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It can be difficult to decrease the water phosphorus (P) concentration in eutrophic shallow lakes, even if the external P loading is reduced, owing to a high level of internal P loading to surface water from sediment. However, in shallow Lake Suwa, Japan, lake water P concentration has largely decreased in recent years owing to low levels of internal P loading, as well as declining external P loading. We measured water/sediment P and iron (Fe) concentrations and the P release rate from sediment in Lake Suwa, and then compared it with data from the 1970s. In the 1970s, the P concentration throughout the lake water was high during the hypoxic period. Recently, however, the P concentration has increased only in the hypolimnion during the hypoxic period. This suggests that internal P loading from sediment to surface water has largely been suppressed during the hypoxic period in recent years. This may be due to (i) stronger water stratification from global warming, (ii) a greater decrease in the P release rate from the sediment owing to a decline in sediment P concentration from the 1970s to 2020, and (iii) stronger formation of the Fe–P cycle in Lake Suwa recently, compared with that in the 1970s. Our results indicated the need to reduce both external P loading, and internal P loading from sediment to water, for effective water quality improvement in shallow lakes.

Measurement(s) Ice-on and ice-off dates • Lake characteristics Technology Type(s) Observations • Historical records Sample Characteristic - Environment ice-covered lake Sample Characteristic - Location Northern Hemisphere

A novel comprehensive assessment system, consisting of a bioassay and chemical analysis, was developed to quickly evaluate the human health risk posed by toxic chemicals discharged due to natural disasters. To analyze samples quickly, a yeast-two-hybrid assay (Y2H) and GC–MS equipped with an automated identification and quantification system (AIQS-GC) were employed for the bioassay and chemical analysis, respectively. Since the analysis of 1000 substances by AIQS could be finished within two days following the Y2H assay for screening, this method would complete the risk assessment within three days. To confirm the applicability of this method in real environmental samples, we examined it using sediments circulated by Typhoon Hagibis. In one sediment sample, a distinctive response was indicated by the Y2H assay, and relatively high DDT concentration was identified by AIQS-GC in the same sediment. Therefore, using the results obtained from this method, a human health risk assessment of DDT was conducted, which indicated that the risk could be ignored. Additionally, the contamination of PAHs and alkanes was suggested as well. In this study, the pollution risk assessment could be completed within three days. Therefore, to our knowledge, this is the first study to demonstrate an assessment system with a rapid combination method for emergencies. Consequently, it is believed that this type of novel system would be needed in the future due to the increasing number of natural disasters predicted worldwide.