Connectivity of post-fire runoff and sediment from nested hillslopes and watersheds

Wildfire increases the potential connectivity of runoff and sediment throughout watersheds due to greater bare soil, runoff and erosion as compared to pre-fire conditions. This research examines the connectivity of post-fire runoff and sediment from hillslopes (< 1.5 ha; n = 31) and catchments (< 1000 ha; n = 10) within two watersheds (< 1500 ha) burned by the 2012 High Park Fire in northcentral Colorado, USA. Our objectives were to: (1) identify sources and quantify magnitudes of post-fire runoff and erosion at nested hillslopes and watersheds for two rain storms with varied duration, intensity and antecedent precipitation; and (2) assess the factors affecting the magnitude and connectivity of runoff and sediment across spatial scales for these two rain storms. The two summer storms that are the focus of this research occurred during the third summer after burning. The first storm had low intensity rainfall over 11 hours (return interval <1–2 years), whereas the second event had high intensity rainfall over 1 hour (return interval <1–10 years). The lower intensity storm was preceded by high antecedent rainfall and led to low hillslope sediment yields and channel incision at most locations, whereas the high intensity storm led to infiltration-excess overland flow, high sediment yields, in-stream sediment deposition and channel substrate fining. For both storms, hillslope-to-stream sediment delivery ratios and area-normalised cross-sectional channel change increased with the percent of catchment that burned at high severity. For the high intensity storm, hillslope-to-stream sediment delivery ratios decreased with unconfined channel length (%). The findings quantify post-fire connectivity and sediment delivery from hillslopes and streams, and highlight how different types of storms can cause varying magnitues and spatial patterns of sediment transport and deposition from hillslopes through stream channel networks.     

The effect of lithology on valley width,terrace distribution,and bedload provenance in a tectonically stable catchment with flat‐lying stratigraphy

How rock resistance or erodibility affects fluvial landforms and processes is an outstanding question in geomorphology that has recently garnered attention owing to the recognition that the erosion rates of bedrock channels largely set the pace of landscape evolution. In this work, we evaluate valley width, terrace distribution, and bedload provenance in terms of reach scale variation in lithology in the study reach and discuss the implications for landscape evolution in a catchment with relatively flat‐lying stratigraphy and very little uplift. A reach of the Buffalo National River in Arkansas was partitioned into lithologic reaches and the mechanical and chemical resistance of the main lithologies making up the catchment was measured. Valley width and the spatial distribution of terraces were compared among the different lithologic reaches. The surface grain size and provenance of coarse (2–90 mm) sediment of both modern gravel bars and older terrace deposits that make up the former bedload were measured and defined. The results demonstrate a strong impact of lithology upon valley width, terrace distribution, and bedload provenance and therefore, upon landscape evolution processes. Channel down‐cutting through different lithologies creates variable patterns of resistance across catchments and continents. Particularly in post‐tectonic and non‐tectonic landscapes, the variation in resistance that arises from the exhumation of different rocks in channel longitudinal profiles can impact local base levels, initiating responses that can be propagated through channel networks. The rate at which that response is transmitted through channels is potentially amplified and/or mitigated by differences between the resistance of channel beds and bedload sediment loads. In the study reach, variation in lithologic resistance influences the prevalence of lateral and vertical processes, thus producing a spatial pattern of terraces that reflects rock type rather than climate, regional base level change, or hydrologic variability. Copyright © 2017 John Wiley & Sons, Ltd.     

Algal δ15N values detect a wastewater effluent plume in nearshore and offshore surface waters and three-dimensionally model the plume across a coral reef on Maui, Hawai'i, USA

The coral reef at Kahekili, Maui is located ~300 m south of the Lahaina Wastewater Reclamation Facility which uses four Class V injection wells to dispose of 3-5 million gallons of wastewater effluent daily. Prior research documented that the wastewater effluent percolates into the nearshore region of Kahekili. To determine if the wastewater effluent was detectable in the surface waters offshore, we used algal bioassays from the nearshore region to 100 m offshore and throughout the water column from the surface to the benthos. These algal bioassays documented that significantly more wastewater effluent was detected in the surface rather than the benthic waters and allowed us to generate a three-dimensional model of the wastewater plume in the Kahekili coastal region. Samples located over freshwater seeps had the highest δ(15)N values (~30-35‰) and the effluent was detected in surface samples 500 m south and 100 m offshore of the freshwater seeps (~8-11‰).     

High accuracy measurements of water storage change in Mining Lake 111, Germany

Several pressure sensors were deployed in a small lake to determine its storage change. It could be shown that a deep enough deployment and an averaging over a time interval of 1 hour and 5 measuring points allowed for a measurement of 1 or 2 kg/m² (i.e. 2 mm of water column) of changes in the storage on the scale of the lake size. This accuracy for the lake storage could not be achieved by other methods, especially if conditions were difficult, e.g. snowfall, or in cases when precipitation was small. Finally, the pressure measurement - originally intended to roughly determine the water level - turned out to be a direct measurement of water mass in the lake, which was the proper magnitude for exchanges between atmosphere and lake. Hence the measurement of lake storage could become an interesting approach even for meteorological measurements, such as precipitation and evaporation on a water surface.     

Loose threads: The translocal making of public space policy in Hanoi

This paper analyses the recent developments in public space policy in the city of Hanoi, Vietnam. It has three aims. The first is to look at a potentially progressive urban policy in contrast to most work on ‘policies in motion’ that has primarily been concerned with neoliberal policies. The second is to put the process of public space policymaking in Hanoi in historical and cultural perspective. We therefore describe public space in Hanoi as historically constituted by different layers of meaning and physical urban patterns. The paper's third aim is to analyse the translocal connections involved in a policy that is still in the making, and therefore characterized by a series of ‘loose threads’. We show how different types of connections – policy mobility, topological relations and inter‐referencing – relate Hanoi to multiple locales elsewhere. The conclusion reflects on the ‘politics of reception’ showing how analysing a policy in the making develops a critical analysis of policies in motion.     

Airborne Laser-Induced Fluorescence (LIF) Light Detection and Ranging (LiDAR) for the Quantification of Dissolved Organic Matter Concentration in Natural Waters

Analysis of dissolved organic matter (DOM) concentration and composition is essential to quantifying biological and chemical oxygen demand and atmosphere?Cocean heat flux exchange in natural waters. However, manual water sampling is costly and time consuming over large areas. The purpose of this research was to analyze the applicability of airborne laser-induced fluorescence light detection and ranging (LiDAR) for the detection of DOM in estuarine ecosystems impacted by agriculture. A fluorescence LiDAR system (Airborne Marine) (FLS-AM) was used to assess the DOM concentration of the Annapolis River and Basin, Nova Scotia, Canada, as well as three rivers and their estuaries in Prince Edward Island, Canada. Two FLS-AM flight missions were conducted in the summers of 2008 and 2009 and the resulting datasets were compared with spectral fluorescence signature (SFS DOM) and dissolved organic carbon (DOC) analysis of in situ water samples. Significant positive correlations were found at five of seven sites between the FLS-AM DOM and SFS DOM relationship which indicates that the FLS-AM sensor is a good surrogate for traditional sample collection of DOM data in estuaries in this region. Positive correlations were also found at all sites between FLS-AM DOM values and DOC. FLS-AM DOM patterns show that DOM values are significantly higher in rivers and estuaries that drain watersheds which are heavily impacted by agricultural practices. The results of this study show that the FLS-AM can be used efficiently as a general indicator for how estuaries are affected by runoff from agricultural watersheds in real time and thus reduce the requirement for traditional water sample collection and laboratory analysis methods.     

Evolution of anthropogenic and biomass burning emissions of air pollutants at global and regional scales during the 1980�C2010 period

Several different inventories of global and regional anthropogenic and biomass burning emissions are assessed for the 1980?C2010 period. The species considered in this study are carbon monoxide, nitrogen oxides, sulfur dioxide and black carbon. The inventories considered include the ACCMIP historical emissions developed in support of the simulations for the IPCC AR5 assessment. Emissions for 2005 and 2010 from the Representative Concentration Pathways (RCPs) are also included. Large discrepancies between the global and regional emissions are identified, which shows that there is still no consensus on the best estimates for surface emissions of atmospheric compounds. At the global scale, anthropogenic emissions of CO, NO_x and SO₂ show the best agreement for most years, although agreement does not necessarily mean that uncertainty is low. The agreement is low for BC emissions, particularly in the period prior to 2000. The best consensus is for NO_x emissions for all periods and all regions, except for China, where emissions in 1980 and 1990 need to be better defined. Emissions of CO need better quantification in the USA and India for all periods; in Central Europe, the evolution of emissions during the past two decades needs to be better determined. The agreement between the different SO₂ emissions datasets is rather good for the USA, but better quantification is needed elsewhere, particularly for Central Europe, India and China. The comparisons performed in this study show that the use of RCP8.5 for the extension of the ACCMIP inventory beyond 2000 is reasonable, until more global or regional estimates become available. Concerning biomass burning emissions, most inventories agree within 50?C80%, depending on the year and season. The large differences between biomass burning inventories are due to differences in the estimates of burned areas from the different available products, as well as in the amount of biomass burned.