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.     

Concentration, fractionation and characterisation of soluble organic phosphorus in river water entering lough neagh

The mean concentration of soluble organic phosphorus in the 6 major rivers entering Lough Neagh from 1975 to 1979 was 38 μg P 1⁻¹. Soluble organic phosphorus constituted 16% of the total phosphorus input during this period. The chemical nature and availability for algal growth of soluble organic phosphorus is largely unknown. An adsorption-precipitation technique for concentrating soluble organic phosphorus from 1001. volumes of river water was developed using lanthanum. From the lanthanum-phosphorus precipitate acid-soluble and alkali-soluble concentrated solutions of organic phosphorus were obtained. 25% of the soluble organic phosphorus from 6 river samples was acid-soluble and 40% was subsequently alkali-soluble. These concentrated solutions were subjected to gel filtration chromatography on a preparative scale using Sephadex G-50 and G-75 when soluble organic phosphorus compounds were fractionated by molecular weight. Of the acid-soluble organic phosphorus 40% was of mol. wt > 10,000, 20% was of mol. wt between 10,000 and 1500 and 40% was of mol. wt < 1500. When the alkali-soluble organic phosphorus was fractionated 70% was of mol, wt > 50,000. Although the acid-soluble concentrates were yellow in colour and may have contained fulvic acids, further gel filtration chromatography of the acid-soluble organic phosphorus with mol. wt > 10,000 indicated that the organic phosphorus was itself coloourless. Alkali-soluble concentrates were red-brown in colour and may have contained humic acids. Sufficient of the alkali-soluble organic phosphorus with mol. wt > 50,000 was isolated by precipitation on acidification for elemental analyses and infrared spectroscopy. Elemental analyses (45.9%, C, 6.6% H, 5.7% N, 0.6% P) showed that the composition of the precipitated material was not identical to the composition of soil humic acids being lower in carbon and higher in hydrogen, nitrogen and phosphorus. Infrared absorption spectra were, however, characteristic of humic substances. Phosphorus may be an integral part of the humic acid structure or an organic phosphorus-metal-organic matter complex may exist. Iron was present in the structure but the phosphorus to iron ratio was not constant between river samples. Algal bioassays on the acid-soluble organic phosphorus with mol. wt > 10,000 and the alkali-soluble organic phosphorus with mol. wt > 50,000 showed that 10 and 32% respectively were available for growth under the conditions of the test.     

Per capita phosphorus loading from domestic sewage

To assess the phosphorus contribution from domestic sewage to Lough Neagh, Northern Ireland, daily per capita loadings were measured by monitoring the effluent from a housing estate. A modern estate with 472 houses was chosen because it was free from industry and had separate foul and storm drainage systems. By a house-to-house census the total population was found to be 1645. Daily loadings in the foul sewer were calculated from measured hourly flow rates and concentration data. The effective population contributing to the foul sewer was estimated by making allowances for export from or import to the estate of excrement by workers and school-children. An attempt was made to verify the assumptions used in estimating the effective population by monitoring the loading in the foul sewer of creatinine, a metabolic end-product excreted in constant amounts in urine. Predicted creatinine loadings, using population data and per capita excretion values, were in good agreement with measured loadings. Per capita daily loadings of soluble orthophosphate, total soluble phosphorus, total phosphorus and BOD were calculated using the effective population and measured loadings for Mondays to Fridays during three weekly survey periods. The results indicated a per capita value of 1.8 g day⁻¹ for total phosphorus in domestic sewage.     

Suppression of phosphorus release from lake sediments by the addition of nitrate

An assessment was made of the effectiveness of nitrate in reducing phosphorus release from the anoxic sediments of a small dimictic lake, White Lough, N. Ireland. Laboratory experiments on sediment cores showed that nitrate delayed and reduced phosphorus release with an input of 61 gN m⁻² causing complete suppression. The addition of 24 gN m⁻² of nitrate to the sediment of White Lough resulted in a delay and reduction of phosphorus release similar to that observed in the laboratory core experiments. Sediment release of iron in the lake was also delayed and reduced but manganese release and the rate of hypolimnetic deoxygenation were unaffected by the nitrate addition. Ammonium release rates in the sediment cores and in the whole lake experiment did not vary with nitrate input. Comparing the costs of using nitrate or iron/aluminium salts to suppress sediment phosphorus release indicated that the nitrate method was at least 80% more expensive.     

Factors affecting nutrient loads in some Iowa streams

The export and concentration of inorganic nitrogen and total phosphorus from 34 watersheds in a northwestern Iowa lake district were measured during March 1971–August 1973. Annual nutrient losses were approximately 0.35 kg ha⁻¹ P. 6.7 kg ha⁻¹ NO₃-N, and 1.0 kg ha⁻¹ NH₃-N. A statistical analysis of the relationship between land-use and plant nutrients was used to determine differences among streams. Animal units in feedlots were significantly correlated with phosphorus and ammonia nitrogen (mg l⁻¹ and kg ha⁻¹ yr⁻¹). Nitrate nitrogen was negatively correlated with the percentage of watershed in marshland. Tile drainage and surface runoff from grasslands, feedlots, cornfields, and soybean fields were analyzed for nitrogen and phosphorus in spring 1974: mean values are given.     

The identification of phosphorus as a growth-limiting nutrient in lough neagh using bioassays

Algae were used in monthly bioassays of Lough Neagh water to evaluate nutrient limitation. Blue-green algae were limited by chelated iron; but once this limitation was overcome both nitrogen and phosphorus were necessary to produce a large growth response. The green alga Selenastrum showed a low requirement for chelated iron. Addition of phosphorus was necessary in all bioassays for prolonged algal growth, confirming the strategy of removing phosphorus from sewage effluents to reduce algal levels in the Lough.     

Statistical models of river loadings of nitrogen and phosphorus in the Lough Neagh system

To establish nutrient budgets of Lough Neagh in N. Ireland, and provide strategies for the reduction of nitrogen and phosphorus it became necessary to obtain estimates of their inputs to the lake. On the six major rivers entering the lake continuous flow metering was available but chemical concentrations were only available every 8 or 15 days. To associate river chemical concentrations and loadings with flows for these observed dates, and hence predict from their relation the loads at the unobserved dates a computer program using eight possible statistical relations was used. Those methods examined included various regressions with adjustments, higher order (polynomial) fits, logarithmic and other transforms, and different rising and falling flow relations. Results produced by the various methods with discussion of their relative merits are presented. Reasons are given for the final selection of a simple log load on log flow relation for rivers derived from terrestrial catchments.     

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.     

Evaluation of an enzymatic method for orthophosphate determination in freshwaters

An automated enzymatic method for orthophosphate determination was applied to freshwaters. The basis of the assay was the reaction of glyceraldehyde-3-phosphate with orthophosphate to form 1,3-diphosphoglycerate in the presence of glyceraldehyde-3-phosphate dehydrogenase and oxidized nicotinamide-adenine dinucleotide. Nicotinamide-adenine dinucleotide, reduced form, was produced in equimolar amounts to orthophosphate and was determined colorimetrically. The method was tested up to 200 μg P l⁻¹ and had a limit of detection of 5 μg P l⁻¹. Silicate or arsenite did not interfere but arsenate caused a positive interference. The results of the analysis of 100 freshwater samples by the enzymatic orthophosphate method and by the well-established soluble reactive phosphorus method indicated that a form of phosphorus was present which was determined as soluble reactive phosphorus but not as enzymatic orthophosphate. The mean soluble reactive phosphorus concentration was 71 μg P l⁻¹ compared with a mean enzymatic orthophosphate concentration of 56 μg P l⁻¹. A hydrous ferric oxide-orthophosphate complex was postulated to explain why soluble reactive phosphorus was greater than enzymatic orthophosphate.     

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.     

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.     

Use of large submerged chambers to measure sediment-water interactions

Submerged chambers were designed and constructed primarily to study in situ sediment phosphorus release in Shagawa Lake, Minnesota. Initial experiments indicated anoxic phosphorus release rates of 7 mg m⁻² day⁻¹. Oxygen consumption rates within the chambers were also measured; an average consumption rate of 0.17 g m⁻² day⁻¹ was obtained.     

Azolla–Anabaena's behaviour in urban wastewater and artificial media – Influence of combined nitrogen

The results of using the nitrogen fixing symbiotic system Azolla–Anabaena to improve the quality of treated urban wastewater, particularly on what concerns phosphorus removal efficiencies (40–65%), obtained in continuous assays performed during the past few years and presented earlier, were very promising. Nevertheless, the presence of combined nitrogen in some wastewaters can compromise the treatment efficiency. The main goal of this work was to compare plants behaviour in wastewater and in mineral media with and without added nitrogen.Azolla filiculoides's specific growth rates in wastewater and in mineral media without added nitrogen or with low nitrate concentration were very similar (0.122 d⁻¹–0.126 d⁻¹), but decreased in the presence of ammonium (0.100 d⁻¹). The orthophosphate removal rate coefficients were similar in all the growth media (0.210 d⁻¹–0.232 d⁻¹), but ammonium removal rate coefficient in wastewater was higher (0.117 d⁻¹) than in mineral medium using that source of nitrogen (0.077 d⁻¹).The ammonium present in wastewater, despite its high concentration (34 mg N L⁻¹), didn't seem to inhibit growth and nitrogen fixation, however, in mineral media, ammonium (40 mg N L⁻¹) was found to induce, respectively, 18% and 46% of inhibition.     

The effects of geology and land use on the export of phosphorus from watersheds

The export of total phosphorus from 34 watersheds in Southern Ontario was measured over a 20-month period. The annual average export for igneous watersheds (i.e. those of the Canadian Shield) that were forested was 4.8 mg m⁻² yr⁻¹, significantly different from the average (11.0 mg m⁻² yr⁻¹) for watersheds that included pasture as well as forest. Similarly, on sedimentary rock, the mean export from forested watersheds (10.7 mg m⁻² yr⁻¹) differed significantly from those with forest and pasture (28.8 mg m⁻² yr⁻¹). The differences between watersheds of different geology but similar land use were also highly significant.Additional data from the literature supported our conclusions. Other forested igneous watersheds of plutonic origin averaged 4.2 mg m⁻² yr⁻¹ of total phosphorus exported: forested igneous watersheds of volcanic origin, however, averaged 72 mg m⁻² yr⁻¹. The overall average export from each type of watershed as classified by geology and land use was very similar to that for the same classification found in our study.The effects of agriculture and urbanization were to greatly increase the total phosphorus exported. Wide ranges of values probably reflect the intensity of land use.     

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 acute toxicity of dissolved elemental phosphorus to cod (Gadus morhua)

The acute toxicity of dissolved elemental phosphorus to cod (Gadus morhua) has been investigated in the absence of colloidal phosphorus. The 48 h lc₅₀ for dissolved elemental phosphorus is 14·4 μg l⁻¹, and evidence is presented that the incipient lethal level is ca. 1–2 μg l⁻¹. Elemental phosphorus was rapidly assimilated into the body tissues of the test animals. The distribution of phosphorus was homogeneous in the muscle tissue with levels ca. 10–30 times the exposure level, highest concentrations were measured in the liver.Preliminary data are reported which indicate that the biological half life of accumulated elemental phosphorus is very short when exposure is ended.     

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.     

Some components of particulate phosphorus in river water entering Lough Neagh

Particulate phosphorus obtained by continuous-flow centrifugation of 1001, volumes of each of the 6 major rivers entering Lough Neagh was subjected to fractionation by acid and alkali treatments. The major acid-soluble component was inorganic phosphorus (36%) while the major alkali-soluble component was organic phosphorus (24%). The insoluble residue accounted for 36% of the total particulate phosphorus. Acid and alkali extracts were subjected to gel filtration chromatography and the organic phosphorus divided into molecular weight ranges. The alkali-soluble organic phosphorus of mol. wt > 50,000 was isolated in sufficient quantity for elemental analysis and infra-red spectroscopy to be performed. Results indicated that the organic matter resembled humic acid. Iron may also have been associated with the phosphorus and organic matter. Phosphorus may have been an integral part of the humic acid structure or an organic phosphorus iron organic matter complex may have existed. No algal availability studies were performed but the fractionation data from the study would not conflict with the suggestion of other workers that algal available particulate phosphorus is about 20% of total particulate phosphorus.     

Internal phosphorus loading in a shallow eutrophic lake

Internal loading of phosphorus has been implicated as a major eutrophicating factor in Long Lake, Washington (Kitsap County). As a result of such loading, summer total phosphorus concentrations approach or exceed 100 μgP l⁻¹. Most of the summer loading of phosphorus is thought to have been released directly from the rich, flocculent sediment in the mid and northern part of the lake as a result of high pH (up to 10) related to phytoplankton photosynthesis. The lake also supports a dense submersed macrophyte crop (areal weighted mean dry weight of about 220 g m⁻²) composed primarily of Elodea densa. Although excretion of phosphorus from healthy E. densa was found to be minimal, the potential contribution of P indirectly from sediment via macrophyte uptake and subsequent decomposition in the winter was on the order of 200–400 kg yr⁻¹ or about 25–50% of the external loading. Nevertheless, loading of phosphorus during predrawdown summers is thought to have originated largely as a direct release from sediment due to high pH. Estimates of sediment phosphorus release determined from laboratory experiments, mass balance and core analyses ranged from 2.2 to 5.6 mg m⁻² day⁻¹.As a component of the restoration program, the lake (mean depth of 2 m) was drawn down nearly 2 m for 4 months during the summer and fall of 1979. The lake's trophic status was expected to improve due to sediment consolidation and/or macrophyte reduction. The drawdown resulted in an 84% reduction in macrophyte biomass in 1980 but minimal sediment consolidation (0.1 m). Winter decomposition of the much smaller macrophyte crop, apparently provided insufficient phosphorus in the spring to stimulate phytoplankton and to enrich midlake sediments, which has probably occurred in previous years. Low water column pH during the postdrawndown summer of 1980 resulted from relatively low rates of plankton photosynthesis. During the summer of 1980 internal loading of phosphorus was reduced and total phosphorus remained below 50 μg l⁻¹.     

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.