生態系服務與核算模型評估農地與資源鏈結

Abstract

農業生態環境的維護對於農地永續管理至為重要。農地蘊含豐富的土壤資源，不僅提供作物生產，對碳、水、養分等關鍵生態循環系統也發揮重要的功能。然而，農地資源也受到都市化發展的壓力威脅，許多農地被轉作工商業土地利用，這顯示了農業的生態環境效益被低估。為解決這種低估問題，生態系服務（ES）概念提供了全面性的框架來評估農業為社會帶來的多元福祉，除了傳統經濟所重視之糧食供給服務，農業生態系透過土壤資源還提供碳固存、水質淨化和養分保留等過程關鍵的調節服務。因此，從生態系服務觀點評估農地能更全面地理解其真實價值，進而更永續的管理農地。 儘管生態系服務概念具備此等潛力，土壤資源所提供的更廣泛調節服務卻缺乏系統性的量化與貨幣化；過去生態系服務評估並未廣泛整合到國家環境經濟核算框架中，例如環境經濟核算系統–生態系核算（SEEA-EA）框架；農業生態系服務的空間分布也較少繪製，這項資訊對於地方農民與決策者在永續農地資源管理決策上至為重要；此外，傳統評估常多關注於正面服務，卻忽略了農業的負面影響，即生態系負服務（EDS），這對於農業永續性的平衡視角至關重要。因此，系統性評估土壤資源提供的農地生態系服務，分析生態系服務的地圖，並與國家核算框架接軌，同時涵蓋正面效益與負面服務，是本文擬解決之重要挑戰。 為此，本論文進行農地土壤的生態系服務評估研究，以土壤資源為基礎選擇生態系服務指標，選擇其最終服務，避免傳統雙重計算問題，以呈現農地對人類福祉而非作物產量的貢獻。分析指標包含：作物供給、土壤碳儲存、水量調節、營養鹽（氮與磷）保留、以及水土保持等，並回答以下主要問題：（一）如何在生態系核算框架下量化和評估農業生態系服務，以促進永續土壤管理；（二）稻米生產安全與土壤相關之生態系服務之間存在哪些協同作用，以及如何轉化為有效的政策。（三）如何在農業景觀中全面評估正面與負面服務，並以水-能源-食物鏈結（WEF nexus）視角提升永續性。 （一）以生態系核算架構量化農地土壤資源的生態系服務 本研究首先綜合現地調查資料與InVEST模型，建立一套空間明確、具物理與貨幣量化的評估方法，並依據SEEA-EA框架、以台灣雲林縣為研究區域，編製生態系核算帳戶，包含生態系範圍、生態系條件狀態、生態系服務的物理與貨幣流量、以及生態系資產價值等帳戶。研究結果顯示，平原農地生態系占了當地將近一半的範圍（47 %），其土壤條件狀態具有高pH值、陽離子交換能力、有機質與鉀、銅、鋅含量等特性。在生態系服務帳戶中，繪製了當地生態系服務空間差異，並比較現地調查與模型評估結果，無論是作物供給或碳儲存服務，現地資料皆提供較高精度的空間分布資訊。平原耕地在作物供給、水量調節、營養鹽（氮與磷）保留等調節服務表現優異，在碳儲存與水土保持則略遜其他土地利用。在貨幣估值方面，以模型估算每公頃年均生態系服務價值為40,472美元，現地資料則為45,853美元，相差約13%。其中調節服務占比97%，供給服務僅3%。其中當地的平原農地每年對水量調節與營養鹽保留的貢獻分別高達約4億與12億美元。在整體生態系資產方面，總值估計為1,281億美元，其中平原農地貢獻了高達約908億美元。整體而言，本研究透過繪製生態系服務地圖，凸顯了土壤調節功能的關鍵價值及其對平原農地的重要性，有助於支持農地在土地利用規劃的價值與地方實施永續土壤管理。同時，本研究也凸顯生態系核算帳戶的編製成果的重要性，支持將生態系服務納入台灣的環境與經濟帳。 （二）稻米供給安全與土壤相關生態系服務的關聯研究 本研究聚焦於彰化地區，以稻米產量、生態系的調節服務、以及土壤屬性間的關係為核心，探討生態系服務與糧食安全間的關聯。其關聯研究為透過相關性分析與雙變量莫蘭指數（bivariate Moran’s I），來評估生產與調節服務間、土壤屬性與調節服務之間的關聯性；最後並計算整體的生態系服務價值，透過經濟價值評估計算整體的生態系服務，並利用局部的莫蘭指數（Anselin Local Moran’s I）進行生態系服務聚類與異常分析，以提供地區永續農業策略。研究結果顯示，當地每公頃耕地的生態系服務年均貢獻為：稻米供給服務9.99 ± 4.08公噸、碳儲存服務34.86 ± 8.80公噸、水量調節服務3,659 ± 749立方公尺、營養鹽保留5.10 ± 4.43公斤氮與2.00 ± 1.03公斤磷、水土保持66.52 ± 46.09公噸等。稻米供給與多數調節服務呈正相關，顯示健康土壤功能對穩定糧食生產的重要性。水量調節與營養鹽保留間亦有中至高度正相關，可能受流域特性影響。粗質土壤具有排水限制，則有利於提升碳儲存服務表現。生態系服務的每年價值約為每公頃37,678.81美元，以碳儲存服務與營養鹽保留貢獻最大。聚類與異常分析結果可瞭解農業生態系服務的熱點區域，可做為優先實施永續農業管理的區域。總體而言，本研究突顯土壤性質與調節服務之間的密切關聯，並且支持稻米生產，為農業綠色環境支付和在不同地區推廣永續農業措施提供了見解。未來應進一步提升作物、土壤與管理行為的空間與時間解析度，並結合衛星遙測提升分析精度。 （三）以糧食-能源-水資源鏈結架構探討農業生態系的正面與負面服務 本研究聚焦於將生態系負面服務納入農業永續評估，解決傳統糧食-能源-水資源鏈結研究僅聚焦生態系正面服務的限制，並納入水質層面作為評估指標。研究量化了生態系正面與負面服務，並分析土地利用對其的影響、兩者間的協同與權衡關係，以及透過聚類分析辨識生態系服務組合型態。研究結果顯示生態系服務的空間分析，生態系正面服務的每公頃中位數為：作物供給服務892美元、水量調節服務16,023.34立方公尺、營養鹽保留服務39.60公斤、碳儲存服務626.91公噸二氧化碳當量(CO2e)，以及水土保持6,048.08公噸。負面服務的中位數為：營養鹽流失11.41公斤、溫室氣體排放5.97公噸CO2e，以及水土流失1.13公噸。與土地利用的分析結果顯示，生態系的正面與負面服務在農業區與森林區間呈現明顯差異：如坡地果園的營養鹽流失與水土保持值較高，而都市與平原耕地的溫室氣體排放值亦較高。調節服務之間具有明顯的正向協同作用，而負面服務與作物供給或營養鹽保留間則呈現顯著的權衡關係。聚類分析將研究區域分為三大類型：山區型、農業型與都市型：山區型具高調節服務，但坡地農業也導致顯著的水質相關負面服務（如營養鹽流失與水土流失）；農業型地區具有高作物供給與營養鹽保留服務，但也伴隨較高的營養鹽流失與溫室氣體排放；都市型地區則呈現高度溫室氣體排放與中等作物供給服務，尤以城鎮周圍的郊區最為明顯。這些分析結果顯示將生態系負向服務與水質指標納入糧食-能源-水資源鏈結框架可提升農業永續性，將能發展出更具地方適應性的管理策略，並建議在坡地地區加強農地使用管制、平原農地優化施肥管理，以降低負向服務，維持關鍵的生態系服務功能。

The sustainable management of farmland environments fundamentally relies on the robust maintenance of their inherent ecosystems. Farmlands, with their rich soil resources, offer a multitude of vital benefits far beyond mere crop production. These lands are, in fact, integral to crucial carbon, water, and nutrient cycles, acting as essential natural regulators. However, these farmland resources are increasingly threatened by mounting pressures from rapid urbanization, which frequently converts productive agricultural land into industrial or commercial uses. This prevalent trend suggests that the multifaceted ecological benefits of agriculture are often severely underestimated in land-use decisions. To address this undervaluation, the ecosystem services (ES) concept provides a powerful framework for comprehensively assessing the diverse benefits agriculture confers upon society. Beyond supplying food, agricultural ecosystems provide crucial regulating services that deliver societal benefits through processes like carbon sequestration, water purification, and nutrient retention. Evaluating farmland through an ES lens offers a holistic understanding of its true value, thereby promoting more sustainable land use management. Despite this potential, the broader regulating services provided by soil resources have lacked systematic quantification and monetization. Additionally, ES assessments have not been consistently integrated into national environmental-economic accounting frameworks like the System of Environmental-Economic Accounting – Ecosystem Accounts (SEEA-EA), and the spatial heterogeneity of ES provision has often been overlooked. A further limitation is the traditional focus on only positive benefits, neglecting crucial negative impacts, or ecosystem disservices (EDS), which are vital for a balanced perspective on agricultural sustainability. Therefore, the three integrated studies in this dissertation aim to address these challenges by systematically assessing farmland ES, encompassing both benefits and disservices, providing insights into spatial variations, and aligning with national accounting frameworks. The dissertation selected ES indicators as final services presenting the contribution of farmland to human well-being rather than crop yield. The analysis includes crop provisioning (CP), carbon storage (CS), water retention (WR), nutrient retention (NR), and soil conservation (SR) as indicators. The research is driven by the following key questions: (1) How can agricultural ES be accurately quantified and valued within an ecosystem accounting framework to promote sustainable soil management? (2) What are the synergies between rice production and soil-related ES, and how can these relationships inform effective policy? (3) How can both positive and negative services be comprehensively assessed within agricultural landscapes, and how can this be integrated into a Water-Energy-Food (WEF) nexus perspective for enhanced sustainability? 1. Quantifying Farmland Ecosystem Services under an Ecosystem Accounting Framework The study, conducted in Yunlin County, Taiwan, addressed limitations in cropland ES assessment by developing a spatially explicit, physically, and monetarily quantified valuation method that integrates detailed field survey data with the InVEST model. We compiled comprehensive ecosystem accounts under the SEEA-EA framework. Ecosystem extent and condition accounts revealed plain farmland constitutes nearly half (47.13%) of the overall ecosystem, predominantly as paddy and dry fields, characterized by high pH values and elevated levels of cation exchange capacity (CEC), organic matter, potassium, copper, and zinc. While both field data and model outputs for CP and CS showed varying values, field data consistently provided a more accurate spatial distribution. Importantly, plain croplands demonstrated superior performance in CP, NR, nitrogen retention (NRN), and phosphorus retention (NRP) compared to other ecosystems, though they exhibited lower values for CS and SR. These visualized outputs can inform sustainable management practice analysis and integrate into regional strategic planning. Economic valuation underscored the profound contribution from regulating services in plain cropland. Our modeling approach estimated total ES flow value at US$40,472 per hectare per year, while field-data observations yielded a significantly higher US$45,853 per hectare per year (13% difference). Regulating services consistently accounted for over 85% of total ES flow value, with provisioning services comprising only 12%. Plain farmland played a particularly vital role, contributing substantially to CS (US$1,078 million/year) and NRN and NRP (US$1,240 million/year) across the county. Finally, the total economic value of ecosystem assets was estimated at US$128 billion, with plain farmland contributing a substantial US$91 billion, underscoring the critical regulatory value embedded in its soil resources. Overall, the results underscore the critical value of soil regulating functions in plain farmlands. Through ES mapping, this research provides a basis for valuing farmland in land-use planning and for implementing sustainable soil management practices locally. This comprehensive assessment, which is consistent with the SEEA-EA framework, provides vital insights for sustainable agricultural practices and informed land management. 2. Synergies of Rice Production and Soil-Related ES The study aimed to deepen our understanding of the intricate connections linking ES, food security, and soil characteristics within agroecosystems, particularly in Taiwan's prominent rice-cultivating region of Changhua. The study investigated the interplay among ESs, crop output, and soil conditions through correlation analysis and spatial associations using bivariate Moran's I to inform sustainable food production. We also monetized and analyzed the clustering of ESs using Anselin Local Moran's I to identify spatial prioritization for promoting sustainable farming. The evaluation of ESs resulted in the following annual physical contributions per hectare of cropland: 9.99 tonnes of rice (CP), 34.86 tonnes of carbon (CS), 3,659 cubic meters of water (WR), 5.10 kilograms of nitrogen and 2.00 kilograms of phosphorus (NR), and 66.52 ± 46.09 tonnes of soil (SR). Relationship analysis indicated CP exhibited a positive correlation with most regulating ESs, underscoring the significance of preserving soil regulating services for robust food security. Furthermore, WR showed a positively moderate to strong relationship with NR services in both cropland-only areas and the broader study area, potentially influenced by differences in river basin characteristics. Correlation analysis also demonstrated soils with coarse textures and low drainage capacity improved CS. Ultimately, the economic analysis estimated the total annual ES value to be approximately US$37,678.81 per hectare, with CS and NR representing the largest contributing components. Hotspot and outlier detection identified key areas and highlighted varied ES features across the study site, offering crucial insights for promoting sustainable farming methods. In summary, these findings highlight the critical role of soil in supporting regulating services, underscoring the need to conserve soil ES to maintain rice productivity and ensure ecological sustainability. The result also provides insights for green payment policies and the promotion of sustainable agricultural practices. While assessment accuracy is currently limited by spatiotemporal resolution of data concerning crops, soil, and management practices, future advancements in satellite remote sensing could significantly improve data precision, enhancing result quality across both time and space. 3. Ecosystem Services and Disservices in the Agricultural Landscapes from a Water-Energy-Food Nexus Perspective The third study extended the understanding of agricultural sustainability by incorporating both ES and often-overlooked ecosystem disservices within the Water-Energy-Food (WEF) nexus framework. While the WEF nexus primarily focuses on ES, it typically overlooks EDS and crucial aspects like water quality. This study quantified both ES and EDS using local surveys and data, analyzed influences from land use on ES, the relationship between ES and EDS, and the pattern of ES bundles using cluster analysis. The study resulted in the median values per hectare for ES: crop provisioning (US$892.00), water yield (16,023.34 m3), nutrient retention (39.60 kg), carbon storage (626.91 Mt-CO2e),and soil retention (6,048.08 tonnes). For EDS, median values were: nutrient export (11.41kg), greenhouse gas emissions (5.97 Mt-CO2e), and soil erosion (1.13 tonnes). Correlation analysis revealed positive synergies within regulating ES but trade-offs between EDS and crop provisioning or nutrient retention. Cluster analysis identified three distinct types of ES bundles across mountainous, agricultural, and urban areas. Agricultural towns featured high crop provisioning and nutrient retention but also emitted some greenhouse gases. Mountainous towns regulated ES but exhibited nutrient export and soil erosion. Urban towns emitted significant volumes of greenhouse gases but supported moderate crop provisioning. This study critically demonstrated that EDS and water quality considerations must be explicitly included in the WEF nexus framework to genuinely enhance agricultural sustainability and inform local management. It recommends increasing land use regulations in areas with steep gradients and optimizing fertilization practices on plains to mitigate EDS and maintain essential ES.

Keywords: ecosystem service, ecosystem accounting, soil health, water-energy-food nexus, ecosystem disservice