Production enhancement by artificial upwelling: a simulation study

A coupled physical–chemical–biological ocean model was applied to study primary production in an idealized 60-km long and 4-km wide fjord. Three different scenarios were simulated: (a) Without fresh water runoff; (b) A river at the head of the fjord adds 100 m³ s^–1 fresh water to the surface layer; (c) The river adds 90 m³ s^–1 fresh water to the surface layer and 10 m³ s^–1 enters the fjord through a pipe at 50 m depth. The average productions in the inner 40 km of the fjord for the three scenarios are 68, 70 and 233 g C m^–2 year^–1 respectively. It is thus shown that there is a considerable potential for increasing the primary production in many fjords and coastal areas by submerging some of the river runoff. Because of the higher silicate content of the deeper water, artificial upwelling tends to stimulate diatom more than flagellate growth. This may be beneficial to mariculture developments. The sensitivity of the simulated primary production to horizontal and vertical resolution, horizontal viscosity, vertical diffusivity and viscosity, discharge depth, wind forcing, sill depth and pulsating the discharge is also studied. A simulation where a large river flux (90 m³ s^–1) was submerged, showed that primary production was significantly enhanced in the outer parts of the fjord as well as along the coastline.     

A comparison of primary production measurements using two laboratory systems with differences in light quality

Primary production measurements were carried out simultaneously, using two laboratory systems with different light conditions: (1) a'classical' incubator and (2) a Laboratory Scale Enclosure. The model used for calculating primary production (STEELE, 1965) does not correct for spectral changes caused by high phytoplankton biomass. In the incubator, light of almost all wavelengths decreased more or less according to the attenuation of total PhAR in water. In the LSE, high absorption was found of the blue light and some of the red light, which was due to the high sestonic concentration. The Steele function provided a good fit for both sets of data. The depth integrated gross production values derived from the simultaneous measurements were not significantly different.     

Lake Horowhenua: a computer model of its limnology and restoration prospects

Lake Horowhenua, a small (2.9 km²) shallow (< 2 m deep), coastal dune lake on the west coast of the North Island of New Zealand, receives the runoff from intensive agriculture within its catchment and, until 1987, the treated sewage effluent from the town of Levin. Consequently the lake is highly enriched but with an annual cycle of algal P-limitation in winter and N-limitation in summer. There have been several schemes proposed to accelerate the improvement of the lake's water quality for recreational use. A computer hydraulic and nutrient model of Lake Horowhenua was developed using rainfall, evaporation and nutrient data to describe the nutrient budget. To match the lake nutrient concentrations, terms for in-lake processes of sedimentation, seasonal sediment nutrient release, phytoplankton production, and denitrification were required. The computer model results indicated that denitrification was the major natural restoration process accounting for a net loss of more than 50% of the N from the lake each year. Application of the model also allowed lake managers to evaluate the potential effects of a number of proposed restoration schemes.     

The dynamics of the N/P ratio and stratification in a large nitrogen-limited estuary as a result of upwelling: a tendency for offshore Nodularia blooms

The effect of upwelling on the preconditions for noxious cyanobacterial blooms in a nitrogen-limited estuary is studied with Nodularia blooms in the Gulf of Finland especially in mind. An idealised physical–chemical model is derived and integrated. The physical development in the model agrees with a classical picture of upwelling for the scales of interest. The chemical component indicates a transient minimum of dissolved inorganic nitrogen to phosphorus ratio in the middle of the gulf, coinciding with the stratification maximum resulting from physical dynamics. A general tendency for offshore cyanobacterial blooms in similar physical and biological conditions is deduced from these results.     

Phytoplankton biomass and production in northern South China Sea during summer: Influenced by Pearl River discharge and coastal upwelling

Chlorophyll a and primary production were studied in northern South China Sea during summer from 2007 to 2008. Microplankton dominated total phytoplankton biomass in the coast, while picoplankton dominated in the offshore. Algae bloom caused by Thalassionema nitzschioides was found at the subsurface of upwelling regions (D2, C2) in 2008, and maximum of phytoplankton abundance reached 1.58 × 10⁶ ind L^?1. Integrated primary production ranged from 189.3 to 976.2 mg m^?2 d^?1 in 2007, and ranged from 652.1 to 6601 mg m^?2 d^?1 in 2008. PP showed positive relationship with IPP (p < 0.01) and negative relationship with SST (p < 0.05). Coastal upwelling and Pearl River discharge sustained high PP, and played important role in regulating the phytoplankton biomass and production.     

Phytoplankton biomass and production in northern South China Sea during summer: Influenced by Pearl River discharge and coastal upwelling

Chlorophyll a and primary production were studied in northern South China Sea during summer from 2007 to 2008. Microplankton dominated total phytoplankton biomass in the coast, while picoplankton dominated in the offshore. Algae bloom caused by Thalassionema nitzschioides was found at the subsurface of upwelling regions (D2, C2) in 2008, and maximum of phytoplankton abundance reached 1.58 × 10⁶ ind L^?1. Integrated primary production ranged from 189.3 to 976.2 mg m^?2 d^?1 in 2007, and ranged from 652.1 to 6601 mg m^?2 d^?1 in 2008. PP showed positive relationship with IPP (p < 0.01) and negative relationship with SST (p < 0.05). Coastal upwelling and Pearl River discharge sustained high PP, and played important role in regulating the phytoplankton biomass and production.     

Controlled experiments of habitat fragmentation: a simple computer simulation and a test using small mammals

Habitat fragmentation involves a reduction in the effective area available to a population and the imposition of hard patch edges. Studies seeking to measure effects of habitat fragmentation have compared populations in fragments of different size to estimate and area effect but few have examined the effect of converting open populations to closed ones (an effect of edges). To do so requires a shift in spatial scope-from comparison of individual fragments to that of fragmented versus unfragmented landscapes. Here we note that large-scale, controlled studies of habitat fragmentation have rarely been performed and are needed. In making our case we develop a simple computer simulation model based on how individual animals with home ranges are affected by the imposition of habitat edges, and use it to predict population-level responses to habitat fragmentation. We then compare predictions of the model with results from a field experiment on Peromyscus and Microtus. Our model treats the case where home ranges/territories fall entirely within or partially overlap with that of sample areas in continuous landscapes, but are restricted to areas within habitat fragments in impacted landscapes. Results of the simulations demonstrate that the imposition of hard edges can produce different population abundances for similar-sized areas in continuous and fragmented landscapes. This edge effect is disproportionately greater in small than large fragments and for species with larger than smaller home ranges. These predictions were generally supported by our field experiment. We argue that large-scale studies of habitat fragmentation are sorely needed, and that control-experiment contrasts of fragmented and unfragmented microlandscapes provide a logical starting point.     

Spatial and temporal variability in benthic processes along a mangrove-seagrass transect near the Bangrong Mangrove,Thailand

Benthic primary production and nutrient dynamics were examined along a transect in the Bangrong mangrove forest in Thailand. Six stations were established extending from a high-intertidal site within the mangrove forest to low-intertidal flats and seagrass beds in front of the mangrove forest. Benthic processes (O₂ and CO₂ fluxes) and nutrient dynamics (mineralization, sediment-water fluxes, pore water and sediment pools) were measured under light and dark conditions during wet and dry seasons over a 2-yr period. The sediments were mostly autotrophic, only the mangrove forest sites were net heterotrophic during the wet season. Maximum daily net primary production was found at the non-vegetated tidal flats (40–75 mmol O₂ m^-2d^-1), where light and nutrient availability were highest. The variation in benthic mineralization along the transect was minor (1.6–4.3 mmol CO₂ m^-2h^-1) and did not reflect the large changes inorganic matter content (organic carbon: 0.7–4.2% DW) and quality (C:N ratio varied from 25 to 100), suggesting that the mineralizable pool of organic matter was of similar magnitude at all sites. There was only minor seasonal variation in rates of mineralization. The net primary production showed more variation with lower rates in the mangrove forest (reduced with 74%) and higher rates at the tidal flats (increased with 172%) and in the seagrass beds (increased with 228%) during the wet season. The nutrient pools and fluxes across the sediment-water interface were generally low along the transect, and the sediments were efficient in retaining nitrogen in the nutrient limited mangrove/seagrass environment. Pools and fluxes of phosphorus were generally very low suggesting that benthic primary production was phosphorus limited along the transect. This revised version was published online in July 2006 with corrections to the Cover Date.     

Karyotype displacement in a laboratory population of the two spotted spider mite Tetranychus urticae (Koch): Experiments and computer simulations

Three different strains, homozygous for a radiation induced structural chromosome mutation (T), exhibiting negative hererosis, were tested for their ability to displace the standard (wild-type) karyotype from experimental populations. The experimental populations were initiated by mixing fertilized females of both a T strain and the standard strain at different ratios. Two of the T strains showed the ability to displace the standard karyotype if the initial frequency of the T karyotype was at least 0.65. The additional release of T males into the experimental population accelerated considerably the process of displacement of the standard karyotype, especially if the initial T karyotype frequency was 0.65.A computer model for simulating the process of population displacement in Tetranychus urticae was developed. The model accounts for variation in developmental time and for the age dependency of variables related to fitness. The simulations showed a good correlation with the experimental results. A system analysis on the sensitivity of the model output to varying different population parameters demonstrated that especially the relative number of males produced by a T strain and the female developmental rate were of significant importance to the population displacement ability of a T strain. The negative influence of genetic markers on general fitness and various aspects of practical application of the method are discussed.     

Could specialization to cold‐water upwelling systems influence gene flow and population differentiation in marine organisms? A case study using the blue‐footed booby,Sula nebouxii

Aim We assessed population differentiation and gene flow across the range of the blue‐footed booby (Sula nebouxii) (1) to test the generality of the hypothesis that tropical seabirds exhibit higher levels of population genetic differentiation than their northern temperate counterparts, and (2) to determine if specialization to cold‐water upwelling systems increases dispersal, and thus gene flow, in blue‐footed boobies compared with other tropical sulids. Location Work was carried out on islands in the eastern tropical Pacific Ocean from Mexico to northern Peru. Methods We collected samples from 173 juvenile blue‐footed boobies from nine colonies spanning their breeding distribution and used molecular markers (540 base pairs of the mitochondrial control region and seven microsatellite loci) to estimate population genetic differentiation and gene flow. Our analyses included classic population genetic estimation of pairwise population differentiation, population growth, isolation by distance, associations between haplotypes and geographic locations, and analysis of molecular variance, as well as Bayesian analyses of gene flow and population differentiation. We compared our results with those for other tropical seabirds that are not specialized to cold‐water upwellings, including brown (Sula leucogaster), red‐footed (S. sula) and masked (S. dactylatra) boobies. Results Blue‐footed boobies exhibited weak global population differentiation at both mitochondrial and nuclear loci compared with all other tropical sulids. We found evidence of high levels of gene flow between colonies within Mexico and between colonies within the southern portion of the range, but reduced gene flow between these regions. We also found evidence for population growth, isolation by distance and weak phylogeographic structure. Main conclusions Tropical seabirds can exhibit weak genetic differentiation across large geographic distances, and blue‐footed boobies exhibit the weakest population differentiation of any tropical sulid studied thus far. The weak population genetic structure that we detected in blue‐footed boobies may be caused by increased dispersal, and subsequently increased gene flow, compared with other sulids. Increased dispersal by blue‐footed boobies may be the result of the selective pressures associated with cold‐water upwelling systems, to which blue‐footed boobies appear specialized. Consideration of foraging environment may be particularly important in future studies of marine biogeography.     

Carbon, nitrogen and phosphorus dynamics in creek water of a southeast Asian mangrove forest

Water column dynamics of carbon, nitrogen and phosphorus in the main creek of the Bangrong mangrove forest, Phuket Island, Thailand, were examined during the dry season. Water sampled from the upper and lower reaches of the creek throughout entire neap and spring tide periods was incubated under saturated irradiation and in the dark. The activity of microbial primary producers and heterotrophs were evaluated from changes in O₂, TCO₂, DOC, DIN, DON and PO₄ ^3- concentrations. Gross primary production was moderate (1.6–2.4 M C h^–1) with no pronounced spatial and temporal variations. A large fraction of the assimilated inorganic carbon and nitrogen was released in the form of DOC (50–90%) and DON (50–60%) indicating that primary producers were under stress or nutrient depleted. PO₄ ^3- and occasionally DIN appeared to be the limiting nutrients. The pelagic heterotrophic community was supported by DOC (50–100%) and DON (40–90%) excreted by primary producers when exposed to light. However, rapid light attenuation in the turbid creek water rendered the entire water column strongly heterotrophic at all times (1.1–2.8 M C h^–1). The microbial heterotrophs are therefore largely supported by particulate and dissolved substrates derived from tidal resuspension, mangrove root exudates and leachates from fallen leaves on the forest floor. The relatively high concentrations of metabolites (e.g. CO₂, NH₄ ⁺) in creek water were primarily supplied by microbial mineralization. Water seeping from creek banks, which was only enriched in TCO₂ (2 times) and PO₄ ^3- (20–100 times) compared with creek water, is not considered an important source of solutes in the waterways of the Bangrong mangrove forest. Although the results obtained here are only strictly representative for the dry season, water column processes in the wet season are not expected to differ much due to the limited seasonal variations with respect to physical, chemical and biological parameters in the Bangrong area.     

Diagnosing and assessing uncertainties of terrestrial ecosystem models in a multimodel ensemble experiment: 1. Primary production

We conducted an ensemble modeling exercise using the Terrestrial Observation and Prediction System (TOPS) to evaluate sources of uncertainty in carbon flux estimates resulting from structural differences among ecosystem models. The experiment ran public‐domain versions of biome‐bgc, lpj, casa , and tops‐bgc over North America at 8 km resolution and for the period of 1982–2006. We developed the Hierarchical Framework for Diagnosing Ecosystem Models (HFDEM) to separate the simulated biogeochemistry into a cascade of three functional tiers and sequentially examine their characteristics in climate (temperature–precipitation) and other spaces. Analysis of the simulated annual gross primary production (GPP) in the climate domain indicates a general agreement among the models, all showing optimal GPP in regions where the relationship between annual average temperature (T, °C) and annual total precipitation (P, mm) is defined by P=50T+500. However, differences in simulated GPP are identified in magnitudes and distribution patterns. For forests, the GPP gradient along P=50T+500 ranges from ～50 g C yr^?1 m^?2 °C^?1 (casa ) to ～125 g C yr^?1 m^?2 °C^?1 (biome‐bgc ) in cold/temperate regions; for nonforests, the diversity among GPP distributions is even larger. Positive linear relationships are found between annual GPP and annual mean leaf area index (LAI) in all models. For biome‐bgc and lpj , such relationships lead to a positive feedback from LAI growth to GPP enhancement. Different approaches to constrain this feedback lead to different sensitivity of the models to disturbances such as fire, which contribute significantly to the diversity in GPP stated above. The ratios between independently simulated NPP and GPP are close to 50% on average; however, their distribution patterns vary significantly between models, reflecting the difficulties in estimating autotrophic respiration across various climate regimes. Although these results are drawn from our experiments with the tested model versions, the developed methodology has potential for other model exercises.     

A method of determining rooting depth from a terrestrial biosphere model and its impacts on the global water and carbon cycle

We outline a method of inferring rooting depth from a Terrestrial Biosphere Model by maximizing the benefit of the vegetation within the model. This corresponds to the evolutionary principle that vegetation has adapted to make best use of its local environment. We demonstrate this method with a simple coupled biosphere/soil hydrology model and find that deep rooted vegetation is predicted in most parts of the tropics. Even with a simple model like the one we use, it is possible to reproduce biome averages of observations fairly well. By using the optimized rooting depths global Annual Net Primary Production (and transpiration) increases substantially compared to a standard rooting depth of one meter, especially in tropical regions that have a dry season. The decreased river discharge due to the enhanced evaporation complies better with observations. We also found that the optimization process is primarily driven by the water deficit/surplus during the dry/wet season for humid and arid regions, respectively. Climate variability further enhances rooting depth estimates. In a sensitivity analysis where we simulate changes in the water use efficiency of the vegetation we find that vegetation with an optimized rooting depth is less vulnerable to variations in the forcing. We see the main application of this method in the modelling communities of land surface schemes of General Circulation Models and of global Terrestrial Biosphere Models. We conclude that in these models, the increased soil water storage is likely to have a significant impact on the simulated climate and the carbon budget, respectively. Also, effects of land use change like tropical deforestation are likely to be larger than previously thought.     

Some ecological observations on a permanent pond in southern England: Primary production and planktonic seasonal succession

A one year study of a 0.9 hectare permanent alkaline pond (mean depth lm) in southern England has shown that phytoplankton productivity was highest during fall and spring. Hourly rates of photosynthesis ranged from almost zero in the winter to a peak of 475 mgC/m³/h in the fall. Daily gross primary productivity per unit area varied from 0.1–2.5 gC/m²/d. The annual gross primary productivity of phytoplankton was estimated to be .157 KgC/m²/y.The submerged angiosperm, Ceratopyllum demersum was the dominant macrophyte covering over 55% of the pond in the summer. It reached a peak biomass of 235 g/m² (ash free) in July. This macrophyte had a net annual primary productivity of 2.89 metric tons (ash free)/ha/y. When phytoplankton gross production was converted to net, it showed an energy production of 3.29 × 10⁶ J/m²/y compared with 6.25 × 10⁶ J/m²/y for macrophytes. Values of net production efficiencies ranged from .11% for phytoplankton to .21% for macrophytes. Cryptomonas dominated the microphytoplankton in terms of numbers for most of the year. Diatoms were abundant especially during the spring bloom. The genus Cocconeis dominated fall and winter diatom standing crops while Cyclotella and Navicula dominated the spring peak. Diatom abundance varied inversely with silica concentrations. Peridinium, the dinoflagellate, seemed to prosper when Cryptomonas was scarce. The colonial alga, Volvox aureus, had an intense growth in October probably due to heavy rains and relatively low nitrogen levels.The pond zooplankton diversity was low. Copepod and cladoceran populations were predominantly of one species. The copepod Cyclops fimbriatus and the cladoceran Chydorus sphaericus were fall/winter forms. They were succeeded by Cyclops vicinus and Bosmina longirostris in the spring. Rotifers were very abundant during a spring peak prospering on algal cells produced in the spring bloom two weeks earlier.     

Biome-BGC模型模拟阔叶红松林碳水通量的参数敏感性检验和不确定性分析

生态过程模型的发展为研究者在长时间序列和区域尺度的研究提供了便利, 但模型模拟的准确性受到模型自身结构、模型参数估计合理性的影响。敏感性分析能够定量或定性筛选出对模型模拟结果影响较大的敏感参数, 是模型参数校准过程中的重要工具, 也是建模和应用的先决条件。该文以阔叶红松林为研究对象, 采用全局敏感性分析方法——傅里叶幅度灵敏度检验扩展法(EFAST)对Biome-BGC模型的生理生态参数进行了敏感性分析, 分别分析了红松(Pinus koraiensis)和阔叶树的净初级生产力(NPP)、蒸散(ET)对参数变化的敏感性。结果表明: (1)模拟红松NPP的不确定性高于阔叶树, 但二者的模拟ET的不确定性均较小。阔叶树的NPP和ET对生理生态参数的敏感性总体上都小于红松。(2)无论是红松、阔叶或其他植被类型, 模拟NPP均表现出对叶片碳氮比、细根碳氮比、比叶面积(SLA)和冠层截留系数的敏感性, 这4个参数的高敏感性主要是由模型自身结构所决定的, 与植被类型和研究地区的关系较小。对模拟ET而言, 细根与叶片碳分配比、新茎与新叶碳分配比和SLA均是影响红松和阔叶树ET的敏感参数, 但红松ET主要受参数与参数间的二阶或多阶交互作用的间接影响, 而阔叶树ET则主要是受到敏感参数直接效应的影响。(3)除了上述影响红松和阔叶树碳水通量的共性参数外, 诸如核酮糖-1,5-二磷酸羧化酶中叶氮含量、叶片与细根周转率、所有叶面积与投影叶面积之比等也是对模拟结果有影响的重要参数, 但是其敏感程度随物种不同和研究区不同而不同, 所以这类参数可以根据具体情况进行参数本地化, 对于其他不敏感参数则可以采用模型缺省值。     

Inter‐laboratory validation of a rapid assay for the detection and quantification of Legionella spp. in water samples

Aims: To compare the standard culture method with a new, rapid test (ScanVIT‐Legionella?) using fluorescently labelled gene probes for the detection and enumeration of Legionella spp. The new technique was validated through experiments conducted on both artificially and naturally contaminated water and through an inter‐laboratory comparison. Methods and Results: All samples were processed by the ScanVIT test according to the manufacturer’s instructions and by a culture method (ISO 11731). ScanVIT detected significantly more positive samples, although concentrations were similar and a strong positive correlation between the two methods was observed (r = 0·888, P < 0·001). The new test was more accurate in identifying the co‐presence of Legionella pneumophila and Leg. non‐pneumophila. ScanVIT showed a slightly higher Legionella recovery from water samples artificially contaminated with Leg. pneumophila alone or together with Pseudomonas aeruginosa. Lastly, the inter‐laboratory comparison revealed that the ScanVIT test exhibits a lower variability than the traditional culture test (mean coefficient of variation 8·7 vs 16·1%). Conclusions: The results confirmed that the ScanVIT largely overlaps the reference method and offers advantages in terms of sensitivity, quantitative reliability and reduced assay time. Significance and Impact of the Study: The proposed method may represent a useful validated alternative to traditional culture for the rapid detection and quantification of Legionella spp. in water.     

Environmental factors influencing methanogenesis in a shallow anoxic aquifer: a field and laboratory study

Summary The environmental factors influencing methanogenesis in a shallow anoxic aquifer were probed in a combined field and laboratory study. Field data collected over a year revealed that in situ rates of methane production were depressed in winter and elevated in summer. Over the same period, ground water pH values ranged from 6.0 to 7.8 while temperatures varied from 7–22°C. In situ methanogenesis was severely inhibited at temperatures < 13°C or by pH values < 7. The influence of these factors on microbial methane formation from both endogenous and exogenous substrates were tested in aquifer slurries adjusted to pH 5–9 and incubated at temperatures ranging from 5–45°C. Temperature optima for methane production from endogenous substrates varied as a function of pH, but the pH optimum was 8 at all temperatures. Optimal conditions for acetoclastic methanogenesis were found at pH 8 and 35°C. An analysis of variance revealed that pH, temperature, and a pH-temperature interaction are all significant variables influencing aquifer methanogenesis. In addition transient sulfate accumulations were also found to limit methane production in some areas. A comparison of field and laboratory methane production patterns suggest that pH, temperature, and sulfate accumultations are important, but not the only environmental variables influencing the mineralization of organic matter in shallow aquifers.     

Biomass changes and trophic amplification of plankton in a warmer ocean

Ocean warming can modify the ecophysiology and distribution of marine organisms, and relationships between species, with nonlinear interactions between ecosystem components potentially resulting in trophic amplification. Trophic amplification (or attenuation) describe the propagation of a hydroclimatic signal up the food web, causing magnification (or depression) of biomass values along one or more trophic pathways. We have employed 3‐D coupled physical‐biogeochemical models to explore ecosystem responses to climate change with a focus on trophic amplification. The response of phytoplankton and zooplankton to global climate‐change projections, carried out with the IPSL Earth System Model by the end of the century, is analysed at global and regional basis, including European seas (NE Atlantic, Barents Sea, Baltic Sea, Black Sea, Bay of Biscay, Adriatic Sea, Aegean Sea) and the Eastern Boundary Upwelling System (Benguela). Results indicate that globally and in Atlantic Margin and North Sea, increased ocean stratification causes primary production and zooplankton biomass to decrease in response to a warming climate, whilst in the Barents, Baltic and Black Seas, primary production and zooplankton biomass increase. Projected warming characterized by an increase in sea surface temperature of 2.29 ± 0.05 °C leads to a reduction in zooplankton and phytoplankton biomasses of 11% and 6%, respectively. This suggests negative amplification of climate driven modifications of trophic level biomass through bottom‐up control, leading to a reduced capacity of oceans to regulate climate through the biological carbon pump. Simulations suggest negative amplification is the dominant response across 47% of the ocean surface and prevails in the tropical oceans; whilst positive trophic amplification prevails in the Arctic and Antarctic oceans. Trophic attenuation is projected in temperate seas. Uncertainties in ocean plankton projections, associated to the use of single global and regional models, imply the need for caution when extending these considerations into higher trophic levels.