Effects of oil spill on seawater infiltration and macrobenthic community in tidal flats

Tidal flat ecosystem simulators are used to clarify the effects of stranded fuel oil on tidal flat ecosystems. Results show that oil spills increase the periphyton on sediment by decreasing the predation stress caused by deposit feeders. About a month after an oil spill, the total population density of the macrobenthos recovered. The oxidation-reduction potential in the surface sediment drops to a negative value after the oil spill, and the anaerobic condition throughout the sediment seems to be responsible for the decrease in the population density of the macrobenthos. The infiltration volume of seawater into the oil-stranded sediment decreases to a third of that without the oil spill. The recovery of infiltration volume after about a month coincides with the recovery of the population density of the macrobenthos. This result suggests that the macrobenthic population is highly dependent on the infiltration of seawater.     

A modular injection system, multilevel sampler, and manifold for tracer tests

Ground water injection and sampling systems were developed for bacterial transport experiments in both homogenous and heterogeneous unconsolidated, surficial aquifers. Two types of injection systems, a large single tank and a dynamic mixing tank, were designed to deliver more than 800 L of amended ground water to the aquifer over 12 hours, without altering the ground water temperature, pH, Eh, or dissolved gas composition. Two types of multilevel samplers (MLSs) were designed and installed. Permanent MLSs performed well for the homogenous surficial aquifer, but their installation procedure promoted vertical mixing, which could obfuscate experimental data obtained from vertically stratified, heterogeneous aquifers. A novel, removable MLS was designed to fit in 2- and 4-inch wells. Expandable O-rings between each sampling port hydraulically isolated each port for sample collection when a nut was tightened at the land surface. A low-cost vacuum manifold system designed to work with both MLS designs used 50 mL centrifuge tubes to efficiently sample 12 MLS ports with one peristaltic pump head. The integrated system was developed and used during four field campaigns over a period of three years. During each campaign, more than 3000 ground water samples were collected in less than one week. This system should prove particularly useful for ground water tracer, injection, and push-pull experiments that require high-frequency and/or high-density sampling.     

The Seto Inland Sea--eutrophic or oligotrophic?

The present water quality conditions in the Seto Inland Sea of Japan are described along with an historical background before and after the measures taken to reduce eutrophication. The directive to reduce phosphorus discharge into this area was very effective, reducing the number of red tides from about 300 cases per year at their peak in 1976 to the recent level of about 100 cases per year, indicating the improvement of seawater quality. However, the hastiness of the measures taken to reduce phosphorous seems to have led to a depletion of dissolved inorganic phosphorus that is an essential nutrient for the growth of phytoplankton. Fishery production has also decreased with the reduction of phosphorus, showing a time lag, and the relationship between them shows a hysteresis-like pattern indicating that the condition of fishery production is currently in a critical stage of collapse. This implies that the phosphorus reduction could have lowered the phytoplankton primary production and also caused a detrimental effect on the fishery production. Noteworthy is the change in the phytoplankton species composition. The dominant species that form red tides have changed from non-harmful diatoms to harmful raphidophytes in the eutrophication process and then finally to harmful/toxic dinoflagellates in the oligotrophication process. This indicates that the measures to reduce phosphorus have caused a change in phytoplankton species composition, thereby altering the food web structure, suggesting that this might be the major cause of the reduction of fishery production. In conclusion, the Seto Inland Sea of Japan is apparently in an oligotrophic condition, and it could be said to be in the state of "cultural oligotrophication" caused by the hasty reduction of phosphorus loading. Dam construction, as another possible cause of the cultural oligotrophication, is also discussed, and evidence relating to the existence of numerous dams in this area is also shown. Stress is placed on the regulation of the level of nutrients and their elemental ratio in the seawater, because these factors are considered to be effective in preventing the generation of harmful algae and in sustaining the fishery production through preservation of the natural environment. A proposal is also described regarding how these factors could be controlled.     

Antifouling herbicides in the coastal waters of western Japan

Residue analyses of some antifouling herbicides (Diuron, Irgarol 1051 and the latter's degradation product M1, which is also known as GS26575), were conducted in waters collected along the coast of western Japan. In total, 142 water samples were collected from fishery harbours (99 sites), marinas (27 sites), and small ports (16 sites) around the Seto Inland Sea, the Kii Peninsula, and Lake Biwa, in August 1999. A urea-based herbicide, Diuron, was positively identified for the first time in Japanese aquatic environments. Diuron was detected in 121 samples (86%) up to a highest concentration of 3.05 microg/l, and was found in 86% of samples from fishery harbours, 89% from marinas, and 75% from ports. Four freshwater samples out of 11 collected at Lake Biwa contained Diuron. Neither Irgarol 1051 nor M1 was found in the lake waters, but both were found in many coastal waters. Irgarol 1051 was found in 84 samples (60%) at a highest concentration of 0.262 microg/l. The concentrations detected were of similar magnitude to those in our previous surveys, taken in 1997 and 1998. M1 was found in 40 samples (28%) up to a highest concentration of 0.080 microg/l. The concentrations detected were generally lower than those found in our previous surveys. The detection frequency among fishery harbours, marinas, and ports was 57-70% for Irgarol 1051 and 25-30% for M1. Ninety-five per cent of the coastal waters in which M1 was detected also contained Irgarol 1051, and 93% of the samples in which Irgarol 1051 was detected also contained Diuron. These results clearly suggest that commercial ship-bottom paints containing both Diuron and Irgarol 1051 are used extensively in the survey area.     

Survey of dioxins in Tokyo Bay bottom sediment

This paper examines dioxin profiles in bottom sediments from Tokyo Bay, Japan using sedimentation dating based on 210Pb measurements and dioxin measurements based on particle size distributions. Dioxin concentrations in surface sediment ranged from 3.2 to 52 pg-TEQ g(-1), with the concentrations in the bay back and central region being higher than those at the front of the bay. The vertical dioxin concentration in sediment core samples showed peak levels from years 1962 to 1980, with the maximum being 110 pg-TEQ g(-1). Principal component analysis indicates that the main source of dioxins in bottom sediment from the back of bay are herbicides such as CNP, while in the front of bay atmospheric deposition due to incineration activities are responsible. Dioxins in bottom sediment were mainly found in the particles <75 microm in size.     

Impacts by heavy-oil spill from the Russian tanker Nakhodka on intertidal ecosystems: recovery of animal community

The impact of a heavy-oil spill from the Nakhodka on an intertidal animal community, and the recovery process of animals from the damage were surveyed from the autumn of 1997 to the spring of 2001. The field study was carried out in the rocky coast of Imago-Ura Cove, located along the Sea of Japan, where clean-up operations for oil pollution had been conducted less intensely than in other polluted areas. We have examined individual number of each animal taxon by continuously placing a quadrat of 5 m width along the entire intertidal zone of the cove. A total of 76 invertebrate taxa including 57 species of mollusks, 10 species of crustaceans were observed during the survey. The number of taxa increased from 1998 to 1999 in areas where the initial oil pollution was intense. Total individual number of benthic animals continued to increase from 1998 to 2000 in the polluted areas. The impact of oil on benthic animals was different from species to species. Some species such as Cellana toreuma and Monodonta labio confusa increased rapidly after the oil spill, whereas other species such as Patelloida saccharina lanx and Septifer virgatus did not show any apparent temporal tendencies. Population size structure of P. saccharina lanx varied greatly among years, however that of M. labio confusa did not. For P. saccharina lanx, recruitment was unsuccessful in 1997, possibly due to the effect of oil pollution. These differences in responses to oil pollution among benthic animals are considered to be caused by the differences in habitat use, susceptibility to heavy-oil, life history and migration ability. The findings suggest that it took at least 2-3 years for the intertidal animal community to recover to its original level after the oil spill.     

Toxicity of 17alpha-ethynylestradiol and norethindrone,constituents of an oral contraceptive pill to the swimming and reproduction of cladoceran Daphnia magna,with special reference to their synergetic effect

Toxicity of 17alpha-ethynylestradiol (EE2) and norethindrone (NOR), constituents of low dosage oral contraceptives, was assessed for the freshwater cladoceran Daphnia magna. Acute toxicity tests showed that 5 ppm of EE2, the highest concentration in this study, never inhibited swimming, whereas NOR inhibited swimming at >3 ppm: 48 h EC(50) for NOR was 6.41 ppm. Chronic toxicity tests were carried out for 25 days by measuring the number of offspring, moltings and sex ratios of neonates at 20, 100 and 500 ppb. EE2>100 ppb significantly decreased the number of offspring to 75% of the control; however, no effect was observed in molting and sex ratios at <500 ppb. NOR did not affect reproduction and sex ratios at <500 ppb. Mixture of EE2 (5.88 ppb) and NOR (94.12 ppb) also significantly decreased the number of offspring to 57% of the control. This result indicates the importance of examining synergetic effects of chemicals in the context of natural environments which face exposure to myriad chemicals.     

2001年日本兵库县北部地震（Mw5．2）的破裂过程及余震活动与静态应力变化比较

2001年日本西南兵库县北部地区发生的一次地震（Mw5．2），一些余震群沿着不同于主震走向的方向发生。首先，我们通过近源强地面运动波形反演对此次事件的破裂过程进行研究。虽然这是一次5级地震，但高密度强震观测台网记录到了高质量的波形数据。为了取得震源反演的精确格林函数，我们通过对小事件实测波形数据的前向模拟来标定地壳结构模型。从0．4至2．0Hz波形数据反演得出的破裂过程似乎较为简单。较大的滑动区位于破裂成核点周围。其次，我们还研究了主震和大余震造成的静态应力变化对后续地震活动的影响。我们利用波形反演得到的主震断层面上的不均匀滑动分布，并考虑到随后大余震的影响，对库仑破裂函数（ACFF）变化进行了计算。因此，我们得出了震源区库仑破裂函数复杂的时空分布。大多数偏离主震断层的余震都发生在正库仑破裂函数区域内。这种结果表明，这些余震强烈地受到由主震和大余震引起的库仑破裂函数的影响。