SNOWPACK CHANGES RESULTING FROM TIMBER HARVEST INTERCEPTION,REDISTRIBUTION, AND EVAPORATION1

ABSTRACT: Three processes were examined as causing snowpack changes in forest clearings. Two of the three contribute to increases and one counteracts by reducing snowpack. The two that increase snowpack are redistribution and decreased loss to interception. Snow evaporation from a clearing counteracts snowpack increases. Research has indicated that as vegetation density increases, so too does the loss to interception. As snow in the canopy reaches the limit that the canopy can hold (the threshold amount) evaporation increases. Aerodynamics of the forest canopy were studied as well. As timber is cut, wind patterns are disturbed, creating disruptions in the wind velocity gradient depositing snow in openings. This redistribution leads to an increased snow water equivalent and augments runoff. Snow evaporation was shown to increase proportionally with opening size. Evaporation offsets the water yield gains derived from forest cut. It was found that this offset is inclusive to the measurements of water yield changes in experimental forests. An optimal size of harvest block may be five tree heights in width as suggested by numerous studies.     

不同生境下瘤胃菌丛菌体密度与VFA的关系

在温度，搅动强度和Ｃ／Ｎ经３个生态因素发生梯度变化的情况下，本文在人工瘤胃装置内对瘤胃菌从９５０２３－１进行了连续发酵试验，逐日测定瘤肋细菌数量和ＶＦＡ产量的变化，对两者之间的关系进行了相关和回归分析。     

人─—化学农药──作物病虫害循环灾害与控制途径

立足于目前农业生产上化学农药使用的现状，从“人—化学农药—作物病虫害”系统阐述了化学农药滥用所造成的危害和灾难，并剖析了发生灾难的主要原因．用事实说明了化学农药的利弊；指出使用者的素质是能否科学用药的关键．最后，提出了克服灾害的主要途径。     

When is overfishing underfishing?

The term overfishing is being used with increasing frequency to designate an undesirable level of fisheries exploitation. All too often, however, the term is taken as being self-evident. This article demonstrates that many definitions of overfishing are possible, depending essentially on what objective is being pursued for the fishery. Various possible biological and economic objectives are considered, both in a static and dynamic model of the fishery. Consideration is given to the best utilization of the fish stock from the viewpoint of the individual fishermen as well as that of society. It is shown that overfishing by one definition may be underfishing by another, and it is concluded therefore that anyone using the term overfishing ought, as a matter of course, to define it.     

EFFECTS OF A NORTH CENTRAL WASHINGTON WILDFIRE ON RUNOFF AND SEDIMENT PRODUCTION1

ABSTRACT: Runoff was measured from a 564-ha catchment located on the Entiat Experimental Forest for nine years before a severe wild-fire in 1970 destroyed the mixed conifer vegetation. Runoff records from the Chelan River (2 393 km²) were used as control data for determining changes in water yield during the seven years following the fire. The first post-fire year was a period of transition in which the soil profile retained more water than in previous years and measured runoff was 8.9 cm greater than the predicted value based on pre-fire conditions. Runoff from the burned catchment during subsequent years was much greater than measured values before the fire. Measured minus predicted runoff, based on the pre-fire calibration equation, varied from 10.7 cm during the dry year of 1977 to 47.2 cm during the abnormally wet year of 1972. Flow duration curves indicated that runoff at each percent value after the fire was at least double the comparable pre-fire value. Sediment production increased dramatically after the fire because of increased flow rates, increased overland flow caused by reduced infiltration capacity, and mass soil movement. Sediment yield is beginning to decrease as stream channels become stabilized and vegetation on upper slopes improves infiltration capacity.     

DELIVERY OF SUSPENDED SEDIMENT AND POLLUTANTS FROM NONPOINT SOURCES DURING OVERLAND FLOW1

ABSTRACT: Delivery of sediment and particulate pollutants from diffuse sources is shown to be related to the loss of sediment carrying energy of runoff during the overland flow phase. The loss is caused by the termination of rainfall and by reduction of flow energy during the recession phase of the overland flow hydrograph. It has been demonstrated both by theoretical analyses and experimental measurements that the saturated sediment concentration in overland flow is a function of rainfall erosivity and the runoff flow rate. The hypotheses were verified by field measurements from a small homogeneous watershed.     

THE CONCEPT OF SAFE GROUNDWATER YIELD IN COASTAL AQUIFERS1

The traditional factors used to determine safe yield of a groundwater basin (water supply, economics, water quality and water rights) do not include environmental effects. Because of the unique estuarine ecosystems associated with many coastal aquifers, environmental effects should be included in the determination of the safe yield of these aquifers. Controlled saline-water intrusion should be considered as a management tool in coastal aquifers. Artificial aquifer recharge using treated wastewater may be used to increase the safe yield of a coastal aquifer system while preserving the ecology of the coastal ecosystems.     

STREAMFLOW CHARACTERISTICS OF SMALL WATERSHEDS IN THE BLUE MOUNTAINS OF OREGON1

ABSTRACT: Streamflow data for water years 1978–84 were evaluated to identify streamflow characteristics for 13 small watersheds (0.46–7.00 mi²) in the Blue Mountains of eastern Oregon and to determine differences among grazing intensities and vegetation types. The ranges for mean annual water yields, peak flows, and 7-day low flows for the 13 watersheds were 5.5–28.1 inches, 2.0–34.7 cfsm, and 0.006–0.165 cfsm, respectively. Two classes of vegetation were evaluated: (1) western larch-Douglas-fir (nine watersheds) and (2) other (four watersheds representing fir-spruce, lodgepole pine, ponderosa pine, and mountain meadow). The means for annual peak flows and the slopes of the flow.duration curve were significantly different (p=0.05) for the two vegetation classes; differences in mean annual water yield were marginallysignificant(0.05< p <0.10). After they were adjusted for precipitation, the means for annual water yield, peak flows, and slopes of the flow-duration curve were significantly different for the two vegetation classes; differences in the means for annual 7-day low flows were marginally significant. The western larch-Douglas-fir group had somewhat lower water yields but, overall, tended to have more favorable streamfiow characteristics including lower peak flows, higher low flows, and more evenly distributed flow regimes (flatter flow-duration curves) than the “other” class. Four levels of grazing intensity had no effect on streamilow characteristics.     

ERRORS IN ESTIMATED STREAMFLOW PARAMETERS AND STORAGES FOR UNGAUGED CATCHMENTS1

ABSTRACT: For a set of 81 catchments in southeast Victoria, Australia, predictive equations were developed by least squares regression of the mean and coefficient of variation of annual Streamflow against a variety of rainfall and physiographic parameters. The data were also divided into subsets according to catchment size, subregion, or record length of investigate if the relationships differed significantly between subsets. Only the catchment area and some rainfall statistical parameters were found to be significant. Streamflow parameters predicted by the regression equations were used to estimate storage requirements in ungauged catchments. The influence of errors in the Streamflow parameters on the storage error was examined.     

FOREST HARVESTING AND WATER: THE LAKE STATES EXPERIENCE1

ABSTRACT: The impact of forests on water has_- been a subject of argument for more than a century. It still is; and many studies conform that there is no single right answer in the debate. In the Lake States, clearcutting natural peatlands will not change annual stream-flow nor will it seriously impact water quality if logging is done on frozen soils. However, clearcutting will cause water tables to fluctuate more, ranging from 9 cm higher to 19 cm lower than in peatlands with mature forests. Clearcutting upland hardwoods or conifers will increase annual strearnflow by 9 to 20 cm (a 30- to 80-percent increase). Streamfiow returns to preharvest levels in 12 to 15 years. Annual peak flows are at least doubled and snowmelt flood-peak increases may persist for 15 years. Water quality is not widely impacted, but operating logging equipment in stream channels will cause channel clogging by filamentous algae and loss of fish habitat. Permanent changes from forest to agricultural and urban land use on two-thirds or more of a watershed will significantly increase the size of flood peaks in the 2- to 30-year return interval storm or snowmelt.