Seston dynamics and tripton sedimentation in the pelagic zone of a shallow eutrophic lake

The transport of organic matter from the water column to the sediment and the relationship between the dynamics of the settleable fraction and that of the total suspended particulate matter were studied in shallow eutrophic Lake Wingra, Wisconsin. Tripton sedimentation was closely related to the dynamics of seston with a lag of 2 to 4 weeks. Sedimentation rate of tripton ranged from 0 to 8 g m^–2 day^–1 (in May and August respectively). Relative t0 the standing crop 0f seston the maximum sedimentation rate was 8% seston per day (in September). The annual tripton sedimentation was estimated at 632 g dry weight or 215 g C per m² which was equivalent t0 55% of the annual phytoplankton production and 42% of the phytoplankton and macrophytes annual production. It was estimated that 70% of the settling organic matter is decomposed annually, consequently only a small fraction 0f tripton is involved in the long term accumulation of bottom deposits. Factors influencing tripton sedimentation are discussed.Research supported by the Eastern Deciduous Forest Biome US-IBP, funded by the National Science Foundation under Interagency Agreement AG-199 BMS69-01147 A09 with the Energy Research and Development Administration-Oak Ridge National Laboratory. Contribution N0. 233 from the Eastern Deciduous Forest Biome US-IBP.Research supported by the Eastern Deciduous Forest Biome US-IBP, funded by the National Science Foundation under Interagency Agreement AG-199 BMS69-01147 A09 with the Energy Research and Development Administration-Oak Ridge National Laboratory. Contribution N0. 233 from the Eastern Deciduous Forest Biome US-IBP.     

Population responses of Lake Michigan phytoplankton to nitrogen and phosphorus enrichment

A natural phytoplankton assemblage from Grand Traverse Bay, Lake Michigan, was treated with factorial enrichments of nitrate and phosphorus, with maintained nutrient concentrations ranging from 5 to 60 μg total soluble phosphorus liter⁻¹ and 0.225 to 1.12 mg nitrate-nitrogen liter⁻¹.One container was spiked with added vitamins, a chelator, and trace metals. The assemblage response was monitored at the species level. Significant differences in growth rates as a function of nutrient enrichment were detected at both the division and the species levels. Growth rates associated with the various levels of enrichment are reported for several diatom taxa. Many of the diatom taxa exhibited highly significant (P < 0.01) increases in growth rate after phosphorus enrichment, with the largest effects occurring between 5 and 15 μg total soluble phosphorus liter⁻¹. Significant (P < 0.05) N effects were also observed, and the nature of these effects was found to be taxon-specific. Taxa also showed significant changes in percent composition, due both to time and to nutrient enrichment, indicating a substantial heterogeneity in response at the species level. Experimentally induced population changes were qualitatively similar to those observed in regions of the Great Lakes which have undergone anthropogenic eutrophication. Contribution No. 222 of the Great Lakes Research Division, University of Michigan. Work was supported by funds from the Michigan Sea Grant Program and the Environmental Protection Agency. Contribution No. 222 of the Great Lakes Research Division, University of Michigan. Work was supported by funds from the Michigan Sea Grant Program and the Environmental Protection Agency.     

Difference characteristics of phosphorus in Chara and two submerged angiosperm species: implications for phosphorus nutrient cycling in an aquatic ecosystem

Phosphorus speciation in three submerged macrophytes species, Chara fibrosa Agardh ex Bruzelius, Najas marina Linnaeus and Vallisneria gigantea Graebner, and the implications for phosphorus nutrient cycling in an aquatic ecosystem were studied, using sequential phosphorus fractionations. The results showed that C.␣fibrosa had a far higher residual ash and calcium content compared with the two angiosperm species, but lower total phosphorus content. Two different fractionation methods for phosphorus showed that the bioavailable water-soluble phosphorus (H₂O-P) and ammonium chloride extractable phosphorus (NH₄Cl-P) of the extractions used represented the major part of total plant phosphorus in the two angiosperm species, while organic phosphorus (NaOH-P) represented a relatively large fraction in C. fibrosa. In this species, about 12–15% of total plant phosphorus was calcium-bound phosphorus (HCl-P), occurring as co-precipitation with calcite encrustation, but this fraction was negligible in the two angiosperm species, i.e. less than 1%. The redox-insensitive forms of HCl-P are considered less bioavailable and not affected by anoxic conditions of bottom sediment, thus have potential as a phosphorus nutrient sink in aquatic ecosystems.     

Nitrogen and phosphorus recycling in Lake Sammamish,a temperate mesotrophic lake

This paper presents nitrogen and phosphorus budgets for spring and summer for the trophogenic (0–9 m) and tropholytic (9–27 m) zones of Lake Sammamish. The objective of constructing the budgets is to evaluate the efficiency of nutrient recycling and increase knowledge of the overall nutrient dynamics.The budgets reveal that uptake and solubilization are the dominant fluxes and that nutrient recycling is generally efficient, with the possible exception of early spring during the diatom bloom. This leads to greater reductions in the dissolved N and P pools in spring than summer. Sedimentation is greater in spring because of a pulse immediately following the diatom bloom.Solubilization of particulates is much less in the tropholytic zone than the trophogenic zone. This is due to slower decomposition rates there and to the efficiency of solubilization in the overlying trophogenic zone which results in a relatively small particulate influx. Turnover times for the N and P pools are therefore much faster in the trophogenic zone than in the tropholytic zone. In the trophogenic zone, however, the dissolved N pool turns over much more slowly than the dissolved P pool because of its larger size relative to algal growth requirements.Overall there is a net loss of N and P from the water column in spring primarily due to sedimentation and denitrification whilst in summer there is a small net gain because of sediment release and a slight excess of inflow over outflow.The work was supported by National Science Foundation grants DEB 74-20744, BMS 74-20744 and GB 36810F to the International Biological Program, Western Coniferous Biome (US/IBP) and grant R 008512 from the US Environmental Protection Agency. Contribution no. 373 by the Western Coniferous Biome.The work was supported by National Science Foundation grants DEB 74-20744, BMS 74-20744 and GB 36810F to the International Biological Program, Western Coniferous Biome (US/IBP) and grant R 008512 from the US Environmental Protection Agency. Contribution no. 373 by the Western Coniferous Biome.     

Sediment phosphorus cycling in a large shallow lake: spatio-temporal variation in phosphorus pools and release

Sediment and water column phosphorus fractions were recorded monthly for one year (April 2004–April 2005) in a shallow lake recovering from nutrient pollution (Loch Leven, Scotland). Equilibrium phosphate concentration (EPC0) and gross sediment phosphorus (P) release rates were estimated from laboratory experiments. Pore water and organic P pools were lowest during warm water periods whereas bottom water P was lowest during cold water periods. Reductant-soluble, organic, metal oxide-adsorbed, residual and sediment total phosphorus pools all varied significantly with overlying water depth. Short-term, high magnitude, redox initiated P release events occurred in late summer and winter as a result of anoxic sediment conditions. Lower magnitude long-term release conditions were maintained for most of the year, most likely as a result of organic P cycling and maintenance of high concentration gradients between the pore and bottom water P pools. Estimates of summer P uptake/release rates, across an intact sediment-water interface, suggested that maximum gross internal release was ~12 mg SRP m⁻² lake surface area d⁻¹ with EPC0 values ranging between 180 and 270 μg P L⁻¹. This study highlights the biological mediation of internal loading in shallow eutrophic lakes, and in particular, the role of sediment algae in decreasing, and sediment bacteria in enhancing, sediment P release.     

Diatom taxa and assemblages for establishing nutrient criteria of lakes with anthropogenic hydrologic alteration

Stressor-response models offer guidance for concentration-based nutrient criteria in lakes under human intervention. Diatom-based statistics from biological responses were incorporated to derive taxon-specific and community-level change points (thresholds) of phosphorous and nitrogen in 77 Yangtze floodplain lakes. Diatom metrics relating with conductivity were adopted as response variables, since conductivity explained the maximum variation (38.1%) in diatom assemblages via Bootstrapped regression trees. Nonparametric change-point analysis and Threshold Indicator Taxa ANalysis showed threshold responses of diatom community structure at 0.05–0.08 mg TP/L in connected lakes and 0.02–0.04 mg TP/L in isolated lakes. Distinct community change points of sensitive diatoms occurred at 0.96–1.63 mg TN/L in connected lakes and 0.52–0.63 mg TN/L in isolated lakes. Diatom community structures of tolerant taxa were substantially altered beyond 0.22–0.23 mg/L in connected lakes and 0.52–0.69 mg NO_x/L in isolated lakes. Hydrological river-lake connectivity differed significantly in ecological nutrient criteria with more TN/TP criteria and less NO_x criteria in connected lakes. Given the ecological significance and biological integrity, diatom-based statistics can provide more reliable change points (thresholds) for nutrient criteria than Chl a-nutrient relationships.     

Biogeography and ecology of freshwater diatoms in Subantarctica: a review

Subantarctica is situated between the Antarctic and the Subtropical Convergence and consists of the islands in the southern Atlantic, Indian and Pacific Oceans. Diatoms are an important component of all Subantarctic aquatic, moss and soil habitats. Taxonomic studies reveal a high diversity and species richness in both the present-day and the fossil diatom flora. Planktonic diatoms are almost completely absent. A similarity analysis of the diatom composition from different localities in the southern zone (below 40°S) resulted in a biogeographical zonation. Three regions could be formed, based on their diatom composition: Subantarctica, Maritime Antarctica and the Antarctic Continent. The diatom communities in the different regions are all characterized by a high proportion of cosmopolitan species. A second feature of the southern diatom floras is the decreasing diversity when moving southwards.     

RpoA: a useful gene for phylogenetic analysis in diatoms

The aim of this study was to compare the usefulness of two chloroplast-encoded genes (rpoA and rbcL) and the nuclear-encoded small subunit (SSU) ribosomal RNA for reconstructing phylogenetic relationships among diatoms at lower taxonomic levels. To this end, the rpoA and rbcL genes for selected centric and pennate diatoms were sequenced. The new rpoA and rbcL sequences, and an existing nuclear-encoded SSU rRNA data set, were subjected to weighted/unweighted parsimony, maximum likelihood, minimum evolution, and Bayesian analyses. All of the tree-building methods employed showed, based on the support values, that the rpoA gene was the most useful, relative to the rbcL and SSU rRNA genes, in determining phylogenetic relationships among the sampled diatoms. The support values for the relationships among the pennate lineages were, in many instances, greater in the rpoA trees than in the SSU rRNA trees. These results suggest that rpoA might be of value in determining phylogenetic relationships among pennate lineages.     

Measurement and verification of rates of sediment phosphorus release for a hypereutrophic urban lake

The contribution of sediment release to the phosphorus budget of hypereutrophic Onondaga Lake was determined through laboratory measurements made on intact cores. Rates ranged from 9–21 mg P m^–2 d^–1 with a mean of 13 mg P m^–2 d^–1, values similar to those observed in other lakes of comparable trophic state. There was no statistically significant trend in rates in time (July versus September) or in space (location along the major N/S axis of the lake). Rates of sediment phosphorus release measured in the laboratory compared favorably with the observed rate of soluble reactive phosphorus accumulation in the lake's hypolimnion. The sediments are the second largest source of phosphorus for Onondaga Lake, contributing 24% of the overall phosphorus load to the system.     

Influence of hydropattern and vegetation type on phosphorus dynamics in flow-through wetland treatment systems

Phosphorus (P) flux from wetland soil can be a significant factor affecting overall wetland treatment performance. The purpose of our study was to quantify the effects of water level drawdown on P exchange between surface water and organic soil in a constructed wetland. We used 12 fiberglass mesocosms filled with 30 cm of peat soil to quantify nutrient exchange between surface water and organic soil in a wet-dry-wet cycle. Six mesocosms were planted with emergent macrophytes and six mesocosms were maintained free of emergent vegetation. We evaluated four treatments including continuously and intermittently flooded treatments, both with and without emergent macrophytes. Each treatment was replicated three times and every mesocosm was plumbed to monitor flow volumes and water chemistry. Effluent P concentrations were similar for all four treatments prior to first drawdown period. However, upon re-flooding, all intermittently flooded tanks exhibited a three to fourfold increase in surface water P concentration, which lasted for a period of up to ten weeks. The magnitude of nutrient flux to surface water and the time period over which P release took place were season dependent, with longer duration of high nutrient flux during dry-season drawdowns. Results of repeated measures analysis indicated that hydropattern was the dominant factor affecting P-flux to overlying surface water, while presence or absence of emergent vegetation had no significant influence on effluent concentrations. Organic and particulate phosphorus fluxes were substantially higher in treatments lacking emergent macrophytes, subsequent to the dry-season drawdowns. Intermittently flooded treatments with no emergent vegetation generated the most dissolved and particulate phosphorus. Our results indicate that maintaining saturated soil is sufficient to retain stored P, while plants played no significant role in P retention for a wetland receiving P-loading rate on the order of 0.1 g week⁻¹ during a wet-dry-wet cycle.     

日本中部10种树木叶片中氮和磷的季节变化及其转移

从叶完全展开到生长季结束,对常绿阔叶树种日本米储、具柄冬青、铁冬青、红楠和海桐及落叶阔叶树种袍栎、栓皮栎、日本朴、银杏和日本树五加的叶N和P含量进行了测定．结果表明,在整个生长季中,常绿阔叶树种中的日本米储和铁冬青的新叶和老叶的N和P含量呈现初期高、中期较低、后期上升的趋势;具柄冬青和海桐新叶的N和P含量的变化趋势与日本米储和铁冬青相似,而其老叶的N和P含量随季节推移而逐渐下降;红楠新叶和老叶的N含量呈现上升的趋势,其新叶和老叶的P含量则呈下降趋势;落叶阔叶树种的叶N和P含量随着时间的推移不断减少．各树种的N转移率为43％～75％,P为62％～84％．常绿阔叶树种的N平均转移率与落叶阔叶树种相似,而其P平均转移率大于落叶阔叶树种．所有树种的N平均转移率小于P平均转移率．     

Aluminum sulfate treatment: Short-term effect on complex phosphorus compounds in a eutrophic lake

Application of aluminum sulfate to the hypolimnion of West Twin Lake, a hardwater eutrophic lake in northeastern Ohio, did not efficiently remove complex phosphorus compounds from the water column. The majority of the complex phosphorus compounds remaining after alum treatment released P0₄ following brief treatment with alkaline phosphatase.     

Temporal and spatial trends in nitrogen and phosphorus inputs to the watershed of the Altamaha River,Georgia, USA

The watershed of the Altamaha River, Georgia, is one of the largest in the southeastern U.S., draining 36,718 km² (including parts of metro Atlanta). We calculated both nitrogen (fertilizer, net food and feed import, atmospheric deposition, and biological N fixation in agricultural and forest lands) and phosphorus (fertilizer and net food and feed import) inputs to the watershed for 6 time points between 1954 and 2002. Total nitrogen inputs rose from 1,952 kg N km⁻² yr⁻¹ in 1954 to a peak of 3,593 kg N km⁻² yr⁻¹ in 1982 and then declined to 2,582 kg N km⁻² yr⁻¹ by 2002. Phosphorus inputs rose from 409 kg P km⁻² yr⁻¹ in 1954 to 532 kg P km⁻² yr⁻¹ in 1974 before declining to 412 kg P km⁻² yr⁻¹ in 2002. Fertilizer tended to be the most important input of both N and P to the watershed, although net food and feed import increased in importance over time and was the dominant source of N input by 2002. When considered on an individual basis, fertilizer input tended to be highest in the middle portions of the watershed (Little and Lower Ocmulgee and Lower Oconee sub-watersheds) whereas net food and feed imports were highest in the upper reaches (Upper Oconee and Upper Ocmulgee sub-watersheds). Although the overall trend in recent years has been towards decreases in both N and P inputs, these trends may be offset due to continuing increases in animal and human populations.     

Influence of bacteria and salinity on diatom biogenic silica dissolution in estuarine systems

Dissolution of diatom biogenic silica (bSiO₂) in estuaries and its control by water salinity and bacteria were investigated using the river euryhaline species Cyclotella meneghiniana as a model. Laboratory-controlled bioassays conducted at different salinities with an estuarine bacteria inoculum showed a faster dissolution of diatom bSiO₂ at the lowest salinity where bacteria were the most abundant. However in another experiment, salinity increase clearly enhanced the dissolution of cleaned frustules (organic matter free). The presence of active bacteria might therefore predominate on the effect of salinity for freshly lysed diatoms whereas salinity might rather control dissolution of organic-matter-free frustule remains. Incubation of cultivated diatoms at different protease concentrations revealed that high proteolytic activities had little effect on bSiO₂ dissolution at a 1-month scale in spite of an efficient removal of organic matter from the frustules. Altogether it is hypothesized that bacterial colonization increases bSiO₂ dissolution by creating a microenvironment at the diatom surface with high ectoproteolytic activity but also via the release of metabolic byproducts since the presence of organic matter seems generally to facilitate diatom bSiO₂ dissolution.     

Occurrence of water phosphorus at the water-sediment interface of a freshwater shallow lake: Indications of lake chemistry

Better understanding of the occurrence of water phosphorus (P) at the water-sediment interface is vital to clarify P sources of origin in freshwater shallow lake ecosystems. This study focused on water-sediment interface systems and explored implicit indications of lake chemistry on water P based on a case study of Baiyangdian Lake, North China. 20 variables from 14 sampling sites collected for six months in two years were investigated, including sequentially extracted P fractions. Exploratory data analysis with multivariate statistical techniques and the index of P maximum solubilization potential were employed to examine interactions of water P and coexisting chemicals, and to accomplish pattern recognition of water-sediment interface systems. Results showed that nine key variables (temperature, conductivity, ammonium nitrogen, total nitrogen, sediment total P, metallic oxide bound P, organic P, aluminum and ferrum) were identified and ranked into four latent parameters (physical factors, nutrients, P species, and metals), accounting for 81% of water P variation. Accordingly, the recognized three patterns of water-sediment interface unraveled spatial partitioning for the domination of external or internal P sources. Four variables (temperature, sediment total P, metallic oxide bound P and organic P) were competent to classify patterns of water-sediment interface with 100% correct assignment of cases. Using two parameters (organic P and metallic oxide bound P), discriminant functions produced 85.7% correct assignations, indicating the importance of the two P species in explaining spatial heterogeneity of water P under oxic and alkaline circumstances. This study provides an operational zoning frame and implications for eutrophication management applicable to freshwater shallow lakes.     

Speciation,phase association and potential bioavailability of phosphorus on a Svalbard glacier

Glacier surfaces are known to harbour abundant and active microbial communities. Phosphorus has been shown to be deficient in glacial environments, and thus is one of the limits on microbial growth and activity. We quantified the phosphorus pool in cryoconite debris and the concentration of dissolved phosphorus in supraglacial water on Werenskioldbreen, a Svalbard glacier. The mean total P content of the cryoconite debris was ~2.2 mg g⁻¹, which is significantly more than would be expected in rock debris from local sources. 57% of this P was present in the fraction defined as organic P. It may account for the P in excess of the rock debris, and could be explained by allochthonous input of organic matter. The concentration of total dissolved P in supraglacial water was very low (5.2–8.5 μg l⁻¹), which was probably caused by efficient flushing and re-adsorption onto mineral surfaces. Dissolved organic P (DOP) was a very important component of the dissolved phosphorus pool on Werenskioldbreen, as concentrations of DOP typically exceeded those of dissolved inorganic P (or SRP) by more than four times in all the glacial water types. It is very difficult to assess whether P was limiting in this environment solely on the basis of the N:P ratios in the debris or biomass. There may be some degree of biological control over the C:N:P ratios in the debris, but the phosphorus cycling in the supraglacial environment on this glacier seems to be mainly controlled by physical and geochemical processes.     

Seasonal dynamics,typhoons and the regulation of lake metabolism in a subtropical humic lake

1. We used high‐frequency in situ dissolved oxygen measurements to investigate the seasonal variability and factors regulating metabolism in a subtropical alpine lake in Taiwan between May 2004 and October 2005, specifically exploring how the typhoon season (from June or July to October) affects lake metabolism. 2. Gross primary production (GPP) and ecosystem respiration (R) both peaked in early summer and mid‐autumn but dropped during the typhoon season and winter. Yuan‐Yang Lake is a net heterotrophic ecosystem (annual mean net ecosystem production ?39.6 μmole O₂ m^?3). 3. Compared to the summer peaks, seasonal averages of GPP and R decreased by approximately 50% and 25%, respectively, during the typhoon season. Ecosystem respiration was more resistant to external disturbances than GPP and showed strong daily variation during typhoon seasons. 4. Changes in the quality and quantity of dissolved organic carbon controlled the temporal dynamics and metabolic regulation. External disturbances (typhoons) caused increased allochthony, increasing DOC and water colour and influencing lake metabolism. 5. Seasonal winter mixing and typhoon‐induced water mixing in summer and autumn play a key role in determining the extent to which the lake is a seasonal carbon sink or source to the atmosphere.     

Changes in phosphorus concentrations in a eutrophic lake as a result of macrophyte-kill following herbicide application

Phosphorus (P) concentrations in water and sediment of a highly eutrophic lake were monitored before and after application of diquat to control the macrophyte Potamogeton crispus. Only a relatively small and short-term increase in P concentration in water occurred shortly after plant die-off resulting from herbicide application. Phosphorus concentrations in shallow water sediments decreased during the summer, and those in deep water sediments increased. Although a large increase in P concentration in the water occurred in late summer, it was not attributed to diquat. No major secondary effects of herbicide application were found during this study.