Particulate organic matter inputs to a glacial stream ecosystem in the Swiss Alps

1. Traps for litterfall and for lateral transport of organic matter were sampled over a 1-year period along longitudinal and lateral transects in a glacial stream system (Val Roseg, Swiss Alps), which is characterized by single-thread reaches and a large subalpine floodplain.
2. Allochthonous inputs to the glacier stream were low close to the glacier terminus but increased as woody riparian vegetation and forests develop. Annual inputs varied from 0.4 g ash free dry matter (AFDM) m^–2 year^–1 (direct input) and 0.7 g AFDM m^–2 year^–1 (lateral input) in the proglacial area to 23.0 g AFDM m^–2 year^–1 (direct input) and 10.7 g AFDM m^–2 year^–1 (lateral input) in the lowest reach with adjacent subalpine forests.
3. Direct inputs of organic matter decreased exponentially from forests at the floodplain edge to the floodplain centre, while lateral inputs of organic matter correlated linearly with distance to trees. Direct litterfall dominated litter input close to the forest, while lateral transport was the major pathway for channels more than 20 m away from the forest.
4. A conceptual framework is developed illustrating the influence of terrestrial vegetation and fluvial morphology on organic matter input along the continuum of glacial streams.     

Sources of organic carbon supporting the food web of an arid zone floodplain river

SUMMARY 1. Many Australian inland rivers are characterised by vast floodplains with a network of anastomosing channels that interconnect only during unpredictable flooding. For much of the time, however, rivers are reduced to a string of disconnected and highly turbid waterholes. Given these features, we predicted that aquatic primary production would be light-limited and the riverine food web would be dependent on terrestrial carbon from floodplain exchanges and direct riparian inputs.
2. To test these predictions, we measured rates of benthic primary production and respiration and sampled primary sources of organic carbon and consumers for stable isotope analysis in several river waterholes at four locations in the Cooper Creek system in central Australia.
3. A conspicuous band of filamentous algae was observed along the shallow littoral zone of the larger waterholes. Despite the high turbidity, benthic gross primary production in this narrow zone was very high (1.7–3.6 g C m⁻² day⁻¹); about two orders of magnitude greater than that measured in the main channel.
4. Stable carbon isotope analysis confirmed that the band of algae was the major source of energy for aquatic consumers, ultimately supporting large populations of crustaceans and fish. Variation in the stable carbon and nitrogen isotope signatures of consumers suggested that zooplankton was the other likely major source.
5. Existing ecosystem models of large rivers often emphasise the importance of longitudinal or lateral inputs of terrestrial organic matter as a source of organic carbon for aquatic consumers. Our data suggest that, despite the presence of large amounts of terrestrial carbon, there was no evidence of it being a significant contributor to the aquatic food web in this floodplain river system.     

Colonization and production of macroinvertebrates on artificial substrata: upstream–downstream responses to a leaf litter exclusion manipulation

1. Macroinvertebrate colonization dynamics were examined on artificial substrata in a stream with terrestrial litter inputs excluded, downstream of the litter-exclusion treatment, and in a reference stream. 2. Short-term examination of the rates of organic matter accrual and invertebrate colonization demonstrated significantly lower accumulation of leaf detritus and invertebrates in the litter-excluded reach and a short distance downstream of that reach. 3. All major fractions of organic matter and invertebrates declined on artificial substrata during the 3-year litter exclusion. Further, secondary production on artificial substrata in the litter-excluded reach decreased from 6.2 to 1.5 g AFDM m⁻² year⁻¹ from pretreatment to the third year of litter exclusion, respectively. 4. Downstream, fine particulate organic matter on artificial substrata decreased during litter exclusion, and there was a significant reduction in colonization of collector-filterers. Total secondary production downstream of the litter exclusion declined >70%, demonstrating that downstream colonization dynamics are linked to upstream detritus inputs and processing by stream invertebrates.     

Changes in stream benthic organic matter following watershed disturbance

Benthic organic matter was collected quarterly from streams draining a 9-yr-old clearcut, an 18-yr-old "old-field", a 25-yr-old successional forest, and two reference watersheds at Coweeta Hydrologic Laboratory in the Appalachian Mountains of North Carolina. USA. Samples were separated into large benthic organic matter (LBOM >1 mm) and fine benthic organic matter (FBOM <1 mm). An additional survey of large (>5 em diam.) and small (1–5 cm diam.) wood was conducted. Standing stocks of LBOM ranged from 124 to 235 g AFDM m⁻² (ash tree dry mass) and were significantly higher in streams draining reference watersheds and the successional forest than in either the recent clearcut or old-field. Reference sites exhibited LBOM peaks in late autumn and spring. No seasonal patterns were observed in disturbed streams. Standing stocks of FBOM averaged 113 to 387 g AFDM m⁻², and the stream draining the successional forest had significantly higher FBOM levels than the other sites. In reference streams, FBOM abundance peaked in spring. In disturbed streams, FBOM standing stocks were highest in summer or late autumn. Standing stocks of large wood ranged from 0 to 3956 g AFDM m⁻² and were significantly higher in the reference streams than in streams draining the old-field or successional forest. Small wood averaged 11 to 342 g AFDM m⁻² and was significantly lower in the stream draining the old-field than at the other sites. Comparisons of organic matter inputs with standing stocks indicated that disturbed streams at Coweeta receive less material and process it faster than reference streams. Disturbed streams also appear to be less retentive than reference streams and exhibit a gradual decline in FBOM during the winter when large, long-duration storms combined with low particle generation rates deplete accumulated FBOM.     

Metabolism of a sub-tropical low gradient black water river

SUMMARY. 1. Single-station diel oxygen curves were used to monitor the oxygen metabolism of the Ogeechee River, a sixth-order blackwater river in the Coastal Plain of southeastern U.S.A., over a period of 4 years. Ecosystem production ( P) and respiration (R) were estimated, and P/R ratios calculated to determine the extent of autotrophy characteristic of this type of river. The potential error in oxygen metabolism caused by photo-oxidation of dissolved organic carbon (DOC) in the water was measured and found to be minor.
2. Rates of ecosystem primary production measured were intermediate compared to other rivers, ranging from 0.49 to 13.99g O₂m⁻² day ^−1.Primary production rates were highest during the summer when water levels were low. Regression analysis indicated that water depth and light absorption by DOM were significant predictors of primary production in this river. Incident light intensities were not significantly correlated with production rate.
3. Respiration rates were unusually high, varying between 3.70 and 11.5 g O₂ m⁻² day ^{− 1}. System respiration also varied seasonally, but less than primary production. Rates were slightly higher in spring and summer.
4. With one exception, P/R ratios were considerably lower than l throughout the study period, indicating that the Ogeechee River was highly heterotrophic. PIR ratios ranged from 0.09 to 1.3, and averaged 0.25.
5. A carbon budget calculated for this river showed floodplain inputs were 7 times autochthonous production. Organic carbon turnover length was 690 km, considerably longer than has been reported for lower-order rivers.     

The seasonal biomass and productivity of the submerged macrophytes in a polluted Wisconsin stream

SUMMARY 1. We measured biomass and light/dark bottle productivity of macrophytes in a Wisconsin stream throughout one growing season. Except for a brief period in early spring when a Cladophora glomerata -filamentous algal community was dominant, Potamogeton pectinatus was the dominant macrophyte species in Badfish Creek.
2. Maximum community biomass was 710 g DW m⁻², with a maximum above ground biomass of 620 g DW m⁻² and a maximum below ground biomass of 120 g DW m⁻². Annual productivity was estimated at 1435 g DW m⁻² year⁻¹, with a calculated P/B of 2.01.
3. In situ net production averaged 2.83g C g AFDW⁻¹ h⁻¹ Net positive carbon gain by the P. pectinatus community occurred when water temperatures were above 15°C, and daylength at least 12h. This is correlated to the onset of tuber germination in spring, and the point of maximal biomass decline in autumn.     

Inputs and transformation of allochthonous particulate organic matter in a headwater stream

Inputs and outputs of allochthonous particulate organic matter were measured during 15 months in the upper part of a beech forest headwater stream. Inputs were estimated to 716 g m⁻² yr⁻¹, and leaves made up 71%. Outputs were estimated to 535 g m⁻² yr⁻¹ and consisted mainly of FPOM (92%). Therefore, a significant transformation of CPOM into FPOM took place. The mean FPOM concentration varied between 0.6 and 3.4 mg 1⁻¹, but the daily variations greatly surpassed the seasonal variations. As discharge was rather constant, the observed variations were due to external disturbances, especially precipitation.
A tentative scheme for leaf processing is established from the present data and previous studies in the area, indicating that a significant part takes place in the MPOM pool and that microbial and invertebrate processing make up about 50% each of total intra-system processing.     

Spatial and temporal patterns of microcrustacean assemblage structure and secondary production in a wetland ecosystem

1. In contrast to extensive studies of zooplankton in lakes, the role of microcrustaceans in wetlands is not well studied. In this study, spatial and temporal patterns of microcrustacean assemblage structure and secondary production were quantified over a 2-year period in a southeastern U.S.A. wetland.
2. Thirty-two species, including 19 cladocerans, 10 copepods and three ostracods, generated different temporal patterns of density and production between vegetated ( Nymphaea ) and non-vegetated (open-water) zones reflecting species-specific differences in life histories.
3. Summer assemblages were dominated by small, planktonic filter-feeders, typified by high annual production/biomass ( P / B ) and daily production. In contrast, winter assemblages were dominated by larger, epibenthic detritivores with low P / B and high biomass. Seasonal shifts in the relative importance of planktonic species in the warmer months to benthic and epiphytic species in the cooler months suggest that energy flow pathways through microcrustaceans may vary seasonally.
4. Total annual production was higher during both years in the Nymphaea zone (13.0 g and 13.6 g DM m⁻² year⁻¹) than the open-water (8.2 and 6.3 g DM m⁻² year⁻¹), and was similar between years for the entire wetland pond (12.3 and 12.2 g DM m⁻² year⁻¹).
5. Although wetland ecosystems have been the subject of considerable ecological research in the past 20 years, our study is one of the few to demonstrate a highly diverse and relatively productive microcrustacean assemblage. Such comprehensive production studies can be used to quantify the ecological importance of microcrustaceans in freshwater wetland ecosystems.     

Life cycle, growth, mortality and production of Ephemerella major Klapalek (Ephemeroptera) in a trout stream in Belgium

SUMMARY. 1. The life cycle of Ephemerella major Klapalek in a chalk trout stream in Belgium took 1 year. Emergence was highly synchronized with a flight period from mid-May to mid-June. Tiny nymphs occurred from June to late August.
2. The mean instantaneous growth rate was high in autumn (3.6% wet wt day⁻¹), very low from November to February (0.8% wet wt day⁻¹) and high until emergence (2.3% wet wt day⁻¹); short day length seemed to be the major factor reducing growth rate during winter.
3. Mortality was close to zero during winter and 1.4—1.7% day⁻¹during other seasons. Total mortality from egg to adult was 99.6%.
4. The annual production was about 9g wet wt m⁻² year⁻¹ and the annual P/ ratio was 7.5. There was good agreement between the production values estimated by four methods. Production rate was highest in May (13 mg wet wt m⁻² day⁻¹) and zero in February.     

Ammonium and phosphate regenerationby the zooplankton of an Amazon floodplain lake

SUMMARY. 1. Regeneration of ammonium and phosphate by macro-zooplankton (Cladocera. adult copepods. and copepodites) was measured in Lake Calado. an Amazon floodplain lake, Macrozooplanktonabundances ranged between 1×10⁴ and 3×10⁵ individuals m⁻².
2. Phosphate regeneration ranged from 0.2 to 1.3 μ mol PO₄ m⁻² b⁻¹at station 1. located 2 km from the Solimoes River, and from 1.6 to8.3 μ mol PO₄ m⁻² h ⁻¹ at station 3, located 7 km from the SolimoesRiver. Ammonium regeneration at stations 1 and 3 ranged from 1.7 to11.9 and from 13.4 to 77.2 μ mol NH₄ m⁻² h⁻¹. respectively.
3. Zooplankton regenerated ammonium and phosphate at similarrates during rising and falling waier. Regeneration by macrozooplankton was low compared to other tropical lakes and compared to microbesand microzooplankton in Lake Calado.     

Paleolimnology and trends in the phosphorus and iron budgets of an old man-made lake, Barton Broad, Norfolk

SUMMARY. Barton Broad, Norfolk is a shallow, eutrophic lake. During the last 30 years submerged macrophytes have declined and phytoplankton numbers have increased. This change is traced through the stratigraphy of a 60-cm mud core. Diatom frustule counts of 1-cm sections of the core showed that an epiphyte-dominated diatom community was replaced by a planktonic community. From chemical analysis and radio-isotope dating of the core, sedimentation rates and past phosphorus and iron loadings are estimated. Sedimentation rates were between 1.2 mm and 3.1 mm year⁻¹ during the early part of the core but doubled in the 1950s to 5 mm year⁻¹, doubled again in the 1960s and have increased to 12 mm year⁻¹ in the 1970s. Retention of phosphorus in the sediment increased from 0.5 g m⁻² year⁻¹ to 18–21 g m⁻² year⁻¹ in two steps. A similar trend is shown for iron. The diatom species composition and chemistry of the core sections are correlated with increased nutrient loading and the decline of macrophytes. Contemporary phosphorus and iron budgets are calculated from inflow–outflow data and balanced using sediment retentions estimated from the core data. It is believed a large proportion of phosphorus and iron enters the Broad by movement of sediment along the river bed. A reduction of 25% of the 1975 phosphorus loadings would probably permit re-establishment of some macrophytes. The present chemistry and algal communities of Barton Broad and the River Ant are described.     

Life-history and production of the amphipod Gammarus pulex in a Dorset chalk stream

SUMMARY. The seasonal variation in population density of Gammarus pulex was studied in a Dorset chalk stream. The numbers increased markedly in June and July and reached a maximum of c. 10000m⁻² in September whilst the most rapid decline in density occurred in October-November and reached a minimum of 820 m⁻² in February. The animals occurred in greater densities in habitats containing Ranunculus or Callitriche than in those devoid of vegetation. The population structure was determined monthly and was split into juveniles (length <4mm), immature males, immature females, mature males and ovigerous females. The percentage of juveniles (39–76) was always the highest of any of the categories. Ovigerous females were found at all times of the year. The sex ratio varied with the time of year both for immatures and matures, although there was approximately a 1:1 ratio for the mature individuals. Seasonal variation in biomass showed a maximum of 7.l g dry wt m⁻² in September and a minimum of 1.4 g dry wt m⁻² in March. Production was calculated by two methods giving values of 12.9 g dry wt m⁻² year⁻¹ and 12.8 g dry wt m⁻² year⁻¹.     

Seasonal biomass and diversity of estuarine fishes coupled with tropical habitat heterogeneity (southern Gulf of Mexico)

Nekton dynamics were studied in two contrasting habitats in Terminos Lagoon, Mexico. Over an annual cycle, a total of 83 fish species used the high-salinity fringing mangrove/ Thalassia testudinum habitat and biomass ranged from 0.43 to 3.43 g m⁻². The highest biomass occurred during the dry season when aquatic primary production was highest (i.e. 333 g C m⁻² year⁻¹). By contrast, 65 species used the freshwater and low-salinity riverine mangrove/Crassostrea virginica/Vallisneria habitat and biomass ranged from 0.57 to 1.48 g m⁻² with the highest biomass occurring during the wet season, the time of highest primary production in this habitat (i.e. 219 g C m⁻² year⁻¹). The high- and low-salinity habitats serve as ecological bridges between freshwater areas and the sea. Fish life histories have evolved to utilize these habitats for spawning, feeding and nursery grounds in a manner which generally leads to the use of different habitats during the periods of highest primary productivity.     

Nutrient dynamics of the highly productive C4 macrophyte Echinochloa polystachya on the Amazon floodplain

1. Echinochloa polystachya forms extensive monotypic stands on the lower levels of the Amazon floodplains. During its annual growth cycle c. 100t (dry mass) ha^–1 of biomass is formed as the floodplain is being submerged (December–September) and a phase of death and decomposition occurs when the water has retreated (October–November). This study examines the mineral nutrient dynamics of this plant and its potential significance to the nutrient status of the floodplain.
2. Echinochloa polystachya was sampled monthly from a study site in the central Amazon. N, P and K contents for different plant organs were determined and net uptake calculated from concurrent measurements of dry matter production and turnover.
3. Leaf N, P and K contents were c. 20, 1·7 and 19gkg^–1, values typical of nutrient-replete stands of C₄ plants. Stem concentrations were c. 12% of those of the leaves. Net N and P uptake followed the rise in the river level, whilst K appeared independent of water level.
4. The vegetation accumulated 377, 51 and 1136kgha^–2 of N, P and K, respectively, during the growth phase. Over a possible 5000km² of these stands in the Várzea, this represents a massive sequestration of nutrients in the flood phase and a high release during the following low-water period. It is suggested that the E. polystachya stands could have a role in maintaining the nutrient status of the Amazon floodplain.     

Litterfall in two Canadian deciduous woods: quality, quantity and timing

Litterfall in two deciduous woods in Ontario, Canada, was caught in bag traps and by new screen traps for two years. The beech-maple wood produced 818 g m⁻² (8.2 t ha⁻¹) and the poplar wood produced only 450 g m⁻² (4.5 t ha⁻¹). Of these totals, canopy leaves alone made up 386 g m⁻² for the beech-maple wood and 270 g m⁻² for the poplar wood leaving 47% and 34%, espectively, for other litter components. Data are presented for seven types of litter in addition to canopy leaves.
Redistribution of litter on the ground causes spatial heterogeneity of substrate and of habitats for decomposers and hence of decomposition.
Temporal distributions of various types of litterfall differ between the two woods in relation to their vegetation structure. The diversity of litter types combines with extensive temporal distribution of litterfall in the beech-maple woodland to give that wood the potential for nearly continuous decomposition activity. In contrast, the poplar woodland has low diversity of litter and short duration of litterfall.     

Biomass and production estimates of a fish community in a small South African estuary

The fish community of the small (17·5 ha) intermittently open East Kleinemonde estuary was sampled between 1994 and 1997 to estimate population size, standing stock, growth and productivity. The estuarine-spawning species were numerically more abundant ( n c . 750 000) but due to their small size contributed only 11·7% to the total biomass. The total annual productivity of all fishes in the estuary ( n c . 890 000), with a standing stock of 28·44 g m ⁻², was calculated at 55·89 g m⁻² year⁻¹. The small sparid Rhabdosargus holubi with a production estimate of 41·35 g m⁻² year⁻¹ accounted for <74% of the total fish production in this estuary.     

Population dynamics and production of Jesogammarus annandalei, an endemic amphipod, in Lake Biwa, Japan

SUMMARY 1. Population dynamics and production of Jesogammarus annandalei , an endemic amphipod in Lake Biwa, were examined from April 1997 to June 1998. The life cycle of this species was 1 year with the new generation beginning in early autumn. They preferred low temperature (<12 °C) and their spatial distribution varied seasonally and accordingly.
2. In deep water, the abundance of J. annandalei ranged from 200 to 63 000 m⁻² and decreased towards summer and the biomass (0.01∼3.6 g C m⁻²) was on average comparable that of zooplankton. The density was much higher than that recorded by a study conducted 35 years ago.
3. Individual growth rate of this amphipod was high in winter and spring but decreased in summer. Annual production of J. annandalei (6.2 g C m⁻² year⁻¹) was only 2% of primary production but was at the higher end of the range reported for amphipods in oligo- and mesotrophic lakes.
4. These results are consistent with the view that Lake Biwa is becoming more eutrophic, with a consequent decrease in the abundance of predatory fish in the profundal zone.     

Simulated chronic nitrogen deposition increases carbon storage in Northern Temperate forests

High levels of atmospheric nitrogen (N) deposition in Europe and North America were maintained throughout the 1990s, and global N deposition is expected to increase by a factor of 2.5 over the next century. Available soil N limits primary production in many terrestrial ecosystems, and some computer simulation models have predicted that increasing atmospheric N deposition may result in greater terrestrial carbon (C) storage in woody biomass. However, empirical evidence demonstrating widespread increases in woody biomass C storage due to atmospheric N deposition is uncommon. Increased C storage in soil organic matter due to chronic N inputs has rarely been reported and is often not considered in computer simulation models of N deposition effects. Since 1994, we have experimentally simulated chronic N deposition by adding 3 g N m⁻² yr⁻¹ to four different northern hardwood forests, which span a 500 km geographic gradient in Michigan. Each year we measured tree growth. In 2004, we also examined soil C content to a depth of 70 cm. When we compared the control treatment with the NO₃⁻ deposition treatment after a decade of experimentation, ecosystem C storage had significantly increased in both woody biomass (500 g C m⁻²) and surface soil (0–10 cm) organic matter (690 g C m⁻²). The increase in surface soil C storage was apparently driven by altered rates of organic matter decomposition, rather than an increase in detrital inputs to soil. Our results, for study locations stretching across hundreds of kilometers, support the hypothesis that chronic N deposition may increase C storage in northern forests, potentially contributing to a sink for anthropogenic CO₂ in the northern Hemisphere.     

Very high secondary production at a lake outlet

SUMMARY. 1. Larvae and pupae of Simulium noelleri Fried, coated the concrete of parts of an artificial lake outlet in southern England.
2. In the first two (of three) summer generations, development was synchronous and this allowed the calculation of their secondary production by the instantaneous growth method. The production of the two summer generations was, respectively, 229.1 g C m⁻² (7.4 g C m⁻²day⁻¹) and 185.5 g C m⁻² (8.8 g C m⁻² day⁻¹) The contribution of the third summer generation, and the overwintering generation, to annual production would be less than that of the first two summer generations. Nevertheless, annual production will have exceeded 500 g C m⁻² at this site.
3. Larvae are suspension feeders and they captured the rich supply of particulate and dissolved organic material which passed over them after export from the lake. As food is brought to the larvae they only require space for attachment and can thus build up very high population densities (which exceeded 1 × 10⁶ m⁻² on some occasions during the summer). The high population densities result in a high biomass and hence in the high levels of production.     

Continuous growth of the giant grass Zizaniopsis bonariensis in subtropical wetlands

1.  Zizaniopsis bonariensis (giant grass) is an emergent macrophyte species endemic to subtropical wetlands in Brazil, Argentina, Paraguay and Uruguay. In this study, we show the effects of its continuous clonal reproduction and its 'phalanx' growth strategy in the Taim Wetland (southern Brazil).
2. The continuous clonal growth of this 3-m high grass gave rise to the emergence of 11.7 new shoots m⁻² per month and a high total above ground production (2870 g dry weight m⁻² year⁻¹). The biomass of the new shoots emerging every month formed a wave of growth, moderated by only weak seasonal variation.
3. We show its phalanx growth strategy by analysing the variations in population density and shoot height within a transect through the stand canopy. The inverse relation between density and height from the border to the interior indicates self-regulation of biomass.
4. The plants modified their environment, enhancing resistance to drought within the stand and thus facilitating their dominance. This positive feedback suggests that the dominance of the plant might constitute an alternative state in subtropical wetlands.