REGION,LANDSCAPE, AND SCALE EFFECTS ON LAKE SUPERIOR TRIBUTARY WATER QUALITY1

ABSTRACT: In 1998 and 1999, third‐order watersheds in high mature forest (HMF) and low mature forest (LMF) classes were selected along gradients of watershed storage within each of two hydrogeomorphic regions in the Lake Superior Basin to evaluate threshold effects of storage on hydrologic regimes and watershed exports. Differences were detected between regions (North and South Shore) for particulates, nutrients, and pH, with all but silica values higher for South Shore streams (p < 0.05). Mature forest effects were detected for turbidity, nutrients, color, and alkalinity, with higher values in the LMF watersheds, that is, watersheds with less that 50 percent mature forest cover. Dissolved N, ammonium, N:P, organic carbon, and color increased, while suspended solids, turbidity, and dissolved P decreased as a function of storage. Few two‐way interactions were detected between region and mature forest or watershed storage, thus threshold based classification schemes could be used to extrapolate effects across regions. Both regional differences in water quality and those associated with watershed attributes were more common for third‐order streams in the western Lake Superior drainage basin as compared with second‐order streams examined in an earlier study. Use of ecoregions alone as a basis for setting regional water quality criteria would have led to misinterpretation of reference condition and assessment of impacts in the Northern Lakes and Forest Ecoregion.     

Class: an Essential Aspect of Watershed Planning

A study of a watershed planning process in the Cache River Watershed in southern Illinois revealed that class divisions, based on property ownership, underlay key conflicts over land use and decision-making relevant to resource use. A class analysis of the region indicates that the planning process served to endorse and solidify the locally-dominant theory that landownership confers the right to govern. This obscured the class differences between large full-time farmers and small-holders whose livelihood depends on non-farm labor. These two groups generally opposed one another regarding wetland drainage. Their common identity as “property owner” consolidated the power wielded locally by large farmers. It also provided an instrument – the planning document – for state and federal government agencies to enhance their power and to bring resources to the region. The planning process simultaneously ameliorated conflicts between government agencies and the large farmers, while enhancing the agencies’ capacity to reclaim wetlands. In this contradictory manner, the plan promoted the environmental aims of many small-holders, and simultaneously disempowered them as actors in the region’s political economy. An erratum to this article is available at .     

DRY AND WET WEATHER FLOW NUTRIENT LOADS FROM A LOS ANGELES WATERSHED1

Effective watershed management requires an accurate assessment of the pollutant loads from the associated point and nonpoint sources. The importance of wet weather flow (WWF) pollutant loads is well known, but in semi‐arid regions where urbanization is significant the pollutant load in dry weather flow (DWF) may also be important. This research compares the relative contributions of potential contaminants discharged in DWF and WWF from the Ballona Creek Watershed in Los Angeles, California. Models to predict DWF and WWF loads of total suspended solids, biochemical oxygen demand, nitrate‐nitrogen, nitrite‐nitrogen, ammonia‐nitrogen, total Kjeldahl nitrogen, and total phosphorus from the Ballona Creek Watershed for six water years dating from 1991 to 1996 were developed. The contaminants studied were selected based on data availability and their potential importance in the degradation of Ballona Creek and Santa Monica Bay beneficial uses. Wet weather flow was found to contribute approximately 75 percent to 90 percent of the total annual flow volume discharged by the Ballona Creek Watershed. Pollutant loads are also predominantly due to WWF, but during the dry season, DWF is a more significant contributor. Wet weather flow accounts for 67 to 98 percent of the annual load of the constituents studied. During the dry season, however, the portion attributable to DWF increases to greater than 40 percent for all constituents except biochemical oxygen demand and total suspended solids. When individual catchments within the watershed are considered, the DWF pollutant load from the largest catchment is similar to the WWF pollutant load in two other major catchments. This research indicates WWF is the most significant source of nonpoint source pollution load on an annual basis, but management of the effects of the nonpoint source pollutant load should consider the seasonal importance of DWF.     

BASE FLOW TRENDS IN URBANIZING WATERSHEDS OF THE DELAWARE RIVER BASIN1

Rapid land development is raising concern regarding the ability of urbanizing watersheds to sustain adequate base flow during periods of drought. Long term streamflow records from unregulated watersheds of the lower to middle Delaware River basin are examined to evaluate the impact of urbanization and imperviousness on base flow. Trends in annual base flow volumes, seven‐day low flows, and runoff ratios are determined for six urbanizing watersheds and four reference watersheds across three distinct physiographic regions. Hydrograph separation is used to determine annual base flow and stormflow volumes, and nonparametric trend tests are conducted on the resulting time series. Of the watersheds examined, the expected effects of declining base flow volumes and seven‐day low flows and increasing stormflows are seen in only one watershed that is approximately 20 percent impervious and has been subject to a net water export over the past 15 years. Both interbasin transfers and hydrologic mechanisms are invoked to explain these results. The results show that increases in impervious area may not result in measurable reductions in base flow at the watershed scale.     

Mowers versus growers: Riparian buffer management in the Southern Blue Ridge Mountains,USA

Despite long-standing knowledge of the benefits of riparian buffers for mitigating nonpoint source pollution, many streams are unprotected by buffers. Even landowners who understand ecological values of buffers mow riparian vegetation to the streambank. Do trends in rural riparian conditions reflect the development of riparian forest science? What motivates residential riparian management actions? Using high-resolution orthoimagery, we quantified riparian conditions and trends between 1998 and 2015 in the rural upper Little Tennessee River basin in Macon County, North Carolina and explored how landowners view riparian zone management and riparian restoration programs. Buffer composition in 2015 was as follows: no buffer (32.5%), narrow (19.3%), forested (26.7%), shrub (7.2%), and intermediate (7.0%). Relative to 1998, the greatest decrease occurred in the no buffer class (−17.7%, 46 km) and the largest increases occurred in the shrub (+72.5%, 20 km) and narrow (12.6%, 14 km) classes. Forested buffer marginally increased. Semi-structured interview data suggest that landowners prioritize recreational and scenic aspects of riparian buffers over ecological functions such as filtration and bank stabilization. Riparian restoration programs might be made more enticing to non-adopters if outreach language appealed to landowner priorities, design elements demonstrated intentional management, and program managers highlighted areas where ecological goals and landowner values align.     

Targeted Application of Seasonal Load Duration Curves Using Multivariate Analysis in Two Watersheds Flowing Into Lake Houston1

Teague, Aarin, Philip B. Bedient, and Birnur Guven, 2011. Targeted Application of Seasonal Load Duration Curves Using Multivariate Analysis in Two Watersheds Flowing Into Lake Houston. Journal of the American Water Resources Association (JAWRA) 47(3):620‐634. DOI: 10.1111/j.1752‐1688.2011.00529.x Abstract: Water quality is a problem in Lake Houston, the primary source of drinking water for the City of Houston, Texas, due to pollutant loads coming from the influent watersheds, including Spring Creek and Cypress Creek. Statistical analysis of the historic water quality data was developed to understand the source characterization and seasonality of the watershed. Multivariate analysis including principal component, cluster, and discriminant analysis provided a custom seasonal assessment of the watersheds so that loading curves may be targeted for season specific pollutant source characterization. The load duration curves have been analyzed using data collected by the U.S. Geologic Survey with corresponding City of Houston water quality data at the sites to characterize the behavior of the pollutant sources and watersheds. Custom seasons were determined for Spring Creek and Cypress Creek watersheds and pollutant source characterization compared between the seasons and watersheds.     

三峡库区小流域不同土地利用类型“土壤-水体”氮磷含量特征及其相互关系

利用长期田间监测数据,分析了三峡库区典型农业小流域不同土地利用类型土壤、浅层地下水氮磷含量分异特征,剖析了坡面土壤氮磷含量与浅层地下水、坡面地表径流氮磷浓度的相互关系.结果表明梯田的土壤TN平均含量显著(P0.05)高于坡耕地,水田梯田平均含量1.49 g·kg~(-1)最高;旱地坡耕地和桑树套种坡耕地土壤TP平均含量显著高于其它地类;旱地梯田土壤NO_3~--N平均含量最高,离散程度最大.坡面土地利用类型对浅层地下水TN、NO_3~--N浓度影响较大,但对TP浓度影响较小;流域浅层地下水TN浓度与NO_3~--N浓度呈极显著正相关,不同坡面浅层地下水NO_3~--N对TN平均贡献率在67.82%~78.51%之间;浅层地下水TN、NO_3~--N月平均浓度变化规律基本一致,春秋两季农作物施肥后均呈现明显上升趋势.坡面土壤TN平均含量与浅层地下水TN浓度呈显著指数关系,坡面土壤NO_3~--N平均含量与浅层地下水NO_3~--N浓度呈对数关系,但与坡面地表径流TN、NO_3~--N浓度无显著相关性;当坡面地表径流TP浓度0.1 mg·L~(-1)时,坡面土壤TP平均含量与其呈显著线性相关;坡面地表径流与浅层地下水TN、NO_3~--N浓度均呈显著幂函数关系,且NO_3~--N相关性更好.     

梁平县境内高滩河水质的空间分布及其对土地利用方式的响应

以梁平县境内高滩河流域为研究对象,综合应用GIS空间分析、Pearson相关分析和RDA冗余分析方法,研究在子流域尺度上COD、BOD5、氨氮和总磷4种水质要素对土地利用方式的生态响应。结果表明:高滩河流域土地利用类型对水质要素有着重要影响,林地能够改善河道水环境,旱地和城镇村和工矿用地是COD、BOD5和氨氮的主要污染来源,园地、交通运输用地以及水域对污染物的影响较弱,说明农业面源污染和农村居民生活污染是高滩河水质恶化的主要原因。     

HSPF水文水质模型应用研究综述

HSPF(Hydrological Simulation Program-Fortran)模型采用FORTRAN语言编写,以Stanford水文模型为基础,能够综合模拟径流、土壤流失、污染物传输、河道水力等过程,并大量应用于气候变化与土地利用变化的流域水环境效应情景模拟.该模型是半分布式水文水质模型的优秀代表,在国外得到广泛的应用.HSPF模型包括PERLND、IMPLND与RCHRES等3个主要模块,分别实现对透水地段、不透水地段与地表水体的水文水质模拟.总体来看,HSPF模型在国外水文、水质过程模拟,以及涉及气候变化和土地利用影响的情景分析中发挥重要作用,但是国内该模型的应用非常有限.HSPF模型存在的主要问题包括:①模型中某些方案和算法还有改进和完善的空间;②模型对数据输入要求较高,模拟的精度受到空间和属性等数据的限制;③模型只限于均匀混合的河流、水库和一维水体模拟,对于复杂流域或水体的模拟研究,需要与其它模型整合以解决更加综合的问题.目前,针对发展与完善HSPF模型的研究仍在继续,包括模型平台开发、模型功能扩展、模型校正方法研究、参数敏感性研究等方面.随着我国基础数据的积累及共享程度的提高,HSPF模型在我国的应用也将更加广泛.     

基于AnnAGNPS模型四岭水库小流域氮磷流失特征的模拟研究

采用流域尺度的农业非点源污染模型——AnnAGNPS模拟预测苕溪流域四岭水库小流域氮磷流失情况,分析氮磷流失空间分布特征.结果表明,单位面积总氮、总磷流失量在空间分布上有一定的相似性,均呈现出南部大于北部,西部高于东部的特点.以竹林地为主的林地是氮磷输出的最主要来源,其对氮、磷流失总量的贡献率在90%以上.设定不施肥处理(CK)、适地养分管理(SSNM)、当地高产竹农普遍采用的施肥方法(FFP)这3种施肥方式对林地主要植被类型竹林进行情景分析,模拟结果表明,与FFP相比,SSNM在一定程度上减少了氮磷输出,其中溶解性氮和颗粒态氮流失量分别削减8.17%、4.33%,溶性磷和颗粒态磷流失量依次减少9.08%、1.02%.