CARBON CONTENT OF SEDIMENTS OF SMALL RESERVOIRS1

ABSTRACT: Carbon content was measured in sediments deposited in 58 small reservoirs across the United States. Reservoirs varied from 0.2 to 4000 km2 in surface area. The carbon content of sediment ranged from 0.3 to 5.6 percent, with a mean of 1.9 ± 1.1 percent. No significant differences between the soil and sediment carbon content were found using a paired t-test or ANOVA. The carbon content of sediments in reservoirs was similar to the carbon content of surface soils (0–10 cm) in the watershed, except in watersheds with shrub or steppe (desert) vegetation. Based on the sediment accumulation rates measured in each reservoir, the calculated organic carbon accumulation rates among reservoirs ranged from 26 to 3700 gC m^-2yr^-1, with a mean of 675 ± 739 gC m^-2yr^-1. The carbon content and accumulation rates were highest in sediments from grassland watersheds. High variability was found in carbon content, carbon accumulation, and sediment accumulation rates due to individual watershed and reservoir characteristics rather than to any broad physiographic patterns. The carbon accumulation rates in these reservoir sediments indicate that reservoir sediments could be a significant sink for organic carbon.     

Relationship of Land‐Use/Land‐Cover Patterns and Surface‐Water Quality in The Mullica River Basin1

Abstract: We describe relationships between pH, specific conductance, calcium, magnesium, chloride, sulfate, nitrogen, and phosphorus and land‐use patterns in the Mullica River basin, a major New Jersey Pinelands watershed, and determine the thresholds at which significant changes in water quality occur. Nonpoint sources are the main contributors of pollutants to surface waters in the basin. Using multiple regression and water‐quality data for 25 stream sites, we determine the percentage of variation in the water‐quality data explained by urban land and upland agriculture and evaluate whether the proximity of these land uses influences water‐quality/land‐use relationships. We use a second, independently collected water‐quality dataset to validate the statistical models. The multiple‐regression results indicate that water‐quality degradation in the study area is associated with basin‐wide upland land uses, which are generally good predictors of water‐quality conditions, and that both urban land and upland agriculture must be included in models to more fully describe the relationship between watershed disturbance and water quality. Including the proximity of land uses did not improve the relationship between land use and water quality. Ten‐percent altered‐land cover in a basin represents the threshold at which a significant deviation from reference‐site water‐quality conditions occurs in the Mullica River basin.     

黄土丘陵区小流域土地覆被变化对径流产沙量的影响

为探讨黄土丘陵区小流域土地覆被变化特征及其对流域径流产沙量的影响,以黄土丘陵区吕二沟、罗玉沟及其嵌套流域(桥子沟)等3个小流域为研究对象,运用数理统计学、配对流域等方法定量分析了3个小流域不同研究时段内土地覆被变化对径流产沙量的影响.结果表明,1982~2004年间,林地面积以1.07%/a的速率快速递增是吕二沟流域土地覆被变化的最明显特征,而罗玉沟流域在国家坡改梯工程影响下,坡耕地面积大幅减少,1986~1995年间约73%坡耕地转化为梯田;结合配对流域法可知,土地覆被变化是导致流域径流和产沙减少的主要原因,在相同降雨条件下,径流深、泥沙量分别减少43.76%和35.23%.流域年径流模数与年降水量和流域森林覆被率均呈指数关系,流域森林覆被率增加5%,径流模数可减少18.43%~37.58%.     

Oregon Hydrologic Landscapes: A Classification Framework1

Wigington, Parker J., Jr., Scott G. Leibowitz, Randy L. Comeleo, and Joseph L. Ebersole, 2012. Oregon Hydrologic Landscapes: A Classification Framework. Journal of the American Water Resources Association (JAWRA) 1‐20. DOI: 10.1111/jawr.12009 Abstract: There is a growing need for hydrologic classification systems that can provide a basis for broad‐scale assessments of the hydrologic functions of landscapes and watersheds and their responses to stressors such as climate change. We developed a hydrologic landscape (HL) classification approach that describes factors of climate‐watershed systems that control the hydrologic characteristics of watersheds. Our assessment units are incremental watersheds (i.e., headwater watersheds or areas draining directly into stream reaches). Major components of the classification include indices of annual climate, climate seasonality, aquifer permeability, terrain, and soil permeability. To evaluate the usefulness of our approach, we identified 30 rivers with long‐term streamflow‐gauging records and without major diversions and impoundments. We used statistical clustering to group the streams based on the shapes of their annual hydrographs. Comparison of the streamflow clusters and HL distributions within river basin clusters shows that the Oregon HL approach has the ability to provide insights about the expected hydrologic behavior of HLs and larger river basins. The Oregon HL approach has potential to be a useful framework for comparing hydrologic attributes of streams and rivers in the Pacific Northwest.     

小流域水质评价方法对比研究

为分析小流域水质评价方法的准确度和适应度,以小安溪流域2017年和2018年的监测数据为基础,利用单因子评价法、综合指数评价法、内梅罗污染指数法和加拿大水质指数法进行水质评价,利用等标水质分析的思想对比了四种方法的评价准确度.评价结果显示:单因子评价法更适合评价水质分布较均匀的流域,内梅罗污染指数法要更为客观一些,加拿...