Impact of long-term alternations of discharge and spate on the chironomid community in the lowland Widawka River (Central Poland)

Spatial and temporal distribution, abundance and production of macroinvertebrate communities were estimated over two years in a fifth-order section of the Widawka River. Discharge of this river has been increased artificially by coal mine water inputs. Additionally, during the second year, one of the highest discharges of the current 20-year period was recorded. Chironomidae were co-dominant in macrobenthos, both in a straight reach (WIA) and in a meandering site (WIB). More mosaic habitats resulted in higher densities of midges, reaching 6215 ind.m^–2 in year 1 and 1141 ind.m^–2 in year 2 at WIA, while at WIB 896 densities were ind.m^–2 and 257 ind.m^–2, respectively. Flooding affected the distribution and abundance of the chironomid assemblages. Recolonization by psammophilous Polypedilum began after the various microhabitats were buried with sand. Chironomid production was estimated on a species-specific basis for the dominant taxa. In year 1 (mean annual water temperature 10.0° C) chironomid production was 12.4 g dry wt m^–2 yr^–1 1 at WIA and 1.9 g dry wt m^–2 yr^–1 at WIB. These values sharply decreased in year 2 (mean annual water temperature 9.8° C) reaching 1.9 g dry wt m^–2 yr^–1 at WIA and 0.4 g dry wt m^–2 yr^–1 at WIB, as effects of the high spate.     

Ecology of invertebrate predators in a Coastal Plain stream

1. The spatial and temporal abundance patterns, production and feeding habits of invertebrate predators were determined in a sand-bottomed, headwater stream in Virginia, U.S.A. 2. Annual mean density and biomass of predators in debris dams were 3897 individuals m^?2 and 2.5 g dry mass m^?2, respectively, but only 711 individuals m^?2 and 0.2 gm^?2 on the sediment. Predator production was 8.36 gm^?2yr^?1 in debris dams compared to 1.52 gm^?2yr^?1 on the sediment. Annual predator production, weighted by habitat availability, was 1.73gm^?2yr^?1. 3. The predominant taxa in terms of production were the chironomids Thienemannimyia spp, complex, Ablabesmyia parajanta, Zavrelimyia sp., and the odonate Cordulegaster maculata. Chironomidae and Odonata together comprised 77% of the production of the predator guild. 4. Based on gut content analysis and calculations of the trophic basis of production, estimated predator production was supported mostly by Chironomidae (38%), detritus (20%), unidentifiable insects (14%), and Ephemeroptera (11%). Total food ingestion by predators was 9.8 gm^?2yr^?1, 63% of which was detritus and 37% of which was animal material on an areal basis. The predator guild consumed an estimated 94% of primary invertebrate consumer production on the channel surface of the stream.     

Production estimates of the dominant taxa of Chironomidae (Diptera) in the modified,River Widawka and the natural,River Grabia,Central Poland

Production and community composition of selected taxa of Chironomidae were estimated in cross-sections of the lower course of two lowland rivers, the Widawka and the Grabia. At the selected site, the Grabia has not changed its morphometry for many years, whereas the discharge of the Widawka has increased (mainly due to inputs of coal mine water) by 75% in comparison with its hypothetical natural discharge. In the Widawka, the production value, for 76.7% of total Chironomidae abundance, amounted to 12.45 g dry wt m^–2 yr^–1, while in the Grabia it amounted to 11.91 g dry wt m^–2 yr^–1 The annual P : B ranged from 14.5 for large-sized species (Chironomus in the Widawka) to 82.0 for small-sized species (Eukiefferiella in the Grabia). The similar production values estimated for both rivers, despite a three times higher density of Chironomidae in the Grabia, is noteworthy.     

Distribution and production of chironomids (Diptera: Chironomidae) in a shallow, alkaline lake (Neusiedler See, Austria)

From July 1990 to July 1991 the benthic community of the open water zone of Neusiedler See, one of the largest shallow lakes in central Europe, was studied with special reference to the chironomids. Only 16 spp. of chironomids inhabited the sediment of the open water zone. The numerically dominant species were Tanypus punctipennis, Procladius cf. choreus, Microchironomus tener and Cladotanytarsus gr. mancus. Most invertebrates showed a distinct horizontal distribution. Species richness and abundance were highest on muddy and organically rich substrates near the reed belt. Chironomid densities in this area reached 54,000 ind m^–2 and biomass was 2.0 g dw m^–2. The two tanypod species accounted for more than 90% of the standing stock of the macrozoobenthos near the reed belt. The sediment of the open lake and of the eastern part of Neusiedler See was composed of compact clay and sand as a result of the erosion of fine material due to strong waves and currents. Individual densities in these areas were much lower. Production of the numerically dominant species T. punctipennis was estimated using the increment-summation method, whereas production of the remaining species was estimated using an empirically derived multiple regression. Mean annual production of chironomids exceeded 6 g dw m^–2 yr^–1 near the reed belt, but it reached only 0.55 g dw m^–2 yr^–1 in the open lake. These values are rather low compared with other lakes and can be explained by unfavourable sediment conditions due to wave action and by physiological stress due to the water chemistry.     

Net primary production and net ecosystem production of a boreal black spruce wildfire chronosequence

Net primary production (NPP) was measured in seven black spruce (Picea mariana (Mill.) BSP)‐dominated sites comprising a boreal forest chronosequence near Thompson, Man., Canada. The sites burned between 1998 and 1850, and each contained separate well‐ and poorly drained stands. All components of NPP were measured, most for 3 consecutive years. Total NPP was low (50–100 g C m^?2 yr^?1) immediately after fire, highest 12–20 years after fire (332 and 521 g C m^?2 yr^?1 in the dry and wet stands, respectively) but 50% lower than this in the oldest stands. Tree NPP was highest 37 years after fire but 16–39% lower in older stands, and was dominated by deciduous seedlings in the young stands and by black spruce trees (>85%) in the older stands. The chronosequence was unreplicated but these results were consistent with 14 secondary sites sampled across the landscape. Bryophytes comprised a large percentage of aboveground NPP in the poorly drained stands, while belowground NPP was 0–40% of total NPP. Interannual NPP variability was greater in the youngest stands, the poorly drained stands, and for understory and detritus production. Net ecosystem production (NEP), calculated using heterotrophic soil and woody debris respiration data from previous studies in this chronosequence, implied that the youngest stands were moderate C sources (roughly, 100 g C m^?2 yr^?1), the middle‐aged stands relatively strong sinks (100–300 g C m^?2 yr^?1), and the oldest stands about neutral with respect to the atmosphere. The ecosystem approach employed in this study provided realistic estimates of chronosequence NPP and NEP, demonstrated the profound impact of wildfire on forest–atmosphere C exchange, and emphasized the need to account for soil drainage, bryophyte production, and species succession when modeling boreal forest C fluxes.     

Distribution, biomass and production of the freshwater mussel, Hyridella menziesi (Gray), in Lake Taupo, New Zealand

SUMMARY.

• 1 A study of the distribution, biomass and production of the freshwater mussel Hyridella menziesi (Gray) was carried out at six sites in Tapuaeharuru Bay, Lake Taupo, New Zealand.
• 21 H. menziesi is common in the littoral zone, with clean sand and angle of slope being the most important environmental variables measured which are positively associated with mussel density. These variables are related to the accumulation of fine material which can clog the filtering mechanism of mussels. The angle of slope may also influence the movement and supply of food.
• 3 Density (5.6 m^-2), biomass (2.8 g dry weight shell free tissue m^-2) and potential production (0.50 g dry weight shell free tissue m^-2 yr^-1) are high compared to values found for mussels from other oligotrophic lakes.
• 4 The age structure of Hyridella suggests recruitment has declined in recent years. A periodicity in generations is proposed.

     

Spatial heterogeneity of ecosystem carbon fluxes in a broadleaved forest in Northern Germany

Carbon fluxes were investigated in a mature deciduous forest, located in Northern Germany (53°47′N–10°36′E), by means of eddy‐covariance technique, stand survey and models. This forest has been managed following a concept of nature‐oriented forestry since the 1980s. One of the goals of the study was to test whether changed management led to increased carbon sequestration. The forest contains several broadleaved tree species. Depending on wind direction, the fetch‐area of the eddy‐covariance data was dominated by different tree species. Three subplots dominated by Oak, Beech or Alder/Ash could be distinguished from the tower data. In each of these subplots, 30 × 30 m² areas were defined to analyse leaf area index, litterfall and the increase of the wood biomass. Eddy‐covariance analysis showed that the gross primary productivity (GPP′) was higher in the Oak subplot (?1794 g C m^?2 yr^?1) in comparison with the Beech plot and the Alder/Ash plot (?1470 and ?1595 g C m^?2 yr^?1, respectively). The total ecosystem respiration (TER) was the highest in the Alder/Ash‐dominated subplot (1401 g C m^?2 yr^?1) followed by the Oak plot and the Beech plot (1235 and 1174 g C m^?2 yr^?1, respectively). The resulting net ecosystem productivity (NEP) was ?559 g C m^?2 yr^?1 for the Oak‐dominated subplot, ?295 g C m^?2 yr^?1 for the Beech plot and ?193 g C m^?2 yr^?1 for the Alder/Ash plot. From Stand survey and modelling, the net primary productivity was estimated as 1103, 702 and 671 g C m^?2 yr^?1 in the Oak, Beech and Alder/Ash plot, respectively. Also carbon flux with litterfall was the highest in the Oak plot 343 g C m^?2 yr^?1 and lowest in Alder/Ash plot (197 g m^?2 yr^?1) with the Beech plot in between (228 g m^?2 yr^?1). The observations indicate an increase of the proportion of litterfall with increasing GPP′ and a different ability of carbon sequestration of the three stands in medium temporary scale. Only in the Oak stand that comprised the oldest trees and the most structured canopy the carbon sequestration was increased compared with conventionally managed forests.     

Life cycle and production of Chironomidae (Diptera) from Lake Banyoles (NE Spain)

1. The life cycles and annual production of the eight most abundant species of chironomids (Prodadius cf. choreus, Tanypus punctipennis, Chironomus bernensis, Chironomus gr. plumosus, Cladopelma virescens, Microchironomus tencr, Tanytarsus gr. lestagei, and Cladotanytarsus atridorsum) were studied from sublittoral and profundal samples taken monthly in Lake Banyoles during 1987 at five sampling stations (depths ranging from 5 to 20 m). 2. The number of generations per year deduced from instar-frequency data varied from one to four, depending on the species, lake basin and depth. Annual temperature range, dissolved oxygen in the stratified period and presence of sulphide are the key factors that may explain the differences in the number of generations. 3. Production estimates were calculated using the size-frequency (SF) method corrected for the number of generations (SFG), and the increment-summation method (IS) when cohorts could be clearly deduced. 4. Production calculated with the SFG method gave results which were comparable with those of the IS method using smoothed-survivorship curves in the three species for which the use of the IS method was possible (C. virescens, M. tener and C. atridorsum). Using these methods production was estimated to range from 23–70 mg AFDW (ash-free dry weight) m^?2 yr^?1 at 12 m to 74–275 mg AFDW m^?2 yr^?1 in the sublittoral zone of the lake (5-m depth). 5. Calculation of production for the other five species using the size-frequency method with the number of generations (SFG) deduced from monthly instar-frequency data gave values ranging from 12 mg AFDW m^?2 yr^?1 (Chironomus bernensis at 20 m depth) to 3.75 g AFDW m^?2 yr^?1(Prodadius cf. choreus at 12 m). 6. Total chironomid production (with the SFG method) varied from 0.8 to 5 g AFDW m^?2 yr^?1 in the profundal and sublittoral, respectively. At each sampling station two species groups accounted for most of the production: Prodadius cf. choreus and Chironomus spp. Annual production/biomass ratio (P/B) varied from very high values for Prodadius (between 11 and 27, as four generations completed each year) to very low values for Chironomus gr. plumosus (2.20), which completed only one generation each year. The annual production of P. cf. choreus in Lake Banyoles is higher than any reported in the literature due to the completion of four generations and to the high densities of this species.     

CO2 fluxes of transitional bioenergy crops: effect of land conversion during the first year of cultivation

The present study examined the effect of land conversion on carbon (C) fluxes using the eddy covariance technique at seven sites in southwestern Michigan (USA). Four sites had been managed as grasslands under the Conservation Reserve Program of the USDA. Three fields had previously been cultivated in a corn/soybean rotation with corn until 2008. The effects of land use change were studied during 2009 when six of the sites were converted to soybean cultivation, with the seventh site kept as a grassland. In winter, the corn fields were C neutral while the CRP lands were C sources, with average emissions of 15 g C m^?2 month^?1. In April 2009, while the corn fields continued to be a C source to the atmosphere, the CRPs switched to C sinks. In May, herbicide (Glyphosate) was applied to the vegetation before the planting of soybean. After tilling the killed‐grass and planting soybean in mid June, all sites continued to be C sources until the end of June. In July, fields previously planted with corn became C sinks, accumulating 15–50 g C m^?2 month^?1. In contrast, converted CRP sites continued to be net sources of C despite strong growth of soybean. The conversion of CRP to soybean induced net C emissions with net ecosystem exchange (NEE) ranging from 155.7 (±25) to 128.1 (±27) g C m^?2 yr^?1. The annual NEE at the reference site was ?81.6 (±26.5) g C m^?2 yr^?1 while at the sites converted from corn/soybean rotation was remarkably different with two sites being sinks of ?91 (±26) and ?56.0 (±20.7) g C m^?2 yr^?1 whereas one site was a source of 31.0 (±10.2) g C m^?2 yr^?1. This study shows how large C imbalances can be invoked in the first year by conversion of grasslands to biofuel crops.     

A Quantitative Food Web Model for the Macroinvertebrate Community of a Northern German Lowland Stream

Trophic interactions and cycling of organic carbon within the macroinvertebrate community of a Northern German lowland stream were analyzed based on a compartment model. The network model describes the structure of the food web quantifying biomass, production, and consumption of their elements, of the entire system and between trophic levels. System primary production is 153.7 g C m⁻² yr⁻¹ and invertebrate production 53.3 g C m⁻² yr⁻¹. Invertebrate consumption amounts to 702.6 g C m⁻² yr⁻¹. Main flows are identified between trophic level 1 and 2 and are connected with highly productive compartments. ‘Anodonta and Pseudanodonta’ and Dreissena polymorpha show the highest consumption of all groups with 269.9 g C m⁻² yr⁻¹ and 114.1 g C m⁻² yr⁻¹, respectively. System consumption is highest on the import from the upstream lake with 532.5 g C m⁻² yr⁻¹, sediment detritus with 135.5 g C m⁻² yr⁻¹, and primary producers with 25.7 g C m⁻² yr⁻¹. The lowest predation pressure is observed for Bivalvia with an ecotrophic efficiency of <10% and highest for Chironomidae with 91%. Approximately 20% of organic matter entering the detritus pool are recycled to the living groups of the system. Transfer efficiencies between discrete trophic levels are generally low except for transfer of detrital material between level I and II.     

A comparative study of above-ground productivity of dominant U.S. Gulf Coast marsh species

Above-ground productivity of dominant freshwater, brackish, and salt-marsh species from the U.S. Gulf Coast was evaluated using both gas exchange techniques and harvest methods. Both techniques showed significant differences in productivity among the study species which represent major components of their respective communities. Estimates of net aerial primary productivity using the harvest method yielded 3683 g dw (dry weight) m^?2yr^?1 for Spartina alterniflora (tall), 2008 g dw m^?2yr^?1 for S. alterniflora (short), 3677 g dw m^?yr^?1 for S. patens and 1641 g dwm^?yr^?1 for Panicum hemitomon. Carbon balance estimated from gas exchange calculation yielded values approximately equivalent to a biomass accumulation of 6024 g dw m^?2yr^?1 for S. alterniflora (tall), 3047 g dw m^?yr^?1 for S. alterniflora (short), 5702 g dw m^?yr^?1 for S. patens, and 2912 g dm^?yr^?1 for P. hemitomon. The net aerial primary production was estimated to be approximately 61% of total productivity in S. alterniflora (tall-form) and 66%o of total productivity in short-form, 64% in S. patens and 56%) in P. hemitomon. The assimilation data also indicated that Spartina alterniflora and S. patens continue carbon fixation throughout the year while assimilation in Panicum hemitomon is absent due to lack of live leaves during the winter. Various aspects of harvest and gas exchange techniques are discussed.     

Dissolved carbon leaching from soil is a crucial component of the net ecosystem carbon balance

Estimates of carbon leaching losses from different land use systems are few and their contribution to the net ecosystem carbon balance is uncertain. We investigated leaching of dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and dissolved methane (CH₄), at forests, grasslands, and croplands across Europe. Biogenic contributions to DIC were estimated by means of its δ¹³C signature. Leaching of biogenic DIC was 8.3±4.9 g m^?2 yr^?1 for forests, 24.1±7.2 g m^?2 yr^?1 for grasslands, and 14.6±4.8 g m^?2 yr^?1 for croplands. DOC leaching equalled 3.5±1.3 g m^?2 yr^?1 for forests, 5.3±2.0 g m^?2 yr^?1 for grasslands, and 4.1±1.3 g m^?2 yr^?1 for croplands. The average flux of total biogenic carbon across land use systems was 19.4±4.0 g C m^?2 yr^?1. Production of DOC in topsoils was positively related to their C/N ratio and DOC retention in subsoils was inversely related to the ratio of organic carbon to iron plus aluminium (hydr)oxides. Partial pressures of CO₂ in soil air and soil pH determined DIC concentrations and fluxes, but soil solutions were often supersaturated with DIC relative to soil air CO₂. Leaching losses of biogenic carbon (DOC plus biogenic DIC) from grasslands equalled 5–98% (median: 22%) of net ecosystem exchange (NEE) plus carbon inputs with fertilization minus carbon removal with harvest. Carbon leaching increased the net losses from cropland soils by 24–105% (median: 25%). For the majority of forest sites, leaching hardly affected actual net ecosystem carbon balances because of the small solubility of CO₂ in acidic forest soil solutions and large NEE. Leaching of CH₄ proved to be insignificant compared with other fluxes of carbon. Overall, our results show that leaching losses are particularly important for the carbon balance of agricultural systems.     

A comparison of Acroneuria lycorias (Plecoptera) production and growth in northern Michigan hard- and soft-water streams

1. Density, biomass, production and growth of a predaceous stonefly, Acroneuria lycorias, were compared between fourth-order hard- and soft-water streams in Michigan's upper peninsula, U.S.A. 2. Mean densities, estimated from Hess samples, were higher (100 ± 17 individuals m^?2) at the hard-water site than at the soft-water site (40 ± 9 ind. m^?2). Mean dry weight biomass was 4.9 times greater at the hard-water site. 3. Mean annual production, calculated using the size frequency method, was 5.0 times greater at the hard-water site (2.18 ± 0.44 g dry weight m^?2yr^?1) than at the soft-water site (0.43 ± 0.02g dry weight m^?2yr^?1). Annual production/mean biomass ratios were similar between sites. 4. Monthly growth rates of naturally occurring nymphs of paired cohorts were similar in both streams. Individual growth rates were similar for nymphs reared in artificial streams at high and low water hardnesses with unlimited food and space. 5. Stonefly production and growth rates were influenced more by indirect physical, biological, or habitat factors than by streamwater cation concentrations.     

Long-term impact of a stand-replacing fire on ecosystem CO2 exchange of a ponderosa pine forest

Ponderosa pine (Pinus ponderosa) forests of the southwestern United States are a mosaic of stands where undisturbed forests are carbon sinks, and stands recovering from wildfires may be sources of carbon to the atmosphere for decades after the fire. However, the relative magnitude of these sinks and sources has never been directly measured in this region, limiting our understanding of the role of fire in regional and US carbon budgets. We used the eddy covariance technique to measure the CO₂ exchange of two forest sites, one burned by fire in 1996, and an unburned forest. The fire was a high‐intensity stand‐replacing burn that killed all trees. Ten years after the fire, the burned site was still a source of CO₂ to the atmosphere [109±6 (SEM) g C m^?2 yr^?1], whereas the unburned site was a sink (?164±23 g C m^?2 yr^?1). The fire reduced total carbon storage and shifted ecosystem carbon allocation from the forest floor and living biomass to necromass. Annual ecosystem respiration was lower at the burned site (480±5 g C m^?2 yr^?1) than at the unburned site (710±54 g C m^?2 yr^?1), but the difference in gross primary production was even larger (372±13 g C m^?2 yr^?1 at the burned site and 858±37 g C m^?2 yr^?1at the unburned site). Water availability controlled carbon flux in the warm season at both sites, and the burned site was a source of carbon in all months, even during the summer, when wet and warm conditions favored respiration more than photosynthesis. Our study shows that carbon losses following stand‐replacing fires in ponderosa pine forests can persist for decades due to slow recovery of the gross primary production. Because fire exclusion is becoming increasingly difficult in dry western forests, a large US forest carbon sink could shift to a decadal‐scale carbon source.     

Fine root dynamics in a Norway spruce forest (Picea abies (L.) Karst) in eastern Sweden

The annual dynamics of live and dead fine roots for trees and the field layer species and live/dead ratios were investigated at a coniferous fern forest (Picea abies L. Karts) in Sweden. Our methods of estimating the average amount of fine roots involved the periodic sampling of fine roots in sequential cores on four sampling occasions. The highest live/dead ratio was found in the upper part of the humus layer for both tree and field-layer species and decreased with depth. Most tree fine roots on the four sampling occasions were found in the mineral soil horizon, where 86, 81, 85 and 89% of <1 mm and 89, 88, 89 and 92% of <2 mm diameter of the total amounts of live fine roots in the soil profile were found. The mean amounts of live fine roots of tree species for the total soil profile on the four sampling occasions was 317, 150, 139 and 248 g m^?2 for <1 mm and 410, 225, 224 and 351 g m^?2 for <2 mm diameter fine roots. The related amount of dead fine roots was 226, 321, 176 and 299 g m^?2 and 294, 424, 282 and 381 g m^?2, respectively. Average amounts of live and dead fine-roots and live/dead ratios from other Picea abies forest ecosystems were within the range of our estimates. The production of fine roots, <1 and <2 mm in diameter, estimated from the annual increments in live fine roots, was 207 and 303 g m^?2. The related accumulation of dead fine roots was 257 and 345 g m^?2, The turnover rate of tree fine roots <1 mm in diameter in the total soil profile amounted to 0.7 yr^?1 for live and 0.8 yr^?1 for dead fine roots. The related turnover rates for tree fine roots <2 mm were 0.4 yr^?1 and 0.7 yr^?1. Our data, although based on minimum estimates of the annual fluxes of live and dead fine roots, suggests a carbon flow to the forest soil from dead fine-roots even more substantial than from the needle litter fall. Fine-root data from several Picea abies forest ecosystems, suggest high turnover rates of both live and dead tree fine-roots.     

Agricultural peatland restoration: effects of land‐use change on greenhouse gas (CO2 and CH4) fluxes in the Sacramento‐San Joaquin Delta

Agricultural drainage of organic soils has resulted in vast soil subsidence and contributed to increased atmospheric carbon dioxide (CO₂) concentrations. The Sacramento‐San Joaquin Delta in California was drained over a century ago for agriculture and human settlement and has since experienced subsidence rates that are among the highest in the world. It is recognized that drained agriculture in the Delta is unsustainable in the long‐term, and to help reverse subsidence and capture carbon (C) there is an interest in restoring drained agricultural land‐use types to flooded conditions. However, flooding may increase methane (CH₄) emissions. We conducted a full year of simultaneous eddy covariance measurements at two conventional drained agricultural peatlands (a pasture and a corn field) and three flooded land‐use types (a rice paddy and two restored wetlands) to assess the impact of drained to flooded land‐use change on CO₂ and CH₄ fluxes in the Delta. We found that the drained sites were net C and greenhouse gas (GHG) sources, releasing up to 341 g C m^?2 yr^?1 as CO₂ and 11.4 g C m^?2 yr^?1 as CH₄. Conversely, the restored wetlands were net sinks of atmospheric CO₂, sequestering up to 397 g C m^?2 yr^?1. However, they were large sources of CH₄, with emissions ranging from 39 to 53 g C m^?2 yr^?1. In terms of the full GHG budget, the restored wetlands could be either GHG sources or sinks. Although the rice paddy was a small atmospheric CO₂ sink, when considering harvest and CH₄ emissions, it acted as both a C and GHG source. Annual photosynthesis was similar between sites, but flooding at the restored sites inhibited ecosystem respiration, making them net CO₂ sinks. This study suggests that converting drained agricultural peat soils to flooded land‐use types can help reduce or reverse soil subsidence and reduce GHG emissions.     

Spatial distribution and population dynamics of a benthic rotifer, Embata laticeps (Murray) (Rotifera, Bdelloidea) in the bed sediments of a gravel brook

• 1 The spatial and temporal distributions of the most abundant bdelloid rotifer, Embata laticeps (Murray), inhabiting the sediment surface and the hyporheic interstitial of a gravel stream were investigated between October 1991 and October 1992. Three temporal peaks of population density occurred during the year at the sediment surface differing in their riming from the density peaks detected within the bed sediments.
• 2 The depth distributions of E. laticeps in pool and riffle areas differed significantly. Higher abundances were found between 10 and 20 cm depth in the pool and between 20 and 30 cm in the riffle area. In these two sites a significant effect of surface discharge (estimated 1 week before sampling) on rotifer densities was found. Discharge greater than 0.424 m³s^?1 significantly reduced the densities in the riffle, while only at values greater than 1.660m³s^?1 were abundances influenced in the pool area.
• 3 The percentages of egg-bearing females were higher within the bed sediment than in the surface layer, and in the pool area than in the riffle. Thus, overall mean values of population increase were higher in the pool habitat (x?= 0.015 ± SE 0.029 day^?1) than in the riffle and at the sediment surface (x?= 0.004 ± 0.025 and 0.005 ± 0.026 day^?1, respectively). In addition, population growth fluctuated more strongly at the sediment surface than within the hyporheic intersiritial. Comparison of the observed values of population increase with a randomization test, where observed densities were randomly permuted, revealed no significant differences between those observed and values from a random model. Thus, a clear trend in population growth of E. laticeps over time could not be demonstrated in this gravel stream.

     

Lake eutrophication and its implications for organic carbon sequestration in Europe

The eutrophication of lowland lakes in Europe by excess nitrogen (N) and phosphorus (P) is severe because of the long history of land‐cover change and agricultural intensification. The ecological and socio‐economic effects of eutrophication are well understood but its effect on organic carbon (OC) sequestration by lakes and its change overtime has not been determined. Here, we compile data from ~90 culturally impacted European lakes [~60% are eutrophic, Total P (TP) >30 μg P l^?1] and determine the extent to which OC burial rates have increased over the past 100–150 years. The average focussing corrected, OC accumulation rate (C AR_FC) for the period 1950–1990 was ~60 g C m^?2 yr^?1, and for lakes with >100 μg TP l^?1 the average was ~100 g C m^?2 yr^?1. The ratio of post‐1950 to 1900–1950 C AR is low (~1.5) indicating that C accumulation rates have been high throughout the 20th century. Compared to background estimates of OC burial (~5–10 g C m^?2 yr^?1), contemporary rates have increased by at least four to fivefold. The statistical relationship between C AR_FC and TP derived from this study (r² = 0.5) can be used to estimate OC burial at sites lacking estimates of sediment C‐burial. The implications of eutrophication, diagenesis, lake morphometry and sediment focussing as controls of OC burial rates are considered. A conservative interpretation of the results of the this study suggests that lowland European meso‐ to eutrophic lakes with >30 μg TP l^?1 had OC burial rates in excess of 50 g C m^?2 yr^?1 over the past century, indicating that previous estimates of regional lake OC burial have seriously underestimated their contribution to European carbon sequestration. Enhanced OC burial by lakes is one positive side‐effect of the otherwise negative impact of the anthropogenic disruption of nutrient cycles.     

Ecosystem–atmosphere exchange of CH4 and N2O and ecosystem respiration in wetlands in the Sanjiang Plain, Northeastern China

Natural wetlands are critically important to global change because of their role in modulating atmospheric concentrations of CO₂, CH₄, and N₂O. One 4‐year continuous observation was conducted to examine the exchanges of CH₄ and N₂O between three wetland ecosystems and the atmosphere as well as the ecosystem respiration in the Sanjiang Plain in Northeastern China. From 2002 to 2005, the mean annual budgets of CH₄ and N₂O, and ecosystem respiration were 39.40 ± 6.99 g C m^?2 yr^?1, 0.124 ± 0.05 g N m^?2 yr^?1, and 513.55 ± 8.58 g C m^?2 yr^?1 for permanently inundated wetland; 4.36 ± 1.79 g C m^?2 yr^?1, 0.11 ± 0.12 g N m^?2 yr^?1, and 880.50 ± 71.72 g C m^?2 yr^?1 for seasonally inundated wetland; and 0.21 ± 0.1 g C m^?2 yr^?1, 0.28 ± 0.11 g N m^?2 yr^?1, and 1212.83 ± 191.98 g C m^?2 yr^?1 for shrub swamp. The substantial interannual variation of gas fluxes was due to the significant climatic variability which underscores the importance of long‐term continuous observations. The apparent seasonal pattern of gas emissions associated with a significant relationship of gas fluxes to air temperature implied the potential effect of global warming on greenhouse gas emissions from natural wetlands. The budgets of CH₄ and N₂O fluxes and ecosystem respiration were highly variable among three wetland types, which suggest the uncertainties in previous studies in which all kinds of natural wetlands were treated as one or two functional types. New classification of global natural wetlands in more detailed level is highly expected.     

Production due to regeneration by Euclymene oerstedi (Claparède) (Polychaeta: Maldanidae) in the maritime basin of the Rance (Northern Britanny)

The polychaete species Euclymene oerstedi (Claparède) forms one of the dominant populations of the muddy fine sand community in the maritime basin of the Ranee (Northern Britanny). Analyses of regular samples of this species indicated that regeneration was an important process within the population. Of the individuals examined 22% were found to be regenerating the anterior and 41% the posterior regions of the body. The distribution of the incision sites demonstrated a distinct preference for the body sections extending from both extremities to segment 3 or 18 inclusive, with the mean recovery times being 1.5 and 1 month respectively. Biomass production from regeneration within the population is estimated as 2 g·m^?2·yr^?1. From a comparison between the total amounts regenerated by individuals protected by cages and those in the surrounding environment, it is suggested that posterior regeneration is essentially linked to epibenthic predation, while regrowth of the anterior region may also be a result of the activities of infaunal predators. The occurrence of these phenomena may be related to the behaviour of E. oerstedi within its tube.