**4. Some results**

**Figure 25.** Instruments adopted in hydrochemistry analysis of water samples: (a) inductively coupled plasma optical

Electrical conductivity (EC) was measured in the field using a portable EC digital analyzer (HQ14d, Hach, USA). Dissolved oxygen (DO), pH, and water temperature were measured in the field using a multi-parameter digital analyzer (HQ40d, Hach, USA). These parameters

Most chemical analyses were undertaken at the Tiexinqiao experiment base of Nanjing Hydraulic Research Institute, China. All water samples were analyzed within 2 weeks of the

by inductively coupled plasma optical emission spectrometry (ICP-OEC, see **Figure 25a**), and

(**Figure 25b**). All samples were filtered through a 0.45 μm filter before laboratory analysis. The analytical precision of the measurement of ions was determined by calculating the absolute error in ionic balance, and the analytical error was less than ±2% for the anions and between

Soil and plant waters were previously obtained via a vacuum extraction system (LI-2000, LICA, China, **Figure 26a**). The δ18O and δD of water samples determined using a liquid water isotope analyzer (908-0008, LGR, USA, **Figure 26b**) or a liquid–gas water isotope analyzer (L2120–i, Picarro, USA, **Figure 26c**). The dual isotopes of nitrate were prepared by quantita-

by automated extraction and purification using Trace Gas Pre-concentrator unit (IsoPrime

mass spectrometer (GV, IsoPrime, **Figure 26d**). Four international nitrate (USGS-32, USGS-34, USGS-35, and IAEA-N3) and experimental reference materials that were treated identically with the water samples were used to calibrate the measured sample data. Each sample was

, K<sup>+</sup>

) were analyzed by DIONEX ICS-2100 ion chromatography

concentrations were determined by a titration assay on

O) using the denitrifier method followed

−

O product using an isotope ratio

and 0.5‰ for δ18O-NO3

− .

, Ca2+, and Mg2+) were analyzed

were determined immediately after water samples had been collected.

−

date of collection. Concentrations of the major cations (Na+

emission spectrometry (ICP-OEC); (b) ion chromatography (ICS-2100, DIONEX, USA).

**3.3. Analyses of water samples**

274 Hydrology of Artificial and Controlled Experiments

*3.3.1. General parameters*

*3.3.2. Hydrochemistry*

the anions (SO4

*3.3.3. Isotopes*

2−, Cl−

±1.5 and ±4% for the cations. HCO3

site or within 24 h of sample collection.

, NO3 − , and F−

tive bacterial reduction of nitrate to nitrous oxide (N2

Ltd., Cheadle Hulme, Cheadle, UK) and analysis of the N<sup>2</sup>

measured in duplicate and the standard error was 0.3‰ for δ15N-NO3

#### **4.1. Explore the possible paths**

Aimed at ending the scientific stalemate on our watershed experimental studies. Since 1982, the origin of CHL, from classic natural experimental watershed, current pedon lysimeter, and the uncompleted experimental system until the Chuzhou WHES, various possible paths are tried for the emerging of some possible paths ([1–6]), to achieve hopefully the sustainable development of the watershed hydrological experimentation. It is found that the intermediate "mesos" including those of controlled-nature and artificial-nature with constrain and add complexity respectively, show its crucial importance for revealing the individual mechanisms hidden deep. Philosophically, it is "the golden mean between two extremes of character" in Book IV of his Ethics of Aristotle, and the idea of "holding the two extremes and using the middle impartial" in China for the "music" of our watershed experimental studies.

#### **4.2. Explore the subsurface runoff components**

• Direct measurement: After progressively improving, the method of longitudinal zerotension lysimeter (layered trough) is used in catchment scale for the direct measurement of surface and subsurface runoff components ([1, 7]).

• Runoff components: Three components are identified including surface runoff (SR), interflow (IF) from unsaturated zone, and groundwater flow (GF) from saturated zone ([5–8]).

• Water tracing using uranium disequilibrium and other tracers for identification of water

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277

• Neutron activation for rain water, river water, and groundwater [30, 31];

**4.8. The post graduates dissertations achieved by working in and/or main source** 

1993: Carol Kendall. Impact of isotopic heterogeneity in shallow systems on stormflow.

2017: Meng Huang. Using isotopes to evaluate nitrogen sources and transformation processes

1986: Xue-Wen Wang. Study on the cropland evapotranspiration. Nanjing Institute of

1990: Jing Huang. Application of satellite image for the GIUH confluence model. Wuhan

1990: Shu-Qin Xie: Application of satellite imagine for the runoff generation using the SCS

2016: Niu Wang: Output characteristics of non-point source nitrogen and phosphorus load in

2017: Nuo Yang: Study on the tracing of precipitation and runoff in the Hydrohill Experimental

The construction and instrumentation of two typical parts of Chuzhou WHES are reviewed, including the Nandadish, a trial target for the CZEB, which is the type of so-called *controllednatural*, and the Hydrohill, another trial target for CZEB, that is, the type of so-called *artificialnatural*. These trials however all are ongoing, in improving, actually the improving maybe

Kirkby had warned during 2004 that "There has been a movement away from field work and toward an almost complete dependence on modelling" [37], more than 10 years later, Burt and McDonnell (2015) described how field scientists have posed strong and sometimes

Model. Wuhan University, Wuhan Institute of Hydraulic and Electric Engineering.

• Isotope-In-Precipitation Network of China [32];

• Nonpoint source of agricultural area [35, 36].

in Chuzhou hydrological watershed. Hohai University.

University, Wuhan Institute of Hydraulic and Electric Engineering.

Catchment using hydrochemistry and isotopes. Hohai University.

endless as the advancing idea with time seems endless.

• Agricultural water demands [33, 34];

sources [27, 28, 29];

**from CHL**

*PhD dissertation*

*Master dissertation*

**5. Conclusions**

Meteorology.

University of Maryland.

Huashan Basin. Hohai University.


#### **4.3. Explore the generation mechanisms of runoff components**

Eleven mechanisms types have been identified including 4 of SR, 4 of IF, and 3 of GF [13, 14].

#### **4.4. Explore the composition of pre-event water**


#### **4.5. Explore the hydrological puzzles**

It emerges that the unsaturated zone is the gremlin, the key to revealing the hydrologic maze because it is closely related to the runoff composition, hydrological heterogeneity and the double paradox in catchment hydrology and hydrogeochemistry [6, 9, 17].

#### **4.6. On some parameters**


#### **4.7. Basic research for applications**

Preliminary methodological studies for applied hydrological projects

• Unreasonableness of current two-component isotope hydrograph separation [6, 24–26];


#### **4.8. The post graduates dissertations achieved by working in and/or main source from CHL**

#### *PhD dissertation*

• Runoff components: Three components are identified including surface runoff (SR), interflow (IF) from unsaturated zone, and groundwater flow (GF) from saturated zone ([5–8]).

• Amount proportion: From 375 runoff generation-events (1982–1995), the total subsurface contribution accounted for 43% of total runoff, 27% of total runoff was contributed from the

• Patterns of rainfall-runoff process: Four patterns are identified according to the dominated

• Rainfall-runoff correlation diagram: scattering of data points including that of surface runoff very likely is caused by different runoff compositions of different sources of water

Eleven mechanisms types have been identified including 4 of SR, 4 of IF, and 3 of GF [13, 14].

• Occurrence of pre-event water: It is identified that the pre-event ("old") water is frequent

• Process of pre-event water: A 4-year case studies show that the pre-event (old) water within 4 different runoff patterns accounted for 0–36% in surface dominated pattern and up to

It emerges that the unsaturated zone is the gremlin, the key to revealing the hydrologic maze because it is closely related to the runoff composition, hydrological heterogeneity and the

• Optimization selection of discharge measuring structures for the application of WHES [20, 21];

• Nuclear methods for the monitoring of evapotranspiration from land surface [23].

• Unreasonableness of current two-component isotope hydrograph separation [6, 24–26];

60% in subsurface pattern, 47–77% and 21–75% the other patterns [9, 11, 15, 16].

double paradox in catchment hydrology and hydrogeochemistry [6, 9, 17].

• Spatiotemporal distribution of soil water 18O in Hydrohill catchment [9];

• Neutron gauging for vadose water and safety evaluation for users [22];

Preliminary methodological studies for applied hydrological projects

• 131I tracing for infiltration and preferential flow [18, 19];

*direct interflow* from the unsaturated zone [9].

276 Hydrology of Artificial and Controlled Experiments

**4.4. Explore the composition of pre-event water**

occurred even in the SR [11, 15].

**4.5. Explore the hydrological puzzles**

**4.7. Basic research for applications**

**4.6. On some parameters**

runoff components, surface flow or subsurface flow [9–11].

**4.3. Explore the generation mechanisms of runoff components**

rather than simply the rainfall characters or, the curve numbers [9, 12].

1993: Carol Kendall. Impact of isotopic heterogeneity in shallow systems on stormflow. University of Maryland.

2017: Meng Huang. Using isotopes to evaluate nitrogen sources and transformation processes in Chuzhou hydrological watershed. Hohai University.

#### *Master dissertation*

1986: Xue-Wen Wang. Study on the cropland evapotranspiration. Nanjing Institute of Meteorology.

1990: Jing Huang. Application of satellite image for the GIUH confluence model. Wuhan University, Wuhan Institute of Hydraulic and Electric Engineering.

1990: Shu-Qin Xie: Application of satellite imagine for the runoff generation using the SCS Model. Wuhan University, Wuhan Institute of Hydraulic and Electric Engineering.

2016: Niu Wang: Output characteristics of non-point source nitrogen and phosphorus load in Huashan Basin. Hohai University.

2017: Nuo Yang: Study on the tracing of precipitation and runoff in the Hydrohill Experimental Catchment using hydrochemistry and isotopes. Hohai University.

## **5. Conclusions**

The construction and instrumentation of two typical parts of Chuzhou WHES are reviewed, including the Nandadish, a trial target for the CZEB, which is the type of so-called *controllednatural*, and the Hydrohill, another trial target for CZEB, that is, the type of so-called *artificialnatural*. These trials however all are ongoing, in improving, actually the improving maybe endless as the advancing idea with time seems endless.

Kirkby had warned during 2004 that "There has been a movement away from field work and toward an almost complete dependence on modelling" [37], more than 10 years later, Burt and McDonnell (2015) described how field scientists have posed strong and sometimes outrageous hypotheses – approaches so needed "in an era of largely model-only research", "go further and further down the rabbit hole of model uncertainty estimation" [38]. A more unified and holistic theory as called for by Sivapalan [39] is still on the way depending on experimental efforts. Education also needs to be the antecedence, "field work's primary purpose must be to teach our students to be curious, to look, to collect data, to test existing ideas, to develop new hypotheses, including outrageous ones" [38]. Watershed hydrological experimentation seems in the risk to be marginalization however, "it now is indeed an exciting time for hydrologists/experimentalists to rise up for a new era of scientific hydrology" [9].

[2] Gu W-Z. On the domain and approach of the experimental hydrology. In: Nanjing Hydrology Institute, editor. Treatise on Hydrology and Water Resources. Beijing: Water

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[5] Gu W-Z, Liu C-M, Song X-F, Yu J-J, Xia J, Wang Q-J, Lu J-J. Hydrological experimental system and environmental isotope tracing: A review on the occasion of the 50th anniversary of Chinese basin studies and the 20th anniversary of Chuzhou hydrology laboratory. In: Research Basins and Hydrological Planning. A.A. Balkema Publishers; 2004. pp. 11-18

[6] Gu W-Z, Liu J-F, Lu J-J, Frentress J. Current challenges in experimental watershed hydrology. In: Bradley P, editor. Current Perspectives in Contaminant Hydrology and Water Resources Sustainability. Rijeka, Croatia: InTech Publisher; 2013. pp. 299-333. DOI:

[7] Kendall C, Wei-Zu G. Development of isotopically heterogeneous infiltration waters in an artificial catchment in Chuzhou, China. In: Isotope Techniques in Water Resources

[8] Kendall C, McDonnell J, Gu W-Z. A look inside 'black box' hydrograph separation models: A study at the Hydrohill catchment. Hydrological Processes. 2001;**15**:1877-1902 [9] Gu W-Z, Liu J-F, Lin H, Lin J, Liu H-W, Liao A-M, Wang N, Wang W-Z, Ma T, Yang N, Li X-G, Zhuo P, Cai Z. Why hydrological maze: The hydropedological trigger? Review of experiments of Chuzhou Hydrology Laboratory. Vadose Zone Journal; **17**:170174. DOI:

[10] Gu W-Z. Field research on surface water and subsurface water relationships in an artificial experimental catchment. In: Dahlblom P, Lindh G, editor. Interaction between Groundwater

[11] Gu W-Z. Challenge on some rainfall-runoff conceptions traced by environmental isotopes in experimental catchments. In: Tracer Hydrology. Rotterdam. Netherlands:

[12] Hansen DP, Jakeman AJ, Kendall C, Weizu G. Identification of internal dynamics in two experimental catchments. Mathematics and Computers in Simulation. 1997;**43**:367-375

[13] Gu W-Z. Various patterns of basin runoff generation identified by hydrological experiment and water tracing. Journal of Hydraulic Engineering. 1995;**5**:9-17. (in Chinese with

[14] Gu W-Z, Freer J. In: Leibundgut Ch, editor. Tracer Technologies for Hydrological Systems. Proceedings of a Boulder Symposium. IAHS Publ.; 1995. Vol. 229. pp. 265-273

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