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.     

Periphyton chemistry and nitrogenase activity in a northern Everglades ecosystem

Cyanobacterial peri­phyton communities are a dominant feature of oligotrophic Everglades marshes, however, little is known regarding the biogeochemical aspects of this ecosystem component. This study was undertaken to investigate the potential for N₂ fixation in the peri­phyton communities of a hydrologically-controlled portion of the northern Everglades marsh (Water Conservation Area 2A, WCA-2A). The objectives of this research were to characterize the temporal patterns of nutrient composition and N₂ fixation of the natural WCA-2A peri­phyton communities and to compare fixation rates of peri­phyton with those of other ecosystem components in both natural and nutrient-impacted WCA-2A areas. In general, N₂ fixation (measured by the acetylene reduction (AR) method) of natural WCA-2A peri­phyton was enhanced under light conditions showing a nitrogenase pattern characteristic of autotrophic cyanobacteria. Winter (November–March) rates of AR expressed per gram organic carbon (gOC) ranged from 147–240 nmol C₂H₂ g OC^–1 h^–1, while summer rates were elevated with an observed peak of 1148 nmol C₂H₂ g OC^–1 h^–1 in July 1998. This translates into an estimated yearly contribution of approximately 10 g N m^–2 to an unimpacted WCA-2A slough ecosystem. Nitrogenase activity did not correlate seasonally with nutrients (Ca, Mg, Fe, N, P, Mn), but closely followed measured N stable isotopic ratios (¹⁵N) in floating peri­phyton. In oligotrophic marsh areas, AR (on a weight basis) decreased in the order floating peri­phyton > benthic peri­phyton floc > soil > water > detrital plant biomass, while highest AR rates were observed for detrital biomass in areas impacted by agricultural discharges.     

Phosphorus budgets in Everglades wetland ecosystems: the effects of hydrology and nutrient enrichment

The Florida Everglades is a naturally oligotrophic hydroscape that has experienced large changes in ecosystem structure and function as the result of increased anthropogenic phosphorus (P) loading and hydrologic changes. We present whole-ecosystem models of P cycling for Everglades wetlands with differing hydrology and P enrichment with the goal of synthesizing existing information into ecosystem P budgets. Budgets were developed for deeper water oligotrophic wet prairie/slough (‘Slough’), shallower water oligotrophic Cladium jamaicense (‘Cladium’), partially enriched C. jamaicense/Typha spp. mixture (‘Cladium/Typha’), and enriched Typha spp. (‘Typha’) marshes. The majority of ecosystem P was stored in the soil in all four ecosystem types, with the flocculent detrital organic matter (floc) layer at the bottom of the water column storing the next largest proportion of ecosystem P pools. However, most P cycling involved ecosystem components in the water column (periphyton, floc, and consumers) in deeper water, oligotrophic Slough marsh. Fluxes of P associated with macrophytes were more important in the shallower water, oligotrophic Cladium marsh. The two oligotrophic ecosystem types had similar total ecosystem P stocks and cycling rates, and low rates of P cycling associated with soils. Phosphorus flux rates cannot be estimated for ecosystem components residing in the water column in Cladium/Typha or Typha marshes due to insufficient data. Enrichment caused a large increase in the importance of macrophytes to P cycling in Everglades wetlands. The flux of P from soil to the water column, via roots to live aboveground tissues to macrophyte detritus, increased from 0.03 and 0.2 g P m⁻² yr⁻¹ in oligotrophic Slough and Cladium marsh, respectively, to 1.1 g P m⁻² yr⁻¹ in partially enriched Cladium/Typha, and 1.6 g P m⁻² yr⁻¹ in enriched Typha marsh. This macrophyte translocation P flux represents a large source of internal eutrophication to surface waters in P-enriched areas of the Everglades.     

Spatial and seasonal patterns of periphyton biomass and productivity in the northern Everglades,Florida, U.S.A.

We sampled periphyton in dominant habitats at oligotrophic and eutrophic sites in the northern Everglades during the wet and the dryseasons to determine the effects of nutrient enrichment on periphytonbiomass, taxonomic composition, productivity, and phosphorus storage. Arealbiomass was high (100–1600 g ash-free dry mass [AFDM]m⁻²) in oligotrophic sloughs and in stands of the emergentmacrophyte Eleocharis cellulosa, but was low in adjacent stands of sawgrass,Cladium jamaicense (7–52 g AFDM m⁻²). Epipelon biomasswas high throughout the year at oligotrophic sites whereas epiphyton andmetaphyton biomass varied seasonally and peaked during the wet season.Periphyton biomass was low (3–68 g AFDM m⁻²) and limitedto epiphyton and metaphyton in open-water habitats at eutrophic sites andwas undetectable in cattail stands (Typha domingensis) that covered morethan 90% of the marsh in these areas. Oligotrophic periphytonassemblages exhibited strong seasonal shifts in species composition and weredominated by cyanobacteria (e.g., Chroococcus turgidus, Scytonema hofmannii)during the wet season and diatoms (e.g. Amphora lineolata, Mastogloiasmithii) during the dry season. Eutrophic assemblages were dominated byCyanobacteria (e.g., Oscillatoria princeps) and green algae (e.g., Spirogyraspp.) and exhibited comparatively little seasonality. Biomass-specific grossprimary productivity (GPP) of periphyton assemblages in eutrophic openwaters was higher than for comparable slough assemblages, but areal GPP wassimilar in these eutrophic (0.9–9.1 g C m⁻²d⁻¹) and oligotrophic (1.75–11.49 g C m⁻²d⁻¹) habitats. On a habitat-weighted basis, areal periphytonGPP was 6- to 30-fold lower in eutrophic areas of the marsh due to extensiveTypha stands that were devoid of periphyton. Periphyton at eutrophic siteshad higher P content and uptake rates than the oligotrophic assemblage, butstored only 5% as much P because of the lower areal biomass.Eutrophication in the Everglades has resulted in a decrease in periphytonbiomass and its contribution to marsh primary productivity. These changesmay have important implications for efforts to manage this wetland in asustainable manner. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of hydrologic and water quality drivers on periphyton dynamics in the southern Everglades

Everglades periphyton mats are tightly-coupled autotrophic (algae and cyanobacteria) and heterotrophic (eubacteria, fungi and microinvertebrates) microbial assemblages. We investigated the effect of water column total phosphorus and nitrogen concentrations, water depth and hydroperiod on periphyton of net production, respiration, nutrient content, and biomass. Our study sites were located along four transects that extended southward with freshwater sheetflow through sawgrass-dominated marsh. The water source for two of the transects were canal-driven and anchored at canal inputs. The two other transects were rain-driven (ombrotrophic) and began in sawgrass-dominated marsh. Periphyton dynamics were examined for upstream and downstream effects within and across the four transects. Although all study sites were characterized as short hydroperiod and phosphorus-limited oligotrophic, they represent gradients of hydrologic regime, water source and water quality of the southern Everglades. Average periphyton net production of 1.08 mg C AFDW⁻¹ h⁻¹ and periphyton whole system respiration of 0.38 mg C AFDW⁻¹ h⁻¹ rates were net autotrophic. Biomass was generally highest at ombrotrophic sites and sites downstream of canal inputs. Mean biomass over all our study sites was high, 1517.30 g AFDW m⁻². Periphyton was phosphorus-limited. Average periphyton total phosphorus content was 137.15 μg P g⁻¹ and average periphyton total N:P ratio was 192:1. Periphyton N:P was a sensitive indicator of water source. Even at extremely low mean water total phosphorus concentrations ( ≤ 0.21 μmol l⁻¹), we found canal source effects on periphyton dynamics at sites adjacent to canal inputs, but not downstream of inflows. These canal source effects were most pronounced at the onset of wet season with initial rewetting. Spatial and temporal variability in periphyton dynamics could not solely be ascribed to water quality, but was often associated with both hydrology and water source.     

Growth and allocation by a keystone wetland plant, <Emphasis Type="Italic">Panicum hemitomon</Emphasis>, and implications for managing and rehabilitating coastal freshwater marshes,Louisiana, USA

This paper attempts to establish linkages between growth by a keystone wetland plant, Panicum hemitomon Schultes, and the independent and interactive effect of nutrient and hydrologic regime to inform management and rehabilitation of thick-mat floating marsh (TMFM). To do so a manipulative glasshouse experiment employing created TMFM similar to that under consideration for field trials and two levels each of N, P and hydrology was conducted. P. hemitomon grew vigorously under saturated (flooding level with the surface of the mat) when compared to inundated (+15 cm flooding) hydrologic conditions, and under enriched (50 g m⁻² year⁻¹) when compared to non-enriched (25 g m⁻² year⁻¹) N. Further, and as inferred from net CO₂ assimilation, shoot biomass and rhizome biomass and length, N-enriched conditions seemed to lessen inundation stress. For all variables the interaction between N and hydrology was non-significant and there was no observable effect of P. We were unable to infer root or mat buoyancy from root specific gravity measurements but it was evident at harvest that saturation or minimal flooding is required for vigorous root and rhizome growth. This study provides insight to the notion that decreased mat buoyancy (and increased flooding level) resulting from sediment deposition associated with Mississippi River diversions could adversely affect TMFM sustainability, but more clearly demonstrates the need to maintain saturated hydrologic conditions for achieving the type of root and rhizome growth we feel is required for TMFM rehabilitation.     

Litter Decomposition and Nutrient Dynamics in a Phosphorus Enriched Everglades Marsh

A field study was conducted in a nutrient-impacted marsh in Water Conservation Area 2A (WCA-2A) of the Everglades in southern Florida, USA, to evaluate early stages of plant litter (detritus) decomposition along a well-documented trophic gradient, and to determine the relative importance of environmental factors and substrate composition in governing decomposition rate. Vertically stratified decomposition chambers containing native plant litter (cattail and sawgrass leaves) were placed in the soil and water column along a 10-km transect coinciding with a gradient of soil phosphorus (P) enrichment. Decomposition rate varied significantly along the vertical water–soil profile, with rates typically higher in the water column and litter layer than below the soil surface, presumably in response to vertical gradients of such environmental factors as O₂ and nutrient availability. An overall decrease in decomposition rate occurred along the soil P gradient (from high- to low-impact). First-order rate constant (k) values for decomposition ranged from 1.0 to 9.2 × 10⁻³ day⁻¹ (mean = 2.8 ×10⁻³ day⁻¹) for cattails, and from 6.7 × 10⁻⁴ to 3.0 ×  10⁻³ day⁻¹ (mean = 1.7 ×  10⁻³ day⁻¹) for sawgrass. Substantial N and P immobilization occurred within the litter layer, being most pronounced at nutrient-impacted sites. Nutrient content of the decomposing plant tissue was more strongly correlated to decomposition rate than was the nutrient content of the surrounding soil and water. Our experimental results suggest that, although decomposition rate was significantly affected by initial substrate composition, the external supply or availability of nutrients probably played a greater role in controlling decomposition rate. It was also evident that nutrient availability for litter decomposition was not accurately reflected by ambient nutrient concentration, e.g., water and soil porewater nutrient concentration.     

Spatial and temporal patterns of aboveground net primary productivity (ANPP) along two freshwater-estuarine transects in the Florida Coastal Everglades

We present here a 4-year dataset (2001–2004) on the spatial and temporal patterns of aboveground net primary production (ANPP) by dominant primary producers (sawgrass, periphyton, mangroves, and seagrasses) along two transects in the oligotrophic Florida Everglades coastal landscape. The 17 sites of the Florida Coastal Everglades Long Term Ecological Research (FCE LTER) program are located along fresh-estuarine gradients in Shark River Slough (SRS) and Taylor River/C-111/Florida Bay (TS/Ph) basins that drain the western and southern Everglades, respectively. Within the SRS basin, sawgrass and periphyton ANPP did not differ significantly among sites but mangrove ANPP was highest at the site nearest the Gulf of Mexico. In the southern Everglades transect, there was a productivity peak in sawgrass and periphyton at the upper estuarine ecotone within Taylor River but no trends were observed in the C-111 Basin for either primary producer. Over the 4 years, average sawgrass ANPP in both basins ranged from 255 to 606 g m⁻² year⁻¹. Average periphyton productivity at SRS and TS/Ph was 17–68 g C m⁻² year⁻¹ and 342–10371 g C m⁻² year⁻¹, respectively. Mangrove productivity ranged from 340 g m⁻² year⁻¹ at Taylor River to 2208 g m⁻² year⁻¹ at the lower estuarine Shark River site. Average Thalassia testudinum productivity ranged from 91 to 396 g m⁻² year⁻¹ and was 4-fold greater at the site nearest the Gulf of Mexico than in eastern Florida Bay. There were no differences in periphyton productivity at Florida Bay. Interannual comparisons revealed no significant differences within each primary producer at either SRS or TS/Ph with the exception of sawgrass at SRS and the C−111 Basin. Future research will address difficulties in assessing and comparing ANPP of different primary producers along gradients as well as the significance of belowground production to the total productivity of this ecosystem.     

Estimation of periphytic microalgae gross primary production with DCMU-fluorescence method in Yenisei River (Siberia, Russia)

Periphyton (epilithon) gross primary production (GPP) was estimated using the DCMU-fluorescence method in the Yenisei River. In the unshaded littoral zone, chlorophyll a concentration (Chl a) and GPP value varied from 0.83 to 973.74 mg m⁻²and 2–304,425 O₂ m⁻² day⁻¹ (0.64–95 133 mg C m⁻² day⁻¹), respectively. Positive significant correlation (r = 0.8) between daily GPP and periphyton Chl a was found. Average ratio GPP:Chl a for periphyton was 36.36 mg C mg Chl a m⁻² day⁻¹. The obtained GPP values for the Yenisei River have a high significant correlation with values predicted by a conventional empirical model for stream periphyton. We concluded that the DCMU-fluorescence method can be successfully used for measuring of gross primary production of stream phytoperiphyton at least as another useful tool for such studies.     

Interactions between nutrient availability and hydroperiod shape macroinvertebrate communities in Florida Everglades marshes

Hydroperiod and nutrient status are known to influence aquatic communities in wetlands, but their joint effects are not well explored. I sampled floating periphyton mat and flocculent detritus (floc) infaunal communities using 6-cm diameter cores at short- and long-hydroperiod and constantly inundated sites across a range of phosphorus (P) availability (total phosphorus in soil, floc and periphyton). Differences in community structure between periphyton and floc microhabitats were greater than any variation attributable to hydroperiod, P availability, or other spatial factors. Multivariate analyses indicated community structure of benthic-floc infauna was driven by hydroperiod, although crowding (no. g⁻¹ AFDM) of individual taxa showed no consistent responses to hydroperiod or P availability. In contrast, community structure of periphyton mat infauna was driven by P availability, while densities of mat infauna (no. m⁻²) were most influenced by hydroperiod (+correlations). Crowding of mat infauna increased significantly with P availability in short-hydroperiod marshes, but was constant across the P gradient in long-hydroperiod marshes. Increased abundance of floating-periphyton mat infauna with P availability at short-hydroperiod sites may result from a release from predation by small fish. Community structure and density were not different between long-hydroperiod and constantly inundated sites. These results have implications for the use of macroinvertebrates as indicators of water quality in wetlands and suggest the substrate sampled can influence interpretation of ecological responses observed in these communities.     

Periphyton biomass,potential production and respiration in a shallow lake during winter and spring

Abundance, depth distribution, potential productivity and respiration of periphyton on short-time (1 month) and long-time incubated strips were followed monthly during the winter–spring (January–May) transition in a shallow eutrophic lake. A taxonomic shift occurred from dominance of diatoms under ice to chlorophyte dominance in spring communities on the long-time incubated strips, while diatoms dominated until May on the short-time incubated strips. Periphyton biomass accrual was low during the ice-covered winter months (November–January: 4 mg chl a m⁻² month⁻¹), but increased to a maximum of 112 mg chl a m⁻² month⁻¹ immediately after ice-out in February. During February–April, the biomass remained constant before declining in May. Periphyton on long-time incubated strips was equally distributed in the water column in winter (January–February), but was higher near the water surface in spring (March–May). Periphyton did not change with depth on the short-time incubated strips. The potential production to respiration ratio (P/R) was negatively correlated with periphyton biomass. Throughout the study, P/R was <1 for the short-time incubated periphyton, while this was only the case in March–April for the long-time incubations. This study showed a high productive capacity of winter periphyton, resulting in accumulation of a relatively high periphytic biomass early in the season. A massive periphyton density in eutrophic lakes already in winter–spring may potentially delay or prevent the establishment and re-occurrence of submerged macrophytes in the early oligotrophication phase following a reduction of the external nutrient loading. Handling editor: Luigi Naselli-Flores     

Seasonal nutrient fluxes variability of northern salt marshes: examples from the lower St. Lawrence Estuary

This study presents the tidal exchange of ammonium, nitrite + nitrate, phosphate and silicate between two salt marshes and adjacent estuarine waters. Marsh nutrient fluxes were evaluated for Pointe-au-Père and Pointe-aux-épinettes salt marshes, both located along the south shore of the lower St. Lawrence Estuary in Rimouski area (QC, Canada). Using nutrients field data, high precision bathymetric records and a hydrodynamic numerical model (MIKE21-NHD) forced with predicted tides, nutrients fluxes were estimated through salt marsh outlet cross-sections at four different periods of the year 2004 (March, May, July and November). Calculated marsh nutrient fluxes are discussed in relation with stream inputs, biotic and abiotic marsh processes and the incidence of sea ice cover. In both marshes, the results show the occurrence of year-round and seaward NH₄ ⁺ fluxes and landward NO₂ ⁻ + NO₃ ⁻ fluxes (ranging from 9.06 to 30.48 mg N day⁻¹ m⁻² and from −32.07 to −9.59 mg N day⁻¹ m⁻², respectively) as well as variable PO₄ ³⁻ and Si(OH)₄ fluxes (ranging from −3.73 to 6.34 mg P day⁻¹ m⁻² and from −29.19 to 21.91 mg Si day⁻¹ m⁻², respectively). These results suggest that NO₂ ⁻ + NO₃ ⁻ input to marshes can be a significant source of NH₄ ⁺ through dissimilatory nitrate reduction to ammonium (DNRA). This NH₄ ⁺, accumulating in marsh sediment rather than being removed through coupled nitrification–denitrification or biological assimilation, is exported toward estuarine waters. From average P and Si tidal fluxes analysis, both salt marshes act as a sink during high productivity period (May and July) and as a source, supplying estuarine water during low productivity period (November and March).     

Impact of altitudinal gradients on energetics and efficiencies of N<Subscript>2</Subscript>-fixation in alder–cardamom agroforestry systems of the eastern Himalayas

The impact of altitudinal gradients on the performance of alder–cardamom agroforestry systems was analyzed on nitrogenase activity, N₂-fixation efficiency, and stand energetics and efficiencies in the eastern Himalayas. Acetylene reduction (AR activity) measurements showed that nitrogenase activity considerably increased with advancing altitudes from 500 to 800 m to a peak at 900–1,200 m. AR activity was fairly high, between 1,300 and 1,700 m, and sharply decreased in the stands between 1,800 and 2,100 m. AR activity increased in the growing season and peaked in the rainy season. This significantly coincided with cardamom flowering during the onset of growing season to full fruiting stage at peak activity period. AR activity was dependent on soil temperature and moisture and showed a positive relationship. Nodule moisture was also a limiting factor for AR activity and showed a positive correlation. Diurnal changes showed a marked variation with highest AR activity between 8 and 12 h. The performance of commercial cardamom crop is dependent on the associated shade trees. Yield potential significantly coincided with the rate of N₂-fixation both at age chronosequence and altitudinal gradients. The management comprises growing large number of alder until 10 years and thinning, and gap filling of cardamom up to 20 years. Such maintenance caused non-equilibrium conditions that favored systems efficiency and excellent production until 20 years. System efficiency sharply declined at low rates of N₂-fixation, AR activity, root nodule production, and agronomic yield due to the influence of stand age and altitudinal gradients. Agroforestry stands at 900–1,700 m were more energy cost-effective due to the lower energy required for per-kg N-fixation with high N supply (115–155 kg ha⁻¹) confirming functionally efficient than those stands at extreme higher and lower altitudinal ranges. Therefore, replantation of alder and cardamom and phase wise agroforestry rotation after 20 years could be an ecologically and economically sustainable management practice.     

Phosphatase activity as an early warning indicator of wetland eutrophication: problems and prospects

A phosphorus (P) loading experiment conducted in the oligotrophic P-limited Everglades was used to assess the utility of phosphatase activity (PA) of periphyton as an early warning (EW) indicator of wetland eutrophication. Phosphorus loads of 0, 0.4, 0.8, 1.6, 3.2, 6.4 and 12.8 g P m^–2 yr^–1 were applied to mesocosms placed in a slough community consisting of Cladium jamaicense Crantz, Eleocharis spp. and calcareous periphyton mats. Phosphatase activity, expressed on a biomass-specific basis, was not a sensitive indicator of P enrichment for epiphytic periphyton growing on acrylic dowels or floating mat periphyton. However, surface-area-specific PA was a sensitive indicator of P enrichment, responding within 2–3 weeks of the initiation of dosing. Surface-area-specific PA of unenriched periphyton ranged from 0.42 to 0.7 nmol cm^–2 min^–1, while PA of periphyton growing in the highest load (12.8 g P m^–2 yr^–1), ranged from 0.11 to 0.29 nmol cm^–2 min^–1. Conclusions drawn from PA analyses were consistent with those obtained from periphyton primary productivity and P content. Phosphatase activity is a potentially valuable EW indicator when used in conjunction with other complementary indicators.     

Variation in soil phosphorus, sulfur, and iron pools among south Florida wetlands

To determine relationships between soil nutrient status and known gradients in primary production, we collected and analyzed soils from 17 LTER sampling sites along two transects through south Florida wetland ecosystems. Through upstream freshwater marsh, a middle reach including the oligohaline marsh/mangrove ecotone, and downstream estuarine habitats, we observed systematic variation in soil bulk density, organic content, and pools of phosphorus (P), inorganic sulfur, and extractable iron. Consistent with observed differences in wetland productivity known to be limited by P availability, total P averaged ~200 μg g dw⁻¹ in soils from the eastern Taylor Slough/Panhandle and was on average three times higher in soils from the western Shark River Slough. Along both transects, the largest pool of phosphorus was the inorganic, carbonate-bound fraction, comprising 35–44% of total P. Greater than 90% of the total inorganic sulfur pool in these south Florida wetland soils was extracted as pyrite. Freshwater marsh sites typically were lower in pyrite sulfur (0.2–0.8 mg g dw⁻¹) relative to marsh/mangrove ecotone and downstream estuary sites (0.5–2.9 mg g dw⁻¹). Extractable iron in freshwater marsh soils was significantly higher from the Taylor Slough/Panhandle transect (3.2 mg g dw⁻¹) relative to the western Shark River Slough transect (1.1 mg g dw⁻¹), suggesting spatial variation in sources and/or depositional environments for iron. Further, these soil characteristics represent the collective, integrated signal of ecosystem structure, so any long-term changes in factors like water flow or water quality may be reflected in changes in bulk soil properties. Since the objective of current Everglades restoration initiatives is the enhancement and re-distribution of freshwater flows through the south Florida landscape, the antecedent soil conditions reported here provide a baseline against which future, post-restoration measurements can be compared.     

Effects of NO2? and NO3? on the Fe(III)EDTA reduction in a chemical absorption–biological reduction integrated NOx removal system

The biological reduction of Fe(III) ethylenediaminetetraacetic acid (EDTA) is a key step for NO removal in a chemical absorption–biological reduction integrated process. Since typical flue gas contain oxygen, NO₂ ⁻ and NO₃ ⁻ would be present in the absorption solution after NO absorption. In this paper, the interaction of NO₂ ⁻, NO₃ ⁻, and Fe(III)EDTA reduction was investigated. The experimental results indicate that the Fe(III)EDTA reduction rate decrease with the increase of NO₂ ⁻ or NO₃ ⁻ addition. In the presence of 10 mM NO₂ ⁻ or NO₃ ⁻, the average reduction rate of Fe(III)EDTA during the first 6-h reaction was 0.076 and 0.17 mM h⁻¹, respectively, compared with 1.07 mM h⁻¹ in the absence of NO₂ ⁻ and NO₃ ⁻. Fe(III)EDTA and either NO₂ ⁻ or NO₃ ⁻ reduction occurred simultaneously. Interestingly, the reduction rate of NO₂ ⁻ or NO₃ ⁻ was enhanced in presence of Fe(III)EDTA. The inhibition patterns observed during the effect of NO₂ ⁻ and NO₃ ⁻ on the Fe(III)EDTA reduction experiments suggest that Escherichia coli can utilize NO₂ ⁻, NO₃ ⁻, and Fe(III)EDTA as terminal electron acceptors.     

Litter decomposition promotes differential feedbacks in an oligotrophic southern Everglades wetland

The differential accumulation or loss of carbon and nutrients during decomposition can promote differentiation of wetland ecosystems, and contribute to landscape-scale heterogeneity. Tree islands are important ecosystems because they increase ecological heterogeneity in the Everglades landscape and in many tropical landscapes. Only slight differences in elevation due to peat accumulation allow the differentiation of these systems from the adjacent marsh. Hydrologic restoration of the Everglades landscape is currently underway, and increased nutrient supply that could occur with reintroduction of freshwater flow may alter these differentiation processes. In this study, we established a landscape-scale, ecosystem-level experiment to examine litter decomposition responses to increased freshwater flow in nine tree islands and adjacent marsh sites in the southern Everglades. We utilized a standard litterbag technique to quantify changes in mass loss, decay rates, and phosphorus (P), nitrogen (N) and carbon (C) dynamics of a common litter type, cocoplum (Chrysobalanus icaco L.) leaf litter over 64 weeks. Average C. icaco leaf degradation rates in tree islands were among the lowest reported for wetland ecosystems (0.23 ± 0.03 yr⁻¹). We found lower mass loss and decay rates but higher absolute mass C, N, and P in tree islands as compared to marsh ecosystems after 64 weeks. With increased freshwater flow, we found generally greater mass loss and significantly higher P concentrations in decomposing leaf litter of tree island and marsh sites. Overall, litter accumulated N and P when decomposing in tree islands, and released P when decomposing in the marsh. However, under conditions of increased freshwater flow, tree islands accumulated more P while the marsh accumulated P rather than mineralizing P. In tree islands, water level explained significant variation in P concentration and N:P molar ratio in leaf tissue. Absolute P mass increased strongly with total P load in tree islands (r ² = 0.81). In the marsh, we found strong, positive relationships with flow rate. Simultaneous C and P accumulation in tree island and mineralization in adjacent marsh ecosystems via leaf litter decomposition promotes landscape differentiation in this oligotrophic Everglades wetland. However, results of this study suggest that variation in flow rates, water levels and TP loads can shift differential P accumulation and loss leading to unidirectional processes among heterogeneous wetland ecosystems. Under sustained high P loading that could occur with increased freshwater flow, tree islands may shift to litter mineralization, further degrading landscape heterogeneity in this system, and signaling an altered ecosystem state.     

Iron interference in the quantification of nitrate in soil extracts and its effect on hypothesized abiotic immobilization of nitrate

Human alteration of the nitrogen cycle has stimulated research on nitrogen cycling in many aquatic and terrestrial ecosystems, where analyses of nitrate (NO₃ ⁻) by standard laboratory methods are common. A recent study by Colman et al. (Biogeochemistry 84:161–169, 2007) identified a potential analytical interference of soluble iron (Fe) with NO₃ ⁻ quantification by standard flow-injection analysis of soil extracts, and suggested that this interference may have led Dail et al. (Biogeochemistry 54:131–146, 2001) to make an erroneous assessment of abiotic nitrate immobilization in prior ¹⁵N pool dilution studies of Harvard Forest soils. In this paper, we reproduce the Fe interference problem systematically and show that it is likely related to dissolved, complexed-Fe interfering with the colorimetric analysis of NO₂ ⁻. We also show how standard additions of NO₃ ⁻ and NO₂ ⁻ to soil extracts at native dissolved Fe concentrations reveal when the Fe interference problem occurs, and permit the assessment of its significance for past, present, and future analyses. We demonstrate low soluble Fe concentrations and good recovery of standard additions of NO₃ ⁻ and NO₂ ⁻ in extracts of sterilized Harvard Forest soils. Hence, we maintain that rapid NO₃ ⁻ immobilization occurred in sterilized samples of the Harvard Forest O horizon in the study by Dail et al. (2001). Furthermore, additional evidence is accumulating in the literature for rapid disappearance of NO₃ ⁻ added to soils, suggesting that our observations were not the result of an isolated analytical artifact. The conditions for NO₃ ⁻ reduction are likely to be highly dependent on microsite properties, both in situ and in the laboratory. The so-called “ferrous wheel hypothesis” (Davidson et al., Glob Chang Biol 9:228–236, 2003) remains an unproven, viable explanation for published observations.     

Comparative study of periphyton community structure in long and short-hydroperiod Everglades marshes

The Florida Everglades is a mosaic of short and long-hydroperiod marshes that differ in the depth, duration, and timing of inundation. Algae are important primary producers in widespread Everglades’ periphyton mats, but relationships of algal production and community structure to hydrologic variability are poorly understood. We quantified differences in algal biomass and community structure between periphyton mats in 5 short and 6 long-hydroperiod marshes in Everglades National Park (ENP) in October 2000. We related differences to water depth and total phosphorus (TP) concentration in the water, periphyton and soils. Long and short-hydroperiod marshes differed in water depth (73 cm vs. 13 cm), periphyton TP concentrations (172μg g⁻¹ vs. 107 μg g⁻¹, respectively) and soil TP (284 μg g⁻¹ vs. 145 μg g⁻¹). Periphyton was abundant in both marshes, with short-hydroperiod sites having greater biomass than long-hydroperiod sites (2936 vs. 575 grams ash-free dry mass m⁻²). A total of 156 algal taxa were identified and separated into diatom (68 species from 21 genera) and “soft algae” (88 non-diatom species from 47 genera) categories for further analyses. Although diatom total abundance was greater in long-hydroperiod mats, diatom species richness was significantly greater in short- hydroperiod periphyton mats (62 vs. 47 diatom taxa). Soft algal species richness was greater in long-hydroperiod sites (81 vs. 67 soft algae taxa). Relative abundances of individual taxa were significantly different among the two site types, with soft algal distributions being driven by water depth, and diatom distributions by water depth and TP concentration in the water and periphyton. Periphyton communities differ between short and long-hydroperiod marshes, but because they share many taxa, alterations in hydroperiod could rapidly promote the alternate community. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

Induction of H2-Uptake and Nitrogenase Activities in the Cyanobacterium Anabaena variabilis ATCC 29413: Effects of Hydrogen and Organic Substrate

A comparative study of the development of uptake hydrogenase and nitrogenase activities in cells of the cyanobacterium Anabaena variabilis was performed. The induction of heterocysts is followed by the induction of both in vivo hydrogen uptake and nitrogenase activities. Interestingly, a low but significant H₂-uptake [2–7 μmoles of H₂ · mg⁻¹ (Chl a) · h⁻¹] occurs in cultures with no heterocysts and with no nitrogenase activity. A slight stimulatory effect (30–40%) of H₂ on in vivo H₂-uptake was observed during the early stages of nitrogenase induction. However, exogenous H₂ does not further stimulate the induction of in vivo hydrogen uptake observed during heterocyst differentiation. Similarly, organic carbon (fructose) did not influence the induction of either in vivo hydrogen uptake or nitrogenase activities. Exogenous fructose supports higher in vivo hydrogen uptake and nitrogenase activities when the cells enter late exponential phase of growth. Received: 22 November 1995 / Accepted: 22 December 1995