Far from farms and cities, dry climates are boosting river nitrate pollution

Source: The Conversation – USA (3)

Typically, when people hear about nitrates, it involvesrunoff from farm fields, sewage systems and citiesthat can fuel harmful algae blooms and raise the risk of a serious illness in infants known as “blue baby syndrome.”

但河流也可以流经人口稀少、农业不发达的地区，仍然含有令人惊讶的高水平这种形式的氮，这种氮可能对水生生物、饮用水和人类健康造成危害。

In a new study, my colleague andIfound a reason why that happens: Dry climate conditions areassociated with high river nitrate concentrations, even in places with little farming or urban development.

We foundnitrate hot spotsin some unexpected places, including the Rocky Mountains of the western United States and northern Africa’s Sahara Desert. Where water is scarce, we found that nitrates – which can naturallyleach into surface water and groundwater from the soilas microbes break down organic material – were able to accumulate and become concentrated rather than being diluted or flushed away.

That raises health concerns for regions where nitrates in rivers and well water might not be given much thought. It also raises questions about how nitrate-related health risks will increase as global temperatures rise.

为了了解这种模式的普遍性，我们结合了来自7000多个监测站点的全球测量数据，并额外提取了关于气候、土壤、土地利用和其他景观特征的信息。随后，我们训练了机器学习模型以estimate long-term average nitrate concentrationsacross nearly 2.9 million river segments worldwide.

The resulting map suggests that nitrates deserve attention well beyond the urban and agricultural regions where they are usually monitored.

Why it matters

High nitrate exposure in water and food is particularly dangerous for infants because it can interfere with the blood’s ability to carry oxygen.Blue baby syndrome, or methemoglobinemia, can result in serious illnesses and be caused by nitrate poisoning.

The U.S.drinking water standardof 10 milligrams of nitrate-nitrogen per liter was established primarily to guard against this acute risk.

We estimate that about 37,000 people worldwide live in areas where rivers exceed the 10 mg/L drinking water standard, predominantly in the U.S. Corn Belt.

That doesn’t mean 37,000 people are drinking water at those concentrations, since river water in many regions is treated before it is supplied for drinking. But it’s a concerning level they should be aware of,particularly those using well water.

Research has also raised concerns about possible effects of long-term exposure to nitrate at lower concentrations,including certain cancersandadverse birth outcomes, such as babies born preterm or with a low birth weight, although those risks are still being studied.

We estimate that about 480 million people worldwide live in areas where nearby rivers have elevated long-term average nitrate concentrations, above 2.5 milligrams per liter.

Many of the rivers our models identified as having elevated nitrate levels are small headwater streams. Many headwater streams cease to flow for some periods of time every year, and nitrates can accumulate to high concentrations under dry or low-flow conditions. These small streams make upmost of the global river networks, have long been overlooked and feed larger rivers that supply drinking water to large populations and help shape the quality of water downstream.

Too much nitrate in rivers and lakes can alsofuel algal growthand disrupt aquatic ecosystems.

What we still don’t know

A global map of nitrate concentrations in river water cannot show what comes out of someone’s tap. Their water may be mixed with other sources ortreated before they drink it. Nitrate concentrations can also rise and fall over time, while our map shows long-term averages.

To understand a person’s actual exposure will require connecting river measurements with drinking water sources, treatment practices and tests of water delivered to households.

Many rivers with nitrate concentrations above 2.5 milligrams per liter flow through sparsely populated regions where access to treated drinking water may be limited. Even where treatment facilities exist,conventional methods remove little nitrate. Removing it requiresspecialized technologiesthat can be costly to operate.

What comes next

我们的研究表明，为什么需要对更多的干旱地区和小型源头河流中的硝酸盐进行监测。它还提出了一个针对变暖世界的问题：如果一个地区变得更干燥，即使人们没有向环境中添加更多的氮，硝酸盐浓度会升高多少？

回答这个问题需要在湿润和干旱时期进行测量，并结合研究水在土壤、地下水和河流中的流动方式。目前，信息很明确：保护水质需要关注气候变化以及将氮投入环境中的人类活动。

Li Li (李丽) does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Original source: https://analysis1.mil-osi.com/2026/11/12/far-from-farms-and-cities-dry-climates-are-boosting-river-nitrate-pollution/