Coastal metabolism and the oceanic organic carbon balance

Net organic metabolism (that is, the difference between primary production and respiration of organic matter) in the coastal ocean may be a significant term in the oceanic carbon budget. Historical change in the rate of this net metabolism determines the importance of the coastal ocean relative to anthropogenic perturbations of the global carbon cycle. Consideration of long-term rates of river loading of organic carbon, organic burial, chemical reactivity of land-derived organic matter, and rates of community metabolism in the coastal zone leads us to estimate that the coastal zone oxidizes about 7 × 1012 moles C/yr. The open ocean is apparently also a site of net organic oxidation (∼16 × 1012 moles C/yr). Thus organic metabolism in the ocean appears to be a source of CO2 release to the atmosphere rather than being a sink for atmospheric carbon dioxide. The small area of the coastal ocean accounts for about 30% of the net oceanic oxidation. Oxidation in the coastal zone (especially in bays and estuaries) takes on particular importance, because the input rate is likely to have been altered substantially by human activities on land.

Remediation of Persistent Organic Pollutants (POPs) in Two Different Soils

Persistent organic pollutants (POPs) are a set of chemicals that are toxic, persist in the environment for long periods of time, and biomagnify as they move up through the food chain. The most widely used method of POP destruction is incineration, which is expensive and could result in undesirable by-products. An alternative bioremediation technology, which is cheaper and environ-mentally friendly, was tested during this experiment. Two different soil types containing high and low organic matter (OM) were spiked with 100 mg/kg each of pyrene and Aroclor 1248 and planted with three different species of grasses. The objective of the study was to determine residue recovery levels (availability) and potential effectiveness of these plant species for the remediation of POPs. The results showed that recovery levels were highly dependent on the soil organic matter content—very low in all treatments with the high OM content soil compared to recoveries in the low OM soil. This indicates that availability, and, hence, biodegradability of the contaminants is dependent on the organic matter content of the soil. Moreover, the degree of availability was also significantly different for the two classes of chemicals. The polyaromatic hydrocarbon (PAH) recovery (availability) was extremely low in the high organic matter content soil compared to that of the polychlorinated biphenyls (PCBs). In both soil types, all of the plant species treatments showed significantly greater PCB biodegradation compared to the unplanted controls. Planting did not have any significant effect on the transformation of the PAHs in both soil types; however, planting with switchgrass was the best remedial option for both soil types contaminated with PCB.

Modeling the effect of ozone loss on photobleaching of chromophoric dissolved organic matter in the St. Lawrence estuary

Temporal trends in total ozone for the St. Lawrence estuary were estimated from ground-based measurements at the NOAA/CMDL station in Caribou, Maine. Linear regression analysis showed that from 1979 to 1999 total ozone has decreased by about 3.3% per decade on an annual basis and ≤6.2% per decade on a monthly basis relative to unperturbed (pre-CFC) levels. The influence of increased ultraviolet-B (280–320 nm) radiation associated with ozone depletion on water column photochemical processes was evaluated by modeling the photobleaching of chromophoric dissolved organic material (CDOM). Linear regression analysis showed small (<0.5% per decade), but statistically significant upward trends in maximum noontime photobleaching rates. Most notably, positive trends in relative rates for May, June, and July, when maximum absolute rates are expected, were predicted. A global model based on TOMS ozone data revealed increases in photobleaching of ≤3% per decade at high latitudes in the Southern Hemisphere. Radiation amplification factors for increases in photochemically weighted UV (280–400 nm) in response to ozone depletion were estimated at 0.1 and 0.08 for photobleaching of CDOM absorbance at 300 and 350 nm, respectively. Application of the laboratory-based model to conditions that more closely resembled those in situ were variable with both overestimation and underestimation of measured rates. The differences between modeled rates and observed rates under quasi-natural conditions were as large or larger than the predicted increases due to ozone depletion. These comparisons suggest that biological activity and mixing play an important, but as yet ill-defined, role in modifying photochemical processes.

Natural 13C abundance as a tracer for studies of soil organic matter dynamics

A method for measuring the long- and medium-term turnover of soil organic matter is described. Its principle is based on the variations of 13C natural isotope abundance induced by the repeated cultivations of a plant with a high 13C/12C ratio (C4 photosynthetic pathway) on a soil which has never carried any such plant. The 13C/12C ratio in soil organic matter being about equal to the 13C/12C ratio of plant materials from which it is derived, changing the 13C content of the organic inputs to the soil (by altering vegetation from C3 type into C4 type) is equivalent to a true labelling in situ of the organic matter. Two cases of continuous corn cultivation (Zea mays: δ13C = −12%.) on soils whose initial organic matter average δ13C is −26%. were studied. The quantity of organic carbon originating from corn (that is the quantity which had turned-over since the beginning of continuous cultivation) was estimated using the 13C natural abundance data. After 13 yr, 22% of total organic carbon had turned-over, in the system studied. Particle size fractions coarser than 50μm on the one hand, and finer than 2μm on the other. contained the youngest organic matters. The turnover rate of silt-sized fractions was slower

Distribution of organic and reduced sulfur forms in marsh soils of coastal Louisiana

Soil samples from a Louisiana Barataria Basin brackish marshes were fractionated into acid-volatile sulfides (AVS), HCl-soluble sulfur, elemental sulfur, pyrite sulfur, ester-sulfate sulfur, and carbon-bonded sulfur. Inorganic sulfur composed 13% of total sulfur in brackish marsh soil with HCl-soluble sulfur representing 63–92% of the inorganic sulfur fraction. AVS represented less than 1% of the total sulfur pool. Pyrite sulfur and elemental sulfur together accounted for 8–33% of the inorganic sulfur pool. Organic sulfur, in the forms of ester-sulfate sulfur and carbon-bonded sulfur, was the most dominant pool representing the majority of total sulfur in brackish marsh. Results were compared to values reported for fresh and salt marshes. Reported inorganic sulfur fractions were greater in adjacent marshes, constituting 24% of total sulfur in salt marsh, and 22% in freshwater marshes. Along a salinity gradient, HCl-soluble sulfur represented 78–86% of the inorganic sulfur fraction in fresh, brackish, and salt marsh. Organic sulfur in the forms of ester-sulfate sulfur and carbon-bonded sulfur was the major constituent (76–87%) of total sulfur in all marshes. Reduced sulfur species, except elemental sulfur, increased seaward along the salinity gradient. Accumulation of reduced sulfur forms through sedimentation processes was significant in marsh energy flow in fresh, brackish and salt marshes.

Methods for physical separation and characterization of soil organic matter fractions

Turnover of soil organic matter (SOM) is coupled to the cycling of nutrients in soil through the activity of soil microorganisms. Biological availability of organic substrate in soil is related to the chemical quality of the organic material and to its degree of physical protection. SOM fractions can provide information on the turnover of organic matter (OM), provided the fractions can be related to functional or structural components in soil. Ultrasonication is commonly used to disrupt the soil structure prior to physical fractionation according to particle size, but may cause redistribution of OM among size fractions. The presence of mineral particles in size fractions can complicate estimations of OM turnover time within the fractions. Densiometric separation allows one to physically separate OM found within a specific size class from the heavier-density mineral particles. Nutrient contents and mineralization potential were determined for discrete size/density OM fractions isolated from within the macroaggregate structure of cultivated grassland soils. Eighteen percent of the total soil C and 25% of the total soil N in no-till soil was associated with fine-silt size particles having a density of 2.07-2.21 g/cm3 isolated from inside macroaggregates (enriched labile fraction or ELF). The amount of C and N sequestered in the ELF fraction decreased as the intensity of tillage increased. The specific rate of mineralization (mug net mineral N/mug total N in the fraction) for macroaggregate-derived ELF was not different for the three tillage treatments but was greater than for intact macroaggregates. The methods described here have improved our ability to quantitatively estimate SOM fractions, which in turn has increased our understanding of SOM dynamics in cultivated grassland systems.

土壤类型和添加有机物料对铵态氮回收的影响

探讨NH4+-N回收率在不同因素下的变化规律。【方法】以黄土高原从北向南不同地区的典型土壤类型为对象,采用Bremner浸取法,研究了土壤类型、植被类型、施肥模式及添加有机物料对铵态氮回收率的影响。【结果】不同类型土壤及不同类型植被间NH4+-N回收率存在极显著差异(P<0.01)。黄土正常新成土的NH4+-N回收率最高(88.8%),极显著大于其他土壤,土垫旱耕人为土的NH4+-N回收率最低(81.0%),简育干润均腐土和干润砂质新成土介于二者之间;不同类型植被间,林地土壤的NH4+-N回收率(91.0%)极显著高于其他类型植被土壤,其他类型植被土壤的NH4+-N回收率表现为农田(85.5%)>裸地(83.8%)>草地(83.6%),但三者之间差异不显著。添加有机物料后,土壤NH4+-N回收率极显著增加(P<0.01),不添加有机物料对照土壤的NH4+-N回收率为84.3%,添加长毛草和苜蓿后的NH4+-N回收率分别为86.6%和85.9%。长期施肥对土壤NH4+-N的回收率无显著影响(P=0.436 5>0.05)。【结论】NH4+-N回收率与粘粒含量呈弱负相关,与有机质含量呈正相关,粘土矿物对N...

半湿润农田生态系统长期施肥对土壤团聚体中有机氮组分的影响

通过对黄土高原半湿润农田生态系统25年的田间肥料定位试验,研究了长期不同施肥模式对土壤有机氮组分及其在各级团聚体中分布的影响.结果表明:长期施肥对水解氨态氮、水解未知氮在土壤各级团聚体中分布的影响最大,对氨基酸态氮的分布有一定影响,而对氨基糖态氮分布的影响较小.长期施用化肥和有机肥能有效地影响水解氨态氮和水解未知氮与团聚体的结合作用,而氨基糖态氮在土壤氮循环转化过程中具有较强的稳定性.长期施肥条件下土壤水解全氮与有机碳、全氮以及团聚体分形维数均呈极显著正相关,其r分别为0.942,0.981,0.910(P<0.001),说明土壤有机氮组分对土壤团聚体的形成和性质具有显著影响.相关分析表明,土壤全氮或有机质对1～2mm和0.25～1mm土壤团聚体中各有机氮组分的影响较大

轮作和施肥对半干旱区作物地上部生物量与土壤有机碳的影响

了解轮作与施肥对土壤有机碳的影响是建立持续发展措施的关键。【方法】以长期定位试验(1984～2002)中的10个典型处理为基础,分析了地上部生物量和耕层(0～20cm)土壤有机碳变化,探讨半干旱区轮作和施肥对0～20cm土层有机碳的影响,10个典型处理分别为休闲(F);冬小麦连作体系中的3个施肥处理:不施肥(W/W+CK)、化肥(W/W+NP)、化肥有机肥(W/W+NP-FYM);冬小麦-冬小麦+糜子-豌豆轮作体系中的3个施肥处理:不施肥(W/WM/P+CK)、化肥(W/WM/P+NP)、化肥有机肥(W/WM/P+NP-FYM)处理;1个冬小麦—冬小麦-红豆草轮作处理(W/W/S+NP);人工苜蓿中2个施肥处理:不施肥(A/A+CK)和化肥有机肥处理(A/A+NP-FYM)。【结果】冬小麦连作体系(W/W)中,不施肥处理(W/W+CK)的地上部生物量平均为3.3t·ha-1,化肥处理(W/W+NP)和化肥有机肥处理(W/W+NP-FYM)依次为7.5和11.2t·ha-1;冬小麦-冬小麦+糜子-豌豆轮作(W/WM/P)体系中,不施肥处理(W/WM/P+CK)地上部生物量平均3.1t·ha-1,W/WM...

黄土高原旱区长期不同轮作施肥对土壤供氮能力的影响

自 1 98 4年开始的长期不同轮作与施肥试验表明 :种植作物可提高土壤供氮能力 6.88%～ 36.58%,以种植苜蓿提高幅度最大 ,是裸地的 1 .37倍。长期施用氮肥、磷肥、有机肥及三者配施可提高土壤供氮能力 9.8%～ 1 33.98%,其中以施氮、磷及有机肥玉米连作提高幅度最大。不同轮作系统中土壤供氮能力 :粮草 3年轮作 >粮草 8年轮作 >粮豆 3年轮作 >粮饲豆 4年轮作 ;种植作物可有效增加土壤有机氮水平 ,提高剖面土壤供氮能力。施用有机肥可有效地增加深层土壤供氮潜力并在 1 0 0 cm处出现迅速减小的现象

黄土丘陵区梯田谷子养分循环特征与生产力关系的研究

以新修梯田7年长期肥料定位试验为依据,研究了不同施肥条件下谷子各部位生物量、养分携出量、养分平衡以及耕层土壤养分时空变化。结果表明,有机肥与N、P肥配合施用可提高谷子的籽粒产量和生物产量。养分携出量的大小顺序为籽粒>叶>糠秕>茎,为同类地区农业生产及生态环境建设提供科学依据。

侵蚀泥沙、有机质和全氮富集规律研究

在自然降雨下 ,研究降雨、坡度、耕作和施肥对侵蚀泥沙、有机质和全N富集率的影响 ,分析土壤和泥沙颗粒组成、富集与泥沙有机质和全N富集的关系 ,揭示土壤有机质和全N在泥沙中的富集规律 .结果表明 ,泥沙粘粒的富集导致有机质和全N的富集 ,泥沙粘粒、有机质和全N富集率分别平均为 1.77、2 .0 9和 1.61.土壤侵蚀模数与泥沙有机质和全N富集率呈显著的负相关关系 ,降雨、坡度、施肥和耕作措施对泥沙有机质富集作用的影响是通过减少土壤侵蚀模数来实现的 ,减少土壤侵蚀的措施可增加泥沙有机质和全N的富集 .

长期定位施肥对黑垆土剖面养分分布特征的影响

对黄土高原旱地 1 5年连续施肥后土壤剖面养分分布的研究发现 ,施化肥对土壤剖面有机质、全N、全P含量的影响深达 1 0 0cm以下 ,所有施肥处理有机质、全N、全P、NO3- N、有效P含量在耕层 (0～ 2 0cm)都有不同程度增加 ;40～ 60、60～ 80cm土层有机质、全N、全P都低于长年不施肥处理 ,造成土壤下层养分的亏缺。长期大量施用氮肥造成N素养分下淋累积 ;长期大量施用磷肥土壤耕层有效P显著提高 ,而 2 0cm以下土层变化不大。

氮磷配合对土壤氮素径流流失的影响

大田试验研究结果表明 :增施N、P均能增加作物的产量和减少水土流失 ;当N、P用量分别达到 5 5 .2kgN/hm2 和 90kgP2 O5/hm2 时 ,泥沙有机质和全氮流失最少 ,流失量分别为 2 0 89和 1 75kg/km2 ;当N、P用量分别为 5 5 .2kgN/hm2 和 4 5kgP2 O5/hm2 时 ,土壤矿质氮流失最小 ,其流失量仅为 2 7.9kg/km2 ;作物对土壤氮素的吸收 ,可减少土壤氮素的流失 .

不同林龄植被培肥改良土壤效益研究

在黄土丘陵沟壑区森林植被能够明显改善生态环境 ,防止土地退化 ,提高土壤中有机质、速效氮和速效钾的含量 ,降低土壤pH和容重 ;快速显著地增加土体中 >0 .2 5mm水稳性团聚体和 >5 0 μm微团粒的数量 ,使土壤结构改善 ,协调供应养分和水分的能力提高 ;能促进黏粒形成 ,坚实度增加 ,土壤的抗蚀性和抗冲性提高 ,有效地减少水土流失。植被对土壤的培肥改良是一种正向持续反馈机制 ,时间越长 ,效益越显著