Cartographie Des Risques De L’erosion Hydrique Par L’equation Universelle Revisee Des Pertes En Sols, La Teledetection Et Les Sig Dans Le Bassin Versant De L’ourika (Haut Atlas, Maroc)

Covering an area of 576 square kilometers, the Ourika watershed is a sub-watershed of the large Tensift basin, located on the northwest slopes of the Marrakech High Atlas, in mid-west Morocco. This basin of dramatic topography, with sparse vegetation cover and friable substrates, is under increasing human action exacerbated by a variable and changing climate. Its vulnerability to water erosion is quite high, increasing risks of wadi flows with significant sediment loads. The aim of this work was to quantify soil loss in the basin using the Revised Universal Soil Loss Equation (RUSLE) and Geographic Information System. The results showed that the Ourika watershed was subject to strong climatic aggressiveness ranging from 55.22 to 100.57 MJ.mm/ha.h. The average soil erodibility value, K, was 0.48 t.ha.h/ha.MJ.mm, with a standard deviation of 0.28 t.ha.h/ha.MJ.mm. Slopes with values higher than 35% represented 72% of the watershed’s area, with the topographic factor, LS, values ranging from 0.01 to 94.5. The vegetation factor was high throughout the Ourika watershed while C values were higher than 0.5 for 73% of the watershed’s area. The average soil loss obtained in the basin was 380 t/ha/year. These results indicated that 48% of the watershed’s area was subject to a soil loss between 50-400 t/ha/year, and between 400 and 1000 t/ha/year for 30% of the watershed. Soil loss below the tolerance level (<7 t/ha/year) represented only 4% of the watershed area. These findings served in highlighting the significance of erosion in the Ourika watershed.

The Toxicity of Oil-Contaminated Sediments During Bioremediation of a Wetland

ABSTRACT Inorganic nutrients were applied to oiled wetland sediments during an experiment to assess the effect of enhanced bioremediation on petroleum degradation and toxicity reduction. For a period of 6 months after the controlled application of oil to experimental plots, oiled wetland sediment samples were tested for acute toxicity. The three treatments evaluated were an oiled control, inorganic nutrient addition, and inorganic nutrient addition plus an alternate electron acceptor. Sediment toxicity was assessed using Microtox® and amphipod bioassays. The Microtox® 100% Test detected significant sediment toxicity up to 29 days after oil and treatment application while the Solid-Phase Test detected significant sediment toxicity up to Day 15. The Microtox 100%® Test showed elevated toxicity on Day 8 for nutrient plus alternate electron acceptor plots and reduced toxicity on Day 15 for nutrient plots, relative to oiled controls. The observed decrease in sediment toxicity from the Microtox® assays correlated with petroleum losses. Oiled sediments were initially highly toxic to amphipods with average mortality rates ranging from 86 to 92%. Amphipod mortality decreased significantly 71 days after treatment to between 47 and 28%. However, a significant increase in mortality was observed at Day 140 in plots receiving nutrient amendments, possibly due to elevated ammonia levels.

Preliminary Results of Demonstration Capping Project in Hamilton Harbour

Placement of a pilot-scale sand cap occurred in Hamilton Harbour between July 31 and September 20, 1995. The harbour site is at a location where contamination of the bottom sediments is of concern. One ha of contaminated finegrained sediments was covered with 6,600 tonnes of clean sand to an average thickness of 30 cm. A very accurate positioning system was required and placement with adequate accuracy was possible up to wind speeds of about 30 km/h. Initial readings of settlement gauges taken in September 1995 show the ultimate settlement due to primary consolidation to range between 6 and 8 cm. Preliminary results indicate that the suspended material found in the water column during cap placement was almost entirely composed of fines associated with the cap sand. Vibracores showed a sharp interface between the sand cap and sediments with no signs of extensive mixing. Based on multibeam echo sounding results and other supporting data collected at the site, the sand cap was successfully placed in the designated area without any significant sediment disturbance. Some horizontal spreading of sand fines occurred beyond the site boundary.

The Northern Muddy Intertidal: Seasonal Factors Controlling Erosion and Deposition — A Review

This review summarizes the seasonal physical and biological processes which take place on and in the muddy intertidal zone during the year and affect the erosion or deposition of sediment. The main physical processes that are considered are the effects of ice, waves, sediment dewatering, rain, and mud and water temperatures. The biological processes include the growth of benthic diatoms, algal mats, and higher plants as well as the effects of bioturbation, pellet formation, biodeposition, and changes in the intertidal microrelief.In the early spring in northern temperate estuaries, ice break-up is the most significant factor affecting muddy intertidal sedimentation. The ice-roughened intertidal has not yet been affected significantly by either plant or animal activity, and is particularly susceptible to sediment resuspension by waves. During the summer, organic processes dominate the intertidal as organisms feed on, pelletize, and bioturbate the sediments. Plant growth, especially benthic diatoms and algal mats, may stabilize the sediment. The few storms during this season combined with lower rainfall insure that the muddy intertidal only rarely undergoes erosion. In fall, seasonal storms increase while both plant and animal activity begin to slow down. Lower rates of bioturbation make the muddy intertidal more resistant to erosion, but the intensity of the fall storms, and higher rainfall, cause significant sediment scouring. With the onset of winter, ice forms over and on the muddy intertidal, reducing resuspension and erosion. However, significant sediment erosion and transportation occurs during winter thaws, when temporary ice break up occurs. But the effect of ice "armoring" all but eliminates sediment resuspension by waves over the muddy intertidal for most of the coldest winter months.Key words: intertidal zone, erosion, deposition