[Characteristics of seawater nutrients during the occurrence of brown tide in the coastal area of Qinhuangdao, China]. / ç§¦çš‡å²›æµ·åŸŸè¤æ½®ç”Ÿæ¶ˆè¿‡ç¨‹ä¸­è¥å »ç›ç‰¹å¾.

Brown tide that occurred in Qinhuangdao coastal waters from 2009 to 2015 caused huge losses of local marine aquaculture and coastal tourism, with devastating effects on marine ecosystems. Nutrients are important biogenic elements for algal growth. It is of great significance to examine the fluctuation characteristics of nutrients in the process of brown tide to understand the nutritional mechanism of brown tide. Based on the survey data of 30 stations located in Qinhuangdao coastal area from April to June 2014, we analyzed nutrient characteristics during the occurrence of brown tide and its relationship with the population dynamics of Aureococcus anophagefferens. The results showed that the concentration of dissolved nitrogen (DN) in April, May and June 2014 was 265.65, 355.36 and 323.71 µg·L-1 respectively, and the concentration of dissolved organic nitrogen (DON) was 196.98, 242.88 and 177.69 µg·L-1, accounting for 74.2%, 68.3% and 54.9% of DN, respectively. The concentration of dissolved phosphorus (DP) in April, May and June was 15.95, 11.39 and 11.14 µg·L-1 respectively. In April and May, PO43--P accounted for a large proportion of the DP, 74.8% and 80.9% respectively. In June, the proportion of PO43--P in DP fell to 33.8%, and the proportion of dissolved organic phosphorus (DOP) in DP rose to 66.2%. The concentration of SiO32--Si in April, May and June was 70.95, 181.13 and 120.68 µg·L-1, respectively. Except for dissolved inorganic nitrogen (DIN) in May and DON, the distribution of other nutrients had clear characteristics that it decreased gradually from inshore to the offshore, with the relatively high concentrations in river mouth. Through R-factor analysis and nutrient structure analysis, it was found that in April, brown tide was at the development stage, and DOP might be the main driving factor for the growth of A. anophagefferens. In May, brown tide was at the maintenance stage, and water temperature became the main controlling factor. When water temperature was higher than 12 ℃, brown tide could occur. In June, brown tide began to decay, and PO43--P had greater effects on the community structure of phytoplankton. DON was the important factor causing the outbreak of brown tide, with a concentration threshold of 150 µg·L-1 and the ratio DON/DIN being greater than 1.

Effects of electrokinetic treatment of a heavy metal contaminated soil on soil enzyme activities.

There is a growing concern on the potential application of a direct current (DC) electric field to soil for removing contaminants, but little is known about its impact on soil enzyme activities. This study investigated the change of enzyme activities of a heavy metal contaminated soil before and after electrokinetic (EK) treatments at lab-scale and the mechanisms of EK treatment to affect soil enzyme activities were explored. After treatments with 1-3 V cm(-1) of voltage gradient for 420 h, soil pH, electrical conductivity (EC), soil organic carbon, dissolved organic carbon (DOC), soil heavy metal concentration and enzyme activities were analyzed. The results showed that the average removal efficiencies of soil copper were about 65% and 83% without and with pH control of catholyte, respectively, and all the removal efficiencies of cadmium were above 90%. The soil invertase and catalase activities increased and the highest invertase activity was as 170 times as the initial one. The activities of soil urease and acidic phosphatase were lower than the initial ones. Bivariate correlation analyses indicated that the soil invertase and acidic phosphatase activities were significantly correlated with soil pH, EC, and DOC at P<0.05, but the soil urease activities had no correlation with the soil properties. On the other hand, the effects of DC electric current on solution invertase and catalase enzyme protein activities indicated that it had negative effect on solution catalase activity and little effect on solution invertase activity. From the change of invertase and catalase activities in soil and solution, the conclusion can be drawn that the dominant effect mechanism is the change of soil properties by EK treatments.