Gross primary production controls the subsequent winter CO2 exchange in a boreal peatland

In high‐latitude regions, carbon dioxide (CO₂) emissions during the winter represent an important component of the annual ecosystem carbon budget; however, the mechanisms that control the winter CO₂ emissions are currently not well understood. It has been suggested that substrate availability from soil labile carbon pools is a main driver of winter CO₂ emissions. In ecosystems that are dominated by annual herbaceous plants, much of the biomass produced during the summer is likely to contribute to the soil labile carbon pool through litter fall and root senescence in the autumn. Thus, the summer carbon uptake in the ecosystem may have a significant influence on the subsequent winter CO₂ emissions. To test this hypothesis, we conducted a plot‐scale shading experiment in a boreal peatland to reduce the gross primary production (GPP) during the growing season. At the growing season peak, vascular plant biomass in the shaded plots was half that in the control plots. During the subsequent winter, the mean CO₂ emission rates were 21% lower in the shaded plots than in the control plots. In addition, long‐term (2001–2012) eddy covariance data from the same site showed a strong correlation between the GPP (particularly the late summer and autumn GPP) and the subsequent winter net ecosystem CO₂ exchange (NEE). In contrast, abiotic factors during the winter could not explain the interannual variation in the cumulative winter NEE. Our study demonstrates the presence of a cross‐seasonal link between the growing season biotic processes and winter CO₂ emissions, which has important implications for predicting winter CO₂ emission dynamics in response to future climate change.     

Temporal variations in microbenthic metabolism and inorganic nitrogen fluxes in sandy and muddy sediments of a tidally dominated bay in the northern Wadden Sea

Factors controlling seasonal variations in benthic metabolism (O₂ flux) and dissolved inorganic nitrogen (DIN) fluxes were examined during a 12–14 month period at three intertidal Wadden Sea stations. Since the flux measurements were made as small-scale laboratory core incubations, the results are primarily related to the microbenthic community (microalgae, bacteria, micro-, meio- and small macrofauna) and cannot be considered representative of the total benthic community in the Wadden Sea. Furthermore, it has to be emphasized that light intensity during day-time simulations were constant and saturating at all times. Benthic primary production and oxygen uptake appeared to be temperature dependent with a ‘seasonal Q₁₀’ of 1.7–1.8 and 2.7–4.3, respectively. Inundation had no effect on oxygen fluxes as evidenced by similar sediment respiration with and without water cover. A stronger temperature dependence of primary production in muddy than in sandy sediment indicated that the overall control in the latter may be complex due to factors like macrofaunal grazing and nutrient availability. Benthic respiration may not be controlled by temperature alone, as sedimentary organic matter content correlated significantly with both temperature and benthic respiration. Annual gross primary production in high intertidal sandy sediment was 10 and 50% higher than in low intertidal sandy and muddy sediments, respectively. Since annual benthic community respiration was 2 times higher in muddy than sandy sediments, the annual net primary production was about 0 in the former and 17–19 mol C m^?2 yr^?1 in the latter. However, heterotrophic contribution by larger faunal components as well as removal of organic carbon by waves and tidal currents, which are not included here, may balance the budget at the sandy stations. There was no or only weak relationships between (light and dark) DIN exchange and factors like temperature, sedimentary organic content, and oxygen fluxes. Factors related to nutrient fluxes, such as denitrification and nutrient concentration in the overlying water, may have hampered any such relationships. In fact, DIN fluxes at all three stations appeared to be strongly controlled by DIN concentrations in the overlying water. On an annual basis, the sediment appeared to be a net sink for DIN.     

Relevance of local scale factors in winter host-plant selection by the rice pest Tibraca limbativentris (Hemiptera: Pentatomidae)

Tibraca limbativentris is a major stink bug pest in paddies of the Neotropics. In Argentina, its populations overwinter in twelve host-plant species that occur inside rice fields. However, it's unknown if there are local scale variations in the abundance of T. limbativentris. Likewise, the role of host-plant community composition (H_pCC) as a factor involved in the winter host-plant selection by the insects is poorly understood. The aims of this work were (a) to assess variations at local scale on the abundance of T. limbativentris in the context of winter H_pCC and incidence of entomopathogenic fungi (EPFs) and (b) to assess the abundance of T. limbativentris considering the relationship between the height of plants of rice cultivars present in target sites during summer, and the height of the hosts selected by T. limbativentris during winter in grassland adjoining rice plots. Sampling was carried out during summer–winter in different commercial rice fields, to assess winter abundance of T. limbativentris, H_pCC in grasslands adjacent to rice plots and incidence of EPFs. Height measurements of winter hosts and summer rice plants in target plots were taken. Our results show that H_pCC differed at the local scale, with significant differences in stink bug abundance between winter hosts in each site. Also, we found differences in the action of EPFs species recorded on the insects and variations in plant height between host species. A positive correlation was obtained between the height of the different rice cultivars used during spring–summer in target sites and the height of the hosts selected by T. limbativentris near to these plots during winter. This shows that the height of the rice cultivar could be a factor related to the local selection of winter hosts by T. limbativentris. These results serve as a framework for future research, contributing to integrated pest management for target sites.     

Songbirds using crops planted on farmland as cover for game birds

We counted songbirds in crops planted on shooting estates specifically for game management purposes on farmland in Britain and elsewhere in Europe. Winter game crops provide cover and feed areas for pheasants Phasianus colchicus and red-legged partridge Alectoris rufa, while summer game crops are designed to provide brood-rearing cover for these species. In central and southern England, 30 plots of winter game crops, either kale, quinoa or cereal up to 2 ha in area, and 30 adjacent arable-field plots, were surveyed for birds up to six times at monthly intervals during the winter 1997–1998. In the Scottish lowlands, six plots of summer game crops up to 4 ha in area, and adjacent arable fields were surveyed in summer 1999 or 2000. The winter game plots contained more than ten songbirds per hectare in most months, while the adjacent arable-field plots contained less than one. In all three winter game crop types, songbird numbers declined significantly in the second half of the winter while numbers in the arable fields did not. Of the 26 species recorded in the winter game crops, 10 have undergone rapid decline over the last 30 years. Considering these declining species alone, the winter game crops still contained more individuals than the adjacent arable fields throughout the winter. Densities in both the kale and quinoa were higher than in the cereal game crop. The six summer game crops sampled in mid-summer contained on average 2.9 songbirds per hectare, while the adjacent arable fields contained 0.4. Of the 14 species recorded in these summer game crops, eight have undergone rapid or moderate declines over the last 30 years. Although winter and summer game crops are planted in relatively small plots and hence concentrate birds, these plots are widely planted and our results suggest that they benefit birds on farmland.     

Dynamics of submersed aquatic vegetation on shallow soft bottoms in the Baltic Sea

Abstract. Persistence and colonization of submersed aquatic plant species were studied in permanent plots (20 cm × 20 cm) at three shallow sites adjacent to Askö island, in the northern Baltic Sea. The study started in 1991 at two of the sites, in 1992 at a third site and continued until 1997. Two major weather‐induced disturbances occurred during the study: a long, stormy period during a mild winter and a cold winter with extreme low water levels. The stormy period caused a large loss of species from plots (95 ± 5% SE) at the most wave‐exposed site, resulting in a low species number per plot (0.8 ± 0.2) the following summer. During the three following years the mean species number increased to 3.6 ± 0.2. The cold winter caused high species turnover and increased species number per plot at the two most wave‐exposed sites. The species turnover at the sheltered site was highest in the two years with low water level in May, possibly due to increased waterfowl herbivory. Annuals, loosely anchored and highly reproductive species had significantly higher plot colonization rates and lower persistence than perennials, well‐anchored species and species with none or low reproduction. The extent of lateral growth had no significant effect on colonization or persistence. Although these disturbances have a large effect on the dynamics, species mobility was also high in other years. Relative to other, similar, studies in terrestrial vegetation mean persistence in plots was remarkably low and mean mobility and species turnover rates were very high.     

Identification, habitats and seasonal occurrence of juvenile whiting (Sillaginidae) in Moreton Bay, Queensland

Three sympatric whiting species-(Sillaginidae)—sand whiting, Sillago ciliata , golden-lined whiting, Sillago analis , and trumpeter whiting, Sillago maculata , are common in Moreton Bay, Queensland. Their identification, habitats and seasonal occurrence of juveniles are studied. A key to identification of these species is provided. Juveniles of the three species inhabit shallow shores including lower sections of creeks and rivers; but 5. ciliata prefer sandy substrates with less than 1 m depth and S. analis favour muddy-sand substrates also with less than 1 m depth, while 5. maculata juveniles stay in muddy-sand to muddy substrates at 1–3 m depth. Sillago analis juveniles appear at the waters' edge from October to May each year.     

海南东寨港红树林滩涂大型底栖动物多样性的初步研究

记录到海南东寨港红树林滩涂大型底栖动物68种,其中软体动物39种,占记录到物种数的57.4%;甲壳动物19种,占记录到物种数的27.9%。冬季优势种是珠带拟蟹手螺(Cerithidea cingulata )、古氏滩栖螺(Batillaria cumingi )和环肋樱蛤(Cyclotellina remies );夏季优势种是珠带拟蟹手螺、环肋樱蛤和红肉河蓝蛤(Potamocorbula rubromuscula )。大型底栖动物的生物量夏季平均为133.0 g/m²,冬季平均为63.0 g/m²; 栖息密度夏季平均为106.4 个/m²,冬季平均为103.5 个/m²。以密度为计量单位的物种多样性指数夏季为1.841,冬季为0.380,均匀度指数夏季为0.514,冬季为0.112;以生物量为计量单位的物种多样性指数夏季为1.994,冬季为1.751, 均匀度指数夏季为0.556,冬季为0.520。大型底栖动物的生物量、栖息密度、物种多样性指数和均匀度指数大都有季节变化及底质差异,基本趋势是夏季明显高于冬季,沙泥底的滩涂高于泥底质的滩涂。     

Effects of grazing on the abundance and diversity of annual plants in Chihuahuan desert scrub habitat

We assess the impact of release from cattle grazing on the abundance and diversity of both winter and summer annual plant communities at an upper Chihuahuan Desert scrub site in south-eastern Arizona. In contrast to previous studies, we found that removal of herbivores (cattle) had little impact on ephemeral plant assemblages at our site. The total number of summer annual individuals per quadrat did not differ significantly, but there were significantly more winter annual plants on ungrazed quadrats. The number of species per quadrat, however, did not differ significantly between sites exposed to, or protected from, grazing in either season. Of 79 annual species recorded (34 in winter, 45 in summer), only 2 species, 1 in each season, responded significantly to the removal of cattle: Stephanomeria exigua and Polygala tweedyi were more abundant on ungrazed plots. Three additional species, Eriastrum diffusum and Cryptantha micrantha in winter, and Mollugo cerviana (summer), approached statistical significance. Differences in the effect of cattle grazing on annual plants between our results and those at other sites in the arid southwest most likely reflect differences in the speed of response by annuals in different areas. Comparisons of this with other studies underscores recent calls for studies at broader spatial and greater temporal scales.     

Long-term trends of subtidal macrobenthos in North Inlet,South Carolina

Analyses of seasonal and yearly trends in subtidal macrobenthic samples collected bi-weekly at a sandy site (1981–1984) and a muddy site (1981–1985) in North Inlet, South Carolina, show large fluctations in abundance and high variability between replicate samples. Sampling variability at the sandy site, thought to be influenced more by physical disturbance than by biotic interactions, was especially high and prevented the interpretation of seasonal trends in abundance. Increased replication at the muddy site in 1985 revealed abundance patterns of winter/spring maxima and summer minima. Despite short-term (seasonal) and high year-to-year variability, the fauna at both sites were characterized by long-term stability in abundance. That is, although abundances varied considerably between seasons or years only 9 of 22 taxa analyzed showed a directional change in abundance. These 9 taxa increased in abundance over the four (sandy site) or five (muddy site) years of examination while the other 13 taxa fluctuated about a mean value. The taxonomic composition of benthic fauna at both sites was also very stable through time, with the sandy site always numerically dominated, in order, by polychaetes, amphipods, and bivalves and the muddy site by polychaetes, oligochaetes, and bivalves.     

Germination and anchorage ofEnteromorpha spp. in sediments of the Wadden Sea

Large quantities of filamentous green algae (Enteromorpha spp.) have regularly occurred on muddy and sandy tidal flats in Königshafen, on the island of Sylt (North Sea), since 1979 — covering the sediments in thick mats during the summer months. While spores ofEnteromorpha were encountered in both mud and sand, germling formation was restricted to sand. However, mud snails (Hydrobia ulvae Pennant) were overgrown with smallEnteromorpha filaments in both habitats, about 50% of them at a muddy site and 20% at a sandy one. Filaments, several cm in length and still adhering to the snails, became tangled into clusters. At the sandy site, with abundantArenicola marina L., these clusters slid into the feeding funnels of lugworm burrows; the importance of this secondary anchorage is demonstrated by a field experiment. We suggest that the primary and secondary attachment ofEnteromorpha filaments provided by benthic fauna is an essential step in the development of green algal mats on sedimentary tidal flats.     

Sediment destabilizing and stabilizing bio-engineers on tidal flats: cascading effects of experimental exclusion

Bioturbating lugworms (Arenicola marina) were excluded from 400 m2 plots of intertidal sand which initiated sequences of direct and indirect changes in the structure of the benthic community. The sessile, tube-building species Polydora cornuta and Lanice conchilega took advantage of the absence of lugworms and settled preferentially on lugworm exclusion plots. The protruding tubes provided attachment for an ephemeral development of algal tufts (Berkeleya colonies and Enteromorpha thalli) which in turn enhanced settlement of the juvenile drifting clams Mya arenaria and Macoma balthica. This causal chain of enhanced bivalve settlement in the presence of above-ground structures, like animal tubes and algae, on lugworm exclusion plots occurred in 2 years at different tidal zones with different tube builders, algae and juvenile clams. A significant response of L. conchilega in a year with relatively low lugworm abundances at the entire site suggests that not only the actual absence of large bioturbators was responsible for the establishment of tube-dwelling species, but also a cumulative change of the sediment in exclusion plots since the onset of the experiment. While the sediment on lugworm plots remained permeable, fine particles and organic matter accumulated at exclusion plots. It is suggested that these differences in sediment characteristics were the product of divergent benthic engineering by sediment destabilizing lugworms on control plots and sediment stabilizing species on exclusion plots. Cumulative changes of the sedimentary habitat and cascading effects in the benthic community may explain the persistence of patches that are dominated by either sediment stabilizing or destabilizing species in the assemblage mosaic of intertidal sediments.     

Variable Importance of Macrofaunal Functional Biodiversity for Biogeochemical Cycling in Temperate Coastal Sediments

Coastal marine systems are currently subject to a variety of anthropogenic and climate-change-induced pressures. An important challenge is to predict how marine sediment communities and benthic biogeochemical cycling will be affected by these ongoing changes. To this end, it is of paramount importance to first better understand the natural variability in coastal benthic biogeochemical cycling and how this is influenced by local environmental conditions and faunal biodiversity. Here, we studied sedimentary biogeochemical cycling at ten coastal stations in the Southern North Sea on a monthly basis from February to October 2011. We explored the spatio-temporal variability in oxygen consumption, dissolved inorganic nitrogen and alkalinity fluxes, and estimated rates of nitrification and denitrification from a mass budget. In a next step, we statistically modeled their relation with environmental variables and structural and functional macrobenthic community characteristics. Our results show that the cohesive, muddy sediments were poor in functional macrobenthic diversity and displayed intermediate oxygen consumption rates, but the highest ammonium effluxes. These muddy sites also showed an elevated alkalinity release from the sediment, which can be explained by the elevated rate of anaerobic processes taking place. Fine sandy sediments were rich in functional macrobenthic diversity and had the maximum oxygen consumption and estimated denitrification rates. Permeable sediments were also poor in macrobenthic functional diversity and showed the lowest oxygen consumption rates and only small fluxes of ammonium and alkalinity. Macrobenthic functional biodiversity as estimated from bioturbation potential appeared a better variable than macrobenthic density in explaining oxygen consumption, ammonium and alkalinity fluxes, and estimated denitrification. However, this importance of functional biodiversity was manifested particularly in fine sandy sediments, to a lesser account in permeable sediments, but not in muddy sediments. The strong relationship between macrobenthic functional biodiversity and biogeochemical cycling in fine sandy sediments implies that a future loss of macrobenthic functional diversity will have important repercussions for benthic ecosystem functioning.     

Impacts of bottom and suspended cultures of mussels <Emphasis Type="Italic">Mytilus</Emphasis> spp. on the surrounding sedimentary environment and macrobenthic biodiversity

The aim of this study was to quantify the effect of bottom and suspended mussel cultures, cultured in different physical environments, on the sedimentary environmental conditions and thereby the biodiversity structure of the associated macrofaunal community. We compared two bottom cultures (Limfjorden: microtidal, wind-driven; Oosterschelde: macrotidal) and one suspended culture (Ria de Vigo in an upwelling coastal region). The sedimentary environmental conditions (mud fraction, POC, PON, phosphorus content, chl a breakdown products) were significantly elevated underneath and surrounding bottom and suspended cultures compared to culture-free sediments that were nearby and hydrodynamically similar. The relative change in environmental conditions was more pronounced in the Oosterschelde compared to Limfjorden, most likely due to differences in hydrodynamic forcing and characteristics of the mussel bed. The effect of the suspended cultures in Ria de Vigo on the surrounding sediments was influenced by local topographic and hydrodynamic conditions. The impact of mussels on the benthic community due to biodeposition was clearly seen in the community structure. The species composition changed from species which are typically present in sandy environments to more small opportunistic species, which are typically present in organically enriched sediments. The impact of bottom cultures on the benthic community due to changes in the habitat under the presence of mussels was positive, especially in the Oosterschelde where an increase in the number of epibenthic species was seen. The influence of bottom cultures on the sedimentary environment and on the macrobenthic community seems to be very local. Within the mussel site in Limfjorden, differences were detected between sites where none or almost no mussels were present with sites where mussels were very abundant.     

不同类型底栖动物对表面流人工湿地系统水质净化的影响

研究以表面流人工湿地为研究对象,探讨不同类型底栖动物在夏季和冬季对人工湿地系统氮磷去除效果的影响,并通过人工湿地系统运行前后不同介质氮磷含量变化及不同介质微生物丰度变化进行水质净化机理分析。结果表明,夏季添加河蚌和添加田螺均能增强人工湿地系统NO3-N和TN去除效果,其中添加河蚌使得系统NO3-N和TN平均去除率较对照组分别提升37.19%和24.32%,添加田螺使得系统NO3-N和TN平均去除率较对照组分别提升22.98%和12.46%。冬季添加摇蚊幼虫使得表面流人工湿地NO3-N、TN和TP平均去除率分别在37.8%、54.0%和94.8%,与对照组相比分别增加了29.51%、15.16%和37.62%,添加河蚌和田螺受底栖动物半冬眠活动和代谢降低影响没有显著水质提升效果。这表明通过添加底栖动物可以增强表面流人工湿地运行效果,选取适合的底栖动物种类组合可能在全年提升人工湿地水质净化效果。机理研究结果表明,底栖动物通过增强底泥和基质中微生物硝化反硝化作用、植物氮吸收和基质氮吸附等促进人工湿地氮去除,通过增强下层基质磷吸附沉淀和植物磷吸收提升水质磷去除。研究结果将为底栖动物在人工湿地的...     

Above-ground herbivory causes rapid and sustained changes in mycorrhizal colonization of grasses

Arbuscular mycorrhizal fungi (AMF) play a vital role in ecosystem functioning. In most grasslands, herbivory by both vertebrate and invertebrate herbivores is common and thus in order to assess herbivore effects on multitrophic-level interactions both should be considered. This study investigated the effects of grazing by rabbit and insect herbivores on root-colonization of grasses by AMF in two lowland grasslands in southern England, UK. A long-term exclosure site was used to provide a temporal assessment in order to elucidate whether any short-term responses to herbivore removal were sustained. Root samples from three grass species at each site were analysed in terms of total mycorrhizal colonization and proportional colonization by individual mycorrhizal structures. Colonization levels were up to 1.6 times greater under moderate levels of rabbit grazing (with summer maxima of 25% and winter minima of 11%) than in intensely grazed swards or fenced plots at both sites. The change was fast (within 8 weeks), consistent throughout the sampled field plots, and temporally sustainable over a 19-year period. There was no significant effect of insect herbivory on total colonization but proportional colonization by different AM structures was affected on some sample dates where vertebrate herbivores had been removed, indicating a slight effect on fungal structure allocation. The results suggest that the type of herbivore and perhaps more importantly the intensity of grazing are key determinants of below-ground effects upon mycorrhizal–host plant symbiosis. The data suggest that the extent of mycorrhizal colonization within grass host plants is strongly influenced by C assimilation and allocation.     

Effects of snow cover on the benthic fauna in a glacier-fed stream

1. Alpine streams above the tree line are covered by snow for 6–9 months a year. However, winter dynamics in these streams are poorly known. The annual patterns of macroinvertebrate assemblages were studied in a glacial stream in the Austrian Alps, providing information on conditions under the snow.
2. Snow cover influenced water temperature, the content of benthic organic matter and insect development. Taxa richness and abundance of macroinvertebrates did not show a pronounced seasonal pattern. The duration of the autumn period with stable stream beds was important in determining the abundance and composition of the winter fauna.
3. There were significant differences in species composition between summer and winter. Two potential strategies in larval survival were evident: adaptation to the extreme abiotic conditions in summer (e.g. Diamesa spp.) or avoidance of these conditions and development during winter (e.g. Ephemeroptera and Plecoptera).
4. A comparison of a stream reach with continuous snow cover and a stream reach that remained open throughout winter showed that conditions under snow are suboptimal. At the open stream site, with higher water temperatures and greater food supply (benthic organic matter content), abundance and taxa richness was higher and larval growth was faster. Several taxa were found exclusively at this site.
5. Winter conditions did not provide an entirely homogeneous environment, abiotic conditions changed rapidly, especially at the onset of snowfall and at snowmelt. Continuous monitoring is necessary to recognize spatial and temporal heterogeneity in winter environments and the fauna of alpine streams.     

Seasonal structuring of a benthic community exposed to regular hypoxic events

The Western Trough of the Lough Hyne Marine Reserve in southern Ireland features annual episodes of profound hypoxia beneath an oxy-thermocline that develops each summer. Previous work had indicated that the hypoxia caused mass mortality of the sessile benthic fauna, but information about the winter fauna, or about mobile species was lacking. Here we report on a combined remote-operated vehicle, SCUBA and baited trap study, backed by regular oxygen-temperature-depth monitoring of the Trough. Our results show that there is community of resident benthic and mobile species during the oxic winter months that disappears in the summer. Mobile fish and crustaceans avoid the hypoxic areas of the Trough, though the prawn Palaemon serratus will venture into the hypoxic zone to scavenge on baits. At the oxy-thermocline itself, burrows of benthic fauna remain evident in summer, but their inhabitants show much reduced activity or death. Regular hypoxic episodes clearly structure the benthic community of the Trough, but this is not a simple matter of alternating mass mortality and recolonization; mobile species are clearly capable of avoiding the hypoxic zone in summer, but benefit from its productivity in winter and spring.     

Seasonal variability of meio- and macrobenthic standing stocks and diversity in an Arctic fjord (Adventfjorden, Spitsbergen)

Strong environmental seasonality is a basic feature of the Arctic system, still there are few published records of the seasonal variability of the Arctic marine biota. This study examined the year-round seasonal changes of soft bottom macro- and meiobenthic standing stocks and diversity on a station located in an Arctic fjord (Adventfjorden, Spitsbergen). The seasonality observed in benthic biota was related to the pelagic processes, primarily the seasonal fluxes of organic and inorganic particles. The highest abundance, biomass and richness of benthic fauna occurred in the spring after the phytoplankton bloom. During the summer, when a high load of glacial mineral material was transported to the fiord, the number of both meio- and macrobenthic individuals decreased remarkably. The strong inorganic sedimentation in summer was accompanied by a decline in macrobenthic species richness, but had no effects on evenness. Redundancy analysis (RDA) pointed to granulometric composition of sediments (depended on mineral sedimentation) and organic fluxes as factors best related to meio- and macrobenthic taxonomic composition, but no clear seasonal trend could be observed on the nMDS plots based on meiobenthic higher taxa or macrobenthic species abundances in the samples. This study addresses the possible effects of changes in the winter ice cover on the fjordic benthic systems because it was performed in a year with no ice cover on the fjord.     

Die benthische Copepodenfauna in einem ufernahen Verschmutzungsgebiet der westlichen Ostsee

Zusammenfassung 1. Der Jahreszyklus und die Verteilung der benthischen Copepodenfauna eines ufernahen Flachwassergebietes in der südlichen Kieler Bucht wurden untersucht.2. Die Populationsdichte zeigt im Juli und November jeweils ein deutliches Maximum. Im Laufe eines Jahres wechseln die dominierenden Arten mehrmals; die Artenvielfalt ist am höchsten im Sommer, am niedrigsten in Winter.3. Die meisten Harpacticoiden des Untersuchungsgebietes sind gegenüber organischer Verschmutzung indifferent. Nur wenige Arten kommen als Indikatoren in Betracht.

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The benthic copepod fauna of an organically polluted sandy area in the Western Baltic Sea

The annual cycle and distribution of the benthic copepod fauna of a shallow inshore area in the South of Kiel Bay (Baltic Sea) were investigated. The species composition found is not typical for medium fine sand, but resembles that characteristic of a mixture of coarser sand, phytal and even soft bottoms. The mean population density was about 10 times smaller than in offshore stations (Scheibel, 1973). Obvious maxima were observed in July and November, and attributable to different species. The dominant harpacticoid species change several times during the year. Species diversity was highest in summer, lowest in winter, when only two species,Paraleptastacus holsaticus andScottopsyllus minor, were dominant. Many species show breeding maxima in spring and summer, a few in autum (e. g.Ameira parvula) or winter (e. g.Scottopsyllus minor). The effect of sewage pollution manifests itself significantly only in the immediate vicinity of the outfall: Species diversity decreases;Scottopsyllus minor, Nitocra spec., N. typica, Paraleptastacus holsaticus, Parastenhelia spinosa, as well asTachidius discipes are rather frequent in this zone. The potential value of these species as indicators of water quality is discussed. Most of the harpacticoids in the investigated area are rather tolerant to domestic waste products.

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Beitrag des Sonderforschungsbereichs 95, Nr. 89.     

Long‐term enhanced winter soil frost alters growing season CO2 fluxes through its impact on vegetation development in a boreal peatland

At high latitudes, winter climate change alters snow cover and, consequently, may cause a sustained change in soil frost dynamics. Altered winter soil conditions could influence the ecosystem exchange of carbon dioxide (CO₂) and, in turn, provide feedbacks to ongoing climate change. To investigate the mechanisms that modify the peatland CO₂ exchange in response to altered winter soil frost, we conducted a snow exclusion experiment to enhance winter soil frost and to evaluate its short‐term (1–3 years) and long‐term (11 years) effects on CO₂ fluxes during subsequent growing seasons in a boreal peatland. In the first 3 years after initiating the treatment, no significant effects were observed on either gross primary production (GPP) or ecosystem respiration (ER). However, after 11 years, the temperature sensitivity of ER was reduced in the treatment plots relative to the control, resulting in an overall lower ER in the former. Furthermore, early growing season GPP was also lower in the treatment plots than in the controls during periods with photosynthetic photon flux density (PPFD) ≥800 μmol m^?2 s^?1, corresponding to lower sedge leaf biomass in the treatment plots during the same period. During the peak growing season, a higher GPP was observed in the treatment plots under the low light condition (i.e. PPFD 400 μmol m^?2 s^?1) compared to the control. As Sphagnum moss maximizes photosynthesis at low light levels, this GPP difference between the plots may have been due to greater moss photosynthesis, as indicated by greater moss biomass production, in the treatment plots relative to the controls. Our study highlights the different responses to enhanced winter soil frost among plant functional types which regulate CO₂ fluxes, suggesting that winter climate change could considerably alter the growing season CO₂ exchange in boreal peatlands through its effect on vegetation development.