Hydroperiods of created and natural vernal pools in central Ohio: A comparison of depth and duration of inundation

Water levels were recorded weekly from six natural vernal pools and 10 created vernal pools at two forested wetland complexes in central Ohio. Vernal pool median water depth and duration of inundation were significantly greater at the created vernal pools than at the natural vernal pools (α = 0.05, P < 0.05). The average period of inundation for created pools was 309 ± 32 days, compared with 250 ± 16 days for natural pools. The created pools produced a range of inundation times, from 163 to 365 days in length, with three pools permanently inundated.     

Comparing carbon sequestration in temperate freshwater wetland communities

High productivity and waterlogged conditions make many freshwater wetlands significant carbon sinks. Most wetland carbon studies focus on boreal peatlands, however, with less attention paid to other climates and to the effects of hydrogeomorphic settings and the importance of wetland vegetation communities on carbon sequestration. This study compares six temperate wetland communities in Ohio that belong to two distinct hydrogeomorphic types: an isolated depressional wetland site connected to the groundwater table, and a riverine flow‐through wetland site that receives water from an agricultural watershed. Three cores were extracted in each community and analyzed for total carbon content to determine the soil carbon pool. Sequestration rates were determined by radiometric dating with ¹³⁷Cs and ²¹⁰Pb on a set of composite cores extracted in each of the six communities. Cores were also extracted in uplands adjacent to the wetlands at each site. Wetland communities had accretion rates ranging from 3.0 to 6.2 mm yr^?1. The depressional wetland sites had higher (P < 0.001) organic content (146 ± 4.2 gC kg^?1) and lower (P < 0.001) bulk density (0.55 ± 0.01 Mg m^?3) than the riverine ones (50.1 ± 6.9 gC kg^?1 and 0.74 ± 0.06 Mg m^?3). The soil carbon was 98–99% organic in the isolated depressional wetland communities and 85–98% organic in the riverine ones. The depressional wetland communities sequestered 317 ± 93 gC m^?2 yr^?1, more (P < 0.01) than the riverine communities that sequestered 140 ± 16 gC m^?2 yr^?1. The highest sequestration rate was found in the Quercus palustris forested wetland community (473 gC m^?2 yr^?1), while the wetland community dominated by water lotus (Nelumbo lutea) was the most efficient of the riverine communities, sequestering 160 gC m^?2 yr^?1. These differences in sequestration suggest the importance of addressing wetland types and communities in more detail when assessing the role of wetlands as carbon sequestering systems in global carbon budgets.     

Annual cycle of CO2 exchange over a reed (Phragmites australis) wetland in Northeast China

Net ecosystem exchange of CO₂ (NEE) was measured during 2005 using the eddy covariance (EC) technique over a reed (Phragmites australis (Cav.) Trin. ex Steud.) wetland in Northeast China (121°54′E, 41°08′N). Diurnal NEE patterns varied markedly among months. Outside the growing season, NEE lacked a diurnal pattern and it fluctuated above zero with an average value of 0.07 mg CO₂ m⁻² s⁻¹ resulting from soil microbial activity. During the growing season, NEE showed a distinct V-like diel course, and the mean daily NEE was −7.48 ± 2.74 g CO₂ m⁻² day⁻¹, ranging from −13.58 g CO₂ m⁻² day⁻¹ (July) to −0.10 g CO₂ m⁻² day⁻¹ (October). An annual cycle was also apparent, with CO₂ uptake increasing rapidly in May, peaking in July, and decreasing from August. Monthly cumulative NEE ranged from −115 ± 24 g C m⁻² month⁻¹ (the reed wetland was a CO₂ sink) in July to 75 ± 16 g C m⁻² month⁻¹ (CO₂ source) in November. The annual CO₂ balance suggests a net uptake of −65 ± 14 g C m⁻² year⁻¹, mainly due to the gains in June and July. Cumulative CO₂ emission during the non-growing season was 327 g C m⁻², much greater than the absolute value of the annual CO₂ balance, which proves the importance of the wintertime CO₂ efflux at the study site. The ratio of ecosystem respiration (R_eco) to gross primary productivity (GPP) for this reed ecosystem was 0.95, indicating that 95% of plant assimilation was consumed by the reed plant or supported the activities of heterotrophs in the soil. Daytime NEE values during the growing season were closely related to photosynthetically active radiation (PAR) (r² > 0.63, p < 0.01). Both maximum ecosystem photosynthesis rate (A_max) and apparent quantum yield (α) were season-dependent, and reached their peak values in July (1.28 ± 0.11 mg CO₂ m⁻² s⁻¹, 0.098 ± 0.027 μmol CO₂ μmol⁻¹ photon, respectively), corresponding to the observed maximum NEE in July. Ecosystem respiration (R_eco) relied on temperature and soil water content, and the mean value of Q₁₀ was about 2.4 with monthly variation ranging from 1.8 to 4.1 during 2005. Annual methane emission from this reed ecosystem was estimated to be about 3 g C m⁻² year⁻¹, and about 5% of the net carbon fixed by the reed wetland was released to the atmosphere as CH₄.     

Influence of soft rush (Juncus effusus) on phosphorus flux in grazed seasonal wetlands

Livestock significantly affect wetland soils and vegetation but their impacts on wetland nutrient dynamics are poorly understood. We set up a full factorial laboratory experiment to assess the effects of Juncus effusus, grazing exclusion, and flooding on P flux from intact cores collected from seasonal wetlands in cattle pastures in south Florida. We collected intact cores from Juncus tussocks and plant interspaces inside and outside 4-year grazing exclosures in five replicate wetlands. We incubated the cores for 50 days under continuous flooding or weekly 1-day flooding cycles and measured P concentrations in surface and pore water. Grazing exclosures had less Juncus (17%) and bare ground (2%) than adjacent grazed areas (Juncus, 48%; bare ground, 12%), but did not affect P fluxes. Initial fluxes of soluble reactive P (SRP) were much higher in cores with Juncus (242 ± 153 mg P m⁻² day⁻¹) than without Juncus (14 ± 20 mg P m⁻² day⁻¹). In weekly flooded cores P fluxes fell to 19.7 ± 13.4 mg P m⁻² day⁻¹ in cores with and 2.7 ± 2.6 in cores without Juncus. The strong effect of Juncus on P flux was an indirect effect of cattle grazing, but 4 years of grazing exclusion did not have a significant effect on P fluxes.     

USDA Conservation Practices Increase Carbon Storage and Water Quality Improvement Functions: An Example from Ohio

We compared potential denitrification and phosphorus (P) sorption in restored depressional wetlands, restored riparian buffers, and natural riparian buffers of central Ohio to determine to what extent systems restored under the U.S. Department of Agriculture's Wetland Reserve Program (WRP) and Conservation Reserve Program (CRP) provide water quality improvement benefits, and to determine which practice is more effective at nutrient retention. We also measured soil nutrient pools (organic C, N, and P) to evaluate the potential for long‐term C sequestration and nutrient accumulation. Depressional wetland soils sorbed twice as much P as riparian soils, but had significantly lower denitrification rates. Phosphorus sorption and denitrification were similar between the restored and natural riparian buffers, although all Natural Resources Conservation Service (NRCS) practices had higher denitrification than agricultural soils. Pools of organic C (2570–3320 g/m²), total N (216–243 g/m²), and total P (60–71 g/m²) were comparable among all three NRCS practices but were greater than nearby agricultural fields and less than natural wetlands in the region. Overall, restored wetlands and restored and natural riparian buffers provide ecosystem services to the landscape that were lost during the conversion to agriculture, but the delivery of services differs among conservation practices, with greater N removal by riparian buffers and greater P removal by wetlands, attributed to differences in landscape position and mineral soil composition. At the landscape, and even global level, wetland and riparian restoration in agricultural landscapes will reintroduce multiple ecosystem services (e.g. C sequestration, water quality improvement, and others) and should be considered in management plans .     

Seasonal and storm event nutrient removal by a created wetland in an agricultural watershed

This study examines the effectiveness of a 1.2-ha created/restored emergent marsh at reducing nutrients from a 17.0 ha agricultural and forested watershed in the Ohio River Basin in west central Ohio, USA, during base flow and storm flow conditions. The primary source of water to the wetland was surface inflow, estimated in water year 2000 (October 1999–September 2000) to be 646 cm/year. The wetland also received a significant amount of groundwater discharge at multiple locations within the site that was almost the same in quantity as the surface flow. The surface inflow had 2-year averages concentrations of 0.79, 0.033, and 0.16 mg L⁻¹ for nitrate + nitrite (as N), soluble reactive phosphorus (SRP), and total phosphorus (TP), respectively. Concentrations of nitrate–nitrite, SRP, and TP were 40, 56, and 59% lower, respectively, at the outflow than at the inflow to the wetland over the 2 years of the study. Concentrations of SRP and TP exported from the wetland increased significantly (α = 0.05) during precipitation events in 2000 compared to dry weather flows, but concentrations of nitrate–nitrite did not increase significantly. During these precipitation events the wetland retained 41% of the nitrate–nitrite, 74% of the SRP, and 28% of the TP (by mass). The wetland received an average of 50 g N m⁻² per year of nitrate–nitrite and 7.1 g m⁻² per year of TP in 2000. Retention rates for the wetland were 39 g N m⁻² per year of nitrates and 6.2 g P m⁻² per year. These are close to rates suggested in the literature for sustainable non-point source retention by wetlands. The design of this wetland appears to be suitable as it retained a significant portion of the influent nutrient load and did not lose much of its retention capacity during heavy precipitation events. Some suggestions are given for further design improvements.     

Accumulation of Carbon and Nitrogen in Residential Soils with Different Land-Use Histories

Urban areas are growing in size and importance; however, we are only beginning to understand how the process of urbanization influences ecosystem dynamics. In particular, there have been few assessments of how the land-use history and age of residential soils influence carbon (C) and nitrogen (N) pools and fluxes, especially at depth. In this study, we used 1-m soil cores to evaluate soil profile characteristics and C and N pools in 32 residential home lawns that differed by previous land use and age, but had similar soil types. These were compared to soils from eight forested reference sites. Residential soils had significantly higher C and N densities than nearby forested soils of similar types (6.95 vs. 5.44 kg C/m² and 552 vs. 403 g N/m², P < 0.05). Results from our chronosequence suggest that soils at residential sites that were previously in agriculture have the potential to accumulate C (0.082 kg C/m²/y) and N (8.3 g N/m²/y) rapidly after residential development. Rates of N accumulation at these sites were similar in magnitude to estimated fertilizer N inputs, confirming a high capacity for N retention. Residential sites that were forested prior to development had higher C and N densities than present-day forests, but our chronosequence did not reveal a significant pattern of increasing C and N density over time in previously forested sites. These data suggest that soils in residential areas on former agricultural land have a significant capacity to sequester C and N. Given the large area of these soils, they are undoubtedly significant in regional C and N balances.     

Nutrient status and retention in pristine and disturbed wetlands in Uganda: management implications

Wetlands in Uganda experience different forms of human pressure ranging from drainage for agriculture and industrial development to over harvesting of wetland products. In order to develop sustainable management tools for wetland ecosystems in Uganda and the Lake Victoria Region, water quality analyses were carried out in a rural undisturbed (pristine) wetland (Nabugabo wetland in Masaka) and two urban wetlands that are experiencing human and urban development pressure (the Nakivubo wetland in Kampala and Kirinya wetland in Jinja). The former wetland forms the main inflow into Lake Nabugabo while the other two border the northern shore of Lake Victoria, Uganda. Nabugabo wetland buffers Lake Nabugabo against surface runoff from the catchment, while Nakivubo and Kirinya wetlands provides a water treatment function for wastewater from Kampala City and Jinja town respectively, in addition to buffering Lake Victoria against surface runoff. Water quality was assessed in all the wetland sites, and in addition nutrient content and storage was investigated in the main plant species (papyrus, Phragmites, Miscanthidium and cocoyam) in Nakivubo and Kirinya wetlands. A pilot experiment was also carried out to assess the wastewater treatment potential of both the papyrus vegetation and an important agricultural crop Colocasia esculenta (cocoyam). Low electrical conductivity, ammonium–nitrogen and ortho-phosphate concentrations were recorded at the inflow into Nabugabo wetland (41.5 μS/cm; 0.91 mg/l and 0.42 mg/l respectively) compared to the Nakivubo and Kirinya wetlands (335 μS/cm; 31.68 mg/l and 2.83 mg/l and 502 μS/cm; 10 mg/l and 1.87 mg/l respectively). The papyrus vegetation had higher biomass in Nakivubo and Kirinya wetlands (6.7 kg DW m⁻²; 7.2 kg DW m⁻² respectively), followed by Phragmites (6.5, 6.7), cocoyams (6.4, 6.6) and Miscanthidium (4.0, 4.2). The papyrus vegetation also exhibited a higher wastewater treatment potential than the agricultural crop (cocoyam) during the pilot experiment (maximum removal degree of ammonium–nitrogen being 95% and 67% for papyrus and yams). It was concluded that urbanisation pressure reduces natural wetland functioning either through the discharge of wastewater effluent or the degradation of natural wetland vegetation. It is recommended that wetland vegetation be restored to enhance wetland ecosystem functioning and for wetlands that are not yet under agricultural pressure, efforts should be made to halt any future encroachment.     

Carbon and nitrogen in a temperate agroforestry system: Using stable isotopes as a tool to understand soil dynamics

Natural exchanges of carbon (C) between the atmosphere, the oceans, and terrestrial ecosystems are currently being modified through human activities as a result of fossil fuel burning and the conversion of tropical forests to agricultural land. These activities have led to a steady increase of atmospheric carbon dioxide (CO₂) over the last two Centuries. The goal of this study was to determine the potential of temperate agroforestry systems to sequester C in soil. Therefore, changes in the soil organic C (SOC) and nitrogen (N) pools were quantified and the δ¹³C and δ¹⁵N stable isotope technique was applied to assess soil C and N dynamics in a 13-year old hybrid poplar alley cropping system in Southern Canada. Results from this study showed that after 13 years of alley cropping the SOC and N pools did not differ significantly (p = 0.01) with distance from the tree row, although a trend of a larger SOC and N pool near the tree row could be observed. Soil organic C after 13 years of alley cropping, was 19 mg C g⁻¹ compared to 11 mg C g⁻¹ upon initiation of agroforestry. Soil organic C and N were not evenly distributed throughout the plow layer. The largest C and N pool occurred in the top 20 cm, which is due to the accumulation of organic material in the upper horizons as a result of no-till cultivation. The entire soil, to a 40 cm depth, showed a δ¹³C shift to that of C₃ residue. This shift reflects the greater input of residues from C₃ plants such as that derived from beans, wheat, and hybrid poplar leaf litterfall. The proportion of C derived from a C₃ source ranged from 64 to 69% to a 40 cm depth. The soil δ¹⁵N signature of this study is similar to that of mineral soil, and reflect values characteristic of N mineralization processes. However, the entire soil shows a positive shift in δ¹⁵N as a result of historical additions of manure and current use of mineral fertilizers, and ongoing processes of denitrification and nitrate leaching, which leads to an enrichment of the soil.     

Effects of vegetation and hydrologic load on sedimentation patterns in experimental wetland ecosystems

Vegetation and water velocity effects on patterns of sediment deposition were tested by monitoring sedimentation rates in dense cattail, open water, and transitional vegetation zones at distances of 5, 10, and 20 m from the inflows of two experimental wetland basins at the Des Plaines River Wetlands Demonstration Project, northeastern Illinois, USA. One basin received a high hydrologic load (up to 50 cm/wk) and one basin received a low load (up to 6 cm/wk). Sediment deposition rates within 20 m of the inflows reached 3300 g dry wt m⁻² day⁻¹ in the high-load basin and 700 g dry wt m⁻² day⁻¹ in the low-load basin. Vegetation patterns did not have a significant effect (P > 0.05) on sediment deposition rates in the high-load basin, whereas water velocity effects on rates of sedimentation were significant (P < 0.01) in three of four periods of monitoring. In the low-load basin, vegetation effects were significant (P < 0.01) during the entire period of investigation. Experimental research at this scale aids in the assessment of design criteria for constructed wetlands.     

Tropical wetlands: seasonal hydrologic pulsing,carbon sequestration,and methane emissions

This paper summarizes the importance of climate on tropical wetlands. Regional hydrology and carbon dynamics in many of these wetlands could shift with dramatic changes in these major carbon storages if the inter-tropical convergence zone (ITCZ) were to change in its annual patterns. The importance of seasonal pulsing hydrology on many tropical wetlands, which can be caused by watershed activities, orographic features, or monsoonal pulses from the ITCZ, is illustrated by both annual and 30-year patterns of hydrology in the Okavango Delta in southern Africa. Current studies on carbon biogeochemistry in Central America are attempting to determine the rates of carbon sequestration in tropical wetlands compared to temperate wetlands and the effects of hydrologic conditions on methane generation in these wetlands. Using the same field and lab techniques, we estimated that a humid tropical wetland in Costa Rica accumulated 255 g C m⁻² year⁻¹ in the past 42 years, 80% more than a similar temperate wetland in Ohio that accumulated 142 g C m⁻² year⁻¹ over the same period. Methane emissions averaged 1,080 mg-C m⁻² day⁻¹ in a seasonally pulsed wetland in western Costa Rica, a rate higher than methane emission rates measured over the same period from humid tropic wetlands in eastern Costa Rica (120–278 mg-C m⁻² day⁻¹). Tropical wetlands are often tuned to seasonal pulses of water caused by the seasonal movement of the ITCZ and are the most likely to be have higher fire frequency and changed methane emissions and carbon oxidation if the ITCZ were to change even slightly.     

Soil GHG fluxes are altered by N deposition: New data indicate lower N stimulation of the N2O flux and greater stimulation of the calculated C pools

The effects of nitrogen (N) deposition on soil organic carbon (C) and greenhouse gas (GHG) emissions in terrestrial ecosystems are the main drivers affecting GHG budgets under global climate change. Although many studies have been conducted on this topic, we still have little understanding of how N deposition affects soil C pools and GHG budgets at the global scale. We synthesized a comprehensive dataset of 275 sites from multiple terrestrial ecosystems around the world and quantified the responses of the global soil C pool and GHG fluxes induced by N enrichment. The results showed that the soil organic C concentration and the soil CO₂, CH₄ and N₂O emissions increased by an average of 3.7%, 0.3%, 24.3% and 91.3% under N enrichment, respectively, and that the soil CH₄ uptake decreased by 6.0%. Furthermore, the percentage increase in N₂O emissions (91.3%) was two times lower than that (215%) reported by Liu and Greaver (Ecology Letters, 2009, 12:1103–1117). There was also greater stimulation of soil C pools (15.70 kg C ha^?1 year^?1 per kg N ha^?1 year^?1) than previously reported under N deposition globally. The global N deposition results showed that croplands were the largest GHG sources (calculated as CO₂ equivalents), followed by wetlands. However, forests and grasslands were two important GHG sinks. Globally, N deposition increased the terrestrial soil C sink by 6.34 Pg CO₂/year. It also increased net soil GHG emissions by 10.20 Pg CO₂‐Geq (CO₂ equivalents)/year. Therefore, N deposition not only increased the size of the soil C pool but also increased global GHG emissions, as calculated by the global warming potential approach.     

Tropical wetlands for climate change research, water quality management and conservation education on a university campus in Costa Rica

EARTH University is a small agronomic university with a theme of sustainability in eastern Costa Rica. Several natural and constructed wetlands on its campus are used for research, water quality improvement, and higher education. It has become an important location for research and teaching on humid tropical wetland ecology and management. A 112-ha flow-through Raphia taedigera (Arecaceae) forested wetland is being used for climate change research, focusing on carbon sequestration and methane generation. Methane emissions are measured seasonally and are comparable to rates in tropical wetlands published elsewhere. Carbon sequestration by the wetland appears to be substantially higher than similar flow-through temperate zone wetlands. Treatment wetlands are used on campus to improve water quality of effluents from an animal farm, a dairy plant, a landfill, and a banana paper plant. Water quality was substantially improved in all of these wetlands except the landfill leachate wetland. All of these campus wetlands have been integrated into the four-year education program of EARTH University and 22 undergraduate projects have been completed on wetlands over the past 14 years.     

Using the floristic quality concept to assess created and natural wetlands: Ecological and management implications

We applied the floristic quality index (FQI) to vegetation data collected across a chronosequence of created wetland (CW) sites in Virginia ranging in age from one to 15 years post-construction. At each site, we also applied FQI to a nearby forested reference wetland (REF). We tested the performance of the index against a selection of community metrics (species richness, diversity, evenness, percent native species) and site attributes (age, soil physiochemical variables). FQI performed better when non-native species (C-value = 0) were removed from the index, and also when calculated within rather than across vegetation layers. A modified, abundance-weighted FQI showed significant correlation with community and environmental variables in the CW herbaceous layer and REF herbaceous and shrub-sapling layers based on Canonical correspondence analysis (CCA) ordination output. These results suggest that a “natives only”, layer-based version of the index is most appropriate for our region, and an abundance-weighted FQI may be useful for assessing floristic quality in certain layers. The abundance-weighted format has the advantage of preserving the “heritage” aspect of the species conservatism concept while also entraining the “ecology” aspect of site assessment based on relative abundances of the inhabiting species. FQI did not successfully relate CW sites to REF sites, bringing into question the applicability of the FQI concept in comparing created wetlands to reference wetlands, and by analogy, the use of forested reference wetlands in general to assess vegetation development in created sites.     

An assessment of soil bacterial community structure and physicochemistry in two microtopographic locations of a palustrine forested wetland

We studied redoximorphic features, field indicators and bacterial communities of soils in hummocks and hollows of a palustrine forested wetland in Virginia. We hypothesized that presence of hydric soils, soil physicochemistry and soil bacterial community structure would differ between hummocks and hollows. We fingerprinted soils collected from different microtopographic locations using Length Heterogeneity Polymerase Chain Reaction (LH-PCR) to study their bacterial community structures. Two hummocks had silty/sandy loam soils with mean chroma values of > 4, showing no indication of ‘hydric soils’ (i.e., wetland soils). Two hollows, however, had clay loam soils with mean chroma values of 2 with gleying and redox concentrations observed, indicative of seasonally inundated wetlands. The soils of hollows also had higher organic matter content and soil moisture compared to the soils of hummocks (P < 0.05). Multidimensional scaling (MDS) and Analysis of similarity (ANOSIM) of the fingerprints revealed differences in soil microbial community structures between hummocks and hollows (Global R = 0.30, P < 0.01). The diversity measures of the fingerprints (Shannon’s H′) were also different by microtopography with higher diversity in hollows relative to hummocks (P < 0.05). LH-PCR proves to be a useful tool in examining bacterial community composition of wetland soils in this study. However, cloning and sequencing of specific community LH-PCR profiles of interest is necessary to fully characterize the community down to genus/species level. With species identities we should be able to not only better explain differences observed in the community profiles, but study their relations to hydrologic and/or physicochemical conditions of wetlands.     

The soil organic carbon in particle-size separates under different regrowth forest stands of north eastern Costa Rica

Despite the importance of the secondary forest (SF) in tropical areas, few studies have quantified the soil organic carbon (SOC) pool in Costa Rica. Most of the studies conducted to date in this country have focused mainly on changes in the soil C pool following conversion of forests to pastures, which is the predominant land use in the tropics. The aim of this study was to measure SOC concentration and pool in particle-size fractions down to 50 cm depth in four SF stands regenerating from different intensities of prior land use in loamy sand and sandy loam soils of northeast Costa Rica: (i) a gallery forest (GF), (ii) a 15-year-old SF enriched with commercially planted native trees (15SF), (iii) a 25-year-old SF (25SF), and (iv) an abandoned Theobromma cacao plantation >60 years old (60SF). Additional objectives were (1) to determine the relationship of SOC concentration with selected physical and chemical soil properties, and (2) to establish the key determinants of the depth distribution of SOC in order to identify meaningful trends in the SOC pool. The SOC pool was highest under the 60SF (221.4 Mg C ha⁻¹) followed by the 15SF (212.1 Mg C ha⁻¹), the 25SF (195.9 Mg C ha⁻¹) and the lowest in the GF (183.5 Mg C ha⁻¹). The SOC concentration decreased significantly from 59.7 to 94.1 g kg⁻¹ in the 0–10 cm layer down to 31.0 to 45.5 g kg⁻¹ in the 40–50 cm layer in all forest stands. The fine silt + clay fraction contained the highest values of SOC concentration in all forest stands. Soil texture and the age of the SF were identified as the main factors that explained the variability in SOC. The age of SF stand influenced the distribution of size class aggregates and SOC.     

Influence of draining on soil phosphorus forms and distribution in a constructed wetland

Seasonal water-table fluctuations in wetlands can result in flooded and drained conditions in the surface soil. In constructed wetlands water level drawdown and soil drainage are used in management to consolidate detrital materials, accelerate soil build up, and provide easy access for other management operations. A greenhouse study was conducted using intact peat soil cores to evaluate the changes in bioavailable P and other fractions following draining and reflooding. Measurements of floodwater dissolved reactive P (DRP) indicated that draining and soil exposure could result in large P flux to the overlying water column. Phosphorus flux in soils drained for 6 weeks was 10-fold higher (334 mg P m⁻² day⁻¹) than in soils drained for 3 weeks (33 mg P m⁻² day⁻¹). Soil exposure also resulted in an increase in bioavailable inorganic P (estimated by KCl extraction) at the expense of labile organic P pool. The KCl-P pool, which was initially less than 2% of total P (TP), increased to 3% and 13% of TP after 3 and 6 weeks draining, respectively. Results suggest that various soil P fractions, particularly those in newly accreted materials, were highly unstable and could be released in a more available form when newly accreted soils undergo drying. Water level drawdown and reflooding could result in significant P release, a possible stimulation of algal blooms and other water quality problems. Therefore, soil characteristics and chemistry and their impact on water quality should be a major consideration when one adopts the flood-drain technique in wetland management.     

Aquatic metabolism as an indicator of the ecological effects of hydrologic pulsing in flow-through wetlands

Water column metabolism is a major component in the functioning of wetland ecosystems and can be used as an indicator of ecosystem health. The effect of hydrologic pulsing on water column metabolism was studied with 2 year's field data and a validated model for two 1-ha created riparian wetlands in Columbus, OH, USA. Aquatic gross primary productivity (GPP) was measured during hydrologic pulses the first week of April, May and June of 2004 and compared to GPP during steady flow-conditions in April, May and June 2005. Pulses reduced diurnal variation of water temperature, pH and dissolved oxygen, and negatively affected GPP rates. Mean GPP measured during hydrologic flood pulses was 5.4 ± 2.6 kcal m⁻² day⁻¹, significantly lower than that measured for comparable months with steady-flow hydrology (10.8 ± 3.3 kcal m⁻² day⁻¹). Solar-normalized productivity values of 0.08 ± 0.01% of solar energy during pulses and 0.2 ± 0.02% for steady-flow conditions were also significantly different. Different hyperbolic curves of optimum productivity with water temperature were seen for pulsing and steady-flow conditions. A simulation model with hydrology, metabolism, and dissolved oxygen sub models was calibrated with 2005 steady-flow year data and validated with 2004 pulse year data. Results from both the field study and model simulations suggest that there was a threshold hydraulic inflow rate between 30 and 50 cm day⁻¹ where aquatic metabolism became negatively affected by flow.     

The impacts of re-introducing Mississippi River water on the hydrologic budget and nutrient inputs of a deltaic estuary

Most wetlands of the Mississippi deltaic plain are isolated from riverine input due to flood control levees along the Mississippi River. These levees have altered hydrology and ecology and are a primary cause of massive wetland loss in the delta. River water is being re-introduced into coastal basins as part of a large-scale ecological engineering effort to restore the delta. We quantified freshwater, nitrogen, and phosphorus inputs to the Breton Sound Estuary for three climatically different years (2000, 2001, and 2002). Water budgets included precipitation, potential evapotranspiration, the diversion, stormwater pumps, and groundwater. Precipitation contributed 48–57% of freshwater input, while the diversion accounted for 33–48%. Net groundwater input accounted for less than 0.05% of freshwater inputs. Inputs of ammonium (NH₄-N), nitrate (NO₃-N), total nitrogen (TN), and total phosphorus (TP) were determined for each of the water sources. Atmospheric deposition was the most important input of NH₄-N (57–62% or 1.44 × 10⁵–2.32 × 10⁵ kg yr⁻¹) followed by the diversion. The diversion was the greatest source of NO₃-N (67–83%, 7.78 × 10⁵–1.64 × 10⁶ kg yr⁻¹) and TN (60–71%). The diversion contributed 41–60% of TP input (1.17 × 10⁵–2.32 × 10⁵ kg yr⁻¹). Annual loading rates of NH₄-N and NO₃-N were 0.17–0.27 and 1.2–2.3 g N m⁻² yr⁻¹, respectively, for the total basin indicating strong retention of nitrogen in the basin. Nitrogen retention through denitrification and burial was estimated for the upper basin.