日本地球惑星科学連合2018年大会

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[EE] Eveningポスター発表

セッション記号 A (大気水圏科学) » A-HW 水文・陸水・地下水学・水環境

[A-HW20] 流域の物質輸送と栄養塩循環-人間活動および気候変動の影響-

2018年5月21日(月) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:齋藤 光代(岡山大学大学院環境生命科学研究科)、小野寺 真一(広島大学大学院総合科学研究科)、細野 高啓(熊本大学大学院先導機構、共同)、Adina Paytan(University of California Santa Cruz)

[AHW20-P20] Effects of agricultural practices in rice crop systems on the diversity of periphyton and phosphorus dynamics in streams of the Yasu River watershed

*岩田 智也1奥田 昇2 (1.山梨大学生命環境学部、2.総合地球環境学研究所)

キーワード:リン負荷、水田、付着藻類

Phosphorus is an essential element for all living organisms, and its availability often limits the productivity of many freshwater ecosystems, such as streams, rivers, and lakes. However, human activities often influence the phosphorus loading to freshwater ecosystems, which may exceed the threshold level that triggers the regime shift from oligotrophic to eutrophic conditions in the systems. Moreover, human-induced excess phosphorus can impact both the community structure and physiological P demand of aquatic organisms, thereby affecting the ecosystem function (e.g., P uptake) of those systems. However, knowledge on effects of human-induced P loading on the community structure and ecosystem function in streams is still limited.

We performed a field study in the Yasu River watershed to clarify the effects of agricultural practices on the diversity of periphyton and phosphorus dynamics in streams during May and June 2016. The Yasu River watershed is mainly composed of three lithological classes: accretionary complex, granite, and sedimentary rock. In the sub-watersheds where sedimentary rock predominates, a large amount of particulate phosphorus originated from rice paddy fields is exported with muddy water to nearby streams during the surface soil paddling period. In contrast, agricultural practices in rice crop systems seem to have relatively minor influences on phosphorus loading to adjacent streams in the sub-watersheds where the other lithological types predominate. We established sampling sites in streams of both sub-watersheds to analyze the P concentration and the community structure of periphyton attached on the streambeds. In addition, we performed the enzyme-labeled fluorescence (ELF) assay for periphyton samples to determine the cell-associated alkaline phosphatase activity (a common marker of P demand) in response to phosphorus loading from rice paddy fields.

In this presentation, we show that the rice crop practices in sedimentary rock areas greatly influenced the total phosphorus but not soluble reactive phosphorus concentrations in streams. The results suggest that agricultural practices (e.g., soil paddling) interacted with geological characteristics to affect the transport of particulate phosphorus (PP) from rice paddy fields. The present study also show how such human activities influence the diversity and community structure of stream periphyton, as well as their physiological P demand. The results will clarify the effects of agricultural practices in rice crop systems with contrasting geological types and the resultant consequences for ecosystem structure and function in streams of agricultural watersheds.