Nitrogen sources and exports in an agricultural watershed in Southeast China

Abstract

The nitrogen (N) budget was developed for Jiulong River Watershed (JRW), an agricultural watershed in a warm and humid area of southeast China. Water quality monitoring, Weld surveys, modelling and GIS techniques were applied to estimate N Xux of atmospheric deposition, mineralization, runoV, denitriWcation, and ammonia volatilization. Over the whole watershed, fertilizers, import of animal feeds, biotic Wxation, mineralization and atmospheric deposition contributed 67.1%, 16.5%, 2.1%, 4.9% and 9.5%, respectively, of total N input (129.3 kg N ha ¡1 year ¡1 ). RunoV, sale of production, denitriWcation, and ammonia volatilization contributed 7.3%, 24.4%, 10.5% and 57.8% of total N output (72.9 kg N ha ¡1 year ¡1 ), respectively. The N budget for the JRW suggested that more than 50% of the N input was lost to the environment, and about 14% was discharged as riverine N, which indicated that agricultural and human activities in the watershed substantially impacted the estuary and coastal water quality, and so altered the N biogeochemistry process.

Changes in nitrogen budget and potential risk to the environment over 20years (1990–2010) in the agroecosystems of the Haihe Basin, China

“…Biological N fixation (N biofixation ). The main source of biological N fixation is the growing of legumes, such as soybean and peanut (Chen et al, 2008). N inputs from biological fixation considered both symbiotic N-fixation crops (peanut and soybean only, as the area in which other symbiotic N-fixation crops were cultivated was very small in the Haihe Basin) and nonsymbiotic N-fixation crops in wheat plantations and other cropland areas, such as rice fields.…”

Modeling increased riverine nitrogen export: Source tracking and integrated watershed-coast management

“…Total atmospheric N deposition rates over major counties in the Jiulong River watershed for the year 2004 have been monitored by Chen et al (2008), and N deposition from 1990 to 2009 in Xiamen city (adjacent to the watershed) has been estimated by . Total atmospheric N deposition rates in Xiamen city in other years were estimated using the relationship between total N deposition rate and DIN concentrations in deposition found in 1990-2009.…”

“…Historical data on crop yield were collected from statistical yearbooks from 1980 to 2010. The N content of each crop was referenced from Chen et al (2008).…”

“…At present, the West River has a larger planting area although its catchment is only half as large as the North River catchment; therefore West River areal fertilizer input to watershed (20,499 kg N km −2 yr −1 ) was four times larger than the North River (5594 kg N km −2 yr −1 ) in the 2000s. A N budget developed for the Jiulong River watershed for the year 2004 suggests that fertilizer contributed 67% of total input to the catchment (Chen et al, 2008). Over-fertilization has resulted in increased N losses via runoff, largely due to low N-use efficiency and poor management Chen et al, 2013).…”

Coastal Innovation Paradox

“…They are the quintessential place of nature's bounty and opportunity. Coastal ecosystems play a pivotal role in the healthy functioning of global biogeochemical systems and processes, for example, intercepting, storing and processing much of the terrestrial nitrogen flux [12,13], acting as nurseries for a range of culturally, recreationally and commercially important species and supporting extraordinary biodiversity [14][15][16]. Martinez et al [16] estimate that the total value of coastal ecosystem services is 77% of the total global ecosystem services value of USD 33,268 × 10 9 per annum (pa) (i.e., $33 trillion pa)-well over twice the total economic (market plus non-market) value of terrestrial ecosystem services-calculated by Costanza et al [17].…”