Non-flooded Conditions Research Articles

Temperature, water content and wet–dry cycle effects on DOC production and carbon mineralization in agricultural peat soils

Agricultural peat soils in the Sacramento-San Joaquin Delta, California have been identified as an important source of dissolved organic carbon (DOC) and trihalomethane precursors in waters exported for drinking. The objectives of this study were to examine the primary sources of DOC from soil profiles (surface vs. subsurface), factors (temperature, soil water content and wet–dry cycles) controlling DOC production, and the relationship between C mineralization and DOC concentration in cultivated peat soils. Surface and subsurface peat soils were incubated for 60 d under a range of temperature (10, 20, and 30 °C) and soil water contents (0.3–10.0 g-water g-soil −1). Both CO 2–C and DOC were monitored during the incubation period. Results showed that significant amount of DOC was produced only in the surface soil under constantly flooded conditions or flooding/non-flooding cycles. The DOC production was independent of temperature and soil water content under non-flooded condition, although CO 2 evolution was highly correlated with these parameters. Aromatic carbon and hydrophobic acid contents in surface DOC were increased with wetter incubation treatments. In addition, positive linear correlations ( r 2=0.87) between CO 2–C mineralization rate and DOC concentration were observed in the surface soil, but negative linear correlations ( r 2=0.70) were observed in the subsurface soil. Results imply that mineralization of soil organic carbon by microbes prevailed in the subsurface soil. A conceptual model using a kinetic approach is proposed to describe the relationships between CO 2–C mineralization rate and DOC concentration in these soils.

Water-level fluctuations affect macrophyte richness in floodplain lakes

The characteristic ecology of floodplain lakes is in part due to their relatively strong water-level fluctuations. We analyzed the factors determining water-level fluctuations in 100 floodplain lakes (during non-flooded conditions) in the active floodplains of the Lower Rhine in the Netherlands. Furthermore, we explored the relationship between water-level fluctuations and macrophyte species richness, and analyzed the suitability of artificially created lakes for macrophyte vegetation. During non-flooded conditions along the Rhine, lake water-level fluctuations are largely driven by groundwater connection to the river. Hence, water-level fluctuations are largest in lakes close to the main channel in strongly fluctuating sectors of the river and smallest in isolated lakes. Additionally, water-level fluctuations are usually small in old lakes, mainly due to reduced groundwater hydraulic conductivity resulting from accumulated clay and silt on the bottom. Species richness of floating-leaved and emergent macrophytes was reduced at both small and large water-level fluctuations, whereas species richness of submerged macrophytes was reduced at small water-level fluctuations only. In addition, species richness of submerged macrophytes was higher in lakes that experienced drawdown, whereas no similar pattern was detected for floating-leaved and emergent macrophytes. The decline in amplitude of lake water-level with lake age implies that the number of hydrologically dynamic lakes will decrease over time. Therefore, we suggest that excavation of new lakes is essential to conserve the successional sequence of floodplain water bodies including conditions of high biodiversity. Shallow, moderately isolated, lakes with occasional bottom exposure have the highest potential for creating macrophyte-rich floodplain lakes along large lowland rivers. The water-level regime of such lakes can in part be designed, through choice of the location along the river, the distance away from the river and the depth profile of the lake.

Soil seed banks of two montane riparian areas: implications for restoration

Understanding the role of seed banks can be important for designing restoration projects. Using the seedling emergence method, we investigated the soil seed banks of two montane, deciduous riparian forest ecosystems of southeastern Arizona. We contrasted the seed banks and extant vegetation of Ramsey Canyon, which is the site of riparian restoration activities, with that of Garden Canyon, which has been less affected by human land uses. Fewer plant species were found at Ramsey Canyon than Garden Canyon, for both the seed bank and extant vegetation, and the vegetation at Ramsey Canyon (seed bank and extant) had consistently drier wetland indicator scores. As well, vegetation patterns within sampling zones (channel margins and adjacent riparian forests) differed between canyons. At Garden Canyon channel margins, the seed bank and extant vegetation had relatively high similarity, with herbaceous wetland perennial species dominating. Extant vegetation in the floodplain riparian forest zone at Garden Canyon had a drier wetland indicator score than the seed bank, suggesting that the floodplains are storing seeds dispersed from wetter fluvial surfaces. Vegetation patterns for Ramsey Canyon channel margins were similar to those for Garden Canyon floodplains. Vegetation patterns in the Ramsey Canyon riparian forest zone were indicative of non-flooded conditions with an abundance of upland species in the soil seed bank and extant vegetation. Channel geomorphology measurements indicated that much of the riparian forest zone at Ramsey Canyon is functionally a terrace, a condition that may be a legacy of channel erosion from historic land uses. Steep, erodible channel slopes may contribute to the low seed bank germinant density at Ramsey Canyon channel margins, and narrower flood-prone area may explain the greater terrestrialization of the vegetation in both sampling zones. We recommend testing the use of donor soils from more diverse stream reaches to restore biodiversity levels at Ramsey Canyon, following restoration activities such as channel-widening. Seed banks from Garden Canyon, for example, although predominantly consisting of herbaceous perennials, would supply species with a range of moisture tolerances, life spans, and growth forms. We also recommend that restorationists take care not to harm seed banks exposed during removal of introduced species; at Ramsey Canyon, soil seed banks were equally diverse in areas with high and low cover of the introduced Vinca major (a legacy of Ramsey Canyon land use).

Zinc mobility and speciation in soil covered by contaminated dredged sediment using micrometer-scale and bulk-averaging X-ray fluorescence, absorption and diffraction techniques

The mobility and solid-state speciation of zinc in a pseudogley soil (pH = 8.2–8.3) before and after contamination by land-disposition of a dredged sediment ([Zn] = 6600 mg kg −1) affected by smelter operations were studied in a 50 m 2 pilot-scale test site and the laboratory using state-of-the-art synchrotron-based techniques. Sediment disposition on land caused the migration of micrometer-sized, smelter-related, sphalerite (ZnS) and franklinite (ZnFe 2O 4) grains and dissolved Zn from the sediment downwards to a soil depth of 20 cm over a period of 18 months. Gravitational movement of fine-grained metal contaminants probably occurred continuously, while peaks of Zn leaching were observed in the summer when the oxidative dissolution of ZnS was favored by non-flooding conditions. The Zn concentration in the <50 μm soil fraction increased from ∼61 ppm to ∼94 ppm in the first 12 months at 0–10 cm depth, and to ∼269 ppm in the first 15 months following the sediment deposition. Higher Zn concentrations and enrichments were observed in the fine (<2 μm) and very fine (<0.2 μm) fractions after 15 months (480 mg kg −1 and 1000 mg kg −1, respectively), compared to 200 mg kg −1 in the <2 μm fraction of the initial soil. In total, 1.2% of the Zn initially present in the sediment was released to the environment after 15 months, representing an integrated quantity of ∼4 kg Zn over an area of 50 m 2. Microfocused X-ray fluorescence (XRF), diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy techniques were used to image chemical associations of Zn with Fe and Mn, and to identify mineral and Zn species in selected points-of-interest in the uncontaminated and contaminated soil. Bulk average powder EXAFS spectroscopy was used to quantify the proportion of each Zn species in the soil. In the uncontaminated soil, Zn is largely speciated as Zn-containing phyllosilicate, and to a minor extent as zincochromite (ZnCr 2O 4), IVZn-sorbed turbostratic birnessite (δ-MnO 2), and Zn-substituted goethite. In the upper 0–10 cm of the contaminated soil, ∼60 ± 10% of total Zn is present as ZnS inherited from the overlying sediment. Poorly-crystalline Zn-sorbed Fe (oxyhydr)oxides and zinciferous phyllosilicate amount to ∼20–30 ± 10% each and, therefore, make up most of the remaining Zn. Smaller amounts of franklinite (ZnFe 2O 4), Zn-birnessite and Zn-goethite were also detected. Further solubilization of the Zn inventory in the sediment, and also remobilization of Zn from the poorly-crystalline neoformed Fe (oxyhydr)oxide precipitates, are expected over time. This study shows that land deposition of contaminated dredged sediments is a source of Zn for the covered soil and, consequently, presents environmental hazards. Remediation technologies should be devised to either sequester Zn into sparingly soluble crystalline phases, or remove Zn by collecting leachates beneath the sediment.

Responses of Nondormant Black Willow (Salix nigra) Cuttings to Preplanting Soaking and Soil Moisture

Abstract The use of willow cuttings for streambank stabilization is a common practice in riparian ecosystems throughout the United States. Many environmental factors govern the outcome of such planting. However, other factors such as preplanting treatments, planting methods, and physiological status of cuttings (dormant vs. actively growing) may also be crucial in determining the survival of willow cuttings. Actively growing (nondormant) Black willow (Salix nigra) cuttings, 30 cm in length and 1 cm in diameter at the base, were subjected to three soaking treatments (0, 7, and 15 days) prior to planting. Following the initial treatment, cuttings were grown in a greenhouse in pots under three soil moisture regimes (well‐watered but not flooded, permanently flooded, and intermittently flooded). Plant gas exchange, growth, biomass, and survival were measured. Results demonstrated that soaking for 7 days was beneficial to early development of cuttings in the well‐watered (control) soil moisture regime, enhancing percent bud flush and survival significantly. However, 15 days of soaking proved to be detrimental to survival of cuttings irrespective of soil moisture regimes. Results also demonstrated that the beneficial effects of 7‐day soaking were limited to the well‐watered soil moisture regime but not to the flooded or intermittently flooded regimes. Soaking nondormant cuttings may be worthwhile if the planting site is likely to present ample soil moisture but nonflooded conditions to the transplanted cuttings.

Flooding, root temperature, physiology and growth of two Annona species.

The effects of root zone temperature (RZT) and flooding on physiology and growth of Annona glabra L. (pond apple) and A. muricata L. (soursop) were investigated. Trees planted in containers were exposed to RZTs of 5, 10, 20, 25 or 35 degrees C in controlled root temperature chambers. Trees at each RZT were either non-flooded (control) or continuously flooded. There were four replications over time for each treatment combination. Pond apple was more flood-tolerant than soursop. A combination of flooding and RZTs of 5 and 10 degrees C resulted in tree mortality of both species by Week 4. Only trees that appeared to develop morphological adaptations survived continuous flooding. In both species, net CO2 assimilation (A) decreased to nearly zero within 1 week following exposure to RZTs of 5 or 10 degrees C and became consistently negative over the remaining experimental period. Flooding reduced leaf chlorophyll index (measured with a SPAD meter), A and plant growth, and increased root electrolyte leakage from soursop. Optimum growth occurred at RZTs of 25 to 35 degrees C for non-flooded pond apple trees and at 20 to 25 degrees C for flooded trees. Soursop exhibited maximum growth at RZTs of 35 degrees C under non-flooded conditions and at 25 degrees C under flooded conditions.

Reduction of global warming potential contribution from a rice field by irrigation, organic matter, and fertilizer management

The major objective of this study is to find a feasible management practice to mitigate the cumulative global warming potential (GWP) from CH4 and N2O emission in an irrigated rice field. Nonflooding (but wet) conditions reduced CH4 emission by 79 and 71% from the fields with and without organic matter (OM) addition, respectively. This was mainly due to the desirable soil redox status in the nonflooded fields with less CH4 production and more CH4 oxidation when CH4 diffused up the soil profile. Increase in N2O emission from the nonflooded fields offset part of the reduction in CH4 emission, especially when OM was not added. Thus the nonflooding treatment reduced the cumulative GWP by 72% in the OM‐added field but only 46% in the field without OM addition. Under flooding conditions, no OM addition reduced CH4 emission by 57%, but rice yield was decreased by 16% in comparison with the OM‐added fields. The best management practice proposed from this study is to keep the fields nonflooded but wet with OM addition, which largely reduced the GWP from the fields with no decrease in rice yield.

Influence of flooding on delta15N, delta18O, 1delta15N and 2delta15N signatures of N2O released from estuarine soils--a laboratory experiment using tidal flooding chambers.

The influence of flooding on N2O fluxes, denitrification rates, dual isotope (delta18O and delta15N) and isotopomer (1delta15N and 2delta15N) ratios of emitted N2O from estuarine intertidal zones was examined in a laboratory study using tidal flooding incubation chambers. Five replicate soil cores were collected from two differently managed intertidal zones in the estuary of the River Torridge (North Devon, UK): (1) a natural salt marsh fringing the estuary, and 2 a managed retreat site, previous agricultural land to which flooding was restored in summer 2001. Gas samples from the incubated soil cores were collected from the tidal chamber headspaces over a range of flooding conditions, and analysed for the delta18O, delta15N, 1delta15N and 2delta15N values of the emitted N2O. Isotope signals did not differ between the two sites, and nitrate addition to the flooding water did not change the isotopic content of emitted N2O. Under non-flooded conditions, the isotopic composition of the emitted N2O displayed a moderate variability in delta18O and 2delta15N delta values that was expected for microbial activity associated with denitrification. However, under flooded conditions, half of the samples showed strong and simultaneous depletions in 1delta15N and delta18O values, but not in 2delta15N. Such an isotope signal has not been reported in the literature, and it could point towards an unidentified N2O production pathway. Its signature differed from denitrification, which was generally the N2O production pathway in the salt marsh and the managed retreat site.

Seed germination ecology of the summer annual Cyperus squarrosus in an unpredictable mudflat habitat

Abstract The purpose of our study was to better understand seed germination ecology of the summer annual sedge Cyperus squarrosus , which grows in various habitats, including mudflats and shallow soil over limestone bedrock (rock outcrops), where timing of the period favorable for germination and completion of the life cycle is unpredictable. Over a 28.5-month period, temperature and light:dark requirements for germination were determined at monthly intervals for seeds collected from mudflats and buried under flooded and under nonflooded conditions at natural temperature regimes. Data on dormancy and germination were compared to those published for seeds collected from plants growing on rock outcrops. Under both flooded and nonflooded conditions, seeds from mudflats exhibited an annual conditional dormancy/nondormancy cycle, similar to those from rock outcrops buried under nonflooded conditions. Seeds from mudflats germinated to higher percentages at mid-summer temperatures (35/20 °C) in mid-summer than those from rock outcrops. On the other hand, seeds from rock outcrops germinated to higher percentages at March temperatures (15/6 °C) in March than those from mudflats. Thus, seeds could germinate on mudflats any time from April through September if dewatering occurred, and they could germinate on rock outcrops any time from March through June and in September if soil moisture was nonlimiting; in both habitats light would be required for germination. Since seeds on mudflats may be flooded for several consecutive years, mudflats are more unpredictable than rock outcrops. Ability of seeds from mudflats to germinate to high percentages in light at 35/20 °C throughout the summer and those from rock outcrops not to do so may be related to the greater unpredictability of the mudflat. Each year for 11 years, seeds germinated in mudflat soil samples kept in a nonheated greenhouse, reaching a total of 22526 ± 1401 (mean ± S.E.) seeds m –2 ; thus, the species has the potential to form a large long-lived persistent soil seed bank.

Switch from intracellular to intercellular invasion during water stress-tolerant legume nodulation.

Rhizobia colonize their legume hosts by different modes of entry while initiating symbiotic nitrogen fixation. Most legumes are invaded via growing root hairs by the root hair-curl mechanism, which involves epidermal cell responses. However, invasion of a number of tropical legumes happens through fissures at lateral root bases by cortical, intercellular crack entry. In the semiaquatic Sesbania rostrata, the bacteria entered via root hair curls under nonflooding conditions. Upon flooding, root hair growth was prevented, invasion on accessible root hairs was inhibited, and intercellular invasion was recruited. The plant hormone ethylene was involved in these processes. The occurrence of both invasion pathways on the same host plant enabled a comparison to be made of the structural requirements for the perception of nodulation factors, which were more stringent for the epidermal root hair invasion than for the cortical intercellular invasion at lateral root bases.

Effect of inoculations with single and multiple juveniles on release of progeny of Meloidogyne graminicola from susceptible rice

AbstractSeedlings of susceptible rice were inoculated with single or with 86 second-stage juveniles (J2) of Meloidogyne graminicola. After inoculation in a sandy substrate, rice seedlings were grown hydroponically to recover progeny. Following inoculation with a single juvenile (SJI), 71-73% of seedlings released J2 progeny at 84 days after inoculation (DAI). This confirmed the ability of this species to reproduce by parthenogenesis. After SJI, the proportion of inoculated seedlings releasing J2 increased steadily from 21-63 DAI. On the contrary, after inoculation with 86 J2, release of progeny was high for all seedlings as early as 28 DAI. Thus progeny formed after SJI remained captive in galls for a longer time. In the same sandy substrate, J2 were able to invade rice roots and develop in flooded conditions as well as in non-flooded conditions.

Antioxidative defenses and water deficit-induced oxidative damage in rice (Oryza sativa L.) growing on non-flooded paddy soils with ground mulching

Rice (Oryza sativa L.) cultivation under non-flooded conditions using polyethylene film as ground mulching materials, namely plastic film-mulching cultivation system (PFMCS), is an alternative to the conventional rice cultivation system in regions where rainfall and fresh water resources are limited. Two-year field trials (1998–1999) were performed in this study to investigate the growth-stage-dependent changes in activities of antioxidative enzymes and lipid peroxidation in leaves of rice subjected to mulching with plastic film or kraft paper and zero mulching under non-flooded conditions compared with continuously flooded treatment. Significantly higher activities of peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX) but lower concentration of malondialdehyde (MDA) were observed in mulching treatments than in zero mulching treatment at all growth stages in the drier growing season (1999). The concentration of MDA was significantly higher especially at late growth stages in zero mulching treatment than in the other treatments. In contrast, essentially no significant difference existed in the activities of the major antioxidant enzymes (except POD) or in the concentration of MDA between any two treatments in the wetter growing season (1998). This change tendency of antioxidant enzyme activity and MDA level over two contrasting growing seasons was in line with both soil and leaf moisture status, and rice yields of different treatments. These results strongly suggest that plastic film-mulching treatment or paper mulching treatment significantly alleviated oxidative damages induced by water-deficit stress in rice. The efficacy of ground-mulching-induced enhancement of antioxidative defense to drought stress is discussed with respect to water deficit status in both soils and rice plants.

Evaluating Recovery of Cupressaceae Taxa After Flooding at Contrasting Temperatures

Abstract Chamaecyparis are ornamental plants that are used extensively in temperate-zone landscapes worldwide. However, due to their low tolerance to environmental stresses Chamaecyparis often perform poorly in urban landscapes. The objective of this research was to evaluate rootstocks of selected Cupressaceae taxa to determine their adaptability to poor drainage and high temperatures found commonly in urban landscapes. To accomplish this objective, 10 taxa (Chamaecyparis, Platycladus, Thuga spp., and x sCupressocyparis leylandii) were grown in 2.8 liter (#1) black plastic containers with a pinebark:sand (8:1 by vol) medium for 19 weeks in two greenhouses with 9/15 hr day/night temperatures of either 22/18C (72/64F) or 30/26C (86/79F). Half the plants in each greenhouse were flooded for 4 weeks. Root relative growth rate (RGR) was a better indicator of plant performance under flooded conditions compared to shoot RGR. At 22/18C (72/64F), root RGR of Chamaecyparis thyoides and Thuja ‘Green Giant’ only declined 10% and 11% between nonflooded and flooded plants, respectively. Chamaecyparis obtusa and x Cupressocyparis leylandii had the largest percentage decline in root RGR from nonflooded to flooded plants with 71% and 213%, respectively. Chamaecyparis thyoides had the highest root RGR at 30/26C (86/79F) in both nonflooded and flooded conditions with a 19% decrease in root RGR between nonflooded and flooded. Chamaecyparis lawsoniana and T. ‘Green Giant’ were ranked 2 and 3 in flooded conditions at 30/26C (86/79F); however, percentage decline increased to 43% and 46%, respectively. At this temperature, the remaining seven taxa had greater than 50% decline in root RGR in flooded conditions compared to nonflooded plants. In nonflooded conditions, shoot and root RGR of all species decreased from 22/18C (72/64F) to 30/26C (86/79F) except for Chamaecyparis thyoides. The shoot and root RGR of Chamaecyparis thyoides grown in 22/18C (72/64F) and 30/26C (86/79F) were similar in nonflooded conditions. Chamaecyparis thyoides demonstrated excellent tolerance to flooding and temperature and could be a desirable understock for other Chamaecyparis when grown in poorly drained locations.

Effects of flooding and temperature on dormancy break in seeds of the summer annual mudflat species Ammannia coccinea and Rotala ramosior (Lythraceae)

Abstract Studies were undertaken on seeds of the summer annual mudflat species Ammannia coccinea and Rotala ramosior to determine the (1) effects of flooding during late autumn to late spring on dormancy break and (2) optimum temperature for dormancy break. At maturity in autumn, about 65–100% of the seeds of these species were dormant. Seeds of both species buried under flooded and under nonflooded conditions in a nonheated greenhouse germinated to 70–98% at 30(day)/15(night)°C and at 35/20°C the following June or July; seeds required light for germination. As dormancy break occurred, seeds of R. ramosior showed a decrease in the minimum temperature for germination, but those of A. coccinea did not. In another experiment, seeds buried under nonflooded conditions in the nonheated greenhouse were flooded in November, December, February, March, April, or May, and all flooded seeds and nonflooded controls were exhumed and tested in July. With few exceptions, seeds of both species flooded for short (May–July)...

Does prolonged flooding prevent or enhance regeneration and growth of Sphagnum?

Site preparation for restoration of peat-mined bogs in eastern Canada frequently involves the construction of bunds or shallow basins to enhance peat moisture content. As a consequence, Sphagnum reintroduced within restored areas may be subjected to extended periods of flooding, particularly following snow melt or heavy rainfall. This paper examines two aspects of the effect of flooding on growth and development of Sphagnum: (1) the production of innovations (growth buds and shoots) and capitula from plant fragments (six species) under continuous, intermittent or non-flooding conditions, and (2) the growth response of whole plants (10 species) under long-term continuous shallow flooding. The development response of Sphagnum fragments to short-term continuous (8–10 cm), intermittent (−1 to +1 cm) or non-flooding conditions (−3 to 0 cm), was investigated in growth chambers. Environmental parameters were selected to investigate the possible differential effects of early spring flooding (10:7 °C, day:night), or inundation following heavy rainfall events later in the season (20–25:20 °C, day:night). Both temperature regimes yielded similar results. After 1 month of flooding the number of innovations was generally similar to that for non-flooded controls. However, after a further 3 months, fragments that had been flooded for 1 month (either continuously or intermittently) produced more capitula than non-flooded fragments. Although S. fuscum, a hummock-forming species, showed delayed formation of innovations, flooding still increased final capitula production. The growth response of whole Sphagnum plants to long-term continuous flooding in the field (+1 cm), revealed that most species grew well, but that several becoming etiolated. These modifications may result in plants more prone to desiccation during drier events than individual with a regular growth form. It is concluded that limited periods of shallow flooding could enhance Sphagnum development in restored areas. Care must be exercised though, as deep or extensive inundation may result in excessive plant etiolation or cause severe physical disturbances to the restorated areas.

Phenotypic plasticity and integration in response to flooded conditions in natural accessions of Arabidopsis thaliana (L.) Heynh (Brassicaceae).

Flood response is a crucial component of the life strategy of many plants, but it is seldom studied in non-flooded tolerant species, even though they may be subjected to stressful environmental conditions. Phenotypic plasticity in reaction to environmental stress affects the whole plant phenotype and can alter the character correlations that constitute the phenotypic architecture of the individual, yet few studies have investigated the lability of phenotypic integration to water regime. Moreover, little has been done to date to quantify the sort of selective pressures that different components of a plant's phenotype may be experiencing under contrasting water regimes. Genetic differentiation and phenotypic plasticity at the single-trait and multivariate levels were investigated in 47 accessions of the weedy plant Arabidopsis thaliana, and the relationship of plastic characters to reproductive fitness was quantified. Results indicate that these plants tend to be highly genetically differentiated for all traits, in agreement with predictions made on the basis of environmental variation and mating system. Varied patterns of apparent selection under flooded and non-flooded conditions were also uncovered, suggesting trade-offs in allocation between roots and above-ground biomass, as well as between leaves and reproductive structures. While the major components of the plants' multivariate phenotypic architecture were not significantly affected by environmental changes, many of the details were different under flooded and non-flooded conditions.

Riparian alder fens — source or sink for nutrients and dissolved organic carbon? — 2. Major sources and sinks

Natural riparian forest wetlands are known to be effective in their ability to remove nitrate by denitrification and sediments with attached phosphorus via sedimentation. On the other hand, litter input and decomposition is a process of crucial importance in cycling of nitrogen and phosphorus in a forest ecosystem. In this study we investigated the amount of nitrogen and phosphorus entering the alder fen ecosystem through leaf litter and its decomposition and the removal capacity of nitrogen and phosphorus by measuring denitrification and sedimentation in the alder fen. We found an average input of leaf litter during fall 1998 of 226 g m −2 yr −1 DW with nutrient concentration of 0.17% P and 1.6% N. This means a yearly input of 0.4 g m −2 yr −1 P and 3.6 g m −2 yr −1 N. The decomposition of leaf litter using litter bags with small and large mesh size resulted in bags with macroinvertebrates (large mesh size) and without macroinvertebrates (small mesh size). After 57 days the litter bags with macroinvertebrates had a decomposition rate of 79%. Denitrification was measured in May and June of 1997 using the acetylene inhibition technique on intact soil cores and slurry-experiments. The average annual denitrification rate was 0.2 g m −2 yr −1 N using data from the core experiments. The denitrification rate was higher after addition of nitrate, indicating that denitrification in the riparian alder fen is mainly controlled by nitrate supply. The sedimentation rate in the investigated alder fen ranged from 0.47 kg m −2 yr −1 DW to 4.46 kg m −2 yr −1 DW in 1998 depending on the study site and method we used. Sedimentation rates were lower in newly designed plate traps than in cylinder traps. The alder fen also showed lower rates than the adjacent creek Briese. Average phosphorus removal rate was 0.33 g m −2 yr −1 P. Input sources for the surface water of the alder fen are sediment mineralization and decomposition of leaf litter; output sources are sedimentation and denitrification. This study showed that a nutrient input of 24.58 kg ha −1 yr −1 N, 8.8 kg ha −1 yr −1 P and 419 kg ha −1 yr −1 DOC into the surface water of the alder fen is possible. Alder fens cannot improve water quality of an adjacent river system. This is only true for a nearly pristine alder fen with the hydrology of 10 months flooded conditions and 2 months non-flooding conditions a year.

Mineralization-immobilization of soil organic S and oxidation of elemental S in subtropical soils under flooded and nonflooded conditions

Information on the influence of soil moisture on elemental sulphur (S0) oxidation and transformation into organic S in semi-arid subtropical soils is scarce. We studied the impact of three moisture regimes on the mineralization of soil organic S, and the oxidation and immobilization of S0 in acidic (pH 4.9), neutral (pH 7.1) and alkaline (pH 10.2) subtropical soils. Repacked soil cores were incubated under aerobic (40% and 60% water-filled pore space, WFPS) and flooded soil conditions (120% WFPS) for 0, 14, 28 and 42 days with and without incorporated S0 (500 µg g–1 soil). Soil moisture had profound effects on these processes and the mineralization of native soil organic S, oxidation of applied S0 and transformation of S0 into soil organic S proceeded most rapidly at 60% WFPS, irrespective of soil pH. Mineralization of native soil organic S resulted in the accumulation of 34, 49 and 44 g SO42–-S g–1 soil in acidic, neutral and alkaline soil in a 42-day period at 60% WFPS. The oxidation rate of added S0 during the initial 14-day period at 60% WFPS was highest in alkaline soil (428 µg S cm–2 day–1), followed by neutral soil (326 µg S cm–2 day–1), and lowest in acidic soil (235 µg S cm–2 day–1). These rates are several folds higher than those reported in earlier studies because now we computed the oxidation rates by including the amount of S0 that was immobilized to organic S. Of the applied S0 at 40% and 60% WFPS, 2.6% and 6.0%, 3.4% and 10.0%, and 9.4% and 14.4% oxidized to SO42–, and 15.0% and 17.6%, 17.6% and 19.6%, and 17.6% and 23.6% transformed into organic S in the 42-day period in acidic, neutral and alkaline soil, respectively. These results suggest that in order to synchronize the availability of S with plant need, S0 may be applied well before the seeding of crops especially in acidic soils and in rainfed regions where soil moisture remains at less than 60% WFPS. Apparently no oxidation of S0 and significant reduction of SO42–-S (7, 53 and 78 µg SO42–-S g–1 in acidic, neutral and alkaline soil, respectively) under flooded conditions suggest that S0 is least effective for correcting S deficiency in flooded soil systems such as rice fields.

Responses of wetland plants to ammonia and water level

Constructed wetland systems receiving animal wastewater may enhance water quality when designed, operated, and maintained properly. In the case of wetlands designed to treat animal waste, system effectiveness may be limited by high ammonia concentrations and inundation, conditions that can adversely affect macrophytic vegetation. We conducted a 4-month greenhouse experiment to assess the impact of ammonia concentration and water level on plants commonly used in constructed wetlands for treating animal waste. We examined the effects of ammonia concentration (0, 50, 100, 200 and 400 mg/l) on the growth and biomass production of Juncus effusus, Sagittaria latifolia, Schoenoplectus tabernaemontani, Typha angustifolia, and Typha latifolia. We also explored interactions between ammonia concentration (0, 50, 100, 200 and 400 mg/l) and water level (flooded and nonflooded conditions) for S. tabernaemontani and T. latifolia. We found that ammonia levels in excess of 200 mg/l inhibited growth for J. effusus, S. latifolia, and T. latifolia after a period of weeks, and levels in excess of 100 mg/l similarly inhibited growth for S. tabernaemontani. Ammonia levels in the range studied had an ambiguous effect on T. angustifolia. Affected species demonstrated similar fertilization/inhibition responses to increased ammonia, but important differences were noted between species. Flooded conditions of 10 cm did not significantly increase ammonia toxicity to S. tabernaemontani or T. latifolia. Our results emphasize the need for careful consideration of the species used in treatment wetlands, and suggest that management of ammonia concentration may enhance plant growth and system function.

Losses in Wheat Due to Waterlogging

Waterlogging stress is one of the limiting factors influencing wheat (Triticum aestivum L.) production, especially in the lower Mississippi valley. A rain-shelter experiment was designed to evaluate the trend response of nine wheat genotypes to four levels of waterlogging treatment: 0, 10, 20, and 30 d of flooding. Genotypes planted in polyvinilchloride (PVC) containers 25 cm long by 10 cm in diameter were waterlogged in plastic tanks under controlled rain conditions. Results indicated significant linear responses for kernels per head and tillers per plant, significant linear and quadratic responses for yield and chlorophyll content, and significant linear and cubic responses for plant height. The linear trend was the most important component, explaining from 92 to 99% of the variability due to waterlogging. Linear prediction equations were obtained to describe the relationship between different traits and waterlogging stress. Losses in yield and yield components were evaluated in a field experiment with 15 genotypes under control and waterlogging treatment. Average yield losses of 44% were mainly caused by a decrease in tiller number and kernels per head. Under waterlogging treatment, tiller number and kernels per head were reduced by 41 and 20%, respectively. Screening of wheat genotypes revealed the potential for waterlogging tolerance in breeding material and identified tolerant cultivars useful for waterlogged environments. ‘Terral LA 422’, ‘Shelby’, and ‘Pioneer 2691’ were the most adapted genotypes for waterlogging treatments. Because of a significant interaction with waterlogging treatment, some of the high-yielding genotypes under non-flooded conditions such as ‘Coker 9663’ and ‘FFR 502W’ showed low tolerance to waterlogging. The results provided information on the methods quantifying losses from waterlogging and identified selection criteria for waterlogging tolerance in wheat.