Assessing uncertainty in annual nitrogen,phosphorus, and suspended sediment load estimates in three agricultural streams using a 21-year dataset

Accurate estimation of constituent loads is important for studies of ecosystem mass balance or total maximum daily loads. In response, there has been an effort to develop methods to increase both accuracy and precision of constituent load estimates. The relationship between constituent concentration and stream discharge is often complicated, potentially leading to high uncertainty in load estimates for certain constituents, especially at longer-term (annual) scales. We used the loadflex R package to compare uncertainty in annual load estimates from concentration vs. discharge relationships in constituents of interest in agricultural systems, including ammonium as nitrogen (NH₄-N), nitrate as nitrogen (NO₃-N), soluble reactive phosphorus (SRP), and suspended sediments (SS). We predicted that uncertainty would be greatest in NO₃-N and SS due to complex relationships between constituent concentration and discharge. We also predicted lower uncertainty with a composite method compared to regression or interpolation methods. Contrary to predictions, we observed the lowest uncertainty in annual NO₃-N load estimates (relative error 1.5–23%); however, uncertainty was greatest in SS load estimates, consistent with predictions (relative error 19–96%). For all constituents, we also generally observed reductions in uncertainty by up to 34% using the composite method compared to regression and interpolation approaches, as predicted. These results highlight differences in uncertainty among different constituents and will aid in model selection for future studies requiring accurate and precise estimates of constituent load.     

Phytoremediation facilitates removal of nitrogen and phosphorus from eutrophicated water and release from sediment

Phosphorus (P) fractions and the effect of phytoremediation on nitrogen and phosphorus removal from eutrophicated water and release from sediment were investigated in the eco-remediation experiment enclosures installed in the Hua-jia-chi pond (Hangzhou city, Zhejiang province, China). The main P fraction in the sediment was inorganic phosphorus (IP). For the mesotrophic sediments, IP mainly consisted of HCl-extractable P (Ca-P). The annual-average concentration of total nitrogen (TN), total phosphorus (TP) in water and the content of TN, TP in different vertical depth of sediment in the experiment enclosures with hydrophyte were always much lower than those in the control enclosure without hydrophyte and those outside of experiment enclosures. It is suggested that phytoremediation was an effective technology for N and P removal from eutrophicated water and release from sediment.     

Losses of nitrogen and phosphorus from agricultural and forest areas in Finland during the 1980s and 1990s

The temporal changes and spatial variability of phosphorus andnitrogen losses and concentrations in Finland during the period1981–1997 were studied in 15 small agricultural and forestedcatchments. In addition, four coastal river basins with highagricultural land use located in southern Finland were includedin the study in order to assess the representativeness ofagricultural loss estimates from small agricultural catchments.The mean annual loss specific for agricultural land was estimatedto be on average 110 kg km^-2 a^-1 for total phosphorusand 1500 kg km^-2 a^-1 for total nitrogen. The resultsfrom small agricultural catchments were in agreement with thecorresponding loss estimates from rivers, with an average of137 kg km^-2 a^-1 for total phosphorus and 1800 kg km^-2a^-1 for total nitrogen. The results from the studiedagricultural catchments and rivers during the period 1981–1997suggest that weather-driven fluctuation in discharge was usuallythe main reason for changes in nutrient losses, and little or noimpact of changes in agricultural production or managementpractises can be observed. In forested areas the total phosphorusloss (average 9 kg km^-2 a^-1) and total nitrogen loss(average 250 kg km^-2 a^-1) were lower than inagricultural areas. In forested catchments the impact of forestryoperations, such as clear-cutting and fertilization, and theimpact of atmospheric nitrogen deposition can be seen in changesin nutrient losses.     

Monitoring changes in soil organic carbon pools, nitrogen, phosphorus, and sulfur under different agricultural management practices in the tropics

Soil organic matter not only affects sustainability of agricultural ecosystems, but also extremely important in maintaining overall quality of environment as soil contains a significant part of global carbon stock. Hence, we attempted to assess the influence of different tillage and nutrient management practices on various stabilized and active soil organic carbon pools, and their contribution to the extractable nitrogen phosphorus and sulfur. Our study confined to the assessment of impact of agricultural management practices on the soil organic carbon pools and extractable nutrients under three important cropping systems, viz. soybean–wheat, maize–wheat, and rice–wheat. Results indicated that there was marginal improvement in Walkley and Black content in soil under integrated and organic nutrient management treatments in soybean–wheat, maize–wheat, and rice–wheat after completion of four cropping cycles. Improvement in stabilized pools of soil organic carbon (SOC) was not proportional to the applied amount of organic manures. While, labile pools of SOC were increased with the increase in amount of added manures. Apparently, green manure (Sesbania) was more effective in enhancing the lability of SOC as compared to farmyard manure and crop residues. The KMnO₄-oxidizable SOC proved to be more sensitive and consistent as an index of labile pool of SOC compared to microbial biomass carbon. Under different cropping sequences, labile fractions of soil organic carbon exerted consistent positive effect on the extractable nitrogen, phosphorus, and sulfur in soil.     

Study on phosphorus loadings in ten natural and agricultural watersheds in subtropical region of China

Water eutrophication in subtropical regions of southern China threatens watershed health and is of major concern. However, annual phosphorus (P) loading and its dominant causes are still unclear, especially at the watershed scale. In this study, we investigated dynamic P loadings and associated factors (e.g., land use, livestock production, and runoff depth) in ten watersheds that varied in area from 9 to 5,212 ha in a hilly area of Hunan Province, China. A flowmeter was installed at the outlet of each watershed, and total P (TP) and soluble P (SP) concentrations were monitored periodically from June 2010 to October 2012. The results showed that annual P loadings (APLs) in the ten watersheds ranged from 22.8 to 247.8 kg P/km² and that P loss primarily occurred from April to June of each year during the main rainfall season in the study area. In addition, the average eutrophication (>0.05 mg P/L) ratio for stream waters was 86.7 % during the study period, which was indicative of a potentially serious condition for the local water environments. Annual P loadings were linearly related to livestock density (LD; R?=?0.92, p?<?0.01), whereas the eutrophication ratio of stream water was significantly (p?<?0.05) correlated with LD (R?=?0.61), percentage cropland (R?=?0.71), and percentage forest cover (R?=??0.68). Thus, it is concluded that the control of livestock production has the greatest potential for reducing P loadings in watersheds in this subtropical area. This will be beneficial to the amelioration and protection of local environment.     

Fractionation of heavy metals and phosphorus in suspended sediments of the Yamuna river,India

The Yamuna river is the largest tributary of the Ganges river system. It originates in the Himalayas and flows through a varied geological terrain encompassing a large basin area. Metals Fe, Mn, Pb, Zn, Cu in different chemical fractions of suspended sediments such as exchangeable, carbonates, Fe–Mn oxides, organics and residual fractions were studied. Phosphorus associated with different chemical forms are discussed. The metals are mostly associated with residual fractions in the sediments followed by organics, Fe–Mn oxides, exhangeable and carbonates. Intensive use of chemical fertilizers and pesticides in agriculture in the basin affects the high inorganic phosphorus content in sediments.     

Load estimation and source apportionment of nonpoint source nitrogen and phosphorus based on integrated application of SLURP model, ECM, and RUSLE: a case study in the Jinjiang River, China

The nonpoint source (NPS) pollution is difficult to manage and control due to its complicated generation and formation. Load estimation and source apportionment are an important and necessary process for efficient NPS control. Here, an integrated application of semi-distributed land use-based runoff process (SLURP) model, export coefficients model (ECM), and revise universal soil loss equation (RUSLE) for the load estimation and source apportionment of nitrogen and phosphorus was proposed. The Jinjiang River (China) was chosen for the evaluation of the method proposed here. The chosen watershed was divided into 27 subbasins. After which, the SLURP model was used to calculate land use runoff and to estimate loads of dissolved nitrogen and phosphorus, and ECM was applied to estimate dissolved loads from livestock and rural domestic sewage. Next, the RUSLE was employed for load estimation of adsorbed nitrogen and phosphorus. The results showed that the 12,029.06 t?a^?1 pollution loads of total NPS nitrogen (TN) mainly originated from dissolved nitrogen (96.24 %). The major sources of TN were land use runoff, which accounted for 45.97 % of the total, followed by livestock (32.43 %) and rural domestic sewage (17.83 %). For total NPS phosphorous (TP), its pollution loads were 570.82 t?a^?1 and made up of dissolved and adsorbed phosphorous with 66.29 and 33.71 % respectively. Soil erosion, land use runoff, rural domestic sewage, and livestock were the main sources of phosphorus with contribution ratios of 33.71, 45.73, 14.32, and 6.24 % respectively. Therefore, land use runoff, livestock, and soil erosion were identified as the main pollution sources to influence loads of NPS nitrogen and phosphorus in the Jinjiang River and should be controlled first. The method developed here provided a helpful guideline for conducting NPS pollution management in similar watershed.     

Spatial and temporal variation of moisture content in the soil profiles of two different agricultural fields of semi-arid region

Modeling spatio-temporal variation of soil moisture with depth in the soil profile plays an important role for semi-arid crop production from an agro-hydrological perspective. This study was performed in Guvenc Catchment. Two soil series that were called Tabyabayir (TaS) and Kervanpinari (KeS) and classified as Leptosol and Vertisol Soil Groups were used in this research. The TeS has a much shallower (0–34 cm) than the KeS (0–134 cm). At every sampling time, a total of geo-referenced 100 soil moisture samples were taken based on horizon depths. The results indicated that soil moisture content changed spatially and temporally with soil texture and profile depth significantly. In addition, land use was to be important factor when soil was shallow. When the soil conditions were towards to dry, higher values for the coefficient of variation (CV) were observed for TaS (58 and 43 % for A and C horizons, respectively); however, the profile CV values were rather stable at the KeS. Spatial variability range of TaS was always higher at both dry and wet soil conditions when compared to that of KeS. Excessive drying of soil prevented to describe any spatial model for surface horizon, additionally resulting in a high nugget variance in the subsurface horizon for the TaS. On the contrary to TaS, distribution maps were formed all horizons for the KeS at any measurement times. These maps, depicting both dry and wet soil conditions through the profile depth, are highly expected to reduce the uncertainty associated with spatially and temporally determining the hydraulic responses of the catchment soils.     

Seasonal changes in the concentrations of nitrogen and phosphorus in farmland drainage and groundwater of the Taihu Lake region of China

Monte Carlo simulations were performed using the GEANT4 code for the investigation of γ-ray absorption in water in different spherical geometries and of the efficiency of a NaI(Tl) detector for different radionuclides in the aquatic environment. In order to test the reliability of these simulations, experimental values of the NaI(Tl) detector efficiency were deduced and seem to be in good agreement with the simulated ones. In addition, using the simulated efficiency, an algorithm was developed to determine the minimum detectable activity in becquerels per cubic meter in situ as a function of energy for typical freshwater and seawater spectra.     

Field assessment of flood event suspended sediment transport from ephemeral streams in the tropical semi-arid catchments

An assessment of suspended sediment transport was carried out in a number of semiarid catchments during flood events in order to quantify the degradation rates. In order to quantify these, a systematic sampling procedure of the episodic flood events was proposed for representative catchments. The procedure allows for an integration over the whole run-off episode using both the rising and falling limbs of the run-off hydrograph to compute the sediment quantities for each individual flood event. Higher sediment concentrations occurred in the rising limb than those at the recession for any stage of flow. The maximum suspended sediment concentration was observed at the peak of the flood hydrograph. An integration of the sediment concentration over its duration gave the total sediment yield from the flood event. For the ephemeral channels, only a small number of flood events were observed over a three-year experimental period each with a duration of the order of 3–6 h. It is notable that high sediment loads were associated with high flow volumes which were effectively the result of the catchment characteristics and incident rainfall causing the flood events in the respective catchments. A large percentage of the annual sediment yield from a catchment is transported by the ephemeral streams during a small number of flood events. The correct determination of the total sediment yield from any of the flood events depends entirely on the accuracy of the measurements. The understanding of run-off and sediment loss for the representative catchments aims at assisting planning, management and control of water and land resources for sustainable development in the semi-arid parts of the tropics. The sediment rates reveal the degradation of catchments which have repercussions on the crop and pasture production and this has a bearing on the soil and water conservation programmes in the delicate ecological balance of the semi-arid areas. Further, these rates will determine the lifespan of the reservoirs planned for the dry river valleys (ephemeral streams) and existing ones which serve livestock and domestic needs. These occasionally will require costly rehabilitation and scooping to increase effective storage unless conservation measures are taken, and these measures are bound to vary from place to place as per the representative catchments output.     

Composition and concentration of hydrocarbons in sediment samples from the oil producing area of the East Shetland Basin, Scotland

The East Shetland Basin is one of the areas that the Fisheries Research Services (FRS) has concentrated on to assess the possible impacts of oil exploration and production on the marine environment. A stratified random survey of the sediment was carried out in 2002. TOCs were low across the basin and were positively correlated with grain size. The total PAH concentrations (2- to 6-ring parent and alkylated PAHs, including the 16 US EPA PAHs) were less than 150 microg kg(-1) dry weight and their composition indicated a predominantly pyrolytic input to the basin in 2002. Minor unresolved complex mixtures in the n-alkane profiles indicated a slight petrogenic input but further examination of the biomarkers (hopanes and steranes) showed a mixed North Sea and Middle Eastern source. The Middle Eastern source is likely due to inputs from shipping activity, as it is widely used as bunker fuel. Grid surveys were carried out in 1986, 1988-89 and 1994 and areas were selected for which there was data for all the historic grid surveys and the 2002 stratified random survey. Although referring to only a small part of the East Shetland Basin, comparison with these historic surveys shows clearly that the concentrations of Forties crude oil equivalents and total PAH concentrations were highest in 1988-89 and by 2002 had returned to concentrations the same as or less than observed in the original survey in 1986.     

Quantification and source identification of polycyclic aromatic hydrocarbons in sediment, soil, and water spinach from Hanoi, Vietnam

Polycyclic aromatic hydrocarbons (PAHs) were quantified in sediment, soil, and plant material from Hanoi, Vietnam, and an aquatic production system in peri-urban Hanoi. The sum of the concentration of 16 US-EPA priority PAHs ( summation PAH16) ranged between 0.44 and 6.21 mg kg(-1) dw in sediment and between 0.26 and 1.35 mg kg(-1) dw in soil, with decreasing concentrations from the urban area to the peri-urban area, indicating contributions from urban and industrial sources. Double plots of diagnostic source ratios indicate that PAHs originate from mixed petrogenic and pyrogenic sources, the latter being predominant. The predominance of low molecular weight (LMW) PAHs in the sediment samples suggests that petrogenic sources are more prevalent in the water environment than in the soil. In contrast, high molecular weight (HMW) PAHs dominated in water spinach which probably reflects the plant's uptake of particle-bound PAHs that originate from pyrogenic sources.     

Leaching of nitrogen, phosphorus, TOC and COD from the biosolids of the municipal wastewater treatment plant of Thessaloniki

Biosolids from the WWTP of Thessaloniki were examined for the leaching of phosphorus (as ), nitrogen (as and ), and organic matter (as TOC and COD), using two tests: (1) a pH static leaching test and (2) a characterization test, relating contaminant release to the liquid to solid (L/S) ratio. Moreover, a Microtox toxicity test was conducted, to examine the pH dependency of the toxicity of the sludge leachate on the Vibrio fischeri bacterium. Maximum phosphorus release was observed at pH < 3 and at pH > 10. Ammonium nitrogen exhibited maximum leachability at near neutral pH conditions, while nitrate nitrogen exhibited a mild increase in the leachate, as the leachant pH increased from 2 to 12. Both TOC and COD exhibited an increase in the leachate concentration, as the leachant pH was increased from 2 to 12. Ecotoxicological analysis showed that maximum toxicity occurred at very low and very high pH-conditions. As liquid-to-solid ratio increased, the leachate concentration (in mg/l) of all parameters studied decreased. The results of the study were used to conduct a release assessment estimate for the case of Thessaloniki.     

Geochemistry of the suspended sediment in the estuaries of the Mandovi and Zuari rivers, central west coast of India

The geochemistry of the suspended particulate matter (SPM) collected during the monsoon was determined to identify the sources of SPM and to understand the physicochemical processes in the Mandovi and Zuari river estuaries. The concentrations of SPM decrease seaward in both estuaries, but are relatively high at bay stations. Kaolinite is the most dominant clay mineral in the upstream of both rivers. Smectite increases seaward in both estuaries and is abundant in the bay. Upstream stations of Mandovi, where ore deposits are stored on the shore, exhibit high Fe, Mn, total rare earth elements (∑REE), and middle REE- and heavy REE-enriched patterns. Channel stations of both estuaries exhibit middle REE- and light REE-enriched patterns, which gradually changed seaward to middle REE- and heavy REE-enriched patterns. Canal stations exhibit the highest concentrations of major and trace metals. High metal/Al ratios occur at stations in the upstream of Zuari and at the confluence of canals in the Mandovi estuary. Enrichment factors of metals indicate that Mn is significantly polluted while other metals are moderately polluted. The δ ¹³C and δ ¹⁵N of organic matter indicate that the terrigenous organic matter at the upstream is diluted seaward by marine organic matter. Organic matter at bay stations is largely marine and altered-type. The compositions of SPM are controlled by the particulates from ore dust, the geology of the drainage basins, and the physicochemical processes in the estuaries. Particulates resuspended from the bay are dominated by ore dust, which are advected into the channels of both estuaries during the lull periods of the monsoon.     

Spatial distribution and source identification of trace elements in topsoil from heavily industrialized region,Aliaga, Turkey

Topsoil samples (n?=?40) were collected from a heavily industrialized region in Turkey. The region includes several scrap processing iron–steel plants with electric arc furnaces (EAFs), a petroleum refinery, a petrochemical complex, steel rolling mills, a natural gas-fired power plant, ship-breaking yards and very dense transportation activities. The region has undergone a rapid transition from an agricultural region to a heavily industrialized region in the last three decades. Collected soil samples were analyzed for 48 trace elements using inductively coupled plasma-mass spectrometry (ICP-MS). The elemental distribution pattern in the region indicated that Nemrut area with dense iron–steel production activities was a hotspot for elemental pollution. In addition to crustal elements, concentrations of anthropogenic trace elements (i.e., Fe, Zn, Pb, Mn, Cu, Cd, Cr and Mo) were very high in the area influencing many parts of the region. Elemental compositions of fugitive sources polluting the soil (i.e., paved and unpaved roads, slag piles, EAFs filter dust piles and coal piles) were also determined. The methods (enrichment factors [EFs] and the index of geoaccumulation [I _geo]) used for determination of pollution status of soil showed that Cr, Ag, Zn, As and Pb were the strongly contaminating elements for the region. Principal component analysis (PCA) clearly indicated that anthropogenic sources (steel production, refinery and petrochemical processes and traffic) were important sources in this region.     

Non-point source contribution and dynamics of soluble and particulate phosphorus from main tributaries of the Zarivar Lake watershed,Iran

The temporal variability of phosphorus (P) transport and the relationships between discharge, suspended sediment concentration and particulate (PP), and soluble (SP) phosphorus were examined. The study was conducted at the event scale in seven tributaries of the Zarivar Lake watershed in Kurdistan Province (Iran) from March 2011 to April 2012. Based on eight runoff events, 82% of the total P was the PP carried out by suspended sediment. Results showed a high variability of P transport during different runoff events. It was found that soil erosion was the source of the high P load. For all tributaries, PP was linearly related to both discharge and suspended sediment concentration. However, the relationships of SP and PP with discharge and suspended sediment concentration showed different hysteresis patterns. The relationship between PP and discharge was generally characterized by a clockwise pattern (i.e., lower part contribution of the sub-watersheds) but the patterns between SP and discharge were mainly anticlockwise (i.e., upper part contribution of the sub-watersheds or perhaps due to a subsurface flow contribution).     

Carbon, nitrogen, and phosphorus stoichiometry of plankton and the nutrient regime in Cabo Frio Bay, SE Brazil

This long-term study, performed during the years 2003–2005 and 2008–2009, investigated the carbon (C), nitrogen (N), and phosphorus (P) contents of the phyto- and zooplankton communities and the nutrient regime of Cabo Frio Bay, SE Brazil. The information intends to serve as baseline of the plankton C, N, and P stoichiometry for the calibration of biogeochemical and ecological models in support to future findings related to the local and regional phenomena of climatic change. Cabo Frio Bay is a small semienclosed system set adjacent to a region subject to sporadic coastal upwelling. Zooplankton exhibited average annual C, N, and P contents of 11.6?±?6.9 %, 2.8?±?1.8 %, and 0.18?±?0.08 %, and phytoplankton (>20 μm) 6.8?±?6.0 %, 1.6?±?1.5 %, and 0.09?±?0.08 %, respectively. The C/N/P ratios correspond to the lowest already found to date for a marine environment. The low C contents must have been brought about by a predominance of gelatinous zooplankton, like Doliolids/ Salps and also Pteropods. Average annual nutrient concentrations in the water were 0.21?±?0.1 μM for phosphate, 0.08?±?0.1 μM for nitrite, 0.74?±?1.6 μM for nitrate, and 1.27?±?1.1 μM for ammonium. N/P ratios were around 8:1 during the first study period and 12:1 during the second. The plankton C/N/P and N/P nutrient ratios and elemental concentrations suggest that the system was oligotrophic and nitrogen limited. The sporadic intrusions of upwelling waters during the first study period had no marked effect upon the systems metabolism, likely due to dilution effects and the short residence times of water of the bay.