Depletion of soil organic carbon and nitrogen under Pinus taeda plantations in Southern Brazilian grasslands (Campos)

Establishment of pine (Pinus spp.) plantations on grasslands could increase carbon (C) sequestration to counteract increased atmospheric carbon dioxide concentrations. In the grasslands of the southern Brazilian highland (Campos), large areas have been converted to Pinus plantations over the last 30 years. In order to assess the impact of this land‐use change on the amount and composition of soil organic matter (SOM), we investigated a grassland pasture site (G), and both an 8‐year‐old (P8) and a 30‐year‐old (P30) plantation with Pinus taeda. Soil samples down to 45 cm were analysed for texture, pH, soil organic carbon (SOC) and total nitrogen (N_tot) concentrations. Chemical composition of SOM was determined by using cross‐polarization magic angle spinning (CPMAS) ¹³C NMR spectroscopy. We analysed for stable C isotope (δ¹³C) and assessed the lignin composition by CuO oxidation. Additionally, contents of pyrogenic organic material (PyOM) were determined because the Campos is regularly burnt. Both pine plantations revealed relatively small SOC concentrations in the mineral soil of 72.6 mg g^?1 (P8) and 56.8 mg g^?1 (P30) and N_tot concentrations of 4.0 mg g^?1 (P8) and 2.9 mg g^?1 (P30) for the A horizon, while grassland showed significantly (P < 0.01) larger contents of 100.2 mg g^?1 for SOC and 5.9 mg g^?1 for N_tot. Accumulation of litter layers suggests decreased input of organic material into the mineral soil under pine, which was confirmed by the δ¹³C values and lignin composition. Smaller contents of vanillyl‐ (V), syringyl‐ (S), and cinnamyl (C)‐phenols, smaller ratios of S/V and C/V, and smaller ratios of acidic to aldehydic forms of V and S phenols indicated a high degree of decomposition of residual grass‐derived SOM in the upper part of the mineral soil (0–10 cm) under pine plantations. This was confirmed by CPMAS ¹³C NMR spectroscopy, showing an increasing Alkyl C/O‐Alkyl C ratio at the same depth. No significant changes in the contents of PyOM could be detected, but all sites tended to show the greatest concentrations at deeper soil depths > 15 cm, indicating a vertical relocation of PyOM. The results suggest that decomposition of residual SOM originating from grassland species contributes to the decrease of SOC and N_tot and to an acidification in the topsoil under pine plantations. We also suggest that slow litter decomposition and incorporation and the absence of fires at the plantations are additional reasons for the reduced amount of SOM. Depletion of SOM and the acidification of the topsoil may reduce the availability and supply of nutrients and diminish the C sequestration potential of the mineral soil.     

Throughfall quality and quantity in polluted and damaged ecosystems in Northern Bohemia

The interaction between high concentrations of polluting gases (SO₂ and NO_x) and damaged forest ecosystems was observed by studying throughfall precipitation in the Erzegebirge Mountains, Northern Bohemia. Qualitative and quantitative data on throughfall for the period November 1989–October 1990 are presented. Weighted averages of SO ₄ ^2? and NO ₃ ^? concentrations in the throughfall were 23.05 mg L^?1 and 13.61 mg L^?1 in a beech and 34.41 mg L^?1 and 11.03 mg L^?1 in a spruce forest respectively. Three variables (the molar ratios of K/Na, N_tot/S and N-NO₃/N-NE₄) were used to compare the spruce throughfall quality to that observed in areas with similar however, less damaged spruce stands. Both K/Na and N-NO₃/N-NH₄ ratios clearly decreased with increasing tree damage, the N_tot/S ratio increased. The results suggest that the throughfall in damaged ecosystems of the Erzegebirge region becomes more like a wet precipitation as the tree canopies get sparser and the trees reduce canopy leaching.     

Nitrogenase activity associated with pasture grasses in Northern New South Wales

Nitrogenase activity associated with roots of grasses was initially examined at 67 sites in New South Wales using an enriched malate medium. Twenty six of the 39 grass species examined produced at least 10 nmol C₂H₄cm^?1 root h^?1—a level accepted as positive presumptive evidence of N₂-fixation: 40 of the 288 samples exceeded 100nmol C₂H₄h^?1. The seasonal N₂ase activity of up to 4 grass species collected in soil cores at 6 sites was measured over 16 months.Activity at field moisture levels, but incubated at 30°C was greatest for cores collected in summer months. Activity was increased in 33.5% of samples by raising soil moisture to field capacity. No single species of grass consistently supported higher activity than any other.Nitrogenase activity was compared in cores of Kikuyu grass (Pennisetum clandestinum) watered to in excess of field capacity and allowed to drain for between 7 and 28 days before re-watering. Activity declined rapidly in the first 7 days and although recovery was also rapid, integration of N₂ase activity over time showed a loss of 20 and 61% for 7 and 28 days drainage respectively. N₂ase activity was greatest at 30°C.Maximum N₂ase activity in field samples was only 246 nmol C₂H₄ core^?1 h^?1 indicating that fixation of N₂ would not be of agronomic significance.     

New method for the estimation of nitrous oxide emission rates from an agricultural watershed

Abstract

We developed a new and improved method, the ‘high-emission-incorporation (HEI) method’, for estimating soil nitrous oxide (N₂O) emission rates at a watershed level based on nitrogen (N) input (consisting of fertilizer, manure, slurry and excreta N) and N surplus (calculated by subtracting the amount of crop yield and consumed N from the N input) of different sites in a livestock farm located in a watershed. The main characteristic of this method is the inclusion of extremely high N₂O emission rates, ‘outlier’, which are normally excluded from estimation. High N₂O emission rates were estimated using the regression model obtained from the measured N₂O values and the amounts of N surplus; normal N₂O emission rates were estimated using the regression model obtained from the measured values and the amount of N input. The probability of occurrence of a high flux was used to incorporate calculated high and normal N₂O emissions into one. The annual N₂O emission rate from the livestock farm in the watershed (467?ha), estimated using the HEI method, was 1156?±?147?kg?N?year^?1 over a 5-year period. The annual N₂O emission rates calculated using the site-specific emission factor (EF?=?0.0789) and the emission factor of the Intergovernmental Panel on Climate Change (EF?=?0.01) were 1838?±?585?kg?N?year^?1 and 673 (522–1103) kg?N?year^?1, respectively. The estimated value using the measure-and-multiply method, in which each land-use area is multiplied by the representative emission rate for each land-use type, was 964 (509–1610) kg?N?year^?1. The N₂O emission rates estimated by our newly developed method were consistent with the values calculated by the measure-and-multiply method and offered improvement over this measure because the new measure can also predict future N₂O emission rates from the watershed.     

N and P losses from a paddy field plot in central Korea

Abstract

The study was carried out to investigate the water balance and runoff and infiltration losses of nutrients in a paddy field plot located in southern Korea. Field monitoring was carried out during the cropping season from May 1, 1999 to September 30, 2000. The soil of the experimental paddy field belonged to the Jisan series (SiL; fine loam, mixed, mesic Fluventic Haplaquepts) covering on area of 5,000 m² (100 m × 50 m). The measured input quantities of N and P into the paddy field were as follows: 122 and 140 kg N ha^?1 and 29 and 30 kg P₂O₅ kg ha^?1 from chemical fertilizer, 20 and 28 kg N ha^?1 and 0.35 and 0.36 kg P ha^?1 from precipitation, and 26 and 35 kg N ha^?1 and 0.57 and 0.72 kg P ha^?1 from irrigation water, respectively. The measured outputs of N and P during the study period were as follows: 48 and 52 kg N ha^?1 and 1.1 and 1.6 kg P ha^?1 from runoff water, and 9 and 12 kg N ha^?1 and 0.04 and 0.05 kg P ha^?1 from infiltration. The runoff loading was the highest in June, presumably because of the higher concentrations of chemical components associated with chemical fertilizer application. The runoff losses of nutrients were compared to the amounts of nutrients supplied by chemical fertilizers. It was found that the losses of N accounted for 34.3 and 42.6% of the chemical fertilizer applied, while those of P accounted for 3.8 and 5.3%. The ratio between nutrient losses by infiltration and the chemical fertilizer applied was 6.4 and 9.8% for N and 0.1 and 0.2% for P, respectively.     

Content of organic carbon and total nitrogen inStagnic Albeluvisols depending on fertilization

Abstract

The content of soil organic carbon (SOC) and total nitrogen (N_tot) was studied in a long-term field experiment with a three-field crop rotation (potato – spring wheat – spring barley) set up on arable sandy loam Stagnic Albeluvisol at Eerika, Tartu, Estonia. The studied factors were: (A) organic fertilizers with three treatments: (i) without organic fertilizer, (ii) farmyard manure (60 t ha^?1) used in every third year, and (iii) different organic (alternative) fertilizers (beet leaves + straw; pure beet leaves; slurry + straw; cereal straw) and (B) mineral nitrogen fertilizer with the rates: N-0; N-40; N-80; N-120 and N-160 kg ha^?1. The study years were 1993, 1996 and 1999. The average content of SOC (1.03%) was significantly influenced by the use of organic fertilizers. Only N_tot (mean value 0.110%) was influenced also by fertilization with mineral nitrogen. The C/N ratio (mean value 9.5) reflected changes in the content of SOC and N_tot     

Nitrogen transformation rates and N<Subscript>2</Subscript>O producing pathways in two pasture soils

Purpose

Better understanding of N transformations and the regulation of N₂O-related N transformation processes in pasture soil contributes significantly to N fertilizer management and development of targeted mitigation strategies.

Materials and methods

¹⁵N tracer technique combined with acetylene (C₂H₂) method was used to measure gross N transformation rates and to distinguish pathways of N₂O production in two Australian pasture soils. The soils were collected from Glenormiston (GN) and Terang (TR), Victoria, Australia, and incubated at a soil moisture content of 60% water-filled pore space (WFPS) and at temperature of 20 °C.

Results and discussion

Two tested pasture soils were characterized by high mineralization and immobilization turnover. The average gross N nitrification rate (n_tot) was 7.28 mg N kg^?1 day^?1 in TR soil () and 5.79 mg N kg^?1 day^?1 in GN soil. Heterotrophic nitrification rates (n_h), which accounting for 50.8 and 41.9% of n_tot, and 23.4 and 30.1% of N₂O emissions in GN and TR soils, respectively, played a role similar with autotrophic nitrification in total nitrification and N₂O emission. Denitrification rates in two pasture soils were as low as 0.003–0.004 mg N kg^?1 day^?1 under selected conditions but contributed more than 30% of N₂O emissions.

Conclusions

Results demonstrated that two tested pasture soils were characterized by fast N transformation rates of mineralization, immobilization, and nitrification. Heterotrophic nitrification could be an important NO₃^?–N production transformation process in studied pasture soils. Except for autotrophic nitrification, roles of heterotrophic nitrification and denitrification in N₂O emission in two pasture soils should be considered when developing mitigation strategies.

     

Spatial variation and interaction of runoff generation and erosion within a semi-arid, complex terrain catchment: a hierarchical approach

Purpose

Closed erosion plots have been used extensively to investigate soil loss and its spatial variation within a watershed. However, erosion rates measured on closed plots at various locations within a watershed may not reflect the “real world” conditions due to plot boundary problems. The purpose of this study was to identify runoff and sediment sources in a semi-arid, complex terrain catchment by using the data collected from open plots, nested catchments, and tunnel systems.

Materials and methods

The study catchment, in the Loess Plateau of China, was partitioned into various-level geomorphic units. Runoff and sediment discharges were measured from 55 storm events between 1963 and 1968 on open plots and nested catchments. Storm flows were also monitored in 14 rainfall events from the tunnel systems between 1989 and 1990. This study combined the data collected from the two periods to investigate runoff and sediment sources from the different geomorphic units of the catchment.

Results and discussion

On the four open plots (S1, S2, S3, and S4) of the hill slope, total runoff depths of 128.5 mm (S1), 84.3 mm (S2), 101.92 mm (S3), and 141.73 mm (S4) were recorded from all the events over the first period, which correspondingly produced total sediment yields of 3.056 kg m^?2 (S1), 9.058 kg m^?2 (S1), 42.848 kg m^?2 (S3), and 97.256 kg m^?2 (S4). The number of runoff events also varied due to a non-uniformity in runoff generation among the different geomorphic units of the catchment. Tunnel flows generally had higher mean sediment concentrations than catchment outflows. Three nested catchments located from the headwaters (C1) to the mouth of the catchment (C3) generated total runoff depths of 120.02 mm (C1), 143.92 mm (C2), and 149.43 mm (C3), and correspondingly produced sediments yields of 62.01 kg m^?2 (C1), 144.02 kg m^?2 (C2), and 123.92 kg m^?2 (C3) for the first period.

Conclusions

Significant variations in runoff and erosion existed within the catchment. The spatial variation of runoff generation on the hill slopes resulted from the variation of soil infiltration. Sediment produced from the lower hill slope zone was disproportionally higher than that from the upper hill slope zone. Nevertheless, a significant portion of the sediment eroded on the lower slope zone was caused by runoff generated from the upper slope zone. Tunnel erosion also played a significant role in sediment production.     

Changes in organic matter,nitrogen, phosphorus and cations in soil as a result of fire and water erosion in a Mediterranean landscape

Fire affects large parts of the dry Mediterranean shrubland, resulting in erosion and losses of plant nutrients. We have attempted to measure these effects experimentally on a calcareous hillside representative of such shrubland. Experimental fires were made on plots (4 m × 20 m) in which the fuel was controlled to obtain two different fire intensities giving means of soil surface temperature of 439°C and 232°C with temperatures exceeding 100°C lasting for 36 min and 17 min. The immediate and subsequent changes induced by fire on the soil's organic matter content and other soil chemical properties were evaluated, together with the impact of water erosion. Seven erosive rain events, which occurred after the experimental fires (from August 1995 to December 1996), were selected, and on them runoff and sediment produced from each plot were measured. The sediments collected were weighed and analysed. Taking into account the variations induced by fire on the soil properties and their losses by water erosion, estimates of the net inputs and outputs of the soil system were made. Results show that the greatest losses of both soil and nutrients took place in the 4 months immediately after the fire. Plots affected by the most intense fire showed greater losses of soil (4077 kg ha^?1) than those with moderate fire intensity (3280 kg ha^?1). The unburned plots produced the least sediment (72.8 kg ha^?1). Organic matter and nutrient losses by water erosion were related to the degree of fire intensity. However, the largest losses of N‐NH₄⁺ and N‐NO₃^– by water erosion corresponded to the moderate fire (8.1 and 7.5 mg N m^?2, respectively).     

Inconspicuous Nutrient Laden Surface Runoff from Mature Forest Sierran Watersheds

It is generally held that surface runoff in heavily forested ecosystems is minimal and therefore nutrient fluxes via runoff are unimportant. This is based in large measure on the absence of direct observation or remnant physical evidence. It is further held that protected forests with heavy understory and litter serve as a nutrient sink due to maximum uptake and interception. Our Sierran studies have detected the presence of surface runoff at several sites in the form of both overland and litter interflow with concentrations of NH₄-N as high as 87.2 mg L^?1, NO₃-N as high as 95.4 mg L^?1, and PO₄-P as high as 24.4 mg L^?1. Data suggest that nutrients are derived from the mature O-horizons, and that there has been little contact with the mineral soil or root zone where strong retention and/or uptake of these ions would be expected. Such contributions from overland/interflow could be particularly important in areas where ultra-oligotrophic lakes (e.g., Lake Tahoe) are now trending towards meso-oligotrophic status. We believe that fire exclusion in these systems may have exacerbated N and P inputs to Lake Tahoe and elsewhere by allowing unnatural buildups of O-horizons that are apparently a source of nutrients to surface runoff.     

Amounts and relative significance of runoff types in the transport of nitrogen into a stream draining an agricultural watershed

The concentration and amounts of NO₃-N and TN transported in surface, accelerated subsurface, and subsurface runoff and stream flow draining a 20 ha pasture watershed were measured over a period of 3 yr. A slight decrease and increase of NO₃-N and particulate N concentrations, respectively, were obtained with increased flow of the runoff types and stream, due to dilution and increased sediment transport, respectively. The concentration of NO₃-N in surface, accelerated subsurface and subsurface runoff and stream flow averaged for the 3 yr was 0.3, 6.6, 4.8, and 4.6 mg 1^?1, respectively, amounting to 0.5, 9.4, 11.6, and 16.8 kg ha^?1 yr^?1, respectively, transported annually. Although NO₃-N accounted for only a minor proportion of the TN transported in surface runoff (10%) it was the main form of N (75%) transported in the other runoff types and in streamflow. Subsurface runoff contributed the major proportion of stream discharge (63%), and NO₃-N (69%), particulate N (44%) and TN (65%) loading of the stream. The results are discussed in terms of non-point pollution of surface waters by NO₃-N.     

Zusammensetzung und Eigenschaften von Sickerwasser aus Stallmiststapeln

Composition and properties of leachates from farmyard manure heaps Besides some rheological characteristics, the N_total, NH₄⁺-N, NO₃^? -N, P, K⁺, dry matter and ash content, as well as chemical oxygen demand and conductivity of farmyard manure leachates were examined. The K⁺ concentration was highest with an average of 5921 mg l^?1, followed by N_total (1139 mg l^?1, 66% of it as NH₄⁺-N and 4% NO₃^?-N) and P (334 mg l^?1). All parameters were highest in leachates of fresh manure and lowest at the end of a 6 months storage period. During the storage, the P concentration in leachates showed a decrease of 67.7%, followed by a decrease in N_t (-57.3%) and K⁺ (-24.0%). In leachates from a manure with an relatively high initial N_t content of 0.51% and a low C:N ratio of 16.8 the N_t concentration was 0.5–1 times higher than that of a manure with 0.44% N_t and a C:N ratio of 19.9. The viscosity and the thixotropy of leachates were both relatively high at the beginning of the manure's storage period, which led to a strongly developed blocking of porous systems. These properties that contribute to explain the high retention rate of nutrients in the top soil layer at manure storage sites, decreased with an increase in storage time.     

Biogeochemistry of a forested watershed in the central Adirondack Mountains: Temporal changes and mass balances

Information on atmospheric inputs, water chemistry and hydrology were combined to evaluate elemental mass balances and assess temporal changes in elemental transport from 1983 through 1992 for the Arbutus Lake watershed. This watershed is located within a northern hardwood ecosystem at the Huntington Forest within the central Adirondack Mountains of New York (USA). Changes in water chemistry, including increasing NO₃ ^? concentrations (1.1 μmol _c , L^?1 yr-1), have been detected during this study period. Starting in 1991 hydrological flow has been measured from Arbutus Lake and these measurements were compared with predicted flow using the BROOK2 hydrological simulation model. The model adequately (r²=0.79) simulated flow from this catchment and was used to estimate drainage for earlier periods when direct hydrological measurements were not available. Modeled drainage water losses coupled with estimates of wet and dry atmospheric deposition were used to calculate solute budgets. Export of SO₄ ^2? (831 mol _c ha^?1 yr^?1) from the greater Arbutus Lake watershed exceeded estimates of atmospheric deposition in an adjacent hardwood stand suggesting an additional source of S. These large drainage losses of SO₄ ^2? also contributed to the drainage fluxes of basic cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺). Most of the atmospheric inputs of inorganic N were retained (average of 74% of wet precipitation and 85% total deposition) in the watershed. There were differences among years (56 to 228 mol ha^?1 yr^?1) in drainage water losses of N with greatest losses occurring during a warm, wet period (1989–1991).     

Mechanized tillage systems effects on soil erosion from an alfisol in watersheds cropped to maize

The degradative effects of mechanized farming operations on soils in the tropics are not widely documented. This study was conducted to quantify the effects of mechanized no-till and conventional tillage systems on runoff, erosion and changes in soil properties. Experiments were conducted on twin watersheds of about 5 ha each. Only the conventionally plowed watershed was terraced to control erosion. Measurements made with a rate-measuring H-Flume indicated that runoff and erosion from the terraced and conventionally tilled watershed were several times greater, compared with the unter-raced no-till watershed. Cumulative runoff in 1979 was 10 times and erosion 42.2 times higher from the plowed watershed than from the no-till watershed. The infiltration capacity 5 years after land development was 3.8 cm h^?1 for the plowed and 10.4 for the no-till watershed. Surface soil from the no-till watershed retained more water at all soil water potentials than that from the plowed treatment. The gravel content in the surface layer of the plowed watershed was 25.1%, compared with 15.8% in the no-till watershed. The maize grain yield from the twelfth consecutive crop was 3 Mg ha^?1 for the no-till and 1 Mg ha^?1 for the plowed watershed.     

Acidity neutralization mechanism in a forested watershed in Central Japan

The contributions of cation exchange and mineral weathering to the neutralization of acidity in the Jingahata watershed in central Japan were estimated through a laboratory weathering experiment and runoff chemistry measurements. The laboratory experiment was conducted in a stirred-flow reactor for a whole soil sample collected from the C horizon in the watershed. The concentration ratios of base cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺) to Si (BC/Si) released during the steady-state stage of the laboratory experiment were in good agreement with the ratios of the net flux of base cations to the flux of Si in the streamwater (BC _{N ET}/Si _L).This result suggests that the acidity in the watershed is neutralized primarily by mineral weathering without causing a net loss of base cations from exchange sites. The alkalinity/acidity balance estimated for the watershed shows that the total weathering rate of base cations is approximately 3.26 keq ha^?1 yr^?1. Weathering of plagioclase (An₄₁) contributes 83% of the total weathering rate. The dominant acidity source is CO₂ released within the soil horizons, accounting for roughly 85% of the total acidity flux (3.20 keq ha^?1 yr^?1). This high internal production of acidity suppresses the relative importance of atmospheric acidity inputs (0.3 keq ha^?1 yr^?1).     

Greenhouse gas emissions and nutrient supply rates in soil amended with biofuel production by-products

Ethanol production results in distiller grain, and biodiesel produces glycerol as by-product. However, there is limited information on effects of their addition on evolution of N₂O and CO₂ from soils, yet it is important to enable our understanding of impacts of biofuel production on greenhouse gas budgets. The objective of this study was to evaluate the direct effects of adding wet distillers grain (WDG), thin stillage (TS), and glycerol at three rates on greenhouse gas emissions (N₂O and CO₂) and nutrient supply rates in a cultivated soil from the Canadian prairies. The WDG and TS application rates were: 100, 200, or 400 kg N ha^?1, whereas glycerol was applied at: 40, 400, or 4,000 kg C ha^?1 applied alone (G???N) or in a combination with 300 kg N ha^?1 (G?+?N). In addition, conventional amendments of urea (UR) and dehydrated alfalfa (DA) were added at the same rates of total N as the by-products for comparative purposes. The production of N₂O and CO₂ was measured over an incubation period of 10 days in incubation chambers and Plant Root Simulator? resin membrane probes were used to measure nutrient (NH ₄ ⁺ -N, NO ₃ ^? -N, and PO ₄ ^?3 -P) supply rates in the soil during incubation. Per unit of N added, urea tended to result in the greatest N₂O production, followed by wet distillers grain and thin stillage, with glycerol and dehydrated alfalfa resulting in the lowest N₂O production. Cumulative N₂O production increased with increasing the rate of N-containing amendments and was the highest at the high rate of UR treatment. Addition of urea with glycerol contributed to a higher rate of N₂O emission, especially at the low rate of glycerol. The DA and WDG resulted in the greatest evolution of CO₂ from the soil, with the thin stillage resulting in less CO₂ evolved per unit of N added. Addition of N fertilizer along with glycerol enhanced microbial activity and decomposition. The amendments had significant impacts on release of available nutrient, with the UR treatments providing the highest NO ₃ ^? -N supply rate. The TS treatments supplied the highest rate of NH ₄ ⁺ -N, followed by WDG compared to the other amendments. The WDG treatments were able to provide the greatest supply of PO ₄ ^?3 -P supply in comparison to the other amendments. Microbial N immobilization was associated with glycerol treatments applied alone. This study showed that the investigated biofuel by-products can be suitable soil amendments as a result of their ability to supply nutrients and N₂O emissions that did not exceed that of the conventional urea fertilizer.     

Headwater lake chemistry during the spring freshet in North-Central Ontario

From data on 30 headwater lakes in north-central Ontario we found that, during the spring snow melt of 1981, all lakes underwent serious declines in alkalinity. Generally, SO₄ ^2?, alkalinity, Ca⁺ and Mg²⁺ concentrations were reduced by runoff and rain then recovered to intermediate levels after the major inputs declined. As expected, a range in responses was evident with lower alkalinity systems showing the greatest changes. The observed changes, however, were consistent with acid loading having depleted alkalinity. In calculating an input-output budget for each lake, we found that changes in Cl^?, Na⁺, and K⁺ were consistent with atmospheric inputs being the major source as the difference between the expected input and the actual contribution from rain and snow had a mean near zero. There appears to be a significant, ? 45%, watershed source of sulphate that we hypothesize is from dry deposition occurring prior to snowfall and is eluted with the melting process. With refinements to a mass balance approach explaining the watershed source of SO₄ ^2? and Al, we feel it is possible to predict springtime lake changes given a few chemical and simple morphometric variables.     

Effect of surface-casting earthworms on the transport of phosphorus and nitrogen in surface runoff from pasture

Treatment of a soil under permanent pasture with carbaryl (a broad spectrum carbamate biocide) resulted in a 2-fold increase in the volume of surface runoff. This was attributed to a 3-fold reduction in infiltration rate as a result of litter accumulation at the soil surface in the absence of surface-casting earthworm activity. The amounts of dissolved inorganic P (DIP), NH⁺₄-N, and NO^?₃-N in surface runoff from pasture treated with carbaryl (1.18, 9.53 and 4.25 kg ha^?1 yr^?1, respectively) were appreciably greater than those from untreated pasture (0.31, 1.63 and 0.52 kg ha^?1 yr^?1). This was attributed to the large amounts of DIP, NH⁺₄-N, and NO^?1₃-N released from decomposing litter. Following incubation at 4°C for 18 days the release of DIP, NH⁺₄-N and NO^?₃-N from litter was 160, 1600 and 950 μg g^?1, respectively. Losses of particulate P and sediment in surface runoff were lower in the absence (0.31 and 290 kg ha^?1 yr^?1, respectively) than in the presence (0.56 and 1120 kg ha^? yr^?1) of surface casts, pointing to the importance of surface casts as a source of sediment. Surface casts accounted for 45 and 75%, respectively, of the annual loading of particulate P and sediment in surface runoff. Nevertheless, the total loss in surface runoff of P and N forms was increased substantially when the production of earthworm casts was eliminated     

Sediment denitrification in waterways in a rice-paddy-dominated watershed in eastern China

Purpose

Rice-paddy-dominated watersheds in eastern China are intensively cultivated, and lands with two crops receive as much as 550–600 kg?ha^–1?year^–1 of nitrogen (N), mainly through the addition of N-based fertilizers. However, stream N concentrations have been found to be relatively low. Waterways in the watersheds are assumed to be effective “sinks” for N, minimizing its downstream movement. We directly measured net sediment denitrification rates in three types of waterways (ponds, streams/rivers, and a reservoir) and determined the key factors that control net sediment denitrification. Such information is essential for evaluating the impact of the agricultural N cycle on the quality of surface water.

Materials and methods

The pond–stream–reservoir continuum was sampled every 2 months at nine sites in an agricultural watershed between November 2010 and December 2011. Net sediment N₂ fluxes/net sediment denitrification rates were determined by membrane inlet mass spectrometry and the N₂/Ar technique. A suite of parameters known to influence denitrification were also measured.

Results and discussion

Net denitrification rates ranged between 28.2?±?18.2 and 674.3?±?314.5 μmol N₂–N?m^–2?h^–1 for the streams, 23.7?±?23.9 and 121.2?±?38.7 μmol N₂–N?m^–2?h^–1 for the ponds, and 41.8?±?17.7 and 239.3?±?49.8 μmol N₂–N?m^–2?h^–1 for the reservoir. The mean net denitrification rate of the stream sites (173.2?±?248.4 μmol N₂–N?m^–2?h^–1) was significantly higher (p?<?0.001) than that of the pond sites (48.3?±?44.5 μmol N₂–N?m^–2?h^–1), and the three types of waterways all had significantly higher (p?<?0.01) mean net denitrification rates in summer than in other seasons. Linear regression and linear mixed effect model analysis showed that nitrate (NO₃ ^?–N) concentration in surface water was the primary controlling factor for net sediment denitrification, followed by water temperature. Using monitoring data on NO₃ ^?–N concentrations and temperature of the surface water of waterways and an established linear mixed effect model, total N removed through net sediment denitrification in the pond–stream–reservoir continuum was estimated at 46.8?±?24.0 t?year^–1 from July 2007 to June 2009, which was comparable with earlier estimates based on the mass balance method (34.3?±?12.7 t?year^–1), and accounted for 83.4 % of the total aquatic N. However, the total aquatic N was only 4.4 % of the total N input to the watershed, and thus most of the surplus N in the watershed was likely to be either denitrified or stored in soil.

Conclusions

High doses of N in a rice-paddy-dominated watershed did not lead to high stream N concentrations due to limited input of N into waterways and the high efficiency of waterways in removing N through denitrification.     

Midwest (U.S.A.) reservoir water quality modification I. Particulate parameters

Both qualitative and quantitative approaches were used to evaluate the impact of a flood control, low flow augmentation reservoir on seven water quality parameters: Suspended solids and total phosphate (particulate parameters); BOD, COD, and ammonia (O₂-demanding parameters); and orthophosphate and nitrite plus nitrate N (soluble nutrients). Fourteen years of weekly sampling data above, in, and downstream of the reservoir both before and after the reservoir became operational were analyzed. This paper considers the effects of the reservoir on the particulate parameters. There was a dramatic decrease in both suspended solids and total phosphate concentrations in the reservoir discharges, particularly during periods of high river flows and high reservoir inflow parameter concentrations. At all sampling stations, the annual parameter loading rates (kg ha^?1 yr^?1) correlated linearly with annual runoff (cm yr^?1). The suspended solids removal efficiency of the reservoir was dependent on annual runoff and averaged about 90%. Non-point source contributions of suspended solids were well over 99% when annual runoff exceeded 6.57 cm y^?1 and over 95% even when annual runoff was as low as 1.63 cm yr^?1