A comparison of created and natural wetlands in Pennsylvania,USA

Recent research suggests that created wetlands do not look, or function, like the natural systems they are intended to replace. Proper planning, construction, and the introduction of appropriate biotic material should initiate natural processes which continue indefinitely in a successful wetland creation project, with minimal human input. To determine if differences existed between created and natural wetlands, we compared soil matrix chroma, organic matter content, rock fragment content, bulk density, particle size distribution, vegetation species richness, total plant cover, and average wetland indicator status in created (n = 12) and natural (n = 14)wetlands in Pennsylvania (USA). Created wetlands ranged in age from two to 18 years. Soils in created wetlands had less organic matter content, greater bulk densities, higher matrix chroma, and more rock fragments than reference wetlands. Soils in reference wetlands had clay loam textures with high silt content, while sandy clay loam textures predominated in the created sites. Vegetation species richness and total cover were both greater in natural reference wetlands. Vegetation in created wetlands included a greater proportion of upland species than found in the reference wetlands. There were significant differences in soils and vegetation characteristics between younger and older created wetlands, though we could not say older created sites were trending towards the reference wetland condition. Updated site selection practices, more careful consideration of monitoring period lengths, and, especially, a stronger effort to recreate wetland types native to the region should result in increased similarity between created and natural wetlands.     

Ecosystem Development After Mangrove Wetland Creation: Plant–Soil Change Across a 20-Year Chronosequence

Mangrove wetland restoration and creation efforts are increasingly proposed as mechanisms to compensate for mangrove wetland losses. However, ecosystem development and functional equivalence in restored and created mangrove wetlands are poorly understood. We compared a 20-year chronosequence of created tidal wetland sites in Tampa Bay, Florida (USA) to natural reference mangrove wetlands. Across the chronosequence, our sites represent the succession from salt marsh to mangrove forest communities. Our results identify important soil and plant structural differences between the created and natural reference wetland sites; however, they also depict a positive developmental trajectory for the created wetland sites that reflects tightly coupled plant-soil development. Because upland soils and/or dredge spoils were used to create the new mangrove habitats, the soils at younger created sites and at lower depths (10–30?cm) had higher bulk densities, higher sand content, lower soil organic matter (SOM), lower total carbon (TC), and lower total nitrogen (TN) than did natural reference wetland soils. However, in the upper soil layer (0–10?cm), SOM, TC, and TN increased with created wetland site age simultaneously with mangrove forest growth. The rate of created wetland soil C accumulation was comparable to literature values for natural mangrove wetlands. Notably, the time to equivalence for the upper soil layer of created mangrove wetlands appears to be faster than for many other wetland ecosystem types. Collectively, our findings characterize the rate and trajectory of above- and below-ground changes associated with ecosystem development in created mangrove wetlands; this is valuable information for environmental managers planning to sustain existing mangrove wetlands or mitigate for mangrove wetland losses.     

Effects of vertebrate herbivores on soil processes, plant biomass, litter accumulation and soil elevation changes in a coastal marsh

1 Submergence of coastal wetlands in Louisiana is currently rapid and widespread. A number of factors contribute to this loss of habitat, including the activities of herbivores. The objective of this study was to examine the effects of large mammals, predominantly nutria and wild boar, on processes controlling soil elevation in coastal marshes.
2 Effects of herbivores on soil and vegetation were assessed by the use of paired fenced and unfenced plots over two successive growing seasons. Above-ground biomass, litter production, changes in soil elevation, vertical soil accretion, shallow subsidence, below-ground production of roots and rhizomes, the thickness of the root zone, soil bulk density, and soil organic matter were measured.
3 Above-ground biomass, below-ground production, soil elevation and the expansion of the root zone decreased due to herbivore activity. Litter production, the rate of soil surface accretion and shallow soil subsidence were all higher in grazed compared to ungrazed plots, while soil organic matter and bulk density did not differ significantly between treatments.
4 The results indicate that herbivores can have a negative effect on soil building processes, primarily by reducing below-ground production and expansion of the root zone. Where natural rates of mineral sediment deposition are high, coastal marshes are expected to persist, despite herbivore activities. However, where sediment inputs are substantially less, herbivores may lead to destruction of habitat.     

Aboveground decomposition dynamics in riparian depression and slope wetlands of central Pennsylvania

We examined two types of groundwater-fed wetlands (riparian depressions and slopes) classified using the hydrogeomorphic (HGM) system. These wetland types had previously been shown to differ hydrologically. Our first objective was to determine if HGM was a useful structuring variable when examining aboveground decomposition dynamics (rate of mass loss and rate of nitrogen loss). Our second objective was to determine what soil variables were related to any differences in aboveground decomposition dynamics we might find regardless of HGM subclass. We used the litterbag field bioassay technique, and employed a standard litter type (Phalaris arundinacea) across all wetlands. Our results indicated that HGM would not readily serve as an adequate structuring variable for aboveground decomposition in riparian depressions and slope wetlands of central Pennsylvania. Discriminant analysis and classification and regression tree (CART) modeling found soil cation exchange capacity, soil pH, soil organic matter, and soil % nitrogen to be potentially important soil variables related to mass loss, and soil % nitrogen and soil pH to be potentially important variables related to nitrogen loss rate.     

Comparison of Soil Organic Matter in Created, Restored and Paired Natural Wetlands in North Carolina

Soil organic matter (SOM) content is a key indicator of soil quality and is correlated to a number of important soil processes that occur in wetlands such as respiration, denitrification, and phosphorus sorption. To better understand the differences in the SOM content of created (CW), restored (RW), and paired natural wetlands (NWs), 11 CW/RW-NW pairs were sampled in North Carolina. The site pairs spanned a range of hydrogeomorphic (HGM) subclasses common in the Coastal Plain. The following null hypotheses were tested: (1) SOM content of paired CW/RWs and NWs are similar; (2) SOM content of wetlands across different HGM subclasses is similar; and (3) interactions between wetland status (CW/RW vs. NW) and hydrogeomorphic subclass are similar. The first null hypothesis was rejected as CW/RWs had significantly lower mean SOM (11.8 ± 3.9%) than their paired NWs (28.98 ± 8.0%) on average and at 10 out of the 11 individual sites. The second and third null hypotheses were also rejected as CW/RWs and NWs in the non-riverine organic soil flat subclass had significantly higher mean SOM content (31.08 ± 14.2%) than the other three subclasses (8.18 ± 2.5, 11.18 ± 8.2, and 10.38 ± 4.2%). Individual sites within this fourth subclass also had significantly different SOM content. This indicated that it would be inappropriate to include the organic soil flat subclass with either the riverine or non-riverine mineral soil flat subclasses when considering restoration guidelines. These results also suggested that if there is a choice in mitigation options between restoration or creation, wetlands should be restored rather than created, especially those in the non-riverine organic soil flat subclass.     

Fifteen Years of Vegetation and Soil Development after Brackish-Water Marsh Creation

Aboveground biomass, macro‐organic matter (MOM), and wetland soil characteristics were measured periodically between 1983 and 1998 in a created brackish‐water marsh and a nearby natural marsh along the Pamlico River estuary, North Carolina to evaluate the development of wetland vegetation and soil dependent functions after marsh creation. Development of aboveground biomass and MOM was dependent on elevation and frequency of tidal inundation. Aboveground biomass of Spartina alterniflora, which occupied low elevations along tidal creeks and was inundated frequently, developed to levels similar to the natural marsh (750 to 1,300 g/m²) within three years after creation. Spartina cynosuroides, which dominated interior areas of the marsh and was flooded less frequently, required 9 years to consistently achieve aboveground biomass equivalent to the natural marsh (600 to 1,560 g/m²). Aboveground biomass of Spartina patens, which was planted at the highest elevations along the terrestrial margin and seldom flooded, never consistently developed aboveground biomass comparable with the natural marsh during the 15 years after marsh creation. MOM (0 to 10 cm) generally developed at the same rate as aboveground biomass. Between 1988 and 1998, soil bulk density decreased and porosity and organic C and N pools increased in the created marsh. Like vegetation, wetland soil development proceeded faster in response to increased inundation, especially in the streamside zone dominated by S. alterniflora. We estimated that in the streamside and interior zones, an additional 30 years (nitrogen) to 90 years (organic C, porosity) are needed for the upper 30 cm of created marsh soil to become equivalent to the natural marsh. Wetland soil characteristics of the S. patens community along upland fringe will take longer to develop, more than 200 years. Development of the benthic invertebrate‐based food web, which depends on organic matter enrichment of the upper 5 to 10 cm of soil, is expected to take less time. Wetland soil characteristics and functions of created irregularly flooded brackish marshes require longer to develop compared with regularly flooded salt marshes because reduced tidal inundation slows wetland vegetation and soil development. The hydrologic regime (regularly vs. irregularly flooded) of the “target” wetland should be considered when setting realistic expectations for success criteria of created and restored wetlands.     

Salvaged-Wetland Soil as a Technique to Improve Aquatic Vegetation at Created Wetlands in Wyoming,USA

Aquatic plants usually establish following wetland creation from a variety of mechanisms including animal transport, inflows from nearby wetlands, wind dispersal, and seed banks if they are available. However, at created wetlands that are isolated from natural wetlands, aquatic plant communities may not establish even after 10 or more years. One method of improving the establishment of aquatic plants is through the use of salvaged-marsh soils. Using this method, wetland soil from a donor site is collected and spread across the basin of the created wetland. When the proper hydrologic regime is reached at the created site, the seed bank from the donor soil is then present to take advantage of the uncolonized site. Over 1500 wetlands have been created in northeast Wyoming, USA from bentonite mining and most of them have not developed submersed and emergent plant communities due to isolation from plant sources. Our goal was to evaluate the effectiveness of using salvaged-wetland soil as a tool for improving plant growth at created wetlands. Our study took place at 12 newly created wetlands that were isolated from other wetlands by >5 km. Six wetlands were treated as reference wetlands, with no introductions of seeds or propagules. At the other six wetlands we spread ≈10–15 cm of salvaged soil from a donor wetland during the winter of 1999–2000. To identify the potential plants in donor soil, we collected 10 random samples from the donor wetlands and placed them within wetland microcosms in a greenhouse where they were treated to either moist-soil conditions (water at or just below the soil line) or submersed conditions (water levels maintained at 15–30 cm). Treatment wetlands were evaluated for plant growth during the fall of 2000 and 2001, whereas the greenhouse samples were grown for two growing seasons then harvested. Our results show that using salvaged wetland soil increases: (1) the number of plant species present at a wetland over time, (2) the total vegetation coverage in a treated wetland over time, and (3) the total plant biomass in a treated wetland. The species pool available in the salvaged wetland soil was limited to 10 obligate wetland species, but several of them are considered valuable to waterfowl and other wildlife. Furthermore, salvaged-wetland soil could be useful for ameliorating poor substrate conditions (i.e., bentonite) and improving conditions for the establishment of additional species. One concern with this technique is the introduction of invasive or exotic species that could form monocultures of undesirable plants (e.g., cattail [Typha spp.]); introducing more desirable species during the application of salvaged soil could reduce this probability. We believe incorporating salvaged-wetland soil during basin construction could be used to increase the value and productivity of created wetlands in this region.     

Increased ectomycorrhizal fungal abundance after long-term fertilization and warming of two arctic tundra ecosystems

Shrub abundance is expected to increase with enhanced temperature and nutrient availability in the Arctic, and associated changes in abundance of ectomycorrhizal (EM) fungi could be a key link between plant responses and longer-term changes in soil organic matter storage. This study quantifies the response in EM fungal abundance to long-term warming and fertilization in two arctic ecosystems with contrasting responses of the EM shrub Betula nana. Ergosterol was used as a biomarker for living fungal biomass in roots and organic soil and ingrowth bags were used to estimate EM mycelial production. We measured 15N and 13C natural abundance to identify the EM-saprotrophic divide in fungal sporocarps and to validate the EM origin of mycelia in the ingrowth bags. Fungal biomass in soil and EM mycelial production increased with fertilization at both tundra sites, and with warming at one site. This was caused partly by increased dominance of EM plants and partly by stimulation of EM mycelial growth. We conclude that cycling of carbon and nitrogen through EM fungi will increase when strongly nutrient-limited arctic ecosystems are exposed to a warmer and more nutrient-rich environment. This has potential consequences for below-ground litter quality and quantity, and for accumulation of organic matter in arctic soils.     

Irrigation and enhanced soil carbon input effects on below-ground carbon cycling in semiarid temperate grasslands

Global climate change is generally expected to increase net primary production, resulting in increased soil carbon (C) inputs. To gain an understanding of how such increased soil C inputs would affect C cycling in the vast grasslands of northern China, we conducted a field experiment in which the responses of plant and microbial biomass and respiration were studied. Our experiment included the below-ground addition of particulate organic matter (POM) at rates equivalent to 0, 60, 120 and 240 g C m(-2), under either natural precipitation or under enhanced precipitation during the summer period (as predicted for that region in recent simulations using general circulation models). We observed that addition of POM had a large effect on soil microbial biomass and activity and that a major part of the added C was rapidly lost from the system. This suggests that microbial activity in the vast temperate grassland ecosystems of northern China is energy-limited. Moreover, POM addition (and the associated nutrient release) affected plant growth much more than the additional water input. Although we performed no direct fertilization experiments, the response of plant productivity to POM addition (and associated release of nutrients) leads us to believe that plant productivity in the semiarid grassland ecosystems of northern China is primarily limited by nutrients and not by water.     

乌梁素海野生芦苇群落生物量及影响因子分析

 对内蒙古乌梁素海湿地野生芦苇(Phragmites australis)生物量的调查基础上,探讨了富营养化湖泊湿地水体的物理化学性质对芦苇生物量的影响。结果表明：1）由于环境因子的影响,芦苇群落生物量变化较大,介于1.73～3.00 kg·m-2之间;地下和地上生物量之比介于1.14～2.19之间;2）芦苇群落生物量受多种因素的影响,其中水深是最主要的限制因子,水上生物量和地上生物量随着水深的增加而增加,而地下与地上生物量的比值则随水深的增加而减少,这主要是由于水深改变了芦苇群落的结构（群落密度）和个体形态(株高和株茎);3）芦苇群落生物量随着水体N浓度增加而增加。芦苇各器官（叶、茎、根状茎和根）的N∶P为7.59～12.21,小于14,这也说明该水体中的N负荷是影响芦苇生长的主要限制因子;4）土壤有机质分解对芦苇生长没有产生毒害作用。     

Creating riverine wetlands: Ecological succession, nutrient retention, and pulsing effects

Successional patterns, water quality changes, and effects of hydrologic pulsing are documented for a whole-ecosystem experiment involving two created wetlands that have been subjected to continuous inflow of pumped river water for more than 10 years. At the beginning of the growing season in the first year of the experiment (1994), 2400 individuals representing 13 macrophyte species were introduced to one of the wetland basins. The other basin was an unplanted control. Patterns of succession are illustrated by macrophyte community diversity and net aboveground primary productivity, soil development, water quality changes, and nutrient retention for the two basins. The planted wetland continued to be more diverse in plant cover 10 years after planting and the unplanted wetland appeared to be more productive but more susceptible to stress. Soil color and organic content continued to change after wetland creation and wetlands had robust features of hydric soils within a few years of flooding. Organic matter content in surface soils in the wetlands increased by approximately 1% per 3-year period. Plant diversity and species differences led to some differences in the basins in macrophyte productivity, carbon sequestration, water quality changes and nutrient retention. The wetlands continued to retain nitrate–nitrogen and soluble reactive phosphorus 10 years after their creation. There are some signs that sediment and total phosphorus retention are diminishing after 10 years of river flow. Preliminary results from the beginnings of a flood pulsing experiment in the two basins in 2003–2004 are described for water quality, nutrient retention, aboveground productivity, and methane and nitrous oxide gaseous fluxes.     

Ecosystem Recovery Across a Chronosequence of Restored Wetlands in the Platte River Valley

Wet meadows in the Platte River valley (PRV) consist of linear wetlands in mesic prairie matrix systems that have been degraded and diminished for agriculture. Restoration in this region is a widespread practice that involves land contouring and seeding native species, however ecosystem recovery following restoration has never been examined. We quantified recovery trajectories and rates of above- and belowground plant biomass, soil physical and chemical properties, and C and N pools in a chronosequence of six restored wet meadows in relation to three natural wetlands. Within each site, we sampled sloughs (deeper habitats) and adjacent margins (slightly higher elevation) for three consecutive years. Varying hydrologic regimes between habitats resulted in differential patterns in ecosystem measurements (bulk density, C mineralization) in both natural and restored wetlands. Total aboveground biomass (TAB), root biomass, root C and N storage, total soil C and N, microbial N, and extractable N increased with years restored in both margins and sloughs. The model predicted rates of increase did not differ between habitats, but elevations of linear regressions were higher in sloughs than margins for root N, total soil C, total soil N, MBN, and extractable total N (P < 0.05). Our results suggest that bulk density and soil organic matter (SOM) represent two useful, easily measured indices of ecosystem recovery, because they were correlated with many pools and fluxes of C and N. Furthermore, we conclude that most change in ecosystem structure and function during the first decade following restoration occurs in shallow soil depths, and ecosystem recovery varies with subtle differences in elevation and associated plant community structure.     

Plant community composition as a driver of decomposition dynamics in riparian wetlands

Riparian wetlands are well known for providing the important ecosystem service of carbon storage. However, changes in land-use regimes surrounding riparian wetlands have been shown to result in alterations to the wetland plant community. These plant community changes have the potential to alter litter quality, decomposition rates, and ultimately the capacity of riparian wetlands to store carbon. To determine the effects of plant community shifts associated with disturbance on decomposition and carbon inputs, we performed a yearlong decomposition experiment using in situ herbaceous material, leaf litter, and control litter and examined biomass inputs in six headwater riparian wetlands in central Pennsylvania. Two sites were classified as Hemlock-Mixed Hardwood Palustrine Forest, two were classified as Broadleaf Palustrine Forest, and two were classified as Reed Canary Grass-Floodplain Grassland (Zimmerman et al. 2012). Plant matter with greater initial percent C, percent lignin, and lignin:N ratios decomposed more slowly while plant matter with greater initial cellulose decomposed more quickly. However, no significant differences were found between plant community types in decomposition rate or amount of carbon remaining at the end of the experiment, indicating that the differences in plant community type did not have a large impact on decomposition in riparian wetlands. This work has important implications for studies that examine the decomposition dynamics of a few select species, as they may not capture the decomposition dynamics of the plant community and thus extrapolating results from these studies to the larger ecosystem may be inappropriate.     

三江源地区不同建植期人工草地植被特征及其与土壤特征的关系

研究了三江源地区不同建植期人工草地群落生物量、物种组成、多样性指数和土壤理化特征,并用多元逐步回归分析法探讨了土壤理化特征对群落生物量、多样性变化的响应.结果表明:研究区不同建植期人工草地植物群落的种类组成、植物功能群组成和群落数量特征存在显著差异;土壤含水量随着物种多样性指数的增加而增加,土壤容重随着物种多样性的增加而减小;土壤微生物生物量碳与土壤含水量、土壤有机质呈极显著正相关,与土壤容重呈极显著负相关;土壤有机碳含量明显呈"V"字型变化,且与土壤含水量的变化趋势相一致,随土壤容重的增加而减少;群落生物量与土壤养分和土壤含水量之间呈显著正相关,群落地上、地下生物量的增加有利于提高土壤养分含量.     

Root Dynamics in Restored and Naturally Regenerated Atlantic White Cedar Wetlands

This work addressed the seasonal and successional factors of root dynamics in natural and restoration Atlantic white cedar (AWC) wetlands. Using minirhizotrons and soil root cores, fine root dynamics were measured in a chronosequence of reference and restoration AWC wetlands to compare trends in ecosystem development after canopy harvest. Seasonal fine root abundance, production, and mortality were sampled during a 439‐day period in one restoration and three reference AWC wetlands. Soil cores were collected to measure fine root biomass and to determine allometric relationships between root length and biomass. Significant seasonal variation of root dynamics was observed in the young reference and restoration sites. The mature and intermediate‐aged sites exhibited little seasonal variability in root abundance and mortality. Root production was variable but not seasonally consistent. Results suggest that root dynamics become less seasonal as AWC communities shift from herbaceous to woody vegetation dominance. No trend in fine root abundance along the chronosequence was observed, suggesting that roots rapidly reestablish following tree harvest. Measurements of annual root length production suggest increasing annual production with decreasing stand age. However, a reversal of this trend was observed when using production estimates calculated from minirhizotron measurements and root length–mass relationships. These findings underscore the importance of supplementing minirhizotron data with root allometric relationships when analyzing vegetation gradients. Overall, results indicate substantial differences in the form and quantity of root contributions to soil organic matter in the restoration site compared to that in the reference chronosequence. Higher initial planting densities of AWC are recommended to achieve similar contributions of roots to soil organic matter accumulation in the restoration site.     

Long- and short-term effects of fire on nitrogen cycling in tallgrass prairie

Fires in the tallgrass prairie are frequent and significantly alter nutrient cycling processes. We evaluated the short-term changes in plant production and microbial activity due to fire and the long-term consequences of annual burning on soil organic matter (SOM), plant production, and nutrient cycling using a combination of field, laboratory, and modeling studies. In the short-term, fire in the tallgrass prairie enhances microbial activity, increases both above-and belowground plant production, and increases nitrogen use efficiency (NUE). However, repeated annual burning results in greater inputs of lower quality plant residues causing a significant reduction in soil organic N, lower microbial biomass, lower N availability, and higher C:N ratios in SOM. Changes in amount and quality of below-ground inputs increased N immobilization and resulted in no net increases in N availability with burning. This response occurred rapidly (e.g., within two years) and persisted during 50 years of annual burning. Plant production at a long-term burned site was not adversely affected due to shifts in plant NUE and carbon allocation. Modeling results indicate that the tallgrass ecosystem responds to the combined changes in plant resource allocation and NUE. No single factor dominates the impact of fire on tallgrass plant production.     

Soil water content and patterns of allocation to below- and above-ground biomass in the sexes of the subdioecious plant Honckenya peploides

Background and aims Dioecious plants often show sex-specific differences in growth and biomass allocation. These differences have been explained as a consequence of the different reproductive functions performed by the sexes. Empirical evidence strongly supports a greater reproductive investment in females. Sex differences in allocation may determine the performance of each sex in different habitats and therefore might explain the spatial segregation of the sexes described in many dimorphic plants. Here, an investigation was made of the sexual dimorphism in seasonal patterns of biomass allocation in the subdioecious perennial herb Honckenya peploides, a species that grows in embryo dunes (i.e. the youngest coastal dune formation) and displays spatial segregation of the sexes at the studied site. The water content in the soil of the male- and female-plant habitats at different times throughout the season was also examined. Methods The seasonal patterns of soil-water availability and biomass allocation were compared in two consecutive years in male and female H. peploides plants by collecting soil and plant samples in natural populations. Vertical profiles of below-ground biomass and water content were studied by sampling soil in male- and female-plant habitats at different soil depths. Key Results The sexes of H. peploides differed in their seasonal patterns of biomass allocation to reproduction. Males invested twice as much in reproduction than females early in the season, but sexual differences became reversed as the season progressed. No differences were found in above-ground biomass between the sexes, but the allocation of biomass to below-ground structures varied differently in depth for males and females, with females usually having greater below-ground biomass than males. In addition, male and female plants of H. peploides had different water-content profiles in the soil where they were growing and, when differences existed (usually in the upper layers of the soil), the water content of the soil was higher for the female plants had than for the male plants. Conclusions Sex-differential timing of investment in reproduction and differential availability and use of resources from the soil (particularly water) are factors that probably offset the costs of reproduction in the above-ground growth in males and females of H. peploides. The results suggest that the patterns of spatial segregation of the sexes observed in H. peploides may contribute to maximize each sex's growth and reproduction.     

A simulation model of organic matter and nutrient accumulation in mangrove wetland soils

The distribution and accumulation of organic matter, nitrogen (N) and phosphorus (P) in mangrove soils at four sites along the Shark River estuary of south Florida were investigated with empirical measures and a process-based model. The mangrove nutrient model (NUMAN) was developed from the SEMIDEC marsh organic matter model and parameterized with data from mangrove wetlands. The soil characteristics in the four mangrove sites varied greatly in both concentrations and profiles of soil carbon, N and P. Organic matter decreased from 82% in the upstream locations to 30% in the marine sites. Comparisons of simulated and observed results demonstrated that landscape gradients of soil characteristics along the estuary can be adequately modeled by accounting for plant production, litter decomposition and export, and allochthonous input of mineral sediments. Model sensitivity analyses suggest that root production has a more significant effect on soil composition than litter fall. Model simulations showed that the greatest change in organic matter, N, and P occurred from the soil surface to 5 cm depth. The rapid decomposition of labile organic matter was responsible for this decrease in organic matter. Simulated N mineralization rates decreased quickly with depth, which corresponded with the decrease of labile organic matter. The increase in organic matter content and decrease in soil bulk density from mangrove sites at downstream locations compared to those at upstream locations was controlled mainly by variation in allochthonous inputs of mineral matter at the mouth of the estuary, along with gradients in mangrove root production. Research on allochthonouns sediment input and in situ root production of mangroves is limited compared to their significance to understanding nutrient biogeochemistry of these wetlands. More accurate simulations of temporal patterns of nutrient characteristics with depth will depend on including the effects of disturbance such as hurricanes on sediment redistribution and biomass production.     

Restoration of vegetation communities of created depressional marshes in Ohio and Colorado (USA): The importance of initial effort for mitigation success

Many studies have attempted to assess the ability of created wetlands to replace the ecological structure and functions of natural wetlands over short time periods (<5 years). Few studies have repeatedly monitored vegetative community development of created depressional wetlands over longer time frames or assessed the return on the level of initial restoration efforts. Here, the vegetation communities of 17 created freshwater marshes in two different geographic regions of the U.S., Ohio and Colorado, ranging from 5 to 19 years old, were monitored over multiple years and compared to natural reference sites. Findings suggest that created marshes in Ohio achieved floristic equivalency with natural reference sites for measures of plant species richness, number of native plant species, number of hydrophytes, and percent plant cover within a decade. Yet, created marshes in Ohio contained double the amount of non-native plant species observed in natural reference sites. In Colorado, created marshes were less successful, failing to achieve floristic equivalency for plant species richness, number of native plant species, and number and percent hydrophytes given more than a decade of restoration. Soil chemistry data suggest that although created marshes achieve certain hydric soil characteristics, they were significantly lower in organic matter, cation exchange capacity, and extractable phosphorus than natural wetlands. Equivalency for soil chemistry will require longer time periods (>14 years). Data suggest that created marshes that seem to be approaching floristic equivalency in early years following construction may level off or even dramatically decline over longer time periods (10–20 years) for certain floristic indicators. Restoration trajectories for Ohio created marshes with strong initial restoration efforts predict floristic equivalency in a median of 14 years compared to 24 years for sites with weak initial efforts. Created marshes with strong initial restoration efforts displayed significantly greater plant species richness, number of native plant species, and number of hydrophytes than sites with low initial efforts, indicating the importance of planting, soil transport and/or contouring in establishing a wetland's restoration trajectory.     

Plant community,primary productivity,and environmental conditions following wetland re-establishment in the Sacramento-San Joaquin Delta,California

Wetland restoration can mitigate aerobic decomposition of subsided organic soils, as well as re-establish conditions favorable for carbon storage. Rates of carbon storage result from the balance of inputs and losses, both of which are affected by wetland hydrology. We followed the effect of water depth (25 and 55 cm) on the plant community, primary production, and changes in two re-established wetlands in the Sacramento San-Joaquin River Delta, California for 9 years after flooding to determine how relatively small differences in water depth affect carbon storage rates over time. To estimate annual carbon inputs, plant species cover, standing above- and below-ground plant biomass, and annual biomass turnover rates were measured, and allometric biomass models for Schoenoplectus (Scirpus) acutus and Typha spp., the emergent marsh dominants, were developed. As the wetlands developed, environmental factors, including water temperature, depth, and pH were measured. Emergent marsh vegetation colonized the shallow wetland more rapidly than the deeper wetland. This is important to potential carbon storage because emergent marsh vegetation is more productive, and less labile, than submerged and floating vegetation. Primary production of emergent marsh vegetation ranged from 1.3 to 3.2 kg of carbon per square meter annually; and, mid-season standing live biomass represented about half of the annual primary production. Changes in species composition occurred in both submerged and emergent plant communities as the wetlands matured. Water depth, temperature, and pH were lower in areas with emergent marsh vegetation compared to submerged vegetation, all of which, in turn, can affect carbon cycling and storage rates.