A comparison of rain-related phosphorus and nitrogen loading from urban, wetland, and agricultural sources

Comprehensive watershed studies have been conducted for two lakes located in the Lake Michigan drainage system. Studies were conducted from March through October of 1979. During that interval, large differences in storm-related nutrient loading were measured from urban, wetland, and agricultural sources. Eliminating runoff due to melt of the snow pack, it was found that rain-related discharge from the urban area studied was 0.578 kg total-P and 3.688 kg total-N ha⁻¹ of watershed. Rain induced runoff from marshes in the same drainage basin transported 0.023 kg total-P and 0.585 kg total-N ha⁻¹ of catchment. Rainfall of approximately the same amount caused runoff from agricultural land of 0.180 kg total-P and 5.965 kg total-N ha⁻¹. Algae of both lakes were phosphorus limited; nitrogen was present in excess. Using constants from Nichols-Dillon relationships in the literature regarding phosphorus, phytoplankton biomass, and secchi disc transparencies, the urban input of phosphorus ha⁻¹ of drainage was sufficient to bring 0.96 ha-m of lake water to undesirable algal bloom status. Similarly, march input ha⁻¹ would bring an estimated 0.04 ha-m into bloom. By the same calculation, storm-related agricultural runoff would result in 0.30 ha-m of lake water becoming undesirably rich in algae. Knowing the number of hectares in these types of catchment and the volume available in a particular lake for phytoplankton production, decisions regarding cost-effective treatment of rain-related discharge can be made.     

The role of woody vegetation in preventing ground water pollution by nitrogen from septic tank leachate

The ability of woody vegetation to remove nitrogen from septic tank leachate was studied in pine upland, oak upland and hardwood wetland habitats of the New Jersey Pinelands. The study was stimulated by the incorporation of a term for plant uptake in nutrient dilution models used for Pinelands land-use management decisions. Plant response was studied at sites involving septic tank leach fields and matched control sites for each habitat type. At each site, total biomass, net production, and tissue N concentrations for the dominant species was determined. The hardwood wetland habitat had a total biomass of 15.9 MT ha⁻¹, a net primary production of 5.4 MT ha⁻¹yr⁻¹ and a net N uptake 75–80 kg N ha⁻¹yr⁻¹. Tissue N values for wetland trees and shrubs did not show significant differences between control and experimental sites. The pine upland communities had a biomass of 55 MT ha⁻¹ and a net production of 5.7 MT ha⁻¹yr⁻¹; net N uptake ranged from 45 kg N ha⁻¹yr⁻¹ (control sites) to 56 kg N ha⁻¹yr⁻¹, (experimental sites). The oak upland communities had a biomass of 59 MT ha⁻¹ and a net primary production of 5.0 MT ha⁻¹yr⁻¹; net uptake ranged from 55 kg N ha⁻¹yr⁻¹ in the control sites to 69.3 kg N ha⁻¹yr⁻¹. Tissue N concentrations showed significant increases for tree but not shrub species in both upland habitats. The capacity of the upland woody plants to increase N uptake and storage appears to be related to rooting depth and to the proximity of the plants to the drain tile: only plants with deep taproots, growing close to (within 1 m) the trench showed significant increases in uptake. It is suggested that only by augmenting appropriate natural vegetation with supplementary tree plantings can upland vegetation be utilized to reduce nitrogen movement to groundwater from septic systems in sandy soil; vegetation at naturally-occurring densities will not have a significant effect on water quality.     

High-rate overland flow

Recommended loading rates for treating raw domestic wastewater by overland flow are 6.3–15 cm wk⁻¹. Information provided in the literature yields little insight regarding the upper range of hydraulic loading rates that could be effectively treated by overland flow. Therefore, field investigations were conducted to evaluate the performance of the overland flow system at overland flow rates from 0.95 m³ day⁻¹ m⁻¹ width of slope (13 cm wk⁻¹ to 4.15 m³ day⁻¹ m⁻¹ (57 cm wk⁻¹).Preliminary treated municipal wastewater was pumped to overland flow slopes, each approx. 3.7 m wide and 36.5 m long. The slope of each plot was 2.5%. The cover crop consisted of a mixture of ryegrass, bluegrass and fescue grass. The plots were operated for 2 years at six different hydraulic loading rates.Effluent BOD₅ concentration averages varied from 6 to 11 mg l⁻¹. The reduction of influent BOD₅ concentration ranged from 87 to 93%. Mean effluent suspended solids values were from 6 to 9 mg l⁻¹ with reductions of influent concentrations of 91–95%. Hydraulic application rate had little effect on percent BOD₅ or suspended solids removal.Total phosphorus reductions were minimal at all hydraulic application rates due to limited soil water contact.Ammonia concentration in the effluent ranged from 1 mg l⁻¹ NH₃-N at the 0.95 m³ day⁻¹ m⁻¹ (13 cm wk⁻¹) applied flow rate of 11.7 mg l⁻¹ NH₃-N at the 4.15 m³ day⁻¹ m⁻¹ (57 cm wk⁻¹) loading rate. Ammonia and nitrogen reductions decreased as the applied flow rate increased. Consequently, lower overland flow rates are necessary for nitrogen removal.The use of high-rate overland flow could potentially reduce the land necessary for this form of land application, if nutrient removal was not a local concern.     

The behaviour of phosphate, nitrate, chloride and hardness in twelve welsh rivers

Selected water quality data from 12 rivers in the area administered by the Welsh Water Authority were analysed for the period 1974–1981. Mean nitrate-nitrogen concentrations varied from 0.4 to 3.7 mg l⁻¹ and were significantly related to the intensity of average catchment run-off; mean orthophosphate-phosphorus concentrations ranged from the limit of analytical detection to 0.730 mg l⁻²; chloride from 11 to 42 mg l⁻¹ and total hardness (as CaCO₃) from 13 to 173 mg l⁻¹. Seasonal patterns of change in concentration were established, generally for all determinands at most sites, but no long-term trends were detected. Relationships between concentration and flow were established for most determinands at many sites, increasing flow generally resulting in decreased concentration. However, positive relationships between nitrate concentration and flow were established at seven sites. Mass flows (kg ha⁻¹ yr⁻¹) were calculated at nine sites only: nitrate-N 4.8–24.6; orthophosphate-P 0.16–3.81; chloride 79–334; total hardness (as CaCO₃) 196–1629. Orthophosphate flows were related to sewered population density, estimates of per capita and land drainage contributions being 1.9 g day⁻¹ and 0.112 kg ha⁻¹ yr⁻¹ respectively.     

Impact of climatic fluctuations and land use change on runoff and nutrient losses in rural landscapes

Results on the influence of land use and climatic changes on nutrient losses in the Porijõgi river catchment, south Estonia, are presented. The main tendency in land use changes is a significant increase in abandoned lands (from 1.7% in 1987 to 12.5% in 1994), and a decrease in arable lands (from 41.8 to 22.5%). Significant climatic fluctuations were observed from 1951–1994. Warmer winters (increase from −7.9 to −5.8°C from 1950–1994) and a change in the precipitation pattern have influenced the mean annual water discharge. This results in more intensive material flow during colder seasons and decreased water runoff in summer. Changes in water discharge and land use are also reflected in the mean annual runoff of total inorganic nitrogen (TIN) and total-P which decreased from 15.6 to 2.7 kg N ha⁻¹ yr⁻¹ (83%) and 0.32 to 0.21 kg P ha⁻¹ yr⁻¹ (34%), respectively during this period. However, nutrient losses from the forest subcatchment (upper course) did not change significantly. In contrast, the mean annual runoff of water, organic matter (after biological oxygen demand: BOD₅), TIN, total-P and SO₄ from cultivated subcatchments showed a significant decrease.     

Effect of exogenous carbon sources on removal of inorganic nutrient by the nitrification-denitrification process

A bench scale study was undertaken to examine the effects of exogenous carbon substrates on the removal of inorganic nitrogen and phosphorus by a simple nitrification-denitrification process. Each plastic tank reactor was subjected to a 7-h aeration followed by a 5-h anoxic stage. Methanol, glucose and sodium acetate, at the concentrations equivalent to theoretical COD values of 100 and 200 mg O₂ l⁻¹ were used as external carbon sources and were added to the reactors prior to the anoxic stage. Effects of these additions on biological phosphate release were also investigated. The results showed that 94% of NH₄⁺-N was removed at the end of the aeration period. During the anoxic stage, reduction of nitrate to nitrogen gas was recorded and the denitrification process was significantly enhanced by the addition of organic carbon substrates. At the end of the anoxic stage, over 90% reduction was achieved in the tanks with exogenous carbon substrates while only 47% of NO₃⁻-N was removed in the control reactors. Among the three substrates, sodium acetate was the most efficient and effective source, followed by methanol and glucose. Addition of sodium acetate not only increased the amount of nitrate reduction but also enhanced the rate of N removal especially when a high dosage of sodium acetate was used. With respect to phosphorus removal, 88% ortho-P was removed after the aerobic stage. Throughout the anoxic stage, P concentration was maintained at about 2 mg l⁻¹ in both control and methanol treated reactors. However, significant increase in effluent P content was recorded in both sodium acetate and glucose treatments indicating that phosphorus was released from the bacterial cells during the anoxic stage. The amount of P-release in these two treatments was related to the concentrations of the carbon substrate used.     

The quality of run-off from an irrigated market garden area in Brazil

This paper presents the results of a study carried out in Brazil to determine the effects of irrigation and fertiliser use on the quality characteristics of run-off from an agricultural area used for intensive cultivation of market garden produce.The results show that during dry weather the discharge of nutrients from the cultivated area when irrigation is taking place is equivalent to 7 kg ha⁻¹ yr⁻¹ N and 1 kg ha⁻¹ yr⁻¹ P. Considerable accumulation of nutrients took place in the soil during the growing season, over the 129-day survey period the nutrient content of the top soil increased by approximately 590 g m⁻²N and P and 780 g m⁻²K. This accumulation was derived from fertilisers which were applied at rates of 1136 kg ha⁻¹N, 978 P and 1367 K. During wet weather the nutrients which had accumulated in the soil were washed out.     

Nitrate reduction by denitrifying bacteria in single and two stage continuous flow reactors

Denitrification by a mixed bacterial population of medium containing 1000 mg NO₃⁻-N1⁻¹ and acetate as carbon source was studied in batch, a single stage continuous flow stirred reactor (CFSTR) and a two stage CFSTR at 30°C. The optimum pH for denitrification, nitratase, nitrite reductase activities and growth was found to be 7.5 in batch culture. A single stage CFSTR growth limited by nitrate had an optimum denitrification rate of 0.13 mg NO₃⁻-N mg⁻¹ cells h at a residence time of 8 h. The experimentally observed carbon to nitrate ratio (mg CH₃ COO⁻-C mg⁻¹ NO₃⁻-N)was 1.7 for the dilution rates of 0.02–0.18 h⁻¹. For the second stage CFSTR, bacteria growing at the maximum rate of 0.25 h⁻¹ and not limited by nitrate had a denitrification rate of 0.24 mg NO₃⁻-N mg⁻¹ h. Dissolved oxygen (up to 9.5 mg 1⁻¹) did not effect denitrification rates in the second stage CFSTR. As the second stage CFSTR runs progressed extensive wall growth occurred and concurrently the output gas contained increasing quantities of nitrous oxide. A development from this study would be a two stage CFSTR with wall growth in the second stage which would make an efficient nitrate removal process.     

Removal of nitrate from effluent following discharge on surface water

The loss of nitrate nitrogen over a 800-m long reach of canal was studied in a field experiment during a 20-days period. The nitrate originated mainly from sewage effluent. Fifty-six percent of the nitrate had disappeared during its flow through the 800-m long reach, where the average retention time was 1.7 days. The average rate of nitrate disappearance during the 20-day period was 913 mg NO₃⁻-N m⁻² day⁻¹. Laboratory experiments with undisturbed water-sediment profiles from the canal showed that the disappearance of nitrate was caused mainly by denitrification in the sediment. Increased knowledge of this phenomenon may lead to an effective and cheap means in inducing denitrification.     

The occurrence and removal of nitrogen in subsurface agricultural drainage from the San Joaquin Valley, California

During the years 1967–1973 there have been extensive studies of subsurface agricultural drainage in the San Joaquin Valley of California. These studies, by cooperating state and federal agencies, were to determine the composition and quantity of drainage waters produced from irrigated agriculture, to evaluate possible methods of removing problem constituents (mainly nitrogen) from these waters, and to obtain an idea of the effectiveness of the treatment methods studied for reducing the waters biostimulatory content with respect to potential receiving waters. The results of the studies indicated that on an annual average, the drainage waters will probably contain about 20 mg NO₃-N I⁻¹ even after 50 years of leaching and that most of the nitrogen is derived from native soil nitrogen. Treatment studies demonstrated that the nitrogen could be reduced from 20 to 3–5 mg N I⁻¹ by any one of several biological treatment processes including bacterial denitrification (filter and pond), algae growth and harvesting, and by a combination plant growth—bacterial denitrification (“symbiotic”) process. Cost estimates for the processes studied ranged from $10 to $36 1000⁻¹ m³ (1969 dollars). Laboratory algal assays demonstrated that the nitrogen removal systems studied effectively reduced the drainage waters biostimulatory content.     

A comparison of nutrient sources and behaviour in two lowland subcatchments of the River Wye

Seasonal changes in concentrations and mass flow of dissolved silicon, orthophosphate and inorganic nitrogen were studied during 1978 in two lowland catchments of the R. Wye, the Frome and the Trothy, which are of similar drainage area but are subjected to different land use. In addition more intensive investigation of water quality changes were undertaken during storm events.Seasonal patterns of silicon concentrations were similar in the two rivers with major depletions in May and annual losses to diatoms were estimated to be equivalent to 5–12% of annual mass flow. Peak concentrations of orthophosphate were generally recorded during periods of low river flow in both rivers but concentrations were substantially greater in the Frome (mean, 0.42 mg l⁻¹) than the Trothy (mean, 0.19 mg l⁻¹), reflecting differences in population density. The principal form of inorganic nitrogen in both catchments was nitrate, but mean concentrations were considerably greater in the Frome (mean NO₃-N. 4.99 mg l⁻¹) than in the Trothy (mean NO₃-N. 2.93 mg l⁻¹) and seasonal variations were markedly different. Concentrations in the Frome increased during the summer months (maximum, 7 mg l⁻¹ whilst concentrations in the Trothy decreased during this period and this was reflected in positive and negative relationships between concentration and river flow respectively. Such differences in behaviour cannot be attributed to contributions from sewage and it is suggested that they may reflect differences in the proportion of groundwater contributing to river flow during the summer period and the nitrate content of that groundwater.Intensive sampling during storm events indicated that, overall, orthophosphate concentrations decreased and silicon and nitrate concentrations increased with increased flow, but there was considerable variation in solute behaviour during different events.     

Upward trend in nitrate concentrations in rivers discharging into lough neagh for the period 1969–1979

The six major rivers discharging into Lough Neagh, Northern Ireland have been sampled at intervals ranging from 7 to 15 days during the study period 1969–1979. The mean concentration of nitrate has increased from 1.41 mg N 1⁻¹ in 1969–1970 to 2.41 mg N 1⁻¹ in 1978–1979. The maximum observed concentrations of nitrate have increased from 2.9 mg N 1⁻¹ in 1969–1970 to 7.5 mg N 1⁻¹ in 1979–1980. A number of possible causes of the increase in concentration have been considered and it was concluded that the greater intensity of grassland management as evidenced by an increase in fertiliser usage from 42 kg N ha⁻¹ in 1969 to 106 kg N ha⁻¹ in 1979 has made a significant contribution to the increase in nitrate. The increase in nitrate concentration may be the causal factor for the marked decline in nitrogen-fixing species of blue-green algae from the phytoplankton of Lough Neagh during the latter half of the study period.     

The effects of phytophagous insects on water and soil nutrient concentrations and fluxes through forest stands of the Level II monitoring network in the UK

The effects of insect defoliators on throughfall and soil nutrient fluxes were studied in coniferous and deciduous stands at five UK intensive monitoring plots (1998 to 2008). Links were found between the dissolved organic carbon (DOC), nitrogen (N) and potassium (K) fluxes through the forest system to biological activity within the canopy. Underlying soil type determined the leaching or accumulation of these elements. Under oak, monitored at two sites, frass from caterpillars of Tortrix viridana and Operophtera brumata added direct deposition of ~ 16 kg ha⁻¹extra N during defoliation. Peaks of nitrate (NO₃-N) flux between 5 and 9 kg ha⁻¹ (×5 usual winter values) were recorded in consecutive years in shallow soil waters. Synchronous rises in deep soil NO₃-N fluxes at the Grizedale sandy site indicate downward flushing, not seen at the clay site. Under three Sitka spruce stands, generation of honeydew (DOC) was attributed to two aphid species (Elatobium abietinum and Cinara pilicornis) with distinctive feeding strategies. Throughfall DOC showed mean annual fluxes (6 seasons) ~ 45-60 kg ha⁻¹ compared with rainfall values of 14-22 kg ha⁻¹. Increases of total N in throughfall and NO₃-N fluxes in shallow soil solution were detected — soil water fluxes reached  8 kg ha⁻¹ in Llyn Brianne, ~ 25 kg ha⁻¹ in Tummel, and ~ 40 kg NO₃-N ha⁻¹ in Coalburn. At Tummel, on sandy soil, NO₃-N leaching showed increased concentration at depth, attributed to microbiological activity within the soil. By contrast, at Coalburn and Llyn Brianne, sites on peaty gleys, soil water NO₃-N was retained mostly within the humus layer. Soil type is thus key to predicting N movement and retention patterns. These long term analyses show important direct and indirect effects of phytophagous insects in forest ecosystems, on above and below ground processes affecting tree growth, soil condition, vegetation and water quality.     

Phosphorus adsorption to riverine suspended matter: Implications for the P-budget of Lake Constance

Dissolved phosphorus from Lake Constance water was adsorbed by particulate matter from the Alpenrhein whenever the equilibrium phosphorus concentration of 0.85 μmol l⁻¹ was exceeded. When shaken in phosphate-free lake water the solids liberated small amounts of P (1% of the total-P). The maximum adsorption capacity of the particles was estimated to be 2.8 μmol g⁻¹ (dry substance). Only part of the phosphorus once experimentally sorbed to the solids was shown to desorbe in P-free lake water.During 1981 1.47·10⁹ kg of particulate matter was discharged into Lake Constance from the Alpenrhein. By adsorption these sedimenting materials had the potential to remove 18–25·10³ kg of dissolved phosphorus from the water column, thus comprising almost 2% of the total P-load in 1981.     

Growth and nutrient uptake of green alga, Scenedesmus dimorphus, under a wide range of nitrogen/phosphorus ratio—I. Experimental study

In order to elucidate the relation between algal growth and nutrients such as nitrogen and phosphorus, a chemostat culture experiment using Scenedesmus dimorphus was performed under the conditions of T-N/T-P ratio of 2–50 mg N mg⁻¹ P and dilution rate of 1–4 day⁻¹. It was ensured from the results that nitrogen and/or phosphorus is the limiting nutrient for the growth of this alga under these conditions. The optimum T-N/T-P ratio for its growth was observed to change from 20 to 5 mg N mg⁻¹ P as the dilution rate varied from 1 to 4 day⁻¹ and, in most of the range of T-N/T-P ratio and dilution rate, its growth rate was not regulated by only one of the available nitrogen and phosphorus concentrations in the medium and algal nitrogen and phosphorus contents. Based on these facts, the multiplicative effect rather than the threshold effect of these two nutrients on its growth was considered to exist. It has been suggested, however, that algal nitrogen and phosphorus contents, especially nitrogen content, are the most important factors regulating its growth. Nitrogen uptake rate of this alga increased at a given concentration of available nitrogen in the medium as T-N/T-P ratio decreased down to 2 or 5 mg N mg⁻¹ P. It is also suggested that a multiplicative effect of nitrogen and phosphorus on uptake of these nutrients by S. dimorphus may exist.     

Inter-relationships between nitrogen balance, pH and dissolved oxygen in an oxidation ditch treating farm animal waste

The pathways of N in aerobic farm waste treatment systems are discussed in relation to the dissolved oxygen (DO) and pH of the mixed liquor. The change in pH, DO, oxygen uptake rate and nitrogen balance were monitored under steady, and non-steady, state conditions in an oxidation ditch treating undiluted pig waste. A kinetic analysis of the mass balance for nitrogen allowed an interpretation of the fate of nitrogen under different prevailing conditions. Undesirable accumulations of nitrite were noted in the presence of high levels of free NH₃ and HNO₂. The process was self-promoting and was encouraged by the influx of raw waste. Concentrations of 500 mg 1⁻¹ NO₂-N and 1200 mg 1⁻¹ NO₃-N were the maximum values observed and were considered to be the concentrations at which product inhibition arrested nitrifying activity. Attainment of these levels prevented complete nitrification despite an adequate retention time. pH and DO were inversely related probably through nitrification, but pH appeared to be lowered by accumulation of nitrite and nitrate anions, and thus by the balance between nitrification and denitrification. Considerable N loss through denitrification was found to occur despite apparently aerobic mixed liquors. At low DO simultaneous nitrification-denitrification could eliminate 90 per cent of the soluble-N. NH₃ desorption in laboratory cultures was found to be first order in free NH₃ but was not a significant mode of N loss under field conditions.     

Domestic and agricultural contributions to the inputs of phosphorus and nitrogen to Lough Neagh

Loadings of nitrogen and phosphorus from the major river catchments that contribute to Lough Neagh have been measured for the years 1971–1974. Analysis of this data indicated that there was a very significant correlation between soluble ortho-P loadings and the human but not the animal population densities of the catchments. The land drainage and agricultural contribution of soluble ortho-P to Lough Neagh was 0.14 kg P-ha⁻¹·yr⁻¹ which was about 25% of the measured soluble ortho-P loading to the Lough. It was estimated that the introduction of phosphorus removal treatment at sewage works connected to populations greater than 2000 could curtail 50% of the phosphorus available to support algal growth in the Lough. There was a good correlation between nitrogen fertilisers usage in Northern Ireland and the nitrate concentration in the major rivers.     

The contribution of mercury and chlorinated organics from urban runoff

The concentration of mercury and chlorinated organics in the combined sewer overflows of Rochester, New York (U.S.A.) have been measured. The resulting annual loadings of 0.034 kg ha⁻¹ (0.034 pounds acre⁻¹) and 0.011 kg ha⁻¹ (0.01 pounds acre⁻¹) of mercury and chlorinated organics measured in urban runoff are significant. A high degree of correlation exists between the measured concentration of the toxicants when compared with rainfall intensity, rainfall duration, antecedent number of dry days and the total suspended solids concentration characteristic of the combined wastwater.     

Hyperconcentrated cultures of Scenedesmus obliquus: A new approach for wastewater biological tertiary treatment?

Algal cultures of Scenedesmus obliquus at low concentrations (0.1–0.2 g dry wt l⁻¹) provide adequate biological tertiary treatment of wastewaters. This research was aimed at studying the possibility of increasing the system performance by using hyperconcentrated cultures of S. obliquus (up to 2.6 g dry wt l⁻¹) at the laboratory scale. The algal culture grown on secondary effluent was first chemically flocculated with chitosan (30 mg l⁻¹) and decanted; the sedimented culture (5 g dry wt l⁻¹) was then resuspended in secondary effluent to obtain algal suspensions at various concentrations, the performance of which was compared to that of a control culture (0.13 g dry wt l⁻¹). The rate of exhaustion of nitrogen (N-NH₄⁺) was proportional to the algal concentration and a complete removal could be obtained within 15 min (at 2.6 g dry wt algae l⁻¹); this result compares favorably to the 2.5 h or so required by the control culture. The unit uptake rate for nitrogen (N-NH₄⁺) had a tendency to increase with the algal concentration, whereas that of phosphorus (P-PO₄³⁻) showed the opposite relationship. Considering the results obtained, it appears that hyperconcentrated algal cultures have a high potential for the tertiary treatment of wastewaters; a significant reduction of pond surface for large scale operations can be anticipated.     

Responses of Cyperus involucratus Rottb. to nitrogen and phosphorus, with reference to wastewater reclamation

There is increasing use of aquatic plants in biosystems to ameliorate wastewaters. Cyperus involucratus Rottb. is a large emergent aquatic plant which may be useful in treating wastewater because it grows quickly, does not die back in winter, has little weed potential and grows in dryland situations. Many wastewaters contain high levels of N and P, and the capacity of C. involucratus to take up these nutrients was studied under glasshouse conditions. Maximum growth was attained between 84 and 168 mg NO₃-Nl⁻¹ and 1–5 mg PO₄-Pl⁻¹. At a low level of supplied NO₃-N, most of the N in plant organs was reduced-N; at levels of supplied NO₃-N above 84 mg l⁻¹, there was considerable accumulation of NO₃-N in plant organs. The accumulation of NO₃-N was greatest in culms where it made up over 50% of their N content when plants were grown on 350 mg NO₃-Nl⁻¹. Linear regression equations best described the relationships between dry matter and reduced-N contents in roots, culms and leaves. Over 60% of the total plant N and P accumulated in above ground organs, and concentrations of up to 0.53% P and 3.4% N (dry wt basis) were recorded in leaves. C. involucratus would be a suitable plant for wastewater reclamation on account of its high dry matter production, its ability to tolerate hyper-eutrophic levels of N and P, and the accumulation of most of the N and P in the harvestable portions of the plant.