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991.
P. A. Glancy A. S. Van Denburgh S. M. Born 《Journal of the American Water Resources Association》1972,8(6):1157-1172
The Truckee River heads in the Sierra Nevada at Lake Tahoe, and terminates in Pyramid Lake. During the 1969 water year, flow about 9 miles upstream from the mouth (974,000 acre-ft) was almost four times the long-term average, due mainly to heavy winter rains and spring snowmelt. A short period of low-altitude rainfall produced the highest concentrations of suspended sediment, whereas a much longer subsequent period of snowmelt yielded a much greater total quantity of material. The upper 90 percent of the basin yielded about 260 acre-feet (630,000 tons) of sediment at the Nixon gage, whereas an estimated 2,800 acre-feet (6.8 million tons) was contributed by erosion of about 200 acres of river bank below the gage. Solute content at the gage ranged from 80 to 450 mg/l, dominated by calcium, sodium, and bicarbonate, plus silica in the most dilute snowmelt and chloride in the most concentrated low flows. Solute load totaled about 130,000 tons, of which the principal constituents in Pyramid Lake-sodium plus equivalent bicarbonate and chloride-amounted to almost 40,000 tons. The total solute load during a year of average flow may be 45,000-55,000 tons, including 18,000-22,000 tons of principal lake constituents. 相似文献
992.
华北地区干旱强度的表征形式及其气候变异 总被引:18,自引:4,他引:18
在分析1951-2001年华北地区降水量、气温及蒸发量变化特征的基础上,确定利用月降水量与蒸发量之差的Z指数表征干旱强度.该指数在时间及空问分布上的实际概率与理论概率均很接近,可以较好地表征华北地区干旱强度状况.分析表明,华北地区干旱强度不但具有显著的年代际变化特征,且年际振荡的信号也很强.华北地区四季的干旱强度变化在干旱期的开始时间、干旱持续时间和干旱强度等方面存在一定的差异. 相似文献
993.
湖泊沉积物中磷的形态分析及其释放研究 总被引:29,自引:1,他引:29
本文讨论了湖泊沉积物中磷的各种存在形态,包括:可交换性溶解磷(Pa-t),可溶性磷(Psol),经结合态磷(Pu),铁结合态磷(PFc),以及闭态磷(O-P),另外,还有部份有机磷(Porg),利用分级提取技术,□□□□□□氧)对湖水复磷影响显著,主要是释放PAf和PFc。 相似文献
994.
Peter P. Brussock Arthur V. Brown John C. Dixon 《Journal of the American Water Resources Association》1985,21(5):859-866
A system is proposed to classify running water habitats based on their channel form which can be considered in three different sedimentological settings: a cobble and boulder bed channel, a gravel bed channel, or a sand bed channel. Three physical factors (relief, lithology, and runoff) are selected as state factors that control all other interacting parameters associated with channel form. When these factors are integrated across the conterminous United States, seven distinct stream regions are evident, each representing a most probable succession of channel forms downstream from the headwaters to the mouth. Coupling these different channel profiles with typical biotic community structures usually associated with each of the channel types should result in considerable refinement of the applicability of the River Continuum Concept and other holistic ecosystem models by realizing the nonrandomness of the effects of geo-morphology on stream ecosystems. Thus, this regional perspective of streams should serve to make persons concerned with water resources more aware of the geographical considerations that affect their study areas. 相似文献
995.
Tharacad S. Ramanarayanan Daniel E. Storm Michael D. Smolen 《Journal of the American Water Resources Association》1995,31(3):421-430
ABSTRACT: Delineation of a welihead protection area (WHPA) is the key element in welihead protection programs for drinking water supplies. WHPAs are often delineated under idealized conditions using simple steady-state assumptions, which lead to an incorrect estimation of area and geometry. In this paper, we compare the results from a simple steady-state procedure commonly employed in WHPA delineation with a more complex transient approach that allows consideration of seasonal variation in pumping rates. We also introduce a transient procedure to delineate time-related capture zones using a numerical ground water flow and transport model. Welihead delineation is examined for two municipal wells in Tipton, Oklahoma, using a ten-year time-of-travel criterion. In the steady-state procedure, where we assumed constant pumping rates, we used GPTRAC, a semi-analytical model, and MOC, a numerical model. The capture zone delineated by GPTRAC is comparable in shape with the capture zone delineated by MOC but not in size due to the differences in solution schemes. In the transient procedure, we used MOC and considered the seasonal variation in pumping rates. The capture zones delineated in this procedure were larger than the capture zones delineated by the steady-state procedure using the same model. Further analysis showed that a higher drawdown was predicted in the transient procedure than in the steady-state procedure, which is the reason for larger capture zones. 相似文献
996.
Matthew F. Knowlton Mark V. Hoyer John R. Jones 《Journal of the American Water Resources Association》1984,20(3):397-408
Summer lake survey measurements of total phosphorus (TP) and chlorophyll a (CHLa) from 188 reserviors and natural lakes in the midwest were analyzed to determine the magnitude of major sources of variability. Median variance among replicate samples collected at the same location and time was about 7-8 percent of the mean for both TP and CHLa. Median observed temporal variability within summers was 27 percent of the mean for TP and 45 percent of the mean for CHLa. Median values of year-to-year variance in average TP and CHLa were 22 percent and 31 percent of the mean, respectively. A range of approximately two orders of magnitude was observed among individual estimates of variance in each of these categories. The magnitude of observed temporal variability was affected only slightly by variance among replicate samples on individual days and was weakly correlated with the length of time during which samples were collected from individual lakes. Observed temporal variation was similar between reservoirs and natural lakes when variances were calculated with logtransformed data. The magnitude of temporal and year-to-year variance can severely limit the power of statistical comparisons of TP and CHLa means, but has less effect on establishing relative rankings of lake means, Sources and relative magnitude of variability are important in the use of TP and CHLa data in regression models and in the planning of lake surveys and subsequent data analysis. 相似文献
997.
Zhe Liu Hao Wei Jie Bai Jing Zhang Dongyan Liu Sumei Liu 《Water, Air, & Soil Pollution: Focus》2007,7(6):607-623
A 3-D biological model was developed and coupled to a hydrodynamic model, i.e., Princeton Ocean Model, to simulate the seasonal
variation and budget of dissolved inorganic nitrogen, phosphate, and silicate in Jiaozhou Bay. The modeled nutrients distribution
pattern is consistent with observation. Silicate, the most important limiting element for phytoplankton growth, is characterized
by consumption in spring, increase in summer and autumn, and accumulation in winter, whereas dissolved inorganic nitrogen
and phosphorous have increasing trend with low rates in spring, due to excessive river loads. Phytoplankton plays an important
role in nutrient renewal by photosynthesis and respiration processes. During an annual cycle, 7.83 × 103 t N, 0.28 × 103 t P, and 3.93 × 103 t Si are transported to the bay’s outer sea, i.e., the Yellow Sea, suggesting that Jiaozhou Bay is a significant source of
nutrients for the Yellow Sea. The spatial distribution of nutrients is characterized by vertically homogeneous profiles, with
high concentration inside the bay and low concentration toward the bay channel. These features are mainly governed by strong
turbulent mixing, fluvial influx, water exchange rate, and Yellow Sea water intrusion. Numerical experiments suggest that
the government should pay enough attention to proper layout of sewage drainage. 相似文献
998.
近48年来广东春旱的变化 总被引:8,自引:0,他引:8
为了更好地做好广东省春旱的短期气候预测,用EOF分析、小波分析和相关分析等方法,对近48年(1957—2004年)来广东受害较大的春旱(2—5月)的变化规律及其成因进行了研究。结果表明,广东春季降水具有明显的2~3年和4年左右的年际变化以及36年左右的年代际变化。春旱主要发生在1960—1971年和1994—2004年,20世纪90年代以来严重春旱的发生呈增多趋势。1976/1977年之后,阶段性的冷与涝、暖与旱相对应,而其之前的这一相关性则不好。广东春季降水的异常主要与极涡、西太平副热带高压的强弱、亚洲大陆及其以北的500hPa环流异常有关。异常春早年500hPa同期环流场上极涡较强,偏向鄂霍次克海,亚洲大陆及其以北为明显的正高度距平,冷空气的活动偏强,副高偏东偏弱。850hpa流场上广东到南海盛行偏北气流,不利于降水的产生。异常涝年的情况则基本相反。 相似文献
999.
M. Deblonde R. de Graaff F. Brom 《Journal of Agricultural and Environmental Ethics》2007,20(1):99-118
Nowadays many debates are going on that relate to the agricultural and food sector. It looks as if present technological and
organizational developments within the agricultural and food sector are badly geared to societal needs and expectations. In
this article we briefly present a toolkit for moral communication within the food chain. This toolkit is developed as part
of a European research project. Next, we discuss what such a toolkit can bring about, given the characteristics of the present
day agricultural and food sector and its wider context. We defend that the toolkit can be seen as one of the mechanisms that
can help enterprises in the agricultural and food sector to be accountable. It should, however, be complemented with other
mechanisms, first, to empower the wider public and, second, to stimulate a dialogue, on a more equal footing, between public
authorities, citizens, and economic actors. 相似文献
1000.
An attempt at population analysis of sables in the Ural–Ob region of the species range was made with the use of vast biological material (craniometry, 1909 specimens; ecological structure, 2157 specimens; and coat color, 439169 pelts). Population groups in the region were mainly described on the basis of morphological, geographic, historical, and ecological criteria. Seven spatially separated population groups were found, which were named after the main rivers of their habitats: the Tavda–Konda–Sos'va, Dem'yanka, Salym–Yugan, Agan–Vakh, Kazym–Nazym, Nadym–Kunovat, and Pur–Taz groups. They distinctly differed from one another with respect to cranial measurements, coat color, and some structural demographic parameters. In some cases, morphological differences reached the subspecies level. The data obtained make it possible to revise the pattern of geographic variation within the species range. 相似文献