Erosion-induced CO2 flux of small watersheds

Soil erosion not only results in severe ecological damage, but also interferes with soil organic carbon formation and decomposition, influencing the global green-house effect. However, there is controversy as to whether a typical small watershed presumed as the basic unit of sediment yield acts as a CO2 sink or source. This paper proposes a discriminant equation for the direction of CO2 flux in small watersheds, basing on the concept of Sediment Delivery Ratio (SDR). Using this equation, watersheds can be classified as Sink Watersheds, Source Watersheds, or Transition Watersheds, noting that small watersheds can act either as a CO2 sink or as a CO2 source. A mathematical model for calculating the two discriminant coefficients in the equation is set up to analyze the conditions under which each type of watershed would occur. After assigning the model parameter values at three levels (low, medium, and high), and considering 486 scenarios in total, the influences are examined for turnover rate of the carbon pool, erosion rate, deposition rate, cultivation depth and period. The effect of adopting conservation measures like residue return, contour farming, terracing, and conservation tillage is also analyzed. The results show that Sink Watersheds are more likely to result in conditions of high erosion rate, long cultivation period, high deposition rate, fast carbon pool turnover rate, and small depth of cultivation; otherwise, Source Watersheds would possibly occur. The results also indicate that residue return and conservation tillage are beneficial for CO2 sequestration. (C) 2012 Elsevier B.V. All rights reserved.Geography, PhysicalGeosciences, MultidisciplinarySCI(E)EI0ARTICLE101-11094-9

Impacts of Urbanization on Base Flow and Recharge Rates, Northeastern Illinois: Summary of Year 1 Activities

During year one of a two-year project to investigate the impacts of urbanization on base flow and ground-water recharge rates in northeastern Illinois, three gaged watersheds in urbanized areas of northeastern Illinois, and one watershed located in rural northwestern Illinois, have been selected for study. The gages have a common period of record extending from October 1952 through the present, a period during which the northeastern Illinois watersheds underwent substantial urbanization. Mean daily discharge data from the gages have been analyzed using an automated hydrograph separation technique, and monthly estimates of mean total discharge, base flow, and direct runoff have been calculated. Spearman rank correlation coefficients indicate a stronger correlation between precipitation and total discharge, base flow, and direct runoff in the northeastern Illinois watersheds than in the rural watershed. Smoothed time-series plots of total discharge, base flow, and direct runoff in the urban watersheds are less consistent with precipitation than similar plots constructed from the rural watershed data. The trends indicate that rates of direct runoff have overtaken rates of base flow in two of the three northeastern Illinois watersheds, but in one of these watersheds, this relationship probably reflects the cessation of effluent discharges to the stream. In general, double-mass curve analysis suggests that, relative to the rural watershed, base flow in the urban watersheds has proportionally decreased, and direct runoff has proportionally increased. The trends suggested by the smoothed time-series plots and the double-mass curves are consistent with a conceptual model of the northeastern Illinois watersheds in which sewering and impervious surfaces have reduced infiltration, and thence ground-water recharge and base flow, in the watersheds.Ope

Key landscape and biotic indicators of watersheds sensitivity to forest disturbance identified using remote sensing and historical hydrography data

Water is one of the most critical resources derived from natural systems. While it has long been recognized that forest disturbances like fire influence watershed streamflow characteristics, individual studies have reported conflicting results with some showing streamflow increases postdisturbance and others decreases, while other watersheds are insensitive to even large disturbance events. Characterizing the differences between sensitive (e.g. where streamflow does change postdisturbance) and insensitive watersheds is crucial to anticipating response to future disturbance events. Here, we report on an analysis of a national-scale, gaged watershed database together with high-resolution forest mortality imagery. A simple watershed response model was developed based on the runoff ratio for watersheds (n=73) prior to a major disturbance, detrended for variation in precipitation inputs. Post-disturbance deviations from the expected water yield and streamflow timing from expected (based on observed precipitation) were then analyzed relative to the abiotic and biotic characteristics of the individual watershed and observed extent of forest mortality. The extent of the disturbance was significantly related to change in post-disturbance water yield (p<0.05), and there were several distinctive differences between watersheds exhibiting post-disturbance increases, decreases, and those showing no change in water yield. Highly disturbed, arid watersheds with low soil: water contact time are the most likely to see increases, with the magnitude positively correlated with the extent of disturbance. Watersheds dominated by deciduous forest with low bulk density soils typically show reduced yield post-disturbance. Postdisturbance streamflow timing change was associated with climate, forest type, and soil. Snowy coniferous watersheds were generally insensitive to disturbance, whereas finely textured soils with rapid runoff were sensitive. This is the first national scale investigation of streamflow postdisturbance using fused gage and remotely sensed data at high resolution, and gives important insights that can be used to anticipate changes in streamflow resulting from future disturbances.Ye

On the equivalence between hierarchical segmentations and ultrametric watersheds

We study hierarchical segmentation in the framework of edge-weighted graphs. We define ultrametric watersheds as topological watersheds null on the minima. We prove that there exists a bijection between the set of ultrametric watersheds and the set of hierarchical segmentations. We end this paper by showing how to use the proposed framework in practice in the example of constrained connectivity; in particular it allows to compute such a hierarchy following a classical watershed-based morphological scheme, which provides an efficient algorithm to compute the whole hierarchy.Comment: 19 pages, double-colum

Hydrographs by Single Linear Reservoir Model

A single linear reservoir (SLR) model is presented which provides a simple means for developing runoff hydrographs for small, urban watersheds. The model only requires one parameter, K, which can be estimated from watershed and precipitation characteristics. Several methods for estimating K and the results of testing the model on various watersheds are presented.Waller Creek Working Grou

Evaluation of Continuous Monitoring as a Tool for Municipal Stormwater Management Programs

The purpose of this study is to evaluate the uncertainty attributable to inadequate temporal sampling of stormwater discharge and water quality, and understand its implications for meeting monitoring objectives relevant to municipal separate storm sewer systems (MS4s). A methodology is presented to evaluate uncertainty attributable to inadequate temporal sampling of continuous stormflow and water quality, and a case study demonstrates the application of the methodology to six small urban watersheds (0.8-6.8 km2) and six large rural watersheds (30-16,192 km2) in Virginia. Results indicate the necessity of high-frequency continuous monitoring for accurately capturing multiple monitoring objectives, including illicit discharges, acute toxicity events, and stormflow pollutant concentrations and loads, as compared to traditional methods of sampling. For example, 1-h sampling in small urban watersheds and daily sampling in large rural watersheds would introduce uncertainty in capturing pollutant loads of 3–46% and 10–28%, respectively. Overall, the outcomes from this study highlight how MS4s can leverage continuous monitoring to meet multiple objectives under current and future regulatory environments

The influence of climate and hydrological variables on opposite anomaly in active-layer thickness between Eurasian and North American watersheds

This study not only examined the spatiotemporal variations of active-layer thickness (ALT) in permafrost regions during 1948-2006 over the terrestrial Arctic regions experiencing climate changes, but also identified the associated drivers based on observational data and a simulation conducted by a land surface model (CHANGE). The focus on the ALT extends previous studies that have emphasized ground temperatures in permafrost regions. The Ob, Yenisey, Lena, Yukon, and Mackenzie watersheds are foci of the study. Time series of ALT in Eurasian watersheds showed generally increasing trends, while the increase in ALT in North American watersheds was not significant. However, ALT in the North American watersheds has been negatively anomalous since 1990 when the Arctic air temperature entered into a warming phase. The warming temperatures were not simply expressed to increases in ALT. Since 1990 when the warming increased, the forcing of the ALT by the higher annual thawing index (ATI) in the Mackenzie and Yukon basins has been offset by the combined effects of less insulation caused by thinner snow depth and drier soil during summer. In contrast, the increasing ATI together with thicker snow depth and higher summer soil moisture in the Lena contributed to the increase in ALT. The results imply that the soil thermal and moisture regimes formed in the pre-thaw season(s) provide memory that manifests itself during the summer. The different ALT anomalies between Eurasian and North American watersheds highlight increased importance of the variability of hydrological variables

Constituent Loads and Trends in the Upper Illinois River Watershed and Upper White River Basin: 2015 October through 2018 September

The Arkansas Natural Resources Commission (ANRC) identified two priority hydrologic unit code (HUC) 8 watersheds, the Upper White River Basin (UWRB; HUC 11010001) and the Upper Illinois River Watershed (UIRW; 11110103), in northwest Arkansas. Nonpoint source (NPS) pollution is a concern in these watersheds, such as excess nutrients from agriculture and sediment from changes in land uses. Several NPS pollution projects have been funded by ANRC, including streambank restoration on Sager Creek and best management practices (BMP) to control urban sediment in Fayetteville. The purpose of this project was to collect water samples at 15 sites in the UWRB and UIRW to estimate constituent loads and understand how water quality has been changing in these priority watersheds over time

LANDHOLDER COOPERATION FOR SUSTAINABLE UPLAND WATERSHED MANAGEMENT: A THEORETICAL REVIEW OF THE PROBLEMS AND PROSPECTS

Despite national legislation and substantial donor investments, watershed degradation continues to threaten the sustained economic development and social welfare of millions of citizens in the developing world. Past efforts have largely concentrated on the physical rather than institutional aspects of watersheds, and have often relied on external incentives to coerce or persuade individuals to adopt conservation practices. In contrast to this conventional "physical" perspective, watersheds can be considered as sets of vested interests (and social relations) within a physically defined space. In essence, watersheds are physically defined subsets of rural society. Actors with vested interests within watersheds are interdependent because of water flow across political boundaries. From this perspective, the achievement of watershed management is a question of social relations, and cooperation between individual actors. Though there is growing realization for an expanded role of local, cooperative institutions in watershed management, theories on how such institutions might be identified, evolve or be promoted are limited. Toward this end, this paper examines some of the theoretical aspects of landholder cooperation for watershed management: the socio-political setting of upland watersheds; the physical attributes of watersheds influencing cooperation; the nature of externalities and incentives in watersheds; and the economic and socio-cultural factors affecting the emergence of collective action units. The processes by which collective action groups actually form are also reviewed. The paper concludes with a synthesis of the prospects for landholder cooperation approaches, the appropriate role of policy and a proposed process for promoting such cooperation.Resource /Energy Economics and Policy,