Andras Jason P, Rubin Rachel L, Rodriguez-Reillo William G, Chatelain Casey D, Morrill Oleander, Ballantine Kate A
Mount Holyoke College, Department of Biological Sciences, USA.
Mount Holyoke College, Department of Environmental Studies, USA; Washington State Department of Natural Resources, USA.
J Environ Manage. 2025 Aug;389:126260. doi: 10.1016/j.jenvman.2025.126260. Epub 2025 Jun 19.
Excess nitrogen from agricultural, urban, and wastewater sources is a major contributor to eutrophication and water quality degradation, necessitating effective mitigation strategies. This study evaluates the effectiveness of woodchip-biochar bioreactors in reducing nitrogen loads in agricultural drainage ditches. Biochar, a highly porous and recalcitrant form of charcoal, was incorporated alongside woodchips due to its known capacity to enhance microbial activity and nutrient retention. Three field-scale bioreactors, composed of a 50:50 volumetric mix of woodchips and biochar, were installed in experimental ditches, with three control ditches left untreated. Over an 18-month monitoring period, nitrate concentrations in bioreactor pore water were reduced by an average of 87 % compared to control ditches, suggesting that denitrification - a microbial process converting nitrate to nitrogen gas in low-oxygen conditions - played a dominant role. Biochar amendment enhanced microbial habitat, improved pH buffering, and increased nutrient retention, fostering conditions favorable for denitrification. Prokaryotic amplicon sequencing revealed a distinct microbial community structure in biochar-amended bioreactors, with enrichment of denitrifying taxa and elevated functional potential for nitrogen removal. While transient increases in ammonia and dissolved organic carbon were observed post-installation, these effects did not extend beyond the bioreactor pore water and diminished over time. These findings underscore the denitrifying potential of bioreactors in general, while highlighting the value of biochar as a strategic enhancement to traditional woodchip systems, supporting their adoption as a scalable, cost-effective strategy for reducing nitrogen pollution in agricultural watersheds.
来自农业、城市和废水源的过量氮是造成富营养化和水质退化的主要因素，因此需要有效的缓解策略。本研究评估了木屑-生物炭生物反应器在降低农业排水渠氮负荷方面的有效性。生物炭是一种高度多孔且难降解的木炭形式，由于其已知具有增强微生物活性和养分保留的能力，因此与木屑一起使用。在实验沟渠中安装了三个现场规模的生物反应器，其由木屑和生物炭按体积比50:50混合组成，另外三个对照沟渠未作处理。在18个月的监测期内，与对照沟渠相比，生物反应器孔隙水中的硝酸盐浓度平均降低了87%，这表明反硝化作用——一种在低氧条件下将硝酸盐转化为氮气的微生物过程——起了主导作用。生物炭改良增强了微生物栖息地，改善了pH缓冲能力，并增加了养分保留，营造了有利于反硝化作用的条件。原核扩增子测序揭示了生物炭改良的生物反应器中独特的微生物群落结构，反硝化类群富集，氮去除功能潜力提高。虽然安装后观察到氨和溶解有机碳有短暂增加，但这些影响并未超出生物反应器孔隙水范围，且随着时间的推移而减弱。这些发现强调了生物反应器总体上的反硝化潜力，同时突出了生物炭作为传统木屑系统战略增强剂的价值，支持将其作为一种可扩展、具有成本效益的策略用于减少农业流域的氮污染。
