Doctoral Thesis

Long-term Variation in Water and Nutrient Balances for
Last 8 Decades in a Rapid Urbanized Coastal Catchment
Influenced by Complex Anthropogenic Activities

Kunyang Wang

Division of Integrated Arts and Sciences
Graduate School of Integrated Arts and Sciences
Hiroshima University

March 2022

Abstract

Land use is a key factor affecting water balance, which in turn affects water
resource availability. Increasing urbanization has altered water balances inriver catchments. Although urbanization impacts have been widely
investigated, most studies focus on changes in land use area only, thepercent imperviousness of urban was usually ignored. Furthermore, thewater balance in upstream forest zones is known to be affected byvegetation community types, phenology, and forest density. Since the1980s, climate change and new forest management policies have yielded
unprecedented modifications in forest ecosystems. Meanwhile, most semienclosed seas have experienced serious eutrophication owing to highnutrient loading from rivers during periods of rapid population growth. InJapan, the coastal areas of some megacities (e.g., Tokyo and Osaka)
experienced significant economic growth during the 1960s–1970s. Thus, it
is important to know the amount of nutrient loading during this period totake timely and appropriate coastal environmental measures forconservation. Unfortunately, achieving such goals is challenging because
water quality data in Asian countries are usually limited or unavailable
during early historic years. The water quality records in Asian countries
usually started late and it is difficult to obtain data from early ages. In thisstudy, streamflow, and nutrient loading in the Yamato River catchment (anurbanized coastal catchment in Asia) was reconstructed using the Soil andWater Assessment

Tool.

This

study

comprehensively

analyzed

anthropologic factors, including land use change, density change in urbaniareas, economic policy impact on forest growth, fertilizer usage change,
construction of wastewater treatment facilities, and climate change
exacerbated by human factors in long-term catchment-scale. Results
showed that (1) the impact of percent imperviousness of urban on surface
runoff and baseflows is sometimes more important than area changes in acatchment area, especially those characterized by rapid urbanization; (2)forest evapotranspiration has increased in recent decades and young orwell-managed forests were more affected; (3) in cases where population
growth occurs before urbanization processes, the nutrient load tends to bevery high; (4) various anthropological activities including the improvementof wastewater treatment equipment effects on nutrient loading are stronger
than climate change effects on long-term scales.

iiContents澳
Abstract..............................................................................................................................................i澳Contents .......................................................................................................................................... iii澳Figure legend ..................................................................................................................................vii澳
Table legend .....................................................................................................................................ix澳
Chapter 1 Introduction ......................................................................................................................1澳
1.1澳

Background .......................................................................................................................1澳

1.1.1 Urbanization and Water Balance......................................................................................2澳
1.1.2 Forest Growth and Evapotranspiration ............................................................................3澳
1.1.3 Long-term Nutrients Loading Assessment.......................................................................5澳
1.1.4 Eutrophication Nutrients and Anthropological Impact ....................................................7澳
1.2澳

Objective ...........................................................................................................................9澳

1.3澳

Research & Technical flow .............................................................................................10澳

1.4澳

Reference ........................................................................................................................10澳

Chapter 2 Materials and Methodology............................................................................................17澳
2.1 Study Area.............................................................................................................................17澳
2.2 Soil and Water Assessment Tool ...........................................................................................21澳
2.3 Model Efficiency Evaluation ................................................................................................24澳
2.4 Reference ..............................................................................................................................25澳
Chapter 3 Urban and Catchment Water Balance influenced by urbanization process considered withincreased PIU ..................................................................................................................................28澳
3.1 Background and Objective....................................................................................................28澳
3.2 Material and Method.............................................................................................................30澳
3.2.1 General Data Processing ................................................................................................30澳
iii

3.2.2 PIU Data Processing ......................................................................................................31澳
3.2.3 Model Implementation ...................................................................................................33澳
3.3.4 Statistical and Analytical Methods.................................................................................35澳
3.3 Results & Discussion ............................................................................................................37澳
3.3.1 Urban PIU Changes .......................................................................................................37澳
3.3.2 Evaluation of the Main Parameters and the Simulation Accuracy .................................37澳
3.3.3 Urban Water Balance to Urban PIU ...............................................................................39澳
3.3.4 The Impact of Increasing PIU on the Water Balance of Catchment...............................44澳
3.4 Conclusions...........................................................................................................................46澳
3.5 Reference ..............................................................................................................................46澳
Chapter 4 Forest and Catchment Water Balance Influenced by Anthropologic Factors and ClimateChange ............................................................................................................................................50澳
4.1 Background and Objective....................................................................................................50澳
4.2 Material and Method.............................................................................................................51澳
4.2.1 Forest Regions in Study Area.........................................................................................51澳
4.2.2 General Data Processing ................................................................................................52澳
4.2.3 Forest Data Processing...................................................................................................53澳
4.2.4 Model Implementation ...................................................................................................55澳
4.2.5 Canopy Evaporation, Transpiration, and Soil Evaporation Estimations ........................57澳
4.3 Results...................................................................................................................................58澳
4.3.1 Model Performance........................................................................................................58澳
4.3.2 Forest Growth Impacts on Water Balance......................................................................61澳
4.4 Discussion .............................................................................................................................63澳
4.4.1 Model Improvements and Uncertainty...........................................................................63澳
4.4.2 Forest growth and its catchment-scale impacts..............................................................66澳
iv

4.5 Conclusions...........................................................................................................................68澳
4.6 Reference ..............................................................................................................................68澳
Chapter 5 Reconstruction of Long-term Nitrogen Loading during the Past Severe-Contamination
Period ..............................................................................................................................................72澳
5.1 Background and Objective....................................................................................................72澳
5.2 Material and Method.............................................................................................................72澳
5.2.1 Data collection and model construction .........................................................................72澳
5.2.2 Simulating anthropogenic factor scenarios ....................................................................75澳
5.3 Results...................................................................................................................................76澳
5.3.1 Model assessment and uncertainty analysis ...................................................................76澳
5.3.2 Estimate of long-term nitrogen transport .......................................................................77澳
5.3.3 Impacts of population growth and WWTP on nitrogen loading.....................................78澳
5.3.4 Impacts of agricultural policy and precipitation on nitrogen loading ............................79澳
5.4 Discussion & conclusion.......................................................................................................80澳
5.5 Reference ..............................................................................................................................82澳
Chapter 6 Long-term Phosphorus Balance Changes influenced by Anthropologic Factors ...........85澳
6.1 Background and Objective....................................................................................................85澳
6.2 Material and method .............................................................................................................86澳
6.3 Results...................................................................................................................................87澳
6.3.1 Model assessment and uncertainty analysis ...................................................................87澳
6.3.2 Estimation of long-term phosphorus transport...............................................................88澳
6.4 Discussion & conclusion.......................................................................................................92澳
6.6 Reference ..............................................................................................................................94澳
Chapter 7 Discussion and conclusion .............................................................................................97澳
7.1 The impact of anthropogenic activities on long-term water balance.....................................97澳v

7.2 The impact of anthropogenic activities on long-term nutrient balance.................................99澳
7.3 Reference ............................................................................................................................103澳
Acknowledgments.........................................................................................................................106澳
Publications List during Doctoral Course .....................................................................................107澳

vi

Figure legend
FIGURE 1 RESEARCH & TECHNICAL FLOW OF THIS STUDY .......................................................................10FIGURE 2 OVERVIEW OF THE YAMATO RIVER CATCHMENT .....................................................................17FIGURE 3 LAND USE AREA CHANGE IN THE YAMATO RIVER CATCHMENT ................................................ 18
FIGURE 4 SOIL DISTRIBUTION IN THE YAMATO RIVER CATCHMENT .........................................................19FIGURE 5 MONTHLY PRECIPITATION CHANGES IN LAST 80-YEARS ...........................................................20FIGURE 6 URBAN REGIONS CLASSIFY ...................................................................................................... 32
FIGURE 7 URBANIZATION SCENARIOS ...................................................................................................... 35
FIGURE 8 PIU CHANGES IN THE YAMATO RIVER CATCHMENT ................................................................. 37
FIGURE 9 OBSERVED AND SIMULATED STREAMFLOW DURING THE PAST FIVE DECADES IN KASHIWARA
HYDROLOGIC STATION ..................................................................................................................... 38

FIGURE 10 SURFACE RUNOFF CHANGE CAUSED BY THE INCREASED PIU ON (A) MONTHLY VALIDATIONPERIOD AND (B) DAILY SIMULATION SCENARIO 1~3 ........................................................................ 40FIGURE 11 ANNUAL URBAN WATER BALANCE RATIO CHANGE CAUSED BY INCREASED PIU IN SCENARIOSSIMULATIONS .................................................................................................................................. 42FIGURE 12 URBAN SURFACE RUNOFF DISCHARGE (USURQ) AND URBAN RAINWATER DISCHARGE FROMRAINWATER DRAINAGE SYSTEM (RWQ) IN SCENARIOS SIMULATIONS .............................................43FIGURE 13 AVERAGE ANNUAL WATER BALANCE RATIO PER DECADE (1970S-2010S) ...............................44FIGURE 14 ANNUAL CATCHMENT WATER BALANCE RATIO IN SCENARIOS SIMULATIONS...........................45FIGURE 15 FOREST REGIONS IN STUDY AREA ...........................................................................................51FIGURE 16 FITTED LEAF AREA INDEX (LAI) GROWTH CURVES FOR THE FOREST REGIONS ........................58FIGURE 17 COMPARISON OF MODIS ET AND SWAT ET DATA DURING THE GLOBAL CALIBRATION PERIOD....................................................................................................................................................... 60FIGURE 18 MONTHLY MEAN STREAMFLOW SIMULATIONS AT EACH HYDROLOGICAL STATION (FOREST)...60FIGURE 19 CHANGES IN FOREST EVAPOTRANSPIRATION (ET) PROCESSES DUE TO FOREST GROWTH ........62vii

FIGURE 20 SURFACE RUNOFF AND BASEFLOW FOR EACH REGION DURING DIFFERENT PERIODS ............... 64FIGURE 21 OBSERVED AND SIMULATED TN FLUXES AT ORIONO (A) AND KASHIWARA (B) HYDROLOGICALSTATIONS IN THE PERIOD 1970–2018............................................................................................... 76

FIGURE 22 YEARLY TN LOADING OF THE STUDIED CATCHMENT AND WASTEWATER DISCHARGE .............78
FIGURE 23 YEARLY NON-POINT SOURCE TN LOADING FROM STUDY CATCHMENT ...................................80
FIGURE 24 RELATIONSHIP BETWEEN NON-POINT SOURCE TN LOADING AND PRECIPITATION ...................80
FIGURE 25 YEARLY CATCHMENT TP LOADING, NON-POINT SOURCE TP LOADING AND WASTEWATERDISCHARGE FROM STUDY CATCHMENT ............................................................................................88

FIGURE 26 CATCHMENT-SCALE PHOSPHORUS BUDGET IN LAST 8 DECADES .............................................90
FIGURE 27 AGRONOMIC PHOSPHORUS BUDGET IN LAST 8 DECADES ........................................................ 91
FIGURE 28 PRINCIPAL COMPONENT ANALYSIS RESULTS ON LONG-TERM IMPACT OF ANTHROPOGENICPOLICIES ON NUTRIENT LOADING .................................................................................................. 101

viii

Table legend
TABLE 1 PREVIOUS STUDIES ON LONG-TERM NUTRIENT LOADING EVALUATION ........................................5TABLE 2 PERCENT IMPERVIOUSNESS OF DIRECTLY CONNECTED TO THE DRAINAGE SYSTEM (PIC) IN THISSTUDY DURING EACH PERIOD (UNIT: %) .......................................................................................... 33TABLE 3 SWAT SCENARIOS: CALIBRATION, VALIDATION, AND SIMULATION SCENARIOS ..........................35TABLE 4 MODEL ACCURACY EVALUATION OF WHOLE CATCHMENT..........................................................39TABLE 5 ANNUAL SURFACE RUNOFF RATIO IN THREE URBAN REGIONS ....................................................41TABLE 6 CALIBRATED PLANT DATABASE PARAMETERS............................................................................ 54TABLE 7 MODEL EFFICIENCY COEFFICIENTS (FOREST WATER BALANCE) .................................................59
TABLE 8 CANOPY DENSITY PARAMETERS AND FITTED CANMX VALUES DURING DIFFERENT PERIODS ....65
TABLE 9 PERFORMANCE OF THE CALIBRATED NITROGEN FLUX IN THE SWAT MODEL .............................76TABLE 10 PERFORMANCE OF THE CALIBRATED PHOSPHORUS FLUX IN THE SWAT MODEL.......................88TABLE 11 TN LOADING CAUSED BY URBANIZATION AND POPULATION GROWTH REPORTED IN PREVIOUS
STUDIES WORLDWIDE ...................................................................................................................... 99ix