Phosphorus cycling and partitioning in an oligotrophic Everglades wetland ecosystem: a radioisotope tracing study

1. Our goal was to quantify short‐term phosphorus (P) partitioning and identify the ecosystem components important to P cycling in wetland ecosystems. To do this, we added P radiotracer to oligotrophic, P‐limited Everglades marshes. ³²PO₄ was added to the water column in six 1‐m² enclosed mesocosms located in long‐hydroperiod marshes of Shark River Slough, Everglades National Park. Ecosystem components were then repeatedly sampled over 18 days. 2. Water column particulates (>0.45 μm) incorporated radiotracer within the first minute after dosing and stored 95–99% of total water column ³²P activity throughout the study. Soluble (<0.45 μm) ³²P in the water column, in contrast, was always <5% of the ³²P in surface water. Periphyton, both floating and attached to emergent macrophytes, had the highest specific activity of ³²P (Bq g^?131P) among the different ecosystem components. Fish and aquatic macroinvertebrates also had high affinity for P, whereas emergent macrophytes, soil and flocculent detrital organic matter (floc) had the lowest specific activities of radiotracer. 3. Within the calcareous, floating periphyton mats, 81% of the initial ³²P uptake was associated with Ca, but most of this ³²P entered and remained within the organic pool (Ca‐associated = 14% of total) after 1 day. In the floc layer, ³²P rapidly entered the microbial pool and the labile fraction was negligible for most of the study. 4. Budgeting of the radiotracer indicated that ³²P moved from particulates in the water column to periphyton and floc and then to the floc and soil over the course of the 18 day incubations. Floc (35% of total) and soil (27%) dominated ³²P storage after 18 days, with floating periphyton (12%) and surface water (10%) holding smaller proportions of total ecosystem ³²P. 5. To summarise, oligotrophic Everglades marshes exhibited rapid uptake and retention of labile ³²P. Components dominated by microbes appear to control short‐term P cycling in this oligotrophic ecosystem.     

Gas chromatography mass spectrometry based profiling of alkyl coumarates and ferulates in two species of cattail (Typha domingensis P., and Typha latifolia L.)

Several long-chain n-alkyl coumarates and ferulates were identified in cattails (Typha domingensis and Typha latifolia) from the Florida Everglades. Characterization of these compounds was achieved based on the interpretation of mass spectra obtained by GCMS as their trimethylsilyl ether derivatives, comparison with published mass spectra and available standards. Both n-alkyl p-coumarates and n-alkyl ferulates were identified in roots and leaves of both Typha species, featuring unique distribution patterns and differences between leaf and root biomass. For both Typha species, roots have higher concentrations and a much greater diversity of n-alkyl p-coumarates and ferulates but with different side chain carbon numbers ranging from C₁₄ to C₂₈. Typha domingensis leaves only contained n-alkyl ferulates with traces of n-alkyl p-coumarates, while both types of compounds were present in Typha latifolia leaf material. These chemicals were not found in the other dominant wetland vegetation, which suggests their potential for application as phytochemical tracers of fresh cattail-derived organic matter in the Everglades ecosystem.     

Problems with the application of diatom-total phosphorus transfer functions: examples from a shallow English lake

1. A diatom‐total phosphorus transfer function has been applied to a sedimentary diatom sequence from Groby Pool, a small shallow lake in Leicestershire, U.K. 2. Extensive aquatic plant records exist for Groby Pool dating back over two centuries. These records, in conjunction with selected aquatic pollen and herbarium diatom data, provide independent, qualitative evidence for the progression of eutrophication and its effects on aquatic plant communities and habitat structure. 3. Before 1800, Groby Pool was probably mesotrophic with clear water and a diverse submerged macrophyte community, but subsequently it experienced considerable nutrient enrichment. Key evidence for this includes: (i) historical plant records indicating the loss of species associated with mesotrophic waters and their replacement by others typical of eutrophic conditions, (ii) a significant increase in the percentage of planktonic diatoms in the lake sediment record (particularly Cyclostephanos dubius) after 1890, and (iii) increases in percentages of Stephanodiscus parvus and Cocconeis placentula in the second half of the twentieth century. 4. Diatom‐inferred total phosphorus (DI‐TP) estimates were inconsistent with the qualitative evidence for eutrophication at Groby Pool. In particular the DI‐TP profile was thought to overestimate phosphorus during the period of dominance by small Fragilaria spp. before 1890, and to misjudge the timing and direction of subsequent changes in nutrient loading. 5. This study highlights some of the problems associated with the application of diatom‐TP transfer functions to sedimentary diatom sequences from shallow lakes. The major problem relates to the frequent dominance of non‐planktonic diatoms in the sediments of these systems, many species of which (particularly small Fragilaria spp.) appear to be more sensitive to changes in habitat availability than to phosphorus. Potential ways of improving diatom‐TP models via altered approaches to sampling are suggested.     

Decomposition of macrophyte litter in a subtropical constructed wetland in south Florida (USA)

The South Florida Water Management District has constructed large treatment wetlands (stormwater treatment areas (STAs)) to reduce total phosphorus concentrations in agricultural runoff before this water enters the Everglades. An important component of nutrient removal and storage in these systems is incorporation of nutrients into aquatic macrophytes and burial of this biomass in the sediments. However, decomposition of plant biomass before burial returns nutrients to the water column and may reduce STA treatment efficiency. As part of research on biogeochemical control of STA performance, we conducted a summer (July–September) and a long-term (12-month) experiment (February–February) that measured decomposition rates and release of chemical constituents from dominant aquatic macrophytes in a constructed wetland located in south Florida. The rank order of mean decomposition rates was Najas/Ceratophyllum (0.0568 d⁻¹) > Pistia (0.0508 d⁻¹) > Eichhornia (0.0191 d⁻¹) > submerged Typha (0.0059 d⁻¹) > aerial Typha (0.0008 d⁻¹). Summer decomposition rates were generally higher than rates from the long-term experiment, which suggested a temperature effect. Decomposition rates were negatively correlated with litter C:N and C:P molar ratios and cellulose and lignin content and positively correlated with N and P content. There was no significant difference in decomposition rates among sampling stations despite the fact that there was a decreasing gradient in water column inorganic phosphorus and nitrogen concentrations at these sites. Relatively little of the initial P mass remained in the litter of all species, except Typha, by the end of both experiments. First-order decomposition models derived using nonlinear regression generally had explanatory power, i.e. accounted for variance, comparable to more complex decreasing-coefficient models. Decomposition rates for the species examined in this study were within the range of published values when comparisons were made either by species or by plant group.     

基于水文地貌分类的滨海湿地生态功能评价——以盐城滨海湿地为例

盐城滨海湿地生态功能的空间差异对该区的保护/开发具有重要的指导意义,水文地貌分类为生态功能的评价提供了良好的前提条件。根据盐城滨海湿地2006-2007年Alos遥感影像数据制作湿地景观图,同时通过DEM和水文水动力条件图,借助Arcgis9.2的空间分析功能确定水文地貌单元(HGMU)。在此基础上,利用实地调查数据和湿地景观数据对不同水文地貌单元的湿地生态功能进行评价。结果表明:(1)盐城海滨湿地包括7类水文地貌单元(HGMU),不同HGMU生态系统类型差异较大;(2)同种HGMU生态功能基本处于同一等级,不同HGMU的生态功能差异明显;(3)盐城海滨湿地不同HGMU单元生态功能由大到小排序为:淡水双向-冲积区(河口)、海水天双向-泥粉砂带、海水月双向-泥滩带、海水年双向-草滩带、淡水单向-冲积区、淡水单向-海积区和淡水单向-冲积海积区。其中,河口湿地、淤泥质滩涂和草滩带湿地在维护盐城海滨湿地生态功能中具有重要地位。     

Limnological characteristics of a subtropical constructed wetland in south Florida (USA)

The Everglades Nutrient Removal Project (ENRP) was a 1544 ha constructed wetland built by the South Florida Water Management District as part of Everglades restoration efforts. The limnology of this wetland is characterized over its 60-month operational history. The ENRP received agricultural runoff containing high levels of C, N, P and other dissolved constituents; had moderately high alkalinity with a circumneutral pH; and had low to moderate DO. The ENRP provided substantial treatment (concentration reduction from inflow to outflow) for Al, Fe, NH₄, NO_x, SRP, TP, TSS and turbidity (high-treatment variables), while Secchi depth increased markedly. These changes were judged biologically significant. Dissolved oxygen, and water temperature had well defined annual cycles, while some level of seasonality was noted for Al, alkalinity, Ca, conductivity, DOC, Fe, hardness, K, Mg, Mn, Na, NH₄, pH, Secchi depth, SiO₂, TOC, TN, turbidity, and TSS. The ENRP was P limited based on TN:TP molar ratios. Dissolved ions were dominated by Ca, Cl, Na, and HCO₃; the stoichiometric balance of both major and minor ions was similar throughout the wetland. The downstream settling of TSS was associated with increased light penetration, but did not appear important in sediment accretion. The adsorption of P to Ca, and perhaps Al and Fe, precipitates is thought to have been an important nutrient removal mechanism. Although there was little net reduction in DOC, we speculate that some incoming material was degraded and replaced by new DOC produced within the wetland.     

Changes in macroinvertebrate community structure and function along a

Aquatic macroinvertebrate communities were sampled between 1994 and 1996 at 13 sites downstream of phosphorus (P)-enriched canal inflows in a northern Everglades marsh to determine the effects of nutrient enrichment on community structure and function. Sampling was performed using sweep nets and Hester–Dendy (HD) samplers. Data were analyzed to assess changes in taxa richness and diversity, species composition, and functional group composition along the gradient. Environmental conditions at each site were characterized to interpret spatial changes in these metrics. Mean water-column total P (TP) increased from 10g l^minus;1at sites in the marsh interior to as high as 160g l^minus;1at sites closest to the canal. Vegetation and habitat composition changed dramatically along the gradient, with sawgrass and slough-wet prairie habitats accounting for most vegetative cover in the interior and cattail accounting for nearly 100%of the cover near the canal. These differences in TP concentrations and vegetation were used to classify sites as reference, enriched, and highly enriched. Daytime dissolved oxygen (DO) concentrations averaged 3mg l^minus;1at reference sites as compared with concentrations 2mg l^minus;1at enriched and highly enriched sites. Total macroinvertebrate densities were significantly higher in sweep samples and significantly lower in HD samples from highly enriched sites as compared with the reference condition. Taxa richness and diversity in sweep samples did not change significantly along the gradient, but declined with enrichment on the HD samplers. Insects were the dominant organisms at all sites, but declined in percent abundance with enrichment in sweep samples due to decreases in dipterans, trichopterans and odonates and an increase in oligochaetes. Changes in major invertebrate classes were less pronounced on HD samplers, although amphipods showed significant declines with enrichment. Principal components analysis revealed a clear distinction in taxonomic composition between reference sites and both enriched and highly enriched sites for sweep samples as common chironomid taxa at reference sites declined with enrichment while pollution-tolerant chironomid and oligochaete taxa increased. A similar, but less dramatic trend was found for HD samples, with selected amphipod, chironomid, and gastropod taxa declining with enrichment and pollution-tolerant taxa reaching peak abundance at enriched sites. The functional composition in sweep samples showed modest changes with enrichment, including a shift in dominance from epibenthic collector–gatherers/deposit feeders, which were predominantly chironomids, to subsurface taxa, which were predominantly oligochaetes. Shifts in invertebrate functional composition on HD samplers with enrichment were attributable to declines in the dominance of shredders and collector-filterer/suspension-feeders. Portions of the Everglades exposed to P-enriched runoff are showing characteristic shifts in macroinvertebrate taxonomic composition related to eutrophication. This shift has occurred without a change in species diversity and with an increase in total invertebrate abundance indicative of an overall increase in marsh productivity. The transition from an oligotrophic to eutrophic community signals a decline in the biological integrity of the Everglades ecosystem in response to P enrichment.     

A hydrologic assessment of the Everglades Nutrient Removal Project, a subtropical constructed wetland in South Florida (USA)

The Everglades Nutrient Removal Project (ENRP), a 1544-ha constructed wetland in south Florida, was intensively monitored throughout its five-year operational history. Water budgets for the ENRP and each of its interior treatment cells were dominated by surface flows (≥85% of inflows; ≥68% of outflows) with smaller contributions from precipitation, evapotranspiration, groundwater flux, and change in storage. The mean water depth, hydraulic loading rate for surface water, and nominal hydraulic retention time for the entire wetland were 0.6 m, 3.1 cm d⁻¹ and 17.7 d, respectively, and were comparable to values anticipated in design. The east flow-way was slightly shallower (0.2 m) and received proportionately more flow (61%) than the west flow-way. The hydrology of other treatment wetlands is often driven by surface flows. All treatment cells in the ENRP were to some extent hydraulically short-circuited. There was net groundwater inflow to the ENRP from Water Conservation Area 1 (WCA-1) resulting from significant head differences between these wetlands. Groundwater outflow to the adjacent farmlands was greatest in Cell 2 and substantially exceeded groundwater inflow. All hydrologic parameters exhibited seasonality to some extent; fluctuation in water depth and groundwater inflows corresponded with the seasonal change in stage in WCA-1. Errors in the ENRP and individual cell water budgets were generally less than 10% and within the range of errors for water budgets from other wetlands.     

Patterns of vertical stratification in a subtropical constructed wetland in south Florida (USA)

The South Florida Water Management District (District) has built large treatment wetlands, known as Stormwater Treatment Areas (STAs), to reduce excess phosphorus loading to the Everglades. The District conducted research in a prototype treatment wetland, the Everglades Nutrient Removal Project (ENRP), to study biogeochemical processes that are important to treatment performance. Vertical profile measurements of water temperature, dissolved oxygen, pH, conductivity and transmission of photosynthetically active radiation (PAR) were made in open-water areas and sites dominated by emergent, floating or submersed vegetation over an annual cycle. Relative thermal resistance to mixing was used to infer the strength of thermal stratification. Long-term diel variation in temperature at the surface and bottom of an open-water and a vegetated site also was measured. Open-water sites were nearly isothermal and had minimal thermal stratification, while vegetated sites were all thermally stratified to some degree. The highest surface water temperatures (>35 °C) occurred in submersed vegetation where much of the light absorbed by leaves and stems was reflected as heat. Oxygen was uniformly low (<4 mg L⁻¹) in emergent and floating vegetation and attributed to shading, high biological oxygen demand and limited reaeration at the surface. Depressed oxygen levels at open-water areas were attributed to high sediment oxygen demand. The highest oxygen concentrations occurred in submersed vegetation beds. Water column pH was unstratified and near circumneutral in the open water and at emergent and floating vegetation sites, while pH was markedly stratified in submersed vegetation, where surface values at times exceeded 9.0. High surface oxygen and pH levels in submersed vegetation were consistent with intense photosynthesis. Conductivity increased at the bottom of emergent and submersed vegetation but not at open-water or floating vegetation sites. PAR transmission was strongly reduced at all sites due to shading and/or absorption by dissolved organic carbon. Light extinction coefficients were markedly higher at vegetated sites compared to the open water. Peak irradiance shifted to longer wavelengths (538–643 nm) and both short (<400 nm) and long (>700 nm) wavelengths were largely attenuated at 60 cm relative to the surface. Long-term monitoring at a vegetated site revealed periods of inverse thermal stratification and dampened diel variation in temperatures at the bottom compared to open water.     

Deep peat warming increases surface methane and carbon dioxide emissions in a black spruce‐dominated ombrotrophic bog

Boreal peatlands contain approximately 500 Pg carbon (C) in the soil, emit globally significant quantities of methane (CH₄), and are highly sensitive to climate change. Warming associated with global climate change is likely to increase the rate of the temperature‐sensitive processes that decompose stored organic carbon and release carbon dioxide (CO₂) and CH₄. Variation in the temperature sensitivity of CO₂ and CH₄ production and increased peat aerobicity due to enhanced growing‐season evapotranspiration may alter the nature of peatland trace gas emission. As CH₄ is a powerful greenhouse gas with 34 times the warming potential of CO₂, it is critical to understand how factors associated with global change will influence surface CO₂ and CH₄ fluxes. Here, we leverage the Spruce and Peatland Responses Under Changing Environments (SPRUCE) climate change manipulation experiment to understand the impact of a 0–9°C gradient in deep belowground warming (“Deep Peat Heat”, DPH) on peat surface CO₂ and CH₄ fluxes. We find that DPH treatments increased both CO₂ and CH₄ emission. Methane production was more sensitive to warming than CO₂ production, decreasing the C‐CO₂:C‐CH₄ of the respired carbon. Methane production is dominated by hydrogenotrophic methanogenesis but deep peat warming increased the δ¹³C of CH₄ suggesting an increasing contribution of acetoclastic methanogenesis to total CH₄ production with warming. Although the total quantity of C emitted from the SPRUCE Bog as CH₄ is <2%, CH₄ represents >50% of seasonal C emissions in the highest‐warming treatments when adjusted for CO₂ equivalents on a 100‐year timescale. These results suggest that warming in boreal regions may increase CH₄ emissions from peatlands and result in a positive feedback to ongoing warming.     

Catabolic diversity of periphyton and detritus microbial communities in a subtropical wetland

The catabolic diversity of wetland microbial communities may be a sensitive indicator of nutrient loading or changes in environmental conditions. The objectives of this study were to assess the response of periphyton and microbial communities in water conservation area-2a (WCA-2a) of the Everglades to additions of C-substrates and inorganic nutrients. Carbon dioxide and CH₄ production rates were measured using 14 days incubation for periphyton, which typifies oligotrophic areas, and detritus, which is prevalent at P-impacted areas of WCA-2a. The wetland was characterized by decreasing P levels from peripheral to interior, oligotrophic areas. Microbial biomass and N mineralization rates were higher for oligotrophic periphyton than detritus. Methane production rates were also higher for unamended periphyton (80 mg CH₄-C kg⁻¹ d⁻¹) than detritus (22 mg CH₄-C kg⁻¹ d⁻¹), even though the organic matter content was higher for detritus (80%) than periphyton (69%). Carbon dioxide production for unamended periphyton (222 mg CO₂-C kg⁻¹ d⁻¹) was significantly greater than unamended detritus (84 mg CO₂-C kg⁻¹ d⁻¹). The response of the heterotrophic microbial community to added C-substrates was related to the nutrient status of the wetland, as substrate-induced respiration (SIR) was higher for detritus than periphyton. Amides and polysaccharides stimulated SIR more than other C-substrates, and methanogenesis was greater contributor to SIR for periphyton than detritus. Inorganic P addition stimulated CO₂ and CH₄ production for periphyton but not detritus, indicating a P limitation in the interior areas of WCA-2a. Continued nutrient loading into oligotrophic areas of WCA-2a or enhanced internal nutrient cycling may stimulate organic matter decomposition and further contribute to undesirable changes to the Everglades ecosystem caused by nutrient enrichment.     

Ecological restoration of rich fens in Europe and North America: from trial and error to an evidence‐based approach

Fens represent a large array of ecosystem services, including the highest biodiversity found among wetlands, hydrological services, water purification and carbon sequestration. Land‐use change and drainage has severely damaged or annihilated these services in many parts of North America and Europe; restoration plans are urgently needed at the landscape level. We review the major constraints on the restoration of rich fens and fen water bodies in agricultural areas in Europe and disturbed landscapes in North America: (i) habitat quality problems: drought, eutrophication, acidification, and toxicity, and (ii) recolonization problems: species pools, ecosystem fragmentation and connectivity, genetic variability, and invasive species; and here provide possible solutions. We discuss both positive and negative consequences of restoration measures, and their causes. The restoration of wetland ecosystem functioning and services has, for a long time, been based on a trial‐and‐error approach. By presenting research and practice on the restoration of rich fen ecosystems within agricultural areas, we demonstrate the importance of biogeochemical and ecological knowledge at different spatial scales for the management and restoration of biodiversity, water quality, carbon sequestration and other ecosystem services, especially in a changing climate. We define target processes that enable scientists, nature managers, water managers and policy makers to choose between different measures and to predict restoration prospects for different types of deteriorated fens and their starting conditions.     

Environmental Variables and Planktonic Communities in Two Ponds of El Hondo Wetland (SE Spain)

The annual cycle of physical and chemical variables and plankton dynamics was studied in two shallow ponds (East and West Ponds) of the El Hondo wetland, an ecosystem of international importance. Water conductivity increased up to 31–49 mS cm^–1 as water level decreased due to high evaporation and minimal water inputs. Initially considered mesohaline, the waters were reclassified as polyhaline during the hot season. EP was subject to successive desiccation‐flooding cycles, and flooding of the dried sediment caused the release of high concentrations of nitrogen and phosphorus compounds, which quickly depleted. The algal species composition was typical of eutrophic ecosystems, and the chlorophyll content indicated that EP was eutrophic and WP mesotrophic. Phytoplanktonic species richness and diversity were low in both ponds. Algal assemblages, in terms of biovolume, were mainly dominated by Dinophyceae in EP and by Cryptophyta in WP. The zooplankton community was dominated by Rotifers (Brachionus and Hexarthra), although Copepods and Ciliates were also important. Different water inputs to the ponds, partial drying in EP during the warm season with the subsequent higher increment of salinity, and the presence of dense populations of submerged macrophytes in WP, explain the differences in plankton communities found between the two ponds.     

上海市崇明东滩湿地生态恢复与重建工程中社会经济价值分析

随着人类活动的增加,崇明东滩自然保护区内已被破坏或改变栖息地利用方式的湿地面积已达到8000hm^2,其逗留、栖息和越冬的鸟类逐年减少。因此,为了保护鸟类,并且提高上海在自然保护和维护物种多样性方面的国际地位,恢复和重建崇明东滩的湿地环境受到上海市政府的高度重视。崇明东旺沙B01号样地的恢复与重建是上海市崇明东滩湿地生态恢复与生态重建工程中的一期工程．结合野外调查,综合运用市场价值法、造林成本法和生态价值法等研究方法,对该样地现有功能价值,以及对样地在恢复和重建之后所产生的功能价值进行了估算,得到该示范区现有功能价值为72．27万元人民币,而初步预计恢复和重建之后的功能价值为7016.95万元人民币。     

Plants for nitrogen management in riparian zones: A proposed trait‐based framework to select effective species

Restoring plants to the riparian zone is regarded as management best practice in river restoration and has the potential to reduce the impact of nitrogen (N) pollution on aquatic organisms and improve water quality for human use. Plant characteristics and the interplay of hydrology and biogeochemistry control N retention in the riparian zone. The balance between processes such as denitrification and plant assimilation determines riparian N retention. Plant traits are likely to mediate these N removal processes through variations in root form, growth character, foliage production (quantity, quality and rate of return to the soil) and by altering conditions in the rhizosphere soil. Vegetation can slow N transfer via direct plant uptake of N (during periods of rapid vegetation growth) and changes induced to soil hydrology, nutrient cycling and microbial activity, principally denitrification. Few studies have focused on species‐dependent effects on N movement through soil and across boundaries. We propose a new framework, based on a literature review of plant traits with respect to N cycling, which can be used to select plant species with traits likely to maximise N removal during transport through the riparian zone. In the proposed framework, inter‐specific differences in traits known to influence N mobility: root form, growth rate, foliar characteristics and rhizosphere processes, are used to describe species’ potential impact on N removal. Plant trait data may be drawn from studies outside the riparian zone; for example forest ecology, horticulture or forestry research, and candidate species are scored to predict N removal efficiency. We apply the framework to New Zealand's native riparian plant assemblages to demonstrate the trait‐based approach. This framework can guide restoration management decisions and investment in riparian revegetation in a manner that is not restricted to geographically specific or well‐studied species.     

A comparison of diatom phosphorus transfer functions and export coefficient models as tools for reconstructing lake nutrient histories

1. We compared the baseline phosphorus (P) concentrations inferred by diatom‐P transfer functions and export coefficient models at 62 lakes in Great Britain to assess whether the techniques produce similar estimates of historical nutrient status. 2. There was a strong linear relationship between the two sets of values over the whole total P (TP) gradient (2–200 μg TP L^?1). However, a systematic bias was observed with the diatom model producing the higher values in 46 lakes (of which values differed by more than 10 μg TP L^?1 in 21). The export coefficient model gave the higher values in 10 lakes (of which the values differed by more than 10 μg TP L^?1 in only 4). 3. The difference between baseline and present‐day TP concentrations was calculated to compare the extent of eutrophication inferred by the two sets of model output. There was generally poor agreement between the amounts of change estimated by the two approaches. The discrepancy in both the baseline values and the degree of change inferred by the models was greatest in the shallow and more productive sites. 4. Both approaches were applied to two lakes in the English Lake District where long‐term P data exist, to assess how well the models track measured P concentrations since approximately 1850. There was good agreement between the pre‐enrichment TP concentrations generated by the models. The diatom model paralleled the steeper rise in maximum soluble reactive P (SRP) more closely than the gradual increase in annual mean TP in both lakes. The export coefficient model produced a closer fit to observed annual mean TP concentrations for both sites, tracking the changes in total external nutrient loading. 5. A combined approach is recommended, with the diatom model employed to reflect the nature and timing of the in‐lake response to changes in nutrient loading, and the export coefficient model used to establish the origins and extent of changes in the external load and to assess potential reduction in loading under different management scenarios. 6. However, caution must be exercised when applying these models to shallow lakes where the export coefficient model TP estimate will not include internal P loading from lake sediments and where the diatom TP inferences may over‐estimate TP concentrations because of the high abundance of benthic taxa, many of which are poor indicators of trophic state.     

Effects of microtopography and water table on Sphagnum palustre L. in subtropical high mountains and implications for peatland restoration

Introduction. Human disturbance has recently led to increasingly serious destruction of Sphagnum L. wetlands in subtropical high mountains, resulting in an urgent need for wetland restoration.

Methods. Through a field experiment conducted in western Hubei Province, China, the effects of four different microtopographic types [concave surface, convex surface, concave and convex surface (CC surface), and flat surface] and water table depth (0 to ?30?cm) on three growth indicators (number of capitula, coverage and biomass) of Sphagnum palustre L. were examined. The objective was to identify the optimal hydrological conditions for S. palustre growth and thus facilitate its rapid recolonisation and restoration of these wetlands.

Key results. The results showed that different microtopographic conditions significantly influenced S. palustre growth. Among them, S. palustre in the CC surface showed the worst growth, while no significant differences existed among the other three microtopographic types. Additionally, as the water table increased, the growth of S. palustre increased, but long-term flooding impeded growth. The water table affected S. palustre growth via effects on its tissue water content.

Conclusions. Microtopographic reshaping was not essential for the success of S. palustre recolonisation, and microtopography that maintained the water table to within ?10?cm of the surface without flooding were best, independent of the microtopographic types. In addition, the growth patterns of S. palustre changed with changes in the environment, which may be related to its long-term adaptation to conditions of a lower water table.