Comparison of bacterial production in sediments, epiphyton and the pelagic zone of a lowland river

1. The microbial metabolism of organic matter in rivers has received little study compared with that of small streams. Therefore, we investigated the rate and location of bacterial production in a sixth‐order lowland river (Spree, Germany). To estimate the contribution of various habitats (sediments, epiphyton, and the pelagic zone) to total bacterial production, we quantified the contribution of these habitats to areal production by bacteria. 2. Large areas of the river bottom were characterized by loose and shifting sands of relatively homogenous particle size distribution. Aquatic macrophytes grew on 40% of the river bottom. Leaf areas of 2.8 m² m^?2 river bottom were found in a 6.6 km river stretch. 3. The epiphyton supported a bacterial production of 5–58 ng C cm^?2 h^?1. Bacterial production in the pelagic zone was 0.9–3.9 μg C L^?1 h^?1, and abundance was 4.0–7.8 × 10⁹ cells L^?1. Bacterial production in the uppermost 2 cm of sediments ranged from 1 to 8 μg C cm^?3 h^?1, and abundance from 0.84 to 6.7 × 10⁹ cells cm^?3. Bacteria were larger and more active in sediments than in the pelagic zone. 4. In spite of relatively low macrophyte abundance, areal production by bacteria in the pelagic zone was only slightly higher than in the epiphyton. Bacterial biomass in the uppermost 2 cm of sediments exceeded pelagic biomass by factors of 6–22, and sedimentary bacterial production was 17–35 times higher than in the overlying water column. 5. On a square meter basis, total bacterial production in the Spree was clearly higher than primary productivity. Thus, the lowland river Spree is a heterotrophic system with benthic processes dominating. Therefore, sedimentary and epiphytic bacterial productivity form important components of ecosystem carbon metabolism in rivers and shallow lakes. 6. The sediments are focal sites of microbial degradation of organic carbon in a sand‐bottomed lowland river. The presence of a lowland river section within a river continuum probably greatly changes the geochemical fluxes within the river network. This implies that current concepts of longitudinal biogeochemical relationships within river systems have to be revised.     

Organic Carbon Flux to a Large Salt Lake: Pyramid Lake,Nevada, USA

Energy flux to a large, deep, salt lake from phytoplankton, periphyton and macrophyte primary production as well as fluvial transport and wind-transported terrestrial vegetation and dust were quantified. Average areal phytoplankton net photosynthesis was 511 mg C m⁻² d⁻¹. Highest rates were during water-blooms of the bluegreen alga, Nodularia spumigena. Although areal daily net photosynthesis by periphyton in Pyramid Lake was comparable to other salt lakes, annual carbon influx by periphyton was small due to the lake's graben morphology and moderate euphotic depth (mean, 11.9 m). Macrophytes were uncommon and, therefore a minor source of energy. Truckee River is the only major fluvial discharge to Pyramid Lake and dissolved organic carbon was the principal organic carbon fraction in river water. Large upstream water diversions coupled with several drought years resulted in an average fluvial organic carbon load of only 7.3 g Cm⁻²y⁻¹ or 4% of median phytoplankton net photosynthesis. Tumbleweeds were the most common terrestrial plant material observed in Pyramid Lake comprising a maximum projected importance of 6% of total annual carbon input. Windborne dust represented < .1% of annual carbon input. Phytoplankton primary production is the predominant energy source to Pyramid Lake, accounting for over 80% of annual carbon influx. The relative magnitude of autochthonous and allochthonous vectors to the annual carbon budget of this desert salt lake are comparable to those of the few other large lakes for which detailed energy input budgets have been calculated.     

Primary production of phytoplankton and standing crops of zooplankton and zoobenthos in hypertrophic Lake Teganuma

Primary production of phytoplankton and standing crops of zooplankton and zoobenthos were intensively surveyed in Lake Teganuma during May 1983–April 1984. The annual mean chlorophyll a concentrations were as high as 304 µg · l^–1–383 µg · l^–1. The daily gross primary production of phytoplankton was high throughout the year. The peak production rate was recorded in August and September, when blue-green algae bloomed. The annual gross primary production was estimated as 1450 g C · m^–2 · y^–1, extremely high as compared with other temperate eutrophic lakes. Zooplankton was predominantly composed of rotifers. The annual mean standing crop of zooplankton was 0.182 g C · m^–2 around the middle between the inlets and the outlet and was lower than in most other temperate eutrophic lakes. Zoobenthos was mostly composed of Oligochaeta and chironomids. The annual mean standing crop of zoobenthos ranged from 0.052 g C · m^–2 to 0.265 g C · m^–2, the lowest values among temperate eutrophic lakes, which is in contrast to the high primary production.     

Growth, production and losses of phytoplankton in the lowland River Spree: carbon balance

1. Phytoplankton carbon assimilation and losses (exudation, dark carbon losses) as well as oxygen release and dark community respiration were measured regularly for 2 years at four stations along the lower Spree (Germany). Carbon balance of river phytoplankton was estimated using measured assimilation, metabolic losses and variations in algal carbon along a stretch of river. 2. The light/dark bottle method was modified to simulate vertical mixing. 3. Waxing and waning of phytoplankton populations dominated the load of particulate organic carbon as well as the oxygen budget of the river. 4. Phytoplankton assimilated 310–358 g C m^?2 yr^?1. A mean value of 586 mg C m^?3 day^?1 was fixed in photosynthesis, with 16.7 mg C being exuded during the day and 20.1 mg lost at night. The measured dark respiration was equivalent to only 28% of the daily gross oxygen production of the plankton community. Phytoplankton washed from upstream lakes and reservoirs was not measurably damaged by turbulent transport. 5. In spring, 18–22% of assimilated carbon was used for net biosynthesis of phytoplankton along the river course. At this time, the carbon balance of this part of the Spree was dominated by autochthonous net production. During summer, however, total carbon losses exceeded the intensive carbon assimilation. The decline of algal biomass along the river course in summer was not explicable by measurable physiological losses. The importance of sedimentation and grazing losses is discussed.     

Factors relating to annual planktonic primary production in five small oligotrophic lakes in Terra Nova National Park,Newfoundland

Annual planktonic primary production in five small oligotrophic lakes in Newfoundland, as measured at maximum depth (P-area) ranged from 5.6 to 12.0 g C/m²/year. Production per unit surface area representative of the whole lake basin (P-area ) was considerably lower in the shallower lakes (3.3 to 6.4 g C/m²/yr), while production expressed per unit volume representative of the whole lake basin (P-vol ) was the higher in the shallower lakes (0.6 to 4.1 g C/m³/yr). Production efficiency varied from lake to lake and throughout the year, but it remained fairly stable in a shorter term. Production efficiency and insolation was used to estimate annual production. Lakes with higher summer concentration of total phosphorus had higher rates of carbon assimilation.     

Carbon, Water, and Energy Exchanges of a Hybrid Poplar Plantation During the First Five Years Following Planting

Eddy covariance was used to measure above-canopy exchanges of CO₂ and water vapor at an operational plantation of hybrid poplar (variety ??Walker??) established on marginal agricultural land in east central Alberta, Canada. Winter ecosystem respiration (R _e) rates were inferred from seasonal changes in the normalized respiration rate at 10°C (R ₁₀) for the growing season and observations of soil CO₂ concentration measured with solid-state probes. Over five consecutive growing seasons following planting, gross ecosystem production (GEP) increased each year, ranging from 21?g?C?m^?2?y^?1 in year 1 to 469?g?C?m^?2?y^?1 in year 5. During this period, the annual carbon balance shifted from a net source of greater than 330?g?C?m^?2 in year 1 to approximately C-neutral in year 5. Total carbon (C) release over 5?years likely exceeded 630?g?C?m^?2. Intra- and interannual variations in temperature and soil water availability greatly affected annual C balance each year. GEP and R _e were particularly sensitive to temperature during spring and to soil water availability in summer: year 5 was notable because a cold spring and accumulating drought caused growth and carbon uptake to fall well below their potential. Annual evapotranspiration (ET) increased slightly with leaf area, from 281?mm in year 1 to 323?mm in year 4, but in year 5 it declined, while exceeding total precipitation (P). This trend of increasing annual ET/P suggests that annual GEP could become increasingly water-limited in years with below normal precipitation, as the plantation achieves maximum leaf area. Measured canopy albedos did not change appreciably over three winters, suggesting that estimates of increased radiative forcing resulting from afforestation in high latitudes could be exaggerated in regions where fast-growing deciduous plantations are managed on short (~20-year) rotations.     

A Three Years' Study of Life Cycle,Population Dynamics and Production of Asellus aquaticus L. in a Macrophyte Rich Stream

Populations of A. aquaticus were sampled quantitatively in 1979–82 at two localities in the river Suså which has a slope of <1 m km⁻¹ and large variations in macrophyte biomass, discharge and stream velocity. The latter two differed significantly between years. A. aquaticus had (1)−2 life cycles per year and summer and winter cohort production intervals of 85 and 290 days. Populations of A. aquaticus varied between 0 and 28,000 ind. m⁻² with an exponential increase in the spring and an exponential decrease in the autumn-winter. The A. aquaticus rate of decrease varied between 0.62 and 5.61 % d⁻¹ and increased with increasing rate of elimination of the macrophyte biomass Differences between the two localities were due to differences in physical heterogeneity. Production varied between 2.8 and 9.1 g DW m⁻² yr⁻¹ and between 12.9 and 55 g DW m⁻² yr⁻¹ at the two localities and P/B ratios were 7.4–9.9 yr⁻¹. Physical limitations are thought to be most important for the populations of A. aquaticus in the Suså, and the macrophyte biomass played an important role in modifying the physical environment. Differences between streams and lake populations are discussed.     

The influence of water transparency on the distribution and abundance of macrophytes among lakes of the Mackenzie Delta, Western Canadian Arctic

SUMMARY 1. Macrophyte abundance and distribution was assessed in a chain of six interconnected lakes (all with the same flooding frequency) in the Arctic, where increasing distance from the Mackenzie River channel resulted in a gradient of water transparency (‘chain‐set’ lakes), and in a group of 26 spatially discrete lakes where increasing frequency and duration of lake flooding with river water (controlled by sill height) also resulted in a transparency gradient (‘sill‐set’ lakes). 2. Among the chain‐set lakes, above‐ground macrophyte biomass increased from 0 to 1000 g m^?2 with increasing water transparency. Among the sill‐set lakes, the transparency gradient among the lakes was less well defined and the relations with biomass were more varied. A decrease in flooding was associated with increasing water transparency and an increasing biomass of macrophytes from about 0 to over 2000 g m^?2. For a specific flood frequency, however, the effect of flooding was much greater when lakes were directly connected to a river channel than when floodwaters flowed first through an intervening lake. Among infrequently flooded lakes the effect of flooding on water transparency and biomass was negligible. 3. Among relatively clear lakes in both sets of lakes, biomass increased with increasing water transparency and decreasing lake depth. Among relatively turbid lakes, however, biomass increased with the combined effect of increasing water colour (decreasing water transparency) and increasing lake water depth. The increases in biomass with increasing water colour (coloured dissolved organic matter) and increasing depth, which together result in reduced light at the bed, may be explained by reduced exposure to ultra violet light. 4. An average light attenuation of 1.3 m^?1 (Secchi depth about 1 m) over the growing season appears to represent a threshold water transparency which, in combination with water depths early in the growing season, is consistent with a light supply on the bed required for growth of the common macrophytes in lakes of the Mackenzie Delta. However, a comparison with other systems indicates that macrophytes among lakes of the Mackenzie Delta grow deeper, for a given level of transparency, than is reported in lakes at lower latitude, despite the lower sun angles and increased reflectivity of water surfaces in the arctic. 5. A complete accounting of water transparency (at PAR and UV wavelengths), lake depth, summer sun angle and duration of sunlight may be necessary to explain patterns of macrophyte growth among lakes across a full range of latitudes.     

Bird abundance and species richness on Florida lakes: influence of trophic status,lake morphology,and aquatic macrophytes

Data from 46 Florida lakes were used to examine relationships between bird abundance (numbers and biomass) and species richness, and lake trophic status, lake morphology and aquatic macrophyte abundance. Average annual bird numbers ranged from 7 to 800 birds km^–2 and bird biomass ranged from 1 to 465 kg km^–2. Total species richness ranged from 1 to 30 species per lake. Annual average bird numbers and biomass were positively correlated to lake trophic status as assessed by total phosphorus (r = 0.61), total nitrogen (r = 0.60) and chlorophyll a (r = 0.56) concentrations. Species richness was positively correlated to lake area (r = 0.86) and trophic status (r = 0.64 for total phosphorus concentrations). The percentage of the total annual phosphorus load contributed to 14 Florida lakes by bird populations was low averaging 2.4%. Bird populations using Florida lakes, therefore, do not significantly impact the trophic status of the lakes under natural situations, but lake trophic status is a major factor influencing bird abundance and species richness on lakes. Bird abundance and species richness were not significantly correlated to other lake morphology or aquatic macrophyte parameters after the effects of lake area and trophic status were accounted for using stepwise multiple regression. The lack of significant relations between annual average bird abundance and species richness and macrophyte abundance seems to be related to changes in bird species composition. Bird abundance and species richness remain relatively stable as macrophyte abundance increases, but birds that use open-water habitats (e.g., double-crested cormorant, Phalacrocorax auritus) are replaced by species that use macrophyte communities (e.g., ring-necked duck, Aythya collaris).     

Response of river metabolism to restoration of flow in the Kissimmee River, Florida, U.S.A.

1. The single station diel oxygen curve method was used to determine the response of system metabolism to backfilling of a flood control canal and restoration of flow through the historic river channel of the Kissimmee River, a sub‐tropical, low gradient, blackwater river in central Florida, U.S.A. Gross primary productivity (GPP), community respiration (CR), the ratio of GPP/CR (P/R) and net daily metabolism (NDM) were estimated before and after canal backfilling and restoration of continuous flow through the river channel. 2. Restoration of flow through the river channel significantly increased reaeration rates and mean dissolved oxygen (DO) concentrations from <2 mg L⁻¹ before restoration of flow to 4.70 mg L⁻¹ after flow was restored. 3. Annual GPP and CR rates were 0.43 g O₂ m⁻² day⁻¹ and 1.61 g O₂ m⁻² day⁻¹ respectively, before restoration of flow. After restoration of flow, annual GPP and CR rates increased to 3.95 O₂ m⁻² day⁻¹ and 9.44 g O₂ m⁻² day⁻¹ respectively. 4. The ratio of P/R (mean of monthly values) increased from 0.29 during the prerestoration period to 0.51 after flow was restored, indicating an increase in autotrophic processes in the restored river channel. NDM values became more negative after flow was restored. 5. After flow was restored, metabolism parameters were generally similar to those reported for other blackwater river systems in the southeast U.S.A. Postrestoration DO concentrations met target values derived from free flowing, minimally impacted reference streams.     

Submerged Macrophyte-bed Effects on Water-Column Phosphorus,Chlorophyll <Emphasis Type="Italic">a</Emphasis>, and Bacterial Production

Submerged macrophytes are a major component of freshwater ecosystems, yet their net effect on water column phosphorus (P), algae, and bacterioplankton is not well understood. A 4-month mass-balance study during the summer quantified the net effect of a large (5.5 ha) undisturbed macrophyte bed on these water-column properties. The bed is located in a slow-flowing (0.05–0.1 cm s^–1) channel between two lakes, allowing for the quantification of inputs and outputs. The P budget for the study period showed that, despite considerable short-term variation, the macrophyte bed was a negligible net sink for P (0.06 mg m^–2 day^–1, range from –0.76 to +0.79 mg m^–2 day^–1), demonstrating that loading and uptake processes in the weedbed roughly balance over the summer. Chlorophyll a was disproportionately retained relative to particulate organic carbon (POC), indicating that the algal component of the POC was preferentially trapped. However, the principal contribution of the weedbed to the open water was a consistent positive influence on bacterioplankton production over the summer. Conservative extrapolations based on measured August specific exports (m^–2 day^–1) of P and bacterial production exiting the weedbed applied to five regional lakes varying in lake morphometry and macrophyte cover suggest that even in the most macrophyte dominated of lakes (66% cover), P loading from submerged weedbeds never exceeds 1% day^–1 of standing epilimnetic P levels, whereas subsidization of bacterioplankton production can reach upward of 20% day^–1. The presence of submerged macrophytes therefore differentially modifies algae and bacteria in the water column, while modestly altering P dynamics over the summer.     

Substance and energy flows formed by the emergence of amphibiotic insects across the water–air boundary on the floodplain lakes of the Volga River

Substance flow across the water–air boundary on the floodplain Lake Holodnoe (Saratov oblast) is generally formed by the Culicomorpha (76.1%) and accounts for 0.35 g/m² of the lake area per year. The energy flow amounts to 1.87 kcal/m², and most of it accounts for the second half of summer and autumn. Annual removal of biogenic elements is 0.18 g/m² for carbon, 0.04 g/m² for nitrogen, and 0.004 g/m² for phosphorus. The greatest contribution to flows of substance and energy is brought by large species of chironomids, as well as chaoborids and medium-sized chironomids, which produce several generations within a year and reach high abundance at a larval stage. Other floodplain lakes of the Volga River with similar biotopical features and species composition of amphibiotic insects are characterized by a quantitatively similar level of exchange processes with adjacent land ecosystems across the water–air boundary.     

Primary production of aquatic macrophytes and their epiphytes in two shallow lakes (Peipsi and Võrtsjärv) in Estonia

In shallow lakes with large littoral zones, epiphytes and submerged macrophytes can make an important contribution to the total annual primary production. We investigated the primary production (PP) of phytoplankton, submerged macrophytes, and their epiphytes, from June to August 2005, in two large shallow lakes. The production of pelagic and littoral phytoplankton and of the dominant submerged macrophytes in the littoral zone (Potamogeton perfoliatus in Lake Peipsi and P. perfoliatus and Myriopyllum spicatum in Lake Võrtsjärv) and of their epiphytes was measured using a modified ¹⁴C method. The total PP of the submerged macrophyte area was similar in both lakes: 12.4 g C m^?2 day^?1 in Peipsi and 12.0 g C m^?2 day^?1 in Võrtsjärv. In Peipsi, 84.2% of this production was accounted for by macrophytes, while the shares of phytoplankton and epiphytes were low (15.6 and 0.16%, respectively). In Võrtsjärv, macrophytes contributed 58%, phytoplankton 41.9% and epiphytes 0.1% of the PP in the submerged macrophyte area. Epiphyte production in both lakes was very low in comparison with that of phytoplankton and macrophytes: 0.01, 5.04, and 6.97 g C m^?2 day^?1, respectively, in Võrtsjärv, and 0.02, 1.93, and 10.5 g C m^?2 day^?1, respectively, in Peipsi. The PP of the littoral area contributed 10% of the total summer PP of Lake Peipsi sensu stricto and 35.5% of the total summer PP of Lake Võrtsjärv.     

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.     

Review and Model-Based Analysis of Factors Influencing Soil Carbon Sequestration Beneath Switchgrass (Panicum virgatum)

A multi-compartment model was developed to summarize existing data and predict soil carbon sequestration beneath switchgrass (Panicum virgatum) in the southeastern USA. Soil carbon sequestration is an important part of sustainable switchgrass production for bioenergy because soil organic matter promotes water retention, nutrient supply, and soil properties that minimize erosion. A literature review was undertaken for the purpose of model parameterization. A sensitivity analysis of the model indicated that predictions of soil carbon sequestration were affected most by changes in aboveground biomass production, the ratio of belowground-to-aboveground biomass production, and mean annual temperature. Simulations indicated that the annual rate of soil carbon sequestration approached steady state after a decade of switchgrass growth while predicted mineral soil carbon stocks were still increasing. A model-based experiment was performed to predict rates of soil carbon sequestration at different levels of nitrogen fertilization and initial soil carbon stocks (to a 30-cm depth). At a mean annual temperature of 13°C, the predicted rate of soil carbon sequestration varied from ?28 to 114?g?C?m^?2?year^?1 (after 30?years) and was greater than zero in 11 of 12 simulations that varied initial surface soil carbon stocks from 1 to 5?kg?C?m^?2 and nitrogen fertilization from 0 to 18?g?N?m^?2?year^?1. The modeling indicated that more research is needed on the process of biomass allocation and on nitrogen loss from mature plantations, respectively, to improve our understanding of carbon and nitrogen dynamics in switchgrass agriculture.     

Effects of logging on macroinvertebrate production in a sand-bottomed, low-gradient stream

1. Macroinvertebrate production and macrophyte growth were studied in logged and unlogged sections of a sand‐bottomed, low‐gradient, blackwater stream on the Coastal Plain of Virginia, U.S.A. A section of the catchment had been clear‐cut 3 years prior to sampling. No logging occurred in the upstream area of the catchment, which had experienced almost no land disturbance by humans for over 100 years. 2. A primary difference among the logged and unlogged sections of the stream was in the abundance of macrophytes. The combined biomass of Sparganium americanum and of Chara sp. was over 300‐times greater in the logged than the unlogged section. 3. Annual macroinvertebrate production in the sediment was higher in the unlogged section (41 g dry mass m^–2) than in the logged section (25 g m^–2). 4. Annual macroinvertebrate production on Sparganium was higher in the logged section (10 g m^–2 of plant surface area) than in the unlogged section (6 g m^–2). Annual production associated with Chara, which occurred only in the logged section, was 196 g m^–2 of stream bottom covered by this plant. 5. Whole‐stream annual macroinvertebrate production, calculated by summing habitat‐specific production that was weighted by habitat availability, was greater in the logged section (103 g m^–2) than in the unlogged section (41 g m^–2). Sediments supported 99% of the annual production in the unlogged section, whereas macrophytes supported 76% in the logged section. 6. Much of the additional macroinvertebrate production in the logged section was by collector‐filterers living on macrophytes. Production by collector‐gatherers was also greater in the logged section, whereas production by other functional feeding groups changed little with logging. 7. Although logging along high‐gradient, rocky streams also results in increased macroinvertebrate production, that increase often is stimulated by greater periphyton growth rather than the macrophyte growth observed in this low‐gradient stream.     

Plant community structure determines primary productivity in shallow,eutrophic lakes

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Primary production of organic matter and phototrophic communities in the soda lakes of the Kulunda steppe (Altai krai)

The rates of photosynthesis and dark CO₂ fixation were determined in 12 soda lakes of the Kulunda steppe. Characterization of the phototrophic communities was given, and the cell numbers of anoxygenic phototrophic bacteria (APB) were determined. The photosynthetic production in different lakes was substantially different, constituting from 0.01 to 1.32 g C m⁻² day⁻¹. The main part of carbon dioxide was assimilated in the process of oxygenic photosynthesis. Anoxygenic photosynthesis was recorded only in 5 of the 12 lakes studied. Its values varied between 0.06 and 0.42 g C m⁻² day⁻¹, constituting from 8 to 34% of the total photosynthetic activity. Anoxygenic photosynthesis was revealed in the lakes where the number of APB reached 10⁷–10⁹ CFU cm⁻³. Dark CO₂ fixation constituted 0.01–0.15 g C m⁻² day⁻¹. Positive correlation was observed between the primary production value and water alkalinity. No relationship between productivity and water mineralization was revealed in the 30–200 g l⁻¹ range, whereas an increase in salinity above 200 g l⁻¹ suppressed the photosynthetic activity. The mechanisms of influence of the environmental factors on the rate of photosynthesis are discussed.     

Gastropods on Submersed Macrophytes in Yangtze Lakes: Community Characteristics and Empirical Modelling

Epiphytic gastropods in Yangtze lakes have suffered from large‐scale declines of submersed macrophytes during past decades. To better understand what controls gastropod community, monthly investigations were carried out in four Yangtze lakes during December, 2001–March, 2003. Composed of 23 species belonging to Pulmonata and Prosobranchia, the community is characterized by the constitution of small individuals. The average density and biomass were 417 ± 160 ind/m² and 18.05 ± 7.43 g/m², with maxima around August. Submersed macrophyte biomass is shown to be the key factor affecting species number, density, and biomass of gastropods. Accordingly, a series of annual and seasonal models yielding high predictive powers were generated. Preference analyses demonstrated that pulmonates and prosobranchs with different respiratory organs prefer different macrophyte functional groups. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Primary production and phytoplankton in two small,polyhumic forest lakes in southern Finland

Primary production and phytoplankton in polyhumic lakes showed a very distinct seasonal succession. A vigorous spring maximum produced by Chlamydomonas green algae at the beginning of the growing season and two summer maxima composed mainly of Mallomonas caudata Iwanoff were typical. The annual primary production was ca. 6 g org. C · m^–2 in both lakes. The mean epilimnetic biomass was 1.1 in the first lake and 2.2 g · m^–2 (ww) in the second one. The maximum phytoplankton biomass, 14 g · m^–2, was observed during the vernal peak in May.