Extracellular phosphatase activity in sediments of the Breitenbach,a Central European mountain stream

Activity of extracellular phosphatases (phosphomonoesterases) was measured in sandy streambed sediments of the Breitenbach, a small unpolluted upland stream in Central Germany. Fluorigenic 4-methylumbelliferyl phosphate served as a model substrate. Experiments were conducted using sediment cores in a laboratory simulation of diffuse groundwater discharge through the stream bed, a natural process occurring in the Breitenbach as well as many other streams.Streambed sediments contained high levels of particulate phosphorus, but concentrations of dissolved phosphorus in the interstitial water were 3 to 4 orders of magnitude lower. These interstitial concentrations were similar to those in the stream and groundwater. Extracellular phosphatase activity was high in the streambed sediments. These enzymes probably contribute significantly to the flux of phosphorus in sediment by hydrolyzing phosphomonoesters, making free phosphate available to the sediment microorganisms.Factors influencing the kinetic parameters V _max (maximum activity) and apparent K _m (enzyme affinity) of phosphatase were discharge rates of water through the sediment, water quality (ground- or stream water), and substrate (phosphomonoesters) as well as dissolved ortho-phosphate concentrations. Enzymes are supposed to be effective at limiting substrate concentrations, where, in this study, changes in discharge rates had little influence on rates of hydrolysis. Higher V _max and lower K _m values were found during percolation of groundwater through the sediment cores, compared with stream water. This indicates that rates of hydrolysis were higher with groundwater, both at substrate limitation and at substrate saturation. This was probably a consequence of the lower levels of dissolved ortho-phosphate in the groundwater.     

Energy requirements for nitrification and biological nitrogen removal in engineered wetlands

Nitrogen in wastewater degrades aquifer and surface water quality. To protect water quality in the United States, nitrogen discharge standards are strict: typically 1.0 mg/L NH₄-N for discharge to surface water and 10 mg/L total nitrogen (TN) for discharge to soil. Passive constructed wetland treatment systems cannot meet the nitrification standards discussed in this paper, using loading rates commonly considered to be cost-effective based on economic conditions in North America. Although partial nitrification can be achieved with some vertically or intermittently loaded, subsurface flow (SSF) wetlands, complete nitrification cannot be achieved in these passive wetland treatment systems. Engineered wetlands (EWs) use mechanical power inputs via pumping of air or water to nitrify wastewater, and have evolved in large part to nitrify wastewater. The design energy requirements for these power inputs have yet to be described in the wetland treatment literature. Our paper investigates the energy and area requirements of three wetland technologies: aerated subsurface flow, tidal flow, and pulse-fed wetland treatment, compared to a mechanical activated-sludge treatment system.     

Effects of hydrology on spatial patterns of soil development in created riparian wetlands

Surficial soil development was studied in four wetland basins created on the floodplain of the Des Plaines River near Chicago, Illinois, USA. These studies determined changes in the spatial distribution of plant-available nutrients as a result of establishing two different wetland hydrologic regimes. Three wetland basins had mineral soils and one an organic soil. A geostatistical analysis including kriging of collected data indicated that all soil parameters showed significant changes in their spatial structure as a result of the water inputs and unidirectional flows. The degree of spatial variability as indicated by autocorrelation in the soil data (i.e., points closer to one another are more similar than points further apart due to the influence of landscape processes) declined for all parameters except Mg⁺². Temporal changes in the spatial patterns of extractable phosphorus (P) and percent organic carbon (OC) tended to be inverse; P declined in areas where OC increased and vice versa. The spatial pattern of these changes was dissimilar in the mineral soils as compared to the organic soil and was related to patterns of primary productivity. Zones of P uptake and OC accumulation were also related to wetland hydrology and primary productivity. Changes in the distribution of nutrients, particularly P, may be viewed as a result of nutrient spirals within the wetlands. By comparison, the reorganization in the concentrations of K⁺ and Ca⁺² appear to have been mediated by cation exchange processes. The formation of new concentration gradients was strongly related to both flow pathways and the different water inflow rates. The formation of concentration gradients in exchangeable cations was not reflected in the average concentrations within each basin. Mean values changed significantly in only a few instances. Reducing data in this way missed important biogeochemical changes occurring within the experimental wetland basins. This revised version was published online in July 2006 with corrections to the Cover Date.     

Primary production, nutrient dynamics, and accretion of a coastal freshwater forested wetland assimilation system in Louisiana

This study reports on the response of a tidal, freshwater forested wetland ecosystem to long-term input of secondarily treated municipal effluent from the City of Mandeville, LA. Measurements of hydrology, nutrients, and aboveground net primary productivity were made from September 1998 through March 2002. Accretion measurements were made in October 2000 and October 2004. The major hydrologic inputs to the system were the effluent, precipitation, and back water flooding from Lake Pontchartrain. Nutrient levels were generally low except in the immediate vicinity of the outfall. Mean net primary production of the freshwater forest system was significantly higher downstream of the effluent discharge (1202 g m⁻² yr⁻¹) compared to the control site (799 g m⁻² yr⁻¹). Downstream of the outfall, accretion rates were double the rate of relative sea level rise in the area. Removal efficiencies of N and P were as high as 75% and 95%, respectively. The relatively constant flow of secondarily treated municipal effluent buffered the downstream area from salinity intrusion during a region-wide drought. Re-direction of nutrient-enhanced effluents from open water bodies to wetland ecosystems can maintain plant productivity, sequester carbon, and maintain coastal wetland elevations in response to sea-level rise in addition to improving overall surface water quality, reducing energy use, and increasing financial savings.     

Impacts of Nutrient Loading on Mercury Fractionation and Mobility in an Estuarine Wetland in Nansi Lake,China

Total mercury is closely related to nutrient status in ecosystems. However, studies specifying the effects of various nutrient forms on the mobility of mercury are rare. In this study, three fractions of mercury (mobile, semi-mobile, and non-mobile) were examined in the soil of an estuarine wetland with excessive nutrient inputs in northern China. The wetland is located in the east route of China's South-to-North Water Transfer Project. Correlations between the three fractions of mercury and four nutrient parameters were analyzed. Results showed that toxic mobile and semi-mobile mercury comprised a great portion of total soil mercury in the studied wetland. Among the four nutrient parameters, ammonium nitrogen showed a significant negative correlation with mobile toxic mercury and was the principal nutrient component that influenced the mobility and toxicity of mercury. Nitrate nitrogen showed a positive correlation with mobile toxic mercury. Moreover, carbon/nitrogen ratio and soil acid were positively correlated with mercury mobility. Given that lower nitrogen loading is required in the watershed to ensure the water quality during the water transfer project, our study suggested that changes in nitrogen inputs might promote the mobility and bioavailability of mercury in the watershed. Thus, more attention should be provided to the potential hazard of mercury in the food web during the water transfer.     

不同设计参数对雨水湿地水量水质的调控规律

基于前置塘+二阶表流湿地组合的雨水湿地系统的室内降雨径流模拟实验数据,研究了不同降雨重现期、不同常水位、不同湿地出水口高度、不同湿地级数以及不同污染负荷等设计参数对湿地水量水质调控效果的影响规律,研究结果表明:前置塘+二阶湿地组合的雨水湿地系统通过截留、缓冲和存储作用,对不同降雨径流条件下的产流时间、流量、径流削减率具有多重调控作用,延长了污染物在流域内部的滞留时间,减少了污染负荷的输出,对降雨径流过程中污染物总量具有较好的截留效果。并随设计参数的变化有明显的变化规律。随着降雨重现期的增加,湿地出水口高度的降低,湿地常水位的增加,以及湿地级数的减少,湿地出流量增加,产流时间提前,出流持续时间延长,径流削减率降低。从场次降雨污染物平均浓度(EMC)削减率上看,降雨过程中,雨水湿地仅对SS削减比较明显,削减率达70%—80%,对其他污染物浓度的削减效果不明显。从场次降雨污染物总量削减率来看,雨水湿地对降雨径流污染物具有较好的截留效果,并随着降雨重现期减少、湿地出水口高度增加、湿地常水位降低,呈逐渐增加趋势。     

Effects of agriculture and wetland restoration on hydrology, soils, and water quality of a Carolina bay complex

We compared hydrology, soils, and water quality of an agricultural field (AG), a two-year-old restored wetland (RW), and two reference ecosystems (a non-riverine swamp forest (NRSF) and a high pocosin forest (POC)) located at the Barra Farms Regional Wetland Mitigation Bank, a Carolina bay complex in Cumberland County, North Carolina. Our main objectives were to: 1) determine if the RW exhibited hydrology comparable to a reference ecosystem, 2) characterize the soils of the AG, RW, and reference ecosystems, and 3) assess differences in water quality in the surface outflow from the AG, RW, and reference ecosystems. Water table data indicated that the hydrology of the RW has been successfully reestablished as the hydroperiod of the RW closely matched that of the NRSF in 1998 and 1999. Jurisdictional hydrologic success criterion was also met by the RW in both years. To characterize soil properties, soil cores from each ecosystem were analyzed for bulk density (D_b), total carbon (C_t), nitrogen (N_t), and phosphorus (P_t), extractable phosphate (PO_4w), nitrogen (N_ex), and cations (Ca_ex, Mg_ex, K_ex, Na_ex), as well as pH. Bulk density, P_t, Ca_ex, Mg_ex, and pH were greatly elevated in the AG and RW compared to the reference ecosystems. Water quality monitoring consisted of measuring soluble reactive phosphorus (SRP), total phosphorus (TP), nitrate + nitrite (NOX), and total nitrogen (TN) concentrations in surface water from the AG, RW, and reference outflows. Outflow concentrations of SRP, TP, and NOX were highest and most variable in the AG, while TN was highest in the reference. This study suggested that while restoration of wetland hydrology has been successful in the short term, alteration of wetland soil properties by agriculture was so intense, that changes due to restoration were not apparent for most soil parameters. Restoration also appeared to provide water quality benefits, as outflow concentrations of SRP, TP, NOX, and TN were lower in the RW than the AG.     

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.     

The effects of in situ drying on sediment–phosphate interactions in sediments from an old wetland

We examined the effects of drying on sediment–P interactions for sediments from a shallow wetland ca. 6000 years old. Sediments from this wetland would have been subjected to numerous drying and wetting episodes during the life of the wetland. The factors affecting potential orthophosphate release were compared in surface sediments that had previously been desiccated for 3 months, surface sediments that had remained inundated and wet sediment 25–30 cm below the surface. All sediments released small amounts of orthophosphate once subjected to anaerobic conditions. Sulfate alone stimulated phosphate release from the surface sediment, irrespective of the previous hydrological status, whereas orthophosphate release from deep sediments was co-limited by carbon and sulfate. Decreases in soluble Fe (II) were measured concurrently with sulfate-stimulated P release, which is consistent with formation of iron sulfides. Similar numbers of culturable sulfate-reducing bacteria were obtained from the wet and dry sediments, their tolerance to desiccation explaining why release could occur after extensive drying of the sediment. Phosphate adsorption isotherms of the sediments showed that sediments from all sites had a relatively low affinity for ortho-phosphate. The adsorption data showed reasonable fit to the Freundlich adsorption isotherm. No difference in the maximum amount of ortho-phosphate uptake was observed if the sediment isotherm experiments were done under an inert atmosphere or, following exposure to air, suggesting that even anoxic sediments were not highly reduced. However, significant variations in the value of the Freundlich constants were observed. The results presented in this study are consistent with the hypothesis that repeated wetting/drying cycles select for bacteria that are tolerant to periods of desiccation and/or oxidation. Furthermore, repeated wetting and drying cycles may result in changes to sediment mineralogy.     

Analyzing the ecosystem carbon and hydrologic characteristics of forested wetland using a biogeochemical process model

A comprehensive biogeochemical model, Wetland‐DNDC, was applied to analyze the carbon and hydrologic characteristics of forested wetland ecosystem at Minnesota (MN) and Florida (FL) sites. The model simulates the flows of carbon, energy, and water in forested wetlands. Modeled carbon dynamics depends on physiological plant factors, the size of plant pools, environmental factors, and the total amount and turnover rates of soil organic matter. The model realistically simulated water level fluctuation, forest production, carbon pools change, and CO₂ and CH₄ emission under natural variations in different environmental factors at two sites. Analyses were focused on parameters and inputs potentially cause the greatest uncertainty in calculated change in plant and soil C and water levels fluctuation and shows that it was important to obtain accurate input data for initial C content, climatic conditions, and allocation of net primary production to various forested wetland components. The magnitude of the forest responses was dependent not only on the rate of changes in environmental factors, but also on site‐specific conditions such as climate and soil. This paper explores the ability of using the biogeochemical process model Wetland‐DNDC to estimate the carbon and hydrologic dynamics of forested wetlands and shifts in these dynamics in response to changing environmental conditions.     

Nutrient fluxes in a snow-dominated, semi-arid forest: Spatial and temporal patterns

We tested five hypotheses regarding the potential effects of precipitation change on spatial and temporal patterns of water flux, ion flux, and ion concentration in a semiarid, snowmelt-dominated forest in Little Valley, Nevada. Variations in data collected from 1995 to 1999 were used to examine the potential effects of snowpack amount and duration on ion concentrations and fluxes. Soil solution NO₃ ^–, NH₄ ⁺, and ortho-phosphate concentrations and fluxes were uniformly low, and the variations in concentration bore no relationship to snowmelt water flux inputs of these ions. Weathering and cation exchange largely controlled the concentrations and fluxes of base cations from soils in these systems; however, soil solution base cation concentrations were affected by cation concentrations during snowmelt episodes. Soil solution Cl^– and SO₄ ^2– concentrations closely followed the patterns in snowmelt water, suggesting minimal buffering of either ion by soils. In contrast to other studies, the highest concentration and the majority of ion flux from the snowpack in Little Valley occurred in the later phases of snowmelt. Possible reasons for this include sublimation of the snowpack and dry deposition of organic matter during the later stages of snowmelt. Our comparison of interannual and spatial patterns revealed that variation in ion concentration rather than water flux is the most important driver of variation in ion flux. Thus, it is not safe to assume that changes in total precipitation amount will cause concomitant changes in ion inputs to this system.     

Nitrogen inputs to a marine embayment: the importance of groundwater

We examined the importance of nitrogen inputs from groundwater and runoff in a small coastal marine cove on Cape Cod, MA, USA. We evaluated groundwater inputs by three different methods: a water budget, assuming discharge equals recharge; direct measurements of discharge using bell jars; and a budget of water and salt at the mouth of the Cove over several tidal cycles. The lowest estimates were obtained by using a water budget and the highest estimates were obtained using a budget of water and salt at the Cove mouth. Overall there was more than a five fold difference in the freshwater inputs calculated by using these methods. Nitrogen in groundwater appears to be largely derived from on site septic systems. Average nitrate concentrations were highest in the region where building density was greatest. Nitrate in groundwater appeared to behave conservatively in sandy sediments where groundwater flow rates were high (> 11/m²/h), indicating that denitrification was not substantially reducing external nitrogen loading to the Cove. Nitrogen inputs from groundwater were approximately 300 mmol-N/m³/y of Cove water. Road runoff contributed an additional 60 mmol/m³/y. Total nitrogen inputs from groundwater and road runoff to this cove were similar in magnitude to river dominated estuaries in urbanized areas in the United States.     

Nitrogen inputs to a marine embayment: the importance of groundwater

We examined the importance of nitrogen inputs from groundwater and runoff in a small coastal marine cove on Cape Cod, MA, USA. We evaluated groundwater inputs by three different methods: a water budget, assuming discharge equals recharge; direct measurements of discharge using bell jars; and a budget of water and salt at the mouth of the Cove over several tidal cycles. The lowest estimates were obtained by using a water budget and the highest estimates were obtained using a budget of water and salt at the Cove mouth. Overall there was more than a five fold difference in the freshwater inputs calculated by using these methods. Nitrogen in groundwater appears to be largely derived from on site septic systems. Average nitrate concentrations were highest in the region where building density was greatest. Nitrate in groundwater appeared to behave conservatively in sandy sediments where groundwater flow rates were high (> 11/m²/h), indicating that denitrification was not substantially reducing external nitrogen loading to the Cove. Nitrogen inputs from groundwater were approximately 300 mmol-N/m³/y of Cove water. Road runoff contributed an additional 60 mmol/m³/y. Total nitrogen inputs from groundwater and road runoff to this cove were similar in magnitude to river dominated estuaries in urbanized areas in the United States.     

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.     

Longitudinal Poisson regression to evaluate the epidemiology of Cryptosporidium, Giardia, and fecal indicator bacteria in coastal California wetlands

Fecal pathogen contamination of watersheds worldwide is increasingly recognized, and natural wetlands may have an important role in mitigating fecal pathogen pollution flowing downstream. Given that waterborne protozoa, such as Cryptosporidium and Giardia, are transported within surface waters, this study evaluated associations between fecal protozoa and various wetland-specific and environmental risk factors. This study focused on three distinct coastal California wetlands: (i) a tidally influenced slough bordered by urban and agricultural areas, (ii) a seasonal wetland adjacent to a dairy, and (iii) a constructed wetland that receives agricultural runoff. Wetland type, seasonality, rainfall, and various water quality parameters were evaluated using longitudinal Poisson regression to model effects on concentrations of protozoa and indicator bacteria (Escherichia coli and total coliform). Among wetland types, the dairy wetland exhibited the highest protozoal and bacterial concentrations, and despite significant reductions in microbe concentrations, the wetland could still be seen to influence water quality in the downstream tidal wetland. Additionally, recent rainfall events were associated with higher protozoal and bacterial counts in wetland water samples across all wetland types. Notably, detection of E. coli concentrations greater than a 400 most probable number (MPN) per 100 ml was associated with higher Cryptosporidium oocyst and Giardia cyst concentrations. These findings show that natural wetlands draining agricultural and livestock operation runoff into human-utilized waterways should be considered potential sources of pathogens and that wetlands can be instrumental in reducing pathogen loads to downstream waters.     

Utilization of limiting concentrations of ortho-phosphate and production of extracellular organic phosphates in cultures of marine diatoms

The utilization of ortho-phosphate by two coastal marine diatomspecies, Nitzschia closterium and Cyclotella cryptica, was studiedin batch cultures. The hypothesis was tested that thresholdconcentrations in the phosphate uptake determine the lower limitof environmental phosphate, permitting the existence of species.The turn-over time of residual medium phosphate in culturesis {small tilde}10 min, indicating a rapid equilibration ofconcentration dependent on uptake with leakage of ortho-phosphate.Increasing phosphate starvation in cultures diminished the residualortho-phosphate in the range of {small tilde}60–<2nmol l^–1, as measured radiochemically after elution onSephadex® G-10 gel. These concentrations encompass the rangeof limiting phosphate concentration in continuous cultures ofthe few microalgae, for which these concentrations are actuallymeasured. The diatoms excreted {small tilde}20–100 nmolI^–1 of organic phosphate. One dominating compound, probablyan unusual nucleotide, was incompletely or not resorbed underphosphate starvation. In contrast, Nitzschia closterium excretedunder ample phosphate supply a series of three related compounds,probably phospholipids, that were resorbed under depletion.The association of the organic phosphates with macromolecularexudates is interpreted, along with the other observations,as an indication for a hardly explored periplasmatic phosphatemetabolism in these algae. ³Dedicated to Prof. Dr. H.-A. von Stosch in honour of his 75thbirthday. ⁴This study was conducted at the University of Marburg undersupport of the Humboldt Foundation Publication no. 64 of theproject "Biological Research of the Eems-Dollard Estuary".     

Biodiversity of constructed wetlands for wastewater treatment

Constructed wetlands are often built for wastewater treatment to mitigate the adverse effects of organic pollution in streams and rivers caused by inputs of municipal wastewater. However, there has been little analysis of biodiversity and related factors influencing the ecosystem functioning of constructed wetlands. The purpose of this study was to evaluate the biodiversity of two free-water-surface integrated constructed wetlands in subtropical Taiwan by analyzing the water quality, habitat characteristics, and biotic communities of algae, macrophytes, birds, fish, and aquatic macroinvertebrates in the treatment cells. Our results indicated that the two integrated constructed wetlands (Hsin-Hai II and Daniaopi Constructed Wetlands) achieved good performance in reducing the concentrations of total nitrogen (TN) and total phosphorus (TP), and loadings of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) from municipal sewage. In total, 58 bird species, 7 fish species, and 34 aquatic macroinvertebrate taxa were recorded in the two wetlands. The results of stepwise multiple regressions showed that the richness, abundance, and diversity of birds increased with wetland area. Fish richness and abundance respectively increased with wetland area and dissolved oxygen, while the diversity decreased with increases in TP concentrations. The richness and density of aquatic macroinvertebrates increased with the cover of aquatic macrophytes, while the diversity increased with wetland area. Ordination analyses indicated that variations in the community structures of birds, fishes, and aquatic macroinvertebrates were respectively best explained by water temperature, wetland area, and species richness of fish. Our results suggest that wetland area, cover of aquatic macrophytes, and water quality were the most important factors governing the diversity in the constructed wetlands, and that the factors influencing community structures varied among different taxonomic groups. In addition to improving water quality, this study implied that the biodiversity of constructed wetlands for wastewater treatment can be enhanced through proper design and management.     

The influence of within-stream disturbance on dissolved nutrient levels during spates

In rivers, variations in concentrations of many dissolved nutrients occur during spates. Increases are usually attributed to concentrated point or non-point inputs, and decreases to dilution associated with rainfall. Increased discharge disturbs sediments and benthic communities, but the effects of such disturbance on nutrient levels are difficult to isolate. Measurements of nutrient levels over three artificial spates revealed that substantial variations in dissolved organic carbon, dissolved phosphate, silicate, nitrate, and potassium levels could result from increased discharge in the absence of allochthonous inputs. Variations were closely related to peaks in suspended solids concentration or water height. Increases in biochemical oxygen demand and suspended bacteria also occurred. Variations in phosphate and silicate could be accounted for by a balance between release of ‘sediment interstitial water’ and exchange processes involving suspended and freshly exposed sediment. An increase in nitrate, during one spate, was probably due to a reduction in the effect of benthic denitrification. Small peaks in dissolved organic matter concentration were detected over each spate. We propose that within-stream disturbance is a factor which may contribute to variations in dissolved nutrient concentration during the rising hydrograph in natural spates.     

Soil and Hydrological Drivers of Typha latifolia Encroachment in a Marl Wetland

Aggressive species competition by Typha latifolia in wetland systems on marl-derived soils may threaten the unique vegetation in these areas. We examined historic water and land use, soil chemistry, soil genesis, and topography in a wetland (Harewood Marsh) that is under encroachment by T. latifolia. An earthen road that bisects the wetland and active pastures in and around the wetland were also considered in the study due to their potential influence on wetland hydrology and nutrient inputs. Historic land uses and trends in surface water patterns were determined via aerial photography. In addition local landowners and city officials were contacted for information about historic water use in the area around the marsh. Soils were augered and sampled in seven locations in the wetland, and at each auger site, vegetation was described. Six wells were installed near the earthen road and weekly water depth measurements were taken from January 2002 to January 2003. In February 2002, 10 A-horizon soil samples (per transect) were taken from three 150-m transects that spanned areas with and without T. latifolia. Results indicate that T. latifolia encroachment is facilitated by a rising water table (the result of the termination of a local municipal water supply source) and N and P inputs, most likely from cattle grazing on the wetland. An increase in the numbers of rare plant species associated with marl wetland habitats appears to have also occurred and is believed partly due to current wetter conditions. Our study provides insight into the dynamics of T. latifolia encroachment in a unique marl wetland habitat and demonstrates how local factors controlling nutrient and hydrologic dynamics can have significant effects on changes in plant community composition.     

Nitrogen and Phosphorus in a Stretch of the Guadalupe River,Texas, with Five Main-Stream Impoundments by

Nitrogen and phosphorus were studied in a 168-km stretch of the Guadalupe River that had five main-stream impoundments. Flow through the study area was controlled by releases from these five reservoirs and from Canyon Reservoir, a deep-storage reservoir, located 30 km upstream. Parameters measured monthly on a diel basis at 16 stations were nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, Kjeldahl nitrogen, inorganic phosphate phosphorus, organic phosphate phosphorus, and total phosphate phosphorus.Inorganic nitrogen concentrations observed in this study were as high or higher than that previously reported for other bodies of water. Nitrate nitrogen entered the study area in relatively high concentrations from Comal Springs which was a major source of water for the Guadalupe River. Water from Canyon Reservoir, the other major source of water, was relatively low in nitrate nitrogen. The concentration of nitrate nitrogen was, therefore, dependent in part upon the portion of the total river flow originating from the two sources. Increased discharge from Canyon Reservoir and utilization by plants in areas of high chlorophyll a resulted in low nitrate-nitrogen levels. Retention of water in reservoirs reduced the concentration of nitrate nitrogen due to increased utilization by plants in areas of low flow. Nitrate nitrogen, in general, reached seasonal minima in summer and maxima in winter. Nitrite nitrogen showed considerable variation with no meaningful pattern except that higher concentrations occurred in association with high chlorophyll a and high Kjeldahl nitrogen, regions and periods of low river flow, and large phytoplankton populations. There was no increase in concentration of any form of nitrogen in the vicinity of sewage outfalls and no downstream accrual.Phosphorus levels in the study area were as high or higher than those reported in studies of other bodies of water. Sewage treatment plants at New Braunfels and Seguin, Texas, were major sources of phosphorus to the Guadelupe River. Total phosphate phosphorus was determined to be the most critical phosphate parameter in assessing eutrophication. Seasonally, it ranged from a winter high to a summer low. Concentrations were highest immediately below sewage outfalls and decreased as water progressed downstream. Inorganic-phosphate-phosphorus concentrations showed no clear seasonal trend but were clearly associated with sewage outfalls. Since large standing crops of phytoplankton were observed in areas of low inorganic phosphate phosphorus, it was not considered to limit photosynthesis. Total organic phosphate phosphorus varied seasonally, with high concentrations occurring during the spring and low concentrations in the fall. Total organic phosphate phosphorus showed no correlation with sewage outfalls, but was correlated to a degree with total Kjeldahl nitrogen and chlorophyll a. No consistent pattern of diel fluctuations was evident for any phosphorus or nitrogen compounds analyzed.