Water Nitrate Nitrogen Research Articles

Biogeography of freshwater plants in four major lakes in Kenya

Freshwater plants play a pivotal role in the health and functioning of freshwater ecosystems, and they also offer a variety of benefits to humans. Despite their importance, there is a significant gap in our understanding of the macroecology of freshwater plants in tropical regions, where biodiversity is typically high, and ecosystems face substantial pressures from human activities. To bridge this knowledge gap, we conducted extensive field surveys and applied statistical methods to understand the patterns of distribution, density, and diversity of freshwater plants and their relationship with abiotic components in four freshwater lakes in Kenya. We aimed to answer four key questions: (1) How many freshwater plant species occur in these lakes? (2) What proportion of these freshwater plant species are native and alien to Kenya? (3) What proportion of these species have a history of being invasive somewhere in the world, including in Kenya? (4) Which water and sediment characteristics are significantly associated with the presence, density, and diversity of freshwater plants in the lakes? We inventoried a total of 163 freshwater plant species, of which 114 were native to Kenya and 49 were alien. Online database searches revealed that 114 species had a history of invasion globally, with 22 species already invasive in Kenya. Our statistical analysis showed that the presence and density of plant species were positively correlated with pH and turbidity, but negatively correlated with soluble reactive phosphorus in both water and sediments, ammonia-nitrogen in sediments, and nitrate-nitrogen in water. Shannon-Wiener diversity of the plant species was positively correlated with ammonia-nitrogen in water and nitrate-nitrogen in sediments but negatively correlated with longitude and electrical conductivity of the water. Pielou’s evenness within the communities showed positive correlations with soluble reactive phosphorus in both water and sediments, ammonia-nitrogen in sediments, and nitrate-nitrogen in water but was negatively correlated with water turbidity and pH. The number of species with a history of invasion was positively correlated with longitude and electrical conductivity but negatively correlated with ammonia-nitrogen and nitrate-nitrogen in water. This extensive inventory not only enriches our understanding of the biodiversity within these freshwater plant communities but also highlights the potential risks posed by species with a history of being invasive. The findings regarding environmental variables linked to the presence, density, diversity, and invasive potential of these species underscore the complexity of freshwater ecosystems and the array of factors influencing the composition of freshwater plant communities.

Study on the transformation of nitrate nitrogen by manganese-catalyzed iron-carbon micro-electrolysis and microbial coupling.

Nitrate-nitrogen pertains to the nitrogen component of the overall nitrate present in a given sample in order to reduce nitrate nitrogen pollution in water, nitrate nitrogen removal methods based on iron-carbon micro-electrolysis have become a key research focus. The process and mechanism of nitrate nitrogen removal by microbial coupling was comprehensively explored in a novel iron-carbon micro-electrolysis (ICME) system. In order to establish the transformation pathway of nitrate nitrogen in water, the transformation paths of nitrate nitrogen in water before and after coupling microorganisms in three groups of continuous flow reaction devices, namely sponge iron (s-Fe0), sponge iron + biochar (s-Fe0/BC) and sponge iron + biochar + manganese sand (s-Fe0/BC/MS), were studied. The morphology and composition changes of sponge iron were analyzed by means of characterization, and the microbial population changes in the three groups were analyzed by high-throughput sequencing. Results showed that the nitrate conversion rate in the s-Fe0, s-Fe0/BC and s-Fe0/BC/MS systems reached 99.48%, 99.57% and 99.36%, respectively, with corresponding ammonia nitrogen generation, rates of 3.77%, 9.34% and 11.24% and nitrogen generation rates of 95.71%, 90.23% and 88.12%. Scanning electron microscopy imaging showed that in the s-Fe0/BC and s-Fe0/BC/MS systems the surface of sponge iron was highly corroded, with granular substances in the corrosion product clusters. X-ray photoelectron spectroscopy analysis found that the relative contents of Fe2O3 in the surface oxides of sponge iron after microbial coupling were 38.02% and 71.27% in the s-Fe0/BC and s-Fe0/BC/MS systems, while the relative Fe3O4 contents were 61.98% and 28.72%, respectively. Microbial high-throughput sequencing analysis revealed that the Chao and Ace index values in the s-Fe0 system were 871.89 and 880.78, while in the s-Fe0/BC system they were 1012.05 and 1017.29, and in the s-Fe0/BC/MS system were 1241.09 and 1198.29, respectively. The relative proportion of Thauera in the s-Fe0, s-Fe0/BC, and s-Fe0/BC/MS systems was 16.76%,14.25% and 10.01%, while the proportion of Acetoanaerobium was 15.36%, 13.27% and 11.11%, and the proportion of Chloroflexi was 0%, 1.11% and 2.18%, respectively. Furthermore, FAPROTAX function annotation found that the expression levels of chemoheterotrophs in the s-Fe0, s-Fe0/BC and s-Fe0/BC/MS systems were 43 316 OTU, 37 289 OTU and 34 205 OTU, while nitrate respiration expression levels were 16 230 OTU, 15 483 OTU and 9149 OTU, with nitrogen respiration expression levels of 16 328 OTU, 15 493 OTU and 9154 OTU, respectively. These findings suggest that nitrate is converted into nitrogen gas and ammonia nitrogen through the actions of the coupled system of sponge iron/biochar/manganese sand and microorganisms. The catalytic effect of MnO2 promotes the conversion of Fe2+ to Fe3+, generating more electrons, allowing denitrifying bacteria to reduce more nitrate nitrogen, effectively coupling the manganese-catalyzed ICME reaction and microbial denitrification. The micro-electrolysis system and the addition of manganese sand enhanced biodiversity within the s-Fe0/BC/MS system. The heterotrophic bacteria Thauera and Acetoanaerobium were the dominant microorganisms in all three systems, although the micro-electrolysis system with added manganese sand significantly reduced the proportion of facultative bacteria Thauera and Acetoanaerobium and promoted the growth of autotrophic Chloroflexi bacteria. The ecological functions of the three systems were mainly nitrate respiration and nitrogen respiration. By comparing the expression levels of nitrate respiration and nitrogen respiration in s-Fe0/BC and s-Fe0/BC/MS systems, it can be seen that the addition of manganese sand reduced microbial activity.

Enhanced nitrogen removal performance of microorganisms to low C/N ratio black-odorous water by coupling with iron-carbon micro-electrolysis

Black-odorous water was caused by urbanization, industrial sewage and domestic sewage. Black-odorous water with low carbon nitrogen ratio (C/N) may inhibit the activity of microorganisms due to the lack of C source during microbial treatment. In this study, iron-carbon micro-electrolysis (ICME) was used to couple nitrifying and denitrifying bacteria. The external factors affecting microbial activity were optimized through experiments, and the effect of low C/N wastewater was studied. The optimal external factors were temperature of 30 ℃, C/N of 3, DO of 3 mg/L and iron-carbon dosage of 150 g/L. Coupled with ICME, it was found that the removal rate of nitrate nitrogen in water increased by 50.74 %, indicating that ICME could make up for the deficiency of microbial C source and improve the removal rate of nitrate nitrogen in low C/N black-odorous water. The improvement of removal rate had much to do with ICME's role as electron donor to provide electrons for denitrification. In addition, the performance of wastewater treatment by this process is tested. The maximum load of ammonia nitrogen, COD, nitrate and total nitrogen was increased to 0.1928, 1.7732, 0.2691 and 0.5181 kg/(m3·d), respectively. High-throughput sequencing results showed that the species of dominant plant population changed after ICME coupling, but the abundance increased significantly, which further indicated that ICME played a synergic role in microbial nitrogen removal, which was related to the release of trace iron by ICME. This study can provide some guidance for the treatment of black-odorous water with high ammonia nitrogen and low C/N.

Performance evaluation of a low-cost loess-based filler for bioretention cells

The sand and gravel fillers used in traditional bioretention cells are expensive and becoming increasingly scarce, and their performance is unstable. It is important to find a stable, reliable, and low-cost alternative filler for bioretention facilities. Using cement as a modified loess filler for bioretention cells is a low-cost and easily obtainable alternative. The loss rate and anti-scouring index of the cement-modified loess (CM) were analyzed under different curing times, cement addition amount, and compactness control conditions. This study found that the stability and strength of the cement-modified loess in water with a density of not less than 1.3 g/cm3, a curing time, of not less than 28 d and a cement addition amount not less than 10% meets the use requirements of the bioretention cell filler. X-ray diffraction and Fourier transform infrared spectroscopy of cement-modified materials with a 10% cement addition and a curing time of 28 days (CM28) and 56 days (CM56). Cement-modified materials with 2% straw and a curing time of 56 days (CS56) showed that the three kinds of modified loess all contain calcium carbonate and that the surface contains hydroxyl and amino functional groups that can effectively remove phosphorus. The specific surface areas of the CM56, CM28, and CS56 samples were 12.53 m2/g, 24.731 m2/g, and 26.252 m2/g, respectively, which are significantly higher than that of sand (0.791 m2/g). At the same time, the adsorption capacity of the ammonia nitrogen and the phosphate that was present in the three modified materials is better than that of sand. CM56, like sand, has rich microbial communities, which can entirely remove nitrate nitrogen in water under anaerobic conditions, indicating that CM56 can be used as an alternative filler for bioretention cells. The production of cement-modified loess is simple and cost-effective, and using modified loess as a filler can reduce the use of stone resources or other on-site materials. Current methods for improving the filler of bioretention cells are mainly based on sand. This experiment used loess to improve the filler. The performance of loess is better than sand, and can completely replace sand as the filler in bioretention cells.

A Study to Enhance the Nitrate-Nitrogen Removal Rate without Dismantling the NF Module by Building a PFSA Ionomer-Coated NF Module.

Water resource pollution by nitrate-nitrogen, mainly caused by anthropogenic causes, induces eutrophication of water resources, and indicates the degree of organic pollution. Therefore, this study devised a method for coating PFSA ionomer with excellent chemical resistance without disassembling the module to improve the removal rate of nitrate-nitrogen in water by using a cyclic coating method on a commercially available nanofiltration membrane (NF membrane) module. Nafion was prepared as a supercritical fluid dispersion using a high-temperature and high-pressure reactor, and the particle size and the degree of dispersion of the dispersion were analyzed by DLS. The crystallinity was confirmed through XRD by drying the dispersion in the liquid state. After the dispersion was prepared as a membrane according to the heat treatment conditions, the characteristics according to the particle size were analyzed by tensile strength and TEM. The nitrate-nitrogen removal rate of the NF membrane module coated with the dispersion was increased by 93% compared to that before coating. Therefore, the result showed that the cycle coating method devised in this study could efficiently coat the already commercialized module and improve performance.

Synthesis of polyoxometalates (POM)/TiO2/Cu and removal of nitrate nitrogen in water by photocatalysis

Nitrate nitrogen is one of the vital issues needed to be addressed in the water purification process utilizing groundwater as a drinking water source. In this study, a sandwich-type polyoxometalate Na [α-SiW9O34] has been synthesized and SiW9/TiO2/Cu composite has been prepared by sol-gel method. Samples have been characterized by XRD, BET, FTIR, SEM, ED-Mapping, UV–Vis, XPS. The catalytic reduction of nitrate was performed in the presence of SiW9/TiO2/Cu composite as photocatalyst. The effects of catalyst loading, initial nitrate concentration, sandwich-type polyoxometalate loading, dissolved O2, and concentration of formic acid on nitrate removal have been investigated. The results showed that the prepared composite catalyst had better photocatalytic activity than the TiO2. 76.53% of nitrate removal with 82.09% of N2 selectivity was obtained under the following conditions: catalyst dosage 0.8 g/L, initial nitrate concentration of 30 mg/L, SiW9/Cu loading percentage of 10%, 30 mmol/L of formic acid, in presence of N2, and 6 h reaction time.

Removal of nitrate nitrogen from water by phosphotungstate-supported TiO2 photocatalytic method.

Nitrate nitrogen in water, especially in groundwater, is a major problem in the current drinking water environment. In this study, copper- and nickel-modified phosphotungstate catalysts supported on TiO2 were prepared by the sol-gel solvothermal method, and photocatalytic reduction by phosphotungstate was used to remove nitrate nitrogen in water under ultraviolet irradiation. The maximum removal rate was 59.60% with 0.8g/L Cu-H3PW12O40/TiO2, 90mg/L nitrate nitrogen, and 60min reaction time. For Ni-H3PW12O40/TiO2, the maximum removal rate of nitrate nitrogen was 54.58%, achieved with a catalyst concentration of 0.8g/L, nitrate nitrogen concentration of 120mg/L, and reaction time of 30min. Both catalysts could remove nitrate nitrogen from water under the condition of photocatalysis.

Quantification of N2O and NO emissions from a small-scale pond-ditch circulation system for rural polluted water treatment

The pond-ditch circulation system (PDCS) is an efficient and economical solution for the restoration of degraded rural water environments. However, little is known about nitrous oxide (N2O) and nitric oxide (NO) emissions in the microbial removal process of nitrogen in PDCSs, and their contribution to nitrogen removal. The aim of this study was to quantify N2O and NO emissions from the PDCS, evaluate their capacities, and elucidate the key environmental factors controlling them. The results showed that N2O and NO fluxes were in the ranges 1.1–2055.1μgNm−2h−1 and 0.1–6.8μgNm−2h−1 for the PDCS, respectively. Meanwhile, the N2O and NO fluxes from the two ponds in the PDCS were significantly higher than those in the static system. Moreover, the amount of N2O and NO emissions in the PDCS accounted for 0.17–4.32% of the total nitrogen (TN) removal. According to the partial least squares (PLS) approach and Pearson's correlation coefficients, nitrate nitrogen in water (W-NO3−-N), dissolved oxygen in water (W-DO), dissolved oxygen in sediment (DO), pH in water (W-pH), pH in sediment (pH), total kjeldahl nitrogen (TKN), and soil organic carbon (SOC) significantly affected the N2O flux (p<0.05), whereas W-NO3−-N, DO, and nitrite nitrogen in sediment (NO2−-N) significantly affected the NO emission (p<0.05).

Distribution of Phragmites australis Communities with Different Habitat Salinity

ABSTRACT Cho, J.-S.; Lee, J.-S., and Kim, J.-W., 2017. Distribution of Phragmites australis communities with different habitat salinity. To analyze vegetation distribution and environmental factors, 22 regions containing Phragmites australis communities were selected from the west to south coastline of South Korea. In the studied soil environments, the average moisture content was 28.07%, soil salinity was 5.86 ppt, and total nitrogen was 1.02 mg/g. In water environments, the average dissolved oxygen was 9.04 mg/L, water salinity was 13.66 ppt, nitrate nitrogen (NOx–N) was 1.0712 mg/L, and ammonia nitrogen (NH4+–N) was 0.3790 mg/L. The correlation analysis of P. australis communities revealed that there was a relatively strong negative correlation between soil salinity and annual production (r = −0.584, N = 22). The ordination using canonical correspondence analysis (CCA) of edaphic factors and water quality factors showed that soil salinity, water salinity, and water nitrate–nitrogen play important roles...

Increase in stream water nitrate nitrogen concentrations caused by a disturbance to a forested catchment by Japanese oak wilt

ABSTRACTIn recent years, Japanese oak wilt (JOW) has become prevalent in Japan and has spread into almost all prefectures. To understand the effects of a JOW disturbance on nitrate nitrogen (NO3–) concentrations in a forest stream, we analyzed the changes in NO3– concentrations over a period of 7 years in a mixed broadleaved-conifer secondary forest in Japan. The JOW disturbance arose in the fifth year and lasted until the seventh year of the study period, resulting in a 4.7%, 3.0%, and 2.5% loss in the total basal area of the forest in the fifth, sixth, and seventh years, respectively, eventually resulting in an estimated canopy cover loss of 9.7%. The mean NO3– concentration after the appearance of JOW (3.99 μmol L–1) was significantly higher than before the start of the disturbance (1.99 μmol L–1). This study demonstrated that even the modest canopy cover loss by JOW-induced dieback of Quercus serrata trees could cause an increase in stream water NO3– concentration.

Distribution of nitrogen forms in suspended sediments and surface sediments of East Tiaoxi River, upper reaches of Taihu Basin and their influence factors

氮是影响和控制水体富营养化的重要因素，不同形态的氮对水体富营养化贡献不同.使用连续提取法对东苕溪干流悬浮物、表层沉积物样品中各形态氮含量进行测定，探讨各形态氮的分布特征及其影响因素.结果表明，东苕溪水体氮污染严重，总氮浓度均值为4.48 mg/L.悬浮物中各形态氮含量均高于沉积物，其中悬浮物中铁锰氧化态氮（IMOF-N）含量所占比例最大，均值为1506.94 mg/kg；沉积物中有机硫化物结合态氮（OSF-N）含量最高，均值为625.31 mg/kg.IMOF-N、OSF-N含量受阳离子交换量、粒径影响显著，均与总氮浓度显著相关.相关性分析表明水体的性质对IMOF-N及OSF-N含量影响较显著，并且总体上对悬浮物的影响强于沉积物.另外，悬浮物有助于水体中的氮发生硝化反应向硝态氮转化，沉积物则有助于水体的氮发生还原作用向氨氮转化.在一定程度上，水体中的悬浮物对藻类具有抑制作用.;Nitrogen is a dominant nutrient influencing and controlling eutrophication, and different nitrogen forms can make diverse contributions to water quality. The contents of different nitrogen forms in suspended sediments and surface sediment of East Tiaoxi River were determined by sequential extraction procedure. In addition,their distribution characteristics and influence factors were discussed. The results showed that the nitrogen pollution in East Tiaoxi River were serious with an average concentration of 4.48 mg/L, and the water quality in the middle reach of East Tiaoxi River was better than that in the upper and lower reaches. The amounts of four nitrogen forms in suspended sediments were significantly higher than those in surface sediment, in addition, the percentage of iron-manganese oxides bound nitrogen (IMOF-N) with the mean concentration of 1506.94 mg/kg were higher than that of other three nitrogen forms in suspended sediment. The percentage of organic matter-sulfide bound nitrogen (OSF-N) with the mean of 625.31 mg/kg was highest in surface sediment. IMOF-N and OSF-N contents were significantly affected by cation exchange capacity and particle size in both suspended sediments and surface sediments, and they were also significantly correlated with total nitrogen(TN),indicating that IMOF-N and OSF-N were the main fractions of TN. The correlation results showed that the water quality had significant influence on IMOF-N and OSF-N,and the influence of water on suspended sediments was stronger than that on surface sediments. Furthermore, suspended particulates were beneficial to produce nitrate nitrogen in water. In contrast, sediments were available for generating ammonia nitrogen in water, and to some extent, suspended sediments has inhibitory effect on algae.

Hodnotenie koncentr�cie anorganick�ch foriem dus�ka v N�rodnej pr�rodnej rezerv�cii Cicovsk� mrtve rameno

The aim of this study was to evaluate of concentrations of nitrate, ammonium and nitrite nitrogen in the water of National Nature Reserve Cicov oxbow during the years 2010 – 2013. The average concentration of nitrate nitrogen in water of National Nature Reserve during the whole monitored period was 3.42 mg*dm-3. Maximum average concentration for the whole monitored period in the month of March and minimum in the month of November was found. Depending on the sampling sites it’s the highest average concentrations were recorded in the first side distributary and the sampling place located in the northeastern part of the national nature reserve. Minimum average concentrations of N-NO3- were recorded at sampling sites located in the first and second side distributary of reservation with the low water level. The average concentration of ammonia nitrogen during the whole monitored period was 0.15 mg*dm-3. The highest average concentrations of N-NH4+ for the entire period were in summer period with maximum in month of June and minimum in month of February. Depending on the sampling place its highest average concentrations were in the sampling points located near the mouth of the Ciližsky channel in the northeastern part of reserve. The lowest average concentrations in the sampling point that was located at the first side distributary were measured. The average concentration of nitrite nitrogen during the whole monitored period represented 0.04 mg*dm-3. The lowest average concentration of N-NO2- for the entire monitored period was in month of January and the highest was in month of July. In terms of sampling place in all sampling sites during the entire period the same average concentration of nitrite nitrogen (0.04 mg*dm-3) was measured.

升温对超富营养型浅水湖泊沉积物营养盐动态迁移影响的初步研究

PDF HTML阅读 XML下载 导出引用 引用提醒 升温对超富营养型浅水湖泊沉积物营养盐动态迁移的影响 DOI: 10.5846/stxb201309102244 作者: 作者单位: 华中农业大学水产学院 湖北武汉,华中农业大学水产学院 湖北武汉,华中农业大学水产学院 湖北武汉,华中农业大学水产学院 湖北武汉,华中农业大学水产学院 湖北武汉,中国科学院水生生物研究所 湖北武汉 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金资助项目(31200359); 国家水体污染控制与治理科技重大专项课题子课题(2012ZX07501001-06); 公益性行业(农业)科研专项(201203083) A preliminary study of effects of warming on the nutrients dynamic in sediment of hypereutrophic shallow lake Author: Affiliation: College of fisheries,Huazhong Agricultural University,College of fisheries,Huazhong Agricultural University,College of fisheries,Huazhong Agricultural University,College of fisheries,Huazhong Agricultural University,College of fisheries,Huazhong Agricultural University, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:在实验室控制条件下,以超富营养型浅水湖泊——武汉南湖表层沉积物和表层水为研究对象,设置18 ℃和22.5 ℃两个温度处理组,模拟武汉地区预测的21世纪末春季变暖的情景,研究升温对沉积物营养盐释放的影响。实验结果表明:整个实验过程中,22.5 ℃处理组水体中正磷酸盐(o-P)和总磷(TP)含量显著高于18 ℃处理组,说明气温升高可以显著促进富营养化浅水湖泊沉积物磷的释放,促进水体中磷含量的显著升高;此外,在实验的初始阶段,升温能够加速水体中氨氮(NH4+-N)向硝态氮(NO3--N)转化的过程,同时水体与沉积物中氮含量的下降可能是水体与沉积物中的氮通过反硝化作用从系统中溢出以及被系统中的底栖生物利用所致,没有观察到气温升高对沉积物中总氮的释放产生显著影响。 Abstract:It is now accepted that human-induced climate change is unavoidable. On average, global surface temperatures have increased by about 0.74 ℃ over the past 100 years with the majority of the increase (0.55 ℃) occurring over the past 30 years. Marked changes may be expected to occur in the global climate during this century. Temperature increase, although only one of several related climate changes, is the key variable of change and one that pervades almost all biological processes. All ecosystems will therefore be affected to some extent by global warming and predicting potential effects on the ecosystems is of great importance for ecology and management. Lake ecosystems are vital resources for aquatic wildlife and human needs, and any alteration of their environmental quality and water renewal rates has wide-ranging ecological and societal implications. However, lakes have always been subject to the impacts of climate change, and natural climate variations in the past have been one of the main reasons that lakes are ephemeral features of the landscape. The sediment in lakes typically has high concentrations of nutrients and organic matter, and hosts a biologically active autotrophic-heterotrophic community. Thus, knowledge of the warming effects on nutrients dynamic in sediment is in urgent need. In the present study, an indoor microcosm system was set up to explore the effects of warming on the nutrients dynamic in sediment of a hypereutrophic shallow lake, Lake Nanhu. Sieved sediment cores were incubated under laboratory conditions, the experimental temperature regimes consisted of decadal spring average of Wuhan city (18 ℃) and an elevated regime with 4.5 ℃ difference from that at baseline (22.5 ℃). The contents of orthophosphate and total phosphorus in the water under the ambient temperature of 22.5 ℃ was significantly higher than those of 18 ℃ during the middle stage of the experiment, which indicated that warming accelerated the release of phosphorus from the sediment into water and the increase of the phosphorus content in the water would further increase the eutrophication. The concentration of the nitrate nitrogen in water raise rapidly accompany with the ammonia nitrogen concentration decreasing fast in the beginning of the experiment. Nevertheless, the contents of total nitrogen in water under two different temperature conditions were not significantly different from each other. The concentrations of total nitrogen in water and sediment were continuously declining at both conditions in all the experimental phases, which may indicate the denitrification and the benthic biological absorption in this experiment system. The total phosphorus content in sediment, loss on ignition of sediment, an indicator for loss of organic matter, and the chlorophyll a in the sediments were not significantly affected by the elevated temperature in this experiment system. In conclusion, warming may profoundly affect the phosphorus dynamics, but no obvious impact on the nitrogen dynamics in sediment. 参考文献 相似文献 引证文献

From Headwaters to Coast: Influence of Human Activities on Water Quality of the Potomac River Estuary

The natural aging process of Chesapeake Bay and its tributary estuaries has been accelerated by human activities around the shoreline and within the watershed, increasing sediment and nutrient loads delivered to the bay. Riverine nutrients cause algal growth in the bay leading to reductions in light penetration with consequent declines in sea grass growth, smothering of bottom-dwelling organisms, and decreases in bottom-water dissolved oxygen as algal blooms decay. Historically, bay waters were filtered by oysters, but declines in oyster populations from overfishing and disease have led to higher concentrations of fine-sediment particles and phytoplankton in the water column. Assessments of water and biological resource quality in Chesapeake Bay and tributaries, such as the Potomac River, show a continual degraded state. In this paper, we pay tribute to Owen Bricker’s comprehensive, holistic scientific perspective using an approach that examines the connection between watershed and estuary. We evaluated nitrogen inputs from Potomac River headwaters, nutrient-related conditions within the estuary, and considered the use of shellfish aquaculture as an in-the-water nutrient management measure. Data from headwaters, nontidal, and estuarine portions of the Potomac River watershed and estuary were analyzed to examine the contribution from different parts of the watershed to total nitrogen loads to the estuary. An eutrophication model was applied to these data to evaluate eutrophication status and changes since the early 1990s and for comparison to regional and national conditions. A farm-scale aquaculture model was applied and results scaled to the estuary to determine the potential for shellfish (oyster) aquaculture to mediate eutrophication impacts. Results showed that (1) the contribution to nitrogen loads from headwater streams is small (about 2 %) of total inputs to the Potomac River Estuary; (2) eutrophic conditions in the Potomac River Estuary have improved in the upper estuary since the early 1990s, but have worsened in the lower estuary. The overall system-wide eutrophication impact is high, despite a decrease in nitrogen loads from the upper basin and declining surface water nitrate nitrogen concentrations over that period; (3) eutrophic conditions in the Potomac River Estuary are representative of Chesapeake Bay region and other US estuaries; moderate to high levels of nutrient-related degradation occur in about 65 % of US estuaries, particularly river-dominated low-flow systems such as the Potomac River Estuary; and (4) shellfish (oyster) aquaculture could remove eutrophication impacts directly from the estuary through harvest but should be considered a complement—not a substitute—for land-based measures. The total nitrogen load could be removed if 40 % of the Potomac River Estuary bottom was in shellfish cultivation; a combination of aquaculture and restoration of oyster reefs may provide larger benefits.

Flow path influence on an N:P ratio in two headwater streams: A paired watershed study

Hydrologic flow paths were assessed and stream water quality was monitored in two adjacent watersheds to improve the understanding of how flow paths impact stream water nitrate nitrogen to total phosphorus ratios (NO3:TP). We hypothesized that a watershed with mostly subsurface flow paths will have high stream water NO3:TP ratios relative to a watershed with a greater tendency to have overland flow paths. Flow paths were assessed with end member mixing analysis (EMMA), stream water temperature, and stream discharge flashiness. The EMMA suggested that groundwater comprised a larger percentage of stream discharge in the west stream compared to the east stream. The analysis of stream water temperature and stream flashiness corroborated the results from the EMMA. Nitrate and TP concentrations were similar in both streams during low discharge. However, during storm flows nitrate decreased and TP increased in the east stream, while nitrate and TP concentrations remained similar during all discharge rates in the west stream. Thus, NO3:TP ratios in the east stream dramatically decreased during peak storm flows, while NO3:TP ratios remained relatively stable during all discharge rates in the west stream. Exploring hydrological processes helped explain the temporal variation within and spatial variation between the two streams, with regard to NO3:TP ratios. Further attention is necessary to understand whether hydrologic flow paths act as a control of other stream water N:P ratios and quantify flow path control relative to in‐stream processes.

Shallow ground water nitrate-N and ammonium-N in cropland and riparian buffers

Abstract The extent of nutrient reduction in shallow ground water flow between cropland and riparian buffers in the Northeast is not well established, yet there is an increasing need to quantify such reductions. A four-year project was initiated in 2002 to determine the relative effectiveness of riparian buffers on reducing nutrients in soil water and shallow ground water flow from adjacent cropland. The main objective of this study was to determine if shallow ground water nitrate nitrogen (NO3–N) and ammonium nitrogen (NH4–N) concentrations differed among cropland (hay or corn), restored riparian buffers (grass and Salix-grass), and established forested riparian buffers. Sixteen paired ground water monitoring wells were established in cropland and riparian buffers at two agricultural research sites during July 2002 and July 2003. Samples of ground water, tile drainage water, and stream water were collected approximately monthly over the 2003 field season and analyzed for NO3–N and NH4–N concentration. Average NO3–N concentration across sites was significantly lower in buffers for each sampling. Average NH4–N concentration was consistently higher beneath buffers, and decreased markedly over the sampling period. Soil drainage, as indexed by depth to water table, was significantly correlated with NO3–N concentrations among cropland and buffer wells at individual sites. We hypothesize that this reflects the relationship between soil drainage and its direct impact on both NO3–N leaching and denitrification potentials across the landscape. Forested buffers had the lowest average NO3–N, highest NH4–N, and the highest water table. Cropland soils with appreciable NO3–N in ground water adjoining riparian buffers on outwash deposits were ineffective at reducing NO3–N. Consistent NO3–N reductions occurred between cropland and buffers where ground water flowed from moderately well and well drained cropland to poorly drained riparian buffer soils.

A relative-flux-correction scheme for analyzing three dimensional data of a tile-drained agricultural plot

The use of simple geostatistical tools is often constrained by data trend (nonstationarity) to characterize the spatial variability of soil properties in the subsurface environment influenced by any site-specific feature(s). Adaptive approaches, such as site-specific robust-resistant schemes, median polishing, trend analysis, etc., are thus used to preprocess the spatial data before analyzing for their spatial structures. Soil water nitrate–nitrogen (NO 3–N) concentration (mg l −1) and soil moisture content (cm) data collected jointly from 175 sites arranged on a 5×7×5 three-dimensional (3-D) grid network of 7.6 m×7.6 m×0.3 m spacings in a tile-drained agricultural plot were analyzed for their three-dimensional spatial distribution and for possible coregionalization. We propose a physical process-based correction scheme to preprocess the nonstationary spatial data of soil NO 3–N concentration and soil moisture content. Using the subsurface-drain flow phenomenon, we developed a relative-Darcy-flux-based correction scheme to remove any tile drainage-induced nonstationarity in the spatial data of soil NO 3–N concentration and soil moisture content prior to conducting the spatial analysis in the 3-D soil volume. 3-D composite semivariograms of relative-flux-corrected NO 3–N concentration and relative-flux-corrected moisture content showed anisotropic linear structures in three principal directions. Linear models characterized by steep slopes were found in the directions perpendicular to tile line as opposed to nugget models found in the direction parallel to the tile line. Good spatial correlation between the relative-flux-corrected NO 3–N concentration and relative-flux-corrected soil moisture content and their anisotropic linear semivariograms produced anisotropic linear cross semivariograms in 3-D. The 3-D composite cross semivariogram will be useful in predicting the more expensive variable, (relative-flux-corrected) soil water NO 3–N concentration, at unsampled locations in the soil profile with a cheaper surrogate, the measured (relative-flux-corrected) soil moisture content.

Metrological support to determining nitrate nitrogen in water

Metrological support to determining nitrate nitrogen in water

Ecology of creeping macrophytes with special reference to Ludwigia peploides (H.B.K.) Raven

Growth strategies are described of five emergent macrophytes, Ludwigia peploides (H.B.K.) Raven, Myriophyllum aquaticum (Vellozo) Verdcourt, Nasturtium officinale R. Br., Hydrocotyle verticillata Thunb., and Oenanthe sarmentosa Presl, which commonly occur in nutrient rich pools, sloughs, and irrigation and drainage canals throughout central and southern California. Because of their creeping mode of growth, the term ‘creeping emergents’ is suggested. These plants are characterized by rapid growth, high nutrogen accumulation, allocation of most biomass and nitrogen into aboveground plant parts, and rapid decomposition. Experiments on L. peploides showed it to be capable of producing up to 50 g dry weight m −2 day −1. In natural stands its average biomass is usually in the range 500–700 g dry weight m −2. In cultivation, with an artificial stem support, it attained a positive growth rate even at high densities, and a biomass corresponding to 1900 g dry weight m −2. It grew well in a broad range of nitrogen concentrations, its biomass production staying approximately the same through the range 20–140 mg l −1 of nitrate-nitrogen in water. Whole plant nitrogen content reached a maximum of 4.5%, leaf nitrogen 6.8%. The rate of photosynthesis decreased in leaves with nitrogen concentrations > 5.5%. L. peploides regenerated well after 95% of the stem length was removed, regaining 67% of biomass of the uncut control in 45 days. Creeping emergents have good potential for use in waste water treatment.

A study of mole drainage with simplified cultivation for autumn-sown crops on a clay soil. 5. Losses of nitrate-N in surface run-off and drain water

Direct drilling of autumn-sown cereal crops reduced the loss of nitrate in drainage. Losses of nitrate nitrogen in water draining from arable land have been measured for 4 seasons, 1980–1984. The field experiment was on a mole-drained clay soil in southern England. Autumn-sown cereal crops were established by direct drilling or after ploughing and traditional seed-bed preparation. Losses ranged from 3 to 75 kg N ha −1 year −1, with an average of 34 kg N ha −1 year −1. Most of the loss (about 90%) was removed via the mole-drain system. Measured loss of nitrate from the direct-drilled soil was 76% (range 48–89%) of that lost from the ploughed soil. Mole drains apparently increased loss of nitrate directly to the river system. In the absence of mole drains, nitrate loss in surface drainage averaged 6 kg N ha −1, compared with 4 kg N ha −1 in the presence of drains. However, in one year, exceptionally high amounts of nitrate (80 kg N ha −1) were lost from undrained, direct-drilled land because of poor crop establishment; deep leaching of nitrate in the undrained soil was not measured. Approximate calculations show that up to half the autumn-applied fertiliser-N was lost by leaching and up to 15% of spring applications.