Long-term phosphorus and nitrogen removal processes and preferential flow paths in Northern constructed peatlands

Four treatment peatlands were studied in Northern Finland in order to determine peat P, Al and Fe concentration distributions and to find removal parameters for nutrient modelling. The sites had been under loading for 10–16 years. About 20 peat samples for analyses of oxalate-extractable and total P, Al and Fe were collected from the depth 0–10 cm in each peatland. The peat P concentration ranged from 0.097 mg g^?1 to 14 mg g^?1 being 1.7 mg g^?1on average. P accumulated in preferential flow path areas. Although P concentrations were locally high, DSSP (the index of potential soil P release from peat to water) was very low in all studied peatlands, indicating that peat was not saturated by phosphorus. The results indicate that Al-based precipitation chemicals increase substantially P retention capacity of peatland and maintain a stabile P reduction in spite of varying P loads. The results also show long-term phosphorus accumulation in peatlands polishing municipal wastewater from activated sludge treatment. The regression analyses showed that k-value for N removal depends on N loading and hydraulic loading. The first-order area model together with regression analysis of the rate constant result in a good agreement between observed and calculated nitrogen concentration. The NH₄-N loading to the peatland should be below 0.10 mg m² d^?1 in order to achieve a high reduction of 70%.     

Comparative ecology of vascular plant,bryophyte and testate amoeba communities in four Sphagnum peatlands along an altitudinal gradient in Switzerland

Monitoring tools are needed to assess changes in peatland biotic communities and ecosystem functions in response to on-going climate and other environmental changes. Although the responses of soil organisms and plants to ecological gradients and perturbations do not always correlate, peatland monitoring is mainly based on vegetation surveys. Testate amoebae, a group of protists, are important contributors to carbon and nitrogen cycling in organic soils and are useful bioindicators in peatland ecology and paleoecology. There is however little comparative data on the value of testate amoebae, vascular plants and bryophytes as bioindicators of micro-environmental gradients in peatlands.We compared the relationships of testate amoebae, bryophytes, and vascular plants with soil temperature, water table depth, micro-habitats and the carbon and nitrogen content of Sphagnum mosses in four peatlands along a 1300 m altitudinal gradient in Switzerland. We used the full diversity of vascular plants and bryophyte but only a selection of ten easily identifiable testate amoeba morpho-taxa (i.e. species or species-complexes).Indirect and direct gradient ordinations, multiple factor analysis (MFA) and transfer function models for inferring water table depth showed that a selection of ten testate amoeba taxa are more powerful (% variance explained in RDA) and accurate (discrimination among habitats) indicators of local conditions (micro-habitat type, water table depth and Sphagnum C/N ratio) than the vegetation (vascular plants and bryophytes either individually or combined and considering the full diversity).Our study showed that a limited list of ten easily identifiable testate amoeba taxa have higher bioindication value than the full bryophytes and vascular plants. Furthermore, testate amoebae can be analyzed on samples collected at any season (accessibility allowing and if precise sampling sites are well marked) – a clear advantage for biomonitoring and can be used to infer past changes from the peat record at the same taxonomic resolution. This simple approach could therefore be very useful for biomonitoring of peatlands.     

Effect of temperature and precipitation on the annual diameter growth of Scots pine on drained peatlands and adjacent mineral soil sites in Finland

The climate conditions of the current and previous growing seasons have been shown to influence growth of coniferous trees in mineral soils sites. These dependencies may be different in peatlands where growth is generally more dependent on variations in soil water conditions. In the Nordic and Baltic countries, millions of hectares of peatlands and wetlands have been drained in order to enhance forest production. These drainage networks do not guarantee stable soil water conditions for the whole stand rotation. It is thus likely that precipitation in particular may have a different influence on annual growth in peatland to that in mineral soil sites. We studied the effect of precipitation and temperature on the inter-annual diameter growth of Scots pine (Pinus sylvestris L.) in Finland in drained peatland forests. The diameter growth data were limited to periods when growth response to drainage had levelled out. For comparison, growth data were also collected from adjacent mineral soil trees. The climate variables were monthly mean temperature and precipitation in a given location estimated from observations at the nearest weather stations by means of spatial smoothing. We used mixed linear models in describing the annual diameter growth of individual trees as a function of tree size and stand properties and expressed the residual variation as a function of climate parameters. The peatland and mineral soil growth variations showed different dependence on climate parameters. Peatland trees within 5 m of a ditch showed different climate responses compared to those located further away. Precipitation in July was negatively correlated with the diameter growth of peatland trees but there was no correlation with temperature. Growth of trees in mineral soils was positively correlated with March and April mean temperatures and May and June mean precipitation. The residual growth indices showed largely similar patterns in peatlands and mineral soil sites.     

Organic matter accumulation in a restored peatland: Evaluating restoration success

Recent advances in peatland restoration techniques have succeeded in establishing Sphagnum moss on the remnant cutover peat surface following peat extraction; however, evaluating restoration success remains a key issue. We argue that a Sphagnum-dominated peatland can only be considered functionally ‘restored’ once organic matter accumulation has achieved a thickness where the mean water table position in a drought year does not extend into the underlying formerly cutover peat surface. Here we monitor the spatio-temporal development of organic matter accumulation in a new peat layer for the first 8 years following the restoration of a Québec peatland and couple a simple acrotelm carbon accumulation model and ecohydrological model to assess peatland restoration success.We determined that organic matter accumulation increased from 2.3 ± 1.7 cm 4 years post-restoration to 13.6 ± 6.5 cm 8 years post-restoration. For comparison, at an adjacent non-restored section of the peatland organic matter accumulation was significantly lower (p < 0.001 for all years), with mean thicknesses of 0.2 ± 0.6 and 0.8 ± 1.2 cm for 24 and 28 years post-extraction, respectively. Given the mean summer water deficit at the site (?64 mm), our ecohydrological modeling results suggest that a 19-cm-thick moss layer would be required to offset the water table decrease induced by the summer water deficit. Given the current rate of organic matter accumulation, net primary productivity and the new peat layer decomposition rates determined using litter bags, we estimate it will take 17 years post-restoration to accumulate a 19-cm moss layer. Consequently, we argue that successful peatland restoration may be achieved in the medium-term and that our simple modeling approach can be useful in assessing the long-term impact of restoration on atmospheric carbon dioxide sequestration.     

Sphagnum re-introduction in degraded peatlands: The effects of aggregation,species identity and water table

In European peatlands which have been drained and cut-over in the past, re-vegetation often stagnates after the return of a species-poor Sphagnum community. Re-introduction of currently absent species may be a useful tool to restore a typical, and more diverse, Sphagnum vegetation and may ultimately improve the functioning of peatland ecosystems, regarding atmospheric carbon sequestration. Yet, the factors controlling the success of re-introduction are unclear. In Ireland and Estonia, we transplanted small and large aggregates of three Sphagnum species into existing vegetation. We recorded changes in cover over a 3-year period, at two water levels (?5 and ?20 cm).Performance of transplanted aggregates of Sphagnum was highly species specific. Hummock species profited at low water tables, whereas hollow species profited at high water tables. But our results indicate that performance and establishment of species was also promoted by increased aggregate size. This mechanism (positive self-association) has earlier been seen in other ecosystems, but our results are the first to show this mechanism in peatlands. Our results do not agree with present management, which is aimed at retaining water on the surface of peat remnants in order to restore a functional and diverse Sphagnum community. More than the water table, aggregate size of the reintroduced species is crucial for species performance, and ultimately for successful peatland restoration.     

Seasonal changes in Sphagnum peatland testate amoeba communities along a hydrological gradient

Testate amoebae are an abundant and functionally important group of protists in peatlands, but little is known about the seasonal patterns of their communities. We investigated the relationships between testate amoeba diversity and community structure and water table depth and light conditions (shading vs. insolation) in a Sphagnum peatland in Northern Poland (Linje mire) in spring and summer 2010. We monitored the water table at five sites across the peatland and collected Sphagnum samples in lawn and hummock micro-sites around each piezometer, in spring (3 May) and mid-summer (6 August) 2010. Water table differed significantly between micro-sites and seasons (Kruskal–Wallis test, p = 0.001). The community structure of testate amoebae differed significantly between spring and summer in both hummock and lawn micro-sites. We recorded a small, but significant drop in Shannon diversity, between spring and summer (1.76 vs. 1.72). Strongest correlations were found between testate amoeba communities and water table lowering and light conditions. The relative abundance of mixotrophic species Hyalosphenia papilio, Archerella flavum and of Euglypha ciliata was higher in the summer.     

A Habitat Suitability Index (HSI) for the Western Prairie Fringed Orchid (Platanthera praeclara) on the Sheyenne National Grassland,North Dakota,USA

The Western Prairie Fringed Orchid (Platanthera praeclara) is a threatened species found on the Sheyenne National Grassland (SNG) in southeast North Dakota, USA. The SNG is subject to management for multiple uses including biodiversity conservation, livestock grazing and recreation. Therefore, there is a need for the development of indicators of suitable orchid habitat. The orchids are continuously monitored, but understanding of the relationship between landscape properties and orchid locations is limited. In this study data that characterize topography, moisture, and groundwater were used to construct indicators of landscape suitability and an overall Habitat Suitability Index (HSI) for the orchid. A LiDAR-derived DEM and groundwater well observations were used to develop landscape indicators. The Topographic Wetness Index (TWI: a measure of moisture on the landscape), the Topographic Position Index (TPI: a measure of position on the landscape), and the distance to groundwater (DTG: a measure of the distance from the land surface to the groundwater surface) provided the best set of indicators of orchid habitat. Point-based field observations of orchid occurrence were used to develop Orchid Suitability Metrics (OSMs) that identified the range of indicator values most strongly associated with orchids. These OSMs were used to define year by year suitability zones for each indicator that were combined to create the HSI. Comparison of orchid locations with groundwater elevations showed that orchids occurred on average 0.98 ± 0.39 (2σ) m above the water table. TWI and TPI demonstrated that orchids occur near flow paths and areas of lower elevation than their surroundings. HSI values of 0.67 and above were associated with 89.8% of all orchid observations used in the analysis. The landscape indicators, OSM concept and HSI could be generally applied to monitoring and conservation management of orchid habitat and the concept may be applicable to other valued species with similar niche properties.     

Leaf growth and population dynamics of intertidal Zostera japonica on the western coast of Korea

Leaf production and population dynamics of Zostera japonica were examined at three elevations of an intertidal transect in Seungbongdo Island on the western coast of Korea. Morphometrics, shoot density, biomass, leaf production, reproductive effort and environmental factors were monitored from October 2001 to October 2002. Z. japonica grew well in the lower intertidal zone from 0.2 to 1.0 m above mean chart datum. The upper station (St. 1) exhibited a finer sediment grain size and richer organic content than the middle (St. 2) and lower stations (St. 3). The size of shoots and leaves was significantly greater at St. 1 than at St. 3, whereas the rhizome internodes were longer at St. 3. Despite differences in morphological characteristics among three stations, seagrass biomass and shoot density were not significantly different among study sites. Shoot density, biomass, morphometrics and leaf productivity exhibited clear seasonal variations, which varied along with seasonal changes of water and air temperature. Leaf productivity measured by the clip and reharvest method was highest in September (4.3 g DW m⁻² d⁻¹) and lowest in February (0.2 g DW m⁻² d⁻¹). Reproductive shoots rapidly increased to maximum density along with the high water temperature in July to September. In the intertidal zone, Z. japonica exhibited faster vegetative growth on muddy sand than on sand, probably due to the difference in nutrient supply. The seasonal changes of water and air temperature were considered to play an important role in the seasonal leaf growth of Z. japonica.     

Nutrient uptake and release in ponds under long-term and short-term lotus (Nelumbo nucifera) cultivation: Influence of compost application

Uptake and release of nutrients from ponds used for lotus cultivation were measured in ponds under short-term (1 yr) cultivation with compost application (pond I) and under long-term (20 yr) cultivation without compost application (pond II). Total inflow loads of TN (irrigation water, rainfall and compost) during lotus cultivation period in ponds I and II were 72.3 and 34.3 kg ha^?1 182 day^?1, respectively. TN removal rates in ponds I and II were 77.3 and 49.8% of total inflow load, respectively. Major removal mechanisms of TN were attributed to microbial processes and uptake by lotus. The total outflow loads (infiltration and runoff) of TN during the lotus cultivation period were 13.9 kg ha^?1 182 day^?1 (19.2% of total inflow TN load) for pond I, and 11.3 kg ha^?1 182 day^?1 (32.9% of total inflow TN load) for pond II. For TP the total inflow loads (irrigation water, rainfall and compost) during lotus cultivation in ponds I and II were 80.8 and 1.9 kg ha^?1 182 day^?1, respectively. TP removal rates in ponds I and II were 84.9 and ?274.1% of total input, respectively. Phosphorus removal was attributed to lotus uptake and soil adsorption. The total outflow loads (infiltration and runoff) of TP during lotus cultivation period were 10.1 kg ha^?1 182 day^?1 (12.5% of total inflow TP load) for pond I, and 6.6 kg ha^?1 182 day^?1 (355.6% of total inflow TP load) for pond II. TN and TP in runoff from pond I (with compost) was higher than that in pond II (without compost), showing that TN and TP in runoff were strongly influenced by compost addition. Therefore, in order to satisfy established water-quality standards, the amount of compost used in lotus cultivation should be evaluated.     

Effects of climatic fluctuations and land-use changes on the hydrology of temperate fluviogenous mire

The upper part of the Narew River valley (NE Poland) belongs to the last extensive undrained, non-reclaimed valley wetlands in Central Europe. However, in recent decades, the fluviogenous mire has experienced a significant change in water resources which may be linked to climatic fluctuations and changes in vegetation. In NE Poland during the last three decades, a clear trend toward milder and drier climate has been observed that has resulted in lower river discharge. Reduction in surface water inflow into the mire, diminished duration and degree of flooding, decrease in summer rainfall and increase in evapotranspiration have led to the substantial fall of the groundwater table in the valley and a decrease in volume of water stored in organic sediments. A comparison of water table measurements made in the 1970s with contemporary observations showed that presently, summer minimum groundwater levels are as much as 60 cm lower than in the past. A significant drop of water table elevation might be additionally attributed to increased ET caused by cessation in agricultural use of the mire and expansion of Phragmites. Between the 1970s and 2002, the total amount of water lost by ET increased by 42%, whereas ET_o rose by 7% only. We found that patches of common reed rushes were hot spots for ET across the Narew wetland landscape. The evaluation of the effectiveness of restoration measures aimed at restoration of the water conditions in the Narew mire led us to the conclusion that raising the river water level by use of in-stream structures may be not adequate to make up the summer moisture deficit and ensure a sufficiently high groundwater level in the adjacent wetland. The restoration goal may be partly achieved by large vegetation manipulation in the form of mowing or grazing. Vegetation management could reduce ET by 170 mm m⁻² year⁻¹, potentially minimizing the extent and the duration of groundwater drawdowns.     

ELM evaluation model of regional groundwater quality based on the crow search algorithm

According to the multi-parameter evaluation of groundwater quality, an evaluation model of groundwater quality based on the improved Extreme Learning Machine (ELM) was proposed to resolve fuzziness of the water quality evaluation and incompatibility of water parameters. A training sample set and testing sample set were randomly generated according to the classification standards of groundwater quality, then Crow Search Algorithm (CSA) was used to optimize the input weights and thresholds of hidden-layer neurons of the ELM; thus, the CSA-ELM evaluation model of groundwater quality was constructed based on optimization of the ELM by the CSA. Base on the training sample set and testing sample set, the CSA-ELM model was tested. The test results indicate that the evaluating precision and generalization ability of the CSA-ELM model reach a high level and can be used for comprehensive evaluations of groundwater quality. The Jiansanjiang Administration in Heilongjiang Province, China, was used as an example; the groundwater quality of 15 farms in this region was evaluated based on the CSA-ELM model. The groundwater quality in this region was generally good, and the groundwater quality appeared to have spatial distribution characteristics. Compared with the Nemerow Index Method (NIM), the CSA-ELM evaluation model of groundwater quality is more reasonable and can be used for the comprehensive evaluation of groundwater quality. The stability of the NIM, ELM model, back propagation (BP) model and CSA-ELM model was analyzed using the theory of serial number summation and Spearman's correlation coefficient. The stability of the NIM and BP model in groundwater quality evaluation was poor, while the stability of the ELM model and CSA-ELM model was relatively superior. The ranked results of stability are CSA-ELM model > ELM model > NIM > BP model. The reliability of the NIM, ELM model, BP model and CSA-ELM model was analyzed using the theory of distinction degree. The reliability of the NIM was not good, although its distinction degree was large; the distinction degrees of the ELM model, BP model and CSA-ELM model were close to each other. The ranked results of reliability are CSA-ELM model > ELM model > BP model. The CSA-ELM model can provide a stable and reliable evaluation method for the evaluation of related fields and thus has important practical applicability.     

Leaf growth and population dynamics of intertidal Zostera japonica on the western coast of Korea

Leaf production and population dynamics of Zostera japonica were examined at three elevations of an intertidal transect in Seungbongdo Island on the western coast of Korea. Morphometrics, shoot density, biomass, leaf production, reproductive effort and environmental factors were monitored from October 2001 to October 2002. Z. japonica grew well in the lower intertidal zone from 0.2 to 1.0 m above mean chart datum. The upper station (St. 1) exhibited a finer sediment grain size and richer organic content than the middle (St. 2) and lower stations (St. 3). The size of shoots and leaves was significantly greater at St. 1 than at St. 3, whereas the rhizome internodes were longer at St. 3. Despite differences in morphological characteristics among three stations, seagrass biomass and shoot density were not significantly different among study sites. Shoot density, biomass, morphometrics and leaf productivity exhibited clear seasonal variations, which varied along with seasonal changes of water and air temperature. Leaf productivity measured by the clip and reharvest method was highest in September (4.3 g DW m⁻² d⁻¹) and lowest in February (0.2 g DW m⁻² d⁻¹). Reproductive shoots rapidly increased to maximum density along with the high water temperature in July to September. In the intertidal zone, Z. japonica exhibited faster vegetative growth on muddy sand than on sand, probably due to the difference in nutrient supply. The seasonal changes of water and air temperature were considered to play an important role in the seasonal leaf growth of Z. japonica.     

Shrub removal facilitates recovery of wetland species in a rewetted fen

Drainage and shrub expansion are the main threats to the biodiversity of fens and fen meadows, whereas rewetting and the removal of shrubby species are frequently applied restoration measures. We examine whether removal of shrubs enhances recovery of target species in a degraded fen subjected to moderate rewetting. The study was located in the drained fen Ca?owanie (central Poland), where remnants of open fen communities and willow-invaded fens exist in former turf-pits, surrounded by degraded meadows on dried peat. All these three habitat types were included in a monitoring grid, which covered an area of 2.2 ha. Within 55 quadrats of 20 m × 20 m we monitored occurrence of 52 species, i.e. two groups of target species (fen indicators and wet meadow indicators) and indicators of two failure scenarios (degraded fen indicators and eutrophic wetland indicators), during six years following shrub removal, rewetting and re-application of conservational mowing, using a 3-step ordinal abundance scale. NMDS ordination revealed a gradual convergence of shrub removal plots and reference plots. We noticed significant effects of year and habitat type on all indicator groups, but only fen indicators have shown a clear (increasing) trend within shrub removal plots. Degraded fen indicators (ruderal and opportunistic species) initially expanded on shrub removal plots, but this effect disappeared in the following years. We conclude that shrub removal enhances establishment of target species in a moderately drained and then rewetted fen and attribute this effect to lowered competition for light. However, given high costs of this method and long-lasting problems with shrub resprouts, we recommend applying shrub removal only to recently overgrown sites, which still retained high botanical diversity. Heavily degraded fen meadows did not react on the increase of moisture, which indicates that more advanced restoration measures, such as top soil removal are needed there.     

Permafrost conditions in peatlands regulate magnitude,timing, and chemical composition of catchment dissolved organic carbon export

Permafrost thaw in peatlands has the potential to alter catchment export of dissolved organic carbon (DOC) and thus influence downstream aquatic C cycling. Subarctic peatlands are often mosaics of different peatland types, where permafrost conditions regulate the hydrological setting of each type. We show that hydrological setting is key to observed differences in magnitude, timing, and chemical composition of DOC export between permafrost and nonpermafrost peatland types, and that these differences influence the export of DOC of larger catchments even when peatlands are minor catchment components. In many aspects, DOC export from a studied peatland permafrost plateau was similar to that of a forested upland catchment. Similarities included low annual export (2–3 g C m^?2) dominated by the snow melt period (~70%), and how substantial DOC export following storms required wet antecedent conditions. Conversely, nonpermafrost fens had higher DOC export (7 g C m^?2), resulting from sustained hydrological connectivity during summer. Chemical composition of catchment DOC export arose from the mixing of highly aromatic DOC from organic soils from permafrost plateau soil water and upland forest surface horizons with nonaromatic DOC from mineral soil groundwater, but was further modulated by fens. Increasing aromaticity from fen inflow to outlet was substantial and depended on both water residence time and water temperature. The role of fens as catchment biogeochemical hotspots was further emphasized by their capacity for sulfate retention. As a result of fen characteristics, a 4% fen cover in a mixed catchment was responsible for 34% higher DOC export, 50% higher DOC concentrations and ~10% higher DOC aromaticity at the catchment outlet during summer compared to a nonpeatland upland catchment. Expansion of fens due to thaw thus has potential to influence landscape C cycling by increasing fen capacity to act as biogeochemical hotspots, amplifying aquatic C cycling, and increasing catchment DOC export.     

The effects of land use change and irrigation water resource on nitrate contamination in shallow groundwater at county scale

The objective of this study was to assess the impacts of land use changes and irrigation water resource on the nitrate contamination in shallow groundwater. 394 water samples were sampled from the same irrigation wells during a period of five years (from 2002 to 2007) in Huantai County in the North China Plain. NO₃-N concentration in irrigation wells was measured. Geostatistical method combined with GIS technique was used to analyze the spatio-temporal distribution of groundwater NO₃-N concentrations in Huantai County. Land use type and irrigation water resource were combined with the variation of NO₃-N concentrations by statistical approach to investigate the relationship between them. The distribution map showed that the percentages of area increased by 13.06%, 14.37%, 12.23% and 3.85% for that had nitrate concentrations of 10–15, 15–20, 20–30 mg L^?1 and greater than 30 mg L^?1 for shallow groundwater, respectively, while decreased by 28.87% and 14.63% for 0–5 and 5–10 mg L^?1. In the well-irrigated field, the NO₃-N concentrations in shallow groundwater had increased for vegetables, wheat–vegetables and wheat–maize rotations. In contrast, fast-growing tree system could act as a buffer to retain shallow groundwater nitrate content which resulted in reduced NO₃-N concentrations. Under the same land use condition, irrigation with sewage, or well and sewage by turns would both enormously add nitrate to groundwater.     

Loss of testate amoeba functional diversity with increasing frost intensity across a continental gradient reduces microbial activity in peatlands

Soil microbial communities significantly contribute to global fluxes of nutrients and carbon. Their response to climate change, including winter warming, is expected to modify these processes through direct effects on microbial functions due to osmotic stress, and changing temperature regimes. Using four European peatlands reflecting different frequencies of frost events, we show that peatland testate amoeba communities diverge among sites with different winter climates, and that this is reflected through contrasting functions. We found that exposure to harder soil frost promoted species β-diversity (species turnover) thus shifting the community composition of testate amoebae. In particular, we found that harder soil frost, and lower water-soluble phenolic compounds, induced functional turnover through the decrease of large species (−68%, >80 μm) and the increase of small-bodied mixotrophic species (i.e. Archerella flavum; +79%). These results suggest that increased exposure to soil frost could be highly limiting for large species while smaller species are more resistant. Furthermore, we found that β-glucosidase enzymatic activity, in addition to soil temperature, strongly depended of the functional diversity of testate amoebae (R² = 0.95, ANOVA). Changing winter conditions can therefore strongly impact peatland decomposition process, though it remains unclear if these changes are carried-over to the growing season.     

Effects of wetland construction on water quality in a semi-arid catchment degraded by intensive agricultural use

Many factors can influence the improvement of water quality in surface-flow constructed wetlands (SFW). To test if water quality was improved, especially in nutrient and salt content, after passage through SFW, 11 wetland plots of various sizes (50, 200, 800 and 5000 m²) were established within constructed wetlands on agricultural soils in the Ebro River basin (NE Spain) that had been affected by salinization. A set of 15 water quality parameters (e.g., nutrients, salts, sediments, and alkalinity) was obtained from samples collected at the inflow and outflow of the wetlands during the first 4 years after the wetlands were constructed. NO₃-N retention rates were as high as 99% in the largest (5000 m²) wetlands. After 4 years, total phosphorus was still being released from the wetlands but not salts. Over the same period, in small wetlands (50, 200, and 800 m²), retention rate relative to the input of NO₃-N increased from 40% to almost 60%. Retention of NO₃-N amounted to up to 500 g N m^?2 per year, for an average load concentration at inflow of ～20 mg l^?1. Release of Na⁺ declined from 16% to 0–2% by volume, for an average load concentration at inflow of ～70 mg l^?1. At the current retention rate of NO₃-N (76–227 g m^?2 per year), 1.5–4% of the catchment should be converted into wetlands to optimize the elimination of NO₃-N.     

Abundance and biomass of planktonic ciliates in the sea area around Zhangzi Island,Northern Yellow Sea

We investigated the abundance and biomass of planktonic ciliates in the sea area around Zhangzi Island, Northern Yellow Sea, from July 2009 to June 2010. Ciliates were sampled monthly from surface to bottom with a 10 m depth interval at 13 sample stations along three transects. A 1 L sample of water from each depth was collected with a 2.5 L Niskin water sampler and fixed in 1% acid Lugol’s iodine solution. Water samples were pre-concentrated using the Utermöhl method and observed using an Olympus IX51 inverted microscope at 100× or 200x. The dimensions of the ciliates were measured and the cell volume of each species was estimated using appropriate geometric shapes. The carbon:volume ratio used to calculate biomass was 0.19 pg C/μm³. Abundance and biomass of the ciliate in water column were calculated as the integral of the abundance and biomass from bottom to surface, respectively. The classification of tintinnids was based on taxonomic literature. The average abundance of non-loricate ciliates was 3066 ± 2805 ind/L, ranging from 165 ind/L (50 m depth of St. B6 in July) to 26,595 ind/L (surface of St. C1 in September). The average biomass of non-loricate ciliates was 2.88 ± 2.68 μg C/L, ranging from 0.05 μg C/L (10 m depth of St. A6 in July) to 20.51 μg C/L (surface of St. A5 in August). The average tintinnid abundance was 142 ± 273 ind/L, ranging from 0 ind/L (monthly) to 2756 ind/L (surface of St. A1 in July). The average tintinnid biomass was 0.84 ± 2.19 μg C/L, ranging from 0.00 μg C/L (every month) to 37.64 μg C/L (20 m depth of St. C5 in July). The results showed that the average abundance of total ciliates was 3208 ± 2828 ind/L, ranging from 166 ind/L (10 m depth of St. A6 in July) to 26,625 ind/L (surface of St. C1 in September); the average biomass of total ciliates was 3.73 ± 3.55 μg C/L, ranging from 0.05 μg C/L (10 m depth of St. A6 in July) to 38.29 μg C/L (20 m depth of St. C5 in July). Abundance and biomass were vertically homogeneous in February, November and December, but decreased dramatically from the surface down to the bottom in other months. 23 tintinnid species were identified, 12 of which were in genus Tintinnopsis. Tintinnid species were more abundant in February, July and August. Tintinnids occupied 6.6 ± 10.2% and 19.7 ± 23.3% of the total ciliate abundance and biomass, respectively, which increased during the warm season and at coastal stations, and decreased during the cold season and at offshore stations. Large non-loricate ciliate species were prevalent in spring, while smaller species dominated in summer and autumn. The average abundance of total ciliates in water column was 132 ± 72 × 10⁶ ind/m², with increases during spring and autumn. The average biomass of total ciliates in water column was 152.57 ± 93.10 mg C/m², with increases during spring and summer. The average abundance and biomass of total ciliates in water column were greater at offshore stations than at coastal stations during spring and autumn, and were lower during summer and winter. Non-loricate ciliates, tintinnids and total ciliates showed significant positive correlation with temperature and significant negative correlation with salinity (p < 0.01). Non-loricate ciliates and total ciliates showed significant positive correlation with Chl a concentration (p < 0.01); however, relationship between Chl a concentration and tintinnids was not significant.     

Patterns of Fungal and Bacterial Carbon Mineralization Across Northern European Peatlands

The fungal and bacterial activity was determined in 20 northern European peatlands ranging from ombrotrophic bogs to eutrophic fens with key differences in degree of humification, pH, dry bulk density, carbon (C) content and vegetation communities using the selective inhibition (SI) technique. These peatlands were partly disturbed and the respective water tables lowered below the surface layer. Basal respiration ranged from 24 to 128 µg CO₂-C g^?1 dry peat d^?1. Bacterial contributions to CO₂ production were high in most peatlands and showed the following pattern: eutrophic >> transitional ≥ mesotrophic >> ombrotrophic peatland types. The fungal-to-bacterial (F:B) ratios varied substantially within peatland type, and this was mainly attributed to differences in peat botanical compositions and chemistry. The computed mean Inhibitor Additivity Ratio (IAR) was quite close to 1 to suggest that the SI techniques can be used to partition eukaryotic and prokaryotic activity in wide range of peatlands. Overall, basal respiration, microbial biomass-C, fungal and bacterial activities varied across the studied peatland types, and such differences could have consequences for C- and nutrient-cycling as well as how bogs and fens will respond to environmental changes.     

Water mites as potential long-term bioindicators in formerly drained and rewetted raised bogs

Many environmental studies of restored peatlands focus on biogeochemical cycles, productivity and decomposition. However, changes in the composition and structure of invertebrate assemblages in restored bogs have received little attention. In the present study we describe effects of rewetting on the water mite faunas (Acari: Hydrachnidia) of four raised bogs located in northwestern Germany. All examined peatlands had been drained in the past, and two of them had been subjected to peat extraction. The examined sites had been rewetted 2, 12, 14 and 25 years prior to our surveys, and currently represent different stages of plant succession. With increasing age after rewetting, the vegetation developed more complex structure as defined by Sphagnum status, and water mite fauna became somewhat similar to the fauna in an undisturbed raised reference bog. Water mites were found almost exclusively in bogs 25 years after wetting, and in these bogs they occurred in sites with more complex vegetation structure. Because water mites have high demands on abiotic and biotic factors due to their complex life cycle (i.e., the larvae are parasites, and the nymphs and adults are predators), we can infer that their mere presence irrespective of species abundance and richness reflects positive effects of the rewetting measures conducted in peat bogs.