Degradation rates of organic phosphorus in lake sediment

Phosphorus (P) binding groups were identified in phytoplankton, settling particles, and sediment profiles by ³¹P NMR spectroscopy from the Swedish mesotrophic Lake Erken. The ³¹P NMR analysis revealed that polyphosphates and pyrophosphates were abundant in the water column, but rapidly mineralized in the sediment. Orthophosphate monoesters and teichoic acids degraded more slowly than DNA-P, polyphosphates, and P lipids. Humic acids and organic acids from phytoplankton were precipitated from the NaOH extract by acidification and identified by ³¹P NMR spectroscopy. The precipitated P was significantly more recalcitrant than the P compound groups remaining in solution, but does not constitute a major sink of P as it did not reach a stable concentration with depth, which indicates that it may eventually be degraded. Since P also precipitated from phytoplankton, the origin of humic-P can not be related solely to allochthonous P.     

The role of Gloeotrichia echinulata in the transfer of phosphorus from sediments to water in Lake Erken

The abundance of Gloeotrichia echinulata colonies in the sediments of Lake Erken and their phosphorus content were investigated to determine the contribution of Gloeotrichia colonies to total sediment phosphorus. Moreover, the potential size of the algal inoculum and the migration to the water during summer were estimated.The surplus phosphorus content of the resting colonies in the sediment was about 45% of total phosphorus, which maximized at 8.5 µg P (mg dw)^–1 or 81 ng P colony^–1. The C:P ratio (by weight) in the early colonies appearing in the lake water was 50:1, while the ratio stabilized at 150 during the major migration period. The internal supply of surplus phosphorus was used during the pelagic growth of the colonies.The internal phosphorus loading to the epilimnion of Lake Erken due to Gloeotrichia migration could, from the measurements of the increase in particulate epilimnetic phosphorus, be estimated at 40 mg P m ^–2 or 2.5 mg P m^–2 d^–1 in late July and early August. Determination of the number of colonies in the sediment before and during the migration verified this value to be a conservative estimate of the internal phosphorus loading due to Gloeotrichia migration to the epilimnion in Lake Erken.The sediment P content calculated from the P concentration in early epilimnion colonies resulted in a value of 35 µg P (g dw)^–1 as a maximum. This corresponds to only 3% of the total phosphorus content in Lake Erken sediment.     

Microscale decoupling of sediment oxygen consumption and microbial biomass in an oligotrophic lake

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Surficial sediment phosphorus fractions along a biogeochemical gradient in Nyanza (Winam) Gulf, northeastern Lake Victoria and their possible role in phosphorus recycling and internal loading

Different phosphorus fractions and metal element composition of surficial sediments were measured on three occasions in 2005 and 2006 along a transect between Nyanza Gulf and offshore Lake Victoria, in order to assess the potential for sediments to contribute to the water column P concentrations in Lake Victoria. Total phosphorus (TP), apatite phosphorus (AP), inorganic phosphorus (IP) and organic phosphorus (OP) increased in sediments along the gulf towards the main lake while the non-apatite inorganic phosphorus (NAIP) increases were less defined. The longitudinal gradient of sediment TP and its fractions in Nyanza Gulf is a result of high rates of terrigenous input and resuspension and transport of the light, phosphorus rich inorganic and organic matter towards the main lake. TP in the sediment ranged from 812.7 to 1,738 mg/kg dry weight (DW) and was highest in the Rusinga Channel, the exchange zone between the gulf and the main lake. AP was the most important TP fraction, contributing between 35 and 57.3% of TP. Ca content in the sediment was strongly associated with TP and AP in the sediment (r² = 0.92 and 0.98, respectively) in the gulf and the channel, indicating the importance of apatite in controlling P availability in these zones. In the gulf and the Rusinga Channel, the less bioavailable apatite phosphorus dominated, whereas in the deeper main lake OP was the major fraction illustrating the importance of anaerobic release of P from sediments and acceleration of internal P loading in the main lake.     

High resolution measurements of sediment resuspension above an accumulation bottom in a stratified lake

A detailed record of suspended particulate matter (SPM) concentrations in the benthic boundary layer (BBL) 1.5 m above an accumulation bottom and 13.5 m below the surface was obtained from frequent (30 min interval) beam attenuation measurements made with a Sea Tech transmissometer in the main basin of Lake Erken, a moderately deep (mean depth 9 m, maximum depth 21 m) dimictic lake in central Sweden. Concentrations of SPM (g m^–3) were not as strongly correlated to the beam attenuation coefficient (c, [m^–1]), as were concentrations of the inorganic SPM fraction. Apparently, this was caused by large optically inactive organic particles which significantly affected the measurements of SPM, but had little effect on the attenuation of light.When the water column was thermally stratified, SPM concentrations in the BBL showed a seasonal increase which was related to an increase in the thermocline depth. As the epilimnion deepened, there was also a marked increase in the occurrence of rapid and large changes in SPM concentration. After the loss of stratification, the amount of SPM and the temporal variability in its concentration was reduced. Since surface waves could not influence sediment resuspension at the depth of measurement, these data show the importance of internal waves in promoting sediment resuspension in areas of sediment accumulation. The relatively short period in each summer, when the thermocline reaches a sufficient depth to allow for resuspension over accumulation bottoms, can have important consequences for both the redistribution of lake sediments and the internal loading of phosphorus.     

Spatial and temporal variation in the biomass and nutrient status of epilithic algae in Lake Erken, Sweden

1. The aim of this study was to estimate patchiness in biomass and in the internal nutrient status of benthic algae on hard substrata (epilithon) in Lake Erken, Sweden, over different levels of distance, depth and time. Knowledge of the sources and scale of patchiness should enable more precise estimation of epilithic biomass and nutrient status for the entire lake. We focused on the horizontal scale, about which little is known. 2. We sampled epilithon by SCUBA diving and used a hierarchical sampling design with different horizontal scales (cm, dm, 10 m, km) which were nested in two temporal scales (within and between seasons). We also compared two successive years and three sampling depths (0, 1 and 4 m). Biomass was measured as particulate carbon and chlorophyll a (Chl a) and internal nutrient status as carbon : nitrogen : phosphorus (C : N : P) ratios and as specific alkaline phosphatase activity (APA). 3. Horizontal variation accounted for 60–80 and 7–70% of the total variation in biomass and in nutrient status, respectively, at all depths and during both years. Both small and large scales accounted for significant variation. We also found variation with time and depth. Biomass increased in autumn after a summer minimum, and the within‐season variation was very high. The lowest biomass was found at 0 m depth. Both N and P limitation occurred, being higher in 1996 than in 1997 and decreased with depth. 4. As a consequence, any sampling design must address variation with distance, depth and time when estimating biomass or nutrient limitation of benthic algae for an entire lake. Based on this analysis, we calculated an optimal sampling design for detecting change in the epilithic biomass of Lake Erken between different sampling days. It is important to repeat the sampling as often as possible, but also the large scales (10 m and km) and the dm scale should be replicated. Using our calculations as an example, and after a pilot study, an optimal sampling design can be computed for various objectives and for any lake. 5. Short‐term impact of the wind, light and nutrient limitation, and grazing, might be important in regulating the biomass and nutrient status of epilithic algae in Lake Erken. Patchiness in the nutrient status of algae was not coupled to the patchiness of biomass, indicating that internal nutrients and biomass were regulated by different factors.     

Spatial heterogeneity in whole lake sediments — towards a loading estimate

Studies of nutrient loadings, to shallow culturally eutrophied Alberta lakes, suggest internal inputs are significant. In this regard, estimation of bottom sediment P loads to Lake Wabamun (80 km², 5.5 m depth) were examined. Initially we determined the spatial variability in Total Organic Content (% loss on ignition) and Total Phosphorus, as indicators. Phosphorus fractions and biologically available phosphorus (BAP) were measured at specific stations. These data showed a very uniform distribution in sediment type with a Total Organic Content of 40.6 ± 3.3 (95% C.L.) at the west end, gradually declining to 26.3 ± 0.9 at the east end. Transects performed at routine monitoring stations indicate the representativeness of each station, e.g., station 2, 40.8 ± 1.3 (10 sites). One explanation of this uniformity is provided from²¹⁰Pb analysis of shallow cores which indicate mixing to a depth of 16 cm. This is also thought to explain the mechanics of P loading to the water phase. Finally, Total Organic Content relates well to BAP (r² = 0.80). It is hoped that this simple technique may well permit more precise extrapolation to whole lake BAP estimates at least on this lake.     

The effect of a shift from macrophyte to phytoplankton dominance on phosphorus forms and burial in the sediments of a shallow hard-water lake

In shallow lakes, increasing phosphorus (P) loading has often been accompanied by a shift from a clear-water, macrophyte-dominated state to a turbid state featuring phytoplankton dominance. The effect of a regime shift on P burial and P fractions in lake sediments, however, is poorly understood. We used sediment cores from a eutrophic hard-water lake (Lake Gollinsee, Germany) that had undergone a regime shift (in approximately 1917) to investigate the effect on the accumulation rate of P and on changes in P forms. The cores were dated using Hg contents and radioisotopes (²¹⁰Pb, ¹³⁷Cs, and ²⁴¹Am). A combination of total organic carbon to total nitrogen ratios (TOC:TN), δ¹³TOC values, X-ray fluorescence calcium (Ca) counts, and sediment colour clearly distinguished sediment layers that were deposited during periods of macrophyte or phytoplankton dominance. The accumulation rate of total P (TP) in the sediments was 1.8 times higher after the regime shift and was associated with changes in the distribution of P fractions. The proportions of loosely-(NH₄Cl-extracted TP) and Ca-(HCl-extracted TP) bound P decreased significantly, whilst the proportions of biogenic P (NaOH-extracted NRP) and aluminium-bound P (NaOH-extracted SRP) increased significantly. A higher dry mass deposition rate, reduced burial of stable Ca-P complexes, and increased contents and proportions of the mobile iron-bound (BD-extracted TP) and biogenic P fractions in the near-surface sediment layers are assumed to have enhanced the internal cycling of P and hence to have helped to maintain a state of phytoplankton dominance.

     

太湖16000年来沉积环境的演变

通过对太湖钻孔岩芯岩性,结构,构造的剖析及粒度,磁化率的测试,发现冰后期东太湖形成于跑今６５００年前,在距今６５００－５８００年,为一水深约２－３ｍ的,经常受到流水作用影响的浅水湖泊,距今约５８００－５７００年,东太湖曾一度干枯或接近于干枯,距今５７００年以来湖泊变浅,平均水深只有１ｍ左右,由于湖泊变浅,湖底经常遭受波浪的扰动,形成波状层理或透镜状层理。西太湖局部洼地集水成湖的时间比东太湖早,并且     

Wind-induced increases in trophic state characteristics of a large (27 km 2), shallow (1.5 m mean depth) Florida lake

Nutrient and chlorophyll concentrations in Lake Newnan (27 km², mean depth 1.5 m), Florida showed dramatic increases from 1991 to 1998. Historical data showed Lake Newnan never had sufficient aquatic macrophyte abundance for a shift in alternate stable states to account for increases in trophic state characteristics. External phosphorus and nitrogen loads from incoming streams were monitored from August 1997 to July 1998 to determine if external supplies of nutrients were responsible for increases in lake nutrient and chlorophyll concentrations. During the study period, external nutrient loading rates were not correlated to lake nutrient concentrations. Phosphorus and nitrogen models based on the external loading estimates predicted the lake total phosphorus and total nitrogen concentrations to be 370% and 680% less, respectively, than the observed lake total phosphorus and total nitrogen mean concentrations. Consequently, phosphorus and nitrogen exports were 280% and 540% greater, respectively, than stream input loading. Data during the study period revealed strong inverse relations between lake stage and total phosphorus (r=–0.78), total nitrogen (r=–0.71), and chlorophyll (r=–0.90) concentrations. Long-term data (1965–1998) also revealed inverse correlations (r=–0.48 to –0.52) between lake stage and total phosphorus, total nitrogen, and chlorophyll concentrations. Applying fundamental wave theory and using a bathymetric map, it is probable that as much as 70% of the lake bottom sediment could be subjected to resuspension 50% of the time when the lake stage falls below 19.9 m mean sea level (msl). Above a lake stage of 19.90 m msl, less than 20% of the lake bottom sediment can potentially be resuspended 50% of the time. A percent frequency distribution from 1991 to 1998 showed that over 30% of the lake stages fell below 19.9 m msl. However, from 1967 to 1990, only 8% of the lake stage values fell below 19.9 m msl. Increases in total phosphorus, total nitrogen and chlorophyll concentrations in Lake Newnan were likely caused by an increased probability of internal loading due to decreased lake levels, and not to external loading of phosphorus and nitrogen.     

Effect of intensive catchment and in-lake restoration procedures on phosphorus concentrations in a eutrophic lake

Lake Okaro is a small, warm monomictic lake in central North Island, New Zealand, which progressed from oligotrophic to eutrophic through the 1960s. Trends in phosphorus (P) concentrations in the lake are linked to multiple restoration efforts over a 5-year period (2003–2008). The restoration procedures include a 2.3 ha constructed wetland established in February 2006 and riparian margin protection to reduce external loading, as well as an Alum application in December 2003 and sediment capping using modified zeolite in September 2008 to reduce internal loading. The annual average total phosphorus (TP) concentration in the lake decreased by 41% from 2004–2005 to 2007–2008. Two predictive models based on external P loading data generally underestimated the measured TP concentrations in the water column due to internal P loading. The relatively rapid response of TP concentrations after reduction of the internal loading using modified zeolite suggests that this technique can effect a rapid decrease in lake water TP concentrations though the trophic state of Lake Okaro showed high resilience to the reduced P loading. It is concluded that the combined effect of all restoration procedures resulted in a relatively rapid decrease in TP concentrations in Lake Okaro, which may be prolonged by continued external load reduction.     

杭州西湖北里湖沉积物氮磷内源静态释放的季节变化及通量估算

通过采集北里湖不同季节的柱状芯样,在实验室静态模拟沉积物氨氮(NH+4-N)和可溶解性磷酸盐(PO3-4-P)的释放,同时研究了沉积物间隙水中NH+4-N及PO3-4-P的垂直分布特征.结果表明,沉积物间隙水NH+4-N随深度的增加有上升的趋势,PO3-4-P随深度的增加呈先升后降的趋势.氮、磷营养盐在沉积物—水界面均存在浓度梯度,表明存在自间隙水向上覆水扩散的趋势.沉积物NH+4-N在春季、夏季、秋季、冬季的释放速率分别为0.074 mg·m-2· d-1、0.340mg· m-2· d-1、0.087 mg· m-2· d-1、0.0004 mg·m-2·d-1,pO3-4-P的释放速率则分别为0.340 mg·m-2·d-1、0.518 mg·m-2·d-1、0.094 mg·m-2·d-1、-0.037 mg· m-2·d-1.不同采样点表现出明显的季节和空间差异性,释放速率表现为夏季＞春季、秋季＞冬季.根据静态模拟出的不同季节下内源氮、磷释放速率计算,全湖内源氮、磷营养盐的贡献分别为0.0037、0.0057t/a.该研究可为北里湖富营养化及内源污染的治理提供基础数据.     

Temperature dependence of sediment-water exchange in Lake Grevelingen,SW Netherlands

Extended abstract Lake Grevelingen is a brackish water lake in the SW Netherlands. The lake has an area of 108 km², a mean depth of 5.3 m (maximum 48 m), a mean chlorinity of 13 to 16%0 Cl⁻, and a hydraulic residence time of about 8 years. Mass budget studies have shown a consistent seasonal pattern in the phosphorus sediment-water exchange in Lake Grevelingen (Kelderman 1980). From May to August a P mobilization from the sediment takes place, estimated atca. 12.5 mg P · m⁻² · day⁻¹. The sediment accumulatesca. 5.5 mg P · m⁻² · day⁻¹ during the rest of the year. Temperature may be an important factor in establishing this pattern. Sediment-water exchange was studied by means of laboratory experiments under specified conditions. Sediment cores (30 cm depth, 11 cm diameter) were taken at four stations in the lake, with sediment types varying from medium- to muddy sand (Fig. 1). The cores with overlying water (ca. 21) were placed in the dark at 5 °C in thermostatically controlled water baths. After a week's incubation time the temperature was slowly raised, such that after three weeks eight cores (four sediment types, duplicates) were at 5 °C, eight were at 10 °C, eight at 15 °C and eight at 20 °C. The same procedure was applied to the four control cores, containing lake water.     

Influence of Sediment Inflow on Phytoplankton Primary Productivity in Lake Tahoe (California-Nevada)

Light, nutrient concentrations and phytoplankton photosynthesis were studied in a Lake Tahoe sediment plume during maximum spring runoff. They were compared with conditions in clear lake waters not influenced by inlets. In the plume, nutrient concentrations increased in proportion to sediment density whereas light transmission of water was reduced with little effect on the spectral composition except for red light. Light inhibition of photosynthesis at the lake surface was less pronounced in the plume than in clear water and light limitation occurred more rapidly in deeper layers. Evidence from both lake experiments and laboratory bioassays suggests that iron had the greatest stimulatory effect on both photosynthetic activity and biomass growth at maximum sediment densities near the stream inlet. Because of less surface inhibition, photosynthetic light energy utilization efficiency was usually higher in the sediment plume which occurred in relatively shallow areas near the shore. In order to estimate overall effects of enhanced turbidity associated with nutrient loading on Lake Tahoe's primary productivity, profiles taken in shallow areas near the lakeshore were extrapolated to the maximum depth of photosynthesis. Light limitation would cause decreasing productivity, but nutrient stimulation would make this effect less pronounced. The overall effect would depend on the extent of sediment loading relative to nutrient loading.     

Long term fertilization effects on soil organic carbon pools in a sandy loam soil of the Indian sub-Himalayas

An understanding of the dynamics of soil organic carbon (SOC) as affected by farming practices is imperative for maintaining soil productivity and mitigating global warming. Results of a long-term (32 years) experiment in the Indian Himalayas under rainfed soybean (Glycine max L.)- wheat (Triticum aestivum L.) rotation was analyzed to determine the effects of mineral fertilizer and farmyard manure (FYM) application at 10 Mg?ha^-1 on SOC stocks and depth distribution of the labile and recalcitrant pools of SOC. Results indicate all treatments increased SOC contents over the control. The annual application of NPK significantly (P?<?0.05) enhanced total SOC, oxidizable soil organic C and its fractions over the control plots. The increase in these SOC fractions was greater with the NPK + FYM treatment. Nearly 16% (mean of all treatments) of the estimated added C was stabilized into SOC both in the labile and recalcitrant pools, preferentially in the 0?C30 cm soil layer. However, the labile:recalcitrant SOC ratios of applied C stabilized was largest in the 15?C30 cm soil layer. About 62% of total SOC was present in the labile pool. Plots under the N + FYM and NPK + FYM treatments contained a larger proportion of total SOC in the recalcitrant pool than the plots with mineral or no fertilizer, indicating that FYM application promoted SOC stabilization.     

Phosphorus fractions and alkaline phosphatase activity in sediments of a large eutrophic Chinese lake (Lake Taihu)

Spatial, vertical, and seasonal variations in phosphorus fractions and in alkaline phosphatase activity (APA) were investigated in sediments in a large-shallow eutrophic Chinese lake (Lake Taihu) in 2003–2004. The phosphorus content was highest in the most seriously polluted lake area. Iron-bound phosphorus (Fe(OOH)～P) dominated (47% on average) among the phosphorus fractions determined according to Golterman (Hydrobiologia 335:87–95, 1996). Notably, organically-bound P comprised a further significant additional portion (acid-soluble + hot NaOH-extractable organic P = 25%), which was highest at the most polluted sites. The Fe(OOH)～P content was the lowest in spring (April, 2004), suggesting that degradation of organic matter led to the release of iron-bound phosphates. Sediment APA showed a significant positive relationship with both organically-bound P and Fe(OOH)～P. Consequently, organically-bound P is an important portion of the sediment phosphorus in Lake Taihu. It is mainly derived from freshly-settled autochthonous particles and from external discharges. Organically-bound P induces APA and may lead to the release of bioavailable phosphates from the organic sediments, thereby accelerating lake eutrophication.     

Factors Controlling the Seasonal Variation of Nitrate in Lake Erken

The seasonal variation of the nitrate concentration in the mesotrophic Lake Erken is markedly regular and shows some important differences compared with that of phosphate. Nitrification occurs mainly at the sediment surface. Nitrate accumulates when the nitrification-denitrification sequence is broken at a time when the nitrate assimilation is small. This occurs in Lake Erken during autumn turnover.     

Paleolimnological evaluation of historical trophic state conditions in hypereutrophic Lake Thonotosassa, Florida, USA

We used paleolimnological methods to evaluate historical water quality in Lake Thonotosassa, Hillsborough County, Florida, USA. Sediment mapping shows that organic deposits are unevenly distributed in the lake. Two short (<130 cm) sediment cores from the depositional zone were analyzed for radioisotopes (²¹⁰Pb, ²²⁶Ra, and ¹³⁷Cs), bulk density, organic matter concentration, nutrients (C,N,P), and diatoms. ²¹⁰Pb results indicate that the profiles represent > 100 years of sediment accumulation. There is an abrupt change in sediment composition at about the turn of the century (80 cm depth), above which bulk density decreases and concentrations of organic matter, total C, total N, total P, and ²²⁶Ra activity increase. Diatom-based reconstructions of historical water-column trophic conditions indicate progressive nutrient enrichment in the lake during the past 100 years. Stratigraphic changes in diatom assemblages suggest that anthropogenic nutrient loading converted Lake Thonotosassa from a naturally eutrophic system to a hypereutrophic waterbody after 1900. Given the edaphic setting of Lake Thonotosassa, efforts to mitigate recent anthropogenic impacts will, at best, yield the eutrophic conditions that characterized the lake prior to human disturbance. This study illustrates the importance of paleolimnological data for targeting realistic water quality conditions when lake restoration is contemplated.Journal Series No. R-05019 of the Florida Agricultural Experiment Station     

The spatio-temporal variations of sedimentary phosphorus in Taihu Lake and the implications for internal loading change and recent eutrophication

Internal phosphorus loading is particularly concerned for the shallow lakes due to the frequent sediment disturbance, which may play a vital role in changing nutrient level in overlying water. A historical perspective on internal phosphorus loading may contribute to understanding its contribution to recent eutrophication. In this work, a study on the changes in internal phosphorus loading and release potential in Taihu Lake, a shallow eutrophic lake in China, was performed based on the analysis of spatio-temporal variations of sedimentary total phosphorus and three operationally defined fractions (NaOH-P, HCl-P and OP). The influencing factors for changing internal loading were discussed. The results showed that internal phosphorus loading was elevated compared to pre-eutrophication periods and the increase has occurred since approximately the late 1970s to early 1980s. Changes in internal phosphorus loading were primarily attributed to the NaOH-P and OP fractions, relating to anthropogenic inputs and enhanced productivity, respectively. The internal phosphorus release potential may be enhanced by up to 22% currently relative to the pre-eutrophication period; however, it should play a secondary role to external input in enhancing nutrient levels and sustaining the eutrophication in Taihu Lake.     

Distribution of Sediment Phosphorus Fractions in Hypertrophic Strongly Stratified Lake Verevi

Lake Verevi is a hypertrophic and strongly stratified (partly meromictic) small temperate lake. Vertical distribution of sediment phosphorus fractions as well as iron, manganese, organic matter and calcium carbonate of the deep bottom sediment was determined. The study focused on the ecologically important layer of the sediment [<20(45) cm]. In the uppermost layers of the sediment, NaOH-NRP (organic P) dominated while HCl-RP (apatite-P) became dominant in some deeper layers below 7 cm. Extremely high concentrations of labile phosphorus fraction (NH₄Cl-RP) indicated the low binding capacity of phosphorus by lake sediment. Due to sediment and hypolimnion anoxia, the internal load of phosphorus in this lake is most likely. Potentially mobile phosphorus fractions (NH₄Cl-RP, BD-RP, NaOH-NRP) formed 301 kg in upper 10 cm thick sediment layer of hypolimnetic bottom sediment (40% of lake bottom area).