Dredged Areas Research Articles

Phytoremediation of Heavy-Metal-Contaminated Soil in a Reclaimed Dredging Area Using Alnus Species

To investigate the possible applications of plants to remediate heavy-metal-contaminated soil, a pilot experiment was performed for four years in a reclaimed dredging area using two Alnus species, i.e., Alnus firma and Alnus hirsuta. In a comparison of phytomass of the two species at two different planting densities, the phytomass of Alnus planted at low density was twice as high as that of Alnus planted at high density after four years. The Alnus species showed active acclimation to the heavy-metal-contaminated soil in a reclaimed dredging area. A. hirsuta showed greater accumulation of phytomass than A. firma, indicating that it is the better candidate for the phytoremediation of heavy-metal-contaminated soils. In the pilot system, Alnus plants took metals up from the soil in the following order; Pb > Zn > Cu > Cr > As > Cd. Uptake rates of heavy metals per individual phytomass was higher for Alnus spp. planted at low density than those planted at high density in the pilot system. Low plant density resulted in higher heavy metal uptake per plant, but the total heavy metal concentration was not different for plants planted at low and high density, suggesting that the plant density effect might not be important with regard to total uptake by plants. The quantity of leached heavy metals below ground was far in excess of that taken up by plants, indicating that an alternative measurement is required for the removal of heavy metals that have leached into ground water and deeper soil. We conclude that Alnus species are potential candidates for phytoremediation of heavy-metal- contaminated surface soil in a reclaimed dredging area.

Relict sand dredging for beach nourishment in the central Tyrrhenian Sea (Italy): effects on benthic assemblages

AbstractThe aim of this study is to analyse the effects in space and time of relict sand‐dredging activities on macrobenthic assemblages, in an area situated offshore Montalto di Castro (central Tyrrhenian Sea, Italy), and to analyse the recolonisation processes of macrobenthos in the dredged areas. The area in question is characterised by relict sand deposits (Holocenic paleo‐beaches), used for beach nourishment along the Latium coast. The effects of sand extraction on benthic assemblages were investigated before, during and after three dredging operations. The sites analysed are located within the dredged areas (inside stations) and in neighbouring, not dredged, areas (outside stations). The results showed that the impact of sand extraction was confined to the dredged stations and to the areas in proximity to the dredged areas. During dredging activities, the structure of benthic assemblages within the impacted stations was characterised by low species richness and diversity. Both the direct removal of sediment and the re‐suspension and consequent deposition of fine sediment affected benthic assemblages of the impacted stations. A few months after the dredgings, a recolonisation process was still observed at all the impacted stations. A gradual recolonisation process was observed at those stations affected by only one dredging, whereas a different recolonisation was observed at those stations affected by two dredgings over time. This study suggests that differences of re‐colonisation processes of benthic assemblages are related to the intensity of dredging operations in terms of dredging frequency.

Mining Sand on the Continental Shelf of the Atlantic and Gulf Coasts of the U.S.

Essentially all marine mining along the East and Gulf coasts of the U.S. is for sand used in beach nourishment projects. The current minimal commercial production of sand and aggregate may increase as conventional, on-shore sources become exhausted or are lost to competing land use. Studies published in the late 1990s document a history of nearly 900 individual episodes of beach nourishment having a total cost in excess of $2 × 109 with several hundred million cubic meters of sand placed along over 645 km (400 mi) of shoreline. As exemplified by studies in Florida, prospecting for sand for use in beach nourishment can begin before site specific needs are identified. A full prospecting starts with assimilation of pertinent literature, local knowledge, and an understanding of the geologic and geomorphic settings in which suitable deposits of sand or aggregate occur. High-resolution seismic profiling follows to outline the three dimensional extent of the sand bodies. Finally, vibratory cores are collected to verify the interpretation of the seismic data and to provide samples for geotechnical, especially granulometric, analyses. The actual method of production often is determined by the local availability of different dredge types. Because the mining of marine sands disturbs meaningful areas of the sea floor, environmental concerns must be considered. While it generally is assumed that dredged areas will be left barren, it is possible to assess the likely rate of recolonization. The disruption of bottom habitat also can affect feeding and spawning areas for fishes and other organisms. Alteration in local currents and wave transformation processes need to be modeled and their consequences assessed.

The Puck Bay as an example of deep dredging unfavorably affecting the aquatic environment

Abstract The presented study is a review of available geochemical data concerning a dredge area in the Puck Bay. It is a small, semi-closed and degraded water body on the Polish Baltic coast. In this region very deep dredging was conducted in the years 1989-95. Five dredge pits were created in the bottom of the bay. Only two of them have been geochemically investigated so far. In the deepwater parts of both the dredge pits organic matter accumulation resulted in sulfate reduction and subsequent hydrogen sulfide production in the sediment, as well as elevated nutrient concentrations in the interstitial waters. Moreover, temporal oxygen deficits in the near bottom waters were observed. Such conditions favor nitrogen and phosphorus release to the water column and potentially enhance the eutrophication. The impact of deep dredging on the chemical conditions in the dredged area seems to be controlled by a complex interplay of the season, phytoplankton biomass production and hydrodynamic conditions. Areas with high biomass production and low water dynamic are probably more vulnerable to environmental degradation due to deep dredging. This implies that some of the dredge pits require different methods of recultivation than others. However the decision if, and with which methods, to remediate dredge pits in the Puck Bay requires successive research including all the pits in all four seasons.

Characteristics of Plant Distribution in the Reclaimed Dredging Area in Gwangyang Bay, Korea

In order to elucidate the mechanisms affecting plant distributions in the reclaimed dredging area in the Gwangyang steelworks, in the Gwangyang Bay, Korea, we examined soil characteristics and plant distributions in four study sites and a control site in the study area. Desalination occurring along a gradient with increasing elevation, resulting in decrease of soil pH, EC, P, K, Cl, Ca, Mg, and salt and an increase in soil T-N, silt, clay contents. From site 1 (the lowest-elevation site) to site 5 (the highest-elevation site), halophytes decreased in abundance and nonhalophytes increased. The dominant species in each site were: Phragmites communis, Limonium tetragonum, and 12 additional species at site 1, Carex pumila, Suaeda japonica, and 15 additional species at site 2, Spergularia marina, Scirpus planiculmis, and 22 additional species at site 3, Miscantus sinensis, Lespedeza bicolor, and 26 additional species at site 4 and Pinus thunberii, Rhododendron mucronulatum, and 39 additional species at site 5, which resembled a naturally-occurring P. thinbergii community. Cluster analysis of the vegetation data matrix grouped the 35 plots into 5 major groups, and cluster analysis using the soil environment data matrix revealed 4 major groups. CCA of the floristic and environmental data matrix showed a positive relationship of SAR, EC, Na, Cl, and Ca, which are related to salt, in the axis and axis, but negative relationships for altitude, organic contents, silt, and clay contents. Notably, plant species in the reclaimed dredging area that were separated along the axis showed strong relationships with factors that related to salt. Long-term exposure to natural rainfall in the reclaimed dredging area changed the soil characteristics, such as salinity. This change in soil characteristics might alter the SAR, which affects plant survival strategies in a given habitat. These results strongly indicated that factors related to salt and elevation play important roles in determining the overall plant distribution in the reclaimed dredging area.

Importance of eelgrass early life history stages in response to oyster aquaculture disturbance

Seagrasses are a critical element in many estuaries and act as drivers of abiotic and biotic processes. One species, Zostera marina L., has been declining globally. A potential contributor to this decline is shellfish aquaculture, although we know little about its impacts. On the US west coast, shellfish aquaculture co-occurs with protected eelgrass habitats. Many aquaculture practices constitute a periodic disturbance, and a key concern is eelgrass recovery. We used observations and experiments to understand how oyster aquaculture practices (i.e. dredging (oysters grown on the bot- tom and harvested mechanically via dredging) and off-bottom longline culture (oysters suspended off the bottom on rope and harvested by hand)) influence eelgrass recovery. Studies of natural recruit- ment showed highest seedling densities in dredged beds (7 seedlings m -2 ) and lowest under long- lines (0.1 seedlings m -2 ). Seed production was highest in dredged beds (295 seeds m -2 ) and lowest in longline beds (52 seeds m -2 ). Seed addition experiments were conducted to understand the effect of oyster aquaculture and adult eelgrass neighbors on seedling germination, growth, and survival. In March 2005, seedling germination was 146% higher in eelgrass removal treatments compared to control plots, with no difference among aquaculture and reference areas. By April 2005, there were no effects of neighbors, but reference areas had greater seed densities (11 seedlings m -2 ) compared to longline areas (3.2 seedlings m -2 ). By August 2005, seedling mortality in longline and reference control plots was 100%. In dredged areas, seedlings in removal plots had greater biomass (0.38 g) than seedlings in control plots (0.14 g). We propose that if eelgrass is to be disturbed by aquaculture, dredge beds may recover more successfully than longline beds.

Mixing Exploitation and Conservation: A Recipe for Disaster

Most governments around the world set conservation policy based on the assumption that resource exploitation and species protection can co-exist in the same place. These policies have led to Orwellian “marine protected areas” that host commercial fishing operations, leading one to wonder who’s protecting whom. A new study reveals the danger of this approach and shows that it’s time to let protection mean protection. For decades, the Dutch government sanctioned mechanical cockle dredging in three-fourths of the intertidal flats of the Wadden Sea—a natural monument protected under two intergovernmental treaties. Before suction dredging began in the 1960s, an estimated 2,000 tons of cockles were hand-harvested from the reserve each year. In 1989, the high-pressure, motor-driven water pumps used in suction dredging sucked up close to 80,000 tons of cockles. By 2004, the Dutch government decided the environmental costs were too great and stopped the practice. Jan van Gils and colleagues investigated the ecological impacts of commercial cockle dredging on intertidal ecosystems by studying a long-distance migrant shorebird that dines principally on cockles, the red knot (Calidris canutus islandica). Up to 50% of the global red knot population uses the Dutch Wadden Sea at some point during their annual cycle. Red knots are exquisitely adapted to their lifestyle. They have a pressure-sensitive bill that senses hard objects buried in the sand and a shell-crushing gizzard to accommodate the birds’ penchant for swallowing their catch whole. They even have a flexible digestive system that minimizes the energy costs of flying up to 16,000 kilometers between their arctic breeding grounds and winter homes in Europe and the tropics—their gizzard expands and contracts to balance daily food intake and energy needs. To determine the effects of dredging on the birds, the authors sampled prey quality and density over 2,800 Wadden Sea sites during the late summer months (late July to early September) for five years starting in 1998. Dredging occurred each year from September to December, immediately after their sample collections. In undredged areas, cockle densities increased by 2.6% each year, and the quality remained stable. In dredged areas, cockle densities remained stable, and their quality (flesh-to-shell ratio) declined by 11.3% each year—paralleling the decline in the quality of the birds’ diet (as measured by droppings). This finding falls in line with evidence that dredging disturbs the silt cockles like to settle in, as well as their feeding conditions—which in turn reduces their quality as a food resource. Based on prey quality and densities, Van Gils et al. predicted the energy intake rate for knots with an average-size gizzard at each site (all sites were pooled into 272 blocks, each with an area of 1 square kilometer), then calculated the percentage of blocks that would not yield sufficient intake rates for knots to avoid starvation. From 1998 to 2002, the percentage of blocks that couldn’t sustain knots increased from 66% to 87%—all attributable to dredging in previously suitable sites. Reduced prey density caused some of this degradation, but most stemmed from declines in both cockle density and quality. The authors caught and color-banded the birds so they could estimate survival rates the following year, and they measured gizzard mass with ultrasonography. As expected, when prey quality declined, birds needed larger gizzards to process the relatively higher proportion of shells in their diet. Their chances of surviving conditions at the Wadden Sea increased as a function of prey quality and gizzard flexibility. Birds that did not return had much smaller gizzards than those that did. Survival rate calculations based on gizzard size and prey quality revealed that if birds could not expand their gizzard and prey quality was low (0.15 grams of flesh per gram of shell), only 47% of arriving birds would avoid starvation. A much greater proportion would survive if their gizzard could expand by at least 1 gram (70% for 1 gram, 88% for 2 grams). These degraded food conditions, the authors conclude, explains why red knot populations have declined by 80% in the Wadden Sea. And increased mortality in the Wadden Sea—which the authors estimate at 58,000 birds over five years—accounts for the 25% decline of red knots across their entire northwest European wintering grounds. Dredging reduced the quality of red knots’ primary food source so drastically that even the birds’ extraordinarily adaptable digestive system could not save them. The authors point out that dredging doesn’t even provide significant economic benefits—only 11 outfits manage 22 fishing boats—yet is “directly responsible” for the widespread decline of a protected shorebird. These findings put the lie to the notion that commercial exploitation is consistent with conservation and underscore the risks of disturbing critical habitat for threatened or endangered species.

Shellfish Dredging Pushes a Flexible Avian Top Predator out of a Marine Protected Area

There is a widespread concern about the direct and indirect effects of industrial fisheries; this concern is particularly pertinent for so-called “marine protected areas” (MPAs), which should be safeguarded by national and international law. The intertidal flats of the Dutch Wadden Sea are a State Nature Monument and are protected under the Ramsar convention and the European Union's Habitat and Birds Directives. Until 2004, the Dutch government granted permission for ~75% of the intertidal flats to be exploited by mechanical dredgers for edible cockles (Cerastoderma edule). Here we show that dredged areas belonged to the limited area of intertidal flats that were of sufficient quality for red knots (Calidris canutus islandica), a long-distance migrant molluscivore specialist, to feed. Dredging led to relatively lower settlement rates of cockles and also reduced their quality (ratio of flesh to shell). From 1998 to 2002, red knots increased gizzard mass to compensate for a gradual loss in shellfish quality, but this compensation was not sufficient and led to decreases in local survival. Therefore, the gradual destruction of the necessary intertidal resources explains both the loss of red knots from the Dutch Wadden Sea and the decline of the European wintering population. This study shows that MPAs that do not provide adequate protection from fishing may fail in their conservation objectives.

Recolonization of defaunated sediments: Fine versus gross sand and dredging versus experimental trays

A field study using experimental trays and small-scale dredging was carried out to: (1) estimate the short-term recovery time of defaunated sediment, (2) evaluate the sediment grain size influence (fine versus gross sand) in the recolonization processes and (3) compare the recolonization in experimental dredged areas and experimental trays. A total of 48 trays (20 × 25 × 7 cm 3) with defaunated fine and gross sand were used and six squares of 1 m 2 were dredged. Spatial and temporal changes of macrobenthic communities in defaunated sediments and dredged areas were analysed using univariate and multivariate statistics, and compared with those in undisturbed natural sediment at the same site. Recolonization of macrobenthos occurred extremely fast indicating the importance of the bedload transport of juveniles and adults, otherwise necessary for many taxa which presented direct development. This quick recolonization of defaunated sediments could have important environmental implications since natural and anthropogenic perturbations may cause partial or total defaunation of marine sediments. Most of the species were able to recolonize both substrates (fine and gross sand) but some species showed clear preferences for one of the sediment types, and the gross sand supported a higher number of species and individuals than fine sand during the short-term recolonization. Multivariate analysis showed that dredged areas (1 m 2) were recolonized in approximately 15 days, recovering similar biotic and abiotic characteristics to the control area (restoration). But in the case of experimental trays, although recovery of abundance and number of species was also quick (30 days), the community structure differed from the control and dredged area, mainly due to the massive recolonization of peracaridean crustaceans in the trays; newly available sediment in the experimental trays acted like patches and allowed more species to colonize than sediment pre-occupied by an established community.

The impact of oyster dredging on the growth of blue cod, Parapercis colias , in Foveaux Strait, New Zealand

Abstract Little is known about the potential impact of habitat modification by bottom fishing gear on the growth of demersal fishes. An analysis is presented for the growth of blue cod in Foveaux Strait, southern New Zealand, based on otoliths of fish captured from two sites in Foveaux Strait in 1999. Each site contained two distinct areas of contrasting benthic habitat complexity, one area of relatively ‘complex’ recovering biogenic reef and another area of relatively ‘simple’ sand and gravel, both previously modified by oyster dredging. Data were fitted to von Bertalanffy growth models for each sex of blue cod from the four areas sampled. No significant difference in growth models was observed for either male or female blue cod compared between the two types of habitat complexity at the eastern site. However, growth differed significantly for both sexes of blue cod from the two habitat types at the western site. Pairwise t‐tests further showed that growth differences only appeared biologically significant for the youngest blue cod sampled (3 years). These fish were, on average, 20% larger in complex biogenic reefs than in simple areas dredged by the oyster fishery. These results suggest that on‐going disturbance and simplification of seabed habitat by the oyster fishery may impede the growth of juvenile blue cod. Areas of recovering biogenic reef may, therefore, provide important habitat for the recruitment and early development of blue cod in Foveaux Strait. Remedial actions may be required to protect some areas of recovering biogenic reef from further damage, and to allow dredged areas sufficient time to recover if the blue cod fishery and related resources are to be managed effectively. Copyright © 2004 John Wiley & Sons, Ltd.

Physical Impacts of Marine Aggregate Dredging on Seabed Resources in Coastal Deposits

A detailed study of the seabed surrounding dredge pits created during the mining of marine aggregate from a small licence off the south coast of the United Kingdom (“Licence Area 122/3”) has been completed. Over 350 km of high-resolution sidescan sonar imagery and 177 sediment samples have been obtained over a study area extending 10 km either side of the dredge zone (representing one full tidal excursion) in order to identify far-field effects on both physical and biological resources of the seabed.The physical results presented here for Area 122/3 clearly show that the physical impact of dredging (without screening) on the seabed is limited to a zone within approximately 300 m downtide of the dredge area. This will generally be within the dredge licence boundary due to operational procedures. There is no evidence of suspended sediments falling to the seabed beyond this zone and causing significant changes, which may be manifested as infilling of small pits by fine sediments, siltation within crevices or development of migratory sand ripples. However, there is some statistical evidence from grab sampling that surface sediments have a greater sand fraction within the excursion track of the plume, than those sediments either side. Despite this small change in seabed particle size distribution, the benthic communities do not exhibit a detectable impact, as reported in the accompanying paper by Newell et al. (2002).Analysis of ADCP backscatter data supports recent evidence for development of a near bed benthic boundary plume some 2–4 metres thick and a few tens of metres wide which extends beyond the limits of the dredge activity. On an extraction licence undertaking cargo screening, this near bed plume may exceed 4.5 kilometres downtide. Such a phenomenon provides a potential mechanism for impacting physical and benthic resources well beyond the dredge licence boundary and requires further investigation.

Characterization of suspended solids in Lake Biwa by measuring their elemental composition of Al, Si, P, S, K, Ca, Ti, Mn, and Fe

We investigated the concentrations of particulate Al, Si, P, S, K, Ca, Ti, Mn, and Fe at various areas of Lake Biwa, such as the limnetic zone in the northern basin, the offshore zone, the dredged area and Akanoi Bay in the southern basin, and reed community areas in the shore. In the wide and deep northern basin, the density of suspended solids was low, and substantial fractions of particulate Si, P, S, and Ca were biogenic matter produced by phytoplankton. In the offshore zone in the narrow and shallow southern basin, the concentration ratios of particulate Si, K, Ca, Ti, and Fe against particulate Al were almost constant throughout the year and were similar to those found in crusts. Therefore, these elements are most likely derived from terrigenous clay matter. In the dredged area where the hypolimnion became anoxic during the stratification period, the concentrations of particulate Fe, Mn, P, S, and Ca increased because of the formation of hydrous Fe and Mn oxides and Fe sulfide. In Akanoi Bay, the ratios of Mn/Al and Fe/Al were high because of the stirring of sediments enriched with Mn and Fe oxides. In the reed community areas, the concentration of suspended solids correlated well with particulate Fe and P, but not with Al or chlorophyll a; therefore these areas seem to be rich in humic organic matter enriched with P and Fe due to microbial activity. Thus, the elemental composition of suspended solids reflects the chemical, biological, and physical processes in the lake and gives us useful indices of the characteristics of the water.

Factors influencing spatial distribution of fish communities on a fringing reef at Mauritius, S.W. Indian Ocean

This paper analyses the spatial patterns of fish communities on a narrow fringing reef of Mauritius and identifies some controlling factors. Canonical Correspondence Analysis revealed that the location in the reef ecosystem, the living coral coverage, and the proximity to a dredged area were the major factors controlling the distribution and abundance of fish species. Two distinct communities were observed across the fringing reef, representing a land-ocean gradient. The low diversity of fish species, and also of invertebrates such as corals, molluscs, and echinoderms is probably a consequence of the narrowness of the fringing reef and of anthropogenic impacts, notably the high pollution by nutrients.

Clay Lumps under Simulated Hydraulic Transport Conditions

Abstract Laboratory experiments with compacted kaolinite-bentonite mixtures indicate that degradation of hydraulically transported clay lumps in a dredge pipeline can be predicted and controlled to some extent. The size reduction of these lumps depends not only on the length of the pipeline but also on the density of the clay being dredged, the plasticity index (PI) of the clay, and the velocity of the dragging slurry in the pipe. A series of graphs shows percent reduction in clay lumps as a function of PI and velocity at three levels of relative compacted density. If the relationships obtained in this study are shown to be valid in the field, this information will be useful in selecting dredging equipment, designing dredged material containment area, and estimating costs. Relatively undisturbed specimens of the in situ clay and simple laboratory tests would provide the necessary information.

Test for Dredged Material Effluent Quality

The quality of effluent discharged from confined dredged material disposal areas is an environmental concern when the sediments to be dredged are contaminated. Sedimentation which occurs during the confined disposal process cannot retain all suspended solids, and both particle-associated and dissolved contaminants may be discharged in the effluent. This study developed a workable and easily applied technique for prediction of the quality of effluent from confined dredged material disposal areas. A modified elutriate test was developed to simulate the physicochemical conditions in confined disposal areas which would affect the release of contaminants. Factorial experiments were conducted to select appropriate test factors for simulating the oxidizing conditions and retention times present in confined disposal areas. The test was found to accurately predict the dissolved concentration of contaminants and the fractions of contaminants associated with the suspended solids in the effluent.

Effects of a Small Suction Dredge on Fishes and Aquatic Invertebrates in Idaho Streams

Abstract A typical dredge (intake diameter 7.6 cm) was operated on four small Idaho streams during July-September 1980 to evaluate some of the effects on aquatic organisms that may result from the use of small suction gold-dredges. Mortality of eggs, sac fry, and fingerlings of several species of trout was monitored, as was that of benthic invertebrates that were entrained through the dredge. The ability of invertebrates to recolonize a dredged area was assessed, and the performance of the dredge was evaluated. Un-eyed cutthroat trout (Salmo clarki) eggs experienced 100% mortality within 1 hour after entrainment. Eyed cutthroat trout eggs showed means of 29% and 35% for 1-hour and 36-hour mortalities, respectively. The 19% mortality of eyed eggs of hatchery rainbow trout (Salmo gairdneri) after 10 days was similar to that of the control group. Hatchery rainbow trout sac fry experienced 83% mortality after 20 days as compared with 9% for the controls. Yolk sacs were detached from approximately 40% of the f...

The effects of oyster shell dredging on an estuarine benthic community

This paper describes the extent and nature of the effects on the benthos of physical disruptions associated with dredging fossil oyster shell. Two dredged areas and one undisturbed control area in Tampa Bay, Florida, were quantitatively sampled before dredging and for one year after dredging. The immediate effects of dredging on the soft-bottom community were reductions in numbers of species (40% loss), densities of macroinfauna (65% loss), and total biomass of invertebrates (90% loss). During months 6–12 after dredging, the analysis used (Mann-Whitney U Test, α=0·05) showed no difference between dredged and control areas in number of species, densities, or biomass (except E 1 ). Community overlap (Czeckanowski's coefficient) between dredged and control areas was reduced directly after dredging, but after 6 months the pre-dredging level of similarity was regained.

Fractionation and mantle heterogeneity in basalts from the Peru-Chile Trench

Five separate exposures of oceanic basalts were dredged in the vicinity of the Peru-Chile Trench between 9° and 27°S latitude. Each dredge is dominated by abundant pillow basalts. Approximately ten of the most unaltered, glassy and fine-grained samples were selected for detailed chemical and petrographic analyses from each dredge area. All basalts recovered in the Peru-Chile Trench are olivine and quartz-normative tholeiites that are believed to have formed at the now extinct Galapagos Rise 30–50 m.y. ago. Detailed chemical analyses of the basalts, including major and selected trace and rare earth elements, indicate that considerable compositional variability exists both within each of the dredged areas as well as between areas. Most of the inherent chemical variability observed within particular basement sections appears consistent with the concept of temporal evolution of magma bodies at a former spreading center by shallow-level fractional crystallization involving primarily plagioclase and olivine. In contrast, important chemical differences between the dredged areas suggest compositional heterogeneities in the mantle source regions. Our results indicate that although shallow-level fractionation has brought about large changes in composition of basalts in each area, compositional trends are distinct and appear to reflect original mantle-derived compositional differences.

Site Use Evaluation for Dredged Material Landfills

The maintenance and development of waterways and harbors in the United States requires the acquisition of almost 3,000 ha of new land annually for the disposal of dredged materials. Presented in this paper is a judgmental site evaluation method that may be used to assess the development potential of such dredged material containment areas. This approach employs judgmental measurements and assessments of site characteristics and use requirements, and feasible site uses are identified as those for which site requirements are most closely matched by available site characteristics. Practical considerations necessitate that feasible uses be evaluated in terms of special development constraints that may exist in the region considered. The illustrative application of this judgmental procedure to four dredged material containment areas in Toledo, Ohio, yielded readily usable information regarding development options that were consistent with both site limitations and long-range plans for the area.