TIMBER HARVEST IMPACTS ON SMALL HEADWATER STREAM CHANNELS IN THE COAST RANGES OF WASHINGTON1

ABSTRACT: We evaluated changes in channel habitat distributions, particle‐size distributions of bed material, and stream temperatures in a total of 15 first‐or second‐order streams within and nearby four planned commercial timber harvest units prior to and following timber harvest. Four of the 15 stream basins were not harvested, and these streams served as references. Three streams were cut with unthinned riparian buffers; one was cut with a partial buffer; one was cut with a buffer of non‐merchantable trees; and the remaining six basins were clearcut to the channel edge. In the clearcut streams, logging debris covered or buried 98 percent of the channel length to an average depth of 0.94 meters. The slash trapped fine sediment in the channel by inhibiting fluvial transport, and the average percentage of fines increased from 12 percent to 44 percent. The trees along buffered streams served as a fence to keep out logging debris during the first summer following timber harvest. Particle size distributions and habitat distributions in the buffered and reference streams were largely unchanged from the pre‐harvest to post‐harvest surveys. The debris that buried the clearcut streams effectively shaded most of these streams and protected them from temperature increases. These surveys have documented immediate channel changes due to timber harvest, but channel conditions will evolve over time as the slash decays and becomes redistributed and as new vegetation develops on the channel margins.     

CHANGING NEAR‐STREAM LAND USE AND RWER CHANNEL MORPHOLOGY IN THE VENEZUELAN ANDES1

ABSTRACT: The shape of a river channel is linked to surrounding land use through interacting hydrologic and geologic processes. This study analyzes the relationship between the change in near‐stream land use and the shape of the adjacent river channel over time. Three watersheds in the foothills of the Venezuelan Andes that have experienced differing degrees of development were studied to determine river channel width, sinuosity, and position relative to surrounding land use. Change in land use over time was obtained from multiple‐date aerial photographs (1946 and 1980) referenced to 1996 Landsat Thematic Mapper (TM) satellite imagery, and verified by field inspection. Measurements of land‐use type and amount and river channel morphology from the two dates were made using geographic information system (GIS) methods. The three watersheds differed in the extent of deforestation, the location of remaining forested land, and how much land‐use change had already occurred by 1946. Change in river channel morphology was greatest at the most deforested sites. Valley shape and channel constraint also had a discernible effect on change in channel morphology. This study introduces a method for analyzing change in coupled terrestrial‐aquatic systems based on multiple‐date, remotely sensed data and GIS analysis of spatial properties. The results document human impacts on river channels through a comparison of multiple watersheds over a 35‐year time interval.     

ANALYZIIG RIPARIAN SITE CAPABILITY AND MANAGEMENT OPTIONS1

ABSTRACT: Riparian areas interact with aquatic and upland conditions and therefore help determine the degree of functionality (streambank stability, shade, sediment, and debris filtering) found in a watershed or catchment. Thus, conditions in riparian areas exert significant influence on water quality. Physical and biological factors (biophysical determinants) that influence these conditions and determine long‐term site ecology include topographic variables, geology, climate, soil texture, and others. These conditions are further modified by management infrastructure (roads, dikes, etc.). Our objective was to develop a system for evaluating site condition in relation to site capability. Since biophysical determinants and infrastructure interact with water quality, our first task was to acquire data concerning the spatial distribution of biophysical determinants and infrastructure constraints and to import them into a GIS system where they could be managed and processed. To expedite analysis, determinants and infrastructure constraints were placed into a hierarchy capable of isolating various site capability types. The hierarchy was designed to incorporate multiscale effects. Site capability areas are georeferenced in this process thereby enabling efficient monitoring and providing a way to focus management on those areas needing improvement. Study tasks included: (1) landscape characterization and hierarchy selection, (2) field assessment, (3) information management and data mining, and (4) information interpretation and adaptive management. This approach appears to be an effective way to isolate general ripananstandardsmaycon site conditions, to provide indications about water quality, and to create strategies necessary for alleviating water quality problems.     

TRANSPORT AND FATE OF ATRAZINE IN MIDWESTERN RIPARIAN BUFFER STRIPS1

ABSTRACT: The fate of pesticides entering the Riparian Buffer Strips (RBS) has not been well documented. This study compared the transport and fate of atrazine in soil of three‐, five‐, and nine‐year‐old switchgrass (Panicum virgatum L.) RBS to that in adjacent soils cropped to a corn‐soybean rotation or a grass‐alfalfa pasture. Undisturbed soil columns were collected from the RBS and cropped areas within the Bear Creek watershed, near Roland, Iowa. Atrazine and bromide breakthrough curves obtained using intact soil columns under saturated conditions were described by a two‐region, mobile‐immobile transport model. Preferential flow of bromide and atrazine was evident in five‐and nine‐year‐old RBS soil, but there was little difference in transport characteristics between these two RBS soils and the adjacent cropped soils. There was a trend towards an increase in dispersion coefficients between the five‐and nine‐year‐old RBS sites, which suggests an increased degree of preferential flow with increasing RBS age. Despite similar texture and organic C contents, atrazine sorption was significantly greater in RBS soil than the adjacent cropped soil. Cropped soil degraded atrazine faster than the RBS soil. The rapid degradation of atrazine in the corn‐soybean soil adjacent to the five‐year‐old RBS (atrazine half‐life of 19 days) appeared to be due to a larger population of atrazine‐degrading microorganisms. Atrazine‐degrading microorganisms in the corn‐soybean soil were 50,940 cells g^‐1 soil compared with 2,970 cells g^‐4 soil in 5‐year‐old RBS soil which resulted in 60 percent mineralization of [¹⁴C‐UL‐atrazine] in the corn‐soybean soil.     

EVALUATION OF COASTAL PLAIN CONSERVATION BUFFERS USING THE RIPARIAN ECOSYSTEM MANAGEMENT MODEL1

ABSTRACT: Riparian buffers are increasingly important as watershed management tools and are cost‐shared by programs such as Conservation Reserve that are part of the USDA Conservation Buffer Initiative. Riparian buffers as narrow as 4.6m (15ft) are eligible for cost‐share by USDA. The Riparian Ecosystem Management Model (REMM) provides a tool to judge water quality improvement by buffers and to set design criteria for nutrient and sediment load reduction. REMM was used for a Coastal Plain site to simulate 14 different buffers ranging from 4.6 m to 51.8 m (15 to 170 ft) with three different types of vegetation (hardwood trees, pine trees, and perennial grass) with two water and nutrient loads. The load cases were low sediment/low nutrient‐typical of a well managed agricultural field and low sediment/high nutrient‐typical of liquid manure application to perennial forage crops. Simulations showed that the minimum width buffer (4.6 m) was inadequate for control of nutrients under either load case. The minimum width buffer that is eligible for cost share assistance on a field with known water quality problems (10.7 m, 35 ft) was projected to achieve at least 50 percent reduction of N, P, and sediment in the load cases simulated.     

Vegetation Mapping for Change Detection on an Arid-Zone River

A vegetation mapping system for change detection was tested at the Havasu National Wildlife Refuge (HNWR) on the Lower Colorado River. A low-cost, aerial photomosaic of the 4200 ha, study area was constructed utilizing an automated digital camera system, supplemented with oblique photographs to aid in determining species composition and plant heights. Ground-truth plots showed high accuracy in distinguishing native cottonwood (Populus fremontii) and willow (Salix gooddingii) trees from other vegetation on aerial photos. Marsh vegetation (mainly cattails, Typha domengensis) was also easily identified. However, shrubby terrestrial vegetation, consisting of saltcedar (Tamarix ramosissima), arrowweed (Pluchea sericea), and mesquite trees (Prosopis spp.), could not be accurately distinguished from each other and were combined into a single shrub layer on the final vegetation map. The final map took the form of a base, shrub and marsh layer, which was displayed as a Normalized Difference Vegetation Index map from a Landsat Enhanced Thematic Mapper (ETM+) image to show vegetation intensity. Native willow and cottonwood trees were digitized manually on the photomosaic and overlain on the shrub layer in a GIS. By contrast to present, qualitative mapping systems used on the Lower Colorado River, this mapping system provides quantitative information that can be used for accurate change detection. However, better methods to distinguish between saltcedar, mesquite, and arrowweed are needed to map the shrub layer.     

Patterns of Avian Nest Predators and a Brood Parasite Among Restored Riparian Habitats in Agricultural Watersheds

In fragmented edge-dominated landscapes, nest predation and brood parasitism may reduce avian reproductive success and, ultimately, populations of some passerine species. In the fragmented agroecosystem of northwest Mississippi, placement of drop-pipe structures has been used as a restoration technique for abating gully erosion along stream banks. These actions have formed small herbaceous and woody habitat extensions into former agricultural lands. We quantified species relative abundances, species richness, and evenness of avian nest predators and a brood parasite within four categories of constructed habitat resulting from drop-pipe installation. Differences in the abundance of two nest predators, cotton mouse (Peromyscus gossypinus) and blue jay (Cyanocitta cristata), were observed among constructed habitats. However, relative abundances of other predators such as common grackle (Quiscalus quiscula), American crow (Corvus brachyrhynchos), and hispid cotton rat (Sigmodon hispidus), and the obligate brood parasite brown-headed cowbird (Molothrus ater) did not differ among four habitat categories. Although species richness, abundance, and evenness of potential nest predators were generally similar among the constructed habitats, predator species composition varied, suggesting that these habitats supported different predator communities. This difference is important because as each predator species is added to or deleted from the community, variation may occur in the framework of prey search methods, predator strategies, and potentially overall predation pressure. We suggest that land managers using drop-pipes as part of stream restoration projects allow for the development of the constructed habitat with the largest area and greatest vegetative structure.     

Conservation practices in U.S. agriculture and their impact on carbon sequestration

Increase in the use of conservation practices byagriculture in the United States will enhance soilorganic carbon and potentially increase carbonsequestration. This, in turn, will decrease the netemission of carbon dioxide. A number of studies existthat calibrate the contribution of various individual,site-specific conservation practices on changes insoil organic carbon. There is a general absence,however, of a comprehensive effort to measureobjectively the contribution of these practicesincluding conservation tillage, the ConservationReserve Program, and conservation buffer strips to anchange in soil organic carbon. This paper fills thatvoid. After recounting the evolution of the use ofthe various conservation practices, it is estimatedthat organic carbon in the soil in 1998 in the UnitedStates attributable to these practices was about 12.2million metric tons. By 2008, there will be anincrease of about 25%. Given that there is asignificant potential for conservation practices tolead to an increase in carbon sequestration, there area number of policy options that can be pursued.     

洱海西部雨季地表径流氮磷污染特征及受土地利用类型的影响

云南高原平坝区地表径流是湖泊氮、磷的主要来源之一.为研究高原平坝区雨季地表径流氮、磷污染特征及受土地利用类型的影响,调查了洱海西部平坝区雨季的径流氮、磷形态特征,并结合遥感影像空间分析与SPSS等统计分析,从汇水区尺度和缓冲区尺度上研究土地利用类型与地表径流水质的关系.结果表明:①研究区雨季地表径流氮、磷质量浓度较高,ρ（TP）为0.16~0.77 mg/L,且以DIP（溶解性无机磷）为主（63.01%）;ρ（TN）为1.75~14.86 mg/L,且以NO₃--N为主（78.15%）.②汇水区尺度上城镇用地对ρ（TP）影响突出.环湖农村居民点对ρ（NH₄+-N）影响突出,耕地中的高施肥种植区对ρ（TN）、ρ（NO₃--N）影响突出;③在缓冲区500、1 000和2 000 m尺度下,随缓冲区距离增加,土地利用类型对地表径流水质的影响减小.研究显示,城镇用地与高施肥种植区对洱海西部雨季地表径流氮、磷质量浓度影响最大,土地利用类型随缓冲区距离增加对水质的影响逐渐减小.      

基于实用弱化缓冲算子的质量成本灰色 DGM 预测模型

目的运用施以弱化缓冲算子的灰色DGM模型进行质量成本的预测。方法利用积分函数去除区间型数据的不确定性,将其转化为信息无偏的实数。进而分析质量成本和相关指标间的关联程度,并引入二阶弱化缓冲算子对受干扰的成本时间序列进行处理,最后建立质量成本估算预测的灰色DGM模型。结果结合案例与常用的指数函数作比较,结果显示,灰色DGM模型对质量成本的模拟精度更高,模拟误差可由指数模型的1.689%下降至0.118%。结论此模型能有效改善预测精度,具有一定的科学性和合理性。