Rice paddy irrigation seasonally impacts stream benthic macroinvertebrate diversity at the catchment level

Abstract

Agriculture is one of the most critical anthropogenic disturbances to freshwater ecosystems globally.In monsoon Asia, rice paddies provide habitats for aquatic species, but how their associated irrigation systems can affect downstream ecosystems is poorly understood. Here, we used structural equation modeling (SEM) to estimate seasonal variations in benthic macroinvertebrate diversity and environments and quantified indirect effects of land use, especially of rice paddy areas, on benthic macroinvertebrate diversity through local environmental alteration. Our study site was the Yasu River tributary of Lake Biwa, Japan, and we performed our investigation during both irrigation and nonirrigation periods, representing different seasons. Seasonal variations in physical and chemical variables and diversity were observed. Seasonal particulate phosphorus concentrations to a large extent determined the abundance and community composition of benthic macroinvertebrates. SEM revealed that the proportions of forest, urban, and rice paddy areas in the catchment had significant indirect effects on biodiversity indices of local benthic macroinvertebrate communities. The proportion of forest area had robust negative effects on water temperature, but the overall indirect effects on the macroinvertebrate diversity contrasted between the two seasonal periods. The proportion of rice paddy area had a strongly negative indirect effect on the diversity through increased particulate phosphorous loading during the irrigation period, while the proportion of urban area had a significantly negative indirect effect during the nonirrigation period only. The seasonal negative impacts of rice paddy irrigation on benthic macroinvertebrate communities were possibly due to siltation arising from rice paddy soils. Our results have implications for environmental restoration and biodiversity conservation in catchment management.

Evaluation of Phosphorus Enrichment in Groundwater by Legacy Phosphorus in Orchard Soils with High Phosphorus Adsorption Capacity Using Phosphate Oxygen Isotope Analysis

“…The average annual precipitation and temperature are 1575 mm and 16.7 °C, respectively. The catchment has an area of 3.62 km 2 and is covered by forest (38.4%), citrus orchards (55.0%), and built-up (6.3%) (Figure S1). The spatial distribution of the lithological properties in the catchment are rhyolite (48.2%), accretionary complex (31.6%), and sedimentary rock (20.2%) (Figure S1).…”

“…Phosphorus (P) is an essential element of all living organisms, and its dynamics are closely related to the production of food and the environmental issues associated with eutrophication and biodiversity of water bodies. − Reactive P is artificially produced through P ore mining and mainly utilized as fertilizer in agricultural soils . Long-term P fertilization results in the accumulation of P in agricultural soil, which is referred to as legacy P .…”

A new method for phosphate purification for oxygen isotope ratio analysis in freshwater and soil extracts using solid‐phase extraction with zirconium‐loaded resin

“…Anthropogenic P loads have increased in numerous watersheds because of industrialization and urbanization, changing P cycling and nutrient balances in the environment 1 . These human‐induced alterations may promote severe eutrophication and can negatively affect biodiversity and food security 1–3 . To address these issues, it is necessary to understand the processes influencing P transformations between inorganic and organic forms 4 in the environment and to identify the source of P reaching water bodies 5,6 …”

“…1 These human-induced alterations may promote severe eutrophication and can negatively affect biodiversity and food security. [1][2][3] To address these issues, it is necessary to understand the processes influencing P transformations…”

A new sampling method with zirconium‐loaded resin for phosphate oxygen isotope analysis in oligotrophic freshwater systems

“…In oligotrophic ecosystems lacking nutrients, especially P, various forms of P are rapidly transformed by organismal metabolism, forming a complex biogeochemical cycle of P. 1 Anthropogenic P loading from untreated, domestic, and agricultural wastewaters to the oligotrophic ecosystems often leads to cultural eutrophication, impairing ecosystem functions and services. [2][3][4] To mitigate the P pollution in oligotrophic ecosystems, it is necessary to trace the movement and transformation of P and to identify the sources of P loading into water bodies. 5,6 The phosphate oxygen isotope ratio (δ 18 O PO4 ) is a promising technique for elucidating the P biogeochemistry of aquatic ecosystems.…”