fractions are shown to be a valid proxy for landscape-scale nutrient status. Changes in soil development for an alpine watershed (Lower Joffre Lake) are inferred from the P fractions in the basin's outlet lake sediments. Glacially sourced mineral P dominates at the base of the core, but several rapid shifts in P geochemistry are evident in the first ∼3000 yr of the record. The latter indicates an interval of early and rapid soil nutrient maturation from ∼9600 to 8500 cal yr BP and a significant influx of slope-derived material into Lower Joffre Lake. A substantial increase in mineral P occurs at ca. 8200 cal yr BP, consistent with the cold event in the vicinity of the North Atlantic at that time. The more recent record reveals a continual increase in the proportion of mineral P from glacial sources to the lake, indicating a trend toward cooler conditions in the Coast Mountains.     

Diatom-inferred depth models in 8 Canadian boreal lakes: inferred changes in the benthic:planktonic depth boundary and implications for assessment of past droughts

Assessment of past drought in boreal regions, a region predicted to be strongly affected by climate warming, can provide insights into future availability of water. However, limited instrumental data and paleoclimatic data are available for this assessment. To address this lack of data in the boreal region of northwest Ontario, a regional study of lakes in the Winnipeg River Drainage Basin was initiated. Diatom-inferred (D-I) depth models were developed based on surface samples collected along a depth gradient within 8 small boreal lakes. Weighted-averaging and modern analog approaches provided robust within-lake depth models for each of the study lakes, with bootstrapped r² values ranging from 0.90 to 0.98, and root-mean-squared-errors of prediction (RMSEP) between 1.1 and 2.5 m. Large differences in the estimated depth optima for three representative, but common diatom species across our 8 study lakes suggested that within-lake calibration datasets are more appropriate for inferring past drought based in depth models than a regional multi-lake calibration dataset, and that light and related variables are controlling factors governing the maximum depth of benthic taxa. A down-core application of the D-I depth models on a near-shore core from Meekin Lake, retrieved near the present-day ecotone between the benthic and planktonic diatom assemblages indicated highly similar trends in inferred depth (r = 0.96). The models have significant correlations with other metrics of changes in depth including diatom species richness (r = 0.74–0.78) and evenness (r = 0.76–0.8), thereby allowing a check on the strength and direction of the depth inferences down-core. Near-shore cores located near the benthic:planktonic transition is a sensitive region that can provide estimates of past droughts in lakes where such inferences have been difficult to estimate.     

Distribution of nitrogen forms in surface sediments of lakes from different regions,China

The characteristics of nitrogen fractions in the surface sediments of lakes from Eastern Plain Region, Yunnan-Guizhou Plateau Region, Northeast China Region, Qinghai-Tibet Plateau Region and Mongolia-Xinjiang Plateau Region were investigated and the differences of five lake regions on nitrogen fractionation were discussed. The results indicated that organic nitrogen (N_org) was the major nitrogen fraction accounting for 76.38–92.02 % of N_tot in sediments. The rank order of average N_org and N_tot of sediments in five lake regions was: Yunnan-Guizhou Plateau Region > Northeast China Region > Mongolia-Xinjiang Plateau Region > Qinghai-Tibet Plateau Region > Eastern Plain Region. The exchangeable nitrogen had a similar distribution as organic nitrogen in the studied sediments. NH₄ ⁺–N is the main exchangeable nitrogen of sediments in the studied lakes except in Lake Qinghai and Lake Yamdrok which contained higher nitrate concentrations than ammonium. Fixed ammonium (N_fix) in the sediments of studied lakes was irregularly distributed with the values ranging from 99.45 to 329.02 mg/kg. TOC was significantly and positively correlated with ammonium, nitrate, N_org and N_tot, while N_fix was negatively correlated with nitrate probably due to electrostatic attraction between N_fix and nitrate in layers of sediments.     

GIS‐based reconstruction of Late Weichselian proglacial lakes in northwestern Russia and Belarus

Reconstructing ice‐lake histories is of considerable importance for understanding deglacial meltwater budgets and the role of meltwater reservoirs for sea‐level rise in response to climate warming. We used the latest data on chronology and ice‐sheet extents combined with an isostatically adjusted digital elevation model to reconstruct the development of proglacial lakes in the area of the Karelian ice stream complex of the Late Weichselian Scandinavian Ice Sheet on the East European Plain. We derived the deglacial ice lake development in seven time‐slices from 19 to 13.8 ka, assuming the individual ice‐marginal positions to be isochronous throughout the studied domain. Modelling is based on mapping of critical drainage thresholds and filling the depressions that are potentially able to hold meltwater. Such an approach underestimates the real dimensions of the ice lakes, because the role of erosion at the thresholds is not considered. Our modelling approach is sensitive to the (local) ice‐margin location. Our results prove the southward drainage of meltwater during the glacier extent maxima and at the beginning of deglaciation whereas rerouting to the west had taken place already around 17.5 ka, which is some 1.5 ka earlier than hitherto supposed. The total ice‐lake volume in the study area was lowest (~300 km³) during the maximum glacier extent and highest (~2000 km³) during the highstand of the Privalday Lake at c. 14.6 ka. At 14.6–14.4 ka, the Privalday Lake drained to the early Baltic Ice Lake. The released ~1500 km³ of water approximately corresponds to 20% of the early Baltic Ice Lake water volume and therefore it is unlikely that it was accommodated there. Thus, we argue that the additional meltwater drained through the Öresund threshold area between the early Baltic Ice Lake and the sea, becoming a part of the Scandinavian Ice Sheet's contribution to the Meltwater Pulse 1A event.     

Forms of phosphorus in sediments from the Goczałkowice Reservoir

The occurrence of Total P (P-Tot) and the mineral forms of P (P-Min) in sediments from Goczałkowice Reservoir were investigated using inductively coupled plasma-optical emission spectrometer (ICP-OES). The method is based on sequential extractions of the sediment samples, each releasing four forms of inorganic P: loosely bound P, P bound to Al (P-Al), P bound to Fe (P-Fe) and P bound to Ca (P-Ca). Sediment samples for studies presented in this work were collected in April, August and November of 2009 from four sites of the Goczałkowice Reservoir. Significant variations in the P forms with sediment grain size were observed. The most abundant form of inorganic P in the bottom sediment was P-Fe. Other P forms were as follows: P-Ca > P-Al > loosely bound-P. Moreover, P compounds were studied using ³¹P NMR. It was found that the predominant form was inorganic orthophosphate.