4. Conclusions

(Figure 11a). The unsaturated soil zone has been recognized as "the most complicated

3. Reactor III. The third zone is the saturated zone, extending from the groundwater table down to bedrock, including the capillary fringe (Figure 11). There are two general cases for

Figure 11. (a) Functioning of the CZEB, (b) the schematic "reactors" corresponding to CZEB, and (c) general monitoring

1. Reactor I includes hydrometeorological and ecohydrological processes, reactor II includes hydropedological and hydroecological processes, while the reactor III is more exclusive for

3. Each reactor has its own lateral flux exchanges Lex via the CZEB lateral boundaries (Figure 11b). Reactor I has vertical fluxes exchange Vex with atmosphere via the upper boundary of CZEB while reactor III has Vex with deep aquifers and/or deep circulation via the bottom boundary of CZEB (Figure 11b). Fluxes include all material and immaterial components. 4. Reactors are closely coupled within the boundaries of CZEB. There are flux exchanges Wex (blue arrows in Figure 11b) between reactors I and II and, and between II and III within the CZEB. There are flux channels MC (Figure 11b) through I to III for materials, and flux

2. There is an overall trend of decreasing operation rates from reactors I to III.

channels IMC (Figure 11b) through I to III for nonmaterials.

biomaterials on the planet" [14, 27].

246 Hydrology of Artificial and Controlled Experiments

3.4.2.3. Functioning of reactors

parameters for the CZEB.

hydrogeological processes.

CZEB, phreatic groundwater and confined aquifers.

The hydrological experimentation is actually a dialog with the hydrological nature; however, such a dialog seems not easy, it depends mostly on the adequate method of questioning, i.e., on the designed objects and the keys for it. If we designate the first phase of basin study until ca. the middle twentieth century as the foundational stage and the second phase during/after the IHD since 1965 as the developmental stage, which has been going on for more than five decades up to now, a third phase of renovation seems ready to come out inevitably. Facing with this transition of the experimental watershed hydrology, it appears worth to have a fundamental rethinking on our previous methods of dialog, which seems challenged, sometimes having a successful beginning but becoming increasingly inadapted with the dynamic nature. The inherent defects of the field basin studies have been summarized from Chinese decades' experiences in their basin studies with zigzagging process especially those based on the concept of experimental basin system.

Facing with the hydrological complex dynamic system, a framework of watershed hydrological experimental system (WHES) is suggested, which is raised from both the viewpoints of the general system theory based on the paralleled concepts of the ancient Chinese and the Western, and that of the Middle-ground perspective philosophy on the Middle Way ("golden mean") that is also based on the paralleled concepts. Thus, the WHES is defined as an experimental system that is designed to dialog with the complex watershed hydrological nature, to drive opening of various doors of their black boxes aimed at revealing mechanisms hidden deep in the system.

Three strategies have been developed for the WHES: the strategy of constrain complexity for the natural watershed, which is the downward or top-down approach, the strategy of add complexity for the physical model, which is the upward or bottom-up approach, and the strategy of manipulation for the operation of both ways including the so-called artificial-natural and the controllednatural. In fact the suggested WHES is trying to reconcile the deterministic and stochastic extremes, "opposites are complementary" as the basic Chinese philosophy have revealed.

As a trial of it, the Chuzhou WHES is ongoing. Most problems involved in WHES fall in the category of complex systems with some degree of organization. It includes three levels with both complexity and randomness from high to low, and an extension part: (1) high level: composed by pure natural EBs, defined as the "macros" of WHES, (2) intermediate level: composed by intermediate chain, the "mesos" of WHES, it includes both the controlled-natural entities and the artificial-natural entities, (3) low level: composed by pure artificial chain, the "micros" of WHES, and (4) extension of WHES: it is the laboratory for geochemical processes by water tracing for all entities. It is the "nucleus" of WHES, an essential condition of it. Different organization levels of WHES will have different treatments; only the "micro" level of WHES is linear, a small part of the "meso" level close to the "micro" level is quasilinear or linearizable, and these two parts can be treated by Newtonian dynamic methods. Most of the intermediate chain, the "meso" level of WHES, should be treated by nonlinear dynamic methods.

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Trying to improve the current idea on the research platform of hydrological experimental basin (EB), which is widely used since IHD of 1965, a CZEB within the Chuzhou WHES was suggested. The boundary and functioning of it are discussed including its interfaces and three compartment zones: aboveground vegetation zone, belowground unsaturated zone including root zone and deeper vadose zone, and the saturated aquifer zone. These zones can be treated as three coupled feed-through reactors. Such CZEB is a watershed hydrological experimental study in the CZ observatory framework.
