Changes in Soil Particulate Organic Matter, Microbial Biomass, and Activity Following Afforestation of Marginal Agricultural Lands in a Semi-Arid Area of Northeast China

Afforestation of agricultural lands has been one of the major land use changes in China in recent decades. To better understand the effect of such land use change on soil quality, we investigated selected soil physical, chemical and microbial properties (0–15 cm depth) in marginal agricultural land and a chronosequence of poplar (Populus euramericana cv. ‘N3016’) plantations (5-, 10-, 15- and 20-years old) in a semi-arid area of Northeast China. Soil bulk density significantly declined after conversion of agricultural lands to poplar plantations. Soil total organic carbon (TOC) and nitrogen (TN) concentrations, microbial biomass C (MBC) and potential N mineralization rate (PNM) decreased initially following afforestation of agricultural lands, and then increased with stand development. However, soil metabolic quotient (qCO₂) exhibited a reverse trend. In addition, soil particulate organic matter C (POM-C) and N (POM-N) concentrations showed no significant changes in the first 10 years following afforestation, and then increased with stand age. These findings demonstrated that soil quality declined initially following afforestation of agricultural lands in semi-arid regions, and then recovered with stand development. Following 15 years of afforestation, many soil quality parameters recovered to the values found in agricultural land. We propose that change in soil quality with stand age should be considered in determining optimum rotation length of plantations and best management practices for afforestation programs.     

Estimation and Spatiotemporal Analysis of Methane Emissions from Agriculture in China

Estimating and analyzing the temporal and spatial patterns of methane emissions from agriculture (MEA) will help China formulate mitigation and adaptation strategies for the nation’s agricultural sector. Based on the Tier 2 method presented in the 2006 guidelines of the Intergovernmental Panel on Climate Change (IPCC) and on existing reports, this article presents a systematic estimation of MEA in China from 1990 to 2006, with a particular emphasis on trends and spatial distribution. Results from our study indicate that China’s MEA rose from 16.37 Tg yr⁻¹ in 1990 to 19.31 Tg yr⁻¹ in 2006, with an average annual increase of 1.04%. Over the study period, while emissions from field burning of crop residues remained rather low, those from rice cultivation and from livestock typically decreased and increased, respectively, showing extremely opposite trends that chiefly resulted from changes in the cultivated areas for different rice seasons and changes in the populations of different animal species. Over the study period, China’s high-MEA regions shifted generally northward, chiefly as a result of reduced emissions from rice cultivation in most of China’s southern provinces and a substantial growth in emissions from livestock enteric fermentation in most of China’s northern, northeastern, and northwestern provinces. While this article provides significant information on estimates of MEA in China, it also includes some uncertainties in terms of estimating emissions from each source category. We conclude that China’s MEA will likely continue to increase in the future and recommend a demonstration study on MEA mitigation along the middle and lower reaches of the Yellow River. We further recommend enhanced data monitoring and statistical analysis, which will be essential for preparation of the national greenhouse gas (GHG) inventory.     

Carbon Sequestration in Dryland Ecosystems

Drylands occupy 6.15 billion hectares (Bha) or 47.2% of the worlds land area. Of this, 3.5 to 4.0 Bha (57%–65%) are either desertified or prone to desertification. Despite the low soil organic carbon (SOC) concentration, total SOC pool of soils of the drylands is 241 Pg (1 Pg = petagram = 10¹⁵ g = 1 billion metric ton) or 15.5% of the worlds total of 1550 Pg to 1-meter depth. Desertification has caused historic C loss of 20 to 30 Pg. Assuming that two-thirds of the historic loss can be resequestered, the total potential of SOC sequestration is 12 to 20 Pg C over a 50-year period. Land use and management practices to sequester SOC include afforestation with appropriate species, soil management on cropland, pasture management on grazing land, and restoration of degraded soils and ecosystems through afforestation and conversion to other restorative land uses. Tree species suitable for afforestation in dryland ecosystems include Mesquite, Acacia, Neem and others. Recommended soil management practices include application of biosolids (e.g., manure, sludge), which enhance activity of soil macrofauna (e.g., termites), use of vegetative mulches, water harvesting, and judicious irrigation systems. Recommended practices of managing grazing lands include controlled grazing at an optimal stocking rate, fire management, and growing improved species. The estimated potential of SOC sequestration is about 1 Pg C/y for the world and 50 Tg C/y for the U.S. This potential of dryland soils is relevant to both the Kyoto Protocol under UNFCCC and the U.S. Farm Bill 2002.

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A Geospatial Methodology to Identify Locations of Concentrated Runoff from Agricultural Fields

A geospatial methodology has been developed that utilizes high resolution lidar‐derived DEMs to help track runoff from agricultural fields and identify areas of potential concentrated flow through vegetated riparian areas in the Coastal Plain of Virginia. Points of concentrated flow are identified across 74 agricultural fields within the Virginia portion of the Chesapeake Bay watershed. On average, 70% of the surface area of the agricultural fields analyzed drains through less than 20 m of the field margin, and on average 81% of the field surface area drains through 1% or less of the field margin. Within the riparian buffer, locations that were predicted by the geospatial model to have high levels of concentrated flow were found to exhibit evidence of channelization. Results indicate that flow concentration and channelized flow through vegetated riparian areas may be common along the margin of agricultural fields, resulting in vegetated riparian areas that are less effective at sediment trapping than assumed. Additional results suggest that the regulations governing the location and width of vegetated riparian may not be sufficient to achieve goals for reducing sediment and nutrient runoff from nonpoint agricultural sources. Combined with the increasing availability of lidar‐derived DEMs, the geospatial model presented has the potential to advance management practices aimed at reducing nonpoint source pollution leaving agricultural fields.     

Deriving Grassland Management Factors for a Carbon Accounting Method Developed by the Intergovernmental Panel on Climate Change

Grassland management affects soil organic carbon (SOC) storage and can be used to mitigate greenhouse gas emissions. However, for a country to assess emission reductions due to grassland management, there must be an inventory method for estimating the change in SOC storage. The Intergovernmental Panel on Climate Change (IPCC) has developed a simple carbon accounting approach for this purpose, and here we derive new grassland management factors that represent the effect of changing management on carbon storage for this method. Our literature search identified 49 studies dealing with effects of management practices that either degraded or improved conditions relative to nominally managed grasslands. On average, degradation reduced SOC storage to 95% ± 0.06 and 97% ± 0.05 of carbon stored under nominal conditions in temperate and tropical regions, respectively. In contrast, improving grasslands with a single management activity enhanced SOC storage by 14% ± 0.06 and 17% ± 0.05 in temperate and tropical regions, respectively, and with an additional improvement(s), storage increased by another 11% ± 0.04. We applied the newly derived factor coefficients to analyze C sequestration potential for managed grasslands in the U.S., and found that over a 20-year period changing management could sequester from 5 to 142 Tg C yr^–1 or 0.1 to 0.9 Mg C ha^–1 yr^–1, depending on the level of change. This analysis provides revised factor coefficients for the IPCC method that can be used to estimate impacts of management; it also provides a methodological framework for countries to derive factor coefficients specific to conditions in their region.     

Land use change effects on forest carbon cycling throughout the southern United States

We modeled the effects of afforestation and deforestation on carbon cycling in forest floor and soil from 1900 to 2050 throughout 13 states in the southern United States. The model uses historical data on gross (two-way) transitions between forest, pasture, plowed agriculture, and urban lands along with equations describing changes in carbon over many decades for each type of land use change. Use of gross rather than net land use transition data is important because afforestation causes a gradual gain in carbon stocks for many decades, while deforestation causes a much more rapid loss in carbon stocks. In the South-Central region (Texas to Kentucky) land use changes caused a net emission of carbon before the 1980s, followed by a net sequestration of carbon subsequently. In the Southeast region (Florida to Virginia), there was net emission of carbon until the 1940s, again followed by net sequestration of carbon. These results could improve greenhouse gas inventories produced to meet reporting requirements under the United Nations Framework Convention on Climate Change. Specifically, from 1990 to 2004 for the entire 13-state study area, afforestation caused sequestration of 88 Tg C, and deforestation caused emission of 49 Tg C. However, the net effect of land use change on carbon stocks in soil and forest floor from 1990 to 2004 was about sixfold smaller than the net change in carbon stocks in trees on all forestland. Thus land use change effects and forest carbon cycling during this period are dominated by changes in tree carbon stocks.     

Soil-erosion and runoff prevention by plant covers in a mountainous area (se spain): Implications for sustainable agriculture

In the Mediterranean region the intensities and amounts of soil loss and runoff on sloping land are governed by rainfall pattern and vegetation cover. Over a two-year period (1998–1999), six wild species of aromatic and mellipherous plants (Thymus serpylloides subsp. Gadorensis, Thymus baeticus Boiss, Salvia lavandulifolia Vahl., Santolina rosmarinifolia L., Lavandula stoechas L. and Genista umbellata Poiret) were selected for erosion plots to determine their effectiveness in reducing water erosion on hillslopes of the Sierra Nevada Mountain (SE Spain). The erosion plots (including a bare-soil plot as control), located at 1,345 m in altitude, were 2 m² (2 m × 1 m) in area and had 13% incline. The lowest runoff and soil erosion rates, ranging from 9 to 26 mm yr⁻¹ and from 0.01 to 0.31 Mg ha⁻¹ yr⁻¹, respectively, over the entire study period, were measured under the Thymus serpylloides. Lavandula stoechas L. registered the highest rates among the plant covers tested, runoff ranging from 77 to 127 mm yr⁻¹ and erosion from 1.67 to 3.50 Mg ha⁻¹ yr⁻¹. In the bare-soil plot, runoff ranged from 154 to 210 mm yr⁻¹ and erosion from 4.45 to 7.82 Mg ha⁻¹ yr⁻¹. According to the results, the lowest-growing plant covers (Thymus serpylloides and Salvia lavandulifolia Vahl.) discouraged the soil erosion and runoff more effectively than did the taller and open medium-sized shrubs (Santolina rosmarinifolia L., Genista umbellata Poiret, Thymus baeticus Boiss and Lavandula stoechas L.). Monitoring allowed more direct linkage to be made between plant covers and the prevention of erosion, with implications for sustainable mountain agriculture and environmental protection.     

Carbon sequestration potential in reclaimed mine sites in seven east-central states

Terrestrial systems represent a significant potential carbon (C) sink to help mitigate or offset greenhouse gas emissions. Nearly 3.2 Mha are permitted for mining activities in the United States, which are required to be reclaimed with vegetative cover. While site-specific studies have assessed C accumulation on reclaimed mine sites, regional analyses to estimate potential C increases have not been conducted. For this analysis, potential C sequestration is analyzed on 567,000 ha of mine land in a seven-state region reclaimed to cropland, pasture, or forest. Carbon accumulation is estimated for cropland, pasture, and forest soils, forest litter layer, and aboveground biomass by estimating average annual rates of C accumulation from site-specific and general C sequestration studies. The average annual rate of C storage is highest when mine land is reclaimed to forest, where the potential sequestration is 0.7 to 2.2 Tg yr(-1). The C from soils, litter layer, and biomass from mine lands reclaimed to forest represents 0.3 to 1.0% of the 1990 CO2 emissions from the study region (919 Tg CO2). To achieve the greenhouse gas (GHG) emission reduction goal of 7% below the 1990 level as proposed by the Kyoto Treaty requires CO2 emissions in the study area to be reduced by just over 64 Tg CO2. The potential carbon storage in mine sites reclaimed to forest could account for 4 to 12.5% of these required reductions.     

An Approach for Estimating Soil Carbon Using the National Nutrient Loss Database

Agricultural lands have the potential to contribute to greenhouse gas mitigation by sequestering organic carbon within the soil. Credible and consistent estimates will be necessary to design programs and policies to encourage management practices that increase carbon sequestration. Because a nationwide survey of soil carbon by the wide range of natural resources and management conditions of the United States is prohibitively expensive, a simulation modeling approach must be used. The National Nutrient Loss Database (NNLD) is a modeling and database system designed and built jointly by the USDA– Natural Resources Conservation Service (NRCS) and Texas A&M University to provide science-based inferences on environmental impacts from changes in agricultural management practices and programs at the regional and national level. Currently, the NNLD simulates 16 crops and covers 1.35 × 10⁸ ha. For estimating soil carbon sequestration, the database will be populated with 1.5 × 10⁶ field-level model runs using the EPIC (Environmental Policy Impact Calculator) model, which includes newly incorporated carbon equations consistent with those in the Century model. Each run will represent a unique situation defined by state, crop, climate, soil, irrigation type, conservation practice, tillage system, and nutrient management treatment (nutrient rate, application frequency, application timing, and manure category). Results are to be assigned to specific National Resource Inventory points (NRI) to simulate regional and national baselines. In this article we present the modeling approach and discuss the strengths and limitations. Published online     

WATER QUALITY MODELING OF ALTERNATIVE AGRICULTURAL SCENARIOS IN THE U.S. CORN BELT1

ABSTRACT: Simulated water quality resulting from three alternative future land‐use scenarios for two agricultural watersheds in central Iowa was compared to water quality under current and historic land use/land cover to explore both the potential water quality impact of perpetuating current trends and potential benefits of major changes in agricultural practices in the U.S. Corn Belt. The Soil Water Assessment Tool (SWAT) was applied to evaluate the effect of management practices on surface water discharge and annual loads of sediment and nitrate in these watersheds. The agricultural practices comprising Scenario 1, which assumes perpetuation of current trends (conversion to conservation tillage, increase in farm size and land in production, use of currently‐employed Best Management Practices (BMPs)) result in simulated increased export of nitrate and decreased export of sediment relative to the present. However, simulations indicate that the substantial changes in agricultural practices envisioned in Scenarios 2 and 3 (conversion to conservation tillage, strip intercropping, rotational grazing, conservation set‐asides and greatly extended use of best management practices (BMPs) such as riparian buffers, engineered wetlands, grassed waterways, filter strips and field borders) could potentially reduce current loadings of sediment by 37 to 67 percent and nutrients by 54 to 75 percent. Results from the study indicate that major improvements in water quality in these agricultural watersheds could be achieved if such environmentally‐targeted agricultural practices were employed. Traditional approaches to water quality improvement through application of traditional BMPs will result in little or no change in nutrient export and minor decreases in sediment export from Corn Belt watersheds.     

GRASS VERSUS TREES: MANAGING RIPARIAN AREAS TO BENEFIT STREAMS OF CENTRAL NORTH AMERICA1

ABSTRACT: Forestation of riparian areas has long been promoted to restore stream ecosystems degraded by agriculture in central North America. Although trees and shrubs in the riparian zone can provide many benefits to streams, grassy or herbaceous riparian vegetation can also provide benefits and may be more appropriate in some situations. Here we review some of the positive and negative implications of grassy versus wooded riparian zones and discuss potential management outcomes. Compared to wooded areas, grassy riparian areas result in stream reaches with different patterns of bank stability, erosion, channel morphology, cover for fish, terrestrial runoff, hydrology, water temperature, organic matter inputs, primary production, aquatic macroinvertebrates, and fish. Of particular relevance in agricultural regions, grassy riparian areas may be more effective in reducing bank erosion and trapping suspended sediments than wooded areas. Maintenance of grassy riparian vegetation usually requires active management (e.g., mowing, burning, herbicide treatments, and grazing), as successional processes will tend ultimately to favor woody vegetation. Riparian agricultural practices that promote a dense, healthy, grassy turf, such as certain types of intensively managed livestock grazing, have potential to restore degraded stream ecosystems.     

NONPOINT SOURCE DISCHARGES OF NUTRIENTS FROM PIEDMONT WATERSHEDS OF CHESAPEAKE BAY1

ABSTRACT: We measured annual discharges of water, sediments, and nutrients from 10 watersheds with differing proportions of agricultural lands in the Piedmont physiographic province of the Chesapeake Bay drainage. Flow-weighted mean concentrations of total N, nitrate, and dissolved silicate in watershed discharges were correlated with the proportion of cropland in the watershed. In contrast, concentrations of P species did not correlate with cropland. Organic P and C correlated with the concentration of suspended particles, which differed among watersheds. Thus, the ratio of N:P:Si in discharges differed greatly among watersheds, potentially affecting N, P or Si limitation of phytoplankton growth in the receiving waters. Simple regression models of N discharge versus the percentage of cropland suggest that croplands discharge 29–42 kg N ha^-1 yr^-1 and other lands discharge 1.2–5.8 kg N ha^-1 yr^-1. We estimated net anthropogenic input of N to croplands and other lands using county level data on agriculture and N deposition from the atmosphere. For most of the study watersheds, N discharge amounted to less than half of the net anthropogenic N.     

BENEFITS OF TRANSFERRING STREAMFLOW PRIORITY FROM AGRICULTURAL TO NON-AGRICULTURAL USE1

ABSTRACT: In Virginia, as in many states, priority to streamflow is held by riparian landowners who are predominantly agricultural users. The streamfiow may also have a high potential value to non-agricultural users who do not have riparian rights. The potential benefits of transferring streamfiow priority rights from agricultural to non-agricultural use were evaluated using simulation for an eastern Virginia watershed. Lowering irrigators' priority to streamflow reduced crop yields and irrigated returns in some years because of inadequate water supplies. However, the transfer of priorities increased the likelihood that the urban reservoir would be able to withdraw water from the stream without interruption. As a result, priority trades reduced the size of reservoir needed to meet a given water requirement by municipal users. The resulting savings in reservoir construction and maintenance costs more than offset the losses to irrigators. Net savings could be achieved even if the reservoir were required to release water periodically to maintain a minimum level of instream flow. The conclusion is that the state should encourage trading of access to streamflow in order to increase the use efficiency of streamfiows. Alternative means by which the state can facilitate water exchanges are discussed.     

Changes in soil organic carbon contents and nitrous oxide emissions after introduction of no-till in Pampean agroecosystems

We reviewed published results to estimate no-till effects on SOC and denitrification in the Argentine Pampas and the potential of no-till to mitigate the global warming effect. On an equivalent mass basis, 42 paired data sets were used for SOC comparisons of no-till vs. plow till (moldboard plow or disk plow), 18 paired data for comparison of no-till vs. reduced till (chisel plow or harrow disk), and 20 paired data for comparison of plow till vs. reduced till. Twenty-six denitrification data sets were used for evaluation of tillage system and fertilization effects on N2O emission. Changes in SOC under no-till were not correlated to time since initiation of experiments. Averaged over years a 2.76 Mg ha(-1) SOC increase (P = 0.01) was observed in no-till systems compared with tilled systems, but no differences were detected between plow and reduced till. The SOC under tillage explained most of the SOC variation under no-till (R2= 0.94, P = 0.01). The model had a positive intercept and predicted a relatively higher increase of SOC in areas of low organic matter level. The conversion of the whole pampean cropping area to no-till would increase SOC by 74 Tg C, about twice the annual C emissions from fossil fuel consumption of Argentina. Emissions of N2O were greater under no-till with a mean increase of 1 kg N ha(-1) yr(-1) in denitrification rate for humid pampean scenarios. The increased emissions of N2O might overcome the mitigation potential of no-till due to C sequestration in about 35 yr, and therefore no-till might produce global warming.     

Where Did the Agricultural Nonpoint Source Trades Go? Lessons from Virginia Water Quality Trading Programs

Governmental agencies, nongovernmental organizations, and agricultural organizations promote water quality trading programs as an innovative policy to engage agricultural producers in conservation activities. Cost analyses suggest regulated sources can reduce compliance costs by purchasing agricultural nonpoint source credits. Yet, such “point‐nonpoint” trades are rare. This article assesses the demand for agricultural nonpoint sources in well‐developed nutrient trading programs in Virginia for industrial and municipal wastewater treatment plants, municipal stormwater programs, and land developers. Evidence suggests nutrient trading programs in Virginia will not stimulate investments in pollutant reduction practices on working agricultural lands. The lack of demand for agricultural nonpoint source credits can be attributed to a substantial degree to the design features and incentives present in multiple overlapping regulatory programs. The legal setting that dampens regulated source demand for nonpoint source credits in Virginia is broadly representative of conditions found elsewhere in the United States.     

A VSA-Based Strategy for Placing Conservation Buffers in Agricultural Watersheds

Conservation buffers have the potential to reduce agricultural nonpoint source pollution and improve terrestrial wildlife habitat, landscape biodiversity, flood control, recreation, and aesthetics. Conservation buffers, streamside areas and riparian wetlands are being used or have been proposed to control agricultural nonpoint source pollution. This paper proposes an innovative strategy for placing conservation buffers based on the variable source area (VSA) hydrology. VSAs are small, variable but predictable portion of a watershed that regularly contributes to runoff generation. The VSA-based strategy involves the following three steps: first, identifying VSAs in landscapes based on natural characteristics such as hydrology, land use/cover, topography and soils; second, targeting areas within VSAs for conservation buffers; third, refining the size and location of conservation buffers based on other factors such as weather, environmental objectives, available funding and other best management practices. Building conservation buffers in VSAs allows agricultural runoff to more uniformly enter buffers and stay there longer, which increases the buffers capacity to remove sediments and nutrients. A field-scale example is presented to demonstrate the effectiveness and cost-effectiveness of the within-VSA conservation buffer scenario relative to a typical edge-of-field buffer scenario. The results enhance the understanding of hydrological processes and interactions between agricultural lands and conservation buffers in agricultural landscapes, and provide practical guidance for land resource managers and conservationists who use conservation buffers to improve water quality and amenity values of agricultural landscape.     

Projecting Large-Scale Area Changes in Land Use and Land Cover for Terrestrial Carbon Analyses

One of the largest changes in US forest type areas over the last half-century has involved pine types in the South. The area of planted pine has increased more than 10-fold since 1950, mostly on private lands. Private landowners have responded to market incentives and government programs, including subsidized afforestation on marginal agricultural land. Timber harvest is a crucial disturbance affecting planted pine area, as other forest types are converted to planted pine after harvest. Conversely, however, many harvested pine plantations revert to other forest types, mainly due to passive regeneration behavior on nonindustrial private timberlands. We model land use and land cover changes as a basis for projecting future changes in planted pine area, to aid policy analysts concerned with mitigation activities for global climate change. Projections are prepared in two stages. Projected land use changes include deforestation due to pressures to develop rural land as the human population expands, which is a larger area than that converted from other rural lands (e.g., agriculture) to forestry. In the second stage, transitions among forest types are projected on land allocated to forestry. We consider reforestation, influences of timber harvest, and natural succession and disturbance processes. Baseline projections indicate a net increase of about 5.6 million ha in planted pine area in the South over the next 50 years, with a notable increase in sequestered carbon. Additional opportunities to expand pine plantation area warrant study of landowner behavior to aid in designing more effective incentives for inducing land use and land cover changes to help mitigate climate change and attain other goals.     

Potential of the Conservation Reserve Program to control agricultural surface water pollution

The Conservation Reserve Program (CRP), initiated by the Conservation Title of the Food Security Act of 1985, is the primary federal program to control nonpointsource pollution in agricultural watersheds of the United States. However, the program is designed primarily to reduce soil erosion rather than to retire croplands in a manner optimal for controlling runoff of sediment and associated pollutants. This study estimates potential enrollment of streamside and floodplain croplands in this ten-year retirement program in order to gauge the potential of the CRP as a water-quality improvement policy. A contingent choice survey design was employed in Fayette County, Illinois, to demonstrate that there is substantial potential for retirement of streamside and floodplain croplands in the CRP. Enrollments in each program climb from less than 6% to over 83% of eligible croplands as the annual rental rate is increased from $20 to $200/acre. Potential retirement of streamside and floodplain croplands declines, however, if tree planting, drainage removal, or a 20-year contract are required. The potential of a CRP-based water-quality program to improve water quality and aquatic ecosystems in agricultural watersheds is thus substantial but constrained by the economic trade-offs that farmers make between crop production and conservation incentives in determining the use of their riparian lands.     

Assessing Riparian Conservation Land Management Practice Impacts on Gully Erosion in Iowa

Well-established perennial vegetation in riparian areas of agricultural lands can stabilize the end points of gullies and reduce their overall erosion. The objective of this study was to investigate the impacts of riparian land management on gully erosion. A field survey documented the number of gullies and cattle access points in riparian forest buffers, grass filters, annual row-cropped fields, pastures in which the cattle were fenced out of the stream, and continuously, rotationally and intensive rotationally grazed pastures in three regions of Iowa. Gully lengths, depths and severely eroding bank areas were measured. Gullies exhibited few significant differences among riparian management practices. The most significant differences were exhibited between conservation and agricultural management practices, an indication that conservation practices could reduce gully erosion. Changes in pasture management from continuous to rotational or intensive rotational grazing showed no reductions in gully erosion. It is important to recognize that more significant differences among riparian management practices were not exhibited because the conservation and alternative grazing practices had recently been established. As gully formation is more impacted by upland than riparian management, gully stabilization might require additional upland conservation practices. The existence of numerous cattle access points in pastures where cattle have full access to the stream also indicates that these could be substantial sources of sediment for streams. Finally, the gully banks were less important sediment contributors to streams than the streambanks. The severely eroding bank areas in streams were six times greater than those in the gullies in the monitored reaches.