Special attention has been paid to three types of processes, that is, source process, removal process and internal cycling. Through the summary of literatures, the mechanisms of typical cycling processes, such as sediment release and denitrification, were discussed. The comparison of contributions of different cycling processes was listed as well. Moreover, the main research approaches of experiment and modeling in this field were well summarized and compared, raising a general framework for the study of nutrients cycling in lakes. With the purpose of looking into the cycling of nutrients, different approaches should be combined together. For example, mechanism models and observation for the mass balance of nutrients, then the microcosmic experiments for the impact factors of cycling processes. It is an efficient way to explore the cycling of nutrients in lakes.

The Present experiments have studied the influences of signaled shock on lymphoid tissue in mice, Male and female Swiss and Balb/c mice of various ages were stressed by signaled shock for 7 days (24 min per session). The animals were then killed for determination of total body weight and the weights of the thymus, spleen and axillary lymph nodes. In addition, the total number of cells in the thymus and the proportion of lymphoid cells in the bone marrow cell population was defined. The results show that stress-induced involution of the thymus was generally more pronounced in older animals, while for the spleen was the opposite. Involution of the thymus was higher in males than in females, but there were no-marked differences between the sexes in the response of the spleen. In general Swiss mice was more sensitive to stress than Balb/c mice. However, for the involution induced by stress on lymph nodes there were not a clear trend with age, sex or strain. In male and female mice of all ages and both strains, stress led to statistically significant reductions in the absolute of cells inside the thymus and spleen and in the proportion of lymphoid cells in the bone marrow.