Translocation,remineralization, and turnover of nitrogen in the roots and rhizomes of Spartina alterniflora (Gramineae)

We used ¹⁵N to quantify rates of N translocation from aerial to belowground tissues, foliar leaching, and turnover and production of root and rhizome biomass in the plant-sediment system of short Spartina alterniflora areas of Great Sippewissett Marsh, Massachusetts. Decay of belowground tissues in litterbag incubations at 1- and 10-cm depths resulted in 80% remineralization of the original plant (¹⁵N-labeled) N and 20% burial after 3 years. Translocation of ¹⁵N from plant shoots in hydrologically controlled laboratory lysimeters maintained under field conditions was 38% of the aboveground pool while leaching of N was 10% from June to October. Most of the translocated N was not retranslocated to new aboveground growth in December but appeared to be either remineralized or buried in the sediment. Injection of ¹⁵N into field stands of grass showed initially high incorporation into plants followed by a continuous decline over the next 7 years yielding a gross tumover time of 1.5–1.6yr. Correcting the gross N turnover for recycling of label via translocation and uptake of remineralized label during this period, a net root and rhizome turnover time of 1.0–1.1 yr was obtained. Combining the turnover time with independent estimates of seasonal belowground biomass yielded an estimate of belowground production of 929–1,022 g C m⁻² yr⁻¹, similar to measurements by traditional biomass harvest, CO² based budgets and models for comparable areas of this marsh. Integration of the production and nitrogen balance estimates for short Spartina marsh yielded translocation, 1.4 g N m⁻² yr⁻¹, leaching, 0.4 g N m⁻² yr⁻¹, remineralization, 14.9–16.3 g N m⁻² yr⁻¹, and burial, 3.7–4.1 g N m⁻² yr⁻¹.     

Primary production of phytoplankton in Lake Valencia (Venezuela)

Lake Valencia is heavily polluted by waste water of domestic, agricultural and industrial origin. The high organic load may have produced important changes in the limnological properties. Cyanobacteria dominated in numbers and biomass (over 90% throughout the year). Chlorophyll-a content averaged 37.7 + 15 μg · 1⁻¹. Maximum concentrations of 50–80 μg · 1⁻¹ were found near the inflows affected by organically polluted affluents. There has been a 50% reduction in the euphotic zone in only 13 years. The maximum rate of gross photosynthesis per hour at light saturation was determined within the uppermost 1-meter layer. The highest value was 16,290 mg O₂ · m⁻³ · h⁻¹. Lake Valencia is among the most productive lakes in the world, with areal net photosynthesis averaging 7.5 g C · m⁻² · d⁻¹.     

Shell productivity of the large benthic foraminifer Baculogypsina sphaerulata,based on the population dynamics in a tropical reef environment

Carbonate production by large benthic foraminifers is sometimes comparable to that of corals and coralline algae, and contributes to sedimentation on reef islands and beaches in the tropical Pacific. Population dynamic data, such as population density and size structure (size-frequency distribution), are vital for an accurate estimation of shell production of foraminifers. However, previous production estimates in tropical environments were based on a limited sampling period with no consideration of seasonality. In addition, no comparisons were made of various estimation methods to determine more accurate estimates. Here we present the annual gross shell production rate of Baculogypsina sphaerulata, estimated based on population dynamics studied over a 2-yr period on an ocean reef flat of Funafuti Atoll (Tuvalu, tropical South Pacific). The population density of B. sphaerulata increased from January to March, when northwest winds predominated and the study site was on the leeward side of reef islands, compared to other seasons when southeast trade winds predominated and the study site was on the windward side. This result suggested that wind-driven flows controlled the population density at the study site. The B. sphaerulata population had a relatively stationary size-frequency distribution throughout the study period, indicating no definite intensive reproductive period in the tropical population. Four methods were applied to estimate the annual gross shell production rates of B. sphaerulata. The production rates estimated by three of the four methods (using monthly biomass, life tables and growth increment rates) were in the order of hundreds of g CaCO₃ m⁻² yr⁻¹ or cm⁻³ m⁻² yr⁻¹, and the simple method using turnover rates overestimated the values. This study suggests that seasonal surveys should be undertaken of population density and size structure as these can produce more accurate estimates of shell productivity of large benthic foraminifers.

     

Aspects of production and biomass of four seagrass species (Cymodoceoideae) from Papua New Guinea

Biomass and production data of the seagrasses Cymodocea serrulata (R. Brown) Aschers. and Magnus, Cymodocea rotundata Ehrenb. et Hempr. ex Aschers., Halodule uninervis (Forssk.) Aschers. and Syringodium iksoetifolium (aschers.) Dandy were collectede in monospecific stands in Bootless Inlet, Papua New Guinea. Cymodocea serrulata and Cymodocea rotundata were studied from November 1980 to November 1981. Total annual mean biomass was 354 and 201 g ADW m⁻², respectively. The largest proportion of these biomass values was contributed by the rhizomes (49 and 36%, respectively) and leaf biomass was ± 30% for both species. Halodule uninervis was studied at an intertidal and a subtidal site. The highest total annual mean biomass (600 g ADW m⁻²) was recorded at the intertidal site, of which 85% was found below ground. The largest proportion of the biomass, at both sites, was contributed by the below-ground vertical axes of the shoots. The biomass of the rhizomes was relatively low (9–12%) for Halodule uninervis. Proportionally, the largest above-ground biomass (40%) was recorded for Syringodium isoetifolium, of which the annual mean biomass was 481 g ADW m⁻².Total production (above and below ground) was 4.9 and 3.0 g ADW m⁻² day⁻¹ for Cymodocea serrulata and Cymodocea rotundata, respectively. Approximately 70% was production of leaves. Total production amounted to 6.0 and 4.0 g ADW m⁻² day⁻¹ for Halodule uninervis at the intertidal and subtidal sites, respectively. The maximum production was recorded for Syringodium isoetifolium, 60% of the 9.0 g ADW m⁻² day⁻¹ was contributed by the leaves. All species reached the maximum production during February and March, when the water temperatures were highest and water was retained above all sites, at all times. The increase of leaf production was mainly due to the increase in biomass of the mature leaves. Significant changes in the plastochrone interval of the leaves were not observed during this period.     

Population Dynamics,Growth and Productivity of Abra ovata (Mollusca,Bivalvia) in the Evros Delta (North Aegean Sea)

Monthly samples of Abra ovata were collected during February 1983-January 1984 in the Evros Delta (N. Aegean Sea). Population density (mean annual value = 2407.5 ind · m⁻²) was characterized by seasonal variation. An analysis of the length frequency distributions shows that one annual recruitment of juveniles (> 2 mm) occurred in October-January; and also that, throughout the year, two age groups existed in the population. One growth ring was formed on the shells of the oldest age group during July-August. Mean growth in shell length can be described by Bertalanffy function. A positive correlation existed between shell length and decalcified dry weight. Secondary production in A. ovata, calculated by the instantaneous growth method, showed a mean biomass of 29.221 g dry weight m⁻²yr⁻¹, a productivity of 17.086 g dry weight m⁻²yr⁻¹ and an annual turnover ratio of 0.59.     

Primary productivity of papyrus (Cyperus papyrus) in a tropical swamp; Lake Naivasha,Kenya

Papyrus (Cyperus papyrus) standing biomass and the primary productivity of undisturbed and previously harvested areas of papyrus was measured in Lake Naivasha swamp, Kenya. Papyrus culm density in undisturbed swamp was estimated to be 13·1±1·9 culms m⁻² and aerial biomass was 3602 g m⁻². In undisturbed swamp the aerial productivity was 14·1 g m⁻² day⁻¹ while the previously harvested swamp reached a peak of 21·0 g m⁻² after 6 months. The annual aerial production rate of papyrus in Lake Naivasha was estimated to be 5150 g m⁻² year⁻¹. To sustain yields of regularly harvested papyrus swamps, the harvest intervals should exceed 1 year.     

First estimates of productivity in Lessonia trabeculata and Lessonia nigrescens (Phaeophyceae, Laminariales) from the southeast Pacific

Lessonia is the main Laminariales found along the southeast Pacific coast. Lessonia nigrescens Bory de Saint‐Vincent in the intertidal and Lessonia trabeculata Villouta et Santelices in the subtidal, are the most important habitat constructors in rocky coastal communities in northern and central Chile. In both species, the seasonal production and erosion of distal tissue were estimated in biomass units using the Area of Constant Biomass Model that combined the individual blade elongation, obtained with the traditional hole‐punching method, with the blade length and biomass distribution along the blade. In austral late spring (December 96) and autumn (May 97), blade production and erosion were transformed to the level of population from standing stock measurements (number and biomass of blades and plants per substrate area), considering that previous blade weight analysis showed the highest and lowest values at these times, as well as the population parameter extremes that were expected to occur. Both species displayed a seasonal pattern, with a production increase in later winter and spring and decrease towards the end of summer that coincided with higher distal tissue erosion. At the level of individual blades, Lessonia trabeculata showed higher mean production (0.026 g dw d⁻¹) and erosion (0.01 g dw d⁻¹) than L. nigrescens (production 0.01 g dw d⁻¹ and loss 0.002 g dw d⁻¹). The standing stocks, with respect to density and biomass, were similar in spring and autumn for both populations. Nevertheless, the net productivity (production minus erosion) of the intertidal L. nigrescens showed greater values due to the greater density of blades (2112 ± 1360 (SE) blades m⁻²) compared with the subtidal L. trabeculata (527 ± 151 (SE) blades m⁻²). Spring net productivities of 42 g dw m⁻²d⁻¹ (254 g ww m⁻²d⁻¹; 11.46 gC m⁻²d⁻¹) for L. nigrescens and 11 g dw m⁻² d⁻¹ (64 g ww m⁻² d⁻¹; 2.46 gC m⁻²d⁻¹) for L. trabeculata were estimated. A preliminary model of production and biomass fate for Lessonia populations is proposed.     

An Analysis of the Nutrient Contribution by Phytoplankton Primary Production to the Food Web of a Small Lake

Phytoplankton primary production was measured for 148 days, from May 31 to October 25, 1971, in Sunfish Lake, Ontario, using the ¹⁴C light and dark bottle technique. The purpose of the experiment was not only to measure the rate of production but also to give some indication of the fates of the material produced by the algae. The following data were calculated for the sampling season: total gross production 57,770.6 mg C m ⁻²; algal respiration 31.74% of gross production; total net production 39,895.4 mg C m ⁻²; extracellular production 9.2% of total net production. The efficiencies of both gross and net total production were inversely correlated with light intensity. The rate of extracellular production was directly correlated with the rate of total production. The rate of respiration was not significantly correlated with either the rate of gross production or with the algal biomass as calculated from differential cell counts. The weekly rate of phytoplankton turnover was calculated by combining measurements of algal biomass with net particulate production measurements. The turnover rates for the phototrophic zone ranged from plus 6,788.5 mg C m ⁻² to minus 1,104.4 mg C m ⁻² The negative figure indicates an increase in algal biomass which can not be accounted for by primary production. The rate of phytoplankton turnover was compared with fluctuations in the standing crop of zooplankton but the correlation was not significant. Gross and net rates of extracellular production were estimated and compared. There was no significant difference between the two measurements and the implications of this are discussed with respect to other work in the field.     

Contribution of the polychaete,Neanthes japonica (Izuka), to the oxygen uptake and carbon dioxide production of an intertidal mud-flat of the Nanakita River estuary,Japan

The benthic oxygen consumption and carbon dioxide production of undisturbed and sieved sediment cores with various values for the biomass of polychaetes collected from the intertidal mud-flat of Nanakita River estuary of Japan were measured simultaneously. The benthic oxygen consumption and carbon dioxide production increased in proportion to the biomass of a dominant polychaete species Neanthes japonica (Izuka). This increase was not explained by the respiration of the animals alone. The residual increase in benthic O₂ and CO₂ fluxes may be due to mineralization processes in the burrow wall and enhanced diffusion caused by the pumping activity of the worms. From the average biomass of polychaetes at the study site, total benthic O₂ and CO₂ fluxes were estimated to be 5.2 mmol·m⁻²·h⁻¹ and 7.3 mmol·m⁻²·h⁻¹, respectively, at 20 ° C. The worms were responsible for 79% of the total O₂ flux and 73% of the total CO₂ flux but the respiration of the worms accounted for only 53% of the total O₂ flux and 36% of the total CO₂ flux. The residual enhanced fluxes were 26% and 37% for the total O₂ and CO₂ fluxes, respectively.     

KINETICS OF GROWTH AND DEATH IN ANABAENA FLOS-AQUAE (CYANOBACTERIA) UNDER LIGHT LIMITATION AND SUPERSATURATION

The kinetics of population growth and death were investigated in Anabaena flos-aquae (Lyngb.) Bréb grown at light intensities ranging from limitation to photoinhibition (5 W·m⁻² to 160 W·m⁻²) in a nutrient-replete turbidostat. Steady-state growth rate (μ, or dilution rate, D) increased with light intensity from 0.44·day⁻¹ at a light intensity of 5 W·m⁻² to 0.99·day⁻¹ at 20 W·m⁻² and started to decrease above about 22 W·m⁻², reaching 0.56·day⁻¹ at 160 W·m⁻². The Haldane function of enzyme inhibition fit the growth data poorly, largely because of the unusually narrow range of saturation intensity. However, it produced a good fit (P < 0.001) for growth under photoinhibition. Anabaena flos-aquae died at different specific death rates (γ) below and above the saturation intensity. When calculated as the slope of a v_x⁻¹ and D⁻¹ plot, where v_x and D are cell viability (or live cell fraction) and dilution rate, respectively; γ was 0.047·day⁻¹ in the range of light limitation and 0.103·day⁻¹ under photoinhibition. Live vegetative cells and heterocysts, either in numbers or as a percentage of the total cells, showed a peak at the saturation intensity and decreased at lower and higher intensities. The ratio of live heterocysts to live vegetative cells increased with intensity when light was limiting but decreased when light was supersaturating. In cells growing at the same growth rate, the ratio was significantly lower under light inhibition than under subsaturation and the cell N:C ratio was also lower under inhibition. The steady-state rate of dissolved organic carbon (DOC) production increased with light intensity. However, its production as a percentage of the total C fixation was lowest at the optimum intensity and increased as the irradiance decreased or increased. The rate and percentage was significantly higher under photoinhibition than limitation in cells growing at the same growth rate. About 22% of the total fixed carbon was released as DOC at the highest light intensity. No correlation was found between the number of dead cells and DOC.     

Partitioning of river metabolism identifies phytoplankton as a major contributor in the regulated Murray River (Australia)

1. River metabolism was measured over an annual cycle at three sites distributed along a 1000 km length of the lowland Murray River, Australia. 2. Whole system metabolism was measured using water column changes in dissolved oxygen concentrations while planktonic and benthic metabolism were partitioned using light‐dark bottles and benthic chambers. 3. Annual gross primary production (GPP) ranged from 775 to 1126 g O₂ m^?2 year^?1 which in comparison with rivers of similar physical characteristics is moderately productive. 4. Community respiration (CR) ranged from 872 to 1284 g O₂ m^?2 year^?1 so that annual net ecosystem production (NEP) was near zero, suggesting photosynthesis and respiration were balanced and that allochthonous organic carbon played a minor role in fuelling metabolism. 5. Planktonic rates of gross photosynthesis and respiration were similar to those of the total channel, indicating that plankton were responsible for much of the observed metabolism. 6. Respiration rates correlated with phytoplankton standing crop (estimated as the sum of GPP plus the chlorophyll concentration in carbon units), yielding a specific respiration rate of ?1.1 g O₂ g C^?1 day^?1. The respiration rate was equivalent to 19% of the maximum rate of phytoplankton photosynthesis, which is typical of diatoms. 7. The daily GPP per unit phytoplankton biomass correlated with the mean irradiance of the water column giving a constant carbon specific photon fixation rate of 0.35 gO₂ g Chl a^?1 day^?1 per μmole photons m^?2 s^?1 (ca. 0.08 per mole photons m^?2 on a carbon basis) indicating that light availability determined daily primary production. 8. Annual phytoplankton net production (NP) estimates at two sites indicated 25 and 36 g C m^?2 year^?1 were available to support riverine food webs, equivalent to 6% and 11% of annual GPP. 9. Metabolised organic carbon was predominantly derived from phytoplankton and was fully utilised, suggesting that food‐web production was restricted by the energy supply.     

CO2 flux in alpine wetland ecosystem on the Qinghai-Tibetan Plateau, China

Using the CO₂ flux data measured by the eddy covariance method in the northeast of Qinghai-Tibetan Plateau in 2005, we analyzed the carbon flux dynamics in relation to meteorological and biotic factors. The results showed that the alpine wetland ecosystem was the carbon source, and it emitted 316.02 gCO₂ · m⁻² to atmosphere in 2005 with 230.16 gCO₂ · m⁻² absorbed in the growing season from May to September and 546.18 gCO₂ · m⁻² released in the non-growing season from January to April and from October to December. The maximum of the averaged daily CO₂ uptake rates and release rates was (0.45 ± 0.0012) mgCO₂ · m⁻² · s⁻¹ (Mean ± SE) in July and (0.22 ± 0.0090) mgCO₂ · m⁻² · s⁻¹ in August, respectively. The averaged diurnal variation showed a single-peaked pattern in the growing season, but exhibited very small fluctuation in the non-growing season. Net ecosystem exchange (NEE) and gross primary production (GPP) were all correlated with some meteorological factors, and they showed a negatively linear correlation with aboveground biomass, while a positive correlation existed between the ecosystem respiration (R_es) and those factors.     

Use of chemostat data for modelling extracellular-inulinase production by Kluyveromyces marxianus in a high-cell-density fed-batch process

Production of extracellular inulinase by low-cell-density (2 kg dry weight·m⁻³) sucrose-limited chemostat cultures of Kluyveromyces marxianus obeyed saturated kinetics at dilution rates ranging from 0.02 to 0.5 h⁻¹. A non-structured Monod-type equation, describing the relation between specific growth rate and specific extracellular-inulinase production rate, was used to fit experimental data. THis equation was subsequently incorporated in a model for the production of biomass and extracellular inulinase in a high-cell-density (> 100 kg dry weight·m⁻³) fed-batchculture of K. marxianus grown on sucrose. The model adequately described biomass production in the fed-batch culture. However, the production of extracellular inulinase in the fed-batch process was slightly higher than predicted by the model. This observation may be related to differences in growth conditions between in the chemostat and fed-batch cultures.     

Lipid and biomass production by the halotolerant microalga Nannochloropsis salina

The effect of environmental factors on cell-lipid content, on the growth rate and on the overall productivity of Nannochloropsis salina was tested in the laboratory and in outdoor cultures. Under optimum conditions in the laboratory, the maximum growth rate (μ_max) was 0·030 h⁻¹, which corresponds to a doubling time of 23 h. Cellular lipid content was affected by the phase of growth and the temperature, but not by nitrogen starvation, pH or the source of sea water. The most important factor affecting the output rate of biomass was the cell concentration. The maximum biomass productivity obtained in outdoor ponds was 24·5 g·m⁻²·day⁻¹, and the lipid production rate was 4·0 g m⁻²·day⁻¹.     

An Analysis of the Biotic Community in a Kumaun Himalayan Lake,Nainital (U. P.), India

A comprehensive study of phyto- and zooplankton and macrozoobenthic components in Lake Nainital showed that species richness was high for plankton and low for macrozoobenthos. The algal biomass was dominated by greens (54 %) and blue-greens (31 %), the zooplankton population by copepods (84 %), and the macrozoobenthic community by a Tubifex-Chironomus association constituting≥95 % of the annual number of the macrobenthic invertebrates. Respiration (807.5g C m⁻² year⁻¹) surpassed gross production (630.5 g C m⁻² year⁻¹). The mean annual ratio between phyto- and zooplankton biomass is 3.3 and between phytoplankton and herbivores it is 4.6. If biomass is treated as a measure of crude production, the relationship among the three trophic levels suggests that herbivory is inefficient while carnivory is efficient, because part of the primary production remains unutilized by dominant herbivorous zooplankters, whereas Mesocyclops leuckarti, the sole carnivore, feeds efficiently on rotifers and juveniles of other copepods. The low diversity of different biotic components and the P/R ratio of less than 1 perhaps suggest that the lake is passing through the stage of heterotrophic succession.     

Population dynamics, growth and production of the neozoon Marenzelleria cf. viridis (Verrill, 1873) (Polychaeta: Spionidae) in a coastal water of the southern Baltic Sea

The propagation of an immigrant from North America, viz. the spionid Marenzelleria cf. viridis in the Darss-Zingst Bodden (DZB) (southern Baltic Sea), was studied at three stations from March 1992 to December 1995. Highest mean abundances (over 28 000 ind. m^-2) and wet weights (400 g m^-2) were recorded at station 2 in 1994. The spionid also reached its highest dominances in terms of biomass (40 to 90%) at this station, which was selected for the population dynamics, growth and secondary production studies. The spionid has a life span of about 3 years, and many individuals achieved sexual maturity after one year. Their growth curve is steepest during the first year of life, during which the animals grow to a length of about 180 segments. However, growth depression was observed during the ripening of the gametes in April, May and June. Secondary production was in the region of 55 to 85 g AFDW m^-2 y^-1. Productivity (P/B) varied considerably from generation to generation, ranging between 0 and 4.8 with an average between 1.2 and 1.6.     

Relations between production and biomass of phytoplankton in four Swedish lakes of different trophic status and humic content

Production and biomass values from phytoplankton populations in four different Swedish lakes were analysed. The production in all lakes was directly proportional to biomass during homothermal periods. When the lakes were stratified there was a strong negative relation between specific growth rate and biomass. The data fitted to a logistic density dependent growth equation of the form: dB/ dt = µ_mB(1-B · K^–1) where B is the biomass, µ_m the maximum specific growth rate and K the carrying capacity. The equation was used to derive the parameters µ · µ_m ^–1 and carrying capacity (the maximum possible biomass). These parameters were then discussed in relation to light climate, phosphorus concentration and humic content.     

Growth and biomass productivity of Scenedesmus vacuolatus on a twin layer system and a comparison with other types of cultivations

Scenedesmus is a genus of microalgae employed for several industrial uses. Industrial cultivations are performed in open ponds or in closed photobioreactors (PBRs). In the last years, a novel type of PBR based on immobilized microalgae has been developed termed porous substrate photobioreactors (PSBR) to achieve significant higher biomass density during cultivation in comparison to classical PBRs. This work presents a study of the growth of Scenedesmus vacuolatus in a Twin Layer System PSBR at different light intensities (600 μmol photons m⁻² s⁻¹ or 1000 μmol photons m⁻² s⁻¹), different types and concentrations of the nitrogen sources (nitrate or urea), and at two CO₂ levels in the gas phase (2% or 0.04% v/v). The microalgal growth was followed by monitoring the attached biomass density as dry weight, the specific growth rate and pigment accumulation. The highest productivity (29 g m⁻² d⁻¹) was observed at a light intensity of 600 μmol photons m⁻² s⁻¹ and 2% CO₂. The types and concentrations of nitrogen sources did not influence the biomass productivity. Instead, the higher light intensity of 1000 μmol photons m⁻² s⁻¹ and an ambient CO₂ concentration (0.04%) resulted in a significant decrease of productivity to 18 and 10–12 g m⁻² d⁻¹, respectively. When compared to the performance of similar cultivation systems (15–30 g m⁻² d⁻¹), these results indicate that the Twin Layer cultivation System is a competitive technique for intensified microalgal cultivation in terms of productivity and, at the same time, biomass density.

     

The Structure of a Macroinvertebrate Community in a Northern German Lake Outlet (Lake Belau,Schleswig-Holstein) with Special Emphasis on Abundance,Biomass and Secondary Production

The structure of macroinvertebrate communities was studied at I I sampling sites of the outlet of Lake Belau in the lowlands of northern Germany. To describe the structures of macrobenthic animal communities three different units were examined: abundance, biomass, and secondary production. 112 taxa were collected from the entire stream. The numbers of species ranged from 31 (fine sand) to 70 (submerged macrophytes). For the stream, average macroinvertebrate density was 18.400 ind. M⁻¹. Density was highest at the macrophytes amounting to 35,630 individuals per m², and lowest in the pure sand with only 3,900 ind. M⁻². Average biomass (dry mass) was 194 g DM m⁻² varying from 9.8 (peat) to 381 g DM m⁻² (gravel with mollusk shells near the upstream lake). For the stream, average annual production was 129 g DM m⁻² varying from 15 (peat) to 286 g DM m⁻² (macrophytes). The highest values for each unit were found in stream sections with gravel and submerged macrophytes. Lower values occured in sections that contained peat and sand. Usually, a single structure of the macroinvertebrate community was dominated by less than ten taxa, which varied at each sampling site depending on the units observed.     

Seasonality in Nutrients and Phytoplankton Production in Two Shallow Lakes: Waigani Lake,Papua New Guinea,and Barton Broad,Norfolk, England

Waigani Lake, near Port Moresby, Papua New Guinea and Barton Broad, Norfolk, England are both shallow lakes nutrient-enriched from sewage effluent disposal. In Waigani Lake phytoplankton biomass varied seasonally with lower levels (100-200 mg chlorophyll α m⁻³) during the wet season increasing to over 400 mg chlorophyll α m⁻³ at the end of the dry season. Secchi disc depths varied between 0. 11 and 0. 34 m. Phytoplankton productivity in Waigani Lake was very high throughout the year (range: A_max 4,370-21,000 mg O₂ m⁻³ h⁻¹) but production was lower during the wet season (range: A_max 4,370-12,700 mg O₂ m⁻³ h⁻¹). High surface productivity was recorded from August to December except on sampling days when the weather was overcast. Productivity throughout the year declined rapidly with depth. Algal biomass in Barton Broad varied from 3-10 mg chlorophyll α m⁻³ in winter but increased in spring and was very high in summer (200-500 mg chlorophyll α m⁻³). Secchi disc depth varied from 0.21 m in August 1976 to 1.76 m in December. Phytoplankton production in Barton Broad was low in winter (range: A_max 247-1,250 mg O₂ m⁻³ h⁻¹) but increased markedly in spring and summer with the highest rate (A_max 6,850 mg O₂ m⁻³ h⁻¹) being recorded in August. Surface inhibition was observed during summer except when the weather was overcast. Seasonality in nutrients and phytoplankton in Waigani Lake appear to be related to rainfall. Nutrient concentrations in Barton Broad are more closely related to phytoplankton activity which, in turn, correlates with seasonality in solar radiation.