Effects of submerged macrophytes on sediment resuspension and internal phosphorus loading in Lake Hiidenvesi (southern Finland)

The effects of submerged macrophytes on sediment resuspension and internal phosphorus loading in the shallow Kirkkoj?rvi basin of Lake Hiidenvesi were studied by sedimentation traps and sediment and water samples. During the 83 d study period, 793 g DW m(-2) of sediment was resuspended within the stand formed by Ranunculus circinatus, Ceratophyllum demersum and Potamogeton obtusifolius. Outside the stand, 1701g DW m(-2) sediment resuspension was measured during the same period. Water turbidity and concentration of suspended solids (SS) were significantly lower within the plant bed compared with the surrounding water area. Despite the higher concentration of inorganic suspendoids, the concentration of chlorophyll a was higher in the open water than within the submerged plant bed, owing to the enhanced nutrient recycling rate in the absence of submerged plants. With the resuspended sediment, 11.8 mg Pm(-2)d(-1) was brought into the water column within the stand and 24.5 mg Pm(-2)d(-1) outside the stand. Within the macrophyte stand, resuspended particles absorbed phosphorus from the water (indicated by the inverse relationship between SS and soluble reactive phosphorus), which was probably connected to the lowered phosphorus concentration of surface sediment due to uptake by macrophytes.     

Sediment nutrient characteristics and aquatic macrophytes in lowland English rivers

Aquatic macrophytes play an important role in the nutrient dynamics of streams. As a result, there is much interest in their use as trophic indicators. However, the relationship between aquatic macrophytes and the trophic status of rivers is a complex one, partly because of the effects of a wide range of environmental variables and partly because submerged, rooted macrophytes can absorb nutrients from the river sediments and/or the water column. Experiments which have tried to establish the relative importance of sediments or water as sources of nutrients are inconclusive and further work is needed to establish how sediment nutrient characteristics vary within and among rivers (spatially and temporally) and the inter-relationships between sediment nutrients, water column chemistry and macrophytes. This paper presents the initial findings from a study of 17 lowland rivers in southern England which is exploring the spatial variability of sediment characteristics (total and inorganic phosphorus, total nitrogen, organic carbon, silt-clay fraction and organic matter content) and the relationship with aquatic macrophytes. The preliminary analysis indicates that although sediment characteristics are highly variable within 100-m river reaches, the variability across the 17 rivers is even greater; this is despite the limited geographic and trophic range of the study sites. The results presented in this paper also give some indication of the sediment characteristics associated with five macrophyte species but it is too early to ascribe sediment preferences for particular species.     

The Management of Sediment in Reservoired Catchments

The rates of sedimentation in Yorkshire reservoirs are high for the UK but low compared with those reported globally. Whilst not likely to jeopardize supply, the behaviour and properties of reservoir sediments have implications for the quantity and quality of the water.
Data suggest that the use of control and diversion structures reduces average sedimentation by 53m³/km² per annum in the case of residuum lodges, and also modifies the nature of the sediment considerably, tending to allow the finer, organic particles into the reservoir. Trapping may be minimized by the diversion of high flows where such facilities exist, or by maintaining water levels at the maximum possible in supply reservoirs.
Management strategies to reduce sedimentation would, in many cases, require fairly simple routine maintenance of existing structures. The short-term cost of discarded water must be weighed against the longer-term benefits of improved quality and reservoir capacity.     

水力负荷对湖滨带人工湿地除磷效果的影响

分析了湖滨带复合人工湿地的各单元在旱季和雨季的除磷效果。结果表明，在进水TP浓度较高时，沉淀池对TP的去除效果较明显，旱、雨季的不同水力负荷对处理效果几乎没有影响。雨季时潜流人工湿地内发生了不溶性磷的吸附和沉积，实现了对磷的去除；旱季时由于水力负荷极小，水体流动性差，系统内处于厌氧状态，出现了磷的释放。雨季时，表面流人工湿地对磷的去除效果没有沉淀池和潜流人工湿地的理想，旱季的低水力负荷对除磷效果没有显著的影响。     

Improvements in small-scale standardized testing of geotextiles used in silt fence applications

Silt fence have been used as a means for intercepting and treating construction site stormwater runoff prior to offsite discharge for well over 30 years. Standard small-scale testing methodologies for evaluating the filtering component of silt fence installations have failed to mimic realistic flows and sediment loadings commonly seen in field applications. To address these issues, this study evaluated the performance capabilities of two nonwoven and three woven silt fence geotextiles using an innovative testing methodology and a newly developed small-scale testing apparatus. The overall intent for conducting the evaluations was to develop a deeper understanding of effluent flow rates, sediment retention capabilities, and water quality impacts associated with geotextile fabrics. Results suggest that effluent flow rates of nonwoven geotextiles are on average 43% lower than woven materials, which results in extensive upstream retention times of impounded stormwater for nonwoven materials. Sediment retention results indicate that nonwoven geotextiles have an average sediment retention rate of 97% while woven geotextiles average 91%. Finally, water quality analyses suggest that the primary means for turbidity reductions rely on the process of sedimentation during the 30-min test period (i.e., 46% reduction) and filtration during the 90-min dewatering period (i.e., 19% reduction).     

The phosphorus budget of the Thame catchment,Oxfordshire: 2. Modelling

The phosphorus budget of the River Thame was modelled at a daily time scale, using estimates of diffuse and point source contributions of discharge. The model simulated suspended sediment (SS), soluble unreactive phosphorus (SUP), soluble reactive phosphorus (SRP) and particulate phosphorus (PP) concentrations within the main river and major tributaries. Diffuse source estimates of phosphorus loads were based on characteristic losses from identified main landscape classes, with hydrology described by a simple conceptual storage model. In-stream flow was modelled using a kinematic wave equation. Transfer of suspended sediment and phosphorus components was approximated by advection. In-stream sources and sinks included uptake and release of soluble reactive phosphorus by bed sediment, instant equilibration between SRP and the PP concentration on suspended sediment, and flow-related entrainment and deposition of suspended sediment. Simulations at sites within the catchment were compared with measurements made in 1998–1999. Results showed the P budget is dominated by mixing of diffuse and point source water, but some within-river processes have been shown to be capable of significantly influencing SRP concentrations. The development of a sediment entrainment and deposition component of the model has proved particularly valuable in emulating the hysteretic relationship between discharge and suspended sediment concentration in the river. It also provides a measure of available bed sediment.     

The effect of a wildfire on stream water quality and catchment water yield in a tropical savanna excluded from fire for 10 years (Kakadu National Park, North Australia)

The wet/dry tropics of the Australian savannas are particularly prone to fire due to the highly seasonal rainfall and accumulation of grassy fuels. The effect of an early dry season wildfire (May, 1998) on the water quality of a seasonally flowing stream (December-June) was examined for a lowland savanna forest in Kakadu National Park (northern Australia) which had remained unburnt for 10 years. The water quality variables assessed were: total and volatile suspended sediment, phosphorus, nitrogen, iron and manganese. Compared to three years of pre-fire water quality data and 5 years of stream flow data, there was no detectable impact of the wildfire on the volume of stream flow, mean concentrations and the total mass transported by the stream for each water quality variable, except possibly nitrogen. The limited effect on water quality is attributed primarily to the timing of the wildfire and the low intensity relative to fires later in the dry season (September). The retention of canopy cover and the accumulation of leaf litter following the wildfire, and the catchment's gently undulating terrain all contributed to the negligible impact on water quality. Early dry season fires appear to be a viable management option for reducing accumulated fuel loads and hence reducing the risk of destructive wildfires later in the dry season.     

Life form dependent impacts of macrophyte vegetation on the ratio of resuspended nutrients

The effects of floating-leaved and submerged macrophytes on sediment resuspension and on the ratio of resuspended nitrogen and phosphorus were studied by sediment traps in the Kirkkojärvi basin in southern Finland. The effect of submerged macrophytes on preventing sediment resuspension was stronger than the effect of floating-leaved plants. On average, among submerged plants the resuspension rate of suspended solids was 43%, and among floating-leaved plants 87% of that in the open water. The floating-leaved Nuphar lutea had a reductive effect on P resuspension but no significant effect on N resuspension. The impact on P resuspension was strong, because root uptake by Nuphar lutea reduced the P content of the sediment. N:P ratio in resuspended nutrients was 6.7 among the plants and 4.1 in the open water. Among suzbmerged plants, sediment N content was strongly increased but P content was not affected due to the pleustophytic life form of the dominant plants (Ceratophyllum demersum, Ranunculus circinatus). The effect of pleustophytes on sediment nutrients was weak, because their nutrient uptake is mostly foliar. The N:P ratio of resuspended nutrients was 7.9 among the submerged plants and 7.0 in the open water. The results suggested that depending on the life form, macrophytes can modify the flux of N and/or P to the water column through their effects on nutrient resuspension and possibly modify phytoplankton communities via their effects on the N:P ratio. If the overall nutrient level is the most important factor for the dominance of cyanobacteria, submerged macrophytes can have stronger effects on phytoplankton community structure than floating-leaved species. If N:P ratio is of importance, the effects of floating-leaved species may be more pronounced.     

Determination of areal sedimentation rates in rivers by using plate sediment trap measurements and flow velocity-settling flux relationship

Not much is known about sedimentation of organic particles in rivers. Plate sediment traps deployed in fast flowing River Spree and in a slowly flowing side arm yielded trapping rates between 0.7 and 52gDW m(-2) d(-1). A linear regression between flow velocity and trapping rates was used to extrapolate from point measurements to areal average trapping rates, which were 11 gDW m(-2) d(-1) in the side arm and 1.4 gDW m(-2) d(-1) in the free flowing river section. These rates are typical for the River Spree, but different from other rivers. The plate trap measurements provide the basic variables for the sedimentation rate sed = C x W*s(1-V/V(crit,sed)), i.e. concentration of particles (C), sinking velocity (Ws) flow velocity (V), and a threshold velocity (V(crit,sed)).     

Plant-SMFC修复富营养化水体及底泥的效果研究

为探讨植物沉积型微生物燃料电池(Plant-SMFC)对富营养化水体和底泥中污染物的去除效果及其产电能力,搭建了5组试验装置,考察了植物类型、阳极材料和石墨烯修饰对PlantSMFC系统的影响。结果表明,3个因素对Plant-SMFC系统产电能力的影响顺序为:植物>石墨烯修饰>阳极材料。由菖蒲-石墨烯修饰碳毡构成的Plant-SMFC系统产电能力和污染物去除效果最好,其输出电压为0. 31 V,对上覆水中COD、氨氮、总氮、总磷的去除率分别为85. 6%、99. 1%、89. 9%、86. 5%,对沉积物中阳极周围有机质和总氮的去除率分别为12. 7%、92. 2%,对总磷的固定率为26. 1%。Plant-SMFC系统对富营养化水体及底泥中的有机物、氮、磷等污染物具有一定的降解能力,应用前景广阔。     

Modelling sedimentation processes in a constructed stormwater wetland

The design and operation of constructed wetlands for the treatment of stormwater relies heavily on promoting sedimentation, and being able to predict accurately the expected effectiveness of the pond in removing material from the inflows. A study of sediment behaviour has been carried out in a stormwater wetland in Adelaide, Australia where computer predictions, based on solving the hydrodynamic equations and the transport equation, have been compared to deposition patterns observed in the field. The long-term residence time distribution has been shown to be useful in predicting overall sediment removal rates. Comparisons between the model and field observations indicate generally good agreement. Sources of potential error identified include the variable nature of the runoff concentrations entering the pond and the sediment size distribution. The importance of the transient nature of the flow events was highlighted by the spread of sediment throughout the whole pond.     

Seasonal nutrient dynamics in a chalk stream: the River Frome, Dorset, UK

Chalk streams provide unique, environmentally important habitats, but are particularly susceptible to human activities, such as water abstraction, fish farming and intensive agricultural activity on their fertile flood-meadows, resulting in increased nutrient concentrations. Weekly phosphorus, nitrate, dissolved silicon, chloride and flow measurements were made at nine sites along a 32 km stretch of the River Frome and its tributaries, over a 15 month period. The stretch was divided into two sections (termed the middle and lower reach) and mass balances were calculated for each determinand by totalling the inputs from upstream, tributaries, sewage treatment works and an estimate of groundwater input, and subtracting this from the load exported from each reach. Phosphorus and nitrate were retained within the river channel during the summer months, due to bioaccumulation into river biota and adsorption of phosphorus to bed sediments. During the autumn to spring periods, there was a net export, attributed to increased diffuse inputs from the catchment during storms, decomposition of channel biomass and remobilisation of phosphorus from the bed sediment. This seasonality of retention and remobilisation was higher in the lower reach than the middle reach, which was attributed to downstream changes in land use and fine sediment availability. Silicon showed much less seasonality, but did have periods of rapid retention in spring, due to diatom uptake within the river channel, and a subsequent release from the bed sediments during storm events. Chloride did not produce a seasonal pattern, indicating that the observed phosphorus and nitrate seasonality was a product of annual variation in diffuse inputs and internal riverine processes, rather than an artefact of sampling, flow gauging and analytical errors.     

Effects of aluminum treatment on phosphorus, carbon, and nitrogen distribution in lake sediment: a 31P NMR study

The effects of aluminum (Al) treatment on sediment composition of carbon (C), nitrogen (N) and phosphorus (P) were investigated in sediment representing pre- and post-treatment years in the Danish Lake S?nderby. 31P NMR spectroscopy analysis of EDTA-NaOH extracts revealed six functional P groups. Direct effects of the Al treatment were reflected in the orthophosphate profile revealing increased amounts of Al-P in the sediment layers representing the post-treatment period, as well as changes in organic P groups due to precipitation of phytoplankton and bacteria at the time of Al addition. Furthermore, changes in phytoplankton community structure and lowered production due to the Al treatment resulted in decreased concentrations of sediment organic P groups and total C. Exponential regressions were used to describe the diagenesis of C, N, and P in the sediment. From these regressions, half-life degradation times and C, N, and P burial rates were determined.     

The 20th century whole-basin trophic history of an inter-drumlin lake in an agricultural catchment

Eight 1-m sediment cores were extracted from across the basin of Friary Lough, a 5.4-ha eutrophic lake in a wholly grassland agricultural catchment in Co. Tyrone, Northern Ireland. Sedimentary TP, diatom inferred TP, Ca, Na, Fe, Mn, loss-on-ignition (LOI), dry weight and density were determined in the core profiles. Core dating and correlation gave a 210Pb, 137Cs and 241Am chronology from 1906 to 1995 and enabled a whole-basin estimate of chemical and sediment accumulation rate over the 20th Century. The major changes for all parameters occurred after c. 1946. Sediment accumulation rate was most influenced by organic matter accumulations, probably of planktonic origin, and increasing after c. 1946. Inorganic sediment accumulation rate was found to be largely unchanging through the century at 10 t km(-2) yr(-1) when expressed as catchment exports. All chemical accumulation rate changes occurred after c. 1946. Total phosphorus accumulation rate, however, was found to be the only chemical to be increasing throughout the epilimnion and hypolimnion areas of the sedimentary basin at an average of 22.5 mg m(-2) yr(-1) between 1946 and 1995. The other chemical parameters showed increasing accumulation rates after c. 1946 in the epilimnion part of the basin only. Interpreted in terms of whole-basin sedimentation and catchment export processes over time, it is suggested that diffuse TP inputs are independent of sediment inputs. This corresponds to hydrochemical models that suggest soluble P as the primary fraction that is lost from grassland catchments. The increase in sedimentary TP accumulation rate, and DI-TP concentration, are also explained with regard to current models that suggest increases in runoff P concentrations from elevated soil P concentrations. Increases in eplimnion chemical and sediment accumulation rate after c. 1946 may be due to local erosion that has limited impact on lake basin sedimentation.     

Lake restoration by hypolimnetic Ca(OH)2 treatment: impact on phosphorus sedimentation and release from sediment

A whole-lake hypolimnetic Ca(OH)₂ addition, that induced calcium carbonate precipitation, combined with deep water aeration has been applied to eutrophic Lake Luzin, Germany during 1996-1998. In this study we investigated the dynamic of phosphorus and its binding forms in seston and sediment before and during the treatment. The sedimentation rates of phosphorus increased within three years of induced calcite precipitation. The phosphorus binding forms shifted to the calcite-bound phosphorus in the settling matter. The increase of calcite-bound P in the settling material did not coincide with the maximum induced CaCO₃-precipitation caused by the hypolimnetic addition of Ca(OH)₂. An impact of chemicals additions and pH on phosphorus binding forms in seston and surface sediments has been studied in laboratory experiments with sediment core incubations and slurry experiments.Laboratory studies showed that the lowest phosphorus flux from sediment was related to the experiment with pH = 7 in overlaying water adjusted with Ca(OH)₂. The adjusting of pH with Ca(OH)₂ leads to a lower P flux of 2.3 mg P m⁻² d⁻¹, while the highest P-flux is attributed to the experiment with the pH which was adjusted with NaOH. Phosphorus fraction which reflects phosphorus binding on carbonates in surface sediments increased within one year of treatment, enhancing the phosphorus retention capacity of sediments.     

On modelling the impacts of phosphorus stripping at sewage works on in-stream phosphorus and macrophyte/epiphyte dynamics: a case study for the River Kennet

A new model of in-stream phosphorus and macrophyte dynamics, ‘The Kennet model’, was applied to a reach of the River Kennet, southern England. The reach, which is 1.5 km long, is immediately downstream of Marlborough sewage treatment works, where phosphorus reduction by tertiary effluent treatment began in September 1997. The model is used to simulate the flow, water chemistry and macrophyte biomass within the reach, both before and after phosphorus removal from the effluent. Monte Carlo experiments coupled with a general sensitivity analysis indicate that the model offers a feasible explanation for the salient aspects of the system behaviour. Model simulations indicate that epiphyte smothering is an important limitation to macrophyte growth, and that higher stream and pore water soluble reactive phosphorus (SRP) concentrations allow the earlier onset of growth for the epiphytes and macrophytes, respectively. Higher flow conditions are shown to reduce the simulated peak epiphyte biomass; though at present, the effect of flow on the macrophyte biomass is unclear. Another simulation result suggests that phosphorus will not be released from the bed sediments in this reach following phosphorus removal from the effluent.     

The significance of atmospheric deposition of heavy metals in four Danish lakes

The atmospheric deposition rate of heavy metals was determined throughout a seventeen month period at four lakes and a control station across Mid-Jutland, Denmark, and its significance was assessed in relation to the concentrations of Zn, Cu, Pb, and Cd in water, sediment and aquatic macrophytes (Phragmites australis (Cav.) Trin, Littorella uniflora (L.) Ashers., Isoetes lacustris L. and Juncus bulbosus L.) from Lake Hampen, Lake Meldgaard, Lake Sortesø, and Lake Gødstrup. Mean annual deposition rates of 1.81–2.77 mg Cu m^?2, 4.09–8.73 mg Pb m^?2, and 0.21–0.37 mg Cd m^?2 were determined. For Zn a mean deposition rate of 15 mg Zn m^?2 year^?1 was used (Hovmand, 1979). The atmospheric deposition per m² of Zn and Cu amounts to 0.2–37%, 0.05–4.3% and 3.4–107% of the contents present in the water column of the lakes, the upper 10 cm of the littoral sediment and in dense vegetation of aquatic macrophytes, respectively. Equivalent figures for Pb and Cd are 1.8–649%, 0.8–30.6%, and 16.8–951%. In the profundal sediments of the oligotrophic Lake Hampen, post-war atmospheric deposition has increased the heavy metal concentration and content up to 180 times. The Pb concentrations in sediments from different depths were significantly correlated with the post-war consumption of gasoline in Denmark. It is concluded that atmospheric deposition of heavy metals results in a significant contamination of lakes, especially oligotrophic lakes for which aerial fallout is the major source. It is further concluded that lake sediments uncontaminated with heavy metals are probably no longer found in Denmark.     

Settling velocity of Cryptosporidium parvum and Giardia lamblia

Understanding transport behavior of Cryptosporidium parvum oocysts and Giardia lamblia cysts (together referred to as (oo)cysts) in overland flow is important for beneficial uses of receiving water bodies. Like sediment, (oo)cysts are subjected to deposition once they are present in overland flow or low flow environments like reservoirs, wetlands and sedimentation basins. The objectives of this paper are to present the theory and experiment to determine the free settling velocity (v(s)) of (oo)cysts and to compare experimental settling velocities to estimates using Stokes' law. A settling experiment was designed to quantify the v(s) of (oo)cysts in an aqueous column. C. parvum oocysts used were spherical with average diameter (+/-1SD) of 6.6+/-1.1 microm. G. lamblia cysts were oval shaped (average eccentricity = 1.48+/-0.19) with average size of 11.8 +/-1.3 microm. Average densities were 1009 kg m(-3) for C. parvum oocysts and 1013 kg m(-3) for G. lamblia cysts. Observed experimental settling velocities are 0.27 microm s(-1) and 0.67 microm s(-1) for C. parvum and G. lamblia, respectively. Estimated average settling velocities using Stokes' law were 0.36 microm s(-1) for C. parvum and 0.84 microm s(-1) for G. lamblia. R-squared values of the observations from the settling experiments with the Stokes' law estimation are 0.87 and 0.88 for G. lamblia and C. parvum, respectively. Our results suggest that Stokes' law can be used to estimate settling velocities of (oo)cysts. Qualitatively, the low settling velocities indicate that (oo)cysts will very slowly settle out of suspension.     

Sediment phosphate composition in relation to emergent macrophytes in the Doñana Marshes (SW Spain)

We have studied the effect of the presence of emergent macrophytes on the sediment phosphate composition of a eutrophic shallow marsh on the NE margin of Do?ana (SW Spain). Top sediment and water samples were collected from both the open-water and the vegetated sites at three areas covered by different plant species: Scirpus maritimus, Juncus subulatus and Phragmites australis. The concentration of organic matter was significantly higher in the top sediment of sites covered by vegetation than in their adjacent open-water sites at the three vegetation areas. The P-fractional composition showed that the sediment was dominated by the inorganic P-fractions in all cases, reaching the highest concentration in the Ca-bound P-fraction (281-372 microg g(-1) d.w.). The sum of all P-fractions was significantly higher in the top sediment of the sites covered by J. subulatus and S. maritimus than in their adjacent open-water sites, and so were the org-P fraction extracted by hot NaOH and the concentration of phytate within this fraction. Deposition of plant material on the top sediment of areas vegetated by J. subulatus and S. maritimus explains these differences. The P-fractional composition of the seeds from J. subulatus showed that they contained a large proportion of organic P-fractions, particularly of the fraction extracted by hot NaOH (1868 microg g(-1) d.w., 85% of which was phytate). The presence of emergent macrophytes, therefore, influenced the distribution of P-fractions in the sediment depending on plant species. The P-bioavailability of shallow aquatic systems must be fully understood if wetlands are to be protected from further eutrophication.     

Sediment-water exchange in Lough Ennell with particular reference to phosphorus

The significance and evaluation of sediment phosphorus in the continuing eutropic conditions noted in Lough Ennell was assessed. A high positive correlation exists between the concentrations of total Fe, citrate dithionite bicarbonate (CDB) extractable Fe, organic content, total Al and a number of phosphorus fractions (total P, inorganic P, organic P, apatite P and CDB extractable P) for all samples recovered. A significant inverse correlation was noted between CaCO₃ and most of the other parameters measured whereas no correlations were found for Mn. The sediment adsorption capacity for orthophosphate was found to be about 450 μg P g⁻¹ sediment. Phosphate release from hypolimnetic anaerobic sediments was considered unimportant in the biological sense due to the lack of mobility of this nutrient to the photic zones. Bioavailable P in the littoral zones (assumed to be non-apatite inorganic phosphorus, NAIP) comprised 14.5 tonnes in the uppermost 2 cm sediment layer, which is about 2.5 times the average annual external total P load. Littoral zone sediments, which are normally aerobic, accounted for an internal areal loading of 134 mg P m⁻² yr⁻¹ which is equivalent to 17 and 30% of the average external total P and inorganic P loadings respectively. This internal loading is a major contributory factor in the continuing eutrophic status of the lake.