Freshwater Marsh Research Articles

Effects of Saltwater Pulses on Soil Microbial Enzymes and Organic Matter Breakdown in Freshwater and Brackish Coastal Wetlands

Coastal freshwater and brackish wetlands are exposed to pulses of saltwater during times of reduced freshwater flows (i.e., dry seasons, droughts), periodic storm surges, and increased tidal extent associated with rising seas. The effects of saltwater pulses on belowground processing rates of detrital organic matter as mediated by microbial activities are uncertain. Our objectives were to quantify whether and how pulses of saltwater (i) change soil porewater physicochemistry, (ii) change soil microbial extracellular enzyme activities, and (iii) change root litter breakdown over time in freshwater and brackish marshes. From 2014 to 2016, we simulated saltwater intrusion as monthly in situ pulsed additions of artificial seawater in experimental dosing chambers (1.4 m diameter) within freshwater and brackish marshes of Everglades National Park. At monthly intervals, we collected soil porewater chemistry, and measured microbial extracellular enzymes, elemental stoichiometric ratios, and breakdown rates (k) of incubated (0–30 cm depth) root litter and compared these responses over time. Saltwater pulses increased sulfate and nitrogen concentrations in porewater at the freshwater site. However, saltwater pulses generally decreased porewater constituents (e.g., dissolved organic carbon, dissolved nitrogen and phosphorus species) at the brackish site. One saltwater pulse increased root litter k by 1.25-fold in the brackish marsh. However, long-term (740 days) k in brackish wetlands, and both short- and long-term k in freshwater wetlands, were not affected by 24 monthly pulses of saltwater. Enzyme activities fluctuated with time and did not respond to multiple saltwater pulses. Our results suggest that detrital organic matter stocks and associated soil microbial activities are relatively resistant to single and multiple (n = 24) pulses of saltwater.

Global change—Local values: Assessing tradeoffs for coastal ecosystem services in the face of sea level rise

Anthropogenic climate change poses a significant threat to Texas’ coastal habitats and in the Galveston Bay region, there is just under 1200 square miles of freshwater marsh and undeveloped dry upland. These habitats provide residents with a variety of key ecosystem services but are threatened by global climate change. Effective management of these resources requires multidisciplinary knowledge, combining an understanding of the potential biophysical habitat alterations associated with sea level rise with the measurement of residents’ value for coastal resources. In this study, we utilize a discrete choice experiment to investigate individuals’ preferences for future conditions of Texas habitats within the Galveston Bay region. Utilizing modeled output for coverage of freshwater marsh and undeveloped dry upland in the year 2050, respondents are asked to make trade-offs between coastal conditions with no further management actions and outcomes associated with specific management interventions. From this framework, we estimate Galveston Bay regional residents’ value for freshwater marshes and undeveloped uplands. Our results indicate that individuals are willing to conserve habitat under threat from sea level rise, but that they are likely unaware of the dynamic nature of that change. As a result, residents may place less emphasis on the role of the habitat migration in response to sea level rise.

Patrones de distribución y estructura de la vegetación en el gradiente de humedales costeros El Castaño, Chiapas, México

Introduction: The characteristics of coastal wetlands are the result of hydrogeomorphological interactions between the continent and the ocean, which cause an environmental gradient, hat results in different vegetation types such as mangroves, freshwater marshes, swamp forests and palm swamps. Objective: To characterize the hydroperiod and physicochemical variables of water and soil and their effect on the distribution of vegetation in the Sistema de Humedales El Castaño. Methods: A total of 11 permanent sampling units (UM) were established by defined strata: five in the mangrove, two in swamp forest, two in freshwater marshes and two in the flooded pasture. From May 2016 to October 2017 the vegetation was characterized and the water levels and physicochemical parameters (superficial, interstitial and groundwater) were sampled monthly for: salinity, and pH; and the soil for: bulk density, humidity percentage, and redox potential. Results: Mangroves are the closest to the sea, have the lowest diversity (H: 1.66) and species richness (14), they are dominated by Laguncularia racemosa and Rhizophora mangle, have the highest values of interstitial and groundwater salinity, (> 10.8 ups), remain flooded for 4 to 12 months per year, and have a redox potential of 14.57 mV. Immediately, inland, there are remnants of the swamp forests (H: 2.18 and 18 species), dominated by Pachira aquatica, with 5 ups interstitial and groundwater salinity, flooded from 0 to 6 months per year, with a redox potential of 119.07 mV. These forests are followed inland by freshwater marshes (H: 1.92 and 16 species), dominated by Typha domingensis with 6.1 ups interstitial and groundwater salinity, flooded for 5 to 8 months per year and a redox potential of 125.9 mV. Finally, furthest inland is the flooded pasture, a modified herbaceous wetland for cattle grazing (H: 3.44 and 50 species) dominated by Paspalum conjugatum, where interstitial and groundwater salinity is less than 0.5 ups, it stays flooded for 5 to 9 months and the redox potential is 151.23 mV. Conclusions: In each type of vegetation, the structure, composition, and diversity are different, with a high turnover of species that indicates a gradient defined by salinity. The vegetation in the SHC follows the patterns of typical organization of the tropical coastal wetlands, mangroves, swamp forests and herbaceous wetlands, in this case the freshwater marshes and flooded pastures. The factor that define the distribution of the vegetation is the salinity and the gradient that is observed are a function of the hydrological dynamics that depends on the mixing of marine and freshwater.

Increasing Rates of Carbon Burial in Southwest Florida Coastal Wetlands

AbstractRates of organic carbon (OC) burial in some coastal wetlands appear to be greater in recent years than they were in the past. Possible explanations include ongoing mineralization of older OC or the influence of an unaccounted‐for artifact of the methods used to measure burial rates. Alternatively, the trend may represent real acceleration in OC burial. We quantified OC burial rates of mangrove and coastal freshwater marshes in southwest Florida through a comparison of rates derived from 210Pb, 137Cs, and surface marker horizons. Age/depth profiles of lignin: OC were used to assess whether down‐core remineralization had depleted the OC pool relative to lignin, and lignin phenols were used to quantify the variability of lignin degradation. Over the past 120 years, OC burial rates at seven sites increased by factors ranging from 1.4 to 6.2. We propose that these increases represent net acceleration. Change in relative sea‐level rise is the most likely large‐scale driver of acceleration, and sediment deposition from large storms can contribute to periodic increases. Mangrove sites had higher OC and lignin burial rates than marsh sites, indicating inherent differences in OC burial factors between the two habitat types. The higher OC burial rates in mangrove soils mean that their encroachment into coastal freshwater marshes has the potential to increase burial rates in those locations even more than might be expected from the acceleration trends. Regionally, these findings suggest that burial represents a substantially growing proportion of the coastal wetland carbon budget.

Carbon Accumulation in Freshwater Marsh Soils: a Synthesis for Temperate North America

Freshwater marshes are prevalent in North America, yet their soil carbon stocks remain poorly quantified. To better understand these stocks, and rates of carbon accumulation over short and long timescales, we synthesize available data on soil properties and rates of carbon accumulation in freshwater marshes in the temperate region of North America. Our findings suggest that freshwater marshes are not defined consistently, and that wetland classification schemes may undervalue presumed carbon stocks in freshwater marsh soils. Rates of carbon accumulation in freshwater marshes are often measured over recent time scales (last 50–100 years); these short-term rates are on average (± SD) 155 ± 74 g C m−2 yr−1 in temperate North America. Long-term rates of carbon accumulation (measured over centuries and millennia) are on average 51 ± 38 g C m−2 yr−1 yet infrequently measured. Our synthesis of rates of carbon accumulation and vertical accretion, bulk densities, and organic carbon contents suggests that freshwater marshes are accumulating carbon at comparable rates to salt marshes over short timescales and temperate peatlands over longer timescales. These timescales need to be clearly defined in order to improve estimates of the capacity for freshwater marshes to be net carbon sinks presently and in the future.

Soil Shear Strength Losses in Two Fresh Marshes with Variable Increases in N and P Loading

We measured soil shear strength (SSS) from 2009 to 2018 in two hydrologically distinct freshwater marshes dominated by Panicum hemitomon after nitrogen (N) and phosphorous (P) were applied to the surface in spring. The SSS averaged over 100-cm depth in the floating and anchored marshes declined up to 30% throughout the profiles and with no apparent differences in the effects of the low, medium, and high N + P dosing. Plots with only N or P additions exhibited significant changes in SSS at individual depths below 40 cm for the anchored marsh, but not the floating marsh. The average SSS for the anchored marsh over the entire 100 cm profile declined when N and P were added separately or together. At the floating marsh, however, the SSS decreased when N and P were added in combination, or P alone, but not for the N addition. Increasing nutrient availability to these freshwater marsh soils makes them weaker, and perhaps lost if eroded or uplifted by buoyant forces during storms. These results are consistent with results from multi-year experiments demonstrating higher decomposition rates, greenhouse gas emissions, and carbon losses in wetlands following increased nutrient availability.

Effects of 10 yr of nitrogen and phosphorus fertilization on carbon and nutrient cycling in a tidal freshwater marsh.

Tidal freshwater marshes can protect downstream ecosystems from eutrophication by intercepting excess nutrient loads, but recent studies in salt marshes suggest nutrient loading compromises their structural and functional integrity. Here, we present data on changes in plant biomass, microbial biomass and activity, and soil chemistry from plots in a tidal freshwater marsh on the Altamaha River (GA) fertilized for 10 yr with nitrogen (+N), phosphorus (+P), or nitrogen and phosphorus (+NP). Nitrogen alone doubled aboveground biomass and enhanced microbial activity, specifically rates of potential nitrification, denitrification, and methane production measured in laboratory incubations. Phosphorus alone increased soil P and doubled microbial biomass but did not affect microbial processes. Nitrogen or P alone decreased belowground biomass and soil carbon (C) whereas +NP increased aboveground biomass, microbial biomass and N cycling, and N, P, and C assimilation and burial more than either nutrient alone. Our findings suggest differential nutrient limitation of tidal freshwater macrophytes by N and microbes by P, similar to what has been observed in salt marshes. Macrophytes outcompete microbes for P in response to long-term N and P additions, leading to increased soil C storage through increased inputs of belowground biomass relative to N and P added singly. The susceptibility of tidal freshwater marshes to long-term nutrient enrichment and, hence their ability to mitigate eutrophication will depend on the quantity and relative proportion of N vs. P entering estuaries and tidal wetlands.

Chronic nitrogen addition promotes dissolved organic carbon accumulation in a temperate freshwater wetland

Temperate wetlands have been undergoing increased nitrogen (N) inputs in the past decades, yet its influence on dissolved organic carbon (DOC) dynamics is still elusive in these ecosystems. Here, using a field multi-level N addition (0, 6, 12, and 24 g N m−2 year−1) experiment, we investigated the changes in aboveground plant biomass, DOC production from plant litters, DOC biodegradation, and DOC concentration in surface water and soil pore water (0–15 cm depth) following 10 years of N addition in a freshwater marsh of Northeast China. We observed that, irrespective of N addition levels, N addition caused an increase in DOC production from plant litters under both non-flooded and flooded conditions. Conversely, DOC biodegradation was inhibited by N addition in both surface water and soil pore water. Because of enhanced DOC production from plant litters and declined DOC biodegradation, N addition elevated DOC concentration in surface water and soil pore water across the growing season. In addition, long-term N addition increased aboveground plant biomass, but decreased species richness. Our results suggest that long-term N enrichment promotes DOC accumulation through the contrasting effects on litter-derived DOC production and microbial decomposition of DOC in temperate wetlands.

Effects of Tidal Channels and Roads on Landscape Dynamic Distribution in the Yellow River Delta, China

Landscape characters in estuarine regions generally controlled by tidal regimes and human activities like road construction. In this work, tidal channels and road construction in the Yellow River Delta (YRD) were extracted by visual interpretation methods so as to decipher impacts of tidal channel development and road construction on landscape patch change during 1989–2016. Spatial distribution history of three wetlands, which covered by Phragmites australis (freshwater marsh, FM), Suaeda salsa (salt marsh, SM), and mudflats (MD) were also established. Results indicated that tidal channel, number, frequency, and fractal dimension were all the maximum in 2003, and the minimum in 1998, respectively. Road length, number, and density showed increasing trend during 1989–2016. MD were the predominant landscape type, followed by FM and SM during 1989–2016. Principal component analysis implied two extracted factors, F1 and F2, which could represent 91.93% of the total variations. F1 mainly proxied tidal channel development, while F2 represented road construction. A multiple linear regression analysis showed positive effects of both F1 and F2 on FM patch numbers and negative impacts on SM patch areaes with R2 values of 0.416 and 0.599, respectively. Tidal channels were negatively related to MD patch numbers, while roads were positively related to that. In any case, road construction showed larger impacts on landscape type shifting than that of tidal channel development in the YRD.

Palaeovegetation and palaeoclimate evolution during the Late Miocene to Early Pliocene of SE Romania

Fossil microfloral assemblages from five sedimentary successions of the Dacian Basin (Eastern Paratethys) are used to reconstruct the palaeovegetation and palaeoclimate of SE Romania during the Late Miocene to Early Pliocene (regional stages Khersonian, Meotian, Pontian, and Dacian). The studied microfloras were deposited under brackish to freshwater conditions in a fairly distal area of the Dacian Basin and are interpreted to reflect changes in the terrestrial ecosystems at a regional scale. The results show that the vegetation dynamic of the area was driven by the interplay of palaeogeographical and climatic changes. Broadleaved deciduous trees characteristic of temperate climatic regimes and a variety of gymnosperms dominated the vegetation during the Khersonian and the Meotian. This type of vegetation underwent a gradual decline throughout the studied time span, probably associated with a long‐term cooling and drying trend. Thermophilous taxa were virtually absent in the area, with the exception of Engelhardia and Taxodioideae, which probably inhabited lowland swamp forests. The effect of an arid phase, which had its acme during the late Khersonian and extended, in an attenuated mode, during the earliest Meotian, is reflected in the palynological assemblages. This event resulted in the development of a xeric flora including Ephedra and Lygeum. The latter genus is cited for the first time in the Neogene flora of the Eastern Paratethys. Although mesic herbaceous taxa generally occur in low numbers throughout the successions, its signal becomes more relevant in the Pontian, suggesting drier conditions favourable for open ecosystems to develop. During the Dacian substage, the transition from brackish to freshwater settings in the basin favoured the development of shallow, freshwater marshes and led to the spread of a diverse hygrophytic flora. At the same time, a significant increase in Celtis pollen is interpreted to represent increased seasonality of precipitation.

Willow-shrub encroachment affects physicochemical properties differently in two subtropical freshwater marshes

Shrub encroachment has been increasing at unprecedented rates worldwide and a knowledge gap exists regarding how nutrient dynamics differ in shrub-encroached wetlands compared to marshes. This study evaluated physicochemical property differences in the soil, water, and vegetation of willow (Salix caroliniana) plots, marsh plots adjacent to willows, and control marsh plots in two wetlands within the St. John’s River watershed, FL. In both wetlands, Moccasin Island and Lake Apopka, willow leaves (484 ± 7 g kg−1) contained more carbon (C) than sawgrass (442 ± 3 g kg−1) and cattail (468 ± 4 g kg−1) leaves. At Moccasin Island, soil nutrient (C, nitrogen, phosphorous) concentrations were doubled in willow and adjacent plots compared to marsh plots, while 37% less soil C was observed in willow plots than marsh plots at Lake Apopka. These results demonstrate willow-encroached marshes have unique properties relative to non-encroached marshes, but the direction and magnitude of the differences are site-specific.

Response of tidal marsh vegetation to pulsed increases in flooding and nitrogen

Worldwide, human activities have modified hydrology and nutrient loading regimes in coastal wetlands. Understanding the interplay between these drivers and subsequent response of wetland plant communities is essential to informing wetland management and restoration efforts. Recent restoration strategies in Louisiana proposes to use sediment diversions from the Mississippi River to build land in adjacent wetlands and reduce the rate of land to open water conversion. In conjunction with sediment delivery, diversions can increase nutrient loads and water levels in the receiving basins. We conducted a greenhouse mesocosm experiment in which we exposed three common tidal freshwater and brackish marsh plants (Panicum hemitomon, Sagittaria lancifolia, and Spartina patens) to two nitrate loading rates [high (35 g N m2 year−1) and low (0.25 g N m2 year−1)], and two flooding treatments (with and without diversion pulsing). Experimental units were set at two different elevations within the treatment tanks to simulate both a healthy and degraded marsh. Plant growth metrics and soil physicochemical properties were measured monthly. Final total biomass was determined at the study’s conclusion. Growth responses differed between species but were not significantly influenced by the treatments. Soil redox potential decreased significantly following the increase in flooding associated with the diversion pulse, but recovered to pre-diversion levels after a 3-month recovery period. Our study suggests short flooding pulses with a recovery period may be key for maintaining healthy marshes, however there remains a need for longer-term empirical studies to understand marsh response to pressures associated with river sediment diversions over time.

Ecological succession and resilience of plankton recovering from an acute disturbance in freshwater marshes

The increase in extreme events such as storms is one of the major threats that coastal ecosystems will have to face in the near future. In such a context, both maturation and ecological successions processes remain at the core of ecology to better anticipate the changes to ecosystem biodiversity and functions facing environmental stressors. However, these concepts are mainly approached through closed experimental studies that oversimplify the mechanisms. A survey was carried out on a ‘natural’ and open ecosystem subjected to an acute disturbance, i.e. a marine submersion of freshwater drained marshes, occurring after a storm. Plankton biomass, production and taxonomic/functional phytoplankton diversity were followed weekly at four stations over 2 months. Most of the stations were disrupted by this acute disturbance and displayed gradual growth and development, as described in the classical maturation process. The main differences between stations were attributed to the heterogeneity of the communities before the storm, the intensity of the disturbance and the different human actions performed to recover the freshwater environment. The concept of ‘ecological resilience’ was thus better suited than ‘engineering resilience’ for such open systems facing constant fluctuations in environmental drivers. With regard to ecological succession, the more impacted stations were marked by a significant change in taxonomic beta-diversity, with numerous stochastic processes, due to taxa dispersion. They first exhibited a convergence in functional traits due to the increase in nutrient availability drained from the catchment basin and then an increase in divergence when nutrients became limited.

A global‐scale analysis of water storage dynamics of inland wetlands: Quantifying the impacts of human water use and man‐made reservoirs as well as the unavoidable and avoidable impacts of climate change

AbstractWetlands such as bogs, swamps, or freshwater marshes are hotspots of biodiversity. For 5.1 million km2 of inland wetlands, the dynamics of area and water storage, which strongly impact biodiversity and ecosystem services, were simulated using the global hydrological model WaterGAP. For the first time, the impacts of both human water use and man‐made reservoirs (WUR) and future climate change (CC) on wetlands around the globe were quantified. WUR impacts are concentrated in arid/semiarid regions, where WUR decreased mean wetland water storage by more than 5% on 8.2% of the mean wetland area during 1986–2005 (Am), with highest decreases in groundwater depletion area. Using output of three climate models, CC impacts on wetlands were quantified, distinguishing unavoidable impacts [i.e., at 2 °C global warming (GW)] from avoidable impacts (difference between 3 °C and 2 °C impacts). Even unavoidable CC impacts are projected to be much larger than WUR impacts, also in arid/semiarid regions. On most wetland area with reliable estimates, avoidable CC impacts are more than twice as large as unavoidable impacts. In case of 2 °C GW, half of Am is estimated to be unaffected by mean storage changes of more than 5%, but only one third in case of 3 °C GW. Temporal variability of water storage will increase for most wetlands. Wetlands in dry regions will be affected the most, particularly by water storage decreases in the dry season. Different from wealthier countries, low‐income countries will dominantly suffer from a decrease in wetland water storage due to CC.

Effect of Increasing Tidewater Inundation on Porewater Geochemistries and CO2 and CH4 Effluxes in the Tidal Freshwater Marshes of the Minjiang River Estuary, Southeast China

While the effect of increasing tidewater inundation caused by sea-level rise on carbon cycling had been well studied in saltmarshes, little is known about the effect of increasing tidewater inundation on CO2 and CH4 effluxes in the tidal freshwater marsh soils. Herein, the effects of tide inundation on porewater geochemistries (NH4+, NO3-, DOC, dissolved CH4, and DIC) and CH4 and CO2 effluxes were examined in the soils of tidal freshwater marshes in the Minjiang River Estuary, East China Sea. By applying "mesocosm" and a simulated tide pool, the tide inundation height increased by 15 cm and 30 cm over the control (CK). The CO2 effluxes decreased by 28.53% and 36.56%, and the dissolved CH4 concentrations increased by 47.83% and 73.91%, in treatments (CK+15 cm) and (CK+30 cm), respectively. The CH4 effluxes did not change significantly in the treatment (CK+15 cm), but increased by 29.27% in treatment (CK+30 cm). The increasing tidewater inundation had no significant impact on DOC concentrations, but increased NH4+ concentrations and decreased DIC and NO3- concentrations. Increasing tide inundation also reduced the temperature sensitivity of CH4 and CO2 effluxes. The study highlighted that the sea level rise-induced increase in tidewater inundation would decrease the annual global warming potential of tidal freshwater wetlands by 28% and 35% in the next 50 and 100 years, respectively.

Depositional environmental controls on the genesis and characteristics of oil shale: Case study of the Middle Jurassic Shimengou Formation, northern Qaidam Basin, north‐west China

Two different types of oil shales (OSs) from the Middle Jurassic Shimengou Formation on the northern margin of the Qaidam Basin, north‐west China, provide a valuable opportunity to study the factors controlling the genesis of oil shales. This study presents the sedimentary characteristics of various types of oil shales from the Shimengou Formation and then discusses their possible genesis based on a comprehensive analysis on drillcores. The Shimengou Formation comprises a lower coal‐bearing member (J2sh1) and an upper shale member (J2sh2). The J2sh1 OS unit is composed of dark grey thin‐layered shales interbedded with coal seams, with total organic carbon (TOC) content of 18.8–34.1 wt.% (averagely 21.5 wt.%), and belonging to type II2 organic matter. The J2sh2 OS unit consists of dark grey to grey‐brown thick‐bedded shales and mudstone. The J2sh2 OS has a moderate abundance in organic matter, TOC contents of 6.3–11.5 wt.% (averagely 9.59 wt.%), and types I and II1 organic matters. During the deposition of the J2sh1 member, both braided river delta and freshwater–marsh facies dominate the succession, and OS developed in shallow lakes and swamps. Soon after, the depositional environment changed rapidly. Plentiful terrestrial and shallow water aquatic plants provided abundant organic matter for the sedimentation of OS and also promoted the formation of thinly‐bedded, high‐quality OS with type II2 organic matter. The frequent changes in depositional environments facilitated the formation of thin layers of oil shale. During the sedimentation of the J2sh2 member, in similar tectonic settings, the stable warm–humid climate makes the lake water deeper than before, and the oil shale was deposited mainly in a relatively deep lake. This led to a reduced supply of terrestrial organic matter, which came mainly from lake algae, leading to the formation of OS with a large, uniform thickness and the presence of types I and II2 organic matter.

Evidence for trait‐based community assembly patterns in hardwood hammock forests

AbstractThe hardwood forests of south Florida, commonly referred to as hammocks, persist as well‐drained patches of broadleaf forest, embedded in a matrix of brackish water swamp, freshwater marsh, or pineland. Little is known about the patterns of community assembly of these subtropical forest communities in the landscape mosaic of south Florida. We used a functional trait approach to understand the composition of these communities and their responses to environmental variation across four areas of south Florida: the pine rocklands and freshwater marshes in Everglades National Park, and the lower and upper Florida Keys, where the hammocks are surrounded by halophytic swamp communities. These sites represent an environmental gradient from less‐productive, more xeric sites in the lower Florida Keys, to more‐productive, wetter sites in the Everglades marshes. We examined the patterns of trait variation at three levels (individual, population, and community) to examine the underlying processes driving assembly in these hammock communities. To understand processes governing community composition in each site, we used methods that partition variance in six traits (maximum tree height, specific leaf area, wood specific gravity, leaf nitrogen, leaf phosphorus, and leaf stable carbon isotope ratios) into internal and external filtering components. Community‐weighted mean trait values for three traits (specific leaf area, height, and leaf phosphorus) increased significantly from dry, less‐productive coastal sites in the Florida Keys to the moist, more‐productive areas on the mainland, while wood specific gravity and leaf δ13C showed the opposite pattern. For one or more traits per site, standardized effect sizes differed significantly from null expectation. Processes such as competition for resources (e.g., water, nutrients, light) and species sorting across microhabitats (i.e., within site) operate to increase local functional trait variation within communities and among species across sites. External filtering on individuals for height and leaf phosphorus differed significantly from null expectations across sites, while external filtering on species was only observed for specific leaf area, maximum tree height, and leaf phosphorus. These results are consistent with strong environmental filtering across the region, among local communities differing in freshwater accessibility or that occupy different positions along strong edaphic gradients. Our results confirm the importance of intraspecific variation among species and reflect a high degree of trait plasticity across the environmental gradient.

FLUXNET-CH4 Synthesis Activity: Objectives, Observations, and Future Directions

AbstractThis paper describes the formation of, and initial results for, a new FLUXNET coordination network for ecosystem-scale methane (CH4) measurements at 60 sites globally, organized by the Global Carbon Project in partnership with other initiatives and regional flux tower networks. The objectives of the effort are presented along with an overview of the coverage of eddy covariance (EC) CH4 flux measurements globally, initial results comparing CH4 fluxes across the sites, and future research directions and needs. Annual estimates of net CH4 fluxes across sites ranged from −0.2 ± 0.02 g C m–2 yr–1 for an upland forest site to 114.9 ± 13.4 g C m–2 yr–1 for an estuarine freshwater marsh, with fluxes exceeding 40 g C m–2 yr–1 at multiple sites. Average annual soil and air temperatures were found to be the strongest predictor of annual CH4 flux across wetland sites globally. Water table position was positively correlated with annual CH4 emissions, although only for wetland sites that were not consistently inundated throughout the year. The ratio of annual CH4 fluxes to ecosystem respiration increased significantly with mean site temperature. Uncertainties in annual CH4 estimates due to gap-filling and random errors were on average ±1.6 g C m–2 yr–1 at 95% confidence, with the relative error decreasing exponentially with increasing flux magnitude across sites. Through the analysis and synthesis of a growing EC CH4 flux database, the controls on ecosystem CH4 fluxes can be better understood, used to inform and validate Earth system models, and reconcile differences between land surface model- and atmospheric-based estimates of CH4 emissions.

Responses of leaf nitrogen and phosphorus allocation patterns to nutrient additions in a temperate freshwater wetland

Abstract Temperate wetlands have been experienced increased nitrogen (N) and phosphorus (P) loadings, but how plant N and P fractions respond to nutrient enrichments and its role in driving vegetation dynamics remain elusive in these ecosystems. Here, we used a 3-year N (6.0 g N m−2 year−1) and P (1.2 g P m−2 year−1) addition experiment to investigate the effects of nutrient enrichment on aboveground plant biomass, leaf N, P, structural N (NS), non-structural N (NNS), inorganic P (PI), and organic P (PO) concentrations of five common species belonging to two growth forms (grass and sedge) in a freshwater marsh, Northeast China. Our results showed that, although leaf N and P concentrations increased with respective nutrient additions, the responses of aboveground plant biomass and leaf nutrient allocation patterns to nutrient enrichments were idiosyncratic. Specifically, N addition simultaneously increased leaf NNS:NN ratio and aboveground biomass of grass species (Deyeuxia angustifolia and Glyceria spiculosa), while P addition increased leaf PI:PO ratio and aboveground biomass of sedge species (Carex meyeriana, C. lasiocarpa, and C. humida). This indicated that the species-specific responses of leaf nutrient fractions to N and P addition may explain the altered vegetation structure in this wetland. Our findings suggest that leaf nutrient fractions are more reliable than total nutrient concentrations to indicate the adaptative strategies of wetland plants to nutrient enrichments, and highlight that the shifts in leaf N and P allocation patterns would be a potential tool to predict the effect of nutrient enrichments on vegetation dynamics in temperate wetlands.

Green Infrastructure as a Solution to Hydrological Problems: Bioswales and Created Wetlands

Green infrastructure is an ecological landscaping method that was first theorized in a 1994 Floridian report titled Creating a Statewide Greenways System, which was presented to the governor at the time, Lawton Chiles (Florida Greenways Commission, MacKay, & Reed 1994). As defined by the European Commission, green infrastructure is “a strategically planned network of natural and semi-natural areas with other environmental features designed and managed to deliver a wide range of ecosystem services” (Communication from The Commission to The European Parliament, 2013, p. 3). This paper will examine two green infrastructure strategies – bioswales and created wetlands – which are crucial in solving some of the water problems that Florida faces. Bioswales are engineered green spaces that collect runoff and remove harmful pollutants from the stormwater before it is discharged into surface water sources. This paper will examine how bioswales function. Besides polluted storm water, the other major water problem is eutrophication. Created wetlands are effective ecological tools for mitigating eutrophication, which is the result of excessive nutrients in water bodies that cause algal blooms and subsequently suffocate other organisms in the water by depleting oxygen. Freedom Park in Naples, Florida is composed of four created freshwater marshes, which filter runoff and reduce heavy metals and nutrients in the stormwater before it enters the Gordon River. This paper examines Freedom Park in Naples, Florida to assess how created wetlands can assist in reducing nutrient loads, mitigating pollutants in stormwater before it enters natural waterways, and restore habitat.