Mean Concentrations Of Total Nitrogen Research Articles

Environmental predictors for the restoration of a critically endangered coral, Acropora palmata, along the Florida reef tract.

The population decline and lack of natural recovery of multiple coral species along the Florida reef tract have instigated the expanding application of coral restoration and conservation efforts. Few studies, however, have determined the optimal locations for the survival of outplanted coral colonies from restoration nurseries. This study predicts the optimal locations for Acropora palmata colonies along the Florida reef tract using a boosted-regression-tree model to examine the relationships between the occurrence of wild A. palmata and ten environmental variables. Our model results predicted A. palmata was most likely to occur in shallow reef habitats with (i) generally low mean chlorophyll-a concentrations (< 1 mg m-3), (ii) moderate fetch (3 kJ m-2), (iii) salinities between 20 and 37.5 ppt, (iv) temperatures between 20 and 32°C, (vi) low mean concentrations of total nitrogen (0.16 ppm), and (iv) irradiance between 26.5 and 53.5 mol m-2 s-1. The most suitable habitats for A. palmata were disproportionately allocated to reefs in Biscayne Bay, the Upper Keys, the western-lower Florida Keys, the Marquesas, and the Dry Tortugas. The middle Florida Keys had unfavorable environmental conditions for A. palmata habitat. Results from this study inform where A. palmata, outplanted as part of restoration and conservation efforts, would have suitable environmental conditions to persist over time. This study also provides decision-making support for management focused on the conservation and restoration of the endangered species A. palmata along the Florida reef tract.

Nitrogen compounds in effluents from a septic tank_

The paper presents the results of long-term studies on the concentrations of total nitrogen and ammonium nitrogen in a septic tank effluent. A statistical analysis concerning the sampling day and the season was performed. The mean concentration of total nitrogen in the effluent was 47±9 g N/m3 and the mean concentration of ammonium nitrogen was 33±11 g N/m3. Results on the cumulative distributions of total nitrogen and ammonium nitrogen in the outflow from the septic tank have also been presented.

Top-down and bottom-up control of plankton structure and dynamics in hypertrophic fishponds

We investigated the effects of strong top-down control by high fish stock on structure and seasonal dynamics of plankton in nine fishponds under conventional fishery management based on auxiliary feeding during two vegetation seasons. Mean concentrations of total nitrogen, phosphorus, and high densities of phytoplankton, bacteria, heterotrophic nanoflagellates, and ciliates indicated hypertrophic state of the fishponds, as well as a markedly reduced control of these microbial food web components by crustacean zooplankton. Mean seasonal densities of zooplankton varied within one order of magnitude for cladocerans, copepods, nauplii, and rotifers. Daphnia were found in most fishponds in densities up to 630 ind. l−1 (median: 53 ind. l−1). While TN and TP concentrations were high, dissolved inorganic N (median: 29 µg l−1) and reactive P (median: 11 µg l−1) indicated possible nutrient deficiency. The fish stock index (defined as the product of biomass and square root of densities) was used as a proxy for fish predation pressure. Multivariate analysis revealed that nutrients and high fish stocks (market carp, carp fry, and/or undesirable small planktivorous fishes) were the main driving forces shaping the fishpond plankton. The resulting trophic structure thus severely reduced the herbivorous zooplankton–fish link during a vegetation season.

Effects of nutrients on the water quality and the algal community of river Nyakomisaro-Riana, Kisii, Kenya

Water quality changes affect the ecological functioning of riverine ecosystems as well as their ability to support organisms and sustain environmental values. The study eighteen months study was conducted from May 2013 to October 2014 to determine the changes in water quality and algal community. Water samples for nutrient and algae composition were collected in triplicates monthly at five sampling sites along the Nyakomisaro-Riana River and laboratory analyses were conducted by following the standard methods described by the American Public Health Association (APHA). Data was oorganized, described and analysed with One-Way Analysis of Variances (ANOVA) and bivariate regression, using the Microsoft Excel 2010 and Minitab software’s and the significance of ddifferences considered at the p-value of  0.05. Tukeys pairwise multiple comparisons were used for post hoc analysis. The level of Total Phosphorous (TP) exhibited a general increasing upstream - downstream trend with an overall mean of 250.99±25.31 µgL-1 and a range of 2.59 - 1281.40 µgL-1. The Soluble Reactive Phosphorous (SRP) concentrations ranged between 1.66 - 632.00 µgL-1 with a spatial mean of 57.24±8.59 µgL-1 within a range of ., while Total Nitrogen (TN) concentration had an overall mean of 996.49±128.60 µgL-1 and ranged between 4.76 - 4332.33 µgL-1. The lowest mean TN concentration (664.87±90.49 µgL-1) was recorded at site NK1 while the highest mean (1349.27±146.48 µgL-1) was recorded at site R1. Nitrate -Nitrogen [NO3-N] concentration ranged between 0.18 - 742.90 µgL-1 with an overall mean of µgL-1 142.28±16.40 µgL-1. Regression analysis showed a positive correlation between Nitrate nitrogen and distance downstream (b = 15.05, a = 112.12, R 2 = 0.40). Out of 135 algal species recorded, 113 had a low percentage occurrence of less than 30%. The algal community comprised of seven genera of diatoms, six genera of chlorophyceae and cyanophyceae and three genera of euglenophyceae. The percentage algal abundance indicated the existence of a climax community,the blue green algae (Microcystis aeruginosa) with a dominance of 34%. This suggested that nutrient loading into Nyakomisaro-Riana River is high. The study recommends that regular monitoring of water quality parameters and algal community changes should be conducted to control the nutrient discharges into the river.

Irrigation with reclaimed water in an urban watershed and nutrient levels in adjacent streams.

Reclaimed water, used commonly for lawn irrigation, can be a complicating factor for watershed managers addressing sources of nonpoint source pollution. This research examined concentrations of total nitrogen (TN) and total phosphorus (TP) in the reclaimed water effluent from the City of St. Petersburg wastewater treatment plant (WWTP) (secondary treatment), the Pinellas County WWTP (tertiary treatment), and four tributary sites in the highly urbanized Joe's Creek watershed in Pinellas County, Florida. Two of the four tributary sites are control sites (35-10 and 35-11). The Bonn Creek tributary is within the tertiary treatment service area, and Miles Creek tributary is within the secondary treatment service area. For the 6-year study period, results show that Bonn Creek's mean TN concentration of 0.92mg/L was lower than Miles Creek's (1.077mg/L), and both control sites were the lowest (0.66mg/L and 0.71mg/L, respectively). Similar results were found for TP concentrations. Bonn Creek's TP concentration was 0.084mg/L slightly lower than Miles Creek's (0.096mg/L), and both control sites were the lowest (0.064mg/L and 0.07mg/L, respectively). Potential TN and TP loadings from each WWTP to their service areas were calculated, as well as potential TN loadings to each landscape. PRACTITIONER POINTS: We investigated TN and TP concentrations from secondary and tertiary WWTPs and streams that receive runoff from two neighborhoods using reclaimed water from these plants for landscape irrigation. As expected, reclaimed water from the secondary WWTP had higher TN and TP concentrations. The surface water concentrations of TN and TP in the adjacent streams within the reclaimed service areas were higher than the concentrations at the control sites outside of the reclaimed service areas. The nitrogen applied to landscapes in the secondary WWTP reclaimed service area was ten times higher than the nitrogen applied to landscapes in the tertiary WWTP reclaimed service area.

Constructed wetlands with subsurface flow for nitrogen removal from tile drainage

Diffuse pollution from agricultural drainage is a severe problem for water quality and it is a major reason for the failure to accomplish “good chemical status of surface waters” according to the Water Framework Directive and for the eutrophication of both freshwaters and coastal waters. Constructed wetlands were proposed as a suitable tool for removal of nitrogen from agricultural drainage in the early 1990s. Until now, the vast majority of constructed wetlands designed to treat tile drainage were free-surface constructed wetlands. In 2018, three experimental constructed wetlands with horizontal subsurface flow were built to treat tile drainage from 15.73 ha watershed. The wetlands have a surface area of 79, 90 and 98 m2 and were planted with Phalaris arundinacea and Glyceria maxima in parallel bands. The substrate in the first two wetlands is gravel (4–8 mm) mixed with birch woodchips (10: 1 volume ratio). In one of those wetlands, the water level is kept 10 cm above the surface, in the second one the water is kept below the surface. The third wetland has 20 cm layer of birch woodchips on top of gravel. The mean total nitrogen concentration eliminations during one-year period were 61.2%, 62.6% and 70.9% for wetlands 1, 2 and 3, respectively. The average load removals amounted to 0.516, 0.323 and 0.399 g N m−2 d−1 or 1885, 1180 and 1457 kg ha−1 yr−1 in wetlands 1, 2 and 3 respectively. The plant uptake and nitrogen sequestration in aboveground biomass contributed only marginally to the overall nitrogen removal. The results revealed that the selection of the best option depends on the fact whether concentration or load is taken as the most important parameter.

Effect of local watershed landscapes on the nitrogen and phosphorus concentrations in the waterbodies of reservoir bays.

Reservoir bays, which are affected by the reservoir and watershed characteristics, are the initial and most sensitive areas in the evolution process of reservoir water quality. However, the relationship between the watershed characteristics and nitrogen and phosphorus concentrations in reservoir bays is poorly understood. We selected 66 bays from the Danjiangkou Reservoir and sampled twice per year (storage and discharge periods) from 2015 to 2018 to monitor the total nitrogen (TN) and total phosphorus (TP) concentration in the waterbodies of the reservoir bays. Four types of watershed characteristic indices (topographic variables, soil variables, land-use composition, and landscape patterns) around these bays were obtained. We quantified the relationship between the TN and TP concentrations and watershed characteristics in the waterbodies of the reservoir bays using partial least squares regression (PLSR). The results showed that the mean concentrations of TN and TP in the storage period (TN:1.69mg·L-1, TP:0.088mg·L-1) were higher than those in the discharge period (TN:1.22mg·L-1, TP:0.063mg·L-1). The optimal PLSR models explained 67.9% and 82.5% of the TN concentration variability, and 65.4% and 67.2% of the TP concentration variability during the storage and discharge period, respectively. Based on the variable importance in the projection (VIP) values, soil erodibility had significant effects on the TN and TP concentrations. The key factors affecting the TN concentration were the slope gradient, basin relief, topographic wetness index, forest and agricultural land use, whereas the factors controlling the TP concentration were the landscape shape index, edge density, Shannon's diversity index and grass land use, although the TP concentration was also controlled by the patch density and contagion during the storage period, and by mean patch size and largest patch index during the discharge period. This study provides critical insights into sustainable landscape planning and effective reservoir water quality management.

Effects of cyanobacterial detritus on water quality and the biomass of periphyton and &lt;i&gt;Limnodrilus&lt;/i&gt; spp. in Lake Taihu

富营养化是现今各国面临的主要水环境问题，其中蓝藻水华暴发是全球富营养化水体最常见的现象之一.蓝藻水华将产生大量的蓝藻碎屑，其对水质及生物的影响还尚不清楚.本研究通过向中宇宙系统添加微囊藻碎屑，分析其对水体不同形态营养盐及水生生物生物量的影响.结果表明：微囊藻碎屑加入后，水体不同形态的营养盐浓度均在短期内迅速增加，其中水体总氮和总磷平均浓度最高分别达到3.86和0.36 mg/L；浮游植物生物量（用叶绿素a表示）在前9天随营养盐浓度的升高而增加，随后逐渐下降至实验初始水平.此外，附着藻类生物量在微囊藻碎屑加入后呈逐渐下降趋势，这可能与浮游植物快速增殖引起的水体透明度下降有关.微囊藻碎屑加入后，水丝蚓生物量随微囊藻碎屑的分解持续增长，在第20天达到生物量最大值.本研究通过模拟太湖梅梁湾生态系统，探讨微囊藻碎屑对水质及水生生物生物量的影响，结果有助于进一步了解蓝藻水华对水生态系统影响的途径及机理，为富营养化湖泊管理提供理论依据.;Eutrophication has become a major water environmental problem all over the world, and cyanobacterial blooms are one of the most common phenomena in eutrophic lakes. Thereafter, a large amount of cyanobacterial detritus will be produced after the blooms, and the effects of these detritus on water quality and biological communities are poorly studied. A 28-day mesocosm experiment was conducted in Meiliang Bay of Lake Taihu to study the effects of cyanobacterial detritus on nutrients dynamics and the biomass of aquatic organisms. We found that the concentration of nutrients increased rapidly after addition of Microcystis detritus, with the maximum mean concentration of total nitrogen (TN) and total phosphorus (TP) up to 3.86 mg/L and 0.36 mg/L, respectively. Meanwhile, phytoplankton biomass (Chl.a) increased dramatically, after detritus addition, in the first nine days, then it gradually declined to the end of the experiment. In addition, the biomass of periphyton decreased gradually after cyanobacterial detritus addition which may be mainly due to the decreasing water transparency caused by the rapid increase of Chl.a limiting the growth of periphyton. Meanwhile, the biomass of Limnodrilus spp. increased gradually, and peaked on day 20, indicating that cyanobacterial detritus facilitates the population development of Limnodrilus spp. Our results have implications for eutrophic lake management and better understanding the effects of cyanobacterial blooms on aquatic ecosystems.

Assessment of nutrient and heavy metal contamination in surface sediments of the Xiashan stream, eastern Guangdong Province, China.

In this study, nutrient and heavy metal contamination in surface sediments of the Xiashan stream were investigated. Determining pollution degree of nutrient and heavy metal were the main objectives of this investigation. For this reason, the concentrations of total nitrogen (TN), total phosphorus (TP), seven heavy metals (Cu, Zn, Pb, Cd, Cr, Ni, Hg), and metalloid (As) were analyzed at 55 sampling sites. The mean TN concentration in surface sediments was 5.007 g/kg, while the mean TP concentration was 0.385 g/kg. Based on the sediment quality guideline (SQGs) and background values of Chinese soil and sediment, the majority of the mean TN concentrations in surface sediments were higher than their background values, while the TP concentrations were different from those observed for TN. For heavy metal concentrations in surface sediments, most of sampling stations were higher than their background values. The mean geo-accumulation (Igeo) indices for heavy metals were ranked as follows: Cd > Hg > Cu > Zn > Pb > Ni > Cr > As. The potential ecological risk index (RI) indicated heavy metal contamination level in Xiashan stream was very high ecological risk. According to Igeo and RI values, heavy metals especially Cd and Hg are influenced significantly by anthropogenic activities. Cd and Hg are not only as pollutant but also considerable contributor to ecological risk. Multivariate statistical investigations showed that there is a significant and positive correlation between Pb, As, and Cd. Cu, Ni, and Cr have similar characteristic and therefore probably originated from the same sources. Suggested by the results, it is necessary to control nitrogen and heavy metal contamination caused by human activities in the study area.

Quantifying the Extent of Anthropogenic Eutrophication of Lakes at a National Scale in New Zealand.

Quantifying environmental changes relative to ecosystem reference conditions (baseline or natural states) can inform assessment of anthropogenic impacts and the development of restoration objectives and targets. We developed statistical models to predict current and reference concentrations of total nitrogen (TN) and total phosphorus (TP) in surface waters for a nationally representative sample of ≥1033 New Zealand lakes. The lake-specific nutrient concentrations reflected variation in factors including anthropogenic nutrient loads, hydrology, geology, elevation, climate, and lake and catchment morphology. Changes between reference and current concentrations were expressed to quantify the magnitude of anthropogenic eutrophication. Overall, there was a clear increase in lake trophic status, with the most common trophic status being oligotrophic under a reference state and mesotrophic under current conditions. The magnitude of departure from reference state varied considerably within the sample; however, on average, the mean TN concentration approximately doubled between reference and current states, whereas the mean TP concentration increased approximately 4-fold. This study quantified the extent of water quality degradation across lake types at a national scale, thereby informing ecological restoration objectives and the potential to reduce anthropogenic nutrient loads, while also providing a modeling framework that can be applied to lakes elsewhere.

Analysis of the effect of green roof substrate amended with biochar on water quality and quantity of rainfall runoff.

Green roofs are becoming a popular ecological alternative in urban areas worldwide. In this study, we constructed two modular green roofs (commercial substrate green roof and biochar substrate green roof) and analyzed the effects that the green roof substrate amended with biochar on the runoff retention capacity, water quality, pollutants releasing characteristic, and pollution load by simulating rainfall experiment (rainfall levels 10~80mm). Results showed that the mean retention ratio was no significant differences between the commercial substrate (72.54%) and the biochar substrate (72.08%). Both the two kinds of substrates showed that the concentrations of total nitrogen (TN), total phosphorus (TP), chemical oxygen demand (COD), and iron (Fe) decreased gradually with the extension of rainfall time. Electrical conductivity (EC) and pH, as well as mean concentrations of TN, COD, TP, total suspended solids (TSS), and Fe, showed no differences between the green roof runoff of two kind of substrate. However, the neutralizing capacity of biochar substrate for the pH of green roof runoff was stronger than the commercial substrate, and the mean concentration of the TN and COD in the commercial substrate (16.14mg/L and 171.79mg/L, respectively) was about two times higher than the biochar substrate (9.85mg/L and 97.31mg/L, respectively). Similarly, the pollution load of TN and COD in the commercial substrate was significantly higher than that in the biochar substrate. Therefore, the biochar substrate could effectively reduce the pollution load of TN and COD in the runoff of green roof. Consequently, we suggest that the biochar could be applied to green roof substrates in order to reduce the impact of city non-point pollution on receiving water bodies.

Temporal variation of major nutrients and probabilistic eutrophication evaluation based on stochastic-fuzzy method in Honghu Lake, Middle China

Honghu Lake, which is listed in the Ramsar Convention, was found to be contaminated with elevated nutrients to a certain extent. This study investigated the seasonal variation of major nutrients and probabilistic eutrophic state in surface water from Honghu Lake. Average concentrations of total nitrogen (TN), total phosphorus (TP), chlorophyll- a (Chl- a ), chemical oxygen demand (CODMn) and transparency (SD) in summer and winter generally exceeded Grade III of the Chinese environmental quality standards for surface water (GB 3838-2002), with the exception of CODMn in winter. Mean concentrations of Chl- a and CODMn in summer were higher than that in winter, while mean concentrations of TN, TP and SD were slightly higher in winter. The improved probabilistic comprehensive trophic level index (PTLI) method based on stochastic-fuzzy theory was established to evaluate the eutrophic state in Honghu Lake. Compared with the Monte-Carlo sampling method, the Latin Hypercube sampling (LH-TFN) method was selected for the evaluation simulation due to its efficiency and stability. Evaluation results indicated that mean PTLI in summer (69.70) and winter (61.96) were both subordinated to Grade IV (Medium eutrophication). The corresponding reliability of eutrophication level subordinating to Grade IV in summer was of relatively low reliability (51.27%), which might mislead decision makers to some extent and suggest recheck. The probabilistic eutrophication level in summer developed with a trend from medium to severe eutrophication. Sensitivity analysis illustrated that CODMn and Chl- a were the priority pollutants in summer, with the contributions to PTLI of 43.3% and 22.5% respectively. Chl- a was the priority pollutant in winter, with the contribution to PTLI up to 51.3%.

The Effects of Tillage and Straw Incorporation on Soil Organic Carbon Status, Rice Crop Productivity, and Sustainability in the Rice-Wheat Cropping System of Eastern China

Soil management practices are used to enhance soil organic carbon, fertility, and crop productivity around the world. However, accurate information about the appropriate amount of straw incorporation is not available, because it is generally believed that at least 30% of the soil surface should be covered by straw, which is not implemented in all field environments. Therefore, a two-year (2016–2017) field experiment was conducted to investigate the impact of different percentages of straw incorporation and tillage methods, i.e., reduced tillage (RT) and conventional tillage (CT), on crop yield, soil organic carbon (SOC), total nitrogen (TN), and soil carbon storage (SCS) in rice–wheat cropping systems, under eight treatments. The experimental results showed that the greatest reduction in soil dry bulk density ( ρ b ) was found under CT with 100% straw coverage (9.79%), whereas the least reduction occurred under CT with no straw (1.31%). The mean TN concentration, soil organic matter (SOM), and soil carbon storage (SCS) were significantly higher by 0.98 g/kg, 17.07%, and 14.20%, respectively, under reduced tillage with 60% straw incorporation (RTsi60) compared with all other treatments. Our findings demonstrate that the incorporated wheat residues resulted in the highest rice production (7.95–8.63 t/ha) under RTsi60. We recommend the adoption of reduced tillage with 60% straw incorporation to increase rice yield, improve soil structure, and enhance TN, SOM, and SCS in paddy soil under rice-wheat rotation fields for agricultural sustainability.

Nitrogen and phosphorus leaching under the potential biennial oilseed plant Lepidium campestre L. in a field trial

ABSTRACTDomestication of biennial Lepidium campestre L. offers possibilities for more varied crop rotations in cold regions, with increased crop cover during winter. In the first winter after sowing, L. campestre can reduce nitrogen (N) leaching before harvesting in the second year. In this system no soil tillage is needed during the first year, unlike in systems with annual crops. A three-year leaching study on loam soil in southern Sweden revealed significantly (p < 0.05) lower flow-weighted mean total nitrogen (TN) concentration in drainage water under L. campestre (5.8 mg TN L−1) compared with a control treatment (no catch crop and autumn mouldboard ploughing) (9.6 mg TN L−1). In two years of observations, Lepidium campestre had lower flow-weighted mean TN concentration (6.2 mg L−1) than a mixed Vicia villosa L. (hairy vetch)/Secale cereale (winter rye) catch crop (10.2 mg L−1) and rather similar concentration to a Raphanus sativus (oilseed radish) catch crop (5.7 mg TN L−1), both sown after harvest of the main crop. However, L. campestre appeared to have a negative effect on total phosphorus (TP) leaching, with TP concentration in drainage of 0.05 mg L−1 compared with 0.01–0.02 mg L−1 for the other catch crops and the control.

Pollution characteristics of nitrogen, phosphate and eutrophication of river network water in central urban area of Tianjin

2013年底天津中心城区河道全部连通，形成中心城区河网.为了掌握河网形成后的水质状况，于2014年3月2015年2月进行了为期1年的定点水质监测，并对其水体氮、磷时空分布及富营养化特征进行分析.结果表明，河网水体氮污染严重，以铵态氮（NH₄⁺-N）为主；磷污染程度较轻，主要形态为磷酸盐（PO₄^3--P）；河网水体中氮、磷浓度顺水流方向均呈上游高、下游低的空间分布特征；氮、磷各项指标浓度时间变化趋势基本一致，3月均最高，10月均最低，冬季处于相对较低水平；与河网形成前相比，海河干流NH₄⁺-N、总磷（TP）和PO₄^3--P浓度年平均值分别下降6.5%、14.7%和16.4%，津河总氮、NH₄⁺-N、硝态氮、TP和PO₄^3--P浓度年平均值分别降低18.6%、34.5%、12.9%、31.6%和32.5%，表明河网形成后氮、磷污染程度较之前有所改善，其中津河改善较为明显；河网水体全年处于中度富营养状态，主要为磷限制性状态；河网富营养化防治应遵循以控制营养盐为主的控源、截污、水环境增容和生态补水策略.;After the completion of the river network in central urban area of Tianjin, pollution characteristics of nitrogen and phosphate were analyzed and water eutrophication status was assessed based on a field survey from March 2014 to February 2015. The results showed that the river network water was seriously polluted by nitrogen, and slightly contaminated by phosphorus. Ammonia nitrogen (NH₄⁺-N) and orthophosphate (PO₄^3--P) were the mainly form of nitrogen and phosphate, respectively. The temporal and spatial variations of nitrogen and phosphate in the river network water were obvious. The concentrations of nitrogen and phosphate in the upper water were both higher than those in the downstream water. During the study period, the concentrations of nitrogen and phosphate reached the highest level in March, then decreased gradually and dropped to the lowest level in October, and kept at low level in winter. Compared with the water status before the river network completion, the annual mean concentration of NH₄⁺-N, total phosphorus, PO₄^3--P in Haihe River water decreased by 6.5%, 14.7%, 16.4%, and the annual mean concentration of total nitrogen, NH₄⁺-N, nitrate nitrogen, total phosphorus, PO₄^3--P in Jinhe River water dropped by 18.6%, 34.5%, 12.9%, 31.6%, 32.5%, respectively. This showed that nitrogen and phosphate pollution problem of river network water had been obviously improved after the completion of the river network. The results of eutrophication evaluation and characteristic analysis indicated that river network water was in the stage of eutrophication, the algal growth in river network water was limited by phosphorus. The multiple ways including pollutant source control, sewage interception, water environmental capacity increase and ecological water compensation should be used together for eutrophication control.

Nitrogen and phosphorus in the subtropical Presidio River, northwestern Mexico

The aim of this study was to assess its nitrogen and phosphorus concentrations in the Presidio River, because it receives large volumes of wastewater with high loads of detergents and fertilizers. The mean concentrations of total nitrogen and phosphorus determined between February 2008 and January 2009 were 640 and 167 µg L -1 , respectively. The permissible phosphorous concentration established by the Official Mexican Standard NOM-001-SEMARNAT-1996 for pollutants discharge into rivers is 5000 µg L -1 . However, according to international standards on phosphorous concentrations in continental water bodies, the Presidio River may be considered hypereutrophic.

Nutrient distribution and risk assessment in drainage ditches with different surrounding land uses

Due to lack of ditch maintenance, many ditches in the upper reaches of the Yangtze River are strongly affected by nutrient over-enrichment. Accordingly, we conducted surveys of nutrient concentrations in ditchwater and sediment in the hilly area of the central Sichuan Basin to investigate the spatiotemporal variations of nutrient concentrations and to promote the restoration of ditches for ecological functions. The results showed that the mean total nitrogen, particulate nitrogen, nitrate nitrogen, ammonia nitrogen, and total phosphorus values in ditchwater were 4.80, 1.09, 0.94, 1.09, and 0.18 mg/L, respectively. The mean concentrations of total nitrogen, nitrate nitrogen, ammonia nitrogen, and total phosphorus in ditch sediment were 1.58 g/kg, 2.62 mg/kg, 1.54 mg/kg, and 6.95 g/kg, respectively. Higher total nitrogen concentrations in ditchwater occurred in western areas, while higher total phosphorus concentrations occurred in central areas. Seasonally, we measured higher nitrogen and phosphorus concentrations in ditchwater close to agricultural areas during the rainy season, while the opposite effect was true for residential areas. Although nutrient concentrations in ditchwater could be affected by both surrounding land uses and ditch water levels, land use was critical. Moreover, nitrogen and phosphorus concentrations were significantly higher in the ditchwater near residential areas when compared to paddy or sloping cropland ditches. However, we found no significant differences between the nutrient contents of sediments in ditches surrounded by different land uses. Our results indicate that water pollution control initiatives in residential areas would be the most critical factor in combating ditchwater and sediment pollution in this region. Therefore, efforts to restore the ecological functions of drainage ditches should take into account rural township sewage management, fertilizer reduction, and especially ditch vegetation restoration.

Nutrient concentrations and fluxes in the upper catchment of the Miyun Reservoir, China, and potential nutrient reduction strategies.

The Miyun Reservoir is Beijing's main drinking water source. Increased nutrient levels in the reservoir have resulted in an increased risk of harmful algal blooms. One hundred ten water samples were collected at a range of spatial scales in the upper catchment of the Miyun Reservoir and were analyzed for total nitrogen (TN), nitrate (NO3 (-)-N), ammonium (NH4 (+)-N), total phosphorus (TP), and the potassium permanganate index (CODMn). Empirical equations were developed from relationships between nutrient concentrations and the main controls on nutrient, and were used to identify parts of the catchment that should be targeted with nutrient load reduction measures. Cropland was the main source of sediment for the streams, and much of the phosphorus was associated with sediment. The annual mean TP concentrations were closely correlated with both the annual mean suspended sediment concentrations and the ratio of the cropland area to the total basin area. There was a linear relationship between the annual mean TN concentration and the population density in the basins. Soil conservation may play an important role in reducing TP concentrations in the upper reaches of the Chao and Bai Rivers. It may be useful to (1) construct natural riparian buffers and vegetated buffers along croplands close to the watercourses, (2) implement management strategies to reduce nitrogen (N) fertilizer applications, and (3) construct additional wetlands to reduce nutrient loads in the study area.

Historical accumulation of N and P and sources of organic matter and N in sediment in an agricultural reservoir in Northern China.

Agriculture has significantly intensified in Northern China since the 1980s. This intensification has caused a series of simultaneous lake ecological environment problems in this area. However, little is known about the role of agricultural intensification in historical nutrient dynamics and lake eutrophication processes. The Yanghe reservoir, a typical artificial reservoir characterized by high-yield grain production in Northern China, has been suffering from serious eutrophication and water quality deterioration. This study evaluates the effect of agricultural intensification on nutrient retention and source in the sediments using (210)Pb and (137)Cs dating techniques combined with stable C and N isotopes (δ(13)C, δ(15)N) and total organic carbon/total nitrogen, as well as total nitrogen (TN), total phosphorus (TP), and P fractions. Results suggested that agricultural intensification was keys to the accumulation of nutrients and was a source of organic matter (OM) and N in sediment for the past three decades. N and P pollution started in the 1980s and worsened from the 1990s. Good water quality status and steady sedimentary environment with low nutrient content (mean concentrations of TN and TP were 815 and 387 mg kg(-1), respectively) were observed before the 1980s. Sediment OM was primarily derived from aquatic plants, whereas N was primarily derived from soil erosion and aquatic plants. However, water quality began to deteriorate while sediment nutrient content began to increase after the 1980s, with values of 1186 mg kg(-1) for TN and 434 mg kg(-1) for TP in 1989. Sediment OM was primarily derived from C3 (sweet potato) and aquatic plants, and the major sources of N were soil erosion, fertilizer, and sewage, which accompany the rapid development of agriculture in the watershed. Following the further growth of grain production and fertilizers, excessive external nutrient loading has resulted in dramatic water quality and ecosystem deterioration since 1990. The increasing rate of TN and TP contents was also augmented during these periods, reaching as high as 2624 and 846 mg kg(-1) in surface sediment, respectively. In addition, sources of OM and N in sediment were similar to those in the 1980s, but the contribution of aquatic organic N in sediment has continued to increase (aquatic organic N that accounts for TN increased from 14.5% before the 1980s to 48% in 2007). This condition could be attributed to the impact of frequent "water bloom" and recession of aquatic plant due to worsening water pollution.

流域背景に基づくダム湖流入河川の栄養塩濃度および負荷量の統計的解析

Reservoirs occupy a large portion of water resources in Japan. Therefore, in this study, relationship between watershed conditions and nutrient concentration, loading and inorganic ratio of inflowing river to reservoirs was investigated by statistical analysis. 52 reservoirs were chosen from all over Japan. The mean concentration of total nitrogen was strongly influenced from artificial factors in basin. Phosphorus and nitrogen loading were estimated by two ways; multiple regression analysis or equations obtained by multiplying influent quantity and nutrient concentration. Those equations were capable of estimating nutrient loadings of inflowing river with high precision.