RESUMEN

Suspended fine sediment has a significant impact on freshwater quality variables such as visual clarity (VC). However, freshwater quality is related to the attributes of the catchment sources contributing fine sediment to the stream network. Here, the extent to which an array of sources defined spatially according to erosion process and geological parent material may be discriminated and classified based on sediment-related water quality (SRWQ) attributes that potentially affect VC was examined. Erosion sources were sampled across two New Zealand catchments representing six types of erosion and eight parent materials. Erosion source measurements focused on particle size, organic matter content, and light beam attenuation (which is convertible to VC). The source data were analysed to: 1) evaluate source variability using a combination of Kruskal-Wallis and principal component analysis; 2) reclassify sources using a Random Forest model; and 3) demonstrate how erosion source affects VC for a range of theoretical sediment concentrations (SC) using a simple empirical model. The results indicate that SRWQ attributes show significant variation across erosion sources. The extent to which attributes differed between sources often related to whether there was a strong association between a specific erosion process and parent material. The 19 a priori source classifications were reduced to 5 distinct sources that combined erosion process and parent material (i.e., bank erosion-alluvium; mass movement-ancient volcanics; mass movement-sedimentary; surficial erosion; gully-unconsolidated sandstone). At low SC, the impact of erosion source on VC became most evident ranging from 2.6 to 5.6 m at SC of 5 g m-3. These findings show how catchment sources of sediment, in addition to sediment concentration, influence VC, and highlight the need to consider quality as well as quantity of material supplied to stream networks when planning erosion control.

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RESUMEN

Deforestation in New Zealand has led to increased soil erosion and sediment loads in rivers. Increased suspended fine sediment in water reduces visual clarity for humans and aquatic animals and reduces penetration of photosynthetically available radiation to aquatic plants. To mitigate fine-sediment impacts in rivers, catchment-wide approaches to reducing soil erosion are required. Targeting soil conservation for reducing sediment loads in rivers is possible through existing models; however, relationships between sediment loads and sediment-related attributes of water that affect both ecology and human uses of water are poorly understood. We present methods for relating sediment loads to sediment concentration, visual clarity, and euphotic depth. The methods require upwards of twenty concurrent samples of sediment concentration, visual clarity, and euphotic depth at a river site where discharge is measured continuously. The sediment-related attributes are related to sediment concentration through regressions. When sediment loads are reduced by soil conservation action, percentiles of sediment concentration are necessarily reduced, and the corresponding percentiles of visual clarity and euphotic depth are increased. The approach is demonstrated on the Wairua River in the Northland region of New Zealand. For this river we show that visual clarity would increase relatively by approximately 1.4 times the relative reduction of sediment load. Median visual clarity would increase from 0.75m to 1.25m (making the river more often suitable for swimming) after a sediment load reduction of 50% associated with widespread soil conservation on pastoral land. Likewise euphotic depth would increase relatively by approximately 0.7 times the relative reduction of sediment load, and the median euphotic depth would increase from 1.5m to 2.0m with a 50% sediment load reduction.

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RESUMEN

Obtaining directional reflectance information for vegetation canopies is often an expensive and time-consuming process. We present here a simple approach based on the use of an inexpensive digital camera equipped with a wide-angle lens. By the imaging of a large homogeneous area, a single image captures multiple views of a vegetation canopy. This gives a directional reflectance distribution fully sampled for view direction and free of variations in Sun elevation and azimuth. We determined the radiometric response of the camera sensor CCD's at the focal point and then extended this calibration to the full CCD array by using averaged images of clear blue sky. We evaluated the utility of the system by obtaining directional reflectance distributions of two vegetation targets, grass (Lolium spp) and pine forest (Pinus radiata), for red visible light. The precision of the derived biangular pattern of reflectance was +/-7%.

RESUMEN

A potassitlim-argon dating method applicable to small quantities of volcanic minerals anid glass has been developed and used to determine the ages of North Pacific sediments. Tertiary sedimentation rates range from less than 1.0 millimeter per 10(3) years for deep-sea "red clay" to 1 centimeter per 10: years for calcareotus-siliceous ooze necrer the continent. The potassium-argon ages obtained from different minerals are concordaat, and in samples withl associated fossils, these ages are compatible with the paleontologic evidence.