Carbon storage of different soil-size fractions in Florida silvopastoral systems

Compared with open (treeless) pasture systems, silvopastoral agroforestry systems that integrate trees into pasture production systems are likely to enhance soil carbon (C) sequestration in deeper soil layers. To test this hypothesis, total soil C contents at six soil depths (0-5, 5-15, 15-30, 30-50, 50-75, and 75-125 cm) were determined in silvopastoral systems with slash pine (Pinus elliottii) + bahiagrass (Paspalum notatum) and an adjacent open pasture (OP) with bahiagrass at four sites, representing Spodosols and Ultisols, in Florida. Soil samples from each layer were fractionated into three classes (250-2000, 53-250, and <53 microm), and the C contents in each were determined. Averaged across four sites and all depths, the total soil organic carbon (SOC) content was higher by 33% in silvopastures near trees (SP-T) and by 28% in the alleys between tree rows (SP-A) than in adjacent open pastures. It was higher by 39% in SP-A and 20% in SP-T than in open pastures in the largest fraction size (250-2000 microm) and by 12.3 and 18.8%, respectively, in the intermediate size fraction (53-250 microm). The highest SOC increase (up to 45 kg m(-2)) in whole soil of silvopasture compared with OP was at the 75- to 125-cm depth at the Spodosol sites. The results support the hypothesis that, compared with open pastures, silvopastures contain more C in deeper soil layers under similar ecological settings, possibly as a consequence of a major input to soil organic matter from decomposition of dead tree-roots.     

Computer programs for calculating soil loss on a watershed basis

A series of computer programs designed to predict gross annual soil loss on a watershed basis by application of the Universal Soil Loss Equation (USLE) have been developed. The programs provide an easy-to-use, flexible, and standardized means of organizing base data and applying the USLE to large land areas. The programs can be used to assess and to evaluate the effects of changing land-use patterns and conservation practices on soil losses. Critical or problem areas can be readily identified. The USLE Computer Programs are a useful research tool for investigators involved in water quality management, 208 planning, or conservation research.The package of computer programs consists of three main components: data input, the Main Program, and the Totals Program. Input data include both field base data describing the watershed and corresponding values for the factors in the USLE. The Main Program calculates the average rate of soil loss (tons/ acre/yr) and the total soil loss (tons/yr) for the smallest subunit of the watershed identified as the soil unit. Also calculated is an RKLS factor, which is an indication of the erosive potential of a given soil type, slope, and slope length, under a particular rainfall regime. The Totals Program aggregates soil unit losses into progressively larger units, that is, field, farm, subwatershed, and watershed units. An example of the programs' versatility and use is presented.     

Wildfire effects on soil nutrients and leaching in a tahoe basin watershed

A wildfire burned through a previously sampled research site, allowing pre- and post-burn measurements of the forest floor, soils, and soil leaching near Lake Tahoe, Nevada. Fire and post-fire erosion caused large and statistically significant (P < or = 0.05) losses of C, N, P, S, Ca, and Mg from the forest floor. There were no statistically significant effects on mineral soils aside from a decrease in total N in the surface (A11) horizon, an increase in pH in the A11 horizon, and increases in water-extractable SO4(2-) in the A11 and A12 horizons. Burning caused consistent but nonsignificant increases in exchangeable Ca2+ in most horizons, but no consistent or statistically significant effects on exchangeable K+ or Mg2+, or on Bray-, bicarbonate-, or water-extractable P concentrations. Before the burn, there were no significant differences in leaching, but during the first winter after the fire, soil solution concentrations of NH4+, NO3-, ortho-P, and (especially) SO4(2-) were elevated in the burned area, and resin lysimeters showed significant increases in the leaching of NH4+ and mineral N. The leaching losses of mineral N were much smaller than the losses from the forest floor and A11 horizons, however. We conclude that the major short-term effects of wildfire were on leaching whereas the major long-term effect was the loss of N from the forest floor and soil during the fire.     

Influence of biochar on nitrogen fractions in a coastal plain soil

Interest in the use of biochar from pyrolysis of biomass to sequester C and improve soil productivity has increased; however, variability in physical and chemical characteristics raises concerns about effects on soil processes. Of particular concern is the effect of biochar on soil N dynamics. The effect of biochar on N dynamics was evaluated in a Norfolk loamy sand with and without NHNO. High-temperature (HT) (≥500°C) and low-temperature (LT) (≤400°C) biochars from peanut hull ( L.), pecan shell ( Wangenh. K. Koch), poultry litter (), and switchgrass ( L.) and a fast pyrolysis hardwood biochar (450-600°C) were evaluated. Changes in inorganic, mineralizable, resistant, and recalcitrant N fractions were determined after a 127-d incubation that included four leaching events. After 127 d, little evidence of increased inorganic N retention was found for any biochar treatments. The mineralizable N fraction did not increase, indicating that biochar addition did not stimulate microbial biomass. Decreases in the resistant N fraction were associated with the high pH and high ash biochars. Unidentified losses of N were observed with HT pecan shell, HT peanut hull, and HT and LT poultry litter biochars that had high pH and ash contents. Volatilization of N as NH in the presence of these biochars was confirmed in a separate short-term laboratory experiment. The observed responses to different biochars illustrate the need to characterize biochar quality and match it to soil type and land use.     

Phosphorus and other soil components in a dairy effluent sprayfield within the central Florida Ridge

There is concern that P from dairy effluent sprayfields will leach into groundwater beneath Suwannee River basins in northern Florida. Our purpose was to describe the effects of dairy effluent irrigation on the movement of soil P and other nutrients within the upper soil profile of a sprayfield over three 12-mo cycles (April 1998-March 2001). Effluent P rates of 70, 110, and 165 kg ha(-1) cycle(-1) were applied to forages that were grown year-round. The soil is a deep, excessively drained sand (thermic, uncoated Typic Quartzipsamment). Mean P concentration in soil water below the rooting zone (152-cm depth) was < or = 0.1 mg L(-1) during 11 3-mo periods. Mehlich-1-extractable (M1) P, Al, and Ca in the topsoil increased over time but did not change in subsoil depths of 25 to 51, 51 to 71, 71 to 97, and 97 to 122 cm. Topsoil Ca increased as effluent rate increased. High Ca levels were found in dairy effluent (avg.: 305 mg L(-1)) and supplemental irrigation water (avg.: 145 mg L(-1)) which likely played a role in retaining P in the topsoil. An effect of effluent rate on P and Al concentrations in the topsoil was not detected, probably due to large and variable quantities present at project initiation. The P retention capacity (i.e., Al plus Fe) increased in the topsoil because Al increased. Dairy effluent contained Al (avg.: 31 mg L(-1)). Phosphorus saturation ratio (PSR) increased over time in the topsoil but not in subsoil layers. Regardless of effluent rate, the P retention capacity and PSR of subsoil, which contained 119 to 229 mg kg(-1) of Al, should be taken into account when assessing the risk of P moving below the rooting zone of most forage crops.     

Degradation of 14C-atrazine bound residues in brown soil and rendzina fractions

The remobilization and the fate of 14C-ring labeled atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) bound residues was examined in relation with the turnover of natural soil organic matter. Soil fractions of a brown soil and a rendzina were incubated under controled laboratory conditions. The mineralization of natural organic matter and atrazine-bound residues was respectively estimated by the amounts of CO2 and 14CO2 evolved during the incubation. The remobilization and distribution of 14C residues among the soil organic fractions were achieved after physical-chemical extractions of the samples. Comparisons of samples in abiotic and biotic conditions allowed us to assess the influence of microbial activity on the fate of atrazine-bound residues. The mineralization curves showed that natural organic matter and atrazine-bound residues had similar decomposition patterns. After 100 d of incubation, 0.8 to 3.6% of total organic C was evolved as CO2, while only 0.1% of the initial radioactivity was mineralized as CO2, and 7 to 15% was becoming extractable with water and methanol. Few differences were observed in the distribution of residues within organic compounds for both fractions of the rendzina, except a decrease of the 14C radioactivity of the 50- to 5000-microm fraction and a slight increase of that of humin. For the 0- to 5000-microm brown soil fraction, increased radioactivity in humin at the expense of humic (HA) and fulvic (FA) acids was detected after incubation, while for the 0- to 50-microm fraction more radioactivity was recovered with FA.     

Modeling sediment and nitrogen export from a rural watershed in eastern Canada using the soil and water assessment tool

Watershed simulation models can be used to assess agricultural nonpoint-source pollution and for environmental planning and improvement projects. However, before application of any process-based watershed model, the model performance and reliability must be tested with measured data. The Soil and Water Assessment Tool version 2005 (SWAT2005) was used to model sediment and nitrogen loads from the Thomas Brook Watershed, which drains a 7.84 km rural landscape in the Annapolis Valley of Nova Scotia, Canada. The Thomas Brook SWAT model was comprised of 28 subbasins and 265 hydrologic response units, most of them containing agricultural land use, which is the main nonpoint nitrogen source in the watershed. Crop rotation schedules were incorporated into the model using field data collected within Agriculture and Agri-Food Canada's Watershed Evaluation of Beneficial Management Practices program. Model calibration (2004-2006) and validation (2007-2008) were performed on a monthly basis using continuous stream flow, sediment, and nitrogen export measurements. Model performance was evaluated using the coefficient of determination, Nash-Sutcliff efficiency (NSE), and percent bias (PBIAS) statistics. Study results show that the model performance was satisfactory (NSE > 0.4; > 0.5) for stream flow, sediment, nitrate-nitrogen, and total nitrogen simulations. Annual corn, barley, and wheat yields were also simulated well, with PBIAS values ranging from 0.3 to 7.2%. This evaluation of SWAT demonstrated that the model has the potential to be used as a decision support tool for agricultural watershed management in Nova Scotia.     

Relevance of organic matter fractions as predictors of wastewater sludge mineralization in soil

Seventeen different wastewater sludges were characterized using both chemical and organic matter fractionation methods (water extraction, Van Soest method, and acid hydrolysis) and 6-mo incubation studies to assess their decomposition in soil. Simple correlation and multiple factor analysis (MFA) were then performed to establish relationships between composition and C and N mineralization of sludges. Carbon and N concentrations covered a wide range of values, but organic carbon (C(o)) to organic nitrogen (N(o)) ratios were relatively low (from 5 to 19). Carbon and N were mainly distributed in the most soluble fractions of the Van Soest method and in the water-insoluble fraction at 100 degrees C. Carbon mineralization varied from 180 to 661 g C kg(-1) organic C added during the 168-d incubation. The addition of sludges led to different inorganic N dynamics: from -3.3 to +120.0 g N kg(-1) sludge organic C mineralized after the 168-d incubation. Fractionation studies showed that the most discriminating method was acid hydrolysis. Carbon mineralization was linked with the proportion of sludge N and C present in the lignin-like fraction (r = -0.68 and -0.65, respectively). Significant relationships were established between N mineralization and N(o) to C(o) ratio (0.88 < r < 0.95) and the C(o) to N(o) ratio of sludges, the C to N ratio of the soluble fraction obtained by the Van Soest method, the water-soluble fraction at 100 degrees C, and the C and N present in the acid-hydrolyzable fraction. Finally, multiple factor analysis also enabled establishing a sludge typology using five clusters based on composition and mineralization characteristics.     

Natural resource degradation in a small watershed in Nepal

Amid growing concern about the conservation of renewable natural resources, the process, extent and symptoms of their degradation are examined with specific reference to the Upper Pokhara Valley. Based on a household survey, field observations, informal deliberations and land use analysis, the results of this study reveal that forests and grazing land have been subject to increasing degradation caused by demographic, socioeconomic and institutional factors. The intensity of degradation varies by watershed. In particular, rainfed pakho land on steep slopes is under the severe threat of accelerating soil erosion, despite the construction of terraces. This calls for the formulation of a comprehensive natural resource conservation strategy which should be based on a framework comprising an integrated population control programme, planned land use changes and institutional reforms .     

Sediment delivery linkages in a chaparral watershed following a wildfire

The purpose of this research is to study the temporal and spatial sediment delivery to and within the stream network following a wildfire on a chaparral watershed in Arizona, USA. Methods include interpretation of channel processes (aggradation, degradation) from sequential aerial photographs, field measurements of sediment delivery, and overland flow from ten microwatersheds having different vegetation cover (no vegetation, chaparral cover, and bare with vegetation buffer strips). The response of the watershed to the fire was very complex. The fire reduced the chaparral cover to zero in most locations and severe erosion led to filling of the channels by sediment. With vegetation recovery, sediment delivery from the watershed practically ceased. Vegetation buffer strips were mainly responsible for arresting the sediment delivered from bare hillslopes. Relatively clear water, entering the channels, caused degradation in the tributaries that delivered the sediment into the main stream at El Oso Creek. Due to high water infiltration by immense volumes of sediment deposits in the middle reach, the sediment from the tributaries was deposited as in-channel fans. In contrast, the upper reach of El Oso Creek behaved similarly to the tributaries. It aggraded after the fire and was followed by degradation. The low reach of El Oso Creek is degrading because it is still adjusting base level to the incision of the master stream. Implications of this study are that land managers, concerned to avoid severe erosion and sedimentation following disturbance, should concentrate on the establishment and enhancement of vegetation buffer strips along channel banks.     

Decadal change in vegetation and soil phosphorus pattern across the Everglades landscape

Wetlands respond to nutrient enrichment with characteristic increases in soil nutrients and shifts in plant community composition. These responses to eutrophication tend to be more rapid and longer lasting in oligotrophic systems. In this study, we documented changes associated with water quality from 1989 to 1999 in oligotrophic Everglades wetlands. We accomplished this by resampling soils and macrophytes along four transects in 1999 that were originally sampled in 1989. In addition to documenting soil phosphorus (P) levels and decadal changes in plant species composition at the same sites, we report macrophyte tissue nutrient and biomass data from 1999 for future temporal comparisons. Water quality improved throughout much of the Everglades in the 1990s. In spite of this improvement, though, we found that water quality impacts worsened during this time in areas of the northern Everglades (western Loxahatchee National Wildlife Refuge [NWR] and Water Conservation Area [WCA] 2A). Zones of high soil P (exceeding 700 mg P kg(-1) dry wt. soil) increased to more than 1 km from the western margin canal into the Loxahatchee NWR and more than 4 km from northern boundary canal into WCA-2A. This doubling of the high soil P zones since 1989 was paralleled with an expansion of cattail (Typha spp.)-dominated marsh in both regions. Macrophyte species richness declined in both areas from 1989 to 1999 (27% in the Loxahatchee NWR and 33% in WCA-2A). In contrast, areas well south of the Everglades Agricultural Area, induding WCA-3A and Everglades National Park (ENP), did not decline during this time. We found no significant decadal change in plant community patterns from 1989 and 1999 along transects in southern WCA-3A or Shark River Slough (ENP). Our 1999 sampling also included a new transect in Taylor Slough (ENP), which will allow change analysis here in the future. Regular sampling of these transects, to verify decadal-scale environmental impacts or improvements, will continue to be an important tool for long-term management and restoration of the Everglades.     

Assessing soil biodiversity across Great Britain: national trends in the occurrence of heterotrophic bacteria and invertebrates in soil

An assessment of the biodiversity of soils was a component of the Countryside Survey 2000 (CS2000). This was the first integrated survey of soil biota and chemical properties at a national scale. A total of 1052 soil samples were collected across Great Britain during CS2000 and analysed for a range of soil microbial and invertebrate characteristics resulting in the production of a series of robust datasets. A principal objective was to use these datasets to investigate relationships between soil biota and environmental factors such as geographical location, vegetation, land use, land cover, soil type and pollutant levels as first stages in characterising the inherent biodiversity of British soils and investigating the potential of soil biodiversity as indicators of soil health at a regional or national scale. Preliminary results for culturable heterotrophic, invertebrate taxa, Acari, Collembola and Oribatid mites are presented here to illustrate the nature of the data collected and the patterns of soil biodiversity in relation to large-scale regional, vegetation and soil characteristics across the British countryside.     

A lidar-based assessment of riparian shade and large wood potential in the Skagit River watershed,WA

Wild salmon stocks in the Pacific Northwest are imperiled by a variety of declining habitat factors, including riparian shade and in-channel large wood. In this paper, a relatively simple lidar model of the riparian canopy was used along anadromous streams in the Skagit River watershed in western Washington State, United States, to delineate where riparian trees were most lacking, and where restoration efforts would have the greatest benefit in terms of shade and large wood recruitment potential. Within a 45-m riparian buffer, 61% of riparian zones were currently incapable of delivering large wood to the stream. Current potential for large wood recruitment is greatest adjacent to stream edges and falls off rapidly with distance from the channel. Approximately 99% of large wood recruitment potential lies within 45 m of the channel edge, and 50% of the wood potential is within 9 m. A hypothetical canopy model in which all trees mature to a 100-year height would provide 18% more shade distributed over the entire watershed, and 90% more shade in the tributaries. Most of the potential gains in improved shade and large wood contributions are in agricultural areas, as opposed to forestry or urban land uses. The shade and large wood models were constructed from widely available geographic information system tools and are readily transferable to other watersheds with similar characteristics. Model outputs are intended for use in planning restoration projects, as an input to stream temperature models, and to inform policy on restoration priorities and regulatory buffer widths.     

Nonpoint source pollution risk assessment in a watershed context

Nonpoint source pollution control requires assessment of the influence of dispersed runoff-contributing areas on downstream water quality. This evaluation must consider two separate phases: site-to-stream loading and downstream fluvial transport. Any model, combination of models, or procedure for making this assessment can be generalized to a simple spatial model or framework, which considers runoff or pollutant loading per unit area and down-stream attenuation, with drainage area as a scaling factor. This spatial model has a probabilistic interpretation and can be used in conjunction with a standard dilution model to give a probabilistic estimate of the impacts at the basin mouth of runoff from a specific upstream contributing area. It is illustrated by applying it to an assessment of the probability that various copper concentrations at the mouth of the urbanized South Platte River basin in Denver, Colorado, USA, will be exceeded as a result of runoff from a subbasin within the city. Determining the probability that a concentration of a pollutant at the basin mouth can be attributed to runoff from a discrete area within the basin is useful for targeting and risk assessment because it enables quantitative risk-based comparisons. The spatial framework is also useful for evaluating management and control options, since actions within the basin can be directly linked to water quality at a downstream point.     

Sulfate-enriched water effects on a floodplain forest in Florida

Sulfate-enriched water that was discharged experimentally into a floodplain forest in Florida caused H₂S formation, and trees showed signs of stress within one year. Chloride-enriched water also caused trees to show signs of stress. Trees in this ecosystem may also be sensitive to changes in hydroperiod.     

Locating Escherichia coli contamination in a rural South Carolina watershed

One of the problems associated with the use of ambient water quality standards in surface water regulation is the difficulty of identifying and regulating nonpoint source pollution, making such standards unenforceable, especially at the local level. We used the Escherichia coli indicator to locate the most contaminated reaches in rural South Carolina's Bush River watershed (297 km(2), 186 stream-km). We divided the watershed into 20 smaller reaches and sampled each reach multiple times, but restricted each sampling round to one day. We located four low order creek reaches, representing just nine stream-km, where we observed geometric mean E. coli densities of over 1250 E. coli/100 mL; in each case, the source of the contamination (riparian grazing of cattle) was easily identifiable. On the Bush River itself, we observed a step change in one reach where geometric means increased from 106 E. coli/100 mL to 565 E. coli/100 mL over the reach's 10 km length. In this case, the sources of contamination were not as obvious as in the lower order streams; in this case, more advanced Microbial Source Tracking techniques will be required to identify the sources. Nevertheless, this sampling protocol helped locate polluted reaches and provided decision-makers with reasonable justifications for concrete action in deciding where (or where not) to install conservation practices and where more sophisticated (and expensive) MST techniques were warranted.     

Fire effects on stable isotopes in a Sierran forested watershed

This study tested the hypothesis that stable C and N isotope values in surface soil and litter would be increased by fire due to volatilization of lighter isotopes. The hypothesis was tested by: (1) performing experimental laboratory burns of organic and mineral soil materials from a watershed at combinations of temperature ranging 100 to 600 degrees C and duration ranging from 1 to 60 min; (2) testing field samples of upland soils before, shortly after, and 1 yr following a wildfire in the same watershed; and (3) testing field soil samples from a down-gradient ash/sediment depositional area in a riparian zone following a runoff event after the wildfire. Muffle furnace results indicated the most effective temperature range for using stable isotopes for tracing fire impacts is 200 to 400 degrees C because lower burn temperatures may not produce strong isotopic shifts, and at temperatures>or=600 degrees C, N and C content of residual material is too low. Analyses of field soil samples were inconclusive: there was a slightly significant effect of the wildfire on delta15N values in upland watershed analyses 1 yr postburn, while riparian zone analyses results indicated that delta13C values significantly decreased approximately 0.71 per thousand over a 9 mo post-fire period (p=0.015), and ash/sediment layer delta13C values were approximately 0.65 per thousand higher than those in the A horizon. The lack of field confirmation may have been due to overall wildfire burn temperatures being <200 degrees C and/or microbial recovery and vegetative growth in the field. Thus, the muffle furnace experiment supported the hypothesis, but it is as yet unconfirmed by actual wildfire field data.     

Land-use dynamics in a southern Illinois (USA) watershed

The Cache River of southernmost Illinois is used as a case study for developing and demonstrating an approach to quantitatively link (1) national agricultural policy and global agricultural markets, (2) landowner's decisions on land use, (3) spatial patterns of land use at a watershed scale, and (4) hydrologic impacts, thus providing a basis to predict, under a certain set of circumstances, the environmental consequences of economic and political decisions made at larger spatial scales. The heart of the analysis is an estimation, using logistic regression, of the affect of crop prices and Conservation Reserve Program (CRP) rental rates on farmland owner's decisions whether to reenroll in the CRP or return to crop production. This analysis shows that reasonable ranges for crop prices (80%–150% of 1985–1995 values) and CRP rental rates (0–125% of 1985–1995 rates) result in a range of 3%–92% of CRP lands being returned to crop production, with crop prices having a slightly greater effect than CRP rental rates. Four crop price/CRP rental rate scenarios are used to display resulting land-use patterns, and their effect on sediment loads, a critical environmental quality parameter in this case, using the agricultural non point source (AGNPS) model. These scenarios demonstrate the importance of spatial pattern of land uses on hydrological and ecological processes within watersheds. The approach developed can be adapted for use by local governments and watershed associations whose goals are to improve watershed resources and environmental quality.     

Integrating water-quality management and land-use planning in a watershed context

The spatial relationships between land uses and river-water quality measured with biological, water chemistry, and habitat indicators were analyzed in the Little Miami River watershed, OH, USA. Data obtained from various federal and state agencies were integrated with Geographic Information System spatial analysis functions. After statistically analyzing the spatial patterns of the water quality in receiving rivers and land uses and other point pollution sources in the watershed, the results showed that the water biotic quality did not degrade significantly below wastewater treatment plants. However, significantly lower water quality was found in areas downstream from high human impact areas where urban land was dominated or near point pollution sources. The study exhibits the importance of integrating water-quality management and land-use planning. Planners and policy-makers at different levels should bring stakeholders together, based on the understanding of land-water relationship in a watershed, to prevent pollution from happening and to plan for a sustainable future.     

Soil and water conservation method adoption in a highly erosive watershed: the case of Southwest Oklahoma's Fort Cobb watershed

A major source of pollution in agricultural landscapes is surface runoff and non-point source pollution generated from agricultural production practices. In-stream, stream bank and riparian conservation/management practices can be implemented to reduce sediment loading solely or in conjunction with upland practices. Survey results from producers in the Fort Cobb Reservoir watershed, a highly erosive watershed in southwest Oklahoma with a history of state and federal conservation programs, provide information required for improving understanding of operators’ likelihood of adoption. Two models of soil and water conservation were estimated, a logit model of likelihood of enrollment and a Poisson model of the total number of practices adopted. Results reinforced previous findings that attitudes, gender and education influence conservation program enrollment. Farming experience, gender and attitudes towards conservation increased the total number of practices adopted.