The distribution characteristics of nitrogen and phosphorus in the ecological system of Mt. Beigu wetland

The Mt. Beigu wetland, which has undergone periodical changes in water level, lies by the Yangtze River, and its dominant plants are Phragmites communis, Phalaris arundinacea and Polygonum lapathifolium. In order to study the distribution characteristics of nitrogen and phosphorus in the ecological system of the Mt. Beigu wetland, the authors measured the contents of total nitrogen and total phosphorus in Phragmites communis, Phalaris arundinacea and Polygonum lapathifolium, and the contents of nitrogen and phosphorus in the wetland soils with different plant species. In addition the authors investigated the influence of various plants on the spatial and seasonal (spring/autumn) distributions of nitrogen and phosphorus in the wetland soil. The contents of nitrogen and phosphoms in Phalaris arundinacea are significantly higher than those of the other two plant species in the same part. Secondary pollution of phosphorus in the wetland results mainly from Phalaris arundinacea. Phragmites com-munis effectively carries away nitrogen and phosphorus in the wetland soil in the wet season. The capacity of Poly-gonum lapathifolium to remove nitrogen is lowest among the 3 species of plants. These findings offer a theoretical foundation for the selection of plant species to restore the ecological environment and for the selection of time and depth for purging silt on the riverside wetland.     

Zooplankton distribution in three estuarine bayous with different types of anthropogenic influence

Zooplankton was sampled in three tributaries of the Calcasieu Estuary: one flowing through an area of petrochemical industries, one through a municipal area, and one through an agricultural area. Synoptic comparisons among the bayous were made on eight trips over a two-year period. Additionally, each bayou was sampled intensively for small-scale distribution on four occasions. Numbers of all zooplankton taxa were consistently higher in the agricultural bayou than in either of the other bayous. Patterns of small-scale spatial variability also differed among the bayous. The agricultural bayou appeared to be a relatively healthy estuarine tributary. The municipal bayou was probably subjected to chronic environmental stress that is very severe in the vicinity of the municipal sewage and storm-drain outfalls. Evidence indicated that the industrial bayou suffered from frequent, but not continuous, episodes of environmental stress throughout its length.     

土地利用方式下岩溶湿地土壤无机磷形态特征及分析方法适用性探讨

本研究利用SMT法和七步连续提取法对桂林市会仙岩溶湿地中典型土地利用方式（水稻田、果园、荒地）的土壤以及河流底泥中磷的赋存形态进行研究。结果表明：岩溶土壤总磷含量大小为底泥＞果园＞水稻田＞荒地;底泥中Ex-P和Fe-P所占比例较大;荒地土壤中Or-P和Res-P为主要磷形态;水稻田和果园土壤中Fe-P所占比例较高。人为干扰明显的果园表层土壤有较大的磷淋溶风险;荒地土壤中磷的生物可利用性低,体现了其缓冲固持湿地水体中磷的生态功能。大量可溶性磷经淋溶迁移富集于底泥中,是河流富营养化的风险源。七步法表现出在提取多种复杂结合态磷上的优势,对岩溶土壤中Ca-P的提取更充分有效,更适用于研究岩溶土壤不同形态的磷分布特征。     

The contribution of inorganic compounds to the particulate carbon,nitrogen, and phosphorus in suspended matter and surface sediments of Chesapeake Bay

Particulate carbon, nitrogen, and phosphorus samples from the water column and surficial sediments of the Maryland portion of Chesapeake Bay were thermally partitioned into their organic and inorganic components. During periods of both high and low fluvial input and high and low phytoplanktonic production, particulate organic carbon accounted for a mean of 99.3% of the total particulate carbon and particulate organic nitrogen accounted for a mean of 99.1% of the total particulate nitrogen. The particulate organic phosphorus contribution was variable both seasonally and spatially, accounting for 14–77% of the total pool of particulate phosphorus. The highest concentrations were found in the surface waters during maximum phytoplanktonic production and low fluvial input. The contribution of particulate inorganic phosphorus to the seston and to total particulate phosphorus decreased as distance from the primary fluvial source increased, reflecting a greater relative inclusion of particulate phosphorus in the biologically bound component in the higher salinity zone seaward of the turbidity maximum. Organic carbon and nitrogen constituted over 99% of the surficial sediment carbon and nitrogen, and organic phosphorus was 10–40% of the surficial sediment phosphorus.     

广西珍珠湾红树林湿地沉积物重金属分布及评价

沉积物中的重金属属于持久性污染物,具有富集性、难降解性和毒性,长时间累积会对生态环境和人体健康造成威胁。为研究珍珠湾红树林湿地表层沉积物中的重金属含量分布特征及质量现状,2021年9月在珍珠湾红树林分布区采集13件表层沉积物样品,分析测试重金属含量。结果表明: 与国内其他红树林湿地相比,珍珠湾红树林湿地表层沉积物中的重金属含量处于相对较低水平; 地累积指数法显示大部分表层沉积物样品无重金属污染,仅有2个站位受到Cd和Hg的轻微污染,潜在生态风险指数法表明湾内各站位均为低生态风险; 相关性分析和主成分分析表明,Cd主要受江平江输入和珍珠湾东南部海水养殖的影响,其他元素主要为自然背景的岩石风化沉积,利用主成分-多元线性回归模型对重金属的来源进行解析认为,表明江平江输入的重金属贡献率为57%,海水养殖影响的重金属贡献率为43%。综上所述,珍珠湾红树林湿地整体生态状况良好,但仍需重点关注Cd的输入。     

Fertilization and pH effects on processes and mechanisms controlling dissolved inorganic phosphorus in soils

We used of a set of mechanistic adsorption models (1-pK TPM, ion exchange and Nica-Donnan) within the framework of the component additive (CA) approach in an attempt to determine the effect of repeated massive application of inorganic P fertilizer on the processes and mechanisms controlling the concentration of dissolved inorganic phosphorus (DIP) in soils. We studied the surface layer of a Luvisol with markedly different total concentrations of inorganic P as the result of different P fertilizer history (i.e. massive or no application for 40 years). Soil pH was made to vary from acid to alkaline. Soil solutions were extracted with water and CaCl₂ (0.01 M). The occurrence of montmorillonite led us to determine the binding properties of P and Ca ions for this clay mineral.Satisfactory results were obtained using generic values for model parameters and soil-specific ones, which were either determined directly by measurements or estimated from the literature. We showed that adsorption largely controlled the variations of DIP concentration and that, because of kinetic constrains, only little Ca-phosphates may be precipitated under alkaline conditions, particularly in the P fertilized treatment. The mineral-P pool initially present in both P treatments did not dissolve significantly during the course of the experiments. The adsorption of Ca ions onto soil minerals also promoted adsorption of P ions through electrostatic interactions. The intensity of the mechanism was high under neutral to alkaline conditions. Changes in DIP concentration as a function of these environmental variables can be related to changes in the contribution of the various soil minerals to P adsorption. The extra P adsorbed in the fertilized treatment compared with the control treatment was mainly adsorbed onto illite. This clay mineral was the major P-fixing constituent from neutral to alkaline pH conditions, because the repulsion interactions between deprotonated hydroxyl surface sites and P ions were sufficiently counterbalanced by Ca ions. The drastic increase of DIP observed at acid pH was due to the effect of the lower concentration of surface sites of Fe oxides and kaolinite.In addition to confirming the validity of our approach to model DIP concentrations in soils, the present investigation showed that adsorption was the predominant geochemical process even in the P fertilized soil, and that Ca ions can have an important promoting effect on P adsorption. However the influence of the dissolution of the mineral-P pool under field conditions remained questionable.     

Seasonal and spatial distribution of cumaceans in the Mobile Bay estuarine system,Alabama

Seasonal occurrence patterns within the Mobile Bay estuary, Alabama, of five species of cumaceans are described.Oxyurostylis smithi was most abundant, followed byLeucon americanus, Cyclaspis varians, Eudorella monodon andAlmyracuma proximoculi. With the exception of the oligohalineA. proximoculi, the cumaceans encountered within the estuary are euryhaline marine species that are most abundant at the lower bay stations and that utilize the estuary only when environmental conditions are favorable.     

Sources of nitrogen and phosphorus to Northern San Francisco Bay

We studied nutrient sources to the Sacramento River and Suisun Bay (northern San Francisco Bay) and the influence which these sources have on the distributions of dissolved inorganic nitrogen (DIN) and dissolved reactive phosphorus (DRP) in the river and bay. We found that agricultural return flow drains and a municipal wastewater treatment plant were the largest sources of nutrients to the river during low river flow. The Sutter and Colusa agricultural drains contributed about 70% of the transport of DIN and DRP by the river above Sacramento (about 20% of the total transport by the river) between August 8 and September 26, 1985. Further downstream, the Sacramento Regional Wastewater Treatment Plant discharged DIN and DRP at rates that were roughly 70% of total DIN and DRP transport by the river at that time. Concentrations at Rio Vista on the tidal river below the Sacramento plant and at the head of the estuary were related to the reciprocals of the river flows, indicating the importance of dilution of the Sacramento waste by river flows. During very dry years, elevated DIN and DRP concentrations were observed in Suisun Bay. We used a steady-state, one-dimensional, single-compartment box model of the bay, incorporating terms for advection, exchange, and waste input, to calculate a residual rate for all processes not included in the model. We found that the residual for DIN was related to concentrations of chlorophylla (Chla). The residual for DRP was also related to Chla at high concentrations of Chla, but showed significant losses of DRP at low Chla concentrations. These losses were typically equivalent to about 80% of the wastewater input rate.     

Effects of agricultural practices on nitrogen distribution in unsaturated soils

Nitrogen fertilizer consumption is very common in the agricultural practices. Nitrogen application could be an important source of groundwater N pollution. Normally, nitrogen can pass through the unsaturated zone to pollute the groundwater. Different agricultural practices have different cultivation methods, accordingly different fertilization and irrigation techniques. Hence, the agricultural practice determines the environment of the unsaturated zone, which subsequently determines the extent of groundwater N pollution. To verify the pollution modes and transformation mechanisms of nitrogen, both in situ and laboratory tests were conducted at four different sites to study the effects of agricultural practices on nitrogen distribution in unsaturated zones. The inorganic nitrogen in soil is extracted by potassium chloride solution, and the soil utilization form and pollution type are identified by δ¹⁵N by comparing with the known standard values. The experimental results indicate that continual fertilization and sewage irrigation in these agricultural regions were the primary sources of nitrogen in the unsaturated zone. In the soils planted with rice, δ¹⁵N–NH₄ ⁺ was relatively elevated due to ammonium volatilization. In the unsaturated zone of rice–wheat rotation fields, NO₃ ^?–N and δ¹⁵N were both elevated because of manure fertilizer. Meanwhile, denitrification also occurred in the hypoxic environment due to the high soil water content.     

Characteristics of the main inorganic nitrogen accumulation in surface water and groundwater of wetland succession zones

Based on the observation of a complete hydrological year from June 2014 to May 2015, the temporal and spatial variations of the main inorganic nitrogen(MIN, referring to NO_3~--N, NO_2~--N, NH_4~+-N) in surface water and groundwater of the Li River and the Yuan River wetland succession zones are analyzed. The Li River and the Yuan River are located in agricultural and non-agricultural areas, and this study focus on the influence of surface water level and groundwater depth and precipitation on nitrogen pollution. The results show that NO_3~-N in surface water accounts for 70%-90% of MIN, but it does not exceed the limit of national drinking water surface water standard. Groundwater is seriously polluted by H_4~+-N. Based on the groundwater quality standard of H_4~+-N, the groundwater quality in the Li River exceeds Class III water standard throughout the year, and the exceeding months' proportion of Yuan River reaches 58.3%. Compared with the Yuan River, MIN in groundwater of the Li River shows significant temporal and spatial variations owing to the influence of agricultural fertilization. The correlation between the concentrations of MIN and surface water level is poor, while the fitting effect of quadratic correlation between H_4~+-N concentration and groundwater depth is the best(R~2=0.9384), NO_3~-N is the next(R~2=0.5128), NO_2~--N is the worst(R~2=0.2798). The equation of meteoric water line is δD =7.83δ~(18) O+12.21, indicating that both surface water and groundwater come from atmospheric precipitation. Surface infiltration is the main cause of groundwater H_4~+-N pollution. Rainfall infiltration in non-fertilization seasons reduces groundwater nitrogen pollution, while rainfall leaching farming and fertilization aggravate groundwater nitrogen pollution.     

Characteristics of the main inorganic nitrogen accumulation in surface water and groundwater of wetland succession zones

Based on the observation of a complete hydrological year from June 2014 to May 2015, the temporal and spatial variations of the main inorganic nitrogen (MIN, referring to NO3--N, NO2--N, NH4+-N) in surface water and groundwater of the Li River and the Yuan River wetland succession zones are analyzed. The Li River and the Yuan River are located in agricultural and non-agricultural areas, and this study focus on the influence of surface water level and groundwater depth and precipitation on nitrogen pollution. The results show that NO3--N in surface water accounts for 70%-90% of MIN, but it does not exceed the limit of national drinking water surface water standard. Groundwater is seriously polluted by NH4+-N. Based on the groundwater quality standard of NH4+-N, the groundwater quality in the Li River exceeds Class III water standard throughout the year, and the exceeding months’ proportion of Yuan River reaches 58.3%. Compared with the Yuan River, MIN in groundwater of the Li River shows significant temporal and spatial variations owing to the influence of agricultural fertilization. The correlation between the concentrations of MIN and surface water level is poor, while the fitting effect of quadratic correlation between NH4+-N concentration and groundwater depth is the best (R2=0.9384), NO3--N is the next (R2=0.5128), NO2--N is the worst (R2=0.2798). The equation of meteoric water line is δD =7.83δ18O+12.21, indicating that both surface water and groundwater come from atmospheric precipitation. Surface infiltration is the main cause of groundwater NH4+-N pollution. Rainfall infiltration in non-fertilization seasons reduces groundwater nitrogen pollution, while rainfall leaching farming and fertilization aggravate groundwater nitrogen pollution.     

The nitrogen distribution in soils formed under widely differing climatic conditions

Amino acids, amino sugars and ammonia were determined in 6N HCl hydrolyzates of soils formed under arctic, cool temperate, subtropical and tropical climates. Soils from warmer climates yielded relatively more amino acids and amino sugars but less NH₃ than did those from colder regions. The amino acid composition of all soils, however, was remarkably similar, resembled that of lake sediments and was somewhat similar to that of bacteria, suggesting the importance of microorganisms in their formation. Climate appears to have little effect on the amino acid composition of soils.     

Wetland-water column exchanges of carbon, nitrogen, and phosphorus in a southern Everglades dwarf mangrove

We used enclosures to quantify wetland-water column nutrient exchanges in a dwarf red mangrove, (Rhizophora mangle L.) system near Taylor River, an important hydraulic linkage between the southern Everglades and eastern Florida Bay, Florida, USA. Circular enclosures were constructed around small (2.5–4 m diam) mangrove islands (n=3) and sampled quarterly from August 1996 to May 1998 to quantify net exchanges of carbon, nitrogen, and phosphorus. The dwarf mangrove wetland was a net nitrifying environment with consistent uptake of ammonium (6.6–31.4 μmol m⁻² h⁻¹) and release of nitrite +nitrate (7.1–139.5 μmol m⁻² h⁻¹) to the water column. Significant flux of soluble reactive phosphorus was rarely detected in this nutrient-poor, P-limited environment. We did observe recurrent uptake of total phosphorus and nitrogen (2.1–8.3 and 98–502 μmol m⁻² h⁻¹, respectively), as well as dissolved organic carbon (1.8–6.9 μmol m⁻² h⁻¹) from the water column. Total organic carbon flux shifted unexplainably from uptake, during Year 1, to export, during Year 2. The use of unvegetated (control) enclosures during the second year allowed us to distinguish the influence of mangrove vegetation from soil-water column processes on these fluxes. Nutrient fluxes in control chambers typically paralleled the direction (uptake or release) of mangrove enclosure fluxes, but not the magnitude. In several instances, nutrient fluxes were more than twofold greater in the absence of mangroves, suggesting an influence of the vegetation on wetland-water column processes. Our findings characterize wetland nutrient exchanges, in a mangrove forest type that has received such little attention in the past, and serve as baseline data for a system undergoing hydrologic restoration.     

A comparison of phytoplankton assemblages and environmental relationships in three estuarine rivers of the lower Chesapeake Bay

A 16-month data set of phytoplankton assemblages and environmental parameters were studied in the lower James, York (-Pamunkey), and Rappahannock rivers using several exploratory statistical approaches. Based on species composition and river station relationships, three site groups were established and subsequently identified as predominantly tidal fresh, oligo-mesohaline, and mesohaline sites. Phytoplankton assemblages within these rivers were influenced and subsequently augmented by the onset of the spring freshet which was different in 1986 and 1987. Five temporal assemblages of phytoplankters were also identified and designated into seasonal groupings of spring 1986, summer-fall, summer-winter, fall-winter, and winter-spring 1987. Discriminant analysis (MANOVA) evaluations were made for water quality parameters to site and seasonal phytoplankton assemblages and these relationships are discussed. Moving downstream along an oligohaline-mesohaline gradient, the nitrogen and phosphorus levels decreased and the phytoplankton composition was more similar at several corresponding site locations in the different rivers than at stations relatively close to each other in the same river. Within these data sets approximately 58% of the explained variance was associated with site (spatial) effects, 30% with temporal effects, and 12% with site-temporal interactions. A transition from dominant bloom-producing freshwater diatoms to estuarine species occurs from the tidally influenced freshwater zone downstream. This change may be rapid as the decline ofSkeletonema potamos, or more gradual, as withCyclotella striata andCyclotella meneghiania. These are replaced downstream bySkeletonema costatum, Cyclotella caspia, andLeptocylindrus minimus as dominant species.     

The influence of wind and river pulses on an estuarine turbidity maximum: Numerical studies and field observations in Chesapeake Bay

The effect of pulsed events on estuarine turbidity maxima (ETM) was investigated with the Princeton Ocean Model, a three-dimensional hydrodynamic model. The theoretical model was adapted to a straight-channel estuary and enhanced with sediment transport, erosion, deposition, and burial components. Wind and river pulse scenarios from the numerical model were compared to field observations before and after river pulse and wind events in upper Chesapeake Bay. Numerical studies and field observations demonstrated that the salt front and ETM had rapid and nonlinear responses to short-term pulses in river flow and wind. Although increases and decreases in river flow caused down-estuary and up-estuary (respectively) movements of the salt front, the effect of increased river flow was more pronounced than that of decreased river flow. Along-channel wind events also elicited non-linear responses. The salt front moved in the opposite direction of wind stress, shifting up-estuary in response to down-estuary winds and vice-versa. Modeled pulsed events affected suspended sediment distributions by modifying the location of the salt front, near-bottom shear stress, and the location of bottom sediment in relation to stratification within the salt front. Bottom sediment accumulated near the convergent zone at the tip of the salt front, but lagged behind the rapid response of the salt front during wind events. While increases in river flow and along-channel winds resulted in sediment transport down-estuary, only reductions in river flow resulted in consistent up-estuary movement of bottom sediment. Model predictions suggest that wind and river pulse events significantly influence salt front structure and circulation patterns, and have an important role in the transport of sediment in upper estuaries.     

Sorption and distribution of adsorbed metals in three soils of India

The mobility and bioavailability of heavy metals depends on the metal retention capacity of soil and also on the geochemical phases with which metals are associated. Laboratory batch experiments were carried out to study the sorption and distribution of Cd, Ni and Pb in 3 soils differing in their physicochemical properties from India: Oxyaquic Haplustalf (SL1), Typic Haplustalf (SL2) and Typic Haplustert (SL3). The heavy metal adsorption was studied by isotherms and the distribution coefficient (K_D) for each metal was obtained from the linear regressions of the concentration of metal remaining in equilibrium solution and the amount adsorbed. In general, the sorption capacity for all the metals decreased in the order: SL3>SL2>SL1. Among metals, the sorption capacity in all the soils decreased in the order: Pb>>Ni>Cd. Distribution of sorbed metals at various equilibrating concentrations was studied by sequential extraction. Results showed significant differences in the distribution of metals in these soils. At higher additions (such as 200 μM l⁻¹) most of the metals were extracted in their more mobile fractions, exchangeable and/or inorganic in contrast to their original partitioning in soils, where they were preferentially associated with the less mobile residual fraction. Largest percentages of metals extracted in the exchangeable fraction corresponded to those soil–metal systems with smaller K_D values, e.g. Cd, Ni and Pb in SL1 and Cd and Ni in SL2. In neutral and alkaline soils (SL2, pH=7.1, and SL3, pH=8.6) Pb was predominantly extracted from the inorganic fractions and this corresponded to higher K_D values for Pb in these soils. The predominance of metals associated with the exchangeable fraction together with low K_D values indicates higher mobility of metals retained in the acidic soil (SL1, pH=5.2) compared with the others.     

黄河三角洲新生湿地磷分布特征及吸附解吸规律

采用改进的 Hedley 磷分级方法研究了黄河三角洲新生湿地由河向海过渡带表层土壤磷形态变化和分布特征,并通过等温吸附解吸实验阐明了沿程土壤对外源磷的持留能力和释放风险。结果表明,各样点无机磷占总磷93%以上,是磷的主要存在形态。土壤中有机磷含量较低,可能与较低的有机质含量有关。无机磷中稀盐酸磷是最主要存在形态,与各样点Ca/Al含量密切相关。有效磷含量在18.6~33.4 mg/kg之间,仅占总磷的3.2%~5.9%,可能会限制湿地植物的生长。覆有植被的土壤中有效磷含量显著高于河滩和海滩土壤,说明植被存在对有效磷的积累有一定促进作用。由吸附解吸实验可知,加入较低浓度（0.05~5 mg/L）的外源磷时,随着初始磷浓度的升高,土壤对磷的吸附量增加,吸附率为70%~99%,解吸率小于7%,这说明各样点土壤的除磷能力较强,且流失风险较低。     

Seasonal growth stimulation of sub-temperate estuarine phytoplankton to nitrogen and phosphorus: An outdoor microcosm experiment

A study of nutrient limitation of phytoplankton biomass production with emphasis on nitrate-nitrogen (NO₃ ^?) and ortho-phosphate-phosphorus (PO₄ ^3?) was conducted in Perdido Bay, Alabama-Florida. The experimental design employed 18-1 outdoor microcosms operated in a static renewal mode. Phytoplankton growth responses (i.e., growth stimulation) measured as chlorophyll a (chl a) fell into three principal categories: primary P stimulation occurred mostly during the cooler months at the upper bay (tidal brackish) and mid bay (lower mesohaline) stations; a total of 12 out of 36 experiments; primary N stimulation occurred mostly during the warmer months primarily at the mid-bay station and infrequently at the upper and lower bay stations (upper mesohaline); a total of 7 out of 36 experiments; and N+P costimulation occurred primarily during the warmer months in the upper bay and mid bay and during both warmer and cooler months of the lower bay; a total of 17 out of 36 experiments. Primary P stimulation was generally associated with high ratios of dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphate (DIP) (ratio range: 18 to 288). Conversely, primary N stimulation was associated with decreasing DIN:DIP ratios (range 8–46). Redfield ratios of particulate organic N (PON) to particulate organic P (POP) often indicated N limitation (i.e., values often less than 10). PON:chl a ratios often indicated N sufficiency, but three occasions were noted where PON:POP and PON:chl a ratios were not congruent. It is difficult to reconcile the inorganic and organic N and P ratios with the relatively low DIP and DIN concentrations. The phytoplankton assemblage appeared not to be strongly nutrient-limited but, given a nutrient increase, responded differentially to N and P, both seasonally and along the longitudinal salinity gradient. Grazing pressure in concert with nutrient limitation was advanced as an hypothesis to explain N+P co-limitation.     

Inputs,transformations, and transport of nitrogen and phosphorus in Chesapeake Bay and selected tributaries

In this paper we assemble and analyze quantitative annual input-export budgets for total nitrogen (TN) and total phosphorus (TP) for Chesapeake Bay and three of its tributary estuaries (Potomac, Patuxent, and Choptank rivers). The budgets include estimates of TN and TP sources (point, diffuse, and atmospheric), internal losses (burial in sediments, fisheries yields, and denitrification), storages in the water column and sediments, internal cycling rates (zooplankton excretion and net sediment-water flux), and net downstream exchange. Annual terrestrial and atmospheric inputs (average of 1985 and 1986 data) of TN and TP ranged from 4.3 g TN m^?2 yr^?1 to 29.3 g TN m^?2 yr^?1 and 0.32 g TP m^?2 yr^?1 to 2.42 g TP m^?2 yr^?1, respectively. These rates of TN and TP input represent 6-fold to 8-fold and 13-fold to 24-fold increases in loads to these systems since the precolonial period. A recent 11-yr record for the Susquehanna River indicates that annual loads of TN and TP have varied by about 2-fold and 4-fold, respectively. TN inputs increased and TP inputs decreased during the 11-yr period. The relative importance of nutrient sources varied among these estuaries: point sources of nutrients delivered about half the annual TN and TP load to the Patuxent and nearly 60% of TP inputs to the Choptank; diffuse sources contributed 60–70% of the TN and TP inputs to the mainstream Chesapeake and Potomac River. The direct deposition of atmospheric wet-fall to the surface waters of these estuaries represented 12% or less of annual TN and TP loads except in the Choptank River (37% of TN and 20% of TP). We found direct, although damped, relationships between annual rates of nutrient input, water-column and sediment nutrient stocks, and nutrient losses via burial in sediments and denitrification. Our budgets indicate that the annual mass balance of TN and TP is maintained by a net landward exchange of TP and, with one exception (Choptank River), a net seaward transport of TN. The budgets for all systems revealed that inorganic nutrients entering these estuaries from terrestrial and atmospheric sources are rapidly converted to particulate and organic forms. Discrepancies between our budgets and others in the literature were resolved by the inclusion of sediments derived from shoreline erosion. The greatest potential for errors in our budgets can be attributed to the absence of or uncertainties in estimates of atmospheric dry-fall, contributions of nutrients via groundwater, and the sedimentation rates used to calculate nutrient burial rates.     

Analytical problems in determining peptide nitrogen in the humic fractions of three Italian soils

Peptides were released from organic matter fractions of three Italian soils (humin, humic and fulvic acids), when the samples were hydrolyzed in Ba(ON)₂-saturated solution at 105°C for 2 hr. The peptides obtained were separated using electrophoresis and paper chromatography. The presence of polypeptides in the soil organic matter was indicated by: (1) their hydrolysis by pronase; (2) the amino acids released by 6 N HCl hydrolysis; (3) The comparison of i.r. spectra of humic fractions before and after hydrolysis with 6 N HCl.Attempts at isolating the native proteinaceous compounds using electrophoresis in polyacrylamide gel failed; additionally, our attempts to hydrolyze proteinaceous components enzymatically in unfractionated soil organic matter, as well as in its fractions, before and after methylation, with pepsin, papain and pronase, were unsuccessful. Pronase demonstrated a weak proteolytic activity only at very low substrate-enzyme ratios (20 : 1) in humic and fulvic fractions and in whole phyrophosphate extract. Deproteinated substrates treated with pronase also released free amino acids, suggesting autodigestion.In humin, humic and fulvic fractions we found a total amino acid content of 40–45%, 12–24% or 1–85, respectively. Amino acid recovery from single fractions was about 70–80% of the total content in the unfractionated soil.